Kinematic alignment-specific femoral knee arthroplasty component

Abstract

A femoral knee arthroplasty component comprising a prosthetic trochlear groove oriented at a prosthetic trochlea angle that is greater than 14.1° valgus but less than 18.1° valgus. A use of the femoral knee arthroplasty component in a method of implanting a femoral knee arthroplasty component in kinematic alignment. A method of implanting a femoral knee arthroplasty component that comprises the steps of: providing a femoral knee arthroplasty component according to any one of claims 1 to 3; and implanting the femoral knee arthroplasty component in kinematic alignment, by affixing the femoral knee arthroplasty component such that: a prosthetic trochlea axis of the femoral knee arthroplasty component is valgus or parallel to a spherical axis of the femur, a posterior condylar line of the femoral knee arthroplasty component is essentially parallel to the natural transcondylar axis of the patients femur in the femoral transverse plane, and a posterior condylar line of the femoral knee arthroplasty component is essentially parallel to the natural transcondylar axis of the patients femur in the femoral transverse plane.

Description

[0001] Kinematic alignment-specific femoral knee arthroplasty component

[0002] Description

[0003] Field of the invention

[0004] The invention relates to a femoral knee arthroplasty component comprising a prosthetic trochlear groove. Moreover, the invention relates to a use of a femoral knee arthroplasty component. The invention further relates to methods of implanting a femoral knee arthroplasty component.

[0005] Background of the invention

[0006] The publication by Tanifuji et al “The Vector of quadriceps pull is directed from the patella to the femoral neck”, Clin Orthop Relat Res (2013) 471:1014, discloses findings that an approximation of the quadriceps vector is closely aligned with a spherical axis defined as an axis connecting the spherical centre of the femoral head to the spherical centre of the medial femoral condyle.

[0007] The publication by Sappey-Marinier et al “The trochlear groove of a femoral component designed for kinematic alignment is lateral to the quadriceps line of force and better laterally covers the anterior femoral resection than a mechanical alignment design”, J Pers Med, 2022 October 16; 12(10): 1724, discloses that the trochlear groove orientation of a femoral arthroplasty component should preferably be lateral to the quadriceps line of force. It further discloses that the quadriceps line of force is directed along the line connecting the anterior inferior iliac spine (Al IS) to the centre of the knee.

[0008] The publication by Howell et al “Better forgotten joint scores when the angle of the prosthetic trochlea is lateral to the quadriceps vector in kinematically aligned total knee arthroplasty”, Knee Surg Sports Traumatol Arthrosc. 2023 Oct 4. doi: 10.1007 / s00167-02307598-3. Epub ahead of print. PMID: 37792084, discloses improved clinical outcome of kinematically aligned total knee arthroplasty when the angle of the prosthetic trochlea is lateral to the quadriceps vector (QV). It further discloses that the QV is orientated towards the Al IS. The publication by Rosa et al "Mismatch between trochlear coronal alignment of arthritic knees and currently available prosthesis: a morphological analysis of 4116 knees and 45 implant designs", Knee Surg Sports Traumatol Arthrosc, 2023. 31(8): p. 3116-3123, discloses that most currently available femoral knee arthroplasty components are designed with a prosthetic trochlear groove oriented at a prosthetic trochlea angle of 6° valgus from a direction vertical to a line connecting distal ends of both the medial and the lateral condyle. It further discloses that, anatomical trochlea orientation deviates from the range of trochlear angles accommodated by existing implants (0° - 15°), in a notable percentage of patients.

[0009] The publication by Eckhoff et al "Three-Dimensional Mechanics, Kinematics, and Morphology of the Knee Viewed in Virtual Reality", J Bone Joint Surg (2005) 87 Suppl 2(12):71-80, discloses findings that flexion and extension of the knee occurs about a fixed flexionextension axis (FEA) centred in the posterior femoral condyles, which are circular in shape.

[0010] The publication by Freeman "How the knee moves", Current Orthopaedics Vol 15, Issue 6, Dec 2001: p 444-450, discloses findings that the axis of longitudinal rotation of the tibia during knee flexion is perpendicular to the flexion-extension axis and approximately intersects the latter in the centre of the medial femoral condylar sphere.

[0011] In some patients, conventional femoral arthroplasty components and methods of their implantation may not be ideal, insofar as the orientation of the prosthetic trochlear groove, for guiding a movement of a patella of the patient upon movement of a knee, may be worthy of improvement. Such improvement may yield better results in terms of Forgotten Joint Score (FJS) or Knee injury and Osteoarthritis Outcome Score (KOOS) in some patients.

