Fusion is the main goal in the surgical management of the injured and unstable spine. A wide variety of implants is available to enhance this. Our study was performed to evaluate the stabilising characteristics of several anterior, posterior and combined systems of fixation. Six thoracolumbar (T11 to L2) spines from 13-week-old calves were first tested intact. Then the vertebral body of T13 was removed and the defect replaced and supported by a wooden block to simulate bone grafting. Dorsal implants consisting of a Universal Spine System (USS) fracture system and an AO The dorsal systems limited ROM in flexion below 0.9° and in extension between 3.3° and 3.6° (median values). The improved Kaneda System SR yielded a mean ROM of 1.8° in flexion and in extension. The median rotation found with the VentroFix (SC/DR) was 3.2° for flexion and 2.8° for extension. Reinforcement of the ventral constructs with a dorsal system reduced the ROM in flexion and extension in all cases to 0.4° and lower. In rotation, the median ROM of the anterior systems ranged from 2.7° to 5.1° and for the posterior systems from 3.9° to 5.7°, while the combinations provided a ROM of 1.2° to 1.9°. In lateral bending, the posterior implants restricted movement to 1.1°, whereas the anterior implants allowed up to 5.2°. The combined systems provided the highest stability at less than 0.6°. Our study revealed distinct differences between posterior and anterior approaches in all primary directions. Also, different stabilisation characteristics were found within the anterior and posterior groups. Combinations of these two approaches provided the highest stability in all directions.
We have assessed the influence of isolated and combined rotational malunion of the radius and ulna on the rotation of the forearm. Osteotomies were made in both the radius and the ulna at the mid-diaphyseal level of five cadaver forearms and stabilised with intramedullary metal implants. Malunion about the axis of the respective forearm bone was produced at intervals of 10°. The ranges of pronation and supination were recorded by a potentiometer under computer control. We examined rotational malunions of 10° to 80° of either the radius or ulna alone and combined rotational malunions of 20° to 60° of both the radius and ulna. Malunion of the ulna in supination had little effect on rotation of the forearm. Malunion of either the radius or of the ulna in pronation gave a moderate reduction of rotation of the forearm. By contrast, malunion of the radius in supination markedly reduced rotation of the forearm, especially with malunion greater than 60°.
We evaluated two reconstruction techniques for a simulated posterolateral corner injury on ten pairs of cadaver knees. Specimens were mounted at 30° and 90° of knee flexion to record external rotation and varus movement. Instability was created by transversely sectioning the lateral collateral ligament at its midpoint and the popliteus tendon was released at the lateral femoral condyle. The left knee was randomly assigned for reconstruction using either a combined or fibula-based treatment with the right knee receiving the other. After sectioning, laxity increased in all the specimens. Each technique restored external rotatory and varus stability at both flexion angles to levels similar to the intact condition. For the fibula-based reconstruction method, varus laxity at 30° of knee flexion did not differ from the intact state, but was significantly less than after the combined method. Both the fibula-based and combined posterolateral reconstruction techniques are equally effective in restoring stability following the simulated injury.
We examined cultured osteoblasts derived from paired samples from the greater tuberosity and acromion from eight patients with large chronic tears of the rotator cuff. We found that osteoblasts from the tuberosity had no apparent response to mechanical stimulation, whereas those derived from the acromion showed an increase in alkaline phosphatase activity and nitric oxide release which is normally a response of bone cells to mechanical strain. By contrast, we found that cells from both regions were able to respond to dexamethasone, a well-established promoter of osteoblastic differentiation, with the expected increase in alkaline phosphatase activity. Our findings indicate that the failure of repair of the rotator cuff may be due, at least in part, to a compromised capacity for mechanoadaptation within the greater tuberosity. It remains to be seen whether this apparent decrease in the sensitivity of bone cells to mechanical stimulation is the specific consequence of the reduced load-bearing history of the greater tuberosity in these patients.
The weight-bearing status of articular cartilage has been shown to affect its biochemical composition. We have investigated the topographical variation of sulphated glycosaminoglycan (GAG) relative to the DNA content of the chondrocyte in human distal femoral articular cartilage. Paired specimens of distal femoral articular cartilage, from weight-bearing and non-weight-bearing regions, were obtained from 13 patients undergoing above-knee amputation. After papain enzyme digestion, spectrophotometric GAG and fluorometric DNA assays assessed the biochemical composition of the samples. The results were analysed using a paired Although there were no significant differences in cell density between the regions, the weight-bearing areas showed a significantly higher concentration of GAG relative to DNA when compared with non-weight-bearing areas (p = 0.02). We conclude that chondrocytes are sensitive to their mechanical environment, and that local loading conditions influence the metabolism of the cells and hence the biochemical structure of the tissue.
