Apparatus for positioning a glenoid implant

Abstract

This disclosure describes an apparatus for positioning a central guide pin into a glenoid cavity. The apparatus (100,100a,200,200a) is made up of: a base plate (110,210,210a); a handle mountable on the base plate; a plurality of barbs projecting (113,213,213a) from a bottom surface of the base plate; a guide tube (170,270,270a) threadedly connected to a lock tube (180,280,280a), wherein a longitudinal bore (d) extends along longitudinal bores of both the guide tube and lock tube, with the lock tube having an anti-rotation collar (185,285); a first protractor mechanism for adjusting an angle of inclination (α) of the guide tube from a vertical X-axis to the base plate; and a second protractor mechanism with a plane of adjustment being perpendicular to a plane of adjusting the first protractor mechanism, so that trajectory of the central guide pin inserted in through the guide tube (170,270,270a) is defined by these two perpendicular planes.

Description

Apparatus For Positioning A Glenoid ImplantRelated Applications

[0001] The present invention claims priority to Singapore patent application no. 10202400408Q filed on 15 February 2024, the disclosure of which is incorporated in its entirety.Field of Invention

[0002] The present disclosure relates to an apparatus for positioning a glenoid implant; the apparatus assists in aligning and inserting a central guide pm when preparing to locate a glenoid component. More specifically, the apparatus possesses a positioning mechanism to allow a user to adjust a guide tube of the apparatus for the central guide pin to be inserted into a glenoid cavity position which is defined by two perpendicular planes.Background

[0003] Shoulder arthroplasty surgeries were known to have been performed as early as in the 1950s in the United States of America. In the past, shoulder arthroplasties were a form of treatment for shoulder fractures, but are now performed for many more reasons, such as relieving arthritic pain in the shoulder joint and to restore motion for people with decreased range of motion that compromises daily activities. Currently, up to about 53,000 people in the USA undergo shoulder arthroplasty yearly, however, this number is minute compared to the 900,000 people undergoing hip and knee replacement surgeries yearly. This can be attributed to the complexity of shoulder arthroplasties and the complications of the surgeries. People over 50 years of age often suffer from long-term wearing and degradation of the articular cartilage, bone and joint capsule, resulting in the development of pain and stiffness, often categorised as arthritis. The average age for patients to undergo reverse shoulder arthroplasty in 2011 is found to be about 72.71 years old, and the presence of chronic pain caused by arthritis was the primary indicator for about 88.63% of total shoulder arthroplasty (TSA). Additionally, people whose work requires heavy lifting, such as shipyard welders, may experience accelerated shoulder wear and disability, resulting in them also being a candidate for TSA. Traditional TSA operations are performed manually by surgeons according to their knowledge of the glenoid anatomy and with the help of preoperative X- ray films or CT images. There are 3 main reasons associated with the challenges faced to accurately position the glenoid component. Firstly, the glenoid has limited bone stock, andarthritic wear and erosion will decrease this glenoid bone stock. Secondly, the glenoid anatomy and anatomical position are highly varied among the population which affects the orientation of the glenoid prosthesis based on the bone structure. Lastly, limited bony landmarks are available to determine the position of the blade of the scapula intraoperatively which is necessary' for the accurate positioning of the glenoid component. These reasons will cause the positioning of the glenoid component to vary from person to person.

[0004] Over the last decade, technological advancements led to the adoption of new techniques to improve the accuracy of glenoid pin insertion and subsequent implant positioning in TSA. These techniques are namely surgical navigation (NAV) and patient-specific instrumentation (PSI). Several studies have ascertained significant improvement in glenoid positioning accuracy, however, these new techniques have yet to be widely adopted. Trade-offs between the potential benefits of these glenoid positioning systems with regards to an increased operation time, increased cost, system reliability and availability', training for operations, and other limitations for adoption and implementation. Patient-specific instrumentation (PST) is the most recent development in the field, with its efficacy demonstrated in both the version and inclination planes of glenoid positioning for shoulder arthroplasty'. With its wide adoption in a range of orthopaedic subspccialtics including hip and knee arthroplasty, PSI is the gold standard for glenoid component placement to date despite existing pitfalls associated with the method. The initial phase of developing patient-specific instrumentation (PSI) and guides is to generate a preoperative plan based on the data acquired from CT scans to locate and orientate the glenoid baseplate. Upon the surgeon's approval, a patient-specific guide is developed using the patient’s glenoid as a reference for the locating and orientating the central guide pin. The location of the central guide pin on the glenoid determines the centre of the glenoid baseplate, while the orientation of the pin will determine the version and inclination angles of the glenoid component. After the central guide pin is inserted into the glenoid, the remaining glenoid implantation will be referenced from the central guide pin and the patient-specific guides will direct the orientation of the glenoid during surgery'. PSI has the potential to provide a similar level of accuracy as surgical navigation, without the above-mentioned problems or additional surgical steps. Therefore, effort has been put into developing an apparatus or system for aligning the central guide pin to yield the best possible therapeutic outcome. For instance, US publication no. 2011040303 discloses an apparatus for dictating and locating insertion of the central guide pin during shoulder joint replacement. The apparatus has a location structure prefabricated with a plurality of spaced passagewaysto be used for guiding and dictating the placement trajectory of the central guide pin. However, the prefabricated passageways may somehow restrict the surgeon from placing the central guide pin at the best trajectory or location, which does not coincide with the prefabricated passageways.