[0012] Object of the invention

[0013] It is an object of the present invention to provide an improved femoral knee arthroplasty component comprising a prosthetic trochlear groove. Moreover, it is an object of the present invention to provide a new use of a femoral knee arthroplasty component. Further, the present invention aims at providing improved methods of implanting a femoral knee arthroplasty component. Solution according to the invention

[0014] In the following, any reference to one (including the articles “a” and “the”), two or another number of objects is, provided nothing else is expressly mentioned, meant to be understood as not excluding the presence of further such objects in the invention. The reference numerals in the patent claims are not meant to be limiting but merely serve to improve readability of the claims.

[0015] According to a first aspect of the invention, the problem is solved by a femoral knee arthroplasty component with the features of claim 1. The femoral knee arthroplasty component comprises a prosthetic trochlear groove which is orientated at a prosthetic trochlea angle that is greater than 14.1° valgus but less than 18.1° valgus.

[0016] As used herein, a degree (indicated by “°”) is the 360th of a full circle. In the context of the present invention, a “prosthetic trochlear groove” is the part of a femoral knee arthroplasty component intended to at least partially replace the surface of the natural trochlear groove of a femur of a patient. The trochlear groove serves for guiding a movement of a patella of the patient’s knee upon flexing or extending the knee. The natural trochlear groove extends from an intercondylar notch at the distal end of the femur, onto which the femoral knee arthroplasty component is to be implanted, in a direction roughly approaching an upper end of a femur. As a result, it is curved. Typically, this curved trochlear groove extends roughly about the flexion-extension axis of the knee but slightly tilted in a lateral direction.

[0017] As used herein, the term “femoral knee arthroplasty component” is a component that at least comprises a prosthetic trochlear groove. In addition, it may also comprise one or two prosthetic condyles. Prosthetic condyles are the part of a femoral knee arthroplasty component intended to at least partially replace the surface of the natural condyles of the patient’s femur. More specifically, a femoral knee arthroplasty component that comprises both a prosthetic lateral condyle and a prosthetic medial condyle, in addition to a prosthetic trochlear groove, is referred to as a “tricompartmental” femoral knee arthroplasty component. In contrast, a “bicompartmental” femoral knee arthroplasty component comprises only one prosthetic condyle, either a prosthetic lateral condyle or a prosthetic medial condyle, in addition to a prosthetic trochlear groove. Finally, a femoral knee arthroplasty component that comprises only a prosthetic trochlear groove, but neither a prosthetic lateral condyle nor a prosthetic medial condyle is referred to as a “patellofemoral” knee arthroplasty component.

[0018] The flexion and extension axis (FEA) of a natural knee or a femoral arthroplasty component can be approximated by their respective “transcondylar axis”, which in the context of the present invention is the axis that extends through the approximate centres of the medial femoral condyle and the lateral femoral condyle. Preferably, for obtaining the centres, the condyles are approximated by spheres as is common practice in the art and the centres of these spheres are considered the centres of the condyles. For determining the transcondylar axis, a line can be constructed that passes through the centres of circles approximating the projections of both femoral condyles in the spherical plane.

[0019] The “spherical axis” is the axis that passes through the centre of the femoral head and the centre of the medial condyle of the femur. For the purpose of determining the centres of the femoral head and the medial femoral condyle, these are preferably approximated by spheres, the centre of said spheres being considered the centres of the femoral head and the medial femoral condyle, respectively. For determining the spherical axis, a line can be constructed that passes through the centres of spheres approximating the femoral head and the medial femoral condyle.

[0020] The “spherical plane” is the plane spanned by the spherical axis and the transcondylar axis. As the spherical plane incorporates the centre of rotation at the hip joint, as well as the approximate centre of rotation about which flexion and extension occur at the knee joint, it may also be referred to as the “functional coronal plane of the femur” or the "femoral coronal plane").

[0021] Conventionally, in the art of arthroplasty, reference is oftentimes made to the anatomical coronal plane, the anatomical sagittal plane and the anatomical transverse plane. Yet, reference to these anatomical planes does not provide generally accepted and precise definitions of the positions and orientations in space for individual bones such as the femur. Only if the patient is positioned such that the femur's transcondylar and spherical axes both extend in or in parallel to the anatomical coronal plane, the spherical plane coincides with-, or is parallel to the anatomical coronal plane, respectively. To address this issue, in the context of the present invention, reference is made to the spherical plane - which, unlike the anatomical coronal plane, unequivocally defines the position and orientation of all relevant components of the femur, regardless of how said femur may be positioned and oriented in space and without having to rely on a specific external anatomical reference such as the "standard anatomical position". Moreover, reference is made to two planes which extend perpendicularly to the spherical plane and to each other: The “femoral sagittal plane” (which may also be referred to as the “sagittal plane of the distal femur” and must not to be confused with the anatomical sagittal plane mentioned above) is the plane that extends through the centre of the medial femoral condyle, perpendicularly to the transcondylar axis. The “femoral transverse plane” (which may also be referred to as the “transverse plane of the distal femur” or the “transcondylar plane” and must not to be confused with the anatomical transverse plane mentioned above) is the plane in which the transcondylar axis lies and which is perpendicular to the spherical plane. Again, only if the patient is positioned such that the femur's transcondylar and spherical axes both extend in or in parallel to the anatomical coronal plane, the femoral sagittal plane and the femoral transverse plane are in parallel to the anatomical sagittal plane and the anatomical transverse plane, respectively.

