Russel C. Huang

Measurement error of lumbar total disc replacement range of motion.

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.

Lumbar Total Disc Replacement: Seven to Eleven-year Follow-up

BACKGROUND Symptomatic lumbar degenerative disc disease is a challenging entity to treat. The results of arthrodesis may be compromised in the short term by pseudarthrosis and in the long term by pain at the iliac-crest donor site and by junctional degeneration. Total disc replacement has the potential to provide long-lasting relief to these patients. The purpose of this study was to present the clinical and radiographic results assessed seven to eleven years following a Prodisc total lumbar disc replacement. METHODS Sixty-four patients had single or multiple-level implantation of a total lumbar disc replacement between 1990 and 1993. The mean duration of follow-up was 8.7 years. Clinical results were evaluated by assessing preoperative and postoperative lumbar pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Preoperative and postoperative radiographs were evaluated as well. Subgroup analysis was performed to determine if gender, an age of less than forty-five years, previous surgery, or multilevel surgery had an effect on outcome. RESULTS At an average of 8.7 years postoperatively, there were significant improvements in the back-pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Thirty-three of the fifty-five patients with sufficient follow-up had an excellent result, eight had a good result, and fourteen had a poor result. Neither gender nor multilevel surgery affected outcome. An age of less than forty-five years and prior lumbar surgery had small but significant negative effects on outcome. Radiographs did not demonstrate loosening, migration, or mechanical failure in any patient. Five patients had approach-related complications. CONCLUSIONS The Prodisc lumbar total disc replacement appears to be effective and safe for the treatment of symptomatic degenerative disc disease. Gender and multilevel surgery did not affect the outcomes, whereas prior lumbar surgery or an age of less than forty-five years was associated with slightly worse outcomes. Longer follow-up of this cohort of patients and randomized trials comparing disc replacement with arthrodesis are needed.

Long-term flexion-extension range of motion of the prodisc total disc replacement.

The rationale for total disc replacement is avoidance of the junctional degeneration seen after arthrodesis by preservation of segmental motion. To justify the use of disc prostheses, it is essential to document maintained range of motion (ROM) and sagittal alignment at long-term follow-up. This is a retrospective radiographic study of 42 patients who had placement of 58 first-generation Prodisc prostheses at a mean follow-up of 8.7 years. Flexion-extension ROM was measured by Cobbs method. Junctional levels were evaluated for junctional degeneration. Pre- and postoperative global and segmental lordosis were measured. Prognostic patient factors predicting ROM of <2° were evaluated. We observed ROM of at least 2° in 66% of Prodisc prostheses at 8.7-year follow-up, although ROM was less than that reported in asymptomatic normal individuals. Mean ROM for disc prostheses with motion was 7.5° at L3–L4, 6.2° at L4–L5, and 4.1° at L5–S1. Mean ROM for all prostheses was 3.8°. The incidence of radiographic junctional degeneration was 24%, although no patients required surgery for symptomatic junctional degeneration. Mean ROM of prostheses below a degenerated junctional disc was 1.6° compared with 4.7° below a normal junctional disc (P < 0.035). Females were 3.5 times more likely to have ROM of <2°. This is the longest published follow-up study of a lumbar disc replacement. The data show that ROM is preserved at long-term follow-up in the majority of patients. Global and segmental sagittal alignment improve after surgery. Furthermore, there is an association between ROM of disc prostheses and the development of junctional degeneration.

Functional and Radiographic Outcome of Thoracolumbar and Lumbar Burst Fractures Managed by Closed Orthopaedic Reduction and Casting

Study Design. Retrospective review. Objectives. To determine clinical and radiographic outcomes of thoracolumbar and lumbar burst fractures without neurologic injury treated by closed reduction and casting. Patient factors associated with poor outcome are identified. Summary of Background Data. The results of ambulatory bracing, surgery, and prolonged recumbency for burst fractures have been reported. There are no reports of results of closed reduction and casting. Methods. Retrospective review of 41 neurologically intact patients with thoracolumbar and lumbar burst fractures was performed. Four patients with neurologic injury who refused surgery were included, for a total of 45 patients. All patients had closed reduction and casting. Functional, pain, and employment status were assessed using the Denis system. Neurologic function was graded using the Frankel scale. Radiographic evaluation of vertebral kyphosis, regional kyphosis, anterior body compression, and sagittal index were performed at time of injury, postreduction, 4 months, and final follow-up. Results. Sixty-four percent of patients had minimal or no pain. Eight percent had constant, severe pain. At time of injury, 71% of patients were employed. At 8-month follow-up, 58% of patients were employed. Closed reduction resulted in significant correction of vertebral wedging from a mean of 15° to 5°. Deformity tended to recur by 4 months, but the degree of residual deformity appears to be less than that reported in other series. No complications resulted from the fracture reduction procedure. Conclusions. Closed reduction and casting of thoracolumbar and lumbar burst fractures is a safe treatment method that yields acceptable functional and radiographic results.

