Long-term Outcomes of 2-Level Total Disc Replacement Using ProDisc-L: Nine- to 10-Year Follow-up.

STUDY DESIGN: A prospective clinical data analysis. OBJECTIVE: To determine the long-term clinical success of 2-level total disc replacement (TDR) in patients with degenerative disc disease. SUMMARY OF BACKGROUND DATA: Early successful clinical results of 2-level TDR have been reported. Few studies exist that have described this procedure's durability in the long term. METHODS: Fifteen patients underwent 2-level lumbar TDR with the ProDisc-L as part of a randomized trial, 13 of whom were available for follow-up. The patients were assessed preoperatively and at 2 years, 5 years, and more than 9 years postoperatively using visual Oswestry Disability Index. At the last follow-up visit, 2 additional questions were asked: satisfaction with surgery and willingness to undergo the same treatment. Finally, clinical success was assessed using a previously described definition. RESULTS: Mean follow-up time was 9.6 years (range, 9.2-10.3 yr). Postoperatively there was a significant improvement in Oswestry Disability Index score from baseline (70.0 vs. 15.7 at 2 yr, P = 0.002) that remained unchanged during the period of follow-up (19.8 at 5 yr, P = 0.003 and 12.9 at 9-10 yr, P = 0.002). Ninety-two percent of patients were "satisfied" or "somewhat satisfied" with treatment and the same number would undergo treatment again. Eighty-five percent of patients achieved clinical success. CONCLUSION: This prospective study demonstrates the durable clinical success of 2-level lumbar TDR as assessed at more than 9 years postoperatively. LEVEL OF EVIDENCE: 4.

Segmental contribution toward total cervical range of motion: a comparison of cervical disc arthroplasty and fusion.

STUDY DESIGN: Prospective radiographic evaluation of patients that underwent cervical total disc replacement (TDR-C) or anterior cervical discectomy and fusion (ACDF) for one-level cervical disc disease. OBJECTIVE: To evaluate the following: (1) total cervical range of motion (ROM) from C2 to C7, and (2) the relative contribution to total cervical ROM from the operative level and each adjacent level after one-level TDR-C or ACDF. SUMMARY OF BACKGROUND DATA: The development of symptomatic adjacent segment disease after ACDF has served as the impetus for the development of motion-preserving alternatives, most notably cervical disc arthroplasty. While previous reports have evaluated device-level and total cervical motion, no study has comprehensively quantified the relative contribution made from each of the adjacent levels to total cervical ROM in TDR-C and ACDF. METHODS: Radiographic review of 187 randomized patients from a multicenter, prospective, randomized trial comparing TDR-C with ACDF for one-level cervical disc disease. There were 93 TDR-C and 94 ACDF patients included. ROM measurements were performed independently using quantitative motion analysis, a custom digitized image stabilization software program, to evaluate total cervical ROM and relative contribution to total ROM from each level from C2 to C7 preoperatively and at 24 months. RESULTS: The most common operative level was C5/C6 (57%) followed by C6/C7 (34%). At 2 years, the TDR-C group underwent a statistically greater improvement in total cervical ROM (+5.9°) compared with ACDF (-0.8°, P = 0.001). In TDR-C, the relative contributions to total cervical ROM from the operative level and each caudal and cranial adjacent level were statistically equivalent from baseline to 24 months. In contrast, ACDF patients had significantly reduced contribution to total cervical ROM from the operative level (by 15%, P < 0.001), and significantly elevated contribution from the caudal adjacent level (by 5.9%, P < 0.001), first cranial adjacent level (by 3.3%, P < 0.001), second cranial adjacent level (by 5.3%, P < 0.001), and third cranial adjacent level (by 3.0%, P < 0.001). CONCLUSION: Compensation for the loss of motion at the operative level in ACDF is seen throughout the unfused cervical spine. Cervical disc arthroplasty, however, increases total cervical ROM compared with ACDF and maintains a physiologic distribution of ROM throughout the cervical spine at 2 years, potentially lowering the risk for adjacent segment breakdown.

Prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of the ProDisc-L total disc replacement compared with circumferential arthrodesis for the treatment of two-level lumbar degenerative disc disease: results at twenty-four months.

BACKGROUND: Disc replacement arthroplasty previously has been shown to be an effective alternative to spine fusion for the treatment of single-level lumbar degenerative disc disease. The purpose of the present study was to determine the twenty-four-month results of a clinical trial of the ProDisc-L total disc replacement as compared with spinal fusion for the treatment of degenerative disc disease at two contiguous vertebral levels from L3 to S1. METHODS: A total of 237 patients were treated in a randomized controlled trial designed as a non-inferiority study for regulatory application purposes. Blocked randomization was performed with use of a 2:1 ratio of total disc arthroplasty to circumferential arthrodesis. Evaluations, including patient self-assessments, physical and neurological examinations, and radiographic examinations, were performed preoperatively, six weeks postoperatively, and three, six, twelve, eighteen, and twenty-four months postoperatively. RESULTS: At twenty-four months, 58.8% (eighty-seven) of 148 patients in the total disc replacement group were classified as a statistical success, compared with 47.8% (thirty-two) of sixty-seven patients in the arthrodesis group; non-inferiority was demonstrated. The mean Oswestry Disability Index in both groups significantly improved from baseline (p < 0.0001); the mean percentage improvement for the total disc replacement group was significantly better than that for the arthrodesis group (p = 0.0282). An established clinical criterion for success, a ≥15-point improvement in the Oswestry Disability Index from baseline, occurred in 73.2% (109) of 149 patients in the total disc replacement group and 59.7% (thirty-seven) of sixty-two patients in the arthrodesis group. The Short Form-36 physical component scores were significantly better for the total disc replacement group as compared with the arthrodesis group (p = 0.0141 at twenty-four months). Visual analog scale scores for satisfaction significantly favored total disc replacement from three to twenty-four months. At twenty-four months, 78.2% (111) of 142 patients in the total disc replacement group and 62.1% (thirty-six) of fifty-eight patients in the arthrodesis group responded "yes" when asked if they would have the same surgery again. Lumbar spine range of motion on radiographs averaged 7.8° at the superior disc and 6.2° at the inferior disc in patients with total disc replacement. Reduction in narcotics usage significantly favored the total disc replacement group at twenty-four months after surgery (p = 0.0020). CONCLUSIONS: Despite the relatively short duration of follow-up and design limitations, the present study suggests that two-level lumbar disc arthroplasty is an alternative to and offers clinical advantages in terms of pain relief and functional recovery in comparison with arthrodesis. Longer-term follow-up is needed to determine the risks for implant wear and/or degenerative segment changes.

T1ρ magnetic resonance imaging and discography pressure as novel biomarkers for disc degeneration and low back pain.

STUDY DESIGN: Prospective magnetic resonance imaging (MRI) study of patients low back pain (LBP) requiring discography as part of their routine clinical diagnoses and asymptomatic age-matched volunteers. OBJECTIVE: To determine whether T1ρ MRI and discography opening pressure (OP) are quantitative biomarkers of disc degeneration in LBP patients and in asymptomatic volunteers. SUMMARY OF BACKGROUND DATA: Disc degenerative disease, a common cause of LBP, is related to the patient's prognosis and serves as a target for therapeutic interventions. However, there are few quantitative measures in the clinical setting. Discography OP and T1ρ MRI are potential biomarkers of disc degenerative disease related to biochemical composition of the intervertebral disc. METHODS: The institutional review board approved all experiments, and informed consent was provided by each subject. Patients being treated for LBP (n = 17; 68 levels; mean age, 44 ± 6 years; and range, 30-53) and control subjects (n = 11; 44 levels; mean age, 43 ± 17 years; and range, 22-76) underwent T1ρ and T2 MRI on a Siemens 3T Tim Trio clinical scanner (Siemens Medical Solutions, Malvern, PA). The LBP patients also received multilevel provocative discography before their MRI. OP was recorded as the pressure when fluid first enters the nucleus of the intervertebral disc. RESULTS: T1ρ was significantly lower in the painful discs (55.3 ± 3.0 ms, mean ± SE) from control (92.0 ± 4.9 ms, P < 0.001) and nonpainful discs (83.6 ± 3.2 ms, P < 0.001). Mean OP for the painful discs (11.8 ± 1.0 psi, mean ± SE) was significantly lower than that for nonpainful discs (19.1 ± 0.7 psi, P < 0.001). Both T1ρ and OP correlated moderately with Pfirrmann degenerative grade. Receiver-operating-characteristic area under the curve was 0.91 for T1ρ MRI and 0.84 for OP for predicting painful discs. CONCLUSION: T1ρ and OP are quantitative measures of degeneration that are consistent across both control subjects and LBP patients. A significant and strong correlation exists between T1ρ values and in vivo OP measurements obtained by discography in LBP patients.