[0022] The “prosthetic trochlea angle” is the angle between the prosthetic trochlea axis built into a femoral arthroplasty component and a vertical on said component’s flexion-extension axis in the spherical plane. As used herein, the “prosthetic trochlea axis” is a projection onto the spherical plane of the approximate path along which the patella travels as the knee flexes and extends once the femoral knee arthroplasty component is implanted as intended. If the path extends along a curved line, the axis is the closest linear approximation to the projection of this curve onto the spherical plane.

[0023] As the prosthetic trochlea axis typically is tilted relatively to the vertical on the transcondylar axis in the spherical plane, the two intersect. It is understood that the planes and axes referred to here are imaginary rather than being embodied by physical tissue or components of the prosthesis. They are introduced here merely for the purpose of defining the spatial arrangement of the features of the femoral knee arthroplasty component of the present invention.

[0024] In the case that the femoral knee arthroplasty component is a tricompartmental component, the “prosthetic trochlea angle” is defined by referring to the prosthetic condyles. In other words, in the case of a tricompartmental component, the FEA and the spherical plane used to obtain the prosthetic trochlea angle are defined by both the medial prosthetic condyle and the lateral prosthetic condyle. However, in the case of a bicompartmental or patellofemoral component, due to the lack of one or both prosthetic condyles, the anatomical position(s) of one or both natural condyles relatively to the intended implant position of the femoral knee arthroplasty component must be considered for defining the prosthetic trochlea angle. More specifically, if the femoral knee arthroplasty component is bicompartmental, the transcondylar axis and the spherical plane used to obtain the prosthetic trochlea angle, are defined by one prosthetic condyle and the one remaining natural condyle as located relative to the component’s intended implant position; and if the femoral knee arthroplasty component is patellofemoral, the transcondylar axis and the spherical plane used to obtain the prosthetic trochlea angle are defined by the natural medial condyle and lateral condyle as located relative to the component’s intended implant position.

[0025] In the context of the present invention, “valgus” means turned outward with respect to a patient’s anatomical sagittal plane, if the femoral knee arthroplasty component is implanted as intended. An axis is “in valgus” relatively to another axis if the upper half-line of the axis is oriented further valgus than the upper half-line of the other axis. In this context, “outward” and “inward” mean the general direction away from and towards the anatomical sagittal plane, respectively, if the prosthesis is implanted as intended; ie, for example, if the prosthesis is intended for the left knee, outward means towards the left and inwards means towards the right side of the prosthesis. An “upper half-line” is the half-line that extends from the intersection between the two projections in the upwards direction. The “upward direction” is the general direction of a vector that extends from the patient's feet towards the patient's head if the prosthesis is implanted as intended, ie, in the case of a tricompartmental femoral knee arthroplasty component, for example, with the component's condyles directed towards the patient's feet rather than towards his or her head.

[0026] More specifically with regard to the prosthetic trochlea angle, the prosthetic trochlea angle of a femoral knee arthroplasty component is in valgus if the prosthetic trochlea axis is in valgus of the vertical on the component's flexion extension axis in the spherical plane. If conversely, the upper half-line of the prosthetic trochlea axis is in varus of the vertical on the component's flexion extension axis in the spherical plane, the prosthetic trochlea angle of said femoral knee arthroplasty component is "varus" rather than valgus. If the prosthetic trochlea axis coincides with or is parallel to the vertical on the component's flexion extension axis in the spherical plane, the prosthetic trochlea angle of said femoral knee arthroplasty component is "neutral".

[0027] According to a second aspect of the invention, the problem is solved by a use of a femoral knee arthroplasty component as disclosed above with the features of claim 11. The femoral knee arthroplasty component is used in a method of kinematic alignment.

[0028] In the context of the present invention, “kinematic alignment” refers to a femoral knee arthroplasty component being implanted in such a way that after implantation, the FEA of the prosthetic implant coincides with the natural "kinematic" FEA of the patient's knee, which typically very closely approximates the patients natural transcondylar axis. The purpose of kinematic alignment is to take the significant phenotypic variability of individual knee alignment into consideration and position the prosthetic component relative to each patient's unique constitutional anatomy, in order to best possibly approximate or even restore the kinematic functionality of the patient's natural knee. Preferably, in kinematic alignment, the femoral knee arthroplasty component is implanted such that the prosthetic FEA after implantation is approximately that of the healthy (typically pre-arthritic) knee of said patient.

