Comparative Outcomes of 8.5 mm Intramedullary Nails Versus Extramedullary Constructs for Femoral Lengthening in Pediatric Patients.

Introduction: Limb-length discrepancies (LLDs) have traditionally been treated with external fixators, but magnetically driven intramedullary nails (MILNs) are increasingly favored for improved comfort and reduced infection risk. This study compared intramedullary (IM) versus extramedullary (EM) lengthening nails in pediatric patients with narrow femoral canals to evaluate mechanical axis deviation, nail bending, tourniquet time, and complications.

Methods: A retrospective, single-center review was conducted of 75 pediatric patients who underwent femoral lengthening between 2015 and 2022, each with at least two years of follow-up. Patients received either an 8.5 mm IM nail or a 10.7/12.5 mm EM nail, combined with a solid, threaded IM nail for stability. Outcomes included preoperative and postoperative limb alignment (MAD, mLDFA, and mPDFA), IM nail bending, operative details (tourniquet time and blood loss), consolidation times, and complication rates classified according to the Cherkashin system.

Results: Forty-two patients were treated with EM nails and 33 with IM nails. Both groups achieved similar distraction amounts (4.7 ± 1.1 cm) and consolidation intervals (7 to 8 mo). However, the EM group demonstrated significantly greater postoperative MAD (12.9 ± 9.5 mm vs.  8.7 ± 7.3 mm, P <0.05), higher nail bending (2 vs.  1.2 degrees, P<0.05), and longer tourniquet use. Overall complication rates were 69% (EM) and 60% (IM), with delayed union and soft tissue infection being the most frequent issues. Unplanned reoperations occurred in 21% of patients overall.

Conclusion: Both nail types correct limb‑length discrepancy, but extramedullary nails demand longer tourniquet times and have higher bending (of the IM component of the EM construct) and complication rates. Implant choice must suit patient factors and further comparative studies are warranted.