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

Abstract

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.

Figure 1

Method used to measure medial and lateral displacement using the bisect offset measurement (28). This was determined by drawing a line connecting the posterior femoral condyles (AB) and then projecting a perpendicular line anteriorly through the deepest portion of the trochlear groove (CD) to a point where it bisected the patellar width line (EF) (left). To obtain data when the trochlear groove was flattened, the perpendicular line was projected anteriorly from the bisection of the posterior condylar line (right). The bisect offset represents the extent of the patella lying lateral to the midline and is expressed as the percentage of patellar width.

Figure 2

Method used to measure the sulcus angle (30). This angle was defined by lines joining the highest points of the medial and lateral condyles and the lowest point of the intercondylar sulcus (AB and CB) (left). In order to obtain data when the trochlear groove lacked discernible depth, the center of the sulcus angle was defined by a perpendicular line that was projected anteriorly from the bisection of the posterior condylar line (right). All sulcus angle measurements are reported in degrees.

Figure 3

Method used to assess patellar tilt (29). Patellar tilt was defined as the angle formed by lines joining the maximum width of the patella (AB) and the posterior femoral condyles (BC). All tilt measurements will be reported in degrees. Normal tilt ranges from 0–5 degrees, and tilt angles of greater than 10 degrees are abnormal.