[0029] In the context of the present invention, “kinematic alignment” encompasses more recent modifications, derivatives and hybrids of this patient-specific alignment concept including restricted kinematic alignment (rKA) as disclosed by Almaawi et al in the publication "The Impact of Mechanical and Restricted Kinematic Alignment on Knee Anatomy in Total Knee Arthroplasty", J Arthroplasty (2017) 32(7), 2133-2140, inverse kinematic alignment (iKA) as disclosed by Winnock de Grave et al. in the publication "Higher satisfaction after total knee arthroplasty using restricted inverse kinematic alignment compared to adjusted mechanical alignment", Knee Surg Sports Traumatol Arthrosc. (2020) doi.org / 10.1007 / s00167-020- 06165-4, adjusted mechanical alignment (AMA) as disclosed by Vanlommel et al in the publication "Slight undercorrection following total knee arthroplasty results in superior clinical outcomes in varus knees", KneeSurg Sports Traumatol Arthrosc 2013;21:2325-30, modified kinematic alignment (mKA) as disclosed by Matsumoto et al in the publication "A radiographic analysis of alignment of the lower extremities-initiation and progression of varus-type knee osteoarthritis", Osteoarthritis Cartilage, 23 (2) (2015 Feb), pp. 217-223 and functional alignment (FA) as disclosed by Lustig et al in the publication "Personalized alignment in total knee arthroplasty: current concepts", SICOT-J (2021), 7, 19. According to a third aspect of the invention, the problem is solved by a method of implanting a femoral knee arthroplasty component with the features of claim 12. The method comprises the steps of: providing a femoral knee arthroplasty component of the kind disclosed above; and implanting the femoral knee arthroplasty component in kinematic alignment.

[0030] According to a fourth aspect of the invention, the problem is solved by a method of implanting a femoral knee arthroplasty component with the features of claim 13. The method comprises the steps of: providing a femoral knee arthroplasty component of the kind disclosed above; and affixing the femoral knee arthroplasty component to the patient's femur such that a prosthetic trochlea axis of said femoral knee arthroplasty component is in valgus or parallel to an orientation of a spherical axis of said femur.

[0031] According to a fifth aspect of the invention, the problem is solved by a method of implanting a femoral knee arthroplasty component with the features of claim 14. The method comprises the steps of: providing a femoral knee arthroplasty component of the kind disclosed above; and affixing the femoral knee arthroplasty component to the patient's femur such that a posterior condylar line of said femoral knee arthroplasty component is essentially parallel to the natural transcondylar axis of the patient's femur in the femoral transverse plane.

[0032] According to a sixth aspect of the invention, the problem is solved by a method of implanting a femoral knee arthroplasty component with the features of claim 15. The method comprises the steps of: providing a femoral knee arthroplasty component of the kind disclosed above; and affixing the femoral knee arthroplasty component to the patient's femur such that a sagittal posterior condylar tangent of the femoral knee arthroplasty component is essentially parallel to the spherical plane.

[0033] It is an achievable advantage of the present invention that for essentially all patients a situation can be avoided in which the trochlea axis of a femoral knee arthroplasty component trochlea is in varus to the spherical axis of the femur, which is implanted with said femoral arthroplasty component.

[0034] In particular, the inventors have found that if the trochlea axis is in varus with respect to the spherical axis, this may compromise mobility of the patient. The inventors consider such situation a Functional Trochlear Malalignment (FTMA). It is an achievable advantage of the present invention that better clinical results, for example in terms of a Forgotten Joint Score (FJS) and Knee injury or Osteoarthritis Outcome Score (KOOS) are achieved by avoiding FTMA.

[0035] Preferred embodiments of the invention

[0036] Preferred features of the invention which may be applied alone or in combination are discussed in the following and in the dependent claims.

[0037] The preferred prosthetic trochlea angle, at which the trochlear groove is oriented, is greater than 14.1°, more preferably greater than 14.6°, more preferably greater than 15.1°, more preferably greater than 15.3°, more preferably greater than 15.5°, more preferably greater than 15.7°, most preferably greater than 15.9° valgus. The preferred prosthetic trochlea angle, at which the trochlear groove is oriented, is less than 18.1°, more preferably less than 17.6°, more preferably less than 17.1°, more preferably less than 16.9°, more preferably less than 16.7°, more preferably less than 16.5°, most preferably less than 16.3° valgus. A particularly preferred prosthetic trochlea angle is essentially 16.1° valgus.

[0038] In one embodiment of the invention, the transcondylar axis used in the above definition of the prosthetic trochlea angle is approximated by the distal condylar line, which is a tangent of the points of the medial and lateral condyle furthest away from a standing patients anatomical transverse plane in a spherical plane projection, ie, a tangent of the points of the medial and lateral condyle furthest away from the femoral transverse plane.

