The unstable knee in congenital limb deficiency

PURPOSE Instability of the knee is a common finding in patients with congenital limb deficiency. The instability can be attributed to soft tissue abnormalities, frontal, sagittal or rotational deformity of the lower limb and bony dysplasia of the patella or of the femoral condyles. In most of the cases, these pathomorphologic changes stay asymptomatic in daily activity. However, instability can appear during deformity correction and bone-lengthening procedures, leading to flexion contracture or subluxation of the knee. METHODS A review of pediatric orthopaedic literature on different factors of knee instability, state-of-the-art treatment options in congenital limb deficiency and in cases of lengthening-related knee subluxation is presented and the authors' preferred treatment methods are described. RESULTS Leg lengthening and deformity correction in patients with congenital limb deficiencies can be achieved with various techniques, such as guided growth, monolateral or circular external fixation and intramedullary lengthening nails. Radiographic assessment and clinical examination of the knee stability are obligatory to estimate the grade of instability prior to surgical procedures. Preparatory surgery, as well as preventive measures such as bracing, bridging of the knee and intensive physical therapy, can help to avoid subluxation during lengthening in unstable knees. CONCLUSIONS Adequate surgical techniques, preventive measures and early detection of signs of subluxation can lead to good functional results in patients with congenital limb deficiency.