Modifications of patellar articular cartilage and subchondral bone following immobilisation and denervation: a histologic and morphometric in vivo study

Abstract

We studied the morphologic effect of immobilisation and denervation on articular cartilage (AC) and subchondral bone (SCB) in 20 lambs. The animals underwent medial arthrotomy at the left knee; ten of them also received an external fixation device to eliminate articularity. Ten right knees were used as controls. Histological analysis revealed an increase in area and width in the central part of AC of all the arthrotomised knees due to a proliferation of the intermediate layer; a gross reduction in SCB trophism was observed in immobilised articulations with respect to the arthrotomised ones and controls. This result was confirmed histomorphometrically: a significant increase in arthrotomised patellar AC with respect to the control group was observed in the central zone corresponding to the vertical ridge of patella; cartilage in the medial aspect presented a significant difference between operated groups in both area (p=0.026) and width (p=0.01). Values from non-immobilised animals were higher than in those from the immobilised animals. The total trabecular area was significantly lower in samples from immobilised knees than in the other groups in all sections. Comparing measures from non-immobilised animals, areas were higher in operated but nonimmobilised knees than in controls: this difference was significant only in the midddle (p=0.002) and medial parts of the SCB. In our model, AC trophism was dependent on share stress and direct loads more than on denervation. Moreover, early postsurgical remobilisation avoids AC atrophy and post-surgical osteoporosis through conservation of SCB area, encouraging systematic denervation of patella during total knee arthroplasty without patellar resurfacing.