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

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.

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.

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).

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.