Rotational alignment of the femoral trochlea in Asians: Implication on implant choice and position for managing isolated patellofemoral osteoarthritis

Introduction Maltracking of the patella is a key contributor to early failure of patellofemoral arthroplasty (PFA). Native femoral trochlear morphology dictates implant rotation and patella tracking of in-lay PFA implants. This is the first study amongst Asians designed to assess the normal rotational alignment of the trochlear groove and evaluate its implication on PFA implant choice and position. Methods Trochlear inclination angle (TIA) was measured from 211 magnetic resonance images of Asian knees retrieved from a single centre in Hong Kong. TIA assesses rotation of the femoral trochlear groove relative to the axis perpendicular to Whiteside’s line (anteroposterior axis of the femur). Results The mean trochlear inclination in normal Asian knees was 11.5°  ±  2.5° (mean  ±  standard deviation) internal rotation. High-grade dysplastic knees, according to Dejour classification, were significantly more internally rotated with a mean of 12.8°  ±  3.6° (p = 0.025). Conclusion Trochlear inclination in Asians is comparable to Caucasians. In-lay PFA implants do not alter native pathological bony trochlear anatomy, and may result in patella maltracking in patients with high grade trochlear dysplasia or excessive trochlear inclination. These patients may benefit from on-lay implants, which allows restoration of normal trochlear inclination, as well as lateralisation and deepening of the trochlear groove. Patella tracking is however, dynamic and multi-factorial. Further clinical studies are therefore warranted to reconcile our anatomical findings with clinical outcomes.