Correlation between range of motion and outcome after lumbar total disc replacement : 8.6-year follow-up

Study Design. Retrospective radiographic and chart review. Objective. To examine the relationship between lumbar total disc replacement (TDR) range of motion (ROM) and clinical outcome at 8.6-year follow-up. Summary of Background Data. There are no studies on the relationship between TDR motion and clinical outcomes. Methods. We reviewed 38 patients who underwent 1 or 2-level TDR implantation with 51 TDR. Flexion-extension ROM was measured on lateral radiographs. Clinical outcomes were measured at 8.6 years by modified Stauffer-Coventry scores, Oswestry Disability Questionnaires (ODQ), and subjective ratings of back pain, leg pain, and disability. Spearman rank correlation coefficient was used to determine if ROM was correlated with clinical outcome. Patients were divided into 2 groups by motion (≤5° and >5°). Statistical differences in outcome were sought. Results. Spearman rank correlation coefficient revealed weak-to-moderate but statistically significant associations between ROM and outcome for postoperative back pain (r = −0.35, P = 0.034), ODQ (r = −0.33, P = 0.046), and modified Stauffer-Coventry scores (r = 0.42, P = 0.0095). Patients with motion of >5° had superior outcomes in ODQ (mean difference 12.6 points, P = 0.026) and Stauffer-Coventry scores (mean difference 2.2 points, P = 0.015). Conclusions. The radiographic ROM at 8.6-year follow-up was positively correlated with several outcomes measures. Patients with motion >5° had clinically modest but statistically better outcomes in ODQ and modifiedStauffer-Coventry scores. Longer follow-ups will be necessary to measure fully the impact of TDR ROM on outcome.

The prevalence of contraindications to total disc replacement in a cohort of lumbar surgical patients

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 author’s (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, 0–5). 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.

The implications of constraint in Lumbar total disc replacement

Lumbar total disc replacement (TDR) is an evolving technique that has the potential to replace arthrodesis as the gold standard surgical treatment of degenerative disc disease. The interaction between host anatomy and physiology and the biomechanical properties of TDR implants will determine the quality of long-term clinical results. However, there is scant literature addressing this subject. The purpose of this article is to discuss the implications of biomechanical constraint in TDR. Based upon available data for normal motion segments and the design of two TDRs currently in clinical trials, unconstrained designs appear to have a kinematic advantage. They are more likely to provide a physiologic mobile instantaneous axis of rotation (IAR), which may explain why they display greater range of motion in vivo. Their lack of constraint may prevent excessive facet joint or capsuloligamentous loads in the extremes of flexion and extension. Furthermore, since the IAR is mobile, they may be less sensitive to small errors in implant placement. On the other hand, constrained devices appear to have an advantage in protection of the posterior elements from shear loading. Spinal shear loads of considerable magnitude occur during activities of daily living. Whether the transference of stresses to the implant and implant-bone interface is clinically significant is unknown. Although this article focuses on two specific TDR designs, future designs will need to account for the same kinematic and loading concerns regarding constraint. We hope this discussion will assist clinicians and researchers in the design, selection, and clinical comparison of present and future TDR implants.

