Histology and ultrastructure of arteries, veins, and peripheral nerves during limb lengthening.

The effects of lengthening of the metacarpal bone on peripheral nerves and blood vessels were studied in 8 calves. Specimens for light and electron microscopy were obtained from the palmar neurovascular bundle at 1 cm (8% of the initial length), 2.5 cm (20% of the initial length), and 4 cm (33% of the initial length) of metacarpal lengthening. In 2 calves, specimens were studied 2 months after the end of the lengthening procedure. At 8% of lengthening, myelinated fibers of the palmar nerve showed moderate degenerative changes in the myelin sheath. This became severe at 20% and 33% of lengthening, and affected the axoplasm as well. At 20% of lengthening, the palmar vein started to show fibrous metaplasia of the smooth muscle tissue of the tunica media. This became much thinner than normal. The palmar artery showed moderate alterations of the inner part of the tunica media and the intima. The palmar nerve and blood vessels recovered their normal structure almost completely 2 months after the end of the lengthening procedure. The morphologic alterations of peripheral nerves and vessels may constitute the pathophysiologic basis of the nervous and circulatory disturbance observed in clinical practice.