2015 ISAKOS Biennial Congress ePoster #903

Chronic Synovial-Based Inflammation in Femoroacetabular Impingement

Geoffrey D. Abrams, MD, Stanford, CA UNITED STATES
Ayala Luria, PhD, Palo Alto, CA UNITED STATES
Nikhul Tendulkar, MD, Palo Alto, CA UNITED STATES
Rebecca A. Carr, BA, Palo Alto, CA UNITED STATES
William H. Robinson, MD, PhD, Palo Alto, CA UNITED STATES
Marc R. Safran, MD, Prof., Redwood City, CA UNITED STATES
Jeremy Sokolove, MD, Palo Alto, CA UNITED STATES

Veterans Administration Palo Alto/Stanford University, Palo Alto, CA, USA

FDA Status Not Applicable

Summary: Patients with femoroacetabular impingement demonstrate synovial-based inflammation




Femoroacetabular impingement (FAI) is currently thought of as having an anatomic and mechanical pathophysiology. Some individuals who have the predisposing anatomy for FAI, however, do not develop hip pain and may not develop osteoarthritis (OA) of the hip. There has been recent recognition of chronic inflammation as a contributor to pain and degenerative OA in the knee. To our knowledge, no data has yet examined whether chronic synovial-based inflammation is present in those with FAI. We hypothesize that chronic synovial-based inflammation exists in patients with diagnosed FAI.


Fifteen patients undergoing hip arthroscopy consented to have synovial biopsies taken from the central and peripheral compartments of the operative hip. Central compartment biopsies were taken from the anterosuperior synovium while peripheral biopsies were taken from within the capsule underneath the iliofemoral ligament. Synovial biopsies were embedded in optimum cutting temperature (OCT) compound and cryosections stained with hematoxylin and eosin (H&E). Serial sections were also stained and assessed by semi-quantitative confocal immunofluorescent microscopy to evaluate for CD45 (pan-leukocyte), CD31 (endothelial cell), and CD68 (macrophage) cell surface markers. A previously published “synovitis score” grading system was utilized to determine the amount of synovitis seen under light microscopy. Quantitative analysis for cell surface marker staining presence and intensity with confocal laser scanning microscopy was carried out using digital image analysis (ImageJ, National Institutes of Health, Bethesda, MD). Scoring was assessed two times with two separate blinded reviewers for the synovitis score and mean values were calculated. Student’s t-tests were used to examine statistical differences between groups and a kappa-statistic was calculated for inter- and intra-observer correlation coefficients (ICC). An alpha value of 0.05 was set as significant.


Of the 15 patients, seven (47%) demonstrated at least mild synovitis in the central compartment (synovitis score 1.4 ± 1.4, range 0-4) and six (40%) showed at least mild synovitis in the peripheral compartment (synovitis score 1.4 ± 1.0, range 0-3). There was no difference in the overall synovitis score between the central and peripheral compartments (p = 0.976) nor was there a significant relationship in the amount of synovitis between compartments within the same patient (p = 0.104). The intra-observer (k = 0.753) and inter-observer (k = 0.888) ICC for synovitis grading under light microscopy demonstrated substantial agreement. Quantitative analysis demonstrated significantly increased CD45 staining intensity in both the central and peripheral compartments versus CD31 and CD68 (p < 0.001).


Nearly half of patients undergoing arthroscopy for FAI demonstrated synovial inflammation in the central and peripheral compartments as determined by light microscopy. Immunofluorescence revealed a significantly increased number of cells expressing CD45 (versus CD31 and CD 68), suggesting the generation of a synovial inflammatory response within at least a subset of patients with FAI.