CRANIO-CAUDAL GRADIENT OF REGENERATION RESOURCES OF THE LOWER LIMBS

Abstract

Since the time of Charles Darwin, it is known that three principles of regeneration explain the similarity of neo-formed tissues, the dependence of regeneration rhythm on age and the position of the animal in the evolutionary chain. The latter principle is know as the Weisman-Pschibram principle. Regeneration depends on several factors: level of tissue specialisation and differentiation, tissue resistance to hypoxia, and other manifestations of generally recognised biological regulation.

According to a fourth principle, the regenerative potential of different parts of the body depend on a cranio-caudal gradient which rhythms their postnatal growth and development. Distinction of this principle is of importance because of its practical applications. Experience with increasing the height of persons with achrondroplasty by lengthening different limb segments reveals that the femur has less regeneration potential despite its long length. Leg lengthening is preferred; saving muscle function, there is a 20% potential for lengthening.

Male subjects are generally considered to be short in height when there is a 10% growth retardation of the longitudinal dimension of the body. In female subjects, generative function is considered deficient if the length of the trunk is less than 73 cm. Using these criteria, experience has shown that leg malformations are not observed in subjects with a 10% growth retardation of the limb. The rate of growth retardation has to reach 40% before growth ceases.

The relative moment of posterior leg muscle force increases with increasing leg length (F = 0.063 x L – 0.7; r=0.965, n=123).

With a 10% growth deficit, the leg lengthening operation limits the amplitude of ankle movement 15% on average. With the same 10% growth deficit, lengthening the femur with the same technique decreases the amplitude of knee movement 22%. It has been noted that a 40% decrease in leg muscle force after leg lengthening does not affect locomotor function. The same decrease in thigh muscles after femur lengthening alters function.

Like the first three principles, the fourth has its exceptions. It is important however to distinguish the influence of biological factors from other, for example technical, factors. Thus orthopaedic surgeons prefer the humerus for lengthening the upper limb, but this results from the difficulty in preserving rotation movements when lengthening the forearm. The important advances obtained in recent years in patients with bony defects of the hand and foot are further arguments clearly in favour of the existence of a cranio-caudal gradient in regenerative potential of the limbs.