MEASUREMENT OF BONE LENGTHENING FORCES AN EXPERIMENTAL-MODEL IN THE LAMB

Objective. To obtain the mechanical behaviour pattern of the lengtheni ng process. Design. in vivo measurement of forces during bone lengthen ing in lambs. Background. A series of parameters of a mechanical and b iological nature have a bearing on all lengthening processes, and most of them are not fully understood. Methods. A strain-gauge-monitored u nilateral fixator was designed and used to obtain data about the chang es which took place in the forces of elongation at a rate of 1 mm/day in four lambs while a 3 cm progressive lengthening of the left tibia w as being performed, analysing how these forces behaved from day to day , and how they changed in the course of a single day. Results. The max imum forces in all the animals each day occur after distraction, and t he forces reach their greatest magnitude between days 21 and 25 after surgery, attaining values of slightly over 8 kg (40-50% of the animal' s weight). The maximum daily force starts to drop 1 h after distractio n, and continues to decrease gradually throughout the day until it rea ches a value slightly greater than the initial force on the previous d ay. Conclusion. This pattern is due to the distraction of soft tissues which gradually adapt to their new situation, thereby reducing the le vel of stress.