Mechanical performance of the Dick internal fixator: a clinical study of 75 patients

Summary

A consecutive series of 75 patients with fractures of the thoracolumbar spine, stabilized with the Dick internal fixator, was studied retrospectively. Posttraumatic kyphosis was measured on the preoperative lateral radiograph by the Cobb angle and the wedge angle and the results were compared with angles measured on the radiographs after instrumentation and after removal of the implants. The presence and number of broken Schanz screws was noted. In the whole group, an average correction of kyphosis of 15.5° was obtained, but 7.6° was lost again at follow-up. In comparing the kyphotic angle with the wedge angle, we found that this loss was almost exclusively situated in the upper intervertebral disc space. In the group of patients with transpedicular intravertebral bone grafting, the relative loss of correction in the wedge angle was smaller than in the group without bone grafting, while the relative loss of correction of the kyphotic angle was similar. Schanz screw breakage was present in 13.3% of patients, occurring in 4.6% of inserted screws. In the group of patients with broken Schanz screws, the loss of correction in the wedge angle was somewhat higher, but not markedly different from that of the patient group without breakage of screws. Risk of screw breakage was enhanced by laminectomy and reduced by transpedicular bone grafting. Screw breakage or important loss of correction did not influence the neurological outcome of the patients. The Dick internal fixator is a very reliable implant, even in patients with highly unstable fractures. To minimize the risk of screw breakage, transpedicular bone grafting is recommended; laminectomy, however, should only be done under certain strictly defined conditions.