Biomechanical comparison of anterior Caspar plate and three-level posterior fixation techniques in a human cadaveric model.

Traumatic cervical spine injuries have been successfully stabilized with plates applied to the anterior vertebral bodies. Previous biomechanical studies suggest, however, that these devices may not provide adequate stability if the posterior ligaments are disrupted. To study this problem, the authors simulated a C-5 teardrop fracture with posterior ligamentous instability in human cadaveric spines. This model was used to compare the immediate biomechanical stability of anterior cervical plating, from C-4 to C-6, to that provided by a posterior wiring construct over the same levels. Stability was tested in six modes of motion: flexion, extension, right and left lateral bending, and right and left axial rotation. The injured/plate-stabilized spines were more stable than the intact specimens in all modes of testing. The injured/posterior-wired specimens were more stable than the intact spines in axial rotation and flexion. They were not as stable as the intact specimens in the lateral bending or extension testing modes. The data were normalized with respect to the motion of the uninjured spine and compared using repeated measures of analysis of variance, the results of which indicate that anterior plating provides significantly more stability in extension and lateral bending than does posterior wiring. The plate was more stable than the posterior construct in flexion loading; however, the difference was not statistically significant. The two constructs provide similar stability in axial rotation. This study provides biomechanical support for the continued use of bicortical anterior plate fixation in the setting of traumatic cervical spine instability.

Bone lengthening in rabbits by callus distraction. The role of periosteum and endosteum.

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.

The effect of distraction upon bone, muscle, and periosteum.

Bone lengthening was achieved on rabbit tibias by means of callus distraction (callotasis) using a dynamic external fixator. The periosteum and the muscle fascia were labeled with metal markers; changes in position of these markers during slow progressive distraction were monitored by soft radiography. During the waiting period before commencing distraction, the periosteal markers around the osteotomy site were elevated from the bone surface by newly formed external callus. There was an apparent lag period until the periosteal reaction occurred after osteotomy. Subperiosteal callus was first formed in an uncalcified state and subsequently became calcified. As distraction began, longitudinal migration of the periosteal markers was observed. It appears that the periosteum slides over the bone cortex, mitigating local stretching of the muscle around osteotomy site. The elongation of muscle occurs throughout the muscle substance and not simply at the site of osteotomy.

Lumbar disc herniation in children.

The symptoms, signs, and radiographic findings of lumbar disc herniation with apophyseal fracture are compared with those of lumbar disc herniation without fracture. Disc herniation with apophyseal fracture characteristically displayed central herniation, postoperative bony ridge formation, and end plate irregularity.

A case of short metatarsal bones lengthened by callus distraction.

Bilateral congenitally short fourth metatarsal bones were osteotomized subperiosteally, held in neutral position for 3 weeks by a small external fixator, and then subjected to slow axial distraction (0.25 mm/12h). The overall treatment time was 11 weeks, and the final increase in length was 14 mm for the left and 12 mm for the right metatarsal bone.

Factors affecting callus distraction in limb lengthening.

Factors affecting the process of callus distraction in limb lengthening include the type of osteotomy, timing and rate of distraction, and stability of fixation. Thirty-two rabbits were studied to evaluate the reliability of transverse osteotomy and delayed distraction and to examine the appropriate rates of distraction. Rabbit tibiae were osteotomized subperiosteally and were subjected to slow distraction using a rigid monolateral external fixator. There was a ten-day waiting period before distraction. The animals were divided into three groups according to the rate of distraction (0.35 mm/12 hours, 0.7 mm/12 hours, 1.4 mm/12 hours). The process of callus formation was monitored by soft x-ray. The reliability of delayed distraction after transverse osteotomy was demonstrated by microangiographic study. Even though intramedullar vessels were interrupted by osteotomy at surgery, blood circulation recovered during the waiting period before distraction. Bone lengthening was successful when distraction was carried out at rates of 0.35 mm/12 hours or 0.7 mm/12 hours. The callus filling a distraction gap showed a characteristic zone structure, i.e., one central radiolucent zone and two adjacent sclerotic zones. Microangiographic study demonstrated the continuity of blood vessels under these rates of distraction. Based on the results of these experiments and clinical experiences on 180 bone lengthenings, the authors believe that a waiting period after osteotomy is more practical than achieving immediate distraction after uncertain corticotomy.

Lengthening of the lower limbs in patients with achondroplasia and hypochondroplasia.

Ten years of experience in lower limb lengthening achieved in 35 patients with achondroplasia and seven patients with hypochondroplasia is reported. A uniform method of callus distraction (callotasis) was used in all cases, although the order of lengthening of each bone differed among the cases. The mean age of the patients at the time of first operation was 14.5 years; at followup, the mean age was 18.8 years. The mean lengthening achieved in the femur was 7.2 cm (range, 4.5-12 cm) and in the tibia 7.1 cm (range, 4.5-13 cm). More lengthening was achieved in the more recent cases. The function of lengthened limbs, evaluated by physical strength tests, was better at followup than before lengthening in the growing children, although the mechanical axes of the lengthened bones were not necessarily in correct alignment.