A method of examining the magnitude and origin of "soft" and "hard" tissue forces resisting limb lengthening

Complications arising from limb-lengthening procedures such as muscle contracture, axial malalignment of the bone and traction injuries to the nerves and vessels, are often severe. Often complications arise from the build-up of forces in the biological tissues which are resisting lengthening. Little is known about the origin and magnitude of these forces, although three studies have identified the regenerate (new bone tissue) as the dominant resisting tissue. This study describes the development of a method to examine these forces. It employs load measurement devices in the structural columns of Ilizarov fixators which measure the compressive load on the frame exerted by the biological tissues. The distribution of this load between the columns of the frame, in conjunction with a transverse radiograph of the limb at the regenerate site, is used to examine the origin of the resisting force. Accuracy was determined by a laboratory simulation which found the predicted position of the force to be within 5 mm of the actual position in all four cases tested. Mean error in the total measured force was 2 N (SD, 1 N). A pilot study on a patient undergoing a 60 mm femoral lengthening revealed a peak force of 717 N originating in the Vastus Lateralis or the illiotibial tract. Negligible contribution to resistance was provided by the regenerate, contrary to that found with other studies.