[0005] Eash, et al., also discloses an adjustable glenoid pin insertion guide in US Patent No. 9,826,994 in that the guiding system includes an axis alignment device bearing a plurality' of through holes extending between a first surface and a second surface with each of the through holes defining a different alignment axis.

[0006] Tonier, et al., offers a system for guiding the central pin in glenoid fixation in US Patent No. 8,187,282; this system is equipped with a securing mechanism adapted to releasably secure a drilling guide, which can be adjusted on a working surface to reach the desired insertion angle. Both systems of Eash, et al., and Tonier. et al., require the alignment of the drill guide to be adjusted off-site (away from the surgery site) considering these systems are not well integrated as a single operable unit. More importantly, the adjustments may likely be done pre-operative based on the images captured from the CT scans. Such practice can be unfavourable especially when the CT images fail to precisely reveal scapular geometry. Therefore, it appears that there are still rooms for improvement associated with the central pin positioning and guiding systems.Summary

[0007] The following presents a simplified summary' to provide a basic understanding of the present invention. This summary is not an extensive overview of the present invention, and is not intended to identify key features of the invention. Rather, it is to present some of the inventive concepts of this invention in a generalised form as a prelude to the detailed description that is to follow.

[0008] The present invention seeks to provide an apparatus to assist a surgeon or medical practitioner in positioning a central guide pin for fixing a glenoid implant into a glenoid cavity . Desirably, the apparatus is equipped with an adjusting mechanism, which allows the user to manoeuvre or manipulate a guide tube within a given space to locate a desired or preferred entry point and a trajectory angle so that the central guide pin allows the glenoidcomponent to be implanted at the desired inclination angle and rotation angle in relation to the glenoid plane. Preferably, the adjustment mechanism permits the guide tube to be manipulated about two perpendicular protractors or two perpendicular planes of adjustments in relation to the glenoid plane. Preferably, the apparatus allows the centre guide pin adjustment to be locked after the inclination and rotation angles are set. Preferably, the apparatus is free from replacing, exchanging, or even removing parts from tire apparatus throughout its use during a surgical procedure, thus, allowing the apparatus to be applied directly on-site.

[0009] In one embodiment, the present invention provides an apparatus to assist positioning and inserting a central guide pin at a glenoid cavity, with the glenoid cavity being defined by a YZ plane and a vertical X-axis, and the apparatus comprises: a base plate with a planar section laying in the YZ plane; a plurality of barbs projecting from a bottom surface of the base plate to locate the base plate at the glenoid cavity; a first protractor mechanism is mountable on the base plate, so that a plane of adjustment of the first protractor mechanism is perpendicular to the base plate or YZ plane; and a second protractor mechanism is mountable on the base plate, so that a plane of adjustment of the second protractor mechanism is perpendicular to the plane of adjustment of the first protractor mechanism.

[0010] In one embodiment, the first protractor mechanism comprises a protractor, a guide tube positioning mechanism and a guide tube locking mechanism disposed between two truncated hemicircular sidewalls of the protractor wherein adjustment of the first protractor mechanism provides a measure of an angle of inclination a of the guide tube from the vertical X axis.

[0011] Preferably, a guide tube of the guide tube positioning mechanism is threadedly connected to a lock tube of the lock tube locking mechanism, wherein the lock tube further comprises an anti-rotation collar, so that the anti-rotation collar is located between the two truncated hemicircular sidewalls of the protractor and dispenses away with use of any tool during use, and wherein the lock tube is threadedly terminated with a part-spherical nut, so that the part-spherical nut is journaled in an aperture passing through a thickness of the base plate, such that the guide tube positioning mechanism is pivotable about a common centre of rotation of the part-spherical nut and the aperture.

[0012] Preferably, the second protractor mechanism comprises the protractor, the base plate and a ball bearing assembly disposed between the protractor and the base plate, so that the second protractor mechanism provides a measure of an angle of rotation p of the protractor with respect to the base plate or YZ plane.

[0013] In another embodiment of the above apparatus, the first protractor comprises : a bridge protractor terminating with two terminal sliders, with the tw o terminal sliders supporting two spaced apart bridge members: two truncated hemicircular tracks that extend vertically from the base plate, wherein the two terminal sliders are fitted to slide on the respective truncated hemicircular tracks; and a protractor keeper terminating with two lower terminal sliders, wherein the two lower terminal sliders arc operable to slide on respective lower hcmicircular tracks, w hich are formed angularly parallel to the associated truncated hemicircular track, so that the sliding movements of the terminal sliders on the respective truncated hemicircular tracks remain positively engaged; wherein the first protractor mechanism is slidable on the spaced apart bridge members of the bridge protractor.

[0014] Preferably, the first protractor mechanism further comprises a guide tube positioning mechanism and a lock tube locking mechanism which are disposed to slide between the two spaced apart bridge members, with the first protractor mechanism providing an inclination angle a of the guide tube positioning mechanism. Preferably, the Lwo truncated hemicircular tracks form the second protractor mechanism, which provides an angle of rotation y of the first protractor mechanism.

