Accelerated degeneration of the segment adjacent to a lumbar fusion

Lumbar stiffness as a collateral outcome of spinal arthrodesis: a preliminary clinical study

BACKGROUND CONTEXT

Although spinal arthrodesis can improve function by correcting deformity and reducing pain, it also by intention reduces spinal mobility. Increased spinal stiffness may have the potential to impair function and ability to perform activities of daily living (ADLs), independent of pain levels.

PURPOSE

To evaluate the ability to discriminate spinal stiffness from pain in ADLs after lumbar spine arthrodesis using two outcome instruments.

STUDY DESIGN

Cross-sectional study.

PATIENT SAMPLE

Consecutive cohort of lumbar spine fusion patients from a single surgeon's practice.

OUTCOME MEASURES

Oswestry Disability Index (ODI), Lumbar Stiffness Disability Index (LSDI), radiographs.

METHODS

We developed the LSDI questionnaire to assess the impact of spinal stiffness on ability to perform different ADLs. The LSDI and ODI were administered to 93 patients who underwent lumbar arthrodesis extending from one to five or more motion segments at a minimum follow-up of 1 year. Comparisons of mean LSDI and ODI scores between patients were made using generalized linear regression. A Pearson correlation coefficient (r) was computed to determine the relationship between the LSDI and ODI scores.

RESULTS

The sample included 61 women and 32 men, with mean age at surgery of 55.0 years (standard deviation [SD], 13.1) and mean time since surgery of 3.4 years (SD, 1.8). The mean LSDI score was 29.6 (SD, 19.2), and the mean ODI score was 39.7 (SD, 19.1). Comparing one-level and five-level arthrodesis, the LSDI scores were significantly different (p=.05), whereas the ODI scores were not significantly different (p=.36). Comparisons between other levels of arthrodesis did not show significant differences for either the LSDI or the ODI. Within the entire study group, LSDI and ODI scores were positively correlated (r=0.69, p<.001).

CONCLUSIONS

Difficulty in performing certain ADLs increases for patients with multilevel lumbar fusions as opposed to one-level arthrodesis. The LSDI distinguishes functional difficulties with ADLs accruing because of spinal stiffness, which appear to be independent of the functional limitations resulting from low back pain as measured by ODI.

A comparison of the clinical outcomes of decompression alone and fusion in elderly patients with two-level or more lumbar spinal stenosis

OBJECTIVE

We compared the results of two surgical techniques by retrospective study of 60 elderly patients (65 years or older) who underwent either decompression alone or fusion for the treatment of two-level or more lumbar spinal stenosis.

METHODS

During the period of 2003 and 2008, two-level or more decompression alone or fusion was performed for lumbar spinal stenosis by three surgeons at our institution. Patients were allocated to two groups by surgical modality, namely, to a decompression group (31 patients) or a fusion group (29 patients). Overall mean age was 71.1 years (range, 65-84) and mean follow-up was 5.5 years (range, 3-9). A retrospective review of clinical, radiological, and surgical data was conducted.

RESULTS

No significant difference between the two groups was found with respect to age, follow-up period, surgical levels, or preoperative condition. At the last follow-up, correction of lumbar lordotic angle (determined radiologically) was better in the fusion group. However, clinical outcomes including visual analogue scale, Oswestry Disability Index, and the Odom's criteria were not significantly different in the two groups. On the other hand, surgical outcomes, such as, operation time, estimated blood loss, and surgical complications were significantly better in the decompression alone group.

CONCLUSION

Our findings suggest that decompressive laminectomy alone achieves good outcomes in patients with two-level or more lumbar spinal stenosis, associated with an advanced age, poor general condition, or osteoporosis.

Gene expression profiling of early intervertebral disc degeneration reveals a down-regulation of canonical Wnt signaling and caveolin-1 expression: implications for development of regenerative strategies

INTRODUCTION

Early degeneration of the intervertebral disc (IVD) involves a change in cellular differentiation from notochordal cells (NCs) in the nucleus pulposus (NP) to chondrocyte-like cells (CLCs). The purpose of this study was to investigate the gene expression profiles involved in this process using NP tissue from non-chondrodystrophic and chondrodystrophic dogs, a species with naturally occurring IVD degeneration.

METHODS

Dual channel DNA microarrays were used to compare 1) healthy NP tissue containing only NCs (NC-rich), 2) NP tissue with a mixed population of NCs and CLCs (Mixed), and 3) NP tissue containing solely CLCs (CLC-rich) in both non-chondrodystrophic and chondrodystrophic dogs. Based on previous reports and the findings of the microarray analyses, canonical Wnt signaling was further evaluated using qPCR of relevant Wnt target genes. We hypothesized that caveolin-1, a regulator of Wnt signaling that showed significant changes in gene expression in the microarray analyses, played a significant role in early IVD degeneration. Caveolin-1 expression was investigated in IVD tissue sections and in cultured NCs. To investigate the significance of Caveolin-1 in IVD health and degeneration, the NP of 3-month-old Caveolin-1 knock-out mice was histopathologically evaluated and compared with the NP of wild-type mice of the same age.

RESULTS

Early IVD degeneration involved significant changes in numerous pathways, including Wnt/β-catenin signaling. With regard to Wnt/β-catenin signaling, axin2 gene expression was significantly higher in chondrodystrophic dogs compared with non-chondrodystrophic dogs. IVD degeneration involved significant down-regulation of axin2 gene expression. IVD degeneration involved significant down-regulation in Caveolin-1 gene and protein expression. NCs showed abundant caveolin-1 expression in vivo and in vitro, whereas CLCs did not. The NP of wild-type mice was rich in viable NCs, whereas the NP of Caveolin-1 knock-out mice contained chondroid-like matrix with mainly apoptotic, small, rounded cells.

CONCLUSIONS

Early IVD degeneration involves down-regulation of canonical Wnt signaling and Caveolin-1 expression, which appears to be essential to the physiology and preservation of NCs. Therefore, Caveolin-1 may be regarded an exciting target for developing strategies for IVD regeneration.

Effect of centers of rotation on spinal loads and muscle forces in total disk replacement of lumbar spine

The placement of artificial disks can alter the center of rotation and kinematic pattern; therefore, forces in the spine during the motion will be affected as a result. The relationship between the location of joint center of artificial disks and forces in the spinal components is not investigated. A musculoskeletal model of the spine was developed, and three location cases of center of rotation were investigated varying 5 mm anteriorly and posteriorly from the default center. Resultant joint forces, ligament forces, facet forces, and muscle forces for each case were predicted during sagittal motion. No considerable difference was observed for joint force (maximum 14%). Anterior shift of center of rotation induced the most ligament forces (200 N) and facet forces (130 N) among the three cases. Posterior and anterior shifts of centers of rotation from the default location caused considerable changes in muscle forces, respectively: 108% and 70% of increase in multifidi muscle and 157% and 187% of increase in short segmental muscle. This study showed that the centers of rotation due to the design and the surgical placement of artificial disk can affect the kinetic results in the spine.

Comparison of the biomechanical effect of pedicle-based dynamic stabilization: a study using finite element analysis

BACKGROUND CONTEXT

Recently, nonfusion pedicle-based dynamic stabilization systems (PBDSs) have been developed and used in the management of degenerative lumbar spinal diseases. Still effects on spinal kinematics and clinical effects are controversial. Little biomechanical information exists for providing biomechanical characteristics of pedicle-based dynamic stabilization according to the PBDS design before clinical implementation.

PURPOSE

To investigate the effects of implanting PBDSs into the spinal functional unit and elucidate the differences in biomechanical characteristics according to different materials and design.

STUDY DESIGN

The biomechanical effects of implantation of PBDS were investigated using the nonlinear three-dimensional finite element model of L4-L5.

METHODS

An already validated three-dimensional, intact osteoligamentous L4-L5 finite element model was modified to incorporate the insertion of pedicle screws. The implanted models were constructed after modifying the intact model to simulate postoperative changes using four different fixation systems. Four models instrumented with PBDS (Dynesys, NFlex, and polyetheretherketone [PEEK]) and rigid fixation systems (conventional titanium rod) were developed for comparison. The instrumented models were compared with those of the intact and rigid fixation model. Range of motion (ROM) in three motion planes, center of rotation (COR), force on the facet joint, and von Mises stress distribution on the vertebral body and implants with flexion-extension were compared among the models.

RESULTS

Simulated results demonstrated that implanted segments with PBDSs have limited ROM when compared with the intact spine. Flexion motion was the most limited, and axial rotation was the least limited, after device implantation. Among the PBDS selected in this analysis, the NFlex system had the closest instantaneous COR compared with the intact model and a higher ROM compared with other PBDS. Contact force on the facet joint in extension increased with an increase of moment in Dynesys and NFlex; however, the rigid or PEEK rod fixation revealed no facet contact force.

CONCLUSIONS

Implanted segments with PBDSs have limited ROM when compared with the intact spine. Center of rotation and stress distribution differed according to the design and materials used. These biomechanical effects produced a nonphysiological stress on the functional spinal unit when they were implanted. The biomechanical effects of current PBDSs should be carefully considered before clinical implementation.

