Objective: This study aimed to investigate the clinical and biomechanical effect of medial fixed-bearing unicompartmental knee arthroplasty (UKA) on the patellofemoral joint (PFJ). However, whether patellofemoral joint (PFJ) degeneration should be considered a contraindication for UKA remains controversial. In addition, the biomechanical effects of UKA on PFJ stress distribution have not been fully elucidated.
Method: Thirty-two patients (35 knees) who underwent medial fixed-bearing UKA were included with a mean of 4.5 years follow-up. The clinical parameters including the Oxford Knee Score (OKS), Western Ontario and McMaster Universities Osteoarthritis Index score (WOMAC), and Visual Analogue Scale (VAS), and radiographic parameters including lateral patellofemoral angle (LPFA), congruence angle (CA), lateral patellar tilt angle (LPTA), posterior tibial slope (PTS), and hip-knee-ankle (HKA) angle were compared. Finite element analysis (FEA) was performed for further investigating PFJ stress change after medial fixed-bearing UKA.
Results: At the final follow-up, the clinical and radiographic parameters were significant improvement compared to the preoperative measurements (p < 0.05); there were not significantly different in the clinical parameters between patients with and without PFJ arthropathy (p > 0.05). As the knee varus angle was gradually corrected using UKA, the excessive stress in the medial PFJ was partially transferred to the lateral PFJ, and the stress in the medial and lateral PFJ tended to be balanced.
Conclusion: Medial fixed-bearing UKA can improve clinical outcomes and optimize the PFJ alignment and stress distribution. The presence of PFJ arthropathy did not compromise the clinical outcomes. However, the presence of preoperative lateral PFJ arthropathy has a risk of inferior clinical outcomes due to increasing stress on the lateral PFJ after medial fixed-bearing UKA.
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