Device for deploying expandable implants

Abstract

A device for deploying an implant in a patient’s body comprises an elongate delivery tube 36 with tube elements in concentric relation in radial outward succession. The tube has an inner element compr

Description

This invention relates to a delivery device for an expandable implant. In particular, but not exclusively, the invention provides solutions to deploy a self-expanding implant or 5 expander to dilate the prostatic urethra of a patient, thereby to treat benign prostatic hyperplasia (BPH). Aspects of the invention therefore relate to a delivery device for locating an expandable implant within the prostatic urethra to treat BPH BPH is a noncancerous disease that results in enlargement of the prostate. The 10 prostate surrounds a section of the urethra adjoining the bladder, namely the prostatic urethra. Thus, as the prostate expands, it tends to press inwardly against the prostatic urethra and the neck of the bladder, making it difficult for a patient to pass urine. In the US alone, more than US$5 billion is spent annually on medication to manage 15 BPH. It is also known to treat BPH using various surgical techniques. However, surgical solutions can be particularly invasive and uncomfortable for the patient. Consequently, there has been a move in the art toward the use of expandable implants or stents that can be inserted into the prostatic urethra to react against inward pressure that may be applied to the urethra and bladder neck by an enlarged prostate. 20 Expandable implants provide a minimally invasive and low-cost solution for treating BPH. However, locating the implant in the correct position within the urethra is essential but is challenging for a clinician. If the implant is deployed incorrectly, it may not provide adequate symptom relief, could fail due to migration or excessive 25 encrustation and can be challenging and invasive to recover from the urethra after deployment. Various examples of expanders for treating BPH are disclosed in WO 2017 / 081326. The expanders of WO 2017 / 081326 are designed to be positioned within the prostatic 30 urethra between the bladder neck and the external sphincter and then to self-expand laterally. The expander thereby applies a radially-outward force on the surrounding walls of the prostatic urethra to alleviate the symptoms of BPH. Deploying an expander correctly within the prostatic urethra requires the expander to 35 be positioned accurately both in a longitudinal direction and circumferentially or angularly. In particular, the expander must be positioned longitudinally at a position 30 06 25 between the bladder neck and the external sphincter and must also be oriented so as to engage the three lobes of the prostate. Incorrect deployment is likely if the expander is deployed accidentally or prematurely or if the clinician cannot properly visualise the structures surrounding the prostatic urethra before deployment. 5 If an expander is deployed in an incorrect position or orientation, an adverse outcome is possible and a complex procedure may be required to remove or reposition the expander. As a result, there is a need for a minimally-invasive delivery device that allows a clinician accurately to position and deploy an expandable implant within the 10 prostatic urethra of a patient. WO 2017 / 081326 describes a device for delivering an expander to a target site within a body lumen such as the prostatic urethra. The delivery device comprises an ejection element with a triangular cross-section configured to engage and support the 15 expander. A delivery tube of the delivery device is inserted into the penile urethra and its distal end is advanced along the urethra to a target site in the prostatic urethra. When the clinician is satisfied that the expander is in the correct position both longitudinally and in angular orientation relative to the lobes of the prostate, the ejection element is advanced distally to eject the expander from within a surrounding sheath of 20 the delivery tube. The delivery device of WO 2017 / 081326 is effective in principle but would benefit from some refinements in practice. For example, a single-step delivery device such as that described in WO 2017 / 081326 would be susceptible to accidental or premature 25 deployment. Also, the device of WO 2017 / 081326 does not ideally enable visual verification of the correct position of the expander relative to the surrounding anatomy before the clinician must decide whether to deploy the expander. Furthermore, unless a clinician withdraws the delivery tube of WO 2017 / 081326 30 proximally while advancing the ejection element distally, the expander could spring or jump forward upon deployment. Unhelpfully, this would tend to alter the position of the expander within the prostatic urethra, both longitudinally and circumferentially, as a consequence of the deployment action. In this respect, relying on the expander to selflocate relative to the anatomy may be unreliable and unpredictable. 30 06 25 WO 2021 / 099646 takes WO 2017 / 081326 as its starting point and discloses improved delivery devices for deploying an expander within the prostatic urethra. Among its improvements, WO 2021 / 099646 discloses provisions to prevent inadvertent deployment of the expander with a detent mechanism; to improve visualisation of the 5 expander relative to the surrounding anatomy before deployment; and to pause or reverse deployment if a clinician determines that the expander could otherwise be positioned incorrectly at the target site. WO 2021 / 099646 also discloses provisions to steer the delivery tube along the penile urethra to the target site. 10 The present invention provides further improvements over WO 2017 / 081326 and WO 2021 / 099646 by offering elegant, compact, effective and reliable solutions for operation of a detent mechanism and for driving and controlling differential longitudinal movement of concentric elements of the delivery tube during in situ visualisation and deployment. As a result, the invention provides an ergonomically-designed delivery 15 device that allows an implant to be deployed accurately with simple, safe and largely one-handed operation. It is against this background that the invention has been devised. From one aspect, the invention resides in a device for deploying an implant in a patient’s body, the device 20 comprising: an elongate delivery tube having delivery tube elements in concentric relation, those delivery tube elements being, in radially outward succession, an inner element comprising an imaging head, an intermediate element comprising implant retainer formations and an outer element comprising an outer sheath that is cooperable with the implant retainer formations, the inner and outer elements being 25 retractable relative to the intermediate element along a longitudinal axis of the delivery tube; and a handle at a proximal end of the delivery tube, the handle having a housing that contains: a hub assembly comprising an inner element hub, an intermediate element hub and an outer element hub, each of those hubs being mounted proximally to a respective one of the delivery tube elements; a hub carriage that is movable 30 longitudinally with respect to the housing and to the intermediate element hub and that supports the inner element hub and the outer element hub for said movement with the hub carriage to retract the inner and outer elements relative to the intermediate element of the delivery tube; and a deployment drive that is configured to drive said movement of the hub carriage in response to operation of a deployment control 35 element that is external to the housing. 30 06 25 The hub carriage may be movable proximally by the deployment drive relative to the housing and the intermediate element hub along a longitudinally-extending retraction path from an undeployed position in which the outer sheath is opposed to and in a distally advanced position relative to the implant retainer formations to a deployed 5 position in which the outer sheath is retracted proximally beyond the implant retainer formations, via an intermediate partially deployed position in which the outer element is retracted proximally from the distally advanced position while still being opposed to the implant retainer formations. 10 The outer element hub and the inner element hub may be movable proximally with the hub carriage from the undeployed position to the partially deployed position. In that case, the outer element hub and the inner element hub may be reversible with the hub carriage in a distal direction along the retraction path from the partially deployed position to the undeployed position. 15 The outer element hub may be movable proximally with the hub carriage relative to the inner element hub as the hub carriage moves from the partially deployed position to the deployed position. In that case, the outer element hub may be fixed relative to the hub carriage and the inner element hub may be releasably latched relative to the hub 20 carriage. For example, a stop formation in fixed relation to the housing may be positioned in the retraction path proximally of the inner element hub to block proximal movement of the inner element hub beyond the partially deployed position of the hub carriage. This causes the inner element hub to unlatch from the hub carriage while allowing continued proximal movement of the hub carriage and the outer element hub 25 from the partially deployed position to the deployed position. The hub carriage may be releasably latched relative to the housing when in the undeployed position, that latching being releasable by operation of the deployment control element. 30 The deployment drive preferably comprises a detent mechanism that is configured to block movement of the hub carriage from the partially deployed position to the deployed position and a detent release element that is operable to release the detent mechanism to allow the hub carriage to move from the partially deployed position to the 35 deployed position. For example, the detent release element may be enabled to release the detent mechanism by virtue of movement of the deployment control element that 30 06 25 acts on the deployment drive to move the hub carriage from the undeployed position to the partially deployed position. In this respect, the deployment control element could block movement of the detent release element when the hub carriage is in the undeployed position. 5 The outer element hub, the intermediate element hub and the inner element hub can be disposed in proximal succession along the hub carriage. The hub carriage may comprise a distal portion that supports the outer element hub, a proximal portion that supports the inner element hub, and a longitudinally-extending intermediate portion that 10 connects the distal and proximal portions and bridges around the intermediate element hub. The intermediate element hub may suitably be sandwiched between the outer element hub and the inner element hub and could be at least partially housed within the hub carriage. 