Evolution of trochlear compartment geometry in total knee arthroplasty.

BACKGROUND: The study aimed to compare trochlear profiles in recent total knee arthroplasty (TKA) models and to determine whether they feature improvements compared to their predecessors. The hypothesis was that recent TKA models have more anatomic trochlear compartments and would display no signs of trochlear dysplasia.

METHODS: The authors analyzed the geometry of the 6 following TKA models using engineering software: PFC and Attune (DePuy), NexGen and Persona (Zimmer), Noetos and KneeTec (Tornier). The mediolateral trochlear profiles were plotted at various flexion angles (0°, 15°, 30° and 45°) to deduce the sulcus angle.

RESULTS: Analysis of sulcus angles reveals general convergence of recent designs towards anatomic values. At 0° of flexion, sulcus angles of recent implant models were between 156.0-157.4°, while those of previous generation models between 154.5-165.5°. At 30° of flexion, sulcus angles of recent models also lie within 145.7-148.6°, but those of previous models are between 149.5-152.0°. All three manufacturers deepened their trochlear profile at 30° of flexion in recent models compared to earlier designs. Sulcus angles converge towards anatomic values but still exceed radiologic signs of dysplasia by 2-5°.

CONCLUSIONS: Recent TKA designs have more anatomic trochlear geometries than earlier TKA models by the same manufacturers, but trochlear compartments still exceed radiologic signs of trochlear dysplasia by 2° to 5°. The hypothesis that recent TKA models display no signs of trochlear dysplasia is therefore refuted. Surgeons should be aware of design limitations to optimize choice of implant and extensor mechanisms alignment.

LEVEL OF EVIDENCE: IV geometric implant analysis.