Motorized Intramedullary Lengthening of the Femur: Antegrade and Retrograde

Intramedullary lengthening nails have revolutionized bone lengthening of the femur. The major limitations for using internal lengthening nails are the size of the femur (length and intramedullary diameter) and the risk of nail insertion in the skeletally immature child. Lengthening nails distract along the anatomic axis of the femur which can introduce mechanical axis deviation. To ensure a neutral mechanical axis is achieved at the end of lengthening, the reverse planning method with acute deformity correction and insertion of blocking screws can be applied. Postoperatively, the three main considerations are: (1) Forming healthy regenerate bone, (2) Maintaining joint range of motion, and (3) Advancing the weight-bearing safely. The majority of complications occur during the distraction and consolidation phases but can occur at any time, even after nail removal. Physical therapy is paramount to minimize joint complications. Regular clinical and radiological follow-up is recommended throughout the postoperative period to continuously monitor the lengthening rate and ensure the formation of good regenerate bone. Despite appearing straightforward, bone lengthening with intramedullary lengthening nails is a highly individualized treatment. The surgeon must be well-trained in limb lengthening to anticipate and manage any potential complications that may arise during the lengthening process.