Rigid or sliding plate. A mechanical evaluation of osteotomy fixation in sheep.

Fracture fixation using rigid plates leads to direct bone union, but it also may lead to complications because of stress protection osteopenia. This study aims to compare the mechanical characteristics restored during the callus formation after an osteotomy is fixed with two types of internal plate fixation. Twenty-four adult female sheep were divided randomly into three groups of eight each, which were euthanized at 2, 4, and 6 months after operation. Half of them had their osteotomized radius fixed with a seven hole dynamic compression plate, whereas in the remainder a sliding plate was used. The sliding plate consists of two halves connected together in such a way as to permit axial sliding of the one within the other, thus allowing cyclic axial load transfer at the fracture site. Bone strips obtained from the healthy (control) and the surgically treated side were subjected to four-point bending tests. The effective modulus of elasticity, ultimate bending strength, and energy absorption to fracture (toughness) were calculated. All parameters were restored more quickly in the sliding plate group, but there was no statistically significant difference observed at 6 months when all the osteotomies were united completely. Thus, the sliding plate, by allowing axial loading at the fracture site, led to a faster callus maturation and hence bony union, which, hopefully, will permit earlier full weightbearing and functional recovery of the injured limb.