Lengthening of the Femur with a Remote-Controlled Magnetic Intramedullary Nail: Retrograde Technique

Introduction: Femoral lengthening with an intramedullary nail inserted through a retrograde approach offers the unique benefit of accurate deformity correction and distraction osteogenesis without the need for external fixation with its inherent challenges.

Indications & Contraindications:

Step 1 Planning The Deformity Correction And Nail Insertion: The key to a successful deformity correction and proper nail placement is preoperative planning.

Step 2 Insert The Rotation Marker Pins And Blocking Screws: Insert 2 Steinmann pins or half-pins into the proximal and distal aspects of the femur to mark any rotational deformity that is being corrected or to ensure that no rotational deformity is created. The Steinmann pins need to be ≥3 mm in diameter to prevent bending with loss of rotational reference. We prefer 5-mm or 6-mm Schanz pins for this role. These sturdy pins may be used as a "joystick" for manipulating the distal fragment to achieve a correction.

Step 3 Prepare The Distal Fragment: This step includes the approach to and reaming of the distal fragment, which is critical to the limb alignment.

Step 4 Osteotomy: Perform the percutaneous osteotomy, which allows for correction of the deformity, prior to reaming the proximal segment.

Step 5 Prepare The Proximal Fragment: While holding the distal fragment in the reduced position, prepare the proximal fragment for nail insertion.

Step 6 Nail Insertion: Insert the nail in a standard fashion, avoiding excessive force that could damage it or jam it into the proximal fragment.

Step 7 Lock The Nail: Lock the nail from the distal or proximal end first. The femoral distractor helps to keep the rotation accurate during locking and helps to serve as a handle to obtain perfect overlapping circles of the locking screw site on fluoroscopy. However, the external fixator may be obstructive for distal locking in particular. The fixator can be removed for distal locking and reattached for proximal locking.

Step 8 Final Blocking Screws: Check the anteroposterior and lateral fluoroscopic images and decide how stable the nail is in the bone. Will the fragment shift into varus, valgus, or flexion?

Step 9 Mark The Magnet And Test The Nail: Mark the position and orientation of the magnet in the nail on the patient's skin to indicate where to place the external magnet for lengthening.

Step 10 Postoperative Care And Lengthening: Postoperative management involves nail distraction, venous thromboembolic (VTE) prophylaxis, and adherence to a specific weight-bearing protocol.

Results: Femoral lengthening with the remote-controlled magnetic intramedullary nail has had excellent clinical efficacy.

Pitfalls & Challenges: