| Pedicle of vertebral arch is the most powerful structure of the rear vertebral body. Through the pedicle of vertebral arch, we can get the three-column immobilization. Having been used over ten years in our country, transpedicular fixation has a reliable outcome, but there were some complications. The breakage and loosing of screws were not neglected indeed. Almost every spinal surgery doctor have met problems like this. To investigate the causes of breakage, bending and loosening of pedicle screw systems in fixation of fractures of the thoracic and lumbar spine, 25 cases(33 bodies of vertebra)of fractures of the thoracic and lumbar spine were studied.From February 1990 to March 2004, 867 cases of fractures of the thoracic and lumbar spine were treated in our hospital, 334 cases were treated with pedicle screws. The breaking, bending and loosing were found in 25 cases (33 bodies of vertebra). This group cases were treated with route of retreat open reduction and pedicle screws in fixation of fractures of the thoracic and lumbar spine. In these cases, the breakage, bending and loosing were founded when the screws were removed, the others were found by taking X rays before operation. The screws were removed from three months to two years after operation, average fifteen months. Before the screws were removed, most patients with breakage or loosing of pedicle screws feel pain or malaise in lumbar part. The breakage part of screws are most on the cross point between pedicle of vertebral arch and screws, the point between thick and thin below the nut or the radical part in the screw thread. One of the break rod part occurred in the upper level 1/4 of the left cross bar and another in the collar. The reasons that the breakage, bending or loosing of pedicle screws were as follows:1. Overloading of the pedicle screw. We can get a satisfactory effect on fixation or restoration when the fractures of the thoracic and lumbar spine were treated with pedicle screws. The pieces of fracture may be restored wholly or partially through over-extension of spine or propped open by instrument, this can release the compression of spinal cord or nerves. But when there are no enough hold power of bone to the pedicle screws or overloading of the implant, the loosing or escaping of pedicle screws appeared. This may lead to the invalid fixation or pseudoarticulation formation. The restoration role of pedicle screws is getted through utilizing the dragging effect of anterior longitudinal ligament, the posterior longitudinal ligament and fibrous rings of intervertebral disc. This can restore the fracture pieces of anterior border of vertebra or protruded to the vertebral canal, replace the sinking vertebral body, restore the height and form of vertebra. At this time, the maintenance of restoring certebral body can be getted by the propping open role of pedicular screws. Because the anterior longitudinal ligament and the anterior fibrous rings of disc are stressful, the interspace of intervertebral are wide, so the force conduction on the spinal column are passing from the superior vertebral body to the inferior through the pedicular screws, but not through the trouble vertebra, the force loaded wholly on the pedicular screws, this can make the screws overloaded. At the same time, although the vertebral body form were restored, the compressed cancellous bone were not restored, and this may contribute to intervertebral narrow and hunchback afterward. 2. The loss of the intravertebral disc heights. In this group, the intervertebral narrow or retrograde disc between wounded and superior vertebral body were found more or less in bursting fracture patients. If the intervertebral disc was not wounded, this mean the injury just take place on the vertebral body, the form of the vertebral body can be restored wholly by posterior traction. The intervertebral disc after healing can maintain the normal function of weight loading. Height loss of intervertebral disc may lead to the narrowing of intervertebra...
|
PDF Full Text Request