Variations in Trochlear Morphology of Contemporary and Legacy Total Knee Arthroplasty Prostheses - A Review of 22 Designs.

INTRODUCTION: The morphology of the trochlear compartment of total knee arthroplasty (TKA) prostheses is a major determinant of postoperative patello-femoral kinematics, particularly with unresurfaced patellae. The objective of this study was to quantify and compare the trochlear morphology of a large series of contemporary and legacy TKA designs.

METHODS: The three-dimensional surface models of twenty-two femoral components (13 contemporary and 9 legacy) were created using high-resolution laser scanning. The trochlear profile of each component was analyzed from proximal to distal in 15° increments around the trochlear axis. In each profile, the following variables were measured: sulcus angle, medio-lateral deviation of the sulcus, the height and width of the facets, and the trochlear groove orientation.

RESULTS: In the contemporary group, the sulcus angle decreased progressively along the trochlear arc to varying degrees, except for two symmetrical designs, whereas the sulcus angle of the legacy designs showed significant variability. The height of the medial facet was very strongly correlated with that of the lateral facet in the contemporary group (R2 =0.89), whereas the correlation was weak for the legacy designs (R2 =0.36). Moreover, the trochlear sulcus deviated laterally from distal to proximal in ten contemporary designs and seven legacy designs, resulting in a trochlear groove orientation of 4.2 to 11.1°, and 4.3 to 10.5°, respectively. In the remaining five designs (3 contemporary and 2 legacy), the sulcus was vertical.

CONCLUSIONS: There is more consistency in trochlear morphology of contemporary TKA designs compared to legacy designs, yet the variations between different designs are still significant.