The effect of implant size and device keel on vertebral compression properties in lumbar total disc replacement.

BACKGROUND CONTEXT: Vertebral end plate support is necessary for successful lumbar total disc replacement (TDR) surgery. Failure to achieve anterior column support as a result of lumbar TDR device undersizing could lead to implant subsidence and fracture. PURPOSE: The purpose of the study was to examine the compressive biomechanical behavior of the vertebral end plate with varying sizes of disc replacement implants. STUDY DESIGN: The study design comprises a biomechanical investigation using a human cadaveric lumbar spine model. METHODS: Fifty-six vertebrae with intact posterior elements were prepared from 13 fresh frozen lumbar spines. Peripheral quantitative computed tomography was performed to assess regional bone density. Vertebrae were potted and subjected to nondestructive compression testing with a small, medium, and large custom-made implants with the footplate geometry of the ProDisc-L TDR (Synthes Spine, West Chester, PA, USA) system and having no keel. Failure testing was performed using the ProDisc-L implant with an intact keel. Pressure sensor film was used to assess contact pressure and distribution. RESULTS: There was a linear correlation between percent coverage of the end plate and implant-end plate stiffness (p=.0001) and an inverse correlation with displacement (p=.01). The difference in implant-end plate stiffness between small-medium, medium-large, and small-large implants was 10.5% (p=.03), 10.2% (p=.02), and 19.6% (p<.0001), respectively. Failure analysis revealed similar trends for implant sizing, but only bone density was found to significantly correlate with failure properties (r=0.76, p<.0001). There was a significant reduction in implant-end plate stiffness of 18% when the keel was intact compared to without the keel (range 6-27%, p=.0008). Pressure film analysis revealed that the implant was loaded peripherally and did not have central contact during nondestructive loading. There was a trend toward greater contact pressure with the small implant when compared with the medium implant (p=.06) and the large implant (p=.06). CONCLUSIONS: Although larger implants reduce end plate displacement, increase apparent implant-end plate stiffness, increase the implant-end plate contact area, and decrease the peak contact pressures, low bone density reduces failure properties. The keel introduces a reduction in stiffness to the implant-end plate interface, the clinical significance of which is currently unknown.

Augmentation improves human cadaveric vertebral body compression mechanics for lumbar total disc replacement.