15 The intermediate element hub may have at least one support that extends laterally beyond the hub carriage to fix the intermediate element hub against movement relative to the housing. In that case, a side wall of the hub carriage could comprise a longitudinally-extending slot that accommodates the laterally-extending support of the intermediate element hub to allow for movement of the hub carriage relative to the 20 intermediate element hub. Such a slot suitably has an open proximal end. The deployment drive may comprise a gearset that acts between the deployment control element and the hub carriage. In that case, the hub carriage may have a longitudinally-extending rack formation that is engaged with a gear of the deployment 25 drive gearset. For example, the rack formation could be on an arm that extends proximally from the hub carriage. The arm may be offset laterally from a central longitudinal axis that extends proximally into the housing from the delivery tube, in which case the rack formation could face that axis. 30 30 06 25 In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a side view of an expander in an expanded state suitable for use 5 with embodiments of the invention; Figure 2 is a cut-away view of a prostate of a patient with the expander of Figure 1 disposed within the prostatic urethra to treat BPH by exerting an outward radial pressure on the walls of the prostatic urethra, hence effecting 10 dilation; Figure 3 is a side view of a delivery device of the invention comprising a handle and a delivery tube; 15 Figure 4 is an enlarged detail perspective view of a distal end portion of the delivery tube containing an undeployed expander, when the device is in a deployment stage zero; Figure 5 corresponds to Figure 4 but shows the device in a deployment stage 20 one with the expander partially deployed; Figure 6 is a schematic view of an image captured by an imaging chip of the device when the device is in deployment stage one as shown in Figure 5, in use; 25 Figure 7 corresponds to Figures 4 and 5 but shows the device in a deployment stage two with the expander fully deployed; Figures 8a, 8b and 8c are sectional side views of the distal end portion of the 30 delivery tube corresponding, respectively, to the deployment stages of the device shown in Figures 4, 5 and 7; Figure 9 is a side view of a shell forming part of a housing of the handle shown in Figure 3; 30 06 25 Figure 10 corresponds to Figure 9 but shows components of the handle fitted to the shell; Figure 11 is a schematic perspective view showing the device of the invention 5 in use, with the distal end portion of the delivery tube advanced into a prostatic urethra and the handle held and operated by a user; Figure 12 is an exploded perspective view showing concentric elements of the delivery tube; 10 Figure 13 is an enlarged perspective view of a proximal hub of an inner delivery tube element shown in Figure 12; Figure 14 is an enlarged cut-away distal perspective view of a camera tip that is 15 attachable to a distal end of the inner delivery tube element shown in Figure 12 Figure 15 is an enlarged cut-away proximal perspective view of the camera tip shown in Figure 14; 20 Figure 16 is an enlarged cut-away distal perspective view of a steering tip at a distal end of an intermediate delivery tube element shown in Figure 12; Figure 17 is an enlarged distal perspective view of the steering tip shown in Figure 16; 25 Figure 18 is an enlarged perspective view of a proximal hub of an outer delivery tube element shown in Figure 12; Figures 19a and 19b are exploded perspective views of a hub casing attached 30 to the proximal hub of the outer delivery tube element shown in Figure 18; Figure 20 is a cut-away perspective view of a proximal hub of an intermediate delivery tube element shown in Figure 12, shown engaged with the housing of the handle; 30 06 25 Figures 21a to 21 d are a sequence of cut-away perspective views showing movement of the hub casing of Figures 19a and 19b relative to the housing of the handle between various deployments stages of the device; 5 Figures 22a to 22d are a sequence of cut-away perspective views showing movement of external control elements relative to the housing of the handle between various deployments stages of the device; Figures 23a to 23d are a sequence of side views showing relative movement of, 10 and interactions between, the control elements shown in Figures 22a to 22d to operate a detent function of the device; and Figures 24a and 24b are perspective views showing operation of a steering mechanism of the device. 15 To place the invention in context, reference is made firstly to Figure 1 which shows an expandable implant or expander 10 suitable for use with embodiments of the present invention. The expander 10 shown in Figure 1 is an example only: the delivery device to be described herein may be suitable for use, or may be adapted for use, with other 20 implants. The expander 10 comprises a single nitinol wire whose opposed ends are joined by a sleeve 12 to form a continuous sinusoidally-undulating ring. When released, the expander 10 can self-expand by elastic recovery from a radially-compressed state for 25 stowage into a radially-expanded state for deployment as shown in Figure 1. Specifically, the nitinol wire ring of the expander 10 acts with superelastic shape memory properties such that when in a compressed state, the expander 10 exerts an outward radial force on a surrounding body structure into which it is deployed, in particular the prostatic urethra. 30 The expander 10 has a proximal end comprising three proximal prongs with respective proximal apices 14 and a distal end comprising three distal prongs with respective distal apices 16. The proximal and distal apices 14, 16 are joined, in circumferential alternation, by longitudinal struts 18. Each strut 18 has an outwardly convex shape that 35 lends a barrel-like profile to the expander 10 when viewed in outline. 30 06 25 When in a radially-compressed state, the expander 10 is narrowed to the extent that it can be advanced along the penile urethra of a patient with minimal discomfort. The expander 10 is delivered to the prostatic urethra in that contracted state and is then released to self-expand in situ. 5 Referring now also to Figure 2, the expander 10 is shown in use within the prostate gland 20 to treat symptoms of benign prostatic hyperplasia (BPH). Specifically, the expander 10 is located in the prostatic urethra 22 within the prostate 20 between the bladder neck 24 and the external sphincter 26. When located in that longitudinal 10 position, the expander 10 exerts an outward radial force against the lobes of the prostatic urethra 22 to ease the passage of urine flowing from the bladder. Care must be taken to ensure that the expander 10 is at the correct longitudinal position between the bladder neck 24 and the external sphincter 26 before deployment. 15 In this respect, positioning the expander 10 too close to either the bladder neck 24 or the external sphincter 26 is undesirable as their muscle action could otherwise cause the expander 10 to migrate along the urethra or into the bladder over time. The expander 10 must also be orientated angularly such that the verumontanum 28 20 and the seminal ducts 30 are unobstructed by the undulating wire of the expander 10, thus preserving the patient’s sexual function. Furthermore, the longitudinal struts 18 of the expander 10 are oriented to engage respective lobes of the prostate 20, thereby exerting an outward radial force on each lobe to maintain an open passage between the bladder neck 24 and the external sphincter 26. 25 Moving on now to Figure 3, a device 32 for deploying a self-expanding implant or expander 10 comprises a proximal handle 34 acting on a flexible delivery tube 36 that extends distally from the handle 34. Initially, as shown in Figures 4 and 8a, the expander 10 is sheathed within a distal end portion of the delivery tube 36 in a radially 30 compressed state, ready for insertion and delivery to a target deployment site in the prostatic urethra. As will be explained, and as shown in Figures 8a, 8b and 8c, the delivery tube 36 comprises three flexible tubular elements in concentric longitudinally-sliding relation, 35 namely: an outer element 38 comprising an outer sheath; an inner element 40 comprising an imaging sheath; and an intermediate element 42 comprising a steering 30 06 25 sheath disposed in an annular gap defined between the outer sheath and the imaging sheath. A user operating the device 32 can operate a steering lever 44 on the handle 34 to 5 steer the delivery tube 36 during navigation along the urethra to the target site. Operation of the steering lever 44 acts on the intermediate element 42 to deflect the distal end portion of the delivery tube 36 relative to a proximal portion of the delivery tube 36. 10 The inner element 40 of the delivery tube 36 has an imaging system at its distal end that provides the user with images of the urethra, taken from a viewpoint on a longitudinal axis that is radially inboard of the expander 10 in the distal end portion of the delivery tube 36. In this example, as shown in Figures 4 and 8a, a camera tip 46 defining the distal extremity of the inner element 40, with image-capturing and lighting 15 components adjacent an irrigation duct, initially protrudes distally from the distal end of the outer element 38. This ensures the best possible field of view as the delivery tube 36 navigates the anatomy before deployment of the expander 10. However, in other examples, the distal extremity of the inner element 40 could be substantially level with the distal end of the outer element 38 or could even be recessed proximally to a small 20 extent, provided that an adequate field of view is maintained. Before reaching the deployment site, the expander 10 can remain sheathed by the outer element 38 within the distal end portion of the delivery tube 36 as shown in Figures 4 and 8a. As deployment of the expander 10 has therefore not yet begun, this 25 stage or initial state will be referred to in the following description as ‘deployment stage zero’. When the expander 10 is at or near to the deployment site, the user operates a deployment control element, namely a trigger 48 external to the handle 34, which acts 30 on the delivery tube 36 to unsheath the expander 10 partially as shown in Figures 5 and 8b. This stage or intermediate state will be referred to in the following description as ‘deployment stage one’. The imaging system of the camera tip 46 can then provide images of the distal end of the expander 10 against the surrounding structures of the prostatic urethra. 30 06 25 When in deployment stage one, the action of the deployment trigger 48 is reversible to return the device 32 to deployment stage zero. Thus, the expander 10 can be resheathed if the user decides to re-position the expander 10 substantially or to abandon the procedure. 5 Figure 8b shows how, in the partially-deployed configuration of deployment stage one, the outer element 38 and the inner element 40, including the camera tip 46, are pulled back proximally relative to the intermediate element 42 and hence also relative to the expander 10 supported by the intermediate element 42. Thus, beneficially, the imaging 10 device of the camera tip 46 when in the retracted position can visualise the expander 10 against a backdrop of the adjacent anatomy, from a viewpoint within the expander 10. The retracted outer element 38 remains out of the field of view of the imaging device. 15 The prongs terminating in the distal apices 14 of the expander 10 can contact the lobes of the prostate 20 so that a user may view and fully appreciate the position of the expander 10 relative to the structures around the prostatic urethra 22 before full deployment. Advantageously, this enables the user to check if the expander 10 is positioned correctly prior to full deployment. 20 To illustrate this, Figure 6 is a schematic view of an image captured by an imaging device of the camera tip 46 when the outer element 38 is in the partially-deployed position. This shows the distal apices 14 of the expander 10 aligned with and contacting the lateral prostatic lobes around the prostatic urethra 22. Specifically, a 25 posterior prong 50 of the expander 10 is shown surrounding or straddling the verumontanum 28 whereas the two anterior prongs 54 of the expander 10 are oriented such that they engage the anterior lateral lobes 56. It will be apparent that the image provided to the user by the imaging device of the 30 camera tip 46 beneficially allows simultaneous visualisation of the longitudinal position of the expander 10 relative to the anatomy, for example the verumontanum 28 and the bladder neck 24, and also the angular position of the expander 10 relative to the verumontanum 28 and the prostatic lobes 56. This facilitates accurate positioning of the expander 10 within the prostatic urethra 22. 