A short history of posterior dynamic stabilization

Interspinous spacers were developed to treat local deformities such as degenerative spondylolisthesis. To treat patients with chronic instability, posterior pedicle fixation and rod-based dynamic stabilization systems were developed as alternatives to fusion surgeries. Dynamic stabilization is the future of spinal surgery, and in the near future, we will be able to see the development of new devices and surgical techniques to stabilize the spine. It is important to follow the development of these technologies and to gain experience using them. In this paper, we review the literature and discuss the dynamic systems, both past and present, used in the market to treat lumbar degeneration.

Revision lumbar surgery in elderly patients with symptomatic pseudarthrosis, adjacent-segment disease, or same-level recurrent stenosis. Part 1. Two-year outcomes and clinical efficacy: clinical article

OBJECT

Same-level recurrent lumbar stenosis, pseudarthrosis, and adjacent-segment disease (ASD) are potential complications that can occur after index lumbar spine surgery, leading to significant discomfort and radicular pain. While numerous studies have demonstrated excellent results following index lumbar spine surgery in elderly patients (age > 65 years), the effectiveness of revision lumbar surgery in this cohort remains unclear. The aim of this study was to assess the long-term effectiveness of revision lumbar decompression and fusion in the treatment of symptomatic pseudarthrosis, ASD, and same-level recurrent stenosis, using validated patient-reported outcomes.

METHODS

After a review of the institutional database, 69 patients who had undergone revision neural decompression and instrumented fusion for ASD (28 patients), pseudarthrosis (17 patients), or same-level recurrent stenosis (24 patients) were included in this study. Baseline and 2-year scores on the visual analog scale for leg pain (VAS-LP), VAS for back pain (VAS-BP), Oswestry Disability Index (ODI), and Zung Self-Rating Depression Scale (SDS) as well as the time to narcotic independence, time to return to baseline activity level, health state utility (EQ-5D, the EuroQol-5D health survey), and physical and mental component summary scores of the 12-Item Short-Form Health Survey (SF-12 PCS and MCS) were assessed.

RESULTS

Compared with the preoperative status, VAS-BP was significantly improved 2 years after surgery for ASD (mean ± standard deviation 9 ± 2 vs 4.01 ± 2.56, p = 0.001), pseudarthrosis (7.41 ± 1 vs 5.52 ± 3.08, p = 0.02), and same-level recurrent stenosis (7 ± 2.00 vs 5.00 ± 2.34, p = 0.003). The 2-year ODI was also significantly improved after surgery for ASD (29 ± 9 vs 23.10 ± 10.18, p = 0.001), pseudarthrosis (28.47 ± 5.85 vs 24.41 ± 7.75, p = 0.001), and same-level recurrent stenosis (30.83 ± 5.28 vs 26.29 ± 4.10, p = 0.003). The Zung SDS score and SF-12 MCS did not change appreciably after surgery in any of the cohorts, with an overall mean 2-year change of 1.01 ± 5.32 (p = 0.46) and 2.02 ± 9.25 (p = 0.22), respectively.

CONCLUSIONS

Data in this study suggest that revision lumbar decompression and extension of fusion for symptomatic pseudarthrosis, ASD, and same-level recurrent stenosis provides improvement in low-back pain, disability, and quality of life and should be considered a viable treatment option for elderly patients with persistent or recurrent back and radicular pain. Mental health symptoms may be more refractory to revision surgery.

ProDisc-L learning curve: 24-Month clinical and radiographic outcomes in 44 consecutive cases

Background

Total disc replacement (TDR) promises preservation of spine biomechanics in the treatment of degenerative disc disease but requires more careful device placement than tradition fusion and potentially has a more challenging learning curve.

Methods

A cohort of 44 consecutive patients had 1-level lumbar disc replacement surgery at a single institution by a single surgeon. Patients were followed up clinically and radiographically for 24 months. Patients were divided into 2 groups of 22 sequential cases each. Clinically, preoperative and postoperative Oswestry Disability Index, visual analog scale, Short Form 12 (SF-12) Mental and Physical Components, and postoperative satisfaction were measured. Radiographically, preoperative and postoperative range of motion (ROM) dimensions, prosthesis deviation from the midline, and disc height were measured. TDR-related complications were noted. Logarithmic curve–fit regression analysis was used to assess the learning curve.

Results

Operative time decreased as cases progressed, with an asymptote after 22 cases. The operative time for the later group was significantly lower (P < .0005), but hospital stay was significantly longer (P = .03). There was no significant difference in amount of blood loss (P = .10) or prosthesis midline deviation (P = .86). Clinically, there was no significant difference in postoperative scores between groups in Oswestry Disability Index (P = .63), visual analog scale (P = .45), SF-12 Mental Component (P = .66), SF-12 Physical Component (P = .75), or postoperative satisfaction (P = .92) at 24 months. Radiographically, there was no significant difference in improvement between groups in ROM (P = .67) or disc height (P = .87 for anterior and P = .13 for posterior) at 24 months. For both groups, there was significant improvement for all clinical outcomes and disc height over preoperative values. One patient in the later group had device failure with subluxation of the polyethylene, which required revision.

Conclusions/level of evidence

Early experience can quickly reduce operative time but does not affect clinical outcomes or ROM significantly (level IV case series).

Clinical relevance

Lumbar TDR is a rapidly learnable technique in treatment of degenerative disc disease.

Prospective study of disc repair with allogeneic chondrocytes presented at the 2012 Joint Spine Section Meeting

OBJECT

The purpose of the study was to evaluate the safety and initial efficacy of NuQu allogeneic juvenile chondrocytes delivered percutaneously for the treatment of lumbar spondylosis with mechanical low-back pain (LBP). NuQu is a cell-based biological therapy for disc repair. The authors report the results at 12 months of the NuQu Phase I investigational new drug (IND) single-arm, prospective feasibility study for the treatment of LBP for single-level degenerative disc disease (Pfirrman Grades III-IV) at L3-S1.

METHODS

Fifteen patients (6 women and 9 men) were enrolled at 2 sites. Institutional review board approval was obtained, and all patients signed a study-specific informed consent. All patients have completed a minimum of 1 year of follow-up. Patients were evaluated pretreatment and at 1, 3, 6, and 12 months posttreatment. Evaluations included routine neurological examinations, serum liver and renal function studies, MRI, the Oswestry Disability Index (ODI), the Numerical Rating Scale (NRS), and the 36-Item Short Form Health Survey (SF-36).

RESULTS

Fifteen patients were treated with a single percutaneous delivery of NuQu juvenile chondrocytes. The mean patient age was 40 years (19-47 years). Each treatment consisted of 1-2 ml (mean injection 1.3 ml) of juvenile chondrocytes (approximately 10(7) chondrocyte cells/ml) with fibrin carrier. The mean peak pressure during treatment was 87.6 psi. The treatment time ranged from 5 to 33 seconds. The mean ODI (baseline 53.3, 12-month 20.3; p < 0.0001), NRS (baseline 5.7, 12-month 3.1; p = 0.0025), and SF-36 physical component summary (baseline 35.3, 12-month 46.9; p = 0.0002) scores all improved significantly from baseline. At the 6-month follow-up, 13 patients underwent MRI (one patient underwent CT imaging and another refused imaging). Ten (77%) of these 13 patients exhibited improvements on MRI. Three of these patients showed improvement in disc contour or height. High-intensity zones (HIZs), consistent with posterior anular tears, were present at baseline in 9 patients. Of these, the HIZ was either absent or improved in 8 patients (89%) by 6 months. The HIZ was improved in the ninth patient at 3 months, with no further MRI follow-up. Of the 10 patients who exhibited radiological improvement at 6 months, findings continued to improve or were sustained in 8 patients at the 12-month follow-up. No patient experienced neurological deterioration. There were no disc infections, and there were no serious or unexpected adverse events. Three patients (20%) underwent total disc replacement by the 12-month follow-up due to persistent, but not worse than baseline, LBP.

CONCLUSIONS

This is a 12-month report of the clinical and radiographic results from a US IND study of cell-based therapy (juvenile chondrocytes) in the treatment of lumbar spondylosis with mechanical LBP. The results of this prospective cohort are promising and warrant further investigation with a prospective, randomized, double-blinded, placebo-controlled study design. Clinical trial registration no.: BB-IND 13985.

Five-year adjacent-level degenerative changes in patients with single-level disease treated using lumbar total disc replacement with ProDisc-L versus circumferential fusion

OBJECT

The authors report the 5-year results for radiographically demonstrated adjacent-level degenerative changes from a prospective multicenter study in which patients were randomized to either total disc replacement (TDR) or circumferential fusion for single-level lumbar degenerative disc disease (DDD).

METHODS

Two hundred thirty-six patients with single-level lumbar DDD were enrolled and randomly assigned to 2 treatment groups: 161 patients in the TDR group were treated using the ProDisc-L (Synthes Spine, Inc.), and 75 patients were treated with circumferential fusion. Radiographic follow-up data 5 years after treatment were available for 123 TDR patients and 43 fusion patients. To characterize adjacent-level degeneration (ALD), radiologists at an independent facility read the radiographic films. Adjacent-level degeneration was characterized by a composite score including disc height loss, endplate sclerosis, osteophytes, and spondylolisthesis. At 5 years, changes in ALD (ΔALDs) compared with the preoperative assessment were reported.