[0039] In one embodiment of the invention, the path along which the patella will be guided, which path is used in the above definition of the curve of the prosthetic trochlear groove, is approximated by the line of lowest points of the trochlear groove. In another embodiment of the invention, the path along which the patella will be guided, which path is used in the above definition of the curve of the prosthetic trochlear groove, is approximated by the lines of the ridges of the trochlear groove, preferably by the midline between the ridges. In yet another embodiment of the invention, the path along which the patella will be guided, which path is used in the above definition of the curve of the prosthetic trochlear groove, is approximated by the lines of the most prominent points between the trochlear ridges and the trochlear groove, where the patella or patella component comes into contact with the trochlear wall. In a preferred embodiment of the invention, any portion of the lateral trochlear ridge is orientated at a prosthetic lateral trochlear ridge angle that is greater than 14° valgus, preferably greater than 15° valgus, more preferably greater than 16° valgus. More preferably, any portion of the lateral trochlear ridge is orientated at a prosthetic lateral trochlear ridge angle that is equal to or greater than the prosthetic trochlea angle.

[0040] Similarly, in a preferred embodiment of the invention, any portion of the medial trochlear ridge is orientated at a prosthetic medial trochlear ridge angle that is less than 16° valgus, preferably less than 15° valgus, more preferably less than 14° valgus. More preferably, any portion of the medial trochlear ridge is orientated at a prosthetic medial trochlear ridge angle that is equal to or less than the prosthetic trochlea angle.

[0041] As used herein, the term “lateral trochlear ridge” is the curve that connects the highest points lateral to the trochlear groove. Likewise, the term “medial trochlear ridge” is the curve that connects the highest points medial to the trochlear groove. In the context of the present invention, the “trochlea ridge angle” is defined in analogy to the prosthetic trochlea angle as the angle between the vertical on the FEA in the spherical plane and a projection of the ridge onto the spherical plane.

[0042] Particularly preferably, the trochlear ridges will open up towards the proximal end of the trochlear groove, ie, the distance between the lateral and medial ridges will increase thus expanding the trochlear groove towards its proximal end.

[0043] The preferred femoral knee arthroplasty component is tricompartmental. Yet, the invention also encompasses bicompartmental and patellofemoral knee arthroplasty components.

[0044] The femoral knee arthroplasty component is preferably implanted in kinematic alignment, such that the prosthetic FEA closely approximates the patients natural FEA, with the prosthetic transcondylar axis preferably coinciding to within 2°, more preferably to within 1°, even more preferably to within 0,5°, even more preferably exactly coinciding with, the patients natural transcondylar axis in the spherical plane.

[0045] In a preferred method of implanting a femoral knee arthroplasty component, the component is affixed to the patient’s femur such that the prosthetic trochlea axis of the femoral knee arthroplasty component is in valgus or parallel to the orientation of the projection of the spherical axis, onto the spherical plane.

[0046] Preferably, the component is affixed to the patient’s femur such that the prosthetic trochlea axis of the femoral knee arthroplasty component is in valgus with respect to the orientation of a spherical axis of the femur. Preferably, the component is affixed to the patient’s femur such that the prosthetic trochlea axis of the femoral knee arthroplasty component is 1° or more, preferably 2° or more, even more preferably 3° or more, even more preferably 4° or more valgus with respect to the orientation of a spherical axis of said patient’s femur.

[0047] Preferably, the component is affixed to the patient’s femur such that the prosthetic trochlea axis of the femoral knee arthroplasty component is 20° or less, preferably 15° or less, even more preferably 11 ° or less, even more preferably 7° or less valgus with respect to the orientation of a spherical axis of said patient’s femur. Particularly preferably, the prosthetic trochlea axis is essentially 5° valgus of the spherical axis.

[0048] Preferably, the femoral knee arthroplasty component is affixed to the patient’s femur such that its posterior condylar line is rotated (either externally or internally) 8° or less, preferably 5° or less, even more preferably 3° or less, even more preferably 1° or less, with respect to the natural transcondylar axis of the patient's femur. The posterior condylar line is the tangent of the most posterior points of its medial and lateral condyle in the femoral transverse plane. The most posterior points of the medial and lateral condyles in the femoral transverse plane are located at the points of contact of the single posteriorly directed radius of best fitting spheres to said femoral condyles that lie in both the femoral transverse plane and the femoral sagittal plane, and the surface of said spheres. Particularly preferably, the posterior condylar line of the femoral knee arthroplasty component is essentially parallel to the natural transcondylar axis of the patient’s femur in the femoral transverse plane.

[0049] Preferably, the component is affixed to the patient's femur such that the sagittal posterior condylar tangent of the femoral knee arthroplasty component is rotated (either anteriorly or posteriorly) 8° or less, preferably 5° or less, even more preferably 3° or less, even more preferably 1° or less, with respect to the natural spherical plane of the patients femur. The sagittal posterior condylar tangent is the tangent of the most posterior point of the component’s medial condyle that lies in the femoral sagittal plane. Again, the most posterior point of the medial condyle is located at the point of contact of the single posteriorly directed radius of best fitting spheres to said femoral condyles that lies in both the femoral transverse plane and the femoral sagittal plane, and the surface of said sphere. Particularly preferably, the sagittal posterior condylar tangent of the femoral knee arthroplasty component is essentially parallel to the spherical plane.

