Knee alignment and patella shape are not associated with persistence of patellofemoral pain.

Introduction: Patellofemoral pain (PFP) is suggested as a precursor of patellofemoral osteoarthritis (PFOA) later in life. This hypothesis is based on shared risk factors for both diseases, such as deviating alignment parameters. In patients with PFOA, certain 2D alignment parameters and 3D shape variations are associated with the progression of PFOA. The relationship between alignment, shape, and PFP persistence remains unclear to date.

Objective: To investigate the association between 2D alignment parameters, 3D bone shape variations, and PFP persistence.

Methods: Questionnaire and MRI data from 64 patients between 14 and 40 years of age with PFP were selected from a case-control study. Participants who completed follow-up questionnaires at one or two years of follow-up were included. PFP persistence, measured using a 7-point Likert scale, was dichotomized. Structural abnormalities were scored using the MRI Osteoarthritis Knee Score (MOAKS), and alignment parameters were determined following standardized methods. The patellae were segmented from the MRI using a semi-automatic segmentation algorithm, and a 3D statistical shape model was created. Shape modes explaining at least 1% of total population variation were included. Regression analyses were performed to determine the association between baseline function (anterior knee pain scale (AKPS)), MOAKS features, alignment parameters, 3D patellar shape modes, and PFP persistence.

Results: 55 participants completed follow-up questionnaires and were included in the current analyses. Participants had a mean (standard deviation) age of 23.2(6.8), and 58.2% were female. AKPS increased statistically significant from 65.7(10.6) at baseline to 75.9(14.9) at follow-up. Nineteen patellar shape modes were included in the analyses, of which four showed a P-value <0.05; however, they were not statistically significant after applying Bonferroni correction. No associations were found between MOAKS, alignment parameters, shape modes, and PFP persistence in the adjusted models. Only AKPS at baseline was associated with pain severity at follow-up (β =-0.13, 95% confidence interval -0.20; -0.07).

Conclusion: No statistically significant associations were found between structural abnormalities, 2D alignment, or 3D shape modes and PFP persistence. Only worse AKPS at baseline was associated with persistent PFP, suggesting that baseline function might be a better predictor than structural abnormalities, alignment, or bone shape.

Level Of Evidence: III.