Lower patella–patellar tendon angle is associated with increased odds of patellofemoral osteoarthritis progression in ACL revision patients: A case control study

Abstract Purpose To investigate whether a lower preoperative patella–patellar tendon angle (P‐PTA) is associated with progression of patellofemoral osteoarthritis (PFOA) in patients undergoing anterior cruciate ligament (ACL) revision surgery. We hypothesised that patients with lower preoperative P‐PTA would have higher odds of PFOA progression. Methods A database search (2015–2023) included patients who underwent ACL revision surgery with magnetic resonance imaging (MRI) available at both initial and revision ACL injuries. Inclusion criteria were primary arthroscopic anterior cruciate ligament reconstruction without cartilage restoration procedures and ≥2 years between ACL injuries. Demographic data, graft type, patellofemoral joint measurements (P‐PTA, Sagittal tibial tubercle‐trochlear groove distance, Insall–Salvati ratio) and PFOA progression were collected at both time points. PFOA progression was defined using MRI osteoarthritis knee score (MOAKS) criteria. Results Sixty‐two knees in 61 patients met the inclusion criteria (mean age at primary injury 30.60 ± 12.30 years; body mass index 26.70 ± 4.40 kg/m 2 ; mean interval between injuries 4.77 ± 3.04 years). Twenty‐two knees (35.50%) had no PFOA progression, and 40 (64.50%) had progression. Preoperative P‐PTA was significantly lower in the progression group (141.90 ± 4.60°) than in the no‐progression group (144.80 ± 5.70°; p = 0.044); this difference persisted at the second injury (142.30 ± 4.90° vs. 145.60 ± 6.60°; p = 0.043). Age ( p = 0.02) and graft type ( p = 0.015) also differed between groups. Insall–Salvati and sTT‐TG at the first injury did not differ between groups. Multivariable logistic regression identified lower preoperative P‐PTA as an independent predictor of progression (OR: 1.15 per 1° decrease; 95% CI: 1.02–1.30; p = 0.022). P‐PTA alone showed limited discrimination (AUC: 0.66, 95% CI: 0.50–0.80), whereas the multivariable model showed higher apparent discrimination (AUC: 0.79, 95% CI: 0.68–0.90). Both receiver operating characteristic analyses were derived and evaluated in the same cohort, and no independent validation was performed. Conclusion In this ACL revision cohort, a lower preoperative P‐PTA was independently associated with MOAKS‐defined PFOA progression. Each 1° decrease in P‐PTA was associated with 15% higher odds of progression. However, the mean between‐group difference was smaller than the MDC95, limiting individual‐level interpretation of P‐PTA measurements. Level of Evidence Level III.