[0050] Brief description of the drawings

[0051] In the following, further preferred embodiments of the invention are illustrated by means of examples. The invention is not limited to these examples, however.

[0052] The drawings schematically show:

[0053] Figure 1 A projection onto the spherical plane of a right tricompartmental femoral knee arthroplasty component;

[0054] Figure 2 A projection onto the spherical plane of a bicompartmental right femoral knee arthroplasty component (left) and a right patellofemoral femoral knee arthroplasty component (right, both for kinematic alignment);

[0055] Figure 3 A section of the spherical axis of a patient’s right femur, superimposed on an image of said femur provided with a right tricompartmental femoral knee arthroplasty component;

[0056] Figure 4 Two perspectives of a right femur with sections of its spherical axis and its transcondylar axis, which together span the spherical plane, superimposed thereon;

[0057] Figure 5 The deviation angle co between the spherical axis and the prosthetic trochlea axis of the femoral component implanted onto a patient’s right femur superimposed on an image of said femur;

[0058] Figure 6 A scatter-plot of the respective prosthetic trochlea- and spherical axes (SA) in 206 patients who were implanted with a standard femoral knee arthroplasty component with a prosthetic trochlea angle of 6°; Figure 7 A stratification of clinical results according to the validated patient-reported outcome measures KOOS and FJS according to the deviation (direction and magnitude) of the FA from the SA;

[0059] Figure 8 An illustration of the definition of the sagittal posterior condylar tangent;

[0060] Figure 9 An illustration of the definition of the posterior condylar line in a first perspective; and

[0061] Figure 10 An illustration of the definition of the posterior condylar line in a second perspective.

[0062] Detailed description of an embodiment of the invention

[0063] In the following description of preferred embodiments of the invention, identical reference numerals refer to identical or similar components.

[0064] Figure 1 is a projection onto the spherical plane of a right femoral knee arthroplasty component 1 for kinematic alignment (KA), designed to replace the femoral joint surface in all three compartments of the knee: the medial femoral condyle 2, the lateral femoral condyle 3 and the femoral trochlea 4. Also indicated are the lateral, medial, proximal and distal sides of the femoral knee arthroplasty component. The left femoral knee arthroplasty component would essentially be a mirror image of Figure 1 , in which the lateral and medial side are inverted. Upon implantation in a patient, the medial side will always be closer to the patient’s anatomical sagittal plane than the lateral side, and the proximal side will be closer to the transverse plane than the distal side.

[0065] The orientation of component 1 is such that the distal condylar line 5 (dashed line) is exactly horizontal and in the spherical plane (which is parallel to the paper plane in Figure 1). This tangent of the distal femoral condyles serves as the approximation for the prosthetic joint line orientation as well as the transcondylar axis. Accordingly, the vertical 6 on the components 1 transcondylar axis extends perpendicularly to the distal condylar line 5 in the spherical plane. The arrow 7 is the prosthetic trochlea axis. It indicates the orientation of the trochlear groove, which extends from the intercondylar notch 8 to the proximo-lateral edge 9 of the femoral shield. The prosthetic trochlear axis 7 is, likewise in the spherical plane but tilted away from the sagittal plane at an angle cp.

[0066] Accordingly, the angle between the vertical 6 on the components 1 transcondylar axis and the prosthetic trochlea axis 7 defines the prosthetic trochlea angle (p in the spherical plane. It is oriented at exactly (p = 16.1° valgus.

[0067] Also shown in Figure 1 are parts of the lateral 10 and the medial 11 ridges of the trochlear groove (dotted lines). Any portion of the lateral trochlear ridge 10 exhibits at least the same or greater degree of valgus orientation as the trochlear groove. Likewise, any portion of the medial trochlear ridge 11 exhibits at least the same or lesser degree of valgus orientation as the trochlear groove.

[0068] A bicompartmental right femoral knee arthroplasty component 1 for kinematic alignment is shown on the left panel of Figure 2. It is designed to replace the femoral joint surface in two compartments of the knee: the medial femoral condyle 2 and the femoral trochlea 4. On the right panel of Figure 2, a right patellofemoral femoral knee arthroplasty component 1 for kinematic alignment is shown, designed to replace only the femoral trochlea 4.

