Patella malalignment, pain and patellofemoral progression: the Health ABC Study.

OBJECTIVE: Patellofemoral (PF) joint osteoarthritis (OA) is strongly correlated with lower extremity disability and knee pain. Risk factors for pain and structural progression in PF OA are poorly understood. Our objective was to determine the association between patella malalignment and its relation to pain severity, and PF OA disease progression.
METHODS: We conducted an analysis of data from the Health ABC knee OA study. Health ABC is a community based, multi-center cohort study of 3075 Caucasian and Black men and women aged 70-79 at enrollment. Weight bearing skyline knee X-rays were obtained in a subset (595) of subjects, with and without knee pain, at year 2 and year 5 (mean follow-up 36 months). Films were read paired, and PF osteophytes (OST) and joint space narrowing (JSN) were scored on a 0-3 scale using the Osteoarthritis Research Society International atlas. We defined progression of PF OA as any increase in JSN score. Three measures of patella malalignment were made: sulcus angle; patella tilt angle; and patella subluxation medially or laterally (bisect offset). Knee symptoms were assessed using a knee specific Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) knee pain subscale. We assessed the relationship between baseline patella malalignment and pain severity (linear regression for WOMAC) and compartment specific PF OA progression (logistic regression for dichotomous outcomes). We classified continuous measures of patella alignment into quartile groups. We performed multivariable adjusted logistic regression models, including age, gender and body mass index (BMI) to assess the relation of baseline patella alignment to the occurrence of PF JSN progression using generalized estimating equations (GEE).
RESULTS: The subjects had a mean age 73.6 (SD 2.9), BMI 28.8 (SD 4.9), 40.3% male, and 46% were Black. Medial displacement of the patella predisposed to medial JSN progression; odds for each quartile 1, 1.2, 1.2, 2.2 (P for trend=0.03), whilst protecting from lateral JSN progression; odds for each quartile 1, 0.7, 0.6, 0.4 (P for trend=0.0004). Increasing patella tilt protected from medial JSN progression; odds for each quartile 1, 0.8, 0.5, 0.2 (P<0.0001) and trended to increasing pain severity (P=0.09).
CONCLUSION: Patella malalignment is associated with PF disease progression. Medial displacement and tilt of the patella predisposes to medial JSN progression, whilst lateral displacement is predictive of lateral JSN progression. The influence of patella malalignment has important implications since it is potentially modifiable through footwear, taping and/or knee bracing.