RESULTS

Changes in ALD at 5 years were observed in 9.2% of TDR patients and 28.6% of fusion patients (p = 0.004). Among the patients without adjacent-level disease preoperatively, new findings of ALD at 5 years posttreatment were apparent in only 6.7% of TDR patients and 23.8% of fusion patients (p = 0.008). Adjacent-level surgery leading to secondary surgery was reported for 1.9% of TDR patients and 4.0% of fusion patients (p = 0.6819). The TDR patients had a mean preoperative index-level range of motion ([ROM] of 7.3°) that decreased slightly (to 6.0°) at 5 years after treatment (p = 0.0198). Neither treatment group had significant changes in either ROM or translation at the superior adjacent level at 5 years posttreatment compared with baseline.

CONCLUSIONS

At 5 years after the index surgery, ProDisc-L maintained ROM and was associated with a significantly lower rate of ΔALDs than in the patients treated with circumferential fusion. In fact, the fusion patients were greater than 3 times more likely to experience ΔALDs than were the TDR patients. Clinical trial registration no.: NCT00295009.

Hybrid dynamic stabilization: a biomechanical assessment of adjacent and supraadjacent levels of the lumbar spine

OBJECT

The object of this study was to evaluate the effect of hybrid dynamic stabilization on adjacent levels of the lumbar spine.

METHODS

Seven human spine specimens from T-12 to the sacrum were used. The following conditions were implemented: 1) intact spine; 2) fusion of L4-5 with bilateral pedicle screws and titanium rods; and 3) supplementation of the L4-5 fusion with pedicle screw dynamic stabilization constructs at L3-4, with the purpose of protecting the L3-4 level from excessive range of motion (ROM) and to create a smoother motion transition to the rest of the lumbar spine. An industrial robot was used to apply continuous pure moment (± 2 Nm) in flexion-extension with and without a follower load, lateral bending, and axial rotation. Intersegmental rotations of the fused, dynamically stabilized, and adjacent levels were measured and compared.

RESULTS

In flexion-extension only, the rigid instrumentation at L4-5 caused a 78% decrease in the segment's ROM when compared with the intact specimen. To compensate, it caused an increase in motion at adjacent levels L1-2 (45.6%) and L2-3 (23.2%) only. The placement of the dynamic construct at L3-4 decreased the operated level's ROM by 80.4% (similar stability as the fusion at L4-5), when compared with the intact specimen, and caused a significant increase in motion at all tested adjacent levels. In flexion-extension with a follower load, instrumentation at L4-5 affected only a subadjacent level, L5-sacrum (52.0%), while causing a reduction in motion at the operated level (L4-5, -76.4%). The dynamic construct caused a significant increase in motion at the adjacent levels T12-L1 (44.9%), L1-2 (57.3%), and L5-sacrum (83.9%), while motion at the operated level (L3-4) was reduced by 76.7%. In lateral bending, instrumentation at L4-5 increased motion at only T12-L1 (22.8%). The dynamic construct at L3-4 caused an increase in motion at T12-L1 (69.9%), L1-2 (59.4%), L2-3 (44.7%), and L5-sacrum (43.7%). In axial rotation, only the placement of the dynamic construct at L3-4 caused a significant increase in motion of the adjacent levels L2-3 (25.1%) and L5-sacrum (31.4%).

CONCLUSIONS

The dynamic stabilization system displayed stability characteristics similar to a solid, all-metal construct. Its addition of the supraadjacent level (L3-4) to the fusion (L4-5) did protect the adjacent level from excessive motion. However, it essentially transformed a 1-level lumbar fusion into a 2-level lumbar fusion, with exponential transfer of motion to the fewer remaining discs.

Upper instrumented vertebral fractures in long lumbar fusions: what are the associated risk factors?

STUDY DESIGN

A retrospective comparative study.

OBJECTIVE

To investigate the risk factors associated with upper instrumented vertebral (UIV) fractures in adult lumbar deformity.

SUMMARY OF BACKGROUND DATA

Long segment lumbar fusions may lead to junctional failures. The purpose of this study was to determine factors associated with junctional failures.

METHODS

Twenty-seven consecutive patients from 2001 to 2008 with minimum 4 levels fused, lower instrumented vertebra (LIV) of L5 or S1, upper instrumented vertebra of T10 or distal, and no previous surgery proximal to the instrumentation were retrospectively reviewed. We describe the UIV angle, the sagittal angle of the upper instrumented vertebra with the horizontal. Patients were divided into 3 groups: group 1, 7 patients with UIV fractures; group 2, 6 patients with other proximal failures; and group 3, 14 patients with no proximal complications.

RESULTS

The mean number of levels fused was 5.7 (4-7), 5.2 (4-8), and 6.2 (4-8); mean age was 64.1, 61.8, and 64.1, and mean body mass index was 33.5, 30.0, and 31.6 for groups 1, 2, and 3, respectively (P > 0.05). Osteotomies were performed in 5 of 7 in group 1, 1 of 6 in group 2, and 5 of 14 in group 3. Mean follow-up was 26.3 months. The average intraoperative UIV angle (UIV0) and immediate postoperative UIV angle (UIV1) were 18.6°/15.4° for group 1, 5.7°/5.3° for group 2, and 10.3°/7.1° for group 3 (P < 0.05). Surgical revision rates were higher in group 1 (71%) compared with groups 2 (50%) and 3 (43%). Eight of 11 (73%) patients with upper instrumented vertebra of L1 or L2 had either UIV fracture or other proximal failure compared with 5 of 16 (31%) in patients with upper instrumented vertebra of T10, T11, or T12.

CONCLUSION

Our series of long lumbar fusions had a high long-term complication and revision rate. A high UIV angle on intraoperative lateral radiograph was strongly associated with UIV fractures. UIVs of L1 or L2 had a higher rate of adjacent segment or UIV failure.

Thoracic myelopathy caused by ossification of the yellow ligament in patients with posterior instrumented lumbar fusion

PURPOSE

The objective of this study was to investigate thoracic myelopathy caused by ossification of the yellow ligament (OYL) in patients with posterior instrumented lumbar fusion.

METHODS

Seven patients, who had undergone posterior instrumented lumbar fusion, presented with thoracic myelopathy caused by OYL. No patient had a history of thoracic myelopathy at previous surgery. Instrumented fusions were performed from L1-5 in two patients, L2-5 in three patients and L1-S1 and L2-S1 in one patient each, respectively. MRI and CT scans were performed to confirm cord compression by OYL. Of the seven patients, six patients underwent decompressive laminectomy and OYL removal while one was treated conservatively.

RESULTS

The average time to presentation after first surgery was 63.4 months. OYL was located at T9-10 in two patients, T11-12 in three patients, and T10-11 and T9-11 in one patient each, respectively. All patients had a myelopathic gait and the average Japanese Orthopaedic Association (JOA) score was 3.9, preoperatively. The average JOA score improved from 3.7 to 8 and the average recovery rate was 58.9 % in the six patients who underwent surgical intervention. However, the JOA score fell from 5 to 4 in the one patient who was treated conservatively.

CONCLUSIONS

We report seven patients who suffered from thoracic myelopathy after instrumented lumbar fusion. Surgeons must be aware of the possibility of thoracic myelopathy caused by OYL at the thoracolumbar junction, especially in patients with a complaint of gait disturbance after long instrumented lumbar fusion.

Kinetic magnetic resonance imaging analysis of lumbar segmental mobility in patients without significant spondylosis

PURPOSE

The purpose of this study was to examine lumbar segmental mobility using kinetic magnetic resonance imaging (MRI) in patients with minimal lumbar spondylosis.

METHODS

Mid-sagittal images of patients who underwent weight-bearing, multi-position kinetic MRI for symptomatic low back pain or radiculopathy were reviewed. Only patients with a Pfirrmann grade of I or II, indicating minimal disc disease, in all lumbar discs from L1-2 to L5-S1 were included for further analysis. Translational and angular motion was measured at each motion segment.

RESULTS

The mean translational motion of the lumbar spine at each level was 1.38 mm at L1-L2, 1.41 mm at L2-L3, 1.14 mm at L3-L4, 1.10 mm at L4-L5 and 1.01 mm at L5-S1. Translational motion at L1-L2 and L2-L3 was significantly greater than L3-4, L4-L5 and L5-S1 levels (P < 0.007). The mean angular motion at each level was 7.34° at L1-L2, 8.56° at L2-L3, 8.34° at L3-L4, 8.87° at L4-L5, and 5.87° at L5-S1. The L5-S1 segment had significantly less angular motion when compared to all other levels (P < 0.006). The mean percentage contribution of each level to the total angular mobility of the lumbar spine was highest at L2-L3 (22.45 %) and least at L5/S1 (14.71 %) (P < 0.001).

CONCLUSION

In the current study, we evaluated lumbar segmental mobility in patients without significant degenerative disc disease and found that translational motion was greatest in the proximal lumbar levels whereas angular motion was similar in the mid-lumbar levels but decreased at L1-L2 and L5-S1.

Influence of lumbar intervertebral disc degeneration on the outcome of total lumbar disc replacement: a prospective clinical, histological, X-ray and MRI investigation

INTRODUCTION

The role of fusion of lumbar motion segments for the treatment of axial low back pain (LBP) from lumbar degenerative disc disease (DDD) without any true deformities or instabilities remains controversially debated. In an attempt to avoid previously published and fusion-related negative side effects, motion preserving technologies such as total lumbar disc replacement (TDR) have been introduced. The adequate extent of preoperative DDD for TDR remains unknown, the number of previously published studies is scarce and the limited data available reveal contradictory results. The goal of this current analysis was to perform a prospective histological, X-ray and MRI investigation of the index-segment's degree of DDD and to correlate these data with each patient's pre- and postoperative clinical outcome parameters from an ongoing prospective clinical trial with ProDisc II (Synthes, Paoli, U.S.A.).

