Does contemporary total knee designs replicate the anatomy of the native trochlea?

Purpose: Registry data shows that less surgeons are resurfacing the patella during total knee arthroplasty (TKA). This tendency highlights the importance of matching trochlear and native patellar anatomy. Currently, there is a lack of consensus on implant design that best accommodates native patellae. The objective of this study was to compare the trochlear morphology of a large selection of contemporary TKA designs with the native trochlear anatomy.

Methods: Three-dimensional models of 13 femoral component designs from seven manufacturers and 37 healthy human femora (average age: 31.2 ± 13.4 years) were reconstructed. The trochlear morphology, including trochlear length, sulcus angle, trochlear groove angle, and height and width of the medial and lateral facets, was measured along the trochlea at 15° increments.

Results: The prosthetic trochlea was shorter and shallower compared to the native trochlea (p < 0.01). The native trochlea was bilinear and had a medial orientation proximally, whereas all asymmetrical TKA designs had a laterally oriented trochlea, resulting in opposite trochlear groove orientation (TKA, 5.8 ± 3.7°; native -3.1 ± 4.1°, p < 0.001). In addition, a strong correlation (R² = 0.89) was found in TKA models between the heights of the medial and lateral facets, which was not observed for the native femora (R² = 0.06).

Conclusion: This study highlights that the lateral trochlear orientation in existing TKA models is not anatomical. Given the rising trend in patellar non-resurfacing during TKA, further studies are necessary to improve trochlear design that better accommodates the native patellar morphology.