STUDY DESIGN: Cadaveric biomechanical study. OBJECTIVE: To quantify the effects of vertebral body augmentation on biomechanics under axial compression by a total disc replacement (TDR) implant. SUMMARY OF BACKGROUND DATA: TDR is a surgical alternative to lumbar spinal fusion to treat degenerative disc disease. Osteoporosis in the adjacent vertebrae to the interposed TDR may lead to implant subsidence or vertebral body fracture. Vertebral augmentation is used to treat osteoporotic compression fracture. This study sought to evaluate whether vertebral augmentation improves biomechanics under TDR axial loading. METHODS: Forty-five L1-L5 lumbar vertebral body segments with intact posterior elements were used. Peripheral quantitative computed tomography scans were performed to determine bone density, and specimens were block-randomized by bone density into augmentation and control groups. A semiconstrained keeled lumbar disc replacement device was implanted, providing 50% endplate coverage. Vertebral augmentation of 17.6% +/- 0.9% vertebral volume fill with Cortoss was performed on the augmentation group. All segments underwent axial compression at a rate of 0.2 mm/s to 6 mm. RESULTS: The load-displacement response for all specimens was nonlinear. Subfailure mechanical properties with augmentation were significantly different from control; in all cases, the augmented group was 2 times higher than control. At failure, the maximum load and stiffness with augmentation was not significantly different from control. The maximum apparent stress and modulus with augmentation were 2 times and 1.3 times greater than control, respectively. The subfailure stress and apparent modulus with augmentation were moderately correlated with bone density whereas the control subfailure properties were not. The augmented maximum stress was not correlated with bone density, whereas the control was weakly correlated. The maximum apparent modulus was moderately correlated with bone density for both the augmented and the control groups. CONCLUSION: Augmentation improved the mechanical properties of the lumbar vertebral body for compression by a TDR implant.

Segmental contribution toward total lumbar range of motion in disc replacement and fusions: a comparison of operative and adjacent levels.

STUDY DESIGN: Radiographic results from a prospective, randomized, multicenter trial assessing patients who underwent lumbar total disc replacement (TDR) or circumferential arthrodesis for 1-level degenerative disc disease. OBJECTIVE: To quantify the relative segmental contribution to total lumbar range of motion (ROM) at the operative level at each adjacent level in lumbar TDR and arthrodesis. SUMMARY OF BACKGROUND DATA: Although previous studies have evaluated ROM in TDR and fusion, no study has quantified or compared the relative segmental contribution to total lumbar ROM. Further, no study to the best of our knowledge has evaluated the kinematic profile of the more cranial adjacent segments (i.e., the second or third adjacent levels) following implantation of either TDR or fusion. METHODS: Radiographic data collected from all randomized 1-level degenerative disc disease patients operated at L4/5 or L5/S1 that participated in the multicenter, prospective, randomized IDE study comparing ProDisc-L with circumferential lumbar arthrodesis were evaluated before surgery and at 24 months. Radiographic measurements were performed independently using custom digitized image stabilization software to generate ROM at the operative level, and at each cranial and caudal adjacent level. RESULTS: There were 200 total patients included (155 ProDisc-L, average age 39 years; 45 arthrodesis, average age 40 years). At 24 months, the L4/5 TDR group experienced a significant improvement in total lumbar ROM from baseline (+6.3 degrees ), whereas there was no change seen with L5/S1 TDR or any fusion group. Between-group comparisons from baseline to 24 months postoperatively revealed: (1) significantly more contribution from the operative level towards total lumbar range in TDR at operative level L4/5 (TDR: -2.5%, fusion: -16.8%, P = 0.006), and operative level L5/S1 (TDR: -5.1%, fusion: -15.9%, P < 0.001), and (2) the relative contribution towards total lumbar range of motion from the first cranial adjacent segment to fusion at L5/S1 increased by 12.1%, compared with -1.2% seen in TDR (P = 0.03). There were elevated contributions from the more cranial adjacent levels to a fusion when compared with TDR, however, these differences were not statistically significant. At operative level L4/5, there was significantly increased ROM from the first caudal segment below TDR (6%, P = 0.03), but not below fusion (3.1%, P = 0.59). CONCLUSION: In conclusion, patients with TDR lost slight relative contribution to total lumbar motion from the operative level which was mostly compensated for by the caudal adjacent level (if operated at L4/5). In contrast, the significant loss of relative range of motion contribution from the operative level in fusions was redistributed among multiple cranial adjacent levels, most notably at the first cranial adjacent level.

Sagittal cervical alignment after cervical disc arthroplasty and anterior cervical discectomy and fusion: results of a prospective, randomized, controlled trial.

