The location of the centre of the proximal quadriceps tendon in kinematically aligned total knee arthroplasty is not associated with poor outcome scores or symptomatic patellar instability

Purpose: A previous study on osteoarthritic knees found that the average position of the centre of the proximal quadriceps tendon (PQT) was 9 mm lateral from the native trochlear groove. In patients with lateral patellar facet osteoarthritis, which indicates patellofemoral instability, the average location was 21 mm. The researchers suggested that a position more lateral than 20 mm might lead to poor outcomes after kinematically aligned total knee arthroplasty (KA TKA)-the current study aimed to test this hypothesis.

Methods: The study involved all patients (n = 302) who underwent KA TKA (n = 313) in 2019, had a post-operative long-leg scanogram and knee computed tomography scan, and completed a 2-year questionnaire. An evaluator measured the location of the PQT relative to the centre of the distal prosthetic trochlear groove. A Spearman's rank correlation coefficient analysis determined whether there was an association between the location of the PQT and the Forgotten Joint Score (FJS) and Oxford Knee Score (OKS) at 2 years.

Results: The mean location of the PQT was 11 ± 8 mm (range, -2 medial to 36 mm lateral), with 16% (N = 46) of the KA TKAs having a more lateral location than 20 mm. The location of the PQT was not associated with the FJS (r = -0.0349, p = 0.7281) and OKS (r = -0.0641, p = 0.9009)-no patient response indicated symptoms or operative treatment for patellofemoral instability.

Conclusion: Even though 16% of patients with a KA TKA had a more lateral location than 20 mm, there is no reason to measure the centre of the PQT relative to the distal prosthetic groove. This is because the location did not show any association with the 2-year FJS and OKS nor had any patient experienced patellofemoral instability.

Level of evidence: IV.