[0069] Figure 3, is an x-ray image with a view onto the spherical plane of a patient's right femur 12. The x-ray image also shows a femoral knee arthroplasty component 1 affixed to the distal end of the femur 12. The projections, onto the spherical plane, of the femoral head 13 and the prosthetic medial condyle 2 are approximated by circles superimposed on the x-ray image. In order to obtain the spherical axis, a section 14 (full line) of such projection is drawn by connecting the centres 15, 16 of these circles. The spherical axis extends along this section 14.

[0070] Figure 4 illustrates how the spherical plane is determined. In the right panel, the image shows the femur in the same perspective onto the spherical plane as in Figure 3, while on the left the femur is rotated by almost 90° about its longitudinal axis. Again, the femoral head 13 and the prosthetic medial condyle 2 are approximated by circles, and the full line represents a section 14 of the spherical axis which connects the centres 15, 16 of these circles. Moreover, part of the transcondylar axis 19 is indicated as a dashed line; the transcondylar axis passes through the centres of the medial femoral condyle (indicated by a full circle) and the lateral femoral condyle (perspectively indicated on the left panel of Figure 4 as a dashed circle). The spherical axis and the transcondylar axis span the spherical plane.

[0071] In Figure 5, onto the same x-ray image of a patient’s right femur 12 and a femoral knee arthroplasty component 2 affixed to the distal end of the femur 12 as in Figure 3, the prosthetic trochlea axis 18 (dotted line) and the spherical axis 17 (full line) are superimposed, and the angle co between these two axes is indicated. The angle co thus indicates the degree of deviation of the prosthetic trochlea axis from the spherical axis in the spherical plane. The upper half-line of the prosthetic trochlea axis 18 is oriented further outward (ie, towards the left of the figure) than the upper half line of the spherical axis 17. Thus, the prosthetic trochlea axis 18 is in valgus with regard to the spherical axis 17. Also, as a result, the deviation angle co is positive.

[0072] The radiographic results of 206 patients that have been fitted with a conventional femoral knee arthroplasty component in unrestricted kinematic alignment are shown in Figure 6. The prosthetic trochlea angle of these components was cp = 6° valgus in all cases. In the graph of Figure 6, the horizontal axis (“Spherical Axis”, “SA”) indicates the angle between the spherical axis - projected vertically onto the femoral coronal plane, ie, the spherical plane - and a vertical in the spherical plane (in the following referred to as the “SA angle”). As can be seen, for the great majority of patients, the spherical axis is in valgus relatively to the vertical in the spherical plane.

[0073] The vertical axis (“Functional axis (FA) of the trochlea”) in Figure 6 indicates the angle between the prosthetic trochlea axis - again projected vertically onto the femoral coronal plane, ie, the spherical plane - and the vertical in the spherical plane (in the following referred to as “FA angle") that results from the above-mentioned prosthetic trochlea angle of cp = 6° valgus of the conventional femoral knee arthroplasty components implanted into the patients, when an unrestricted kinematic alignment implantation technique is used. As can be seen, many of these patients (approx. 36%) experience FTMA: Patients without FTMA (whose FA angle is equal or greater than their SA angle) are represented as black circles, whereas patients with FTMA (whose FA is smaller than their SA) are represented by hollow circles. The solid line represents FA angle = SA angle and thus separates patients without FTMA from patients with FTMA. The dashed line in Figure 6 is parallel to the solid line and marks the patient with the greatest negative deviation angle co, ie, the patient whose FA angle is 5.1° less than the respective SA angle; in the following, the deviation of the FA angle from the SA angle, co, is referred to as the “deviation angle” (“DA”). All patients in this cohort, who have FTMA, are in the corridor between the solid and the dashed line.

[0074] Thus, if a femoral knee arthroplasty component with a prosthetic trochlea angle of (p = 6° + 5.1° = 11.1° instead of cp = 6° had been used in this patient cohort, no single patient would have ended up with FTMA.

[0075] The table in Figure 7 shows validated patient-reported outcome measures KOOS and FJS stratified by the DA. A negative DA (which represents FTMA) indicates that, the prosthetic trochlea axis is in varus with respect to the corresponding spherical axis in the femoral coronal plane, ie, the spherical plane. This situation is associated with the poorest clinical results. Patients with a neutral DA (DA = 0°) have average results. With increasing valgus however, clinical score results progressively improve, culminating at DA = 5° of valgus and subsequently slowly decrease again with further increasing valgus deviation of the FA from the SA.

[0076] The clinical outcome scores observed at 5° of valgus, were statistically significantly (p=0.04) superior compared to the other subgroups. These results suggest that a prosthetic trochlea axis that deviates co = 5° into valgus from an individual patient’s spherical axis is associated with the best clinical outcomes.

[0077] As a prosthetic trochlea angle of 11.1° avoids FTMA in all patients and an additional valgus deviation of co = 5° is associated with the best clinical results, a prosthetic trochlea angle of 16.1° would thus appear to represent the optimum trochlea orientation for a KA-specific femoral arthroplasty component. Taking into account surgical implantation error, angles between 14.1° and 18.1° are acceptable, but angles between 15.1° and 17.1° are preferable for the best clinical outcome.

