The histology and mechanics of leg lengthening by callus distraction were studied in 27 growing rabbits. Tibial diaphyses were subjected to subperiosteal osteotomy, held in a neutral position for 10 days and then slowly distracted at 0.25 mm/12 hours, using a dynamic external fixator. Radiographs showed that the gap became filled with callus having three distinct zones. Elongation appeared to occur in a central radiolucent zone; this was bounded by two sclerotic zones. Histologically, the radiolucent zone consisted of longitudinally arranged cartilage and fibrous tissue while the sclerotic zones were formed by fine cancellous bone. New bone occasionally contained islands of cartilage, suggesting it had been formed by endochondral ossification. After completion of distraction, the two sclerotic zones fused, shrank and were eventually absorbed, leaving tubular bone with a new cortex. When the periosteum had been removed at the operation, callus formation was markedly disturbed and there was failure of bone lengthening. Scraping of endosteum, in contrast, did not have a pronounced effect. These results suggest that the preservation of periosteum is essential if bone lengthening by callus distraction is to succeed, and that preservation of the periosteum is more important than careful corticotomy.

Over the past 19 years we have operated on 269 patients with myelopathy associated with cervical spondylosis. We report our results in 191 cases which we have followed up for 1 to 12 years (average 31 months). The clinical state before and after operation was recorded using the criteria of the Japanese Orthopaedic Association. Posterior operations gave better results than anterior for the more advanced myelopathies such as transverse lesions, the Brown-Sequard syndrome and the motor syndromes, but the brachialgia and cord syndrome and the central cord syndrome were satisfactorily treated by anterior operations. Of the three anterior and three posterior techniques used, no single one showed an overall superiority. A short duration of symptoms before operation was associated with better results, but these were not influenced by the age of the patients.