30 06 25 It will also be noted from Figures 5, 6 and 8b that the aforementioned barrelled outline of the expander 10 causes the distal apices 14 of the expander 10 to converge toward a central longitudinal axis 58 when the camera tip 46 of the inner element 40 is retracted within the expander 10. This brings the distal apices 14 into, or close to, 5 mutual contact and so places them in a prominent central position in the user’s field of view, hence serving as an effective aiming point to guide the user. When satisfied that the expander 10 is correctly positioned at the deployment site, the user can operate the deployment trigger 48 to unsheath the expander 10 fully for 10 deployment as shown in Figures 7 and 8c. This stage or final state will be referred to in the following description as ‘deployment stage two’. Once fully unsheathed by retracting the outer element 38, the expander 10 expands radially at the target site and is thereby released from the delivery tube 36 into a deployed state within the prostatic urethra 20. In the example of the invention to be described, the inner element 40 does 15 not retract further with the outer element 38 so that the viewpoint of the camera tip 46 remains fixed from deployment stage one to deployment stage two. A detent mechanism prevents inadvertent deployment of the expander 10 by blocking operation of the deployment trigger 48 that could otherwise unsheath the expander 10 20 fully. Specifically, at deployment stage one, the user must deliberately depress a detent release element, such as a detent button 60, before the deployment trigger 48 can be operated to unsheath and deploy the expander 10 in deployment stage two. The detent button 60 is rendered inoperable when the device 32 is at deployment stage 25 zero. Movement of the deployment trigger 48 to bring the device 32 to deployment stage one enables operation of the detent button 60. The detent button 60 can then be operated by a separate and deliberate movement of a user’s finger to release the deployment trigger 48 for further movement to bring the device 32 to deployment stage two. 30 During partial and full unsheathing, the axial and angular position of the expander 10 remains fixed relative to the handle 34, steering aside, so as to maintain accurate positioning of the expander 10 at the deployment location. The angular position of the expander 10 also remains fixed relative to the imaging device of the camera tip 46. 30 06 25 Turning next to Figures 9 and 10, the handle 34 comprises a hollow housing 62 of a moulded polymer material that is divided into two shells 64 along a central longitudinal plane. The shells 64 are, substantially, mirror images of each other about the planar interface between the shells 64. The shells 64 are held together by screws that are 5 spaced apart from each other and from components disposed within the housing 62. On their concave inner sides, the shells 64 comprise integrally-moulded locating and guiding formations 66 that support and guide movement of various components disposed within and extending from the housing 62, as will be explained. As can be 10 seen in Figure 10, those components are grouped into various sub-assemblies, namely a hub assembly 68 at a proximal end of the delivery tube 36, a deployment system 70 that acts on the hub assembly 68 to drive longitudinal movement of specific elongate elements of the delivery tube 36 relative to each other, and a steering system 72 for deflecting a distal end portion of the delivery tube 36 when navigating to a deployment 15 site in the patient’s body. The hubs of the hub assembly 68 that are responsive to the deployment system 70 are movable relative to the housing 62 along the central longitudinal axis 58, which extends along and within the housing 62 in alignment with the proximal end of the delivery tube 36. 20 Viewed externally, the housing 62 of the handle 34 has a narrow waist 74 of approximately elliptical cross section and an enlarged proximal portion 76 at which user-operable control elements of the deployment system 70 and the steering system 72 protrude from within the handle 34 through respective openings in the housing 62. 25 Specifically, the control elements of the deployment system 70 are the deployment trigger 48 and the detent button 60, which are disposed beside each other. The deployment trigger 48 and the detent button 60 are movable into and out of the housing 62 along respective axes of operation, namely a trigger axis 78 and a detent axis 80, that are each transverse to the central longitudinal axis 58 of the housing 62. The 30 trigger axis 78 and the detent axis 80 lie beside each other and are substantially straight and parallel in this example. Conversely, the control element of the steering system 72 is the steering lever 44 that can be pivoted relative to the housing 62 about a pivot axis 82 within the housing 62. 35 The pivot axis 82 is transverse to the central longitudinal axis 58 of the housing 62 and to the trigger axis 78 and a detent axis 80. The steering lever 44 can also move into 30 06 25 and out of the housing 62 on a locking axis 84 that intersects the pivot axis 82, whereby pivotal movement of the steering lever 44 can be, respectively, unlocked and locked as will be explained. 5 Figure 11 shows that the device 32 is configured for largely one-handed operation and to allow a user to hold and to operate the device 32 using their left or right hand according to their preference. Consequently, the control elements of the deployment system 70 and the steering system 72, namely the deployment trigger 48, the detent button 60 and the steering lever 44, are disposed on, and are substantially symmetrical 10 about, the central longitudinal plane that divides the shells 64 of the housing 62. The device 32 is configured to be held by a user in an inclined or upright orientation in pistol-grip fashion. When holding the device 32 in that way, the user’s forefinger or index finger aligns with, and so can easily operate, the deployment trigger 48 and the 15 detent button 60 of the deployment system 70. Alternatively, the user could use their index finger to operate the detent button 60 and their second or middle finger to operate the deployment trigger 48. Conversely, the user’s thumb aligns with, and so can easily operate, the steering lever 44 of the steering system 72 that protrudes from the opposite side of the housing 62 and is opposed to the deployment trigger 48 and 20 the detent button 60 about the central longitudinal axis 58 of the housing 62. The user’s other fingers embrace the narrow waist 74 of the housing 62 to hold the device 32 in the palm of the hand while supporting the enlarged proximal portion 76 of the housing 62 above the palm. The delivery tube 36 therefore extends from the 25 housing 62 initially in a generally downward distal direction but can bend from there along its length for its distal portion to follow a desired insertion path into the patient’s prostatic urethra along the penile urethra. The housing 62 further comprises an irrigation port 86 such as a Luer connector 30 located distally with respect to the waist 74 of the housing 62 for conveying irrigation fluid into the delivery tube 36 from an external source. The housing 62 also comprises a power and data port 88 at a distal location opposed to the irrigation port 86. The power and data port 88 enables electrical power to be conveyed from an external power supply to imaging electronics of the delivery tube 36 and for image data to be 35 conveyed from the imaging electronics to an external monitor. 30 06 25 As noted above, the delivery tube 36 comprises three flexible tubular elements in concentric longitudinally-sliding relation, namely: an outer element 38 comprising an outer sheath 90; an inner element 40 comprising an imaging sheath 92; and an intermediate element 42 comprising a steering sheath 94 disposed in an annular gap 5 defined between the outer sheath 90 and the imaging sheath 92. Figure 12 shows those elements 38, 40, 42 separately. It will be apparent that each of the sheaths 90, 92, 94 is fixed to a respective hub 96, 98, 100 that is positioned at, or adjacent to, the proximal end of the associated element 38, 40, 42. 10 As will be explained, the intermediate element 42 is fixed against axial movement relative to the handle 34 whereas the outer and inner elements 38, 40 can move axially relative to both the intermediate element 42 and the handle 34. The hubs 96, 98, 100 lock the respective elements 38, 40, 42 within the system to prevent the outer and inner elements 38, 40 from moving in any direction except axially along a fixed travel 15 path aligned with the central longitudinal axis 58 of the handle 34, as controlled by a user operating the deployment trigger 48 of the handle 34. All of the sheaths 90, 92, 94 are tubular in this example although, in principle, the imaging sheath 92 could instead be a solid but flexible rod with any wiring, cabling or 20 ducting embedded within it, for example in respective parallel channels of an extruded profile. In any event, any such wires or cables must be isolated from each other and from a flow of irrigating liquid that may be conveyed along the imaging sheath 92. The sheaths 90, 92, 94 should be as thin as possible to ensure that the overall 25 diameter of the delivery tube assembly is advantageously small, for example with an outer diameter of less than sixteen French (5.33mm) in the application described. As a non-limiting illustrative example, the outer sheath 90 may have a wall thickness of 0.159mm to 0.254mm, for example about 0.175mm, whereas the main proximal section of the steering sheath 94 may have a wall thickness of about 0.394mm to 30 0.464mm, allowing about 0.61 mm for the expander 10 and for clearance. The wall thickness of the imaging sheath 92 under the expander 10 may, for example, be about 0.114mm to 0.159mm. The sheaths 90, 92, 94 are flexible enough to permit an angle of deflection along their 35 full length of, for example, 40° to 90° so as to accommodate the curvature of the male urethral anatomy and to access the prostatic urethra 22. In particular, the sheaths 90, 30 06 25 92, 94 must be capable of flexing along their length as they extend along the urethra from the point of insertion at the penile meatus through to the bladder neck 24. The sheaths 90, 92, 94 therefore each have a flexible steering section to provide for deflection driven by a steering mechanism controlled by the steering system 72 of the 5 handle 34 at the proximal end of the delivery tube 36. The sheaths 90, 92, 94 also each have a flexible proximal portion to provide for deflection imposed by the anatomy, for example to track through the curvature of the penile canal. As an example, one or more of the sheaths 90, 92, 94 may be braided or coiled for 10 flexibility to accommodate curvature of the anatomy and deflection of the imaging tip. However, the structure of the delivery tube 36 must also be stiff enough axially and circumferentially to resist the forces of insertion, steering, navigation, unsheathing of the expander 10 and, if necessary, re-sheathing of the expander 10. As explained below, any or all of the sheaths 90, 92, 94 may have tailored stiffness and flexion 15 properties for these purposes. The torsional stiffness of the sheaths 90, 92, 94 must be sufficient to allow for angular alignment of the expander 10 about the central longitudinal axis 58. In this respect, the circumferential or angular positioning of the expander 10 within the prostatic urethra 22 20 is controlled by global rotation of the handle 34. The handle 34 thereby applies torque to the sheaths 90, 92, 94 attached to it, noting that the sheaths 90, 92, 94 are fixed against circumferential angular movement relative to the handle 34 and so cannot rotate independently of the handle 34. 