Which disc as visualized by magnetic resonance imaging is actually a source of pain? A correlation between magnetic resonance imaging and discography.

Sixty-three discs in 25 consecutive patients with nonradicular discogenic pain were studied with magnetic resonance imaging and lumbar discography. Sagittal T2 magnetic resonance imaging sequences were blindly classified according to the nuclear signal intensity and to the status of the posterior anulus. A positive discogram had to include abnormal morphology and a provocative pain response of significant intensity and familiar quality. Specific magnetic resonance imaging patterns with a high probability for positive and negative discograms are identified. Also identified are magnetic resonance imaging patterns with intermediate probability, ie, ones that should not be presumed either asymptomatic or symptomatic. In many cases, magnetic resonance imaging could not reliably predict or replace discography.

Is pathology examination of disc specimens necessary after routine anterior cervical discectomy and fusion?

STUDY DESIGN: A retrospective chart review was performed from 1990-1994. OBJECTIVES: To evaluate the outcome of pathologic examination of cervical disc specimens submitted after anterior cervical discectomy. SUMMARY OF BACKGROUND DATA: This study is the first to review the outcome of pathologic examination of disc specimens after anterior cervical discectomy and fusion. METHODS: Charts were reviewed based on the procedure code of anterior cervical fusion and the main diagnoses of cervical disc and spondylosis. The following data were recorded for each patient: symptoms, examination, diagnostic studies, operative procedure, operative findings, and pathology report. Statistical analysis was performed. RESULTS: Five hundred six disc levels in 394 patients were reviewed. All patients had symptoms and examination results consistent with cervical radiculopathy. All patients had cervical radiographs and some combination of myelography, computed tomography, or magnetic resonance imaging. Findings at the time of surgery included the presence of either a herniated disc or degenerative spondylitic changes. The pathologic examination results of all specimens reported fibrocartilaginous tissue consistent with disc material with the presence of degenerative changes. No infectious, benign, or malignant process was identified at the time of surgery or on gross and histologic examination of any of the disc specimens. Using confidence intervals (95%) for exact proportions and given 500 negatives, the chance the next occurrence would be positive would be 0.0060 or 0.60% or six of 1000. CONCLUSIONS: This study shows that if the symptoms, physical examination, radiographic diagnostic studies, and surgical findings are consistent with those of cervical disc herniation of spondylosis, the chance of an unexpected, clinically important pathologic finding within the disc specimen is extremely small. The time and expense involved in routine pathologic examination of cervical disc specimens can be avoided.

Nicotine on the revascularization of bone graft. An experimental study in rabbits.

STUDY DESIGN: In 24 rabbits, the authors transplanted autologous cancellous bone to the anterior chamber of the eye. Half of the rabbits received nicotine and half received placebo (albumin) from mini-osmotic pumps that were implanted subcutaneously. Revascularization of the bone graft was evaluated postoperatively using ophthalmology slit-lamp and fluorescein angiography, and after sacrifice using microvascular silicone injection and histology. OBJECTIVES: The hypothesis that nicotine inhibits the revascularization of bone graft because of its pharmacologic action on the microvasculature was tested. SUMMARY OF BACKGROUND DATA: Pseudoarthrosis after spinal fusion occurs more frequently in smokers as compared with nonsmokers. METHODS: Observations of the bone graft were made regarding the time after implantation when vessels within the graft were noted and the pattern of these vessels. Revascularization of the graft was graded based on the observed percent area of fluorescence after injection of fluorescein. Serum levels of nicotine were measured weekly. Colored silicone was injected at sacrifice to fix the vasculature of the bone graft. Histologic analysis of undecalcified sections was performed. RESULTS: Nicotine, as compared with placebo, was associated with delayed revascularization within the graft, a smaller percent area of revascularization, and a larger number of grafts showing necrosis. CONCLUSIONS: Nicotine inhibits, but does not prevent, the revascularization of cancellous bone grafts. Inhibition of early revascularization by nicotine is proposed as the pathophysiologic mechanism by which smoking may adversely affect the healing of spinal fusions.

Correlations between screw hole preparation, torque of insertion, and pullout strength for spinal screws.

The bone-screw interface is critical in the use of spinal instrumentation. The purpose of these experiments described here was twofold. First, to determine whether a correlation existed between torque generated during screw insertion and the pullout strength. Second, to determine how differing surgical methods of screw hole preparation influenced torque of insertion and screw pullout strength. A series of experiments were carried out in which screws were inserted into synthetic bone (experiment 1) and into calf vertebrae (experiment 2). The method of screw hole preparation (i.e., diameter of entrance hole and pilot hole) was varied while the resulting torque of insertion and the pullout strength of the screw was measured in each case. A torque screwdriver was used to measure the torque of insertion of the screws. Screw pullout strength was measured using a materials testing machine. Two important results emerged from these experiments. First, a higher torque of insertion correlated with a higher screw pullout force. This correlation may be useful intraoperatively in evaluating fixation. Second, torque of insertion and pullout force were more influenced by cortex over-drill diameter than pilot hole diameter. These experiments show the importance of the dorsal cortex in pedicle screw fixation.