The deep fascia in response to leg lengthening with particular reference to the tension-stress principle.

Objective: To investigate the morphological changes of deep fascia subjected to distraction in a rabbit model of leg lengthening.

Methods: The animal model of leg lengthening was established in 20 New Zealand white rabbits using a unilateral external fixator with 4 half pins medially fixed to the tibia, and osteotomy was performed between the second and the third pins. The distraction was initiated 7 days after the osteotomy procedure, with the rate of 1 and 2 mm/d in 2 steps, and proceeded until 10% and 20% increases in the initial length of the tibia had been achieved. The deep fascia samples were studied by the hematoxylin-eosin stain, the Masson-trichome staining, and the JEM2000EX electron microscopy.

Results: Under light, the cross section of normal deep fascia without distraction consisted of 3 layers. Whereas in the longitudinal sections, the deep fascia consisted of wavy collagen fibers. The normal deep fascia consisted of fibrocyte and collagenous fibrils under electron microscopy. After leg lengthening, the morphology of the fascia distracted at each rate changed. Under light, the fascia distracted at each rate kept the normal 3 layers in the cross sections. The fascia subjected to distraction at a rate of 2 mm/d showed injuries of collagen fibers. Under electron microscopy, the fascia distracted at a rate of 2 mm/d showed active metabolism to repair the necrotic collagenous fibrils. Whereas the fascia subjected to distraction at a rate of 1 mm/d showed regenerative changes. The endotheliocyte of capillaries within the deep fascia subjected to distraction at a rate of 1mm/d with 20% lengthening of tibia was metabolically active.

Conclusions: The tension stress, which is applied in leg lengthening and deformity correction as described by Ilizarov, has a great effect upon the fascia, which is always related to the function of the involved limb. The appropriate regimen of distraction at the rate of 1 mm/d with 20% lengthening of tibia leads to the regenerative changes in deep fascia, ultimately close to the morphological structure of normal under the condition of this investigation.