[0015] Preferably, the base plate further comprises a central aperture which allows a tip of the lock tube locking mechanism to extend to the glenoid plane and to facilitate visual inspection when inserting the central guide pin into the glenoid cavity.Brief Description of the Drawings

[0016] This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which:

[0017] FIGs. 1-2 illustrate a picture of a scapula and a glenoid plane at a glenoid cavity into which a glenoid component is to be implanted;

[0018] FIG. 3 illustrates a perspective view an apparatus for positioning a central guide pin according to an embodiment of the present invention, whilst FIG. 4 illustrates a side view of the apparatus, and FIG. 5 illustrates a top view of the apparatus:

[0019] FIG. 6 illustrates an assembly of a protractor with a guide tube, a lock tube and a base plate of the apparatus shown in FIGs 3-5;

[0020] FIG. 7 illustrates a top perspective view of the protractor, whilst FIG. 8 illustrates a bottom perspective view of the protractor and a bearing inner locating ring according to one embodiment;

[0021] FIG. 9 illustrates an exploded view of the guide tube, the lock tube and a spherical nut to show a locking mechanism on the guide tube;

[0022] FIG. 10 illustrates an integrated assembly of the lock tube and spherical nut according to another embodiment;

[0023] FIGs. 11-13 illustrate an apparatus for positioning a central guide pin according to another embodiment of the present invention;

[0024] FIG. 14 illustrates a base plate of the apparatus shown in FIGs. 11-13;

[0025] FIG. 15 illustrates an exploded view of the apparatus shown in FIGs. 11-13;

[0026] FIGs. 16-17 illustrate locking and positioning mechanisms of the apparatus shown in FIGs. 11-13; and

[0027] FIGs. 18-19 illustrate an apparatus according to a variation of the embodiment shown in FIG. 11.Detailed Description

[0028] One or more specific and alternative embodiments of the present invention will now be described with reference to the attached drawings. It shall be apparent to one skilled in the art, however, that this invention may be practised without such specific details. Some of the details may not be described at length so as not to obscure the present invention. For easeof reference, common reference numerals or series of numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0029] The present invention provides apparatuses 100,200,200a for positioning a central guide pin to enter a desired trajectory' into a glenoid cavity where the scapula tissue is dense. FIG. 1 shows a plan view of the glenoid cavity, whilst FIG. 2 shows a side view of the scapula. As shown in FIGs. 1-2, the X-axis indicates the medial-lateral direction, whilst the Y-axis indicates the anterior-posterior direction and the Z-axis indicates the inferior-superior direction of the glenoid cavity. The YZ plane defines a glenoid plane, on which base plates 110,210,210a of the apparatuses of the present invention are parallelly orientated. Angular orientation about or in the YZ plane defines a rotation angle of the central guide pin about the YZ plane, whilst an inclination angle of the central guide pin is defined from the vertical X-axis; in other words, the rotation angle of the central guide pin lays in one plane of adjustment of the apparatus, whilst the inclination angle in a vertical plane from the vertical X-axis axis defines another plane of adjustment, where both planes of adjustments are mutually perpendicular; by setting the central guide pm using these two mutually perpendicular planes, trajectory of the central guide pin into the glenoid cavity is precisely defined.

[0030] FIGs. 3-5 show various views of the apparatus 100 for positioning the central guide pin, which is guided by a hollow guide tube 170. As shown in FIGs. 3-5, the apparatus 100 is made up of a base plate 110, a ball bearing 140, a protractor 160, a lock tube 180, a part- spherical nut 190 and the hollow guide tube 170. Preferably, a handle 130 is connected to the base plate 110 to provide a user a gripping point to hold or stabilize the apparatus 100. A bottom surface 112 of the base plate 110 has a number of barbs 113 projecting to engage with the bone tissue located around the glenoid cavity. The guide tube 170 has a longitudinal bore 172 (along a longitudinal axis CC) which guides insertion of the central guide pm into the glenoid cavity. In use, the base plate 110 is located in the glenoid plane YZ. Also in use, the guide tube 170 is slidable along a longitudinal slot 162 of the protractor 160 to align the guide tube 170 with respect to the vertical X-axis; the inclination angle of the guide tube 170 from the vertical X-axis can be read from protractor graduations 161 marked on a side of the protractor 160 by using a pointer 303 on an incline indicator 300. The protractor 160 is thus configured as a first protractor mechanism. The subassembly of the bearing 140, the protractor 160, the lock tube 180, the part-spherical nut 190 and the guide tube 170 allowsthe lock tube subassembly of the apparatus 100 to be rotated about the glenoid plane YZ, with graduation markings 101 on a top surface 111 of the base plate 110 to indicate the rotation angle; rotation of the lock tube subassembly, enabled by the bearing 140, is thus called a second protractor mechanism . These two perpendicular planes of adjustments or two mutually perpendicular protractor mechanisms thus allow setting of desired inclination angle and rotation angle of the guide tube 170, so that trajectory of the central guide pin into the glenoid cavity is determined where the bone density is dense; these desired inclination angle and rotation angle are obtained from data acquired from preoperative CT scans.