STUDY DESIGN: Radiographic results of a multicenter, prospective randomized study comparing 1-level cervical total disc replacement (TDR-C) with anterior cervical discectomy and fusion (ACDF). OBJECTIVE: To evaluate the effect on device-level lordosis, cranial and caudal adjacent level lordosis, and overall cervical sagittal alignment (C2-C6) after TDR-C or ACDF. SUMMARY OF BACKGROUND DATA: Cervical total disc replacement (TDR-C) has emerged as a promising alternative to ACDF in a select group of patients. The maintenance and/or improvement of sagittal balance is essential in preserving functionality after reconstructive spinal procedures. Recent studies have documented changes in spinal alignment after TDR-C, however, no studies have compared these changes to those noted in matched group of patients that have undergone ACDF. METHODS: Radiographic data were obtained from the randomized group of a multicenter, randomized, prospective, controlled study comparing TDR-C (ProDisc-C, Synthes Spine, West Chester, PA) with ACDF in the treatment of 1-level cervical disc disease. Complete radiographic data were available for 89 TDR-C patients (average age: 42.2 years) and 91 ACDF patients (average age: 41.7 years). Cervical lordosis at the device level, cranial and caudal adjacent levels, and total cervical lordosis (C2-C6) were independently measured before surgery and 2 years after surgery using custom image stabilization software (Quantitative Motion Analysis, Medical Metrics, Inc, Houston, TX). RESULTS: C5-C6 was the most common operative level (TDR-C: 54%; ACDF: 55%). At 2 years after surgery, the TDR-C group experienced statistically significant changes in lordosis of 3.0 degrees (P < 0.001), 0.90 degrees (P = 0.006), and -1.9 degrees (P < 0.001) at the operative, cranial, and caudal adj-acent levels, respectively. ACDF experienced changes in lordosis of 4.2 degrees (P < 0.001), 1.0 degrees (P = 0.001), and -1.5 degrees (P = 0.001), respectively. The between-group differences were significant at the operative level (P = 0.03) and the caudal adjacent level (P = 0.05). Total cervical lordosis increased in both TDR-C and ACDF by 3.1 degrees and 3.8 degrees , respectively (P = 0.49). CONCLUSION: In both TDR-C and ACDF, lordosis increased at the device-level, cranial adjacent level, and in total cervical lordosis, while lordosis decreased at the caudal adjacent level. Although ACDF facilitated a greater increase in device level lordosis (+1.25 degrees ) and less loss of lordosis at the caudal adjacent level compared with TDR-C (-0.39 degrees ), the clinical relevance of the small differences remain unknown.

Total disc replacement positioning affects facet contact forces and vertebral body strains.

STUDY DESIGN: A validated nonlinear three-dimensional finite element (FE) model of a single lumbar motion segment (L3-L4) was used to evaluate the effects of total disc replacement (TDR). The model was implanted with a fixed-bearing TDR (ProDisc-L) at 2 surgically relevant positions and exercised about the 3 anatomic axes. Facet forces, range of motion (RoM), and vertebral body strains were evaluated. OBJECTIVE: The objective of the current study was to evaluate how TDR implantation and positioning affects facet joint forces and vertebral body strains. We hypothesized that facet contact forces (FCFs) would increase with TDR to compensate for the loss of periprosthetic load-bearing structures, and that vertebral body strains would increase in the region around the metallic footplates. SUMMARY OF BACKGROUND DATA: TDR has the potential to replace fusion as the gold standard for the treatment of painful degenerative disc disease. However, complications after TDR include index level facet arthrosis and implant subsidence. Alterations in facet and vertebral body loading after TDR and their dependence on implant positioning are not fully understood. METHODS: An FEM of L3-L4 was created and validated using RoM, disc pressure, and bony strains from previously published data. A TDR was incorporated into the L3-L4 spine model. All models were subjected to a compressive follower load of 500 N and moments of 7.5 Nm about the 3 anatomic axes. RESULTS: Overall RoM and FCFs tended to increase with TDR. FCFs increased by an order of magnitude during flexion. Posterior placement of the device resulted in an unloading of the facets during extension. Areas of strain maxima were observed in the anterior portion of the vertebral body during flexion after TDR. The area of initial bone resorption signal under the metal footplate was greater when the device was anteriorly placed. CONCLUSION: The current study predicted a decrease in segmental rotational stiffness resulting from TDR. This resulted from the removal of load bearing soft tissue structures, and caused increased loading in the facets. Additionally, vertebral body strains were generally higher after TDR, and tended to increase with decreased rotational stiffness. Posterior placement of the device provided a more physiologic load transfer to the vertebral body.