25 The simplest and most basic form of sheath would be a single extrusion comprising a polymer material of a certain durometer value. However, a single-material extrusion with the necessarily thin wall thickness may kink or buckle when deflected by a steering mechanism, or under axial compression, or under other bending loads. For this reason, any or all of the sheaths 90, 92, 94 may benefit from differential material properties 30 along their length to provide the individual sheaths 90, 92, 94, and the stacked sheath assembly of the delivery tube 36, with the design characteristics required to access the prostatic urethra 22, to navigate the anatomy, and to steer and support the expander 10. 35 Examples of characterisation properties to be tailored along the length of a sheath 90, 92, 94 may include: flexibility; kink resistance; trackability; the ability to apply axial force 30 06 25 parallel to the longitudinal axis 58 - i.e. ‘pushability’; and the ability to apply torque about the longitudinal axis 58 - i.e. ‘torquability’. Tailoring may, for example, be achieved by the following options: 5 Hybrid extrusion, in which two or more materials of differing stiffness or durometer properties are joined together by reflows or joints. A fully-braided sheath, this being a custom multi-layered braided sheath with a specific pitch design or angle of braid that is tailored to the stiffness properties 10 required. Braiding may be uniform along its length. A fully-braided coiled sheath, this being a custom multi-layered coiled sheath with a specific pitch design or angle of coil that is tailored to the stiffness 15 properties required. Coiling may be uniform along its length. A hybrid braided sheath, this also being a custom multi-layered braided sheath with a specific pitch design or angle of braid tailored to the stiffness properties required. However, in this case, braiding is varied along its length, for example with tighter and looser braids, or denser and less dense braids, at different 20 longitudinal positions where the sheath is required to be more or less flexible. The angle of the braids relative to central longitudinal axis 58 can also be varied to adjust flexibility along the length of a sheath. A hybrid coiled sheath, this also being a custom multi-layered coiled sheath with 25 a specific pitch design or angle of coil tailored to the stiffness properties required. However, in this case, coiling is varied along its length, for example with tighter and looser coils, or denser and less dense coils, at different longitudinal positions where the sheath is required to be more or less flexible. The angle of the coils relative to central longitudinal axis 58 can also be varied 30 to adjust flexibility along the length of a sheath. A hybrid of braided and coiled sheath, this also being a custom multi-layered braided and coiled sheath with certain sections of the sheath being braided, and certain sections of the sheath being coiled, with a specific pitch design or angle 35 of braid and coil tailored to the stiffness properties required. Braiding and coiling may be varied along its length, for example with tighter and looser braids / coils, 30 06 25 or denser and less dense braids / coils, at different longitudinal positions where the sheath is required to be more or less flexible. The angle of the braids / coils relative to central longitudinal axis 58 can also be varied to adjust flexibility along the length of a sheath. 5 All of the above examples can have varying durometer of polymer jacket reflowed through the braid or coil wire where the sheath is required to be more or less flexible. Varying the thickness of this polymer can also be used to change the properties of the sheath where the sheath is required to be more or less flexible. 10 A rigid moulded tip section may be reflowed, bonded or over-moulded onto a braided sheath. Referring now also to Figure 13, the inner element 40 comprises the imaging sheath 92 15 and an inner element hub 98 that is fixed to the imaging sheath 92 adjacent to a proximal end of the imaging sheath 92. Conversely, Figures 14 and 15 show the moulded camera tip 46 that is fixed to a distal end of the imaging sheath 92 and also forms part of the inner element 40, although the camera tip 46 is not shown in Figure 13. 20 The inner element hub 98 protrudes laterally from the imaging sheath 92. The imaging sheath 92 extends through the inner element hub 98 in this example, although it would be possible instead for the imaging sheath 92 to terminate at or within the inner element hub 98. The inner element hub 98 is overmoulded onto the imaging sheath 92 25 but could instead, or additionally, be bonded or welded to the imaging sheath 92 and / or could be an interference fit around the imaging sheath 92. In this example, the inner element hub 98 is generally cuboidal, receiving the imaging sheath 92 in a through-bore 102 that is centred on mutually-parallel proximal and distal 30 faces of the inner element hub 98. The inner element hub 98 is also penetrated by a pair of parallel side bores 104 extending between the proximal and distal faces, one each side of the central through-bore 102. The side bores 104 accommodate a pair of steering wires 106 extending proximally from the intermediate element 42 of the delivery tube 36, as shown in Figure 12 and as will be explained further. 30 06 25 Opposed side faces of the inner element hub 98, generally orthogonal to the proximal and distal faces, lie generally parallel to each other and to the longitudinal axis of the imaging sheath 92. A wedge formation 108 protrudes laterally from one of the side faces and tapers proximally from a distal shoulder to intersect that side face. 5 The proximal face of the inner element hub 98 is surmounted by a lug 110 that projects from the inner element hub 98 orthogonally with respect to the longitudinal axis of the imaging sheath 92. The lug 110 ensures that the inner element hub 98 is oriented correctly when being incorporated into the hub assembly 68, so that the wedge 10 formation 108 on one of the side faces protrudes from the correct side of the hub assembly 68. The imaging sheath 92 also shown in Figures 14 and 15 contains an irrigation channel and an electronics channel 114 that are disposed beside each other in parallel relation. 15 Specifically, the irrigation channel is defined by an irrigation tube 112 that is offset laterally within the lumen of the imaging sheath 92, whereas the electronics channel 114 is defined in the space remaining within that lumen beside the irrigation tube 112. The irrigation tube 112 is fluidly connected to the irrigation port 86 in the handle 34 whereby irrigating liquid can travel from the proximal end to the distal end of the 20 imaging sheath 92. Close sliding contact between the inner element 40 and the intermediate element 42 is desirable to maintain a tight seal to minimise ingress of liquids into the distal end of the delivery tube 36 between the inner and intermediate elements 40, 42. 25 Figure 13 shows that the inner element 40 comprises a socket 116 at the distal end of the imaging sheath 92. The camera tip 46 shown in Figures 14 and 15 comprises a proximal outer spigot 118 that is received in the socket 116. The camera tip 46 also defines a distally-facing irrigation outlet 120 in fluid communication with the irrigation 30 tube 112. For this purpose, the camera tip 46 comprises a proximal tubular inner spigot 122 that is received in the distal end of the irrigation tube 112. The irrigation channel thereby extends longitudinally from the irrigation tube 112 through the camera tip 46 from the inner spigot 122 to the irrigation outlet 120. 35 Within the camera tip 46, the irrigation channel has a dog-leg shape that offsets the irrigation outlet 120 laterally from the longitudinal axis of the irrigation tube 112. The 30 06 25 irrigation outlet 120 is thereby offset laterally from, and disposed beside, a distally-opening recess that houses a PCB 124, light emitters 126 such as LEDs and a CMOS imaging chip 128 exposed at the distal end of the camera tip 46. The light emitters 126 are disposed beside the imaging chip 128, preferably one on each side of the CMOS 5 chip 128. The ratio of the length of the internal space in the camera tip 46 to the length of the PCB 124 and the CMOS chip 128 is such that CMOS chip 128 does not sit inside the camera tip 46, at least to the extent that the field of view of the CMOS chip 128 could 10 otherwise be limited by the camera tip 46. Thus, the CMOS chip 128 is preferably at, or least substantially flush with, the distal end of the camera tip 46. A cable 130 extending along the electronics channel 114 beside the irrigation tube 112 conveys power from the power and data port 88 of the housing 62 to the PCB, LEDs 15 and the imaging chip and conveys image data from the imaging chip back along the inner element 40 to the power and data port. In this example, the cable 130 is surrounded by a protective sleeve 132 and is received in a longitudinal groove formed externally in the wall of the irrigation tube 112. 20 Returning to Figure 12, the intermediate element 42 comprises the steering sheath 94, an intermediate element hub 100 that is fixed to a proximal end of the steering sheath 94, and a moulded steering tip 134 that is fixed to a distal end of the steering sheath 94. The steering sheath 94 lies on and surrounds the imaging sheath 92, leaving a distally-protruding portion of the imaging sheath 92 defined by the camera tip 46 25 exposed. The intermediate element hub 100 comprises integrally-moulded tabs 136 that are diametrically opposed about, and extend radially from and parallel to, the longitudinal axis of the steering sheath 94. As will be explained, these projecting tabs 136 are 30 received in complementary formations of the housing 62 of the handle 34 to locate the intermediate element 42 against axial and circumferential movement relative to the handle 34. Additionally, integrally-moulded pairs of projections 138 extend laterally from mutually-opposed sides of the intermediate element hub 100 between the opposed tabs 136. In this example, the intermediate element hub 100 is overmoulded 35 onto the steering sheath 94 but could instead, or additionally, be bonded or welded to 30 06 25 the steering sheath 94 and / or could receive the steering sheath 94 as an interference fit. Turning now also to Figures 16 and 17, the intermediate element 42 further comprises 5 a rigid steering pull ring 140 that is oriented circumferentially within the distal end of the steering sheath 94, initially in axial alignment with the central longitudinal axis 58 of the steering sheath 94. In this example, the steering ring 140 is embedded or encased within the tubular wall of the steering sheath 94, sandwiched between inner and outer layers of the steering sheath 94. The steering tip 134 is overmoulded onto, or bonded 10 over, the distal end portion of the steering sheath 94 so as to receive, encircle and engage with the steering ring 140 within a socket 142 formed in a proximal portion of the steering tip 134. The steering ring 140 and the steering tip 134 lie at the interface between the imaging 15 sheath 92 and the steering sheath 94 and facilitate longitudinal movement of the imaging sheath 92 relative to the steering sheath 94. In particular, the imaging sheath 92 slides longitudinally within and with respect to the steering sheath 94, the steering ring 140 and an implant holder defined by the steering tip 134. 