MATERIALS AND METHODS

Nucleus pulposus (NP) and annulus fibrosus (AF) changes were evaluated according to a previously validated quantitative histological degeneration score (HDS). X-ray evaluation included assessment of the mean, anterior and posterior disc space height (DSH). MRI investigation of DDD was performed on a 5-scale grading system. The prospective clinical outcome assessment included visual analogue scale (VAS), Oswestry Disability Index (ODI) scores as well as the patient's subjective satisfaction rates.

RESULTS

Data from 51 patients with an average follow-up of 50.5 months (range 6.1-91.9 months) were included in the study. Postoperative VAS and ODI scores improved significantly in comparison to preoperative levels (p < 0.002). A significant correlation and interdependence was established between various parameters of DDD preoperatively (p < 0.05). Degenerative changes of NP tissue samples were significantly more pronounced in comparison to those of AF material (p < 0.001) with no significant correlation between each other (p > 0.05). Preoperatively, the extent of DDD was not significantly correlated with the patient's symptomatology (p > 0.05). No negative influence was associated with increasing stages of DDD on the postoperative clinical outcome parameters following TDR (p > 0.05). Increasing stages of DDD in terms of lower DSH scores were not associated with inferior clinical results as outlined by postoperative VAS or ODI scores or the patient's subjective outcome evaluation at the last FU examination (p > 0.05). Conversely, some potential positive effects on the postoperative outcome were observed in patients with advanced stages of preoperative DDD. Patients with more severe preoperative HDS scores of NP samples demonstrated significantly lower VAS scores during the early postoperative course (p = 0.02).

CONCLUSION

Increasing stages of DDD did not negatively impact on the outcome following TDR in a highly selected patient population. In particular, no preoperative DDD threshold value was identified from which an inferior postoperative outcome could have been deduced. Conversely, some positive effects on the postoperative outcome were detected in patients with advanced stages of DDD. Combined advantageous effects of progressive morphological structural rigidity of the index segment and restabilizing effects from larger distraction in degenerated segments may compensate for increasing axial rotational instability, one of TDR's perceived disadvantages. Our data reveal a "therapeutic window" for TDR in a cohort of patients with various stages of DDD as long as preoperative facet joint complaints or degenerative facet arthropathies can be excluded and stringent preoperative decision making criteria are adhered to. Previously published absolute DSH values as contraindication against TDR should be reconsidered.

Biomechanical comparison of unilateral and bilateral pedicle screws fixation for transforaminal lumbar interbody fusion after decompressive surgery--a finite element analysis

BACKGROUND

Little is known about the biomechanical effectiveness of transforaminal lumbar interbody fusion (TLIF) cages in different positioning and various posterior implants used after decompressive surgery. The use of the various implants will induce the kinematic and mechanical changes in range of motion (ROM) and stresses at the surgical and adjacent segments. Unilateral pedicle screw with or without supplementary facet screw fixation in the minimally invasive TLIF procedure has not been ascertained to provide adequate stability without the need to expose on the contralateral side. This study used finite element (FE) models to investigate biomechanical differences in ROM and stress on the neighboring structures after TLIF cages insertion in conjunction with posterior fixation.

METHODS

A validated finite-element (FE) model of L1-S1 was established to implant three types of cages (TLIF with a single moon-shaped cage in the anterior or middle portion of vertebral bodies, and TLIF with a left diagonally placed ogival-shaped cage) from the left L4-5 level after unilateral decompressive surgery. Further, the effects of unilateral versus bilateral pedicle screw fixation (UPSF vs. BPSF) in each TLIF cage model was compared to analyze parameters, including stresses and ROM on the neighboring annulus, cage-vertebral interface and pedicle screws.

RESULTS

All the TLIF cages positioned with BPSF showed similar ROM (<5%) at surgical and adjacent levels, except TLIF with an anterior cage in flexion (61% lower) and TLIF with a left diagonal cage in left lateral bending (33% lower) at surgical level. On the other hand, the TLIF cage models with left UPSF showed varying changes of ROM and annulus stress in extension, right lateral bending and right axial rotation at surgical level. In particular, the TLIF model with a diagonal cage, UPSF, and contralateral facet screw fixation stabilize segmental motion of the surgical level mostly in extension and contralaterally axial rotation. Prominent stress shielded to the contralateral annulus, cage-vertebral interface, and pedicle screw at surgical level. A supplementary facet screw fixation shared stresses around the neighboring tissues and revealed similar ROM and stress patterns to those models with BPSF.

CONCLUSIONS

TLIF surgery is not favored for asymmetrical positioning of a diagonal cage and UPSF used in contralateral axial rotation or lateral bending. Supplementation of a contralateral facet screw is recommended for the TLIF construct.

Biomechanical assessment of a PEEK rod system for semi-rigid fixation of lumbar fusion constructs

The concept of semi-rigid fixation (SRF) has driven the development of spinal implants that utilize nonmetallic materials and novel rod geometries in an effort to promote fusion via a balance of stability, intra- and inter-level load sharing, and durability. The purpose of this study was to characterize the mechanical and biomechanical properties of a pedicle screw-based polyetheretherketone (PEEK) SRF system for the lumbar spine to compare its kinematic, structural, and durability performance profile against that of traditional lumbar fusion systems. Performance of the SRF system was characterized using a validated spectrum of experimental, computational, and in vitro testing. Finite element models were first used to optimize the size and shape of the polymeric rods and bound their performance parameters. Subsequently, benchtop tests determined the static and dynamic performance threshold of PEEK rods in relevant loading modes (flexion-extension (F/E), axial rotation (AR), and lateral bending (LB)). Numerical analyses evaluated the amount of anteroposterior column load sharing provided by both metallic and PEEK rods. Finally, a cadaveric spine simulator was used to determine the level of stability that PEEK rods provide. Under physiological loading conditions, a 6.35 mm nominal diameter oval PEEK rod construct unloads the bone-screw interface and increases anterior column load (approx. 75% anterior, 25% posterior) when compared to titanium (Ti) rod constructs. The PEEK construct's stiffness demonstrated a value lower than that of all the metallic rod systems, regardless of diameter or metallic composition (78% < 5.5 mm Ti; 66% < 4.5 mm Ti; 38% < 3.6 mm Ti). The endurance limit of the PEEK construct was comparable to that of clinically successful metallic rod systems (135N at 5 × 10(6) cycles). Compared to the intact state, cadaveric spines implanted with PEEK constructs demonstrated a significant reduction of range of motion in all three loading directions (> 80% reduction in F/E, p < 0.001; > 70% reduction in LB, p < 0.001; > 54% reduction in AR, p < 0.001). There was no statistically significant difference in the stability provided by the PEEK rods and titanium rods in any mode (p = 0.769 for F/E; p = 0.085 for LB; p = 0.633 for AR). The CD HORIZON(®) LEGACY(™) PEEK Rod System provided intervertebral stability comparable to currently marketed titanium lumbar fusion constructs. PEEK rods also more closely approximated the physiologic anteroposterior column load sharing compared to results with titanium rods. The durability, stability, strength, and biomechanical profile of PEEK rods were demonstrated and the potential advantages of SRF were highlighted.

Quantitative MRI analysis of the surface area, signal intensity and MRI index of the central bright area for the evaluation of early adjacent disc degeneration after lumbar fusion

PURPOSE

The aim of this study was to evaluate early ASD at short-term follow-up in fused and unoperated patients with degenerative disc disease, using quantitative magnetic resonance imaging (MRI) analysis of the area, signal intensity and their product, i.e., MRI index of the central bright area of the disc as well as measures of intervertebral disc height and Pfirrmann grading scale. The further purpose was to determine whether fusion accelerates ASD compared with non-surgical treatment in short-term follow-up.

METHODS

One hundred and eight chronic low back patients diagnosed as L4/L5 degeneration undertook either one-level instrumented posterior lumbar interbody fusion or conservative treatment. They were followed up for about 1 year. Finally 46 fused and 45 conservatively treated patients with MRI follow-up were included. Pre- and post-treatment MRIs were compared to determine the progression of disc degeneration at the two cranial adjacent segments.

RESULTS

The area, signal intensity and MRI index of the central bright area of the adjacent discs decreased in the operated and unoperated groups from pre-treatment to follow-up, except for an insignificant decrease of signal intensity at the second adjacent segment in the unoperated group. The changes in these parameters were statistically greater at the first than the second adjacent segment in the fused group, but not in the unoperated group. And the changes in the fused group were more pronounced than those at both neighbouring levels in the unoperated group. However, the Pfirrmann grading scale and intervertebral disc height did not detect any changes at adjacent discs in either group.

CONCLUSIONS

Decrease in the parameters of quantitative MRI analysis indicated early degeneration at discs adjacent to lumbar spinal fusion. Fusion had an independent effect on the natural history of ASD during short-term follow-up. Continued longitudinal follow-up is required to determine whether these MRI changes lead to pathologic changes.

