A kinematic study of the cervical spine before and after segmental arthrodesis.

STUDY DESIGN: The acute kinematic consequence of segmental arthrodesis in the cervical spine on the remaining open motion segments was studied in a cadaveric model. OBJECTIVES: To evaluate the distribution of motion across unfused cervical motion segments after a segmental arthrodesis. The applied load was determined as a function of arthrodesis length and level by using a fixed range of motion for the cervical spine (C2-T1). SUMMARY OF BACKGROUND DATA: An increased incidence of degenerative disease may exist at the levels immediately adjacent to a cervical arthrodesis as a result of alteration in biomechanical behavior at these levels. METHODS: One-, two-, and three-level fusions were simulated in multilevel ligamentous human cervical spines. Specimens were tested nondestructively through a 30 degrees range of sagittal plane rotation. Motion was recorded using three-dimensional stereophotogrammetry. Sagittal plane rotation of each motion segment in the fusion models was compared with the corresponding rotation in the unfused specimen. RESULTS: In the C2-C4 fusion, the increase in motion at C5-C6 was statistically less (P < 0.05) than the increase at C7-T1. In the C2-C5 fusion, the increase in motion at C5-C6 was statistically less (P < 0.05) than the increases at C6-C7 and C7-T1. For each of the five other fusion types tested, no statistical differences existed between the increases in sagittal rotation at any of the open motion segments. The bending moment necessary to produce 30 degrees of sagittal rotation increased nonlinearly as the number of motion segments fused increased. CONCLUSIONS: Under what was considered a realistic loading paradigm, sagittal plane rotation was not increased disproportionately at the motion segments immediately adjacent to a segmental arthrodesis in the cervical spine. The nonlinear rise in applied bending moment to achieve constant displacement was characteristic of the behavior of the ligaments and intervertebral discs throughout the spine as they underwent increasing deformation.

Anterior stabilization of thoracolumbar burst fractures using the Kaneda device: a preliminary report.

Anterior decompression and fusion is a valuable technique in the treatment of thoracolumbar burst fractures. Anterior instrumentation has evolved to correct deformity and stabilize the spinal segments during decompression and bone grafting as a single-stage procedure. One anterior device developed by Kaneda has been used in our institution since 1989. This study is an initial review of our experience with this instrumentation. Anterior decompression and fusion augmented with the Kaneda device was performed in 20 patients with thoracolumbar burst fractures. Timing of surgery was early (< 15 days) in 13 patients, intermediate (16 to 120 days) in 2, and delayed (> 121 days) in 5. Sixteen patients were neurologically intact (Eismont grade D), 3 with distal weakness (Eismont grade B or C) and 1 with complete paraplegia (Eismont grade A). All patients with deficits recovered one Eismont grade after anterior decompression and fusion. Complications included pulmonary problems in 2 patients, a thoracic duct laceration requiring ligation, and a sympathectomy effect of the lower extremity. One patient had a pulmonary embolus and developed a hematoma at the graft harvest site while on anticoagulants with resultant meralgia paresthetica. There have been three screw failures and one definite pseudarthrosis. Anterior decompression and fusion supplemented by the Kaneda device was performed on 20 patients with thoracolumbar burst fractures. The average correction of kyphosis was approximately 50% acutely, with loss of approximately 50% of correction at follow up. In some patients, coronal plane deformity was created by the device. No effect on neurologic recovery could be shown with this small series. Perioperative complication rate was 30%, and 1 patient developed pseudarthrosis.

Pedicular transvertebral screw fixation of the lumbosacral spine in spondylolisthesis. A new technique for stabilization.

Controversy exists about which method is most appropriate for treating moderate- to high-grade spondylolisthesis and symptomatic pseudarthrosis. The authors report preliminary results of pedicular transvertebral screw fixation, a new technique for stabilizing the lumbosacral junction in moderate- to high-grade spondylolisthesis. Using this technique, fusion was successful in three patients, two with an established pseudarthrosis. Pedicular transvertebral screw fixation provides immediate three-column stabilization of the lumbosacral junction. The technique is safe, effective, and employs instrumentation common to spine surgery. Its use in high-grade slips makes the technique more simple to perform than other methods of lumbosacral stabilization.

Anterior cervical corpectomy for the treatment of complex cervical lesions.