The parallax effect in the evaluation of range of motion in lumbar total disc replacement.

BACKGROUND: Range of motion (ROM) has been shown to influence clinical outcomes of total disc replacement (TDR). While the parallax effect in image acquisition has been shown in the literature to influence the accuracy of a variety of measurements, this concept has not been investigated in the assessment of ROM analysis following TDR. We performed an evaluation of the influence of radiograph beam angle on "by hand" and on "gold standard" flexionextension ROM measurements in lumbar total disc replacement. The purpose of this study is to determine (1) the influence of X-ray beam angle on index level angle (ILA) measurements in lumbar TDR using the keel method, and (2) whether the out-of-plane radiographic beam effects cause a difference between true and calculated range of motion. METHODS: Eight blinded orthopaedic surgeons used the keel method to calculate ROM measurements from radiographs of a flexible Sawbones model (Pacific Research Laboratories, Inc., Vashon, Washington) implanted with a ProDisc-L device (Synthes Spine, West Chester, Pennsylvania). Radiographs were obtained at beam angles of 0°, 5°, 10°, and 15° in the sagittal plane from the device center. Calculations were compared to measurements obtained by a validated digitized software method (Quantitative Motion Analysis, QMA, Medical Metrics, Inc., Houston, Texas). Inter- and intraobserver precision and accuracy were determined. RESULTS: Compared with QMA, the radiographic keel method had an average error of 3.7°. No significant effect of variation in beam angle on interobserver precision (N = 16, P = .92) or accuracy (N = 16, P = 0.86) or intraobserver precision (N = 8, P = .09) or accuracy (N = 8, P = 0.07) of ROM measurements was identified. Repeat testing with QMA also revealed no effect of parallax and resulted in nearly identical ROM measurements. CONCLUSIONS: Accuracy and precision of the keel method to determine ROM from index level angle measurements after TDR was not affected by increases in X-ray beam angles up to 15° from the device center. CLINICAL RELEVANCE: Our study demonstrates that range of motion measurements are not influenced by parallax effect when using the keel method to determine index level angle measurements in lumbar total disc replacement.

Advances in Magnetic Resonance Imaging for the assessment of degenerative disc disease of the lumbar spine.

The intervertebral disc is characterized by a tension-resisting annulus fibrosus, and a compression-resisting nucleus pulposus composed largely of proteoglycan. Both the annulus and the nucleus function in concert to provide the disc with mechanical stability. Early disc degeneration begins in the nucleus with proteoglycan depletion. Quantitative MRI techniques have been developed to non-invasively quantify the earliest degenerative changes that occur within the disc. Our ability to identify and quantify these early biochemical changes will provide a better understanding of the pathophysiology of disc degeneration and facilitate the study of interventions that aim to halt or reverse the degenerative process.

Results of the prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of the ProDisc-L total disc replacement versus circumferential fusion for the treatment of 1-level degenerative disc disease.

