The effect of distraction-resisting forces on the tibia during distraction osteogenesis.

BACKGROUND: Distraction-resisting forces that are generated during distraction osteogenesis can be responsible for complications, including a lag effect on fibular distraction leading to a tibiofibular distraction difference, tibial axial deviation, and distraction at the proximal and distal tibiofibular joints. We investigated the nature of distraction-resisting forces by studying their correlation with these parameters.

METHODS: One hundred and eleven tibial lengthening procedures in sixty-three patients were chosen. Seventy-six segments underwent lengthening with an Ilizarov ring fixator, and thirty-five segments had lengthening over an intramedullary nail. Serial radiographs were evaluated with regard to the amounts of tibiofibular distraction difference, proximal tibiofibular joint distraction, distal tibiofibular joint distraction, tibial axial deviation, and heel malalignment. Clinically, laxity at the knee was evaluated and fibular head instability was assessed. Variations in all of these parameters were evaluated with respect to tibiofibular joint fixation, etiology, skeletal maturity, lengthening over an intramedullary nail, and amount of lengthening.

RESULTS: The mean tibiofibular distraction difference was 19.1 +/- 10.6 mm (range, 2 to 51 mm), the mean proximal tibiofibular joint distraction was 10.1 +/- 6.8 mm (range, 0 to 33 mm), and the mean tibial valgus angulation was 8.7 degrees +/- 4.4 degrees . At the time of the latest follow-up, twenty-eight segments (25%) had lateral knee joint laxity at 30 degrees of knee flexion and eight segments (7%) had fibular head subluxation at 90 degrees of knee flexion. Twenty-four (86%) of the twenty-eight cases of knee laxity were observed in skeletally immature patients. The tibiofibular distraction difference, proximal tibiofibular joint distraction, and tibial valgus angulation were significantly greater in the group without fixation of the proximal tibiofibular joint. A significant decrease in the tibial valgus angulation and knee laxity was found in patients with lengthening over an intramedullary nail. In the intramedullary nail group, after fixation of the proximal tibiofibular joint, the tibiofibular distraction difference and the proximal tibiofibular joint distraction decreased; however, the proportion of cases with clinically important tibial valgus angulation (>10 degrees ) increased significantly.

CONCLUSIONS: Fixing both tibiofibular joints with a single Ilizarov wire decreases proximal tibiofibular joint distraction; however, more secure fixation would help to decrease the prevalence of delayed knee laxity. When tibial lengthening is performed over an intramedullary nail, avoiding proximal tibiofibular joint fixation will limit tibial valgus angulation. Limiting lengthening to <25% will decrease the proportion of cases with knee laxity, and limiting lengthening to <50% will significantly limit tibial valgus angulation.