Clinical outcome of lumbar total disc replacement using ProDisc-L in degenerative disc disease: minimum 5-year follow-up results at a single institute

STUDY DESIGN

A retrospective clinical data analysis.

OBJECTIVE

To determine the therapeutic effectiveness of lumbar total disc replacement (TDR) using ProDisc-L (Synthes Spine, West Chester, PA) in the patients with degenerative disc diseases (DDD) with a minimum follow-up of 5 years.

SUMMARY OF BACKGROUND DATA

Early successful clinical results of lumbar TDR have been reported. However, few reports have published its therapeutic effectiveness in the long term.

METHODS

The patients were examined preoperatively and at 3 months, 1 year, 2 years, and more than 5 years postoperatively, and assessed using visual analog scale (VAS), Oswestry disability index (ODI), physical health component summary (PCS) of the 36-Item Short Form Health Survey questionnaire, and sporting activity scale scores. At last follow-up visits, two additional questions were asked: satisfaction with surgery and willingness to undergo the same treatment. Finally, clinical success was assessed using the Food and Drug Administration definition.

RESULTS

Thirty-five patients were included in the study. The mean follow-up period was 72 months (6 years). Postoperatively, all outcome measure scores (VAS, mean ODI, PCS, and sports activity scores) immediately improved and these improvements were maintained at last follow-up visits with statistical significance. However, outcome score improvements were observed to be slightly, though significantly, lower at last follow-up visits than at 1 or 2 years postoperatively. Eighty-eight percent of patients were "satisfied" or "somewhat satisfied" with treatment and 60% were prepared to undergo the same treatment again. Twenty-five patients (71.4%) achieved clinical success.

CONCLUSION

This study reveals that lumbar TDR using ProDisc-L is a safe and effective treatment for chronic back pain caused by lumbar DDD as assessed at more than 5 years postoperatively. Nevertheless, outcome scores were slightly, though significantly lower at last follow-up visits than at 1 and 2 years postoperatively. A longer-term follow-up study is warranted.

Quantification of intradiscal pressures below thoracolumbar spinal fusion constructs: is there evidence to support "saving a level"?

STUDY DESIGN

In vitro cadaveric study.

OBJECTIVE

The purpose of this study was to quantify the relative biomechanical protection resulting from "saving a level" in long spinal fusions.

SUMMARY OF BACKGROUND DATA

"Saving levels" in spinal deformity surgery is desirable. Constructs with lowest instrumented vertebra (LIV) in the lumbar spine may increase loads on unfused lumbar intervertebral discs, leading to accelerated disc degeneration. No study to date has quantified the relative pressure changes that occur in the unfused caudal discs with progressively longer fusions.

METHODS

We used a validated in vitro cadaveric long fusion model to assess intradiscal pressures (IDPs) below simulated fusions. Eight fresh frozen T8-S1 specimens were instrumented from T8 to L5. A follower-type loading system and 7.5-N·m moments were applied in flexion and extension. IDP profiles were assessed with a pressure transducer. After acquiring IDP measurements at a given construct length, the rod was cut 1 level higher until LIV = T12. IDP data from each unfused disc were averaged and normalized to the mean value of the disc when immediately subjacent to the LIV.

RESULTS

In both flexion and extension, the mean normalized IDP of the unfused discs below the LIV increased with increasing fusion length. For each 1-level increase in construct length, pressure increased by 3.2% ± 4.8% in flexion and 4.3% ± 4.5% in extension for each unfused disc. Although the differences in pressure for a given unfused disc with differing LIV were not significant, there were significant differences between unfused discs at a given LIV. With shorter fusion lengths, pressure in the disc immediately subjacent to the fusion was consistently greater than for the caudal-most discs.

CONCLUSION

Unfused caudal lumbar discs experienced increased IDPs with increasing length of instrumentation, most notably at the subjacent discs closest to the LIV.

[Dynamic instrumentation of the lumbar spine. Clinical and biomechanical analysis of success factors]

Total disc replacement and posterior dynamic stabilization represent alternatives to lumbar spinal fusion which should reduce the risk of adjacent segment degeneration. Disc replacement is indicated for pure discopathy without facet joint degeneration. Spinopelvic balance influences the implant's biomechanics. Therefore pelvic incidence, sacral slope, segmental lordosis and the mean axis of rotation need to be considered. Dynamic stabilization is indicated in moderate discopathy and facet joint degeneration, in degenerative spondylolisthesis grade I with a hypermobile segment and in dynamic lumbar stenosis. The combination of caudal fusion and cranial dynamic stabilization allows a better maintenance of lordosis with multiple level instrumentation and prevents adjacent segment degeneration. If pelvic incidence and sacral slope are high, L5-S1 should be fused because of elevated shear forces.

[Importance of sagittal alignment in spinal revision surgery]

Ignoring the sagittal profile in primary spinal fusion surgery is a common reason for revision surgery. Therefore, it is important that in cases of spinal revision surgery the sagittal alignment is realized. The physiological alignment of the instrumented spine should also indirectly influence the profile of the non-stabilized spine cranial and caudal to the fusion. Patients with normal C7 plumb-line and a physiological sacral inclination have a lower incidence of adjacent segment degeneration. Sagittal imbalance after revision surgery is a risk factor for recurrent pseudarthrosis. In cases of pseudarthrosis a combined approach may be more effective in realizing sagittal balance und enhancing rates of fusion.

The influence of different magnitudes and methods of applying preload on fusion and disc replacement constructs in the lumbar spine: a finite element analysis

In a finite element (FE) analysis of the lumbar spine, different preload application methods that are used in biomechanical studies may yield diverging results. To investigate how the biomechanical behaviour of a spinal implant is affected by the method of applying the preload, hybrid-controlled FE analysis was used to evaluate the biomechanical behaviour of the lumbar spine under different preload application methods. The FE models of anterior lumbar interbody fusion (ALIF) and artificial disc replacement (ADR) were tested under three different loading conditions: a 150 N pressure preload (PP) and 150 and 400 N follower loads (FLs). This study analysed the resulting range of motion (ROM), facet contact force (FCF), inlay contact pressure (ICP) and stress distribution of adjacent discs. The FE results indicated that the ROM of both surgical constructs was related to the preload application method and magnitude; differences in the ROM were within 7% for the ALIF model and 32% for the ADR model. Following the application of the FL and after increasing the FL magnitude, the FCF of the ADR model gradually increased, reaching 45% at the implanted level in torsion. The maximum ICP gradually decreased by 34.1% in torsion and 28.4% in lateral bending. This study concluded that the preload magnitude and application method affect the biomechanical behaviour of the lumbar spine. For the ADR, remarkable alteration was observed while increasing the FL magnitude, particularly in the ROM, FCF and ICP. However, for the ALIF, PP and FL methods had no remarkable alteration in terms of ROM and adjacent disc stress.

Management of adjacent segment disease after cervical spinal fusion

Adjacent segment disease (ASD) was described after long-term follow-up of patients treated with cervical fusion. The term describes new-onset radiculopathy or myelopathy referable to a motion segment adjacent to previous arthrodesis and often attributed to alterations in the biomechanical environment after fusion. Evidence suggests that ASD affects between 2% and 3% of patients per year. Although prevention of ASD was one major impetus behind the development of motion-sparing surgery, the literature does not yet clearly distinguish a difference in the rate of ASD between fusion and disk replacement. Surgical techniques during index surgery may reduce the rate of ASD.

Clinical results of lumbar total disc arthroplasty in accordance with Modic signs, with a 2-year-minimum follow-up

STUDY DESIGN

Prospective study.

OBJECTIVE

The aim of this prospective study is to analyze the influence of Modic type on the clinical results of lumbar total disc arthroplasty.

SUMMARY OF BACKGROUND DATA

Some patients with lumbar disc degeneration have endplate signal changes on magnetic resonance images, which have been classified by Modic. Modic-1 endplates changes are associated with an inflammatory phase of the disease whereas Modic-2 endplates changes correspond to a quiescent phase with a fatty replacement. The effect of Modic endplate changes on the clinical results of lumbar fusion has been studied by multiple authors, but the influence of Modic type on clinical outcomes of lumbar disc replacement is not known.

METHODS

A total of 221 patients with a mean age of 42 years were included in this study. Of which, 107 patients were classified Modic 0, 65 Modic 1, and 49 Modic 2. Clinical evaluation (Oswestry Disability Index [ODI], lumbar and radicular pain using the Visual Analog Score [VAS]) was performed preoperatively and at 3, 6, 12, and 24 months minimum postoperatively.

RESULTS

Mean follow-up was 30 months (24-72 months). Significant clinical improvement (P < 0.05) was observed in pain and ODI between the preoperative evaluation and final follow-up. Multivariate analysis between the 3 groups demonstrated a significant difference in Oswestry Disability Index (size of the effect was measured at -0.3 [-0.55-0.04]) and on the radicular pain (size of the effect was measured at -0.4 [-0.7-0.1]), with lower scores in the group classified Modic 1.

CONCLUSION

Superior results were achieved in the group of patients with Modic-1 endplate changes on magnetic resonance images. These data may be helpful in patient selection and in preoperative patient counseling.