20 The pair of steering wires 106 acting on mutually opposed sides of the steering ring 140 extend proximally in parallel relation along the steering sheath 94 in mutual opposition about the central longitudinal axis 58. Like the steering ring 140, the steering wires 106 are embedded within the tubular wall of the steering sheath 94, for example enmeshed with or threaded through a braided structure of that wall. The steering wires 25 106 extend proximally from the steering ring 140 along the steering sheath 94 and through the intermediate element hub 100 to protrude proximally from the intermediate element hub 100, where they are crimped to corresponding wires of the steering system 72. As mentioned above, the steering wires 106 extend through the parallel side bores 104 of the inner element hub 98 when the intermediate element hub 100 30 and the inner element hub 98 are brought together in the hub assembly 68. In use of the device 32, increased tension applied selectively by the steering system 72 to one of the steering wires 106 pulls on the associated side of the steering ring 140, hence tilting the steering ring 140 away from axial alignment with the central 35 longitudinal axis 58. The steering tip 134 also tilts with the steering ring 140 by virtue of the engagement of the steering ring 140 within the socket 142 of the steering tip 134. 30 06 25 Consequently, the steering sheath 94 bends along its length toward the steering wire 106 that is under greater tension, similarly forcing the outer sheath 90 and the imaging sheath 92 of the delivery tube 36 to bend along their length. These concentric elements 5 of the delivery tube 36 bend together preferentially at a distal longitudinal position with respect to the steering sheath 94, immediately proximal of the steering ring 140. The intrados of that bend corresponds to the steering wire 106 that is under greater tension and the extrados of that bend corresponds to the steering wire 106 that is under lesser or no tension. 10 The steering tip 134 serves, in use, as a holder for an implant such as an expander 10. For this purpose, the steering tip 134 has a longitudinally-stepped profile such that its distal portion 144 is narrower than its proximal portion 146. A radially outer side of the distal portion 144 defines a cylindrical support surface of lesser diameter whereas a 15 radially outer side of the proximal portion 146 defines a cylindrical bearing surface of greater diameter. More specifically, the proximal portion 146 of the steering tip 134 is radially oversized relative to the diameter of the steering sheath 94 so that the bearing surface stands proud of the steering sheath 94. It is desirable that the steering sheath 94 is no wider than the proximal portion 146 of the steering tip 134 so as to facilitate 20 telescopic insertion of the intermediate element 42 into the outer element 38 during assembly of the delivery tube 36. In this example, the proximal portion 146 of the steering tip 134 also has a chamfered proximal edge to ease assembly. Whilst the concentric sheaths of the delivery tube 36 may slide past each other with 25 minimal frictional resistance, the proximal portion 146 of the steering tip 134 may optionally help to facilitate sliding movement of the outer sheath 90 relative to the steering sheath 94. In more detail, with particular reference to Figure 17, the distal portion 144 of the 30 steering tip 134 that defines the support surface comprises a support tube extending distally beyond the steering sheath 94, integral with and of lesser outer diameter than the proximal portion 146 of the steering tip 134. A circumferential step 148 effects a sharp reduction in the outer diameter of the steering tip 134 from the proximal portion 146 to the distal portion 144. The step 148 corresponds to a circumferential shoulder 35 between the proximal portion 146 and the distal portion 144 that lies in a plane substantially orthogonal to the longitudinal axis of the steering sheath 94. 30 06 25 Angularly-spaced implant retention formations, exemplified here by retaining lugs 150, protrude radially from the distal portion 144 of the steering tip 134. The height or radial protrusion of the retaining lugs 150 is the same as, or slightly less than, the height of 5 the step 148 defined by the radial extent of the shoulder beyond the distal portion 144. Conversely, the thickness of the wire of the expander 10 is slightly less than the height of the step 148. The expander 10 extends from a proximal end where it is supported by the distal portion 144 of the steering tip 134 to a distal end where it is supported by the camera tip 46 of the imaging sheath 92 in deployment stage zero. The retaining lugs 10 150 hold the expander 10 against axial and circumferential movement relative to the steering sheath 94. In this example, there are two retaining lugs 150 both offset to one side of the central longitudinal axis 58 of the steering sheath 94, with mutual circumferential spacing. The 15 lugs 150 of that pair are spaced apart from each other by a lesser sector spanning about 120° of arc to one side of the steering tip 134 and conversely by a larger sector spanning about 240° of arc to the other side of the steering tip 134. A third proximal apex of the expander 10 is accommodated between the lugs 150 in the larger of those gaps. 20 The retaining lugs 150 are spaced distally from the shoulder defined by the step 148 of the steering tip 134, defining slots or gaps 152 between the lugs 150 and the shoulder. Those gaps 152 receive respective proximal apices 16 of an expander 10 supported by the device 32 when the expander 10 is held against the support surface of the distal 25 portion 144 by the outer sheath 90. Thus, the thickness of the wire of the expander 10 is slightly less than the length of the gaps 152 between the lugs 150 and the step 148. The shoulder defined by the step 148 therefore serves as an additional proximal retention formation that cooperates with the retaining lugs 150, holding the proximal apices 16 of the expander 10 between the shoulder and the respective lugs 150 30 against axial movement relative to the steering tip 134. The retaining lugs 150 are also received between struts 18 of the expander 10 that converge to the respective proximal apices 14. Thus, the retaining lugs 150 locate the expander 10 against circumferential or angular movement relative to the steering tip 35 134. 30 06 25 By virtue of the retaining lugs 150 and the shoulder defined by the step 148, the expander 10 is located against axial and angular movement relative to the handle 34, save to the extent that the distal end of the steering sheath 94, and hence the steering tip 134 and the expander 10, can be deflected relative to the handle 34 by operating 5 the steering system 72. Internally, as shown in Figure 16, the steering tip 134 has a circumferential shoulder 154 that effects a step change in the diameter of its longitudinal lumen from the wider proximal portion 146 to the narrower distal portion 144. The internal diameter of the 10 distal portion 144 is a sliding fit with the imaging sheath 92, which slides longitudinally within and relative to the distal portion 144. The proximal portion 146 of the steering tip 134 accommodates the steering ring 140 as an interference fit. The steering ring 140 could also, or alternatively, be secured in 15 the steering tip 134 by a bonding or welding process suitable for polymers, such as reflow or over-moulding. Adhesives and curing could also be used. The distal end of the steering ring 140 faces or abuts the proximally-facing internal shoulder 154. Thus, this example has an implant holding and steering feature in the form of the 20 steering tip 134 that not only holds the expander 10 but can also steer the expander 10 and therefore the sheaths that support the expander 10. In this respect, it is advantageous to steer from behind the expander 10, i.e. at a position that is proximal relative to the expander 10, so as to guide the expander 10 forward through the anatomy to the deployment location. 25 In proximal succession from the expander 10, therefore, the steering sheath 94 fitted with the steering ring 140 and the steering tip 134 provides: holding features that hold and orient the expander 10; a steering mechanism acting on a flexible steering section; and a flexible proximal portion to track through the penile canal. In conjunction with the 30 imaging sheath 92 and the outer sheath 90, the structure of the steering sheath 94 must provide sufficient tensile or axial strength for unsheathing and re-sheathing the expander 10 and to allow for deflection of the expander 10 through all stages of deployment. The structure of the steering sheath 94 must also provide sufficient torsional strength to orient the expander 10 angularly about its central longitudinal axis 35 58 in response to corresponding angular manipulation of the handle 34 by a user. 30 06 25 Returning once again to Figure 12, the outer element 38 comprises a tubular outer sheath 90 and an outer element hub 96 that is mounted on the outer sheath 90 at or near its proximal end. The outer sheath 90 comprises a distal tip portion that may be coiled rather than braided to improve retention of the expander 10 and to conform to 5 steering deflection and a flexible proximal portion to facilitate navigation of the delivery tube 36, including steering movements of the delivery tube 36 driven by deflection of the steering sheath 94 disposed within the outer sheath 90. The outer sheath 90 also has a series of graduated and numbered external markings 156 along its proximal portion as a guide to the depth of insertion of the delivery tube 36 into the penile 10 urethra. As best appreciated in Figure 18, the outer element hub 96 comprises a tubular body 158 of circular cross-section that is concentric with the outer sheath 90. In this example, the outer element hub 96 is overmoulded onto the outer sheath 90. In other 15 examples, the outer sheath 90 could extend within the outer element hub 96 as an interference fit or could instead, or additionally, be bonded or welded to the outer element hub 96. Integrally-moulded locating formations protrude from the body 158 of the outer element 20 hub 96, namely: a proximal flange 160 that encircles the body 158 and lies in a plane orthogonal to a central longitudinal axis 58 of the outer sheath 90; and an elongate radially-protruding lug 162 that extends in a plane containing that axis 58. These locating formations 160, 162 are received in complementary formations at a distal end of a hub casing 164 of the hub assembly 68 to locate the outer element 38 against 25 axial and circumferential movement relative to the hub assembly 68. Moving on, therefore, to Figures 19a and 19b, the hub casing 164 of the hub assembly 68 is an elongate hollow enclosure that extends along the central longitudinal axis 58 of the housing 62 of the handle 34, in alignment with the corresponding axis of the 30 delivery tube 36. The hub casing 164 comprises a generally cuboidal body 166 and an integral open-ended tubular extension 168 that extends distally from the body 166, the tubular extension 168 being centred on the central longitudinal axis 58 and communicating with the interior of the body 166. 35 The hub casing 164 is divided into two casing parts along a central longitudinal plane that bisects the tubular extension 168 and a pair of mutually-opposed side faces of the 30 06 25 cuboidal body 166. The casing parts are brought together in mutual opposition about their planar interface and fastened together. In this example, the casing parts are fastened together by screws 170, one each side of the central longitudinal axis 58, at the junction between the body 166 and the tubular extension 168 of the hub casing 5 164. Thus assembled, the hub casing 164 receives, encloses and retains the hubs 96, 98, 100 of the outer element 38, the intermediate element 42 and the inner element 40 of the delivery tube 36. The outer element hub 96, the intermediate element hub 100 and 10 the inner element hub 98 are thereby disposed within the hub casing 164 in proximal succession. The hub casing 164 supports the outer element hub 96 at a distal end and the inner element hub 98 at a proximal end, and has a longitudinally-extending intermediate portion that connects the distal and proximal ends and bridges around the intermediate element hub 100. 