[0031] FIG. 6 shows a front view of a positioning mechanism and a locking mechanism of the guide tube 170. As shown in FIG. 6, the guide tube positioning and locking mechanisms include an assembly of the guide tube 170, lock tube 180, part-spherical nut 190, protractor 160, ball bearing 140 and the base plate 110 Tn another embodiment, the guide tube positioning mechanism includes the incline indicator 300 disposed between the guide tube 170 and the protractor 160; the incline indicator 300 is provided to indicate the inclination angle a of the guide tube from the vertical x-axis according to angle markings 161 on the protractor. FIGs. 7-8 show two views of the protractor 160. The ball bearing 140 allows the positioning and locking mechanisms of the guide tube 170 to be adjusted rotatory about the base plate 110, ie. in the YZ plane. There are 3 possible ways of mounting the ball bearing 140 between the protractor 160 and the base plate 110:1. an inner locating ring 142 is connected to a base of the protractor 160 (either by welding or screws, as seen in FIG. 8), whilst an outer race of the ball bearing 140 is welded to the top surface 111 of the base plate 110, so that the ball bearing 140 is removeably press-fitted to the inner locating ring 142; or2. an inner race of the ball bearing 140 is welded to the base of the protractor 160, whilst an outer locating ring 144 is connected on the top surface 111 of the base plate 110 (either by welding or by screws, as seen in FIG. 3 or 5), and press-fitting the ball bearing 140 into the outer locating ring 144, so that the ball bearing is removeably press-fitted to the top surface 111 of the base plate 110; or3. the inner locating ring 142 is connected to the base of the protractor 160 (either by welding or screws) and the outer locating ring 144 is connected to the top surface 111 of the base plate 110 (also either by welding or by screws), so that the ball bearing 140 is removeably press-fitted betw een the base plate 110 and the protractor 160.

[0032] FIGs. 7-8 show the protractor 160 is preferably machined out from a block with a part hemi-circular profile and is formed with a longitudinal slot 162. of width W at a top portion, to create two sidewalls 163, a base 166 and an opening 164 at the base 166. As will be appreciated, the opening 164 at the base 166 is dimensioned to allow the lock tube 180 of the positioning and locating mechanisms to move in the entire range of inclination -a,+a within tire longitudinal slot 162 of tire protractor 160. As seen in FIG. 7, the base 166 of the protractor 160 is provided with two or more holes 167 to receive screws for connecting the inner locating ring 142 onto the base of the protractor 160

[0033] FIG. 9 sho s an exploded view of the guide tube positioning and locking mechanisms. As seen from FIG. 9, a distal end of the guide tube 170 is threadedly joined to an upper end of the lock tube 180, by a female thread 174 on the guide tube and a male thread 182 on the lock tube 180; a lower end of the lock tube 180 is threadedly connected to the part-spherical nut 190 by a male thread 183 on the lock tube and a female thread 193 in the part-spherical nut 190. Tire lock tube 180 has an anti-rotation collar 185 located intermediate between two ends of the lock tube 180; the anti-rotation collar 185 is formed of a square, rectangular or hexagonal section, with at least two across-flat surfaces AF. When assembled, the AF surfaces of the anti-rotation collar 185 fit into the width W of the longitudinal slot 162 of the protractor 160 and prevent rotation of the anti-rotation collar 185 in the longitudinal slot 162 without using any tool; when the guide tube 170 is sub-assembled, a proximal end of the guide tube 170 being located above curved surfaces of the truncated hemi-circular sidewalls 163, and the lower end of the lock tube 183 is threaded terminated by the part-spherical nut 190; this sub-assembly constitutes the guide tube positioning and locking mechanisms. For example, when the guide tube 170 is in the desired inclination angle from the X-axis in a first protractor plane and the protractor 160 is rotated to the desired rotation angle on the base plate 110 about a second protractor plane that is perpendicular to the first perpendicular plane, the guide tube 170 is turned about its length; if the threads on the guide tube 170 and the lock tube 180 are formed with right-hand threads, then turning the guide tube 170 in a clockwise direction will bring the threaded end of the guide tube 170 closer to the threaded end of the lock tube 180; in this manner, by turning the guide tube 170 in a clockwise direction, the proximal end of the guide tube 170 abuts against the truncated hemicircular surfaces at the top of the protractor side walls 163, whilst the part-spherical nut 190, having a part-spherical surface 192, bears against a matching truncated spherical aperture 116 through which the lock tube 180 is located. The truncated-spherical surfaces at the sphericalaperture 116 and the part-spherical nut 190 form a ball -joint, which allows the guide tube 170-lock tube 180 subassembly to be adjusted in the longitudinal slot 162 of the protractor 160 to the desired inclination angle a from the vertical X-axis and for the protractor to rotate angularly p on the base plate 110, before the guide tube 170 is turned to tighten the guide tube-lock tube subassembly onto both the protractor 160 and the base plate 110. To loosen the guide tube positioning and locking mechanisms, turning the guide tube 170 in a reverse manner will loosen the guide tube-lock tube subassembly from the protractor 160 and the base plate 110, thereby allow ing the guide tube 170 to be re-positioned inside the protractor 160 and the protractor to be angularly p re-adjusted with respect to the base plate 110. If the threaded portions of the guide tube 170, the lock tube 180 and the part-spherical nut 190 are formed in the left-hand threads, the above tightening or loosening of the guide tube positioning and locking mechanisms are operated by turning the guide tube 170 is a reverse direction from that described above.

[0034] Referring back to FIG. 9, the longitudinal bore 172 of the guide tube 170 is indicated by dimension d. The lock tube 180 also has a longitudinal bore 187 of dimension d, whilst a bore 194 through the part-spherical nut 190, is also of dimension d: the longitudinal bores 172, 187 and 194 arc aligned and thus provide a channel to allow the central guide pin to enter into the glenoid cavity at the desired inclination angle a in the first protractor mechanism and the rotation angle p about the second protractor plane.

