Behavior of tendons during lower-leg lengthening in dogs using the Ilizarov method.

Twenty-two dogs were provided with a circular fixator. Lengthening of the right lower leg by 2.5 cm was performed on 18 dogs 5 days after tibial osteotomy using a distraction rate of 0.5 mm, twice per day. Nine dogs with leg lengthening and two dogs of the control group without leg lengthening were sacrificed at the end of the distraction phase of 25 days and the remaining dogs after another 25 days. Post mortem, the tendons of the tibialis anterior, extensor digitorum longus, peroneus longus, and the Achilles tendon were taken from the operated-on right side and the left nonoperated-on control side and were analyzed histologically. The control group showed no histologic changes in the tendons of either side nor in those of the unlengthened left side of the operated-on dogs. Thirty-three tendons (41%) of dogs with leg lengthening were seen to have undergone histomorphological changes. An increase of the peritendinous connective tissue was seen, combined with chronic inflammatory cell infiltration in the tendons and/or the epitendinous tissues, edema, tendon fragmentation, necrosis, scarring of the tendons with dystrophic calcification and/or ossification, and broadening of the tenosynovial sheath. Furthermore, signs of histoneogenesis with growth in the tendons were found. Degenerative changes occurred far more often in the tendons of the ventral side of the lower leg and a slight pes equinus was regularly observed in the lengthened extremity. Therefore, pes equinus prevention and physiotherapy are important in the therapeutic use of lower-leg lengthening to minimize possible stress-induced damage of the ventral tendons.