Instability and stenosis of the cervical spine have been treated by posterior decompression and anterior decompression with fusion. In this study the authors evaluate the results obtained in 31 patients who underwent anterior cervical corpectomy for compressive or unstable lesions of the cervical spine. Operative level, preoperative and postoperative symptoms and physical findings were assessed. Twenty-seven patients had preoperative neurologic symptoms and signs, including alterations in sensation, motor findings and reflexes. The average follow-up was 12 months, average number of disc spaces excised was 2.5 and average number of vertebral bodies excised was 1.6. With respect to relief of pain, results were good or excellent in 27 patients. All patients but one had union of the bone graft. No neurologic deterioration occurred. The authors believe that patients with compressive lesions of the cervical spine can benefit from anterior cervical corpectomy with fusion and that complications are minimal.

Drill sleeve for pedicle screw fixation.

Pedicle screw fixation is a popular method of fixation of the spine. Placement of screw and prevention of injury are surgeon dependent. We describe an easily made drill sleeve and depth gauge to assist in the preparation of the vertebral pedicle for pedicle screw application. Use of this device will help prevent soft tissue injury and overpenetration of the drill in the vertebral body.

Magnetic resonance imaging of posttraumatic spinal ligament injury.

We evaluated the role of magnetic resonance imaging (MRI) in the detection of ligament injury in 37 patients after acute traumatic spinal injury. Thirty-five patients had fractures, one had neurologic deficit with normal x-rays, and one had evidence of cervical instability on flexion/extension plain films. MRI examinations were performed acutely (average 10.8 d after injury) using T1- and T2-weighted multiplanar imaging. Two radiologists blindly evaluated all MRI examinations. Subsequently, 35 plain films, 16 tomograms, and 30 computed tomography (CT) scans were also evaluated. Nineteen patients were considered to have torn posterior ligaments on the basis of their clinical, radiographic and surgical findings. MRI detected ligament damage in 17. All patients considered to have intact posterior ligament complexes clinically and radiographically had no evidence of ligament damage on MRI. T2-weighted sequences were essential for detection of ligament injury. We conclude that MRI is an accurate method for assessment of the integrity of spinal ligaments after acute trauma.

Lumbar spine: postoperative MR imaging with Gd-DTPA.

Thirty patients with failed back surgery syndrome were studied to evaluate the effectiveness of magnetic resonance (MR) imaging with gadolinium-diethylenetriaminepentaacetic acid/dimeglumine (Gd-DTPA) in differentiating postoperative epidural fibrosis (scar) from recurrent disk herniation. Pre- and postcontrast MR images were interpreted without access to other diagnostic, surgical, or pathologic findings. Seventeen patients had surgical and pathologic correlation of the MR findings at 19 disk levels. The precontrast studies had a sensitivity, specificity, and accuracy of 100%, 71%, and 89%, respectively. The enhanced MR studies correctly depicted the character of abnormal epidural soft tissue in 17 patients at all 19 levels. Scar showed heterogeneous enhancement on the early T1-weighted spin-echo images obtained within 10 minutes after contrast material administration. Herniated disk did not show significant enhancement on the early studies but showed variable degrees of enhancement on delayed images in nine of 12 cases. Other criteria were found to be less useful than the pattern of enhancement. Results indicate that precontrast and early postcontrast T1-weighted spin-echo studies are highly accurate in separating epidural fibrosis from herniated disk.

Experimental vascularized bone grafts: histopathologic correlations with postoperative bone scan: the risk of false-positive results.

A positive bone scan in an experimental model of bilateral ulna diaphyseal bone grafts demonstrated early bone repair in both vascularized and nonvascularized orthotopic ulna autografts. A positive bone scan did not correlate with the perfusion of the vascularized and nonvascularized grafts as measured by microangiograms done 1 week postoperatively. In this model, if the bone scan is intended to monitor the circulatory status and viability of the bone graft, it must be done earlier than 1 week postoperative prior to the onset of creeping repair in both vascularized and nonvascular ulna autografts.

The posterior deltoid to triceps transfer: a clinical and biomechanical assessment.

Transfer of the posterior deltoid muscle to the triceps insertion for elbow extension provides improved function in patients with C5 and C6 level tetraplegia. We have modified the surgical technique using the tibialis anterior tendon as a graft. The length-tension characteristics and available amplitude of the posterior deltoid muscle were determined with intraoperative electrical stimulation. The excursion of the posterior deltoid muscle was 7.31 cm with a standard deviation of 1.23 cm. Postoperative mean torque measurements of elbow extension power were 36.4 kg cm with a standard deviation of 15 kg cm. All patients had maximal strength between 90 degrees and 120 degrees of elbow flexion. Length-tension curves for the posterior deltoid muscle showed a large range of effective strength and helped confirm optimum tension of the posterior deltoid muscle and proper shoulder and elbow positions at surgery. Clinical results in 10 patients were excellent.

