The relation of patellofemoral joint alignment and trochlear morphology to superolateral Hoffa’s fat pad edema: the most study

Abstract

Purpose: The infrapatellar or Hoffa’s fat pad (HFP) is an intracapsular but extrasynovial fat tissue in the knee joint located inferior to the patella and posterior to the patellar tendon. It is highly innervated and may be a source of knee pain. Impingement of HFP between the lateral femoral condyle and the patellar tendon is hypothesized to cause inflammation/edema in the superolateral region of HFP. This impingement may be a result of patellofemoral joint (PFJ) alignment and abnormal trochlear morphology. Previous studies in young individuals have demonstrated conflicting results as to which measures of PFJ alignment and trochlear morphology are related to superolateral HFP edema. More generalized inflammation/edema in HFP is present in older individuals with knee osteoarthritis (OA). The aim of the current study was to assess whether measures of PFJ alignment and trochlear morphology are related to superolateral HFP edema and if superolateral HFP edema is related to knee pain in older individuals with or at risk for knee OA. Methods: The Multicenter Osteoarthritis (MOST) study is a NIH-funded longitudinal cohort study of older individuals with or at risk for knee OA. For the current cross-sectional study we used data from the 60-month study visit where all eligible subjects had their knee MRI assessed for other structural features of knee OA. Signal changes in three areas (superolateral, infrapatellar and intercondylar) of HFP were assessed on sagittal proton density-weighted fat-suppressed MRI images from 0 to 3 (0 = normal, 1 = mild, 2 = moderate, 3 = severe) by two musculoskeletal radiologists and dichotomized into presence (>1) and absence (=0). PFJ alignment (bisect offset and patellar tilt angle) and trochlear morphology (lateral trochlear inclination, sulcus angle and trochlear angle) were assessed on axial MRI images and divided into quintiles. Subjects were also queried about the presence of frequent knee pain (FKP) defined as pain on most days of the last month. We determined the relation of measures of PFJ alignment and trochlear morphology to the presence of superolateral HFP edema using logistic regression, adjusting for age, sex and body mass index. We additionally determined the relation of superolateral HFD edema to FKP using logistic regression, adjusting for age, sex, body mass index, depressive symptoms, catastrophizing and presence of signal changes in the infrapatellar/intercondylar HFP. Results: To date, 433 knees have been assessed for PFJ alignment, trochlear morphology and superolateral HFP edema. Superolateral HFP edema was present in 63 (17.7%) of knees. Compared with knees in the lowest quartile of bisect offset, those in the highest had 6.4 (2.6, 15.7) times the odds of having superolateral HFP edema. Compared with knees in the lowest quartile of trochlear angle, those in the highest had 2.7 (1.2, 6.3) times the odds of having superolateral HFP edema. There was no relation of other PFJ alignment/trochlear morphology measures to superolateral HFP edema. There was also no relation of superolateral HFP edema to FKP. Conclusions: Knees with the greatest lateral displacement of the patella had the greatest odds of superolateral HFP edema. Treatments that attempt to normalize PFJ alignment may help to reduce the prevalence of superolateral HFP edema.Tabled 1Table. Relation of PFJ alignment and trochlear morphology to superolateral HFP edema% Patella lateral to midline (Bisect Offset)Quartile 1Quartile 2Quartile 3Quartile 4Range33.91–52.5952.6–58.1658.17–64.664.61–92.79# of knees108109109108Superolateral HFP edema%≥16.511.113.828.7Adjusted OR* (95% CI)1.0 (reference)1.9 (0.70, 5.0)2.5 (0.95, 6.4)6.4 (2.6, 15.7)Trochlear Morpholgy (Trochlear Angle)Quartile 1Quartile 2Quartile 3Quartile 4 (flat trochlea)Range−5.32–0.940.95–3.553.56–5.835.84–26.57# of knees108109109108Superolateral HFP edema%≥18.313.814.724.3Adjusted OR* (95% CI)1.0 (reference)1.6 (0.65, 3.8)1.6 (0.67, 3.9)2.7 (1.2, 6.3)∗Adjusted for age, sex and BMI Open table in a new tab ∗Adjusted for age, sex and BMI