THE EFFECT OF FEMORAL LENGTHENING ON KNEE ARTICULAR-CARTILAGE - THE ROLE OF APPARATUS EXTENSION ACROSS THE JOINT

Loss of joint motion is a common complication of limb lengthening desp ite newer methods of incremental bone elongation. A pilot canine study has demonstrated that 30% femoral lengthening causes reproducible kne e cartilage injury manifest by frank loss of cartilage substance or fi brillation. This study was undertaken to examine the potential of knee joint protection by apparatus extension to the tibia. Four dogs under went application of a modified Ilizarov apparatus to the femur and tib ia with coaxial hinges at the knee. After osteotomy, 30% lengthening w as undertaken at 0.75 mm daily in three increments. At the completion of lengthening, experimental and contralateral knee joints were harves ted, assessed grossly, decalcified, sagittally sectioned, and stained with safranin-O. All control joints were normal histologically. All ex perimental joints demonstrated a decrease in proteoglycan staining wit hout evidence of fibrillation or necrosis. These findings suggest a pr otective effect of the tibial apparatus by avoiding joint compression.