15 The tubular extension 168 of the hub casing 164 defines an internal channel of circular cross-section that is a close fit around the body 158 of the outer element hub 96. The screws 170 that fasten together the casing parts can serve to clamp the outer element hub 96 between the distal ends of the casing parts that define the tubular extension 20 168. The tubular extension 168 of the hub casing 164 also has internal locating formations that are complementary to the external locating formations of the outer element hub 96. Specifically, the flange 160 of the outer element hub 96 is received in a circumferential 25 groove within the tubular extension 168 to prevent axial movement of the outer element 38 relative to the hub casing 164. Thus, the outer element 38 of the delivery tube 36 is constrained always to move with the hub casing 164 in longitudinal directions relative to the housing 62 of the handle 34. Similarly, the lug 162 of the outer element hub 96 is received in a longitudinal slot within the tubular extension to lock the outer element 38 30 against angular movement relative to the hub casing 164 about the central longitudinal axis 58. Referring now also to Figure 20, the outer and inner elements 38, 40 of the delivery tube 36 can move axially relative to both the intermediate element 42 and the handle 35 34 as noted previously. For this purpose, the hub casing 164 is movable reciprocally through a stroke range along the central longitudinal axis 58 within, and relative to, the 30 06 25 housing 62. The hub casing 164 is supported between, and is slidably movable along, longitudinally-extending parallel rail formations 172 that are moulded integrally into the inner face of each shell 64 of the housing 62. The hub casing 164 thereby serves as a carriage for the outer element hub 96 and for the inner element hub 98, carrying those 5 hubs 96, 98 for movement along a retraction path that extends longitudinally within the housing 62, parallel to the central longitudinal axis 58. Conversely, as also noted previously, the intermediate element 42 of the delivery tube 36 is fixed against axial movement relative to the handle 34. Consequently, provision is 10 made for the hub casing 164 to move longitudinally around, and relative to, the intermediate element hub 100 that is accommodated within the body 166 of the hub casing 164. For this purpose, the facing edges of the casing parts are cut away at their planar interface to define mutually-opposed longitudinal slots 174 when the casing parts are assembled together. Each slot 174 has a closed distal end and an open 15 proximal end. With reference to Figure 20, the slots 174 penetrate the aforementioned pair of side faces of the body of the hub casing 164 to accommodate the diametrically-opposed tabs 136 that extend laterally from the intermediate element hub 100. Those tabs 136 20 protrude from the hub casing 164 through the slots 174 to engage in respective socket formations 176 that are moulded integrally into the inner face of each shell 64 of the housing 62. In this way, the intermediate element hub 100 is locked against axial or angular movement relative to the housing 62, while the slots 174 provide clearance around the tabs 136 for the hub casing 164 and the outer and inner element hubs 96, 25 98 to move longitudinally relative to the intermediate element hub 100. The hub casing 164 slides over the aforementioned projections 138 of the intermediate element hub 100 disposed between the opposed tabs 136, which maintain lateral alignment between the hub casing 164 and the intermediate element hub 100. 30 Returning to Figure 19a, the cuboidal body 166 of the hub casing 164 has a further side face 178 disposed between the slotted pair of side faces. That further side face 178 is penetrated by slits in a C-shaped arrangement that define resiliently-deflectable tongues 180, 182 formed integrally with the body. One of those tongues 180 is at a distal location on the side face 178 and another of those tongues 182 is at a proximal 35 location on the side face 178. 30 06 25 The distal tongue 180 has an integral flange 184 at its distally-facing free end that protrudes outwardly from the surrounding side face 178 of the body 166. As shown in Figure 21a, the flange 184 snap-engages in a complementary inwardly-facing groove 186 in the adjacent rail formation of the housing 62 that guides longitudinal movement 5 of the hub casing 164 relative to the handle 34. Engagement between the flange and the groove latches the hub casing 164 against that longitudinal movement. This is to prevent inadvertent retraction of the outer element 38 of the delivery tube 36, hence transitioning the device 32 from deployment stage zero to deployment stage one, until a user applies enough force to the deployment trigger 48 to effect that transition 10 deliberately. In that case, as shown in Figure 21b, the distal tongue deflects 180 inwardly to disengage the flange 184 from the groove 186, thereby to free the hub casing 164 for movement relative to the housing 62. Returning again to Figure 19a, the proximal tongue 182 lies flush with the surrounding 15 side face 178 of the body 166 but the transverse slit 188 at its proximally-facing free end is enlarged to receive and engage with the aforementioned wedge formation 108 on a side face of the inner element hub 98. Initially, that engagement holds the inner element hub 98 at the proximal end of the hub casing 164. In this way, with reference to Figures 21a to 21c, the inner element hub 98 is constrained to move with the hub 20 casing 164 and with the outer element hub 96 as the device 32 transitions from deployment stage zero to deployment stage one. In the same way, the inner element hub 98 is constrained to move with the hub casing 164 and with the outer element hub 96 if the device 32 is returned from deployment stage one to deployment stage zero. 25 Unlike the outer element hub 96, the inner element hub 98 is not fixed to the surrounding hub casing 164 but can instead move relative to the hub casing 164 within a limited longitudinal range. With reference to Figure 21 d, this enables movement of the outer element hub 96, and therefore the outer sheath 90, to be decoupled from movement of the inner element hub 98, and therefore the imaging sheath 92, as the 30 device 32 transitions from deployment stage one to deployment stage two. Thus, as shown in Figures 21a to 21c, the inner element hub 98 moves proximally with the hub casing 164 from deployment stage zero to deployment stage one. Then, as shown in Figure 21 d, continued proximal movement of the inner element hub 98 35 ceases but the hub casing 164 undergoes further proximal movement independently from, and relative to, the inner element hub 98 from deployment stage one to 30 06 25 deployment stage two. Outward deflection of the proximal tongue 182 to clear the wedge formation 108 releases the inner element hub 98 to allow that relative movement of the hub casing 164. The proximal tongue 182 then returns resiliently inwardly to slide smoothly down the incline of the wedge formation 108 as the hub 5 casing 164 moves proximally relative to the inner element hub 98. The inner element hub 98 is decoupled from the hub casing 164 by using a barrier that blocks proximal movement of the inner element hub 98 but allows proximal movement of the hub casing 164 relative to the housing 62 to continue. Specifically, as shown in 10 Figures 21c and 21 d, proximal movement of the inner element hub 98 is blocked by encountering an integrally-moulded stop formation 190 of the housing 62. The stop formation 190 is aligned with the proximally-open longitudinal slot 174 of the hub casing 164 to be received in that slot 174 as proximal movement of the hub casing 164 continues. 15 As will now be explained with reference to Figures 22a to 22d, the deployment system 70 drives longitudinal movement of the hub casing 164 via an integral rack extension 192 that is cantilevered from the proximal end of the body 166. Conveniently, as shown in Figures 19a and 19b, the rack extension 192 is moulded integrally with one of the 20 casing parts. The rack extension 192 is offset laterally from, but otherwise extends generally parallel to, the central longitudinal axis 58 of the housing 62. An integrally-moulded rack formation 194 comprising a series of transverse teeth extends along a face of the rack extension 192 facing toward the central longitudinal axis 58. 25 Figures 22a to 22d show that the deployment system 70 comprises a transmission geartrain 196 that receives drive input from linear movement of the deployment trigger 48 along the trigger axis 78 and delivers corresponding drive output to the rack extension 192 of the hub casing 164. The rack extension 192 converts rotary motion of the geartrain 196 into linear movement of the hub casing 164 that faithfully follows 30 linear movement of the deployment trigger 48, albeit in a longitudinal direction that is transverse to the trigger axis 78. The geartrain 196 comprises an input gear 198 that is meshed with a rack 200 extending from the deployment trigger 48 parallel to the trigger axis 78. The input gear 35 198 is meshed with an output gear 202 that is meshed, in turn, with the rack extension 192 of the hub casing 164. The reversal of drive direction thus effected through the 30 06 25 geartrain 196 ensures that depressing the deployment trigger 48 along the trigger axis 78 causes the hub casing 164 to move proximally within the handle 34 as the device 32 transitions from deployment stage zero to deployment stages one and two. 5 If a user decides to reverse the device 32 from deployment stage one back to deployment stage zero, the user simply pulls or retracts the deployment trigger 48 out of the housing 62 of the handle 34 to cause the hub casing 164 to move distally within the handle 34. For this purpose, the external part of the deployment trigger 48 has concave recesses 204 on opposite sides to help the user to grip the deployment trigger 10 48 between their thumb and index finger. The overall gearing ratio of the geartrain 196 is chosen for mechanical advantage, allowing a user operating the deployment trigger 48 easily to move the hub casing 164 that acts on the outer element 38 and the inner element 40 of the delivery tube 36. The 15 gearing ratio is also chosen for sensitivity, in that a small movement of the deployment trigger 48 along the trigger axis 78 generates a large movement of the hub casing 164 in response. This reflects that it is desirable for the device 32 to transition quickly and positively from one deployment stage to another, and therefore for the hub casing 164 not to remain for any significant period in an intermediate position when in transition 20 between deployment stages. The detent provisions protect against inadvertent operation of the device 32 despite its deliberate sensitivity to movement of the deployment trigger 48. Within the housing 62, as shown in Figures 23a to 23d, the deployment trigger 48 25 serving as a deployment control element comprises an integral trigger ramp 204 that faces toward the detent axis 80. The trigger ramp 204 tapers away from the detent axis 80 in an inward direction extending into the housing 62, parallel to the trigger axis 78. At an inward end of the trigger ramp 204, a base platform 206 faces toward the detent axis 80 whereas at the outward end of the trigger ramp 204, an inwardly-facing 30 shoulder 208 extends toward the detent axis 80. On its inward side, the detent button 60 serving as a detent release element comprises an integral follower-engagement formation being a protrusion 210 that tapers in an inward direction extending into the housing 62, parallel to the detent axis 80. The taper 35 of the protrusion 210 defines a detent ramp 212 that faces away from the trigger axis 78. 