Factors influencing bone regenerate healing in distraction osteogenesis.

BACKGROUND The dynamics and effectiveness of new bone formation in the Ilizarov method varies according to different factors. Some of them may result in substantial prolongation of treatment time. The lengthening index (LI), defined as the number of months in a frame necessary to achieve 1 cm lengthening, is the main indicator of bone healing potential. The purpose of the study was to assess the effectiveness of distraction osteogenesis by analysing the lengthening index (LI) in relation to: age, limb length discrepancy, aetiology, bone segment involved, axial correction and lengthening achieved. We studied 251 patients between the ages of 3 to 50 years (mean 15.3) treated with the Ilizarov method because of lower limb inequality. A total of 319 lengthening procedures were analyzed (tibia--155, femur--164). MATERIAL AND METHODS Total treatment time (time in a frame) and magnitude of lengthening were recorded in all patients to calculate LI (months per 1cm of lengthening). Patients were divided into several groups according to these factors. RESULTS Mean LI in the entire sample was 1.6 months/cm (from 0.7 to 5.9). The lowest LI (1.4) was recorded in the youngest patients (from 3 to 9 years) and increased with age, amounting to 1.6 in the 10-17 years' age group, 1.7 in the 18-21 years' age group and 2.4 in the 22-50 years' age group. The mean LI for femoral lengthening was lower (1.5) than for the tibias (1.8). In a group of 63 cases of lengthening up to 4 cm, LI was 2.3; in another group (from 4 to 7 cm - 189 procedures) LI was lower (1.6), and in the last group (more than 7 cm) it was 1.2. There was no significant difference in mean LI between the groups with and without axial correction. However, differences between aetiology groups were statistically significant, with a mean LI of 1.2 in achondroplasia patients, 1.4 in post-septic patients and patients with and Ollier disease, 1.6 in patients with congenital deformities, 1.8 in post-traumatic patients and 2.0 in neurogenic and clubfoot patients. CONCLUSION According to the lengthening index analysis, the effectiveness of distraction osteogenesis is related to age, aetiology, bone segment involved and the magnitude of lengthening, while it is not related to axial correction.