Insufficient Bone Regenerate after Intramedullary Femoral Lengthening: Risk Factors and Classification System

Abstract

Control of distraction rate with an intramedullary skeletal kinetic distractor (ISKD) may be problematic and a high distraction rate may result in insufficient bone regenerate. Are distraction problems preventable when using the ISKD, and what are the risk factors for and radiologic types of insufficient bone regenerate during ISKD lengthening? We analyzed 37 consecutive ISKD femoral lengthening procedures in 35 patients with a mean age 33 ± 11 years and minimum followup of 12 months (average, 27 ± 9 months; range, 12–55 months). The average length gain was 42.8 ± 12.9 mm. Eight patients had problems during distraction: seven had “runaway nails” and one had a nondistracting nail. Insufficient bone regenerate developed in eight patients. Important risk factors were a distraction rate greater than 1.5 mm/day (9.1 times higher risk), age 30 years or older, smoking, and lengthening greater than 4 cm. Less important risk factors identified were creation of the osteotomy at the site of previous trauma or surgery and acute correction of associated deformities. We proposed a radiologic classification for failure of bone regeneration: partial regenerate failure (Type I) or complete failure resulting in a segmental defect subdivided according to a length of 3 cm or less (Type IIa) or greater than 3 cm (Type IIb). Distraction problems with the ISKD were related mostly to internal malfunction of the lengthening mechanism. A distraction rate greater than 1.5 mm/day should be avoided in femoral intramedullary lengthening. Smoking should be a contraindication for femoral lengthening. Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.