Pedicle-screw-based dynamic implants may increase posterior intervertebral disc bulging during flexion

Abstract Posterior disc bulging may lead to nerve root compression and radicular pain, and in extreme cases to a local pressure on the dural sac and thus to back pain. Compared to when standing, posterior disc bulging is increased during extension and decreased during flexion, in an uninstrumented spine. The aim of this study was to determine the effect of a pedicle-screw-based dynamic implant on posterior disc bulging. A finite element model of the lumbosacral spine was used to calculate posterior disc bulging before and after implantation of a dynamic implant for different loading cases. The elastic modulus of the longitudinal rod was varied, and the influence of distraction of the bridged segment on disc bulging was also determined. In addition, the centre of rotation (CoR) was determined. Due to a dynamic implant, the magnitude of posterior disc bulging was reduced compared to that for "standing without an implant" during extension, lateral bending, and axial rotation. During flexion, however, disc bulging was usually increased. With increasing stiffness of the dynamic implant, the CoR moved towards the longitudinal rod. This posterior shift of the CoR led to a compression of the entire intervertebral disc during flexion and thus to an increase of disc bulging.

STABILIZATION EFFECTS OF GRAF LIGAMENTOPLASTY

Graf ligamentoplasty with or without decompression was performed consecutively in 22 patients of lumbar degenerative diseases with segmental instability. The clinical course of the patients was evaluated using the criteria of the Japanese Orthopaedic Association (JOA) for assessing treatment of low back pain (29 points in total), and radiological alteration in angular and translational displacements were measured in flexion, extension, or neutral position. The change of an intervertebral vacuum phenomenon (Knutsson's sign), as a sign of segmental instability, was observed before and after the surgery.

A preoperative JOA score of 13.7 points was significantly improved to 25.0 points with an improvement rate of 75.7% on average by Graf ligamentoplasty. Radiological measurements revealed that the operation reduced the range of motion of the involved segment in both angular and translational modes with the segment realigned in extension. The short-term results of Graf ligamentoplasty was acceptable for lumbar degenerative diseases. The patients in whom Knutsson's sign was reduced or disappeared after Graf ligamentoplasty had a better outcome than those with the sign unchanged or increased in size. This suggests that Knutsson's sign can be a predictive indicator of the outcome of the surgery.

Mid-range outcomes in 64 consecutive cases of multilevel fusion for degenerative diseases of the lumbar spine

In the treatment of multilevel degenerative disorders of the lumbar spine, spondylodesis plays a controversial role. Most patients can be treated conservatively with success. Multilevel lumbar fusion with instrumentation is associated with severe complications like failed back surgery syndrome, implant failure, and adjacent segment disease (ASD). This retrospective study examines the records of 70 elderly patients with degenerative changes or instability of the lumbar spine treated between 2002 and 2007 with spondylodesis of more than two segments. Sixty-four patients were included; 5 patients had died and one patient was lost to follow-up. We evaluated complications, clinical/radiological outcomes, and success of fusion. Flexion-extension and standing X-rays in two planes, MRI, and/or CT scans were obtained pre-operatively. Patients were assessed clinically using the Oswestry disability index (ODI) and a Visual Analogue Scale (VAS). Surgery performed was dorsolateral fusion (46.9%) or dorsal fusion with anterior lumbar interbody fusion (ALIF; 53.1%). Additional decompression was carried out in 37.5% of patients. Mean follow-up was 29.4±5.4 months. Average patient age was 64.7±4.3 years. Clinical outcomes were not satisfactory for all patients. VAS scores improved from 8.6±1.3 to 5.6±3.0 pre- to post-operatively, without statistical significance. ODI was also not significantly improved (56.1±22.3 pre- and 45.1±26.4 post-operatively). Successful fusion, defined as adequate bone mass with trabeculation at the facets and transverse processes or in the intervertebral segments, did not correlate with good clinical outcomes. Thirty-five of 64 patients (54%) showed signs of pedicle screw loosening, especially of the screws at S1. However, only 7 of these 35 (20%) complained of corresponding back pain. Revision surgery was required in 24 of 64 patients (38%). Of these, indications were adjacent segment disease (16 cases), pedicle screw loosening (7 cases), and infection (one case). At follow-up of 29.4 months, patients with radiographic ASD had worse ODI scores than patients without (54.7 vs. 36.6; P<0.001). Multilevel fusion for degenerative disease still has a high rate of complications, up to 50%. The problem of adjacent segment disease after fusion surgery has not yet been solved. This study underscores the need for strict indication guidelines to perform lumbar spine fusion of more than two levels.

Long-term magnetic resonance imaging follow-up demonstrates minimal transitional level lumbar disc degeneration after posterior spine fusion for adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To describe long-term clinical and imaging results focusing on the uninstrumented lumbar spine after posterior spinal fusion for adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Although previous studies found rates of low back pain after long fusion for adolescent idiopathic scoliosis which are comparable to rates found in the general population, many surgeons believe that the long lever arm associated with the fusion mass will result in increased stress at uninstrumented caudal intervertebral discs and accelerated degenerative changes.

METHODS

This is a retrospective chart and imaging review of adolescent idiopathic scoliosis patients treated with posterior fusion and segmental instrumentation. Patients completed follow-up examination, outcome questionnaires, radiographs, and magnetic resonance (MR) imaging. MR images were scored for evidence of degeneration of lumbar discs below the level of the fusion.

RESULTS

Twenty patients participated in the study, providing 90 discs below fusions for evaluation. The average follow-up was 11.8 years. The distal level of fixation was at L1 on average. The major curve averaged 55° ± 11° before surgery and was corrected to 25° ± 10° at follow-up. Follow-up MR imaging demonstrated new disc pathology in 85% of patients enrolled. Only one patient demonstrated significant degenerative disc disease at the junctional level, whereas most pathology was seen at the L5-S1 disc. The average Pfirrmann grade at uninstrumented levels deteriorated from 1.1 before surgery to 1.8 at follow-up. The greatest degree of degeneration was seen at the L5-S1 disc space where average degenerative scores increased from 1.2 before surgery to 2.3 after surgery. Three patients with severe disc disease were taking nonsteroidal anti-inflammatory drugs for pain, but no narcotics. Only mild scoliosis research society (SRS) and Oswestry changes were noted in this severe degeneration group.

CONCLUSION

Despite demonstrating an accelerated rate of L5-S1 disc degeneration, our study group has good functional scores and maintenance of correction over 10 years postfusion. In this long-term MR imaging follow-up study, disc degeneration was found remote to the lowest instrumented vertebra.

Wallis interspinous implantation to treat degenerative spinal disease: description of the method and case series

The Wallis interspinous implant is most commonly used in the treatment of intervertebral disc herniation and for tears in the outer layer of the disc. The dynamic vertebral fixation concept was first initiated in 1984 with the goal of imitating the physiologic spinal kinetic. A total of 15 years later, a second generation of implant has been developed, termed the 'Wallis interspinous Implant', which aims to preserve the mobility of the operated spinal segment. To underline our own experience, a retrospective review of 15 patients that were treated with 'Wallis implantation' at our institution between January 2006 and March 2008. Our main inclusion criterion for Wallis implantation was low back pain because of degenerative lumbar spinal stenosis associated with segmental instability along with Modic changes 0-1 and with UCLA arthritic grade <II, while the main exclusion criteria were previous lumbar surgery, severe osteoporosis or degeneration UCLA grade >II in the adjacent two segments cephalad to implantation. The outcome was analyzed according to clinical and radiological parameters. One (n = 9), two (n = 4) and three levels (n = 2) were operated on using Wallis implantation, ranging from L2-L3 to L5-S1. We used implants of 8-14 mm in size. There was a reduction in low back pain (73 vs 43%) and gait disturbances (73 vs 14%) at the 3-month follow-up compared with preoperative values. In line with these results, the modified Japan Orthopedic Association Score (mJAOS) was increased from 12 preoperatively to 18 at 3 months and 20 at 12 months postoperatively. A reduction in low back pain could only be demonstrated for implants that were 10 mm in size or greater at 3 months and 12-15 months postoperatively. An improvement was seen in Modic grades after the operations as compared with those observed at preoperative MRI. The outcome in our patients was rated as good or excellent according to Odom's criteria in all cases, independent of the levels that were used. Wallis implantation is therefore a safe procedure with a good to excellent outcome in the short- and mid-term follow-up and can lead to disc rehydration, as confirmed by postoperative MRI. Principal postoperative (clinical) success is based on the correct implant size.

Prosthetic total disk replacement--can we learn from total hip replacement?

Total lumbar disk replacement has become a routine procedure in many countries. However, discussions regarding its use are ongoing. Issues focus on patient selection, technical limitations, and avoidance or management of complications or long-term outcomes. A review of the development of this technology, since the development of the first successful implantation of a total lumbar disk prosthesis in 1984, shows an amazing analogy to the history of total hip replacement. This article is a one-to-one comparison of the evolution of total hip and total lumbar disk replacement from "skunk works" to scientific evidence.

Surgical outcomes of degenerative spondylolisthesis with L5-S1 disc degeneration: comparison between lumbar floating fusion and lumbosacral fusion at a minimum 5-year follow-up

STUDY DESIGN

A retrospective clinical and radiographic study was performed.

OBJECTIVE

The purpose of this study was to compare outcomes of patients with degenerative spondylolisthesis and a preexisting degenerative L5-S1 disc treated with a lumbar floating fusion (LFF) versus lumbosacral fusion (LSF).