STUDY DESIGN: A prospective, randomized, multicenter, Food and Drug Administration-regulated Investigational Device Exemption clinical trial. OBJECTIVE: To evaluate the safety and effectiveness of the ProDisc-L (Synthes Spine, West Chester, PA) lumbar total disc replacement compared to circumferential spinal fusion for the treatment of discogenic pain at 1 vertebral level between L3 and S1. SUMMARY OF BACKGROUND DATA: As part of the Investigational Device Exemption clinical trial, favorable single center results of lumbar total disc replacement with the ProDisc-L have been reported previously. METHODS: Two hundred eighty-six (286) patients were treated on protocol. Patients were evaluated before and after surgery, at 6 weeks, 3, 6, 12, 18, and 24 months. Evaluation at each visit included patient self-assessments, physical and neurologic examinations, and radiographic evaluation. RESULTS: Safety of ProDisc-L implantation was demonstrated with 0% major complications. At 24 months, 91.8% of investigational and 84.5% of control patients reported improvement in the Oswestry Low Back Pain Disability Questionnaire (Oswestry Disability Index [ODI]) from preoperative levels, and 77.2% of investigational and 64.8% of control patients met the > or =15% Oswestry Disability Index improvement criteria. Overall neurologic success in the investigational group was superior to the control group (91.2% investigational and 81.4% control; P = 0.0341). At 6 weeks and 3 months follow-up time points, the ProDisc-L patients recorded SF-36 Health Survey scores significantly higher than the control group (P = 0.018, P = 0.0036, respectively). The visual analog scale pain assessment showed statistically significant improvement from preoperative levels regardless of treatment (P < 0.0001). Visual analog scale patient satisfaction at 24 months showed a statistically significant difference favoring investigational patients over the control group (P = 0.015). Radiographic range of motion was maintained within a normal functional range in 93.7% of investigational patients and averaged 7.7 degrees. CONCLUSIONS: ProDisc-L has been found to be safe and efficacious. In properly chosen patients, ProDisc-L has been shown to be superior to circumferential fusion by multiple clinical criteria.

Evaluation of spinal kinematics following lumbar total disc replacement and circumferential fusion using in vivo fluoroscopy.

STUDY DESIGN: In vivo fluoroscopic analysis of lumbar spinal motion with total disc replacement (TDR), fusions, and controls. OBJECTIVES: Compare and contrast lumbar spinal motion profiles in TDR, circumferential fusion, and controls. SUMMARY OF BACKGROUND DATA: TDR has been shown to preserve motion and possibly prevent abnormal loading at the adjacent level. Although in vitro cadaveric studies have provided invaluable information, they are not capable of assessing the physiologic motion profile of the lumbar spine that is initiated and stabilized by in vivo trunk muscular contractions. METHODS: Cross-sectional evaluation using high-frequency low-dose pulsated video fluoroscopy to evaluate lumbar spinal motion in subjects who underwent TDR (n = 8), circumferential fusion (n = 5), and controls (n = 4). Angulation and translation were recorded at 20 time points during the extension-flexion arc. Motion gradients, or slopes of the motion curves, were generated to allow for comparison of lumbar spinal motion profiles. RESULTS: Circumferential fusions exhibited significantly steeper motion gradients at the proximal adjacent level compared with TDR during flexion. TDR had more physiologic motion profiles at the proximal adjacent level than fusions during flexion and extension. At operative levels L4/5 and L5/S1, TDR and controls exhibited similar motion profiles in flexion, while fusions exhibited significantly less motion. In extension, however, TDR had a steeper slope than controls at the L4/5 operative level. Between L3 and S1, the total range of motion accounted for by the L4/5 proximal adjacent level was 59% in 1-level fusions, 38% in 1-level TDR, and 29% in controls. While no control or TDR subjects underwent sagittal plane translation >3 mm during flexion-extension, 80% of fusions did (average 3.7 mm), most notably during the latter phase of extension. CONCLUSIONS: TDR produces physiologic lumbar spinal motion profiles in flexion and extension at the operative and proximal adjacent levels. Fusions, however, produced steeper motion gradients at the proximal adjacent level, while undergoing significantly greater sagittal plane translation during flexion-extension.

In vivo quantification of human lumbar disc degeneration using T(1rho)-weighted magnetic resonance imaging.

