Kinematic Evaluation of the GMK Sphere Implant During Gait Activities: A Dynamic Videofluoroscopy Study

Abstract

Joint stability is a primary concern in total knee joint replacement. The GMK Sphere prosthesis was specifically designed to provide medial compartment anterior-posterior (A-P) stability, while permitting rotational freedom of the joint through a flat lateral tibial surface. The objective of this study was to establish the changes in joint kinematics introduced by the GMK Sphere prosthesis during gait activities in comparison to conventional posterior-stabilized (PS) fixed-bearing and ultra-congruent (UC) mobile-bearing geometries. The A-P translation and internal/external rotation of three cohorts, each with 10 good outcome subjects (2.9 ± 1.6 years postop), with a GMK Sphere, GMK PS or GMK UC implant were analysed throughout complete cycles of gait activities using dynamic videofluoroscopy. The GMK Sphere showed the smallest range of medial compartment A-P translation for level walking, downhill walking, and stair descent (3.6 ± 0.9 mm, 3.1 ± 0.8 mm, 3.9 ± 1.3 mm), followed by the GMK UC (5.7 ± 1.0 mm, 8.0 ± 1.7 mm, 8.7 ± 1.9 mm) and the GMK PS (10.3 ± 2.2 mm, 10.1 ± 2.6 mm, 11.6 ± 1.6 mm) geometries. The GMK Sphere exhibited the largest range of lateral compartment A-P translation (12.1 ± 2.2 mm), and the largest range of tibial internal/external rotation (13.2 ± 2.2°), both during stair descent. This study has shown that the GMK Sphere clearly restricts A-P motion of the medial condyle during gait activities while still allowing a large range of axial rotation. The additional comparison against the conventional GMK PS and UC geometries, not only demonstrates that implant geometry is a key factor in governing tibio-femoral kinematics, but also that the geometry itself probably plays a more dominant role for joint movement than the type of gait activity. © 2019 The Authors. Journal of Orthopaedic Research^® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2337-2347, 2019.

Keywords: gait activities; medial congruent; moving fluoroscope; single plane fluoroscopy; total knee arthroplasty.

Figure 1

Implant coordinate systems for the femoral and tibial components of the GMK Sphere (left), GMK PS (centre), and GMK UC (right), including the nearest points for stance (red) and swing (green) phases for exemplary trials of level walking presented in the associated coordinate system of the tibial component. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 2

Subject means of condylar anterior–posterior (A–P) translation and tibial rotation for the GMK Sphere (red tones), GMK PS (blue tones), and GMK UC (green tones) throughout full cycles of level walking. The average instance of toe‐off of each subject is shown as a vertical line. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 3

Subject means of condylar anterior–posterior (A–P) translation and tibial rotation for the GMK Sphere (red tones), GMK PS (blue tones), and GMK UC (green tones) throughout full cycles of downhill walking. The average instance of toe‐off for each subject is shown as a vertical line. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 4

Subject means of condylar anterior–posterior (A–P) translation and tibial rotation for the GMK Sphere (red tones), GMK PS (blue tones), and GMK UC (green tones) throughout full cycles of stair descent. The average instance of toe‐off for each subject is shown as a vertical line. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 5

Average positions of the femoral component of the GMK Sphere, represented by lines connecting the nearest points of the medial and lateral condyles relative to the tibial tray for specific time points during the gait cycles of the three activities. Solid lines represent the loaded stance phase and dotted lines the unloaded swing phase. Mean and standard deviation of flexion/extension (flex/ex) as well as the anterior–posterior (A–P) translation of the medial (med) and lateral (lat) condyles over the subject group for the selected time points are also presented. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 6

Average positions of the femoral component of the GMK PS, represented by lines connecting the nearest points of the medial and lateral condyles relative to the tibial tray for specific time points during the gait cycles of the three activities. Solid lines represent the loaded stance phase and dotted lines the unloaded swing phase. Mean and standard deviation of flexion/extension (flex/ex) as well as the A–P translation of the medial (med) and lateral (lat) condyles over the subject group for the selected time points are also presented. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 7

Average positions of the femoral component of the GMK UC, represented by lines connecting the nearest points of the medial and lateral condyles relative to the tibial tray for specific time points during the gait cycles of the three activities. Solid lines represent the loaded stance phase and dotted lines the unloaded swing phase. Mean and standard deviation of flexion/extension (flex/ex) as well as the anterior–posterior (A–P) translation of the medial (med) and lateral (lat) condyles over the subject group for the selected time points are also presented. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 8

A–P translation of the medial (left) and lateral (centre) condyle as well as tibial rotations (right) for specific flexion angles. Mean and standard deviations over the subject groups are presented for the GMK Sphere (red/orange), GMK Primary PS (blue/light blue), and GMK Primary UC (green/light green) for the loaded stance (dark) and unloaded swing (light) phases of level walking, downhill walking, and stair descent. [Color figure can be viewed at wileyonlinelibrary.com]