Distraction-resisting force during tibial diaphyseal lengthening and consolidation--a study on a rabbit model.

BACKGROUND: Distraction-resisting force is generated in the soft tissues and callus during limb lengthening. Monitoring this force may offer a method of studying the behaviour of soft tissue and detecting the distraction osteogenesis related problems, and help to prevent complications. Changes in the post distraction period have not been previously investigated and there are no reports on the contribution of gastrocnemius to the distraction-resisting force. METHODS: Sixteen immature New Zealand White rabbits underwent 30% (left) tibial diaphyseal lengthening at a rate of two 0.4 mm increments per day. Using an instrumented bilateral fixator, the passive distraction-resisting force and the contribution made by gastrocnemius were measured at the end of lengthening and 5 weeks after lengthening. FINDINGS: The distraction-resisting force at the end of lengthening (mean 44 N (SD 10)) was statistically higher (p < 0.01) than that five weeks after lengthening (mean 20 N (SD 8)), so was the contribution of the gastrocnemius to the force (mean 11 N (SD 5 N) or 25% (SD 7) at the end of lengthening and 3 N (SD 1) or 13% (SD 5.2) five weeks later). INTERPRETATION: The callus rather than the surrounding muscles generates most of the passive DRF and its share of the force increased during consolidation period.