Insufficient bone regenerate after intramedullary femoral lengthening: risk factors and classification system.

Background: 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.

Questions/purposes: 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?

Patients And Methods: 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.

Results: 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).

Conclusions: 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 Of Evidence: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.