30 06 25 The housing 62 contains a follower 214 that acts on, and is acted on by, the deployment trigger 48 and the detent button 60. The follower 214 is biased toward the trigger axis 78 by an integral spring 216 that acts in compression between the adjacent 5 outer wall of the housing 62 and the follower 214. The spring 216 presses the follower 214 against the trigger ramp 204 and the detent ramp 212 in turn so that those ramps 204, 212 act successively on the follower 214 with a cam action as the deployment trigger 48 and the detent button 60 are depressed inwardly in sequence. 10 The follower 214 has a trigger bearing edge 218 positioned to bear against the trigger ramp 204 and a detent bearing edge 220 positioned to bear against the detent ramp 212. Specifically, the trigger bearing edge 218 is at the free end of the follower 214 closest to the trigger axis 78 whereas the detent bearing edge 220 is closer to the spring 216, in this example defined by an inner edge of a window 222 that penetrates 15 the follower 214. More specifically, the detent bearing edge 220 is on a transverse barrier member 224 of the follower that is defined in this example by an inner side of a frame around the window 222, adjoining the spring 216 of the follower 214. The window 222 is wide enough to accommodate the protrusion 210 on the inward side of the detent button 60. 20 By interactions of the trigger ramp 204 and the detent ramp 212 with the trigger bearing edge 218 and the detent bearing edge 220 respectively, the follower 214 can adopt any of three positions determined by the positions of the deployment trigger 48 and the detent button 60. Specifically, the follower 214 adopts: a detent stop position when the 25 deployment trigger 48 is in the outward position corresponding to deployment stage zero as shown in Figure 23a; a deployment stop or trigger stop position when the deployment trigger 48 is depressed into the intermediate position corresponding to deployment stage one as shown in Figure 23b; and a deployment release or trigger release position when the detent button 60 is depressed at deployment stage one as 30 shown in Figure 23c. This allows further inward movement of the deployment trigger 48 to the fully inward position corresponding to deployment stage two, as shown in Figure 23d. Movements of the follower 214 from the detent stop position to the intermediate trigger stop position and from there to the trigger release position all take place against the bias of the spring 216. 30 06 25 Thus, inward movement of the deployment trigger 48 to bring the device 32 to deployment stage one moves the follower 214 to the trigger stop position shown in Figure 23a at which further inward movement of the deployment trigger 48 is blocked but inward movement of the detent button 60 is enabled. Thus, the trigger stop position 5 can also be regarded as a detent release position. Inward movement of the detent button 60 then moves the follower 214 to the trigger release position that enables further inward movement of the deployment trigger 48 to transition the device 32 from deployment stage one to deployment stage two. 10 Specifically, when the deployment trigger 48 is in an outward position corresponding to deployment stage zero, the trigger bearing edge 218 of the follower 214 rests against the base platform 206 at the inward end of the trigger ramp 204 as shown in Figure 23a. The barrier member 224 of the follower 214 is then aligned with the protrusion 210 of the detent button 60 to block inward movement of the detent button 60. 15 When the deployment trigger 48 is depressed inwardly toward an inward position corresponding to deployment stage one as shown in Figure 23b, the trigger ramp 204 slides past the trigger bearing edge 218 of the follower 214 and thereby forces the follower 214 away from the trigger axis 78 against the bias of the spring 216. Inward 20 movement of the deployment trigger 48 continues until the follower 214 encounters the shoulder 208 at the outward end of the trigger ramp 204, at a position of the deployment trigger 48 corresponding to deployment stage one. Interaction between the follower 214 and the shoulder 208 initially prevents further inward movement of the deployment trigger 48 beyond deployment stage one. 25 Movement of the follower 214 away from the trigger axis 78 under the action of the trigger ramp 204 moves the barrier member 224 of the follower 214 out of alignment with the protrusion 210 of the detent button 60, and conversely brings the window 222 of the follower 214 into alignment with the protrusion 210 of the detent button 60. This 30 enables inward movement of the detent button 60 as the protrusion 210 is received in the window 222. As the protrusion 210 of the detent button 60 enters the window 222 of the follower 214, the detent ramp 212 comes into contact with the detent bearing edge 220 on the 35 transverse barrier member 224 that defines the inner edge of the window 222. Continued inward movement of the detent button 60 causes the detent ramp 212 to 30 06 25 slide past the detent bearing edge 220 and so forces the follower 214 further away from the trigger axis 78 against the bias of the spring 216. This further movement of the follower 214 frees the follower 214 from the shoulder 208 at the outward end of the trigger ramp 204, thus enabling further inward movement of the deployment trigger 48 5 beyond deployment stage one into deployment stage two. If movement of the deployment trigger 48 is reversed to return the device 32 from deployment stage one to deployment stage zero, the follower 214 returns to its initial position in which the trigger bearing edge 218 of the follower 214 rests against the 10 base platform 206 at the inward end of the trigger ramp 204. The barrier member 224 of the follower 214 is then aligned again with the protrusion 210 of the detent button 60 to block inward movement of the detent button 60. Thus, the detent button 60 enables movement of the deployment trigger 48 into 15 deployment stage two by virtue of being enabled by movement of the deployment trigger 48 from deployment stage zero to deployment stage one. Inward movement of the deployment trigger 48 to bring the device 32 to deployment stage one moves the follower 214 against the bias of the spring 216. That movement enables inward movement of the detent button 60. Inward movement of the detent button 60 enables 20 further inward movement of the deployment trigger 48 to transition the device 32 from deployment stage one to deployment stage two. Turning finally to Figures 24a and 24b, the steering lever 44 of the steering system 72 acts on a steering dial 226 that pivots about the pivot axis 82 within the housing 62. 25 Steering wires (not shown) extend distally from respective opposed sides of the steering dial 226 and are crimped to the corresponding steering wires 106 that extend proximally from the intermediate element hub 100. Pivoting the steering dial 226 under angular forces applied via the steering lever 44 thereby applies tension selectively to the steering wires 106 to deflect the steering sheath 94 of the delivery tube 36 as 30 described previously. At its inward end within the housing 62, the steering lever 44 comprises an integral yoke 228 that surrounds the pivot axis 82 of the steering lever 44. The aforementioned locking axis 84, being a longitudinal axis of the steering lever 44, extends along a 35 radius that intersects the pivot axis 82. 30 06 25 The yoke 228 surrounds, and is engaged with, a complementary hub spigot 230 of the steering dial 226. The yoke 228 is oversized relative to the hub spigot 230 parallel to the locking axis 84 whereas in directions transverse to that axis 84, the hub spigot 230 is a close sliding fit within the yoke 228. Specifically, parallel side facets of the hub 5 spigot 230 bear against opposed side limbs of the yoke 228 to lock the yoke 228 against angular movement relative to the hub spigot 230. Consequently, torque transmitted from angular movement of the lever 44, for example when operated by a user’s thumb, turns the dial 226 about the pivot axis 82. Conversely, the yoke 228 is able to reciprocate to a limited extent in directions parallel to the locking axis 84. In that 10 case, the side facets of the hub spigot 230 slide within the opposed side limbs of the yoke 228. A spring 232 surrounds the locking axis 84 on an outboard side of the pivot axis 82 and acts in compression between the yoke 228 and the hub spigot 230 to bias the steering 15 lever 44 outwardly along the locking axis 84. Thus, a user’s thumb can press the steering lever 44 inwardly into the housing 62 in translation against the bias of the spring 232 to unlatch the steering lever 44 for angular movement. When inward thumb pressure is released, the bias of the spring 232 returns the steering lever 44 to an outward position in which the steering lever 44 is latched to prevent inadvertent angular 20 movement. For the purpose of latching the steering lever 44, the yoke 228 comprises latch formations that face outwardly along the locking axis 84. The latch formations are exemplified here by a convex-curved array 234 of teeth that is opposed to a 25 complementary concave-curved array 236 of teeth facing inwardly from an inner face of the housing 62. The arrays 234, 236 of teeth are each curved along their length with a substantially constant radius of curvature centred on the pivot axis 82. The teeth of the arrays 234, 30 236 are spaced apart along the length of the arrays 234, 236 and so are angularly spaced about the pivot axis 82. In this example, the teeth are oriented orthogonally with respect to the length of the respective arrays 234, 236. Elegantly, as shown here, the concave-curved array 236 of teeth facing inwardly from the housing 62 is integrally moulded with one or both of the shells 64 of the housing 62, which have corresponding 35 curvature about the pivot axis 82. 30 06 25 When the steering lever 44 is released, the bias of the spring 232 urges the latch formations of the yoke 228 outwardly, together with the yoke 228, to engage with teeth of the inwardly-facing array 236 that correspond to the angular position of the steering lever 44. This latches the steering lever 44 at a desired angular position. Conversely, 5 depressing the steering lever 44 against the bias of the spring 232 releases the latch formations from the teeth of the inwardly-facing array 236 to unlatch the steering lever 44 for angular movement. Many other variations are possible within the inventive concept. For example: the 10 device could comprise an on-board power supply; imaging could be effected by a nondigital imaging system other than a chip, such as by conveying images along a fibreoptic bundle; the stiffness of the imaging sheath can be tailored to vary along its length - for example, with tailored braiding comprising braided or coiled elements of varying density, pitch, angle and / or thickness and polymer durometer - so as to provide stable 15 support for the implant and yet to navigate easily within the deflected steering sheath. In the example shown, the implant holding feature is the moulded steering tip component that accommodates the steering ring as a separate component. However, in another embodiment, the implant holding feature and a pull ring or other steering 20 formation could instead be integrated into one component. The ramp formations of the deployment trigger and the detent button could instead, or additionally, be provided on the follower. 30 06 25

