Retrograde Intramedullary Femur Lengthening with Fitbone™ Lengthening System: Tips and Tricks

Abstract
The Fitbone™ lengthening system (Orthofix Medical LLC, Lewisville, TX, USA) utilizes a telescopic, stainless steel, motorized intramedullary device that is powered by transcutaneous electricity. The system utilizes a unique approach for bone preparation and stability. As each step of surgery and aftercare has distinctive features, this work aims to share technical suggestions for successful femur lengthening with this implant system.

Keywords: Femur lengthening, Fitbone, intramedullary nail, limb lengthening

David Benjamin Frumberg,
Franck Accadbled¹,
Jan Duedal Rölfing²

¹ Department of Orthopaedics & Rehabilitation, Yale School of Medicine, New Haven, CT, USA
² Department of Orthopaedics, Children’s

Article summary

This article reviews technical tips for retrograde femoral lengthening with the Fitbone motorized nail. As in most of the orthopedic procedures in limb reconstruction, success is linked to careful preoperative planning and disciplined postoperative monitoring.

Key surgical points and practical pearls

• Use calibrated full-length alignment imaging and reverse planning before surgery
• Check both coronal and sagittal alignment, because the femur has a natural bow and the nail is straight
• Mark the skin carefully with the trial nail and staples to define osteotomy level, reaming depth, and implant position
• Control rotation with Schanz pins and confirm alignment during the procedure
• Ream line-to-line rather than aggressively overreaming
• Keep the nail recessed enough to allow the cable to pass without blocking the knee pathway

The technique is not the same as standard trauma nailing. A working tube system helps maintain trajectory during reaming and protects the knee joint from debris. In most cases, angular correction should be completed before final reaming of the proximal segment. Intraoperative testing of the system can confirm that distraction is working before closure.

Aftercare

The authors describe a distraction protocol in which 27 pulses correspond to 1 mm of lengthening, with some surgeons using 9 pulses three times per day. The exact rhythm should be individualized according to biology and mechanics.

Radiographs should be checked every 7 to 14 days, and clinical examination should include hip, knee, and ankle motion at each visit. Lengthening should be slowed or stopped if knee extension loss, ankle equinus, or hip contracture appears. During distraction, weight bearing should be limited to 20 kg.

Troubleshooting

• If there is no audible activation, check receiver position, soft tissue depth, implant integrity, and compliance with weight-bearing restrictions.
• If the nail activates but pulse count does not rise, the feedback loop may be blocked by swelling; reassess the receiver and reduce edema.
• If the nail activates and pulse count rises but there is no radiographic distraction, look for premature consolidation.

FITBONE: 5 steps to remember

1. PLAN

Calibrated long-leg imaging + reverse planning.

2. MARK

Staples define osteotomy level, reaming depth, and nail position.

3. PROTECT

Use guided reaming, avoid anterior cortex breach, and control rotation.

4. TEST

Confirm cable, receiver, and initial distraction before closure.

5. FOLLOW

27 pulses = 1 mm; check motion and X-rays every 7–14 days.

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