Site-specific variation in femoral head cartilage composition in dogs at high and low risk for development of osteoarthritis: insights into cartilage degeneration

Objective: To determine which characteristics of cartilage lesion pathology are detected in dogs at high risk to develop osteoarthritis prior to diagnosis by standard radiographs or macroscopic cartilage abnormality on necropsy. Methods: Fourteen disease-free dogs were assigned to risk groups based on hip distraction index. For seven dogs, three dimensional images of hip joints from computed tomography were available. At necropsy, ligamentum capitis femoris volumes were measured and articular cartilage was harvested and analyzed for percent water, swelling, glycosaminoglycan, and fibronectin. Comparisons were made with nine dogs with macroscopic cartilage lesions (OA group). Results: Ligament volumes were greater in the high distraction index group (P=0.000). Water content was elevated in the lesion area in both low and high risk dogs (P=0.000); no additional increase was noted in the high risk group. Glycosaminoglycan content was slightly elevated in the surrounding area in both groups (P<0.02) but loss was noted histologically in the lesion area of the high risk group. Fibronectin was increased in the lesion area and in the high risk group (P=0.000). The magnitude of this increase was greatest in the lesion area (P=0.000) in explants. Computed tomography indicated dorsal acetabular rim impingement on the lesion area in high risk dogs. Conclusions: Water content and swelling suggest matrix structure is weaker at the site of lesion predilection in all dogs regardless of risk status. Computed tomography imaging is consistent with site specific initiation of lesions by mechanical factors. (C) 1999 OsteoArthritis Research Society International.