Claims

1. A device for deploying an implant in a patient’s body, the device comprising:5 an elongate delivery tube having delivery tube elements in concentric relation,those delivery tube elements being, in radially outward succession, an inner element comprising an imaging head, an intermediate element comprising implant retainer formations and an outer element comprising an outer sheath that is co-operable with the implant retainer formations, the inner and outer10 elements being retractable relative to the intermediate element along alongitudinal axis of the delivery tube; anda handle at a proximal end of the delivery tube, the handle having a housing that contains:15a hub assembly comprising an inner element hub, an intermediate element hub and an outer element hub, each of those hubs being mounted proximally to a respective one of the delivery tube elements;20 a hub carriage that is movable longitudinally with respect to the housingand to the intermediate element hub and that supports the inner element hub and the outer element hub for said movement with the hub carriage to retract the inner and outer elements relative to the intermediate element of the delivery tube; and25a deployment drive that is configured to drive said movement of the hub carriage in response to operation of a deployment control element that is external to the housing.30 2. The device of Claim 1, wherein the hub carriage is movable proximally by thedeployment drive relative to the housing and the intermediate element hub along a longitudinally-extending retraction path from an undeployed position in which the outer sheath is opposed to and in a distally advanced position relative to the implant retainer formations to a deployed position in which the outer sheath is retracted proximally35 beyond the implant retainer formations, via an intermediate partially deployed position30 06 25in which the outer element is retracted proximally from the distally advanced position while still being opposed to the implant retainer formations.

3. The device of Claim 2, wherein the outer element hub and the inner element hub are 5 movable proximally with the hub carriage from the undeployed position to the partially deployed position.

4. The device of Claim 3, wherein the outer element hub and the inner element hub are reversible with the hub carriage in a distal direction along the retraction path from the10 partially deployed position to the undeployed position.

5. The device of Claim 3 or Claim 4, wherein the outer element hub is movable proximally with the hub carriage relative to the inner element hub as the hub carriage moves from the partially deployed position to the deployed position.

156. The device of Claim 5, wherein the outer element hub is fixed relative to the hub carriage and the inner element hub is releasably latched relative to the hub carriage.

7. The device of Claim 6, further comprising a stop formation in fixed relation to the20 housing and positioned in the retraction path proximally of the inner element hub to block proximal movement of the inner element hub beyond the partially deployed position of the hub carriage, causing the inner element hub to unlatch from the hub carriage while allowing continued proximal movement of the hub carriage and the outer element hub from the partially deployed position to the deployed position.

258. The device of any of Claims 2 to 7, wherein the hub carriage is releasably latched relative to the housing when in the undeployed position, that latching being releasable by operation of the deployment control element.30 9. The device of any of Claims 2 to 8, wherein the deployment drive comprises a detentmechanism that is configured to block movement of the hub carriage from the partially deployed position to the deployed position and a detent release element that is operable to release the detent mechanism to allow the hub carriage to move from the partially deployed position to the deployed position.30 06 2510. The device of Claim 9, wherein the detent release element is enabled to release the detent mechanism by virtue of movement of the deployment control element that acts on the deployment drive to move the hub carriage from the undeployed position to the partially deployed position.

511. The device of Claim 10, wherein the deployment control element blocks movement of the detent release element when the hub carriage is in the undeployed position.

12. The device of any preceding claim, wherein the outer element hub, the intermediate 10 element hub and the inner element hub are disposed in proximal succession along the hub carriage.

13. The device of any preceding claim, wherein the hub carriage comprises a distal portion that supports the outer element hub, a proximal portion that supports the inner 15 element hub, and a longitudinally-extending intermediate portion that connects the distal and proximal portions and bridges around the intermediate element hub.

14. The device of any preceding claim, wherein the intermediate element hub is sandwiched between the outer element hub and the inner element hub and is at least 20 partially housed within the hub carriage.

15. The device of any preceding claim, wherein the intermediate element hub has at least one support that extends laterally beyond the hub carriage to fix the intermediate element hub against movement relative to the housing.2516. The device of Claim 15, wherein a side wall of the hub carriage comprises a longitudinally-extending slot that accommodates the laterally-extending support of the intermediate element hub to allow for movement of the hub carriage relative to the intermediate element hub.3017. The device of Claim 16, wherein the longitudinally-extending slot has an open proximal end.

18. The device of any preceding claim, wherein the deployment drive comprises a35 gearset that acts between the deployment control element and the hub carriage.

19. The device of Claim 18, wherein the hub carriage comprises a longitudinally-extending rack formation that is engaged with a gear of the deployment drive gearset.

20. The device of Claim 19, wherein the rack formation is on an arm that extends5 proximally from the hub carriage.

21. The device of Claim 20, wherein the arm is offset laterally from a central longitudinal axis that extends proximally into the housing from the delivery tube and wherein the rack formation faces that axis.30 06 25

Images