Abstract
Summary Statement
This study quantifies compositional differences in cartilage between CAM deformities of symptomatic FAI patients and normal cadaver controls. It shows a resemblance of CAM-FAI cartilage with those of osteoarthritic hips, objectively supporting previous hypothesis of abnormal contact stresses in CAM-FAI.
Introduction
Degeneration of cartilage within articular joints is a pathological feature of osteoarthritis (OA). Femoroacetabular impingement (FAI), a condition of abnormal contact between the articular surfaces of the femur and acetabulum, has been widely associated with early onset OA of the hip. The purpose of this study was to quantitatively compare the proteoglycan (PG) content of the weight-bearing cartilage in surgical FAI patients versus those of cadavers without FAI.
Patients and Methods
Osteochondral bone plugs were taken from the antero-superior weight-bearing surface of cam-deformities on the femoral heads of 11 surgical cam-FAI patients. These were compared to control specimens taken from 11 cadaveric hips (7 donors) at approximately the same location. The PG content of the specimens were then histologically compared using the model presented by Martin et al. In this method, Safranin-O binds to chondroitin sulfate, a PG abundant in cartilage, allowing it to be visualised and quantitatively compared. Specifically, the specimens were fixed in formalin, decalcified in EDTA and then sectioned to 7um thick. They were then stained with Safranin-O, which binds specifically and stoichiometrically with proteoglycan. This model allows for quantitative comparison of PG content whereby the red content (Rc) of the sample is linearly correlated with the amount of PG present in the sample when viewed under 4x microscopic magnification. Here, the red content was sampled by depth coordinate with superficial and deep zones analyzed.
Results
In general, the RC in the cartilage of surgical patients was lower than that of the cadaveric controls in both the superficial and deep layers tested. This correlates to a decrease in the PG of the test subjects. In the surgical specimens, RC ranged from 0 – 31.9 in the superficial layer and 0 – 139.6 in the deep. When compared by layers, the RC of the superficial 30% specimens averaged an RC of 17.5 compared to 88.6 in the cadaveric controls. This represents an 80.2% depletion in the PG content. In the deep 70% layer, the average RC of the test subjects was 52.4, compared with 129.2 in the cadaveric controls. This represents a 59% depletion in the PG content of the deep layer. These results show large compositional change in the cartilage of surgical FAI versus control specimens that were statistically significant in all levels (superficial, deep, total yielding p<0.001, p=0.001, p<0.001, respectively).
Discussion
The idea of abnormal cartilage at the cam deformity has been previously demonstrated through similar resection and staining techniques. Wagner et al showed cellular activity and qualitatively noted PG depletion in the cartilage on the Cam deformity, consistent with OA. However a quantitative assessment of PG content provides a better estimate of impingement severity and disease state. Results from this current study objectively corroborate previously obtained qualitative data, supporting existing hypothesis of abnormal contact stresses in cam-FAI while giving a more robust, objective quantification of cartilage breakdown at CAM sites.