SUMMARY OF BACKGROUND DATA

Fusion for treatment of degenerative spondylolisthesis often ends at the L5 level. These patients usually had a preexisting L5-S1 disc degeneration; however, no literature mentions the role of prophylactic LSF in degenerative spondylolisthesis associated with L5-S1 disc degeneration.

METHODS

A total of 107 patients with a minimum 5-year follow-up who had lumbosacral or LFF with pedicle instrumentation for degenerative spondylolisthesis were included. UCLA (University of California, Los Angeles) classification was used to evaluate the radiographic results of the L5-S1 segment. The Oswestry Disability Index (ODI) and modified Brodsky's criteria were used to evaluate patients' clinical results. The incidence of adjacent segment disease (ASD) (includes radiographic and clinical ASD) of both ends was recorded.

RESULTS

There were no statistically significant differences in sex, age distribution, or amount of follow-up between the LFF and LSF groups. The LSF group had a higher percentage of patients that underwent total L5 laminectomy with loss of L5-S1 posterior ligament integrity (LSF = 92% vs. LFF = 67%, P = 0.019). The higher incidence of cephalic ASD in the LSF group was statistically significant (LSF = 25% vs. LFF = 9.7%, P = 0.049). Although no patient in the LSF group developed L5-S1 ASD, need for L5-S1 segment revision surgery was not prevented with LSF. Clinical outcomes on the basis of the success rate (LFF = 85.5% vs.LSF = 70.8%, P = 0.103) and ODI difference (LFF = 28.97 ± 15.82 vs. LSF = 23.04 ± 10.97, P = 0.109), there were no statistically significant difference between these two groups.

CONCLUSION

Posterior instrumentation with posterolateral LFF for the treatment of degenerative spondylolisthesis with concomitant L5-S1 disc degeneration results in a high percentage of satisfactory clinical results. Extended fusion to the sacrum did not provide a better clinical result. LSF could not reduce the incidence of revision surgery at the L5-S1 segment and involved greater incidence of cephalic ASD.

Effects of nonlinearity in the materials used for the semi-rigid pedicle screw systems on biomechanical behaviors of the lumbar spine after surgery

Recently, various types of semi-rigid pedicle screw fixation systems have been developed for the surgical treatment of the lumbar spine. They were introduced to address the adverse issues commonly found in traditional rigid spinal fusion--abnormally large motion at the adjacent level and subsequent degeneration. The semi-rigid system uses more compliant materials (nitinol or polymers) and/or changes in rod design (coiled or twisted rods) as compared to the conventional rigid straight rods made of Ti alloys (E = 114 GPa, υ = 0.32). However, biomechanical studies on the semi-rigid pedicle screw systems were usually limited to linear modeling of the implant and anatomic elements, which may not be capable of reflecting realistic post-operative motions of the spine. In this study, we evaluated the effects of nonlinearity in materials used for semi-rigid pedicle screw fixation systems to evaluate the changes in biomechanical behaviors using finite element analysis. Changes in range of motion (ROM) and center of rotation (COR) were assessed at the operated and adjacent levels. Actual load-displacement results of the semi-rigid rod from mechanical test were carried out to reflect the nonlinearity of the implant. In addition, nonlinear material properties of various spinal ligaments studies were used for the finite element modeling. The post-operative models were constructed by modifying the previously validated intact model of the L1-S1 spine. Eight different post-operative models were made to address the effects of nonlinearity-with a traditional stiffness modulus rod (with linear ligaments, case 1; with nonlinear ligaments, case 5), with a rigid rod (with linear ligaments, case 2; with nonlinear ligaments, case 6), with a soft rod (with linear ligaments, case 3; with nonlinear ligaments, case 7), and with a nonlinear rod (with linear ligaments, case 4; with nonlinear ligaments, case 8). To simulate the load on the lumbar spine in a neutral posture, follower load (400 N) was applied and then the hybrid loading condition was applied to measure the ROM and COR in the sagittal plane. The more the nonlinearity was included in the model the closer the motion behavior of the device was to that of the intact spine. Furthermore, our results showed that the nonlinearity of the semi-rigid rod was a more sensitive factor than the nonlinearity of the spinal ligaments on biomechanical behavior of the lumbar spine after surgery. Therefore, for better understanding of the surgical effectiveness of the spinal device, more realistic material properties such as nonlinearity of the device and anatomic elements should be considered. In particular, the nonlinear properties of the semi-rigid rod were considered more than the nonlinearity of spinal ligaments.

The quantitative assessment of risk factors to overstress at adjacent segments after lumbar fusion: removal of posterior ligaments and pedicle screws

STUDY DESIGN

Finite element method.

OBJECTIVE

To investigate the changes in the disc stress and range of motion (ROM) at adjacent segments after lumbar fusion based on whether or not pedicle screws are removed and whether or not the continuity of the proximal posterior ligament complex (PLC) is preserved.

SUMMARY OF BACKGROUND DATA

The ablation of proximal PLC continuity and the presence of pedicle screws have been reported to affect the biomechanics at adjacent segments after lumbar fusion. However, there have been few studies regarding the quantitative assessment of their contribution to overstress at adjacent segments after lumbar fusion.

METHODS

In the validated intact lumbar finite element model (L2-L5), four types of L3-L4 fusion models were simulated. These models included the preservation of the PLC continuity with pedicle screws (Pp WiP), the preservation of PLC continuity without pedicle screws (Pp WoP), the sacrifice of PLC with pedicle screws (Sp WiP), and the sacrifice of PLC without pedicle screws (Sp WoP). In each scenario, the ROM, maximal von Mises stress of discs, and the facet joint contract force at adjacent segments were analyzed. RESULTS.: Among the four models, the Sp WiP yielded the greatest increase in the ROM and the maximal von Mises stress of the disc at adjacent segments under four moments. Following the SP WiP, the order of increase of the ROM and the disc stress was Pp WiP, Sp WoP, and Pp WoP. Furthermore, the increase of ROM and disc stress at the proximal adjacent segment was more than at the distal adjacent segment under all four moments in each model. The facet joint contact was also most increased in the Sp WiP under extension and torsion moment.

CONCLUSION

The current study suggests that the preservation of the PLC continuity or the removal of pedicle screws after complete fusion could decrease the stress at adjacent segments, and their combination could act synergistically.

Models that incorporate spinal structures predict better wear performance of cervical artificial discs

BACKGROUND CONTEXT

Wear simulators and their corresponding wear predictive models provide limited information on wear characteristics of artificial discs. Analyses in previous studies that controlled loading profiles according to International Standards Organization (ISO)/American Society for Testing and Materials standards did not account for factors such as the influence of anatomic structures. Retrieval analyses reveal failure modes that are not observed in benchtop simulations and thus indicate deficiencies associated with existing approaches.

PURPOSE

To understand the impact of the adjoining spinal structures of a ligamentous segment on the wear of an artificial cervical disc.

STUDY DESIGN

Prediction of wear in artificial disc implants (total disc replacement [TDR]) in situ using finite element modeling.

METHODS

A novel predictive finite element model was used to evaluate wear in a simulated functional spinal unit (FSU). A predictive finite element wear model of the disc alone (TDR Only) was developed, along the lines of that proposed in the literature. This model was then incorporated into a ligamentous C5-C6 finite element model (TDR+FSU). Both of these models were subjected to a motion profile (rotation about three axes) with varying preloads of 50 to150 N at 1 Hz, consistent with ISO 18192. A subroutine based on Archard law simulated abrasive wear on the polymeric core up to 10 million cycles. The TDR+FSU model was further modified to simulate facetectomy, sequential addition of ligaments, and compressive load; simulations were repeated for 10 million cycles.

RESULTS

The predicted wear patterns in the isolated disc (TDR Only) and in TDR+FSU were completely inconsistent. The TDR+FSU model predicted localized wear in certain regions, in contrast to the uniformly distributed wear pattern of the TDR-only model. In addition, the cumulative volumetric wear for the TDR-only model was 10 times that of the TDR+FSU model. The TDR+FSU model also revealed a separation at the articulating interface during extension and lateral bending. After facetectomy, the wear pattern remained lopsided, but linear wear increased eightfold, whereas volumetric wear almost tripled. This was accompanied by a reduction in observed liftoff. The addition of anterior longitudinal ligament/posterior longitudinal ligament did not affect volumetric or linear wear. On the removal of all ligaments and facet forces, and replacement of follower load with a compressive load, the wear pattern returned to an approximation of the TDR-only test case, whereas the cumulative volumetric wear became nearly equivalent. In this case, the liftoff phenomenon was absent.

CONCLUSIONS

Anatomic structures and follower load mitigate the wear of an artificial disc. The proposed model (TDR+FSU) would enable further study of the effects of clinical parameters (eg, surgical variables, different loading profiles, different disc designs, and bone quality) on wear in these implants.

Adjacent segment degeneration after instrumented posterolateral lumbar fusion: a prospective cohort study with a minimum five-year follow-up

PURPOSE

To (1) clarify the role of various risk factors in the development of ASD, (2) compare instrumentation configuration with the development of ASD, (3) correlate the radiological incidence of ASD and its clinical outcome and (4) compare the clinical outcome between patients with radiological evidence of ASD and without ASD.