Segmental spinal instrumentation in idiopathic scoliosis. A preliminary report.

Eighty-six patients with idiopathic scoliosis who underwent a posterior spinal fusion using sublaminar segmental spinal instrumentation were analyzed retrospectively. There were two operative groups: group 1, 66 patients who had Harrington rod instrumentation and segmental wiring, and group 2, 20 patients who had Luque rod instrumentation. The clinical and radiographic data of the two groups were similar except for the passage of more sublaminar wires and increased intraoperative blood loss in group 2. Twenty intraoperative or postoperative complications occurred in 19 patients (22%) including 14 neurologic complications. Three patients (3%) had major spinal cord injuries, while 11 patients (13%) had transient sensory changes. There was no significant difference in the incidence of neurologic complications between group 1 or group 2. The remaining intraoperative complications were due either to anesthesia, positioning during surgery, or technique (dural tear). Late complications occurred in two patients in group 1 only: one each with rod breakage and hook displacement. Only one patient (1%) has required additional surgery. Our results indicate that although segmental instrumentation can be beneficial in idiopathic scoliosis, the incidence of complications, primarily neurologic, will be higher than expected. The major reason appears to be surgeon inexperience with passage of sublaminar wires. As experience increases, the incidence of complications declines and becomes comparable with conventional Harrington rod instrumentation alone.

Postoperative neurological deficits in segmental spinal instrumentation. A study using spinal cord monitoring.

We retrospectively analyzed the postoperative neurological complications in 137 patients who underwent a posterior spine fusion for scoliosis and had concomitant somatosensory cortical evoked-potential spinal-cord monitoring. The patients were divided into three specific operative groups: group 1, forty-nine patients who had a Harrington rod with segmental wiring (segmental spinal instrumentation); group 2, twenty patients who had Luque segmental spinal instrumentation; and group 3, sixty-eight patients who had a Harrington rod without segmental spinal instrumentation. There were neurological complications in twelve (17 per cent) of the sixty-nine patients in groups 1 and 2. Three patients (4 per cent) had a major injury to the spinal cord and nine patients (13 per cent) had only transient sensory changes. No difference was apparent between group 1 and group 2 in the degree of operative correction of curves or in the incidence of neurological complications. The one neurological complication (1.5 per cent) that occurred in the sixty-eight patients in group 3 was a Brown-Séquard syndrome. The factors related to increased risk for spinal cord injury in groups 1 and 2 included: (1) the passage of sublaminar wires in the thoracic and thoracolumbar spine, (2) intraoperative correction exceeding the preoperative bending correction, and (3) the surgeon's lack of adequate experience with the technique. With spinal cord monitoring we were able to predict the impending major neurological deficits, but the transient (sensory) changes that may be associated with segmental wiring were less reliably predicted.

The effect of redundancy and tension on microvascular vein grafts.

Variation in length and tension occurs with microvascular vein grafts in clinical practice. The length and tension of a vein-grafted segment was varied in 50 Sprague-Dawley rats. This enabled a full range of redundancy and tension across the 1 mm diameter vein grafts. The initial patency rate was 100%. Wounds were reexplored 2 weeks after operation. A linear increase in microaneurysm formation was found with increasing tension. There was a mild but not statistically significant observed effect on patency. Increasing tension in rat vein graft anastomosis has an adverse effect with an increased incidence of microaneurysm formation and should be avoided.

Patency of anastomosed arteries and veins subjected to reapplication of microvascular clamps.

One hundred and two rat femoral vessels, both vein and artery, were transected and repaired with a standard technique. After a 30-minute observation period, vessel clamps were reapplied in a standardized manner. The repairs were reexplored at 2 weeks. The results demonstrated no serious reduction in vessel patency in the first period or at the 2 week exploration. Reapplication of vessel clamps after an initial flow period post anastomosis does not have a significant effect on vessel patency.

Pre- and postnatal toxicity induced in guinea pigs by N-nitrosomethylurea.

Oral administration of N-nitrosomethylurea at maximally tolerated doses to guinea pigs on alternate days from days 34-58 of pregnancy induced prenatal toxicity, as evidenced by a high frequency of stillbirths and intrauterine growth retardation, and postnatal toxicity, as evidenced by stunting and progressive mortality. Similar administration of N-nitrosomethylurethane at maximally tolerated doses did not induce such toxic effects.