Viscoelastic behavior of tissue in leg lengthening by distraction.

The leg lengthening distraction procedure was analyzed with objectives of understanding complications which arise due to overstretching, establishing guidelines to the optimum distraction rates and the frequency of distraction, and, determining the final amount of leg lengthening. An electronic recording system was devised to provide continuous monitoring of the tractive load resulting from distraction of the leg during the elongation procedure. The mechanical behavior patterns of the involved stretched tissues domonstrate time-dependent viscoelastic effects during distraction. During a leg lenthening procedure it is desirable to establish, if possible, a regular pattern of distraction early in the process. If it is necessary in the course of treatment to reduce the distraction rate for clinical reasons, then it is preferable to keep the same number of distraction events but reduce the distraction amount. Distract at equally spaced time intervals to obtain repetitive load cycles and thereby reduce peak values of load and maintain similar stress relaxation patterns for each instantaneous load increase. The total amount of lengthening depends on the characteristics of each individual leg length discrepancy and the physical properties of each distracted tissue.