[0035] In FIG. 9, the lock tube 180 and the part-spherical nut 190 are formed as separate parts. It is possible that the lock tube 180 and the part-spherical nut 190 can be formed integrally, as shown in FIG. 10. Of course, the truncated spherical aperture 116 at the base plate 110 has to be shaped or dimensioned for the anti-rotation collar 185 to pass through during sub-assembling of the guide tube positioning and locking mechanisms.

[0036] Tn one embodiment, a terminal or distal end of the guide tube 170 is ribbed to provide positive grip by the user. In another embodiment, the terminal end of the guide tube is knurled.

[0037] Referring back to FIG. 6 and the above description, the ball bearing 140 is located on the protractor 160 or the base plate 110, or removeably located between the protractor 160 and the base plate 110 by the inner locating ring 142 and the outer locating ring 144. Theball bearing is obtainable from HiPicco (China), with model part number 6802-2RS. FIG. 6 also shows a common centre O of the part-spherical nut 190 and truncated spherical aperture 116; the curved edges 163 of the protractor 160 are truncated hemicircularly and are shown with a radius R from the spherical centre O.

[0038] Referring back to FIGs. 3-5, a tapped hole 117 is provided at a peripheral edge of the base plate 110; the tapped hole 117 is used to fix the T-shaped handle 130 to the base plate 110. The tapped hole 117 or T-shaped handle 130 may be orientated with respect to the positions of the barbs 113, so as to define a reference mark for graduations of the rotation angle P about the second protractor mechanism. Tn another embodiment, the base plate 110 is oval in shape and has a major diameter (along the Z-axis) of substantially 50 mm and a minor diameter (along the Y-axis) of substantially 40 mm; these dimensions give a reader a sense on the minuteness of the apparatus 100 and the ball bearing 140, and these dimensions are therefore non-restrictive.

[0039] In terms of material of construction of the above apparatus 100, the material should be able to withstand repeated mechanical brushing or chemical sterilization. In one embodiment, a suitable material for making the components of the apparatus 100 is stainless steel, preferably of a surgical grade, or titanium. In another embodiment, it is possible that a base plate 110a is made of a transparent material, such as, PMMA (or poly(methyl methacrylate)). This apparatus with the base plate 110a being transparent allows the user to visually check positioning of the centre guide pin 170 before or during a surgical procedure. When non-steel materials are used for the base plate 110 and the protractor 160, the ball bearing 140, the inner locating ring 142 or outer locating ring 144 can be connected to the base plate 110 or the protractor 160 by an adhesive, preferably after curing.

[0040] FIGs. 11 -17 show the apparatus 200 according to a second embodiment of the present invention. As shown in FIGs. 11-17, the apparatus 200 is made up of a base plate 210 and a pair of spaced apart truncated hemicircular tracks 250a,250b; a bridge protractor 260 with terminal sliders 262a, 262b to slide on the truncated hemicircular tracks; a protractor keeper 260a; a guide tube 270; a lock tube 280, an incline indicator 300a, and a T-shaped handle 230. The bridge protractor 260 and the protractor keeper 260a form a first protractor mechanism, which is operable to incline to the vertical X-axis in a first vertical plane. The truncated hemicircular tracks 250a, 250b extend from the base plate 210 and together with the terminal sliders 262a, 262b form a second protractor mechanism, with an axis of rotationof the truncated hemicircular tracks 250a,250b laying in the glenoid plane YZ; in other words, the truncated hemicircular tracks 250a, 250b provide angular rotation of the guide tube 270 subassembly in a second plane that is perpendicular to the first vertical plane. Thus, by setting the guide tube 270 about two mutually perpendicular planes, the direction of positioning of the guide tube 270 is defined and trajectory of the central guide pm passing through the bore 272 of the guide tube 270 is determinate.

[0041] FIG. 13 shows a plan view of the apparatus 200, whilst FIG. 14 shows a perspective view of the base plate 210. As seen from FIG. 14, the right-side truncated hemicircular track 250a is formed of a truncated hemicircular arch, with an upper track surface 253a and a lower track surface 254a which is angularly' parallel to the upper track surface 253a; the leftside truncated hemicircular track 250b is formed of a truncated hemicircular structure with a recess 252 located on an inside facing surface; the inside recess 252 thus forms a lower track surface 254b, which is angularly parallel to an upper track surface 253b that is relatively wider than that of the right-side truncated hemicircular track 250a. The radius of curvature R of the truncated hemicircular tracks 250a, 250b from the glenoid plane is shown in FIGs. 15-17.

