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STUDY DESIGN.: A retrospective review of lumbar total disc replacement (TDR) radiographs.OBJECTIVE.: To determine the error and variability in measuring TDR radiographic range of motion (ROM).SUMMARY OF BACKGROUND DATA.: Motion preservation is the driving force behind lumbar TDR technology. In the recent literature, sagittal radiographic TDR ROM as low as 2° has been reported. In these studies, ROM was determined by using the Cobb method to measure TDR sagittal alignment angles in flexion-extension lateral radiographs. However, previous studies in the spinal deformity literature have shown that the Cobb method is very susceptible to measurement error.METHODS.: There were 5 observers, including 2 attending orthopedic spine surgeons, 1 spine fellow, 1 fifth-year resident, and 1 fourth-year resident, who measured the ROM of 50 ProDisc II (Synthes Spine Solutions, New York, NY) TDRs on standard flexion-extension lumbar spine radiograph sets. Repeated measurements were made on 2 occasions using the Cobb method. Measurement variability was calculated using 3 statistical methods.RESULTS.: The 3 statistical methods resulted in extremely similar values for TDR ROM observer variability. Overall, the intraobserver variability of TDR ROM measurement was ±4.6°, and interobserver variability was ±5.2°.CONCLUSIONS.: To be 95% certain that an implanted TDR prosthesis has any sagittal motion, a ROM of at least 4.6° must be observed, which is the upper limit of intraobserver measurement variability for a TDR with a true ROM of 0°. To be 95% certain that a change in TDR ROM has occurred between 2 measurements by the same observer, a change in ROM of at least 9.6° must be observed (the entire range of ±4.6° intraobserver variability). ROM measurement variability should be considered when evaluating the success or failure of motion preservation in lumbar TDR. [ABSTRACT FROM AUTHOR]

STUDY DESIGN.: A retrospective chart and radiographic review of 122 pedicle screws placed with computerized stereotactic image-guidance into posterolateral fusion masses.OBJECTIVES.: To determine the accuracy rate of computerized stereotactic image-guided pedicle screw placement in previously fused lumbar spines.SUMMARY OF BACKGROUND DATA.: Placement of pedicle screws into a previously fused lumbar spine is challenging. The normal anatomic landmarks used to determine the starting point and trajectory of the screws have either been removed or are obscured by the fusion mass. Computerized frameless stereotaxis provides precise intraoperative real time multiplanar image-guidance and may be valuable in this clinical situation.METHODS.: Computerized frameless stereotactic image-guidance was used to place pedicle screws into 78 consecutive patients with prior lumbar spine fusions. Postoperative computed tomography was available on 35 patients (231 screws). One hundred and twenty-two screws were placed into fusion masses. Pedicle cortical perforations were characterized by the direction (medial, inferior, lateral, or superior) and magnitude (in 2-mm increments) of perforation.RESULTS.: Five (4.1%) of the 122 pedicle screws placed into previously fused levels were found to have unintentional cortical violations. There were 1 superior (<2 mm), 1 medial (<2 mm), and 3 lateral perforations (<2, 4, and 6 mm). None of these perforations led to clinically apparent radicular pain or weakness. No pedicle screws required revision for malpositioning.CONCLUSIONS.: The accuracy rate of stereotactic image-guided pedicle screw placement into previously fused lumbar spine levels is 96%. Computerized stereotactic image-guidance may have particular application in situations in which posterior element anatomy is altered, such as in the presence of a prior fusion mass. [ABSTRACT FROM AUTHOR]

STUDY DESIGN.: This is a retrospective review of the epidemiology of contraindications to lumbar total disc replacement (TDR). OBJECTIVE.: To define the prevalence of contraindications to lumbar total disc replacement in a cohort of patients undergoing lumbar surgery in the senior authors (F.P.C.) practice. SUMMARY OF BACKGROUND DATA.: No published reports have documented the prevalence of contraindications to lumbar total disc replacement. METHODS.: We performed a retrospective review of 100 consecutive patients who had lumbar surgery by one surgeon between September and December 2002. Procedures performed and contraindications to TDR were recorded. Contraindications to TDR included central or lateral recess stenosis, facet arthrosis, spondylolysis or spondylolisthesis, herniated nucleus pulposus with radiculopathy, scoliosis, osteoporosis, and postsurgical pseudarthrosis or deficiency of posterior elements. Patients were divided into fusion and nonfusion groups. The percentage of patients without contraindications to TDR was calculated. RESULTS.: Of 100 patients, 56 had fusions and 44 had nonfusion surgery. In the fusion group, 56 of 56 patients had contraindications to TDR. In the nonfusion group, 11% (5 of 44) were candidates for TDR. Overall, 5% of patients in this series were candidates for TDR. The average number of contraindications to TDR was 2.48 (range, 05). CONCLUSIONS.: Predictions that TDR will replace fusion are premature. A small percentage (5%) of the patients currently indicated for lumbar surgery at our institution have no contraindications to TDR. Future growth in TDR implantation will result from the indication of patients for surgery who would not be indicated today or from the elimination of current contraindications. [ABSTRACT FROM AUTHOR]