Unilateral hindpaw amputation causes bilateral articular cartilage remodeling of the rat hip joint

The purpose of this paper was to describe the remodeling of adult coxofemoral articular cartilage (AC) in response to altered weight bearing. Twelve adult male Sprague-Dawley rats underwent unilateral hindpaw transection at the distal tibiofibular junction (AmpCont group); another group of eight rats served as normal controls (Norm group). Subpopulations of both groups were injected with ³⁵SO₄ 24 hr before harvest. All femora were harvested after 8 weeks. Safranin O stained longitudinal sections were used to determine AC thickness, cellularity, and proteoglycan (PG) staining. Regional grain counting was performed on autoradiographs. Analysis of the data revealed that the AC of Norm hips in the region near the fovea capitis femoris was significantly thicker, had a lower cell density, a greater PG density, and a lower ³⁵SO₄ incorporation rate per chondrocyte than the AC of the Norm lateral edge region. The intact limbs of the AmpCont animals demonstrated a relative thinning of the AC near the fovea capitis femoris, compared with the edge region, and reduced ³⁵SO₄ incorporation rate in the lateral edge region, compared with normal values. The operated limb of the AmpCont animals displayed a relative increase of PG density in the edge region compared with foveal region and reduced ³⁵SO₄ incorporation rate in the lateral edge region, compared with normal values. We concluded that rat coxofemoral AC responds bilaterally to unilateral hindpaw amputation through appropriate morphologic remodeling.