[0042] FIG. 15 shows an exploded view of the apparatus 200, and a positioning mechanism and a locking mechanism of the guide tube 270. These positioning and locking mechanisms of the guide tube 270 are more clearly' described with FIGs. 16 and 17. As seen from FIGs. 11, 13 and 15, the bridge protractor 260 is made up of two parallel arcuate members that arc spaced apart, with the right-hand end of the bridge protractor 260 terminating with the terminal slider 262a, whilst the left-hand end terminating with the terminal slider 262b. The terminal slider 262a fits and slides on the upper track surface 253a of the truncated hcmicircular track 250a; in addition, the terminal slider 262a also has an outer guide 265a that extends over the edge of the upper track surface 253a, so that sliding on the right-side truncated hemicircular track 250a is smooth and guided. In addition, the protractor keeper 260a is spaced apart below the bridge protractor 260, so that a right-side terminal 263a of the protractor keeper 260a has a terminal surface 264a that is shaped and dimensioned to slide on the lower surface 254a of the right-side truncated hemicircular track 250a. When the bridge protractor 260 and the protractor keeper 260a are assembled and held in place by the positioning and locking mechanisms, the right-side terminal 263a of the protractor keeper 260a ensures that the terminal slider 262a is positively guided to slide on the lower tracksurface 254a and prevents the terminal slider 262a from disengaging from the truncated hemicircular track 250a. In a similar manner, the left-side terminal slider 262b of the bridge protractor 260 fits and slides on the upper track surface 253b of the left-side truncated hemicircular track 250b and has an outer guide 265b that extends over a side-edge of the truncated hemicircular track 250b. The left-side terminal 263b of the protractor keeper 260a has a terminal surface 264b that is shaped and dimensioned to fit and slide on the recessed, lower surface 254b of the left-side truncated hemi circular track 250b, thus ensuring that the sliding of the protractor 260 on the truncated hemicircular track 250b is smooth, guided and prevented from disengaging.

[0043] In another embodiment of the bridge protractor 260, an inner guide 267a (as seen in FIG. 16) is provided on the right-side terminal slider 262a that engages with an inner sideedge of the right-side truncated hemicircular track 250a to further guide the sliding of the bridge protractor 260 on the truncated hemicircular track 250a. Similarly, an inner guide 267b is provided on the left-side terminal slider 262b to engage with an inner side-edge of the left-side truncated hemicircular track 250b to further guide the sliding of the bridge protractor 260 on the left-side truncated hemicircular track 250b.

[0044] Referring to FIGs. 16 and 17, functions the positioning and locking mechanisms of the guide tube 270 arc now described. The positioning mechanism of the guide tube 270 allows adjustments of the guide tube 270, ie. inclining the guide tube 270 with the bridge protractor 260 from the vertical X-axis, and angularly sliding the guide tube 270 subassembly on the truncated hemicircular tracks 250a,250b, ie . angularly rotating the guide tube 270 subassembly in the glenoid plane YZ (ie. about an axis laying in the glenoid plane YZ). As in the above embodiment, the guide tube 270 has an internal bore 272 to guide insertion of the central guide pin and a lower end of the guide tube has a female thread 274; the female thread 274 is threaded connected to a male thread 282 located on the lock tube 280 The lock tube 280 has an anti-rotation collar 285, which is shaped and dimensioned to fit between the two arcuate members of the bridge protractor 260; below the anti-rotation collar 285 is a stopper collar 286 (as seen more clearly in FIG. 15); the stopper collar 286 is substantially rectangular in profile and is shaped and dimensioned to contact the lower edges of the protractor keeper 260a. The incline indicator 300a is disposed to slide on the bridge protractor 260 with a pointer 303 to facilitate reading of inclination angle markings 261 located on the bridge protractor 260; the incline indicator 300a has a substantially U-shapedprofile where two side members 301 fit over the bridge protractor 260 to provide a sliding fit: a central member of the U-shaped incline indicator 300a has a hole 302 through which the lock tube 280 passes. When assembled, the guide tube 270, the lock tube 280, the bridge protractor 260, the protractor keeper 260a form the locking mechanism of the guide tube 270, with the incline indicator 300a to show the inclination angle a of the guide tube 270 from the vertical X-axis. FIG. 16 show's the locking mechanism of the guide tube 270 subassembly is in the unlocked state, in which the right-side terminal surface 264a of the protractor keeper 260a is spaced from contact with the lower surface 254a of the right-side truncated hemicircular track 250a; at the same time, the left-side terminal surface 264b of the protractor keeper 260 is spaced from contact with the recessed, lower surface 254b at the left-side truncated hemicircular track 250b. To lock or tighten the locking mechanism, the guide tube 270 is turned in the clockwise direction (as shown in FIG. 17) and this causes the lock tube 280 to move up, resulting in the stopper collar 286 pressing against the lower edges of the protractor keeper 260a against the bridge protractor 260, if the threaded connections 274 and 282 are formed with right-hand threads; if the threaded connections 274 and 282 are formed with left-hand threads, turning the guide tube 270 in the anticlockwise direction would tighten the locking mechanism of the guide tube 270. When the locking mechanism of the guide tube 270 is in the unlocked state, the lock tube 270 is adjusted by inclining it to the vertical X-axis, ie. by sliding the lock tube 270 along the bridge protractor 260, and at the same time angularly rotating the entire bridge protractor 260 sub-assembly on both the truncated hemicircular tracks 250a,250b (ie. rotating the lock tube 270 subassembly in the YZ plane) to the desired inclination a and rotation y angles; these desired inclination and trajectory angles of the central guide pin are obtained from data acquired from preoperative CT scans and are translated to the inclination angle a and rotation angle y of the apparatus 200. The locking mechanism is then tightened in steps to ensure that the guide tube 270 remains in the both desired inclination and rotation angles to guide insertion of the central guide pin; once the desired inclination and rotation angles arc set, the guide tube 270 is further turned to positively lock its position on the apparatus 200.

