This study aimed to observe the effect of femoral lengthening on proprioceptive nerve endings of the anterior cruciate ligament in rabbits and to evaluate the relationship between changes in the number of mechanoreceptors and electrophysiologic abnormalities, and histomorphological changes in the ligament, according to the length gain.

Forty rabbits were divided into two groups, such as 10% and 20% lengthening. Each ipsilateral femur was distracted by gradual method and the contralateral side was used for the sham group. Distraction at a rate of 1 mm per day was started on the 5th day postoperatively. The frequency of distraction was 2 steps per day. At the end of the experiment, nerve conduction studies including amplitude, latency and area of compound muscle action potential (CMAP) were measured. Modified gold-chloride stain was used for detection of proprioceptive nerve endings of the anterior cruciate ligament and hematoxylin-eosin stain was used for light microscopic examinations of the anterior cruciate ligament. Among 40 animals, 7 were excluded in our study due to experimental faults which were 3 inadequate osteotomy, 2 premature consolidation and 2 sepsis. Three types of mechanoreceptors were identified by Freeman and Wyke criteria.

There was a statistically significant reduced number of three morphological kinds of corpuscles in anterior cruciate ligaments in the 20% lengthening group than in the sham group (p<0.03) . Morphological changes of synovium on the anterior cruciate ligaments were more evident in the lengthened groups rather than in the ligament itself. However, there was little relationship between abnormalities of nerve conduction velocity and the change in number of proprioceptive nerve endings.

This study provided morphological evidence of the harmful effects on proprioceptive function of adjacent joints due to lengthening, and that femoral lengthening may alter the neurophysiological function of the knee joint by decreasing the number of mechanoreceptors in the anterior cruciate ligament. As well, this morphological change by limb lengthening did not seem to be related to distraction neuropathy.