[0078] Figure 8 illustrates the definition of the sagittal posterior condylar tangent 21. It is the tangent of the most posterior point 20 of the component’s medial condyle that lies in the femoral sagittal plane (the paper plane in Figure 8). The most posterior point 20 of the medial condyle is located at the point of contact of the single posteriorly directed radius of best fitting spheres to said femoral condyles that lies in both the femoral transverse plane and the femoral sagittal plane, and the surface of said sphere. In Figure 8, the sagittal posterior condylar tangent 21 of the femoral knee arthroplasty component 1 is essentially parallel to the spherical plane.

[0079] Figures 9 and 10 illustrate the definition of the posterior condylar line 22. It is the tangent of the most posterior points 20 of its medial and lateral condyle in the femoral transverse plane (the paper plane in Figure 9). The most posterior points 20 of the medial and lateral condyles in the femoral transverse plane are located at the points of contact of the single posteriorly directed radius of best fitting spheres to said femoral condyles that lie in both the femoral transverse plane and the femoral sagittal plane, and the surface of said spheres. In Figures 9 and 10, the posterior condylar line 22 of the femoral knee arthroplasty component 1 is essentially parallel to the natural transcondylar axis 19 of the patient’s femur 12 in the femoral transverse plane.

[0080] The features as described in the above description, claims and figures can be relevant individually or in any combination to realise the various embodiments of the invention.

Claims

Claims1. A femoral knee arthroplasty component comprising a prosthetic trochlear groove, characterised in that the trochlear groove is orientated at a prosthetic trochlea angle that is greater than 14.1° valgus but less than 18.1° valgus.

2. The femoral knee arthroplasty component of claim 1 , characterised in that the trochlear groove is orientated at a prosthetic trochlea angle that is greater than 15.1° valgus.

3. The femoral knee arthroplasty component of claim 1 or 2, characterised in that the trochlear groove is orientated at a prosthetic trochlea angle that is less than 17.1° valgus.

4. The femoral knee arthroplasty component of claim 3, characterised in that the trochlear groove is orientated at a prosthetic trochlea angle that is essentially 16.1° valgus.

5. The femoral knee arthroplasty component of any one of claims 1 to 4, characterised in that any portion of the lateral trochlear ridge is orientated at a prosthetic lateral trochlear ridge angle that is greater than or equal to the prosthetic trochlea angle.

6. The femoral knee arthroplasty component of any one of claims 1 to 5, characterised in that any portion of the medial trochlear ridge is orientated at a prosthetic medial trochlear ridge angle that is less than the prosthetic trochlea angle.

7. The femoral knee arthroplasty component of any one of claims 1 to 6, characterised in that it is more specifically a tricompartmental femoral knee arthroplasty component.

8. The femoral knee arthroplasty component of any one of claims 1 to 6, characterised in that it is more specifically a bicompartmental femoral knee arthroplasty component.

9. The femoral knee arthroplasty component of any one of claims 1 to 6, characterised in that it is more specifically a patellofemoral femoral knee arthroplasty component.

10. The femoral knee arthroplasty component of any one of claims 1 to 9 for implanting in kinematic alignment.

11. Use of the femoral knee arthroplasty component of any one of claims 1 to 10 in a method of implanting a femoral knee arthroplasty component in kinematic alignment.

12. A method of implanting a femoral knee arthroplasty component, the method comprising the steps of:- providing a femoral knee arthroplasty component according to any one of claims 1 to 10; and- implanting the femoral knee arthroplasty component in kinematic alignment.

13. A method of implanting a femoral knee arthroplasty component, the method comprising the steps of:- providing a femoral knee arthroplasty component according to any one of claims 1 to 10; and- affixing the femoral knee arthroplasty component to the patient’s femur such that a prosthetic trochlea axis of the femoral knee arthroplasty component is in valgus or parallel to an orientation of a spherical axis of the femur.

14. A method of implanting a femoral knee arthroplasty component, the method comprising the steps of:- providing a femoral knee arthroplasty component according to any one of claims 1 to 10; and- affixing the femoral knee arthroplasty component to the patient’s femur such that a posterior condylar line of the femoral knee arthroplasty component is rotated 8° or less with respect to the natural transcondylar axis of the patient’s femur or is essentially parallel to the natural transcondylar axis of the patient's femur in the femoral transverse plane.

15. A method of implanting a femoral knee arthroplasty component, the method comprising the steps of:- providing a femoral knee arthroplasty component according to any one of claims 1 to 10; and- affixing the femoral knee arthroplasty component to the patient’s femur such that a sagittal posterior condylar tangent of the femoral knee arthroplasty component isrotated 8° or less with respect to the natural transcondylar axis of the patient’s femur or is essentially parallel to the spherical plane.

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