[0045] In FIGs. 15-17, the YZ plane is shown below the base plate 210, by a predetermined distance P to lay in the glenoid plane; P may be substantially a height of the barbs 213; the tip of the lock tube locking mechanism, when unlocked, is thus projected below the base plate 210 to lay in the glenoid plane; at this position, the tip of tire lock tube 280 remains stationary' w'hen the angles of inclination a and rotation y are being adjusted; the centralaperture 205 thus allows the user visual inspection as the central guide pin is inserted into the glenoid cavity. In another embodiment, the YZ plane is aligned along a bottom surface of the base plate 210; adjusting the angles of inclination a and rotation y remain the same except that the depth of the central guide pin will need to be adjusted by substantially P / cosacosy.

[0046] In FIG. 15, the left-side terminal slider 262b is substantially V-shaped and is constructed with two amis 265b; located between the two amis 265b is a pointer 266; the pointer 266 is provided to facilitate reading of the rotation angle y markings 251 located on a wall of the left-side truncated hemicircular track 250b.

[0047] Tn addition, a T-shaped handle 230 is provided to extend from the base plate 210 to allow the user to hold the apparatus 200 whilst setting the inclination and rotation angles of the guide tube 270. Preferably, the T-shaped handle 230 is removeably connected to the base plate 210 via a threaded joint 217. Also preferably, the threaded joint 217 is formed with a boss 218; these are more clearly shown in FIG. 14.

[0048] As similar to the above embodiment 100, the base plate 210 profile is oval in shape with the major diameter being substantially 50 mm and the minor diameter being substantially 40 mm. However, in this apparatus 200, the base plate 210 has the centre aperture 205 of substantially 20 mm. Advantageously, the aperture 205 allows the user to visually check insertion of the central guide pin when it exits the bores 272,287 of the guide tube 270 and the lock tube 280.

[0049] In one embodiment, the apparatus 200 is fabricated from stainless steel, preferably of a surgical grade, or titanium. In another embodiment, the guide tube 270 and the lock tube 280 are made of surgical grade stainless steel, whilst other components of the apparatus 200 are 3D printed using ABS (Acrylonitrile Butadiene Styrene), PLA (polylactic acid or polylactide) or PCL (polycaprolactone); these 3D printed materials are selected for their ability to withstand mechanical brushing or chemicals that are used for repeated sterilization.

[0050] FIGs. 18-19 show a variation 200a of the above apparatus 200 without altering the principles underlying the present invention; for eg., a guide tube 270a is connected to a lock tube 280a and the subassembly is supported on an incline indicator 300a, a bridge protractor 260a, with terminal sliders 262aa,262ba slidable on hemicircular tracks 250aa,250ba, andangular protractor graduations 251a,261a. In addition, aperture 205a allows visual inspection of the tip of the lock tube 280a where the central guide pin exits during setting of the apparatus. Briefly, some features of the variation 200a that differ from the components of the above apparatus 100,200 are:1. a base plate 210a is now L-shaped and has a rectangular outline, instead of the oval outline of the above base plate 110,210;2. a handle 230a is now connected to the L-shapcd portion of the base plate 210a, instead of being located inline with the bridge protractor 260 of the apparatus 200; as a result, the external dimensions of the base plate 210a are smaller, for eg., are substantially 33mm x 26mm;3. the handle 230a is now locked to the base plate 210a by a jam screw 231, which allows the angular orientation of the handle 230a to be adjustable with respect to the base plate 210a according to a need;4. the hemicircular tracks 250aa,250ba are now of substantially similar width, whereas the left-hand semicircular track 250b of the apparatus 200 is wider than the right-hand semicircular track 250a; in addition, the left-hand semicircular track 250ba is formed of an arch, and this allows unobstructed viewing of the end of the lock tube 280a during setting of the apparatus 200a; and5. spikes 213a extend integrally from a lower surface of the base plate 210a, instead of discrete spikes 113,213 of the above apparatus 100,200.

[0051] While specific embodiments have been described and illustrated, it is understood that many changes, modifications, variations and combinations of variations disclosed in the text description and drawings thereof could still be made to the present invention without departing from the scope of the present invention. For example, a locking mechanism may be provided to further lock the left-side terminal slider 262b to the left-side truncated hcmicircular track 250b once adjustments of the apparatus 100,200,200a arc set.

Claims

CLAIMS1. An apparatus to assist positioning and inserting a central guide pin at a glenoid cavity, with the glenoid cavity being defined by a YZ plane and a vertical X-axis, and the apparatus comprises: a base plate with a planar section laying in the YZ plane; a plurality of barbs projecting from a bottom surface of the base plate to locate the base plate at the glenoid cavity; a first protractor mechanism is mountable on the base plate, so that a plane of adjustment of the first protractor mechanism is perpendicular to the base plate or YZ plane; and a second protractor mechanism is mountable on the base plate, so that a plane of adjustment of the second protractor mechanism is perpendicular to the plane of adjustment of the first protractor mechanism.

2. The apparatus according to claim 1 , wherein the first protractor mechanism comprises a protractor, a guide tube positioning mechanism and a guide tube locking mechanism disposed between two truncated hemicircular sidewalls of the protractor wherein adjustment of the first protractor mechanism provides a measure of an angle of inclination a of the guide tube from the vertical X axis.