Lumbar Total Disc Replacement

BACKGROUND: Symptomatic lumbar degenerative disc disease is a challenging entity to treat. The results of arthrodesis may be compromised in the short term by pseudarthrosis and in the long term by pain at the iliac-crest donor site and by junctional degeneration. Total disc replacement has the potential to provide long-lasting relief to these patients. The purpose of this study was to present the clinical and radiographic results assessed seven to eleven years following a Prodisc total lumbar disc replacement. METHODS: Sixty-four patients had single or multiple-level implantation of a total lumbar disc replacement between 1990 and 1993. The mean duration of follow-up was 8.7 years. Clinical results were evaluated by assessing preoperative and postoperative lumbar pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Preoperative and post-operative radiographs were evaluated by assessing preoperative and postoperative lumbar pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Preoperative and post-operative radiographs were evaluated as well. Subgroup analysis was performed to determine if gender, an age of less than forty-five years, previous surgery, or multilevel surgery had an effect on outcome. RESULTS: At an average of 8.7 years post-operatively, there were significant improvements in the backpain, radiculopathy, disability, and modified Stauffer-Coventry scores. Thirty-three of the fifty-five patients with sufficient follow-up had an excellent result, eight had a good result, and fourteen had a poor result. Neither gender nor multilevel surgery affected outcome. An age of less than forty-five years and prior lumbar surgery had small but significant negative effects on outcome. Radiographs did not demonstrate loosening, migration, or mechanical failure in any patient. Five patients had approach-related complications. CONCLUSIONS: The Prodisc lumbar total disc replacement appears to be effective and safe for the treatment of symptomatic degenerative disc disease. Gender and multilevel surgery did not affect the outcomes, whereas prior lumbar surgery or an age of less than forty-five years was associated with slightly worse outcomes. Longer follow-up of this cohort of patients and randomized trials comparing disc replacement with arthrodesis are needed.

Three-level anterior cervical discectomy and fusion with plate fixation: radiographic and clinical results.

Study Design. Retrospective review of patients with cervical spondylosis treated with 3-level anterior cervical discectomy and fusion with plate fixation. Objective. To assess the radiographic and clinical outcome of 3-level instrumented anterior cervical discectomy. Summary of Background Data. Three-level cervical discectomy without plate fixation has shown high rates of pseudarthrosis and poor outcomes. The addition of internal fixation may improve these parameters. Methods. A total of 46 patients were observed for an average of 17.6 months (range, 6–51 months). All had 3-level anterior cervical discectomy and fusion with tricortical iliac crest autograft (4 cases), fibular ring allograft (38 cases), or titanium cage (4 cases). Allografts and cages were filled with iliac crest autograft. All patients had semirigid plating. Clinical and radiographic follow-up data were obtained. Clinical outcomes were measured as described by Robinson and with the Nurick scale. Results. Forty-four patients achieved solid fusion. Two patients had additional surgery for junctional disease, and in 1 of them pseudarthrosis repair was also performed. One asymptomatic pseudarthrosis was noted. With a successful result defined as an excellent or good outcome accompanied by significant pain relief, 38 patients had a successful result (83%). Radiographic adjacent level disease was diagnosed in 11 patients after surgery and was symptomatic in 5. Conclusion. Three-level anterior cervical discectomy with plate fixation has a high rate of fusion, a low complication rate, and acceptable outcome in the treatment of multilevel cervical spondylosis.

Alendronate inhibits spine fusion in a rat model.

Study Design. A posterolateral lumbar fusion model in rats. Objective. To study the effects of alendronate on posterolateral lumbar fusion in rats. Summary of Background Data. To our knowledge, there are no studies that show a significant inhibition of manual palpation-assessed spine fusion by alendronate. Methods. A total of 75 Sprague-Dawley rats underwent intertransverse fusion with 7-tailbone autograft at L4–L5. Animals received saline (control), alendronate equivalent to human dose (dose1, 5 &mgr;g/kg/day), or 10 times the human dose (dose10, 50 &mgr;g/kg/day) via subcutaneous osmotic pumps starting the day of surgery. Eight weeks after surgery, animals were euthanized, and fusion was assessed by manual palpation. Radiographic area and optical density of fusion masses were calculated. Histomorphometry was used to assess the percentage area of fusion masses occupied by bone or marrow tissues. Results. Manual palpation fusion rates were lower in alendronate groups (50% and 40%, respectively) than in the control group (95%, P = 0.002). Interobserver and intraobserver kappa values were high (0.97−1.00). There were dose-dependent and statistically significant (P < 0.001) increases in fusion mass area and optical density with increasing alendronate dose. Fusion masses in dose10 animals had significantly higher percent area of bone tissue (P = 0.01) and lower percent area of marrow elements (P < 0.001) when compared to control animals. Conclusions. Alendronate inhibits spine fusion in rats. Fusion masses in alendronate-treated animals appeared radiographically larger and denser than those in control animals despite lower fusion rates. Quantitative histomorphometry confirmed that alendronate inhibited bone graft resorption and incorporation. We recommend that patients undergoing spine arthrodesis should not take alendronate until fusion is achieved.