Diagnostic methods and biomarkers of early disc degeneration are needed as emerging treatment technologies develop (e.g., nucleus replacement, total disc arthroplasty, cell therapy, growth factor therapy) to serve as an alternative to lumbar spine fusion in treatment of low back pain. We have recently demonstrated in cadaveric human discs an MR imaging and analysis technique, spin-lock T(1rho)-weighted MRI, which may provide a quantitative, objective, and non-invasive assessment of disc degeneration. The goal of the present study was to assess the feasibility of using T(1rho) MRI in vivo to detect intervertebral disc degeneration. We evaluated ten asymptomatic 40-60-year-old subjects. Each subject was imaged on a 1.5 T whole-body clinical MR scanner. Mean T(1rho) values from a circular region of interest in the center of the nucleus pulposus were calculated from maps generated from a series of T(1rho)-weighted images. The degenerative grade of each lumbar disc was assessed from conventional T(2)-weighted images according to the Pfirmann classification system. The T(1rho) relaxation correlated significantly with disc degeneration (r=-0.51, P<0.01) and the values were consistent with our previous cadaveric study, in which we demonstrated correlation between T(1rho) and proteoglycan content. The technique allows for spatial measurements on a continuous rather than an integer-based scale, minimizes the potential for observer bias, has a greater dynamic range than T(2)-weighted imaging, and can be implemented on a 1.5 T clinical scanner without significant hardware modifications. Thus, there is a strong potential to use T(1rho) in vivo as a non-invasive biomarker of proteoglycan loss and early disc degeneration.

Preoperative evaluation of adult isthmic spondylolisthesis with diskography.

Fourteen consecutive patients with a diagnosis of isthmic spondylolisthesis (grade I and II) underwent provocative lumbar diskography (L2-S1) to evaluate the disk adjacent to the spondylolisthesis. Seven (50%) of 14 patients had concordant pain at the disk above the slip and 2 patients had no pain at the slip level. Surgical treatment included anteroposterior fusion of the slip level and any adjacent concordant levels. Clinical results included 3 excellent, 7 good, 2 fair, and 1 poor outcome. This data supports the hypothesis that the disk adjacent to an isthmic slip is predisposed to symptomatic degeneration in the adult patient with axial pain. It does not prove that a fusion is indicated or that clinical outcomes would be improved with this approach.

Clinical and radiographic outcomes of anterior lumbar interbody fusion using recombinant human bone morphogenetic protein-2.

STUDY DESIGN: A prospective, nonblinded, multicenter study of outcomes in patients undergoing single-level anterior lumbar discectomy and interbody fusion with InFUSE Bone Graft. OBJECTIVE: To determine the safety and effectiveness of InFUSE Bone Graft applied to an absorbable collagen sponge in anterior lumbar interbody fusion with threaded cortical allografts. SUMMARY OF BACKGROUND DATA: In primates, InFUSE Bone Graft used with allograft dowels was shown to increase rates of interbody fusion by promoting osteoinduction and enhancing incorporation of the allograft. Recently, in a small series of human patients undergoing anterior lumbar interbody fusion with a tapered cylindrical metal fusion cage, InFUSE Bone Graft has been shown to promote osteoinduction and fusion. METHODS: Forty-six patients underwent a single-level anterior lumbar discectomy and interbody fusion at five investigational sites. They were randomly assigned to one of two groups, and the results in the investigational patients who received threaded cortical allograft dowels with InFUSE Bone Graft were compared with those in the control patients who received threaded allograft dowels with autogenous iliac crest bone graft. Patients' clinical outcomes were assessed using neurologic status, work status, and Oswestry Low Back Pain Disability, Short Form-36, and back and leg pain questionnaires. Anteroposterior, lateral, flexion-extension radiographs, and computed tomography scans were used to evaluate the progression of fusion at 6, 12, and 24 months after surgery. RESULTS: All patients who received InFUSE Bone Graft showed radiographic evidence of bony induction and early incorporation of the cortical allografts. All patients in this group had fusions at 12 months that remained fused at 24 months. At 12 and 24 months, the investigational group showed higher rates of fusion and improved neurologic status and back and leg pain when compared with the control group. There were no unanticipated adverse events related to the use of InFUSE Bone Graft. CONCLUSION: The use of InFUSE Bone Graft is a promising method of facilitating anterior intervertebral spinal fusion, decreasing pain, and improving clinical outcomes in patients who have undergone anterior lumbar fusion surgery with structural threaded cortical allograft bone dowels.