3. The apparatus according to claim 2, wherein a guide tube of the guide tube positioning mechanism is threadedly connected to a lock tube of the lock tube locking mechanism, wherein the lock tube further comprises an anti-rotation collar, so that the antirotation collar is located between the two truncated hemicircular side walls of the protractor and dispenses away with use of any tool during use, and wherein the lock tube is threadedly terminated with a part-spherical nut, so that the part-spherical nut is journaled in an aperture passing through a thickness of the base plate, such that the guide tube positioning mechanism is pivotable about a common centre of rotation of the part-spherical nut and the aperture.

4. The apparatus according to any one of the preceding claims, wherein the second protractor mechanism comprises the protractor, the base plate and a ball bearing assembly disposed between the protractor and the base plate, so that the second protractor mechanism provides a measure of an angle of rotation of the protractor w ith respect to the base plate or YZ plane.

5. The apparatus according to claim 3 or 4, wherein the threaded connection of the guide tube and the lock tube is operable to be turned to bring the guide tube and the lock tube close together, so that an end of the guide tube bearing on upper edges of the truncated hemicircular sidewalls and the part-spherical nut bearing on the aperture at the base plate form the guide tube locking mechanism, which, when turned to a locked position locks both the first and the second protractor mechanisms, and when turned to an unlock position loosens both the first and the second protractor mechanisms, thus allowing adjustments or resetting of both the protractor mechanisms.

6. The apparatus according to any one of claims 3-5, further comprises an incline indicator located to slide on the upper edges of the truncated hemicircular sidewalls of the protractor, with the lock tube passing through the incline indicator, so that the incline indicator is slidable on the truncated hemicircular sidewalls to indicate the inclination angle a of the first protractor mechanism.

7. The apparatus according to any preceding claims, wherein the base plate is made of a transparent poly (methyl methacrylate) (PMMA).

8. The apparatus according to any one of claims 3-7, wherein the lock tube and the part- spherical nut is integrally formed.

9. The apparatus according to claim 1, wherein the first protractor comprises: a bridge protractor terminating with two terminal sliders, with the two tenninal sliders supporting two spaced apart bridge members; two truncated hemicircular tracks that extend vertically from the base plate, wherein the two terminal sliders arc fitted to slide on the respective truncated hcmicircular tracks; and a protractor keeper terminating with two lower terminal sliders, wherein the two lower terminal sliders are operable to slide on respective lower truncated hemicircular tracks, which are angularly parallel to the associated truncated hemicircular track, so that the sliding movements of the terminal sliders on the respective truncated hemicircular tracks remain positively engaged;wherein the first protractor mechanism is slidable on the spaced apart bridge members of the bridge protractor.

10. Hie apparatus according to claim 9, wherein the first protractor mechanism further comprises a guide tube positioning mechanism and a lock tube locking mechanism which are disposed to slide between the two spaced apart bridge members, with tire first protractor mechanism providing an inclination angle a of the guide tube positioning mechanism.

11. The apparatus according to claim 9 or 10, wherein the two truncated hemicircular tracks form the second protractor mechanism, which provides an angle of rotation y of the first protractor mechanism.

12. The apparatus according to claim 10 or 1 1 , wherein a guide tube of the guide tube positioning mechanism is threadedly connected to a lock tube of the lock tube locking mechanism, and the lock tube further comprises: an anti-rotation collarthat fits loosely between the two spaced apart bndge members, and a stopper collarthat is contiguous with the anti-rotation collar; wherein, when the threaded connection of the guide tube and the lock tube is operable to be turned to bring the guide tube and the lock tube close together, the stopper collar clamps the protractor keeper against the bridge protractor, and the two lower terminal sliders of the protractor keeper bear against the two truncated hemicircular tracks of the inside recesses, at the same time, the two terminal sliders of the bridge protractor bear against the respective truncated hemicircular tracks to lock the guide tube positioning and lock tube locking mechanisms onto the bridge protractor, and wherein, when the threaded connection of the guide tube and the lock tube is operable to bring the guide tube and the lock tube away from each other, the two lowerterminal sliders of the protractor keeper become spaced apart from the two truncated hcmicircular tracks of the inside recesses to release the guide tube and lock tube locking mechanisms, thus allowing both an angle of inclination a and a rotation angle y of the first protractor mechanism to be further adjusted.

13. The apparatus according to any one of claims 10-12, wherein the guide tube positioning and lock tube locking mechanisms further comprise an incline indicator to facilitate reading of angular markings on the bridge protractor.

14. The apparatus according to claim any one of claims 11-13, wherein the truncated hemicircular tracks are provided with graduation marks to facilitate reading of the angle of rotation y.

15. The apparatus according to any one of claims 10-14, wherein tire base plate further comprises a central aperture which allows a tip of the lock tube locking mechanism to extend to the glenoid plane and to facilitate visual inspection when inserting the central guide pin into the glenoid cavity.

16. The apparatus according to any one of claims 9-15, wherein the base plate and the truncated hemicircular tracks, the bridge protractor and the protractor keeper are 3D printed from ABS ( Acrylonitrile Butadiene Styrene), PLA (polylactic acid or polylactide) or PCL (poly caprolactone) .

17. The apparatus according to any one of claims 2-16, wherein the guide tube positioning and lock tube locking mechanisms are made of stainless steel or titanium.

18. The apparatus according to any one of claims 3-8 and 10-17, wherein a free end of the guide tube is ribbed or knurled to provide positive grip.

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