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 despite newer methods of incremental bone elongation. A pilot canine study has demonstrated that 30% femoral lengthening causes reproducible knee cartilage injury manifest by frank loss of cartilage substance or fibrillation. This study was undertaken to examine the potential of knee joint protection by apparatus extension to the tibia. Four dogs underwent application of a modified Ilizarov apparatus to the femur and tibia with coaxial hinges at the knee. After osteotomy, 30% lengthening was undertaken at 0.75 mm daily in three increments. At the completion of lengthening, experimental and contralateral knee joints were harvested, assessed grossly, decalcified, sagittally sectioned, and stained with safranin-O. All control joints were normal histologically. All experimental joints demonstrated a decrease in proteoglycan staining without evidence of fibrillation or necrosis. These findings suggest a protective effect of the tibial apparatus by avoiding joint compression.