METHODS

This study prospectively examined 74 consecutive patients who underwent instrumented lumbar/lumbosacral fusion for degenerative disease with a minimum follow-up of 5 years. Among the patients, 68 were enrolled in the study. All of the patients had undergone preoperative radiological assessment and postoperative radiological assessment at regular intervals. The onset and progression of ASD changes were evaluated. The patients were divided in two groups: patients with radiographic evidence of ASD (group 1) and patients without ASD changes (group 2). Comprehensive analysis of various risk factors between group 1 and group 2 patients was performed. The Visual Analog Scale (VAS) was used to evaluate the clinical outcome and the functional outcome was evaluated using the Oswestry Disability Index (ODI) before and after surgery along with radiological assessment.

RESULTS

Radiographic ASD occurred in 20.6% (14/68) of patients. Preoperative disc degeneration at an adjacent segment was a significant risk factor for ASD. Other risk factors such as the age of a patient at the time of surgery, gender, preoperative diagnosis, length of fusion, instrumentation configuration, sagittal alignment and lumbar or lumbosacral fusion were not significant risk factors for the development of ASD. There was no correlation between ASD and its clinical outcome as determined at the final follow-up session. In addition, clinical outcome of patients with ASD and without ASD were not comparable.

CONCLUSIONS

Patients with preoperative disc degeneration at an adjacent segment were more at risk for the development of ASD. Other risk factors including instrumentation configuration were not significantly associated with ASD. There was no correlation between both the radiological development of ASD and its clinical outcome and the clinical outcome of patients with and without ASD.

Thermosensitive chitosan-gelatin-glycerol phosphate hydrogel as a controlled release system of ferulic acid for nucleus pulposus regeneration

In the degenerative disc, overproduction of reactive oxygen species (ROS) involves in apoptosis and senescence of nucleus pulposus (NP) cells that could accelerate the degenerative process. Ferulic acid (FA) has been reported to have an excellent antioxidant property. In the study, injectable thermosensitive chitosan/gelatin/glycerol phosphate (C/G/GP) hydrogel was applied as a controlled release system for FA delivery. The study was aimed to evaluate possible therapeutic effects of FA-incorporated C/G/GP hydrogel on hydrogen peroxide (H(2)O(2))-induced oxidative stress NP cells. The results showed that the release of FA from C/G/GP hydrogel could decrease the H(2)O(2)-induced oxidative stress. Post-treatment of FA-incorporated C/G/GP hydrogel on H(2)O(2)-induced oxidative stress NP cells showed up-regulation of Aggrecan and type II collagen and down-regulation of MMP-3 in mRNA level. The results of sulfated-glycosaminoglycans (GAGs) to DNA ratio and alcian blue staining revealed that the GAGs production of H(2)O(2)-induced oxidative stress NP cells could reach to normal level. The results of caspase-3 activity and TUNEL staining indicated that FA-incorporated C/G/GP hydrogel decreased the apoptosis of H(2)O(2)-induced oxidative stress NP cells. The results suggested that the C/G/GP hydrogel was very suitable for sustained delivery of FA. The FA-incorporated C/G/GP hydrogel would be used to treat the degenerative disc in the early stage before it developed into the latter irreversible stages.

How does lumbar degenerative disc disease affect the disc deformation at the cephalic levels in vivo?

STUDY DESIGN

Case-control study.

OBJECTIVE

To evaluate the effect of lumbar degenerative disc disease (DDD) on the disc deformation at the adjacent level and at the level one above the adjacent level during end ranges of lumbar motion.

SUMMARY OF BACKGROUND DATA

It has been reported that in patients with DDD, the intervertebral discs adjacent to the diseased levels have a greater tendency to degenerate. Although altered biomechanics have been suggested to be the causative factors, few data have been reported on the deformation characteristics of the adjacent discs in patients with DDD.

METHODS

Ten symptomatic patients with discogenic low back pain between L4 and S1 and with healthy discs at the cephalic segments were involved. Eight healthy subjects recruited in our previous studies were used as a reference comparison. The In Vivo kinematics of L3-L4 (the cephalic adjacent level to the degenerated discs) and L2-L3 (the level one above the adjacent level) lumbar discs of both groups were obtained using a combined magnetic resonance imaging and dual fluoroscopic imaging technique at functional postures. Deformation characteristics, in terms of areas of minimal deformation (defined as less than 5%), deformations at the center of the discs, and maximum tensile and shear deformations, were compared between the two groups at the two disc levels.

RESULTS

In the patients with DDD, there were significantly smaller areas of minimal disc deformation at L3-L4 and L2-L3 than the healthy subjects (18% compared with 45% of the total disc area, on average). Both L2-L3 and L3-L4 discs underwent larger tensile and shear deformations in all postures than the healthy subjects. The maximum tensile deformations were higher by up to 23% (of the local disc height in standing) and the maximum shear deformations were higher by approximately 25% to 40% (of the local disc height in standing) compared with those of the healthy subjects.

CONCLUSION

Both the discs of the adjacent level and the level one above experienced higher tensile and shear deformations during end ranges of lumbar motion in the patients with DDD before surgical treatments when compared with the healthy subjects. The larger disc deformations at the cephalic segments were otherwise not detectable using conventional magnetic resonance imaging techniques. Future studies should investigate the effect of surgical treatments, such as fusion or disc replacement, on the biomechanics of the adjacent segments during end ranges of lumbar motion.

Genipin-crosslinked fibrin hydrogels as a potential adhesive to augment intervertebral disc annulus repair

Treatment of damaged intervertebral discs is a significant clinical problem and, despite advances in the repair and replacement of the nucleus pulposus, there are few effective strategies to restore defects in the annulus fibrosus. An annular repair material should meet three specifications: have a modulus similar to the native annulus tissue, support the growth of disc cells, and maintain adhesion to tissue under physiological strain levels. We hypothesized that a genipin crosslinked fibrin gel could meet these requirements. Our mechanical results showed that genipin crosslinked fibrin gels could be created with a modulus in the range of native annular tissue. We also demonstrated that this material is compatible with the in vitro growth of human disc cells, when genipin:fibrin ratios were 0.25:1 or less, although cell proliferation was slower and cell morphology more rounded than for fibrin alone. Finally, lap tests were performed to evaluate adhesion between fibrin gels and pieces of annular tissue. Specimens created without genipin had poor handling properties and readily delaminated, while genipin crosslinked fibrin gels remained adhered to the tissue pieces at strains exceeding physiological levels and failed at 15-30%. This study demonstrated that genipin crosslinked fibrin gels show promise as a gap-filling adhesive biomaterial with tunable material properties, yet the slow cell proliferation suggests this biomaterial may be best suited as a sealant for small annulus fibrosus defects or as an adhesive to augment large annulus repairs. Future studies will evaluate degradation rate, fatigue behaviors, and long-term biocompatibility.

Nucleus disc arthroplasty with the NUBAC™ device: 2-year clinical experience

Low back pain (LBP) due to degenerative disc disease (DDD) is a common condition that can be treated along a continuum of care: from conservative therapies to several surgical choices. Nucleus arthroplasty is an emerging technology that could potentially fill part of the gap in the spine continuum of care. The introduction of recent technologies that allow the replacement of the degenerated disc nucleus using prosthetic devices may be considered an additional therapeutic tool that can be used by the surgeon in selected cases of LBP due to DDD. Nucleus arthroplasties are designed to treat early stages of DDD, which are one of the most common spinal disorders in the population under 65 years of age. NUBAC™ is the first articulating nucleus disc prosthesis, designed to optimally respect the lumbar anatomy, kinematics, and biomechanics, constructed in unique two-piece manufactured from polyetheretherketone (PEEK) with an inner ball/socket articulation. The optimal indications for NUBAC™ implantation are: disc height >5 mm, degenerative disc changes at an early stage (Pfirmann 2, 3), single level affection, integrity of posterior facet joints, lack of local anatomical contraindication, failure of conservative treatment for at least 6 months. From December 2006 to January 2009, a total of 39 patients underwent nucleus disc arthroplasty with NUBAC™ device. 22 cases have 2-year follow up. There have been no major intra-operative or post-operative vascular or neurological complications in this series. The data showed that there were significant decreases in both Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) after the procedure, with a meaningful improvement of symptoms in all patients. Although preliminary, the initial results are encouraging. The absence of any major intra-operative and post-operative complications supports the design rationale of the NUBAC™, being less invasive comparing to total disc replacement (TDA) and with a low rate of surgical risk. The effectiveness of data as seen in 2-year follow-up on both VAS and ODI have also suggested that the NUBAC™ could be considered a viable treatment option for patients with LBP caused by DDD.

Does anterior lumbar interbody fusion promote adjacent degeneration in degenerative disc disease? A finite element study

BACKGROUND

The increase in the number of anterior lumbar interbody fusions being performed carries with it the potential for the long-term complication of adjacent segmental degeneration. While its exact mechanism remains uncertain, adjacent segment degeneration has become much more widespread. Using a nonlinear, three-dimensional finite element model to analyze and compare the biomechanical influence of anterior lumbar interbody fusion and lumbar disc degeneration on the superior adjacent intervertebral disc, we attempt to determine if anterior lumbar interbody fusion aggravates adjacent segment degeneration.

METHODS

A normal three-dimensional non-linear finite element model of L3-5 has been developed. Three different grades of disc degeneration models (mild, moderate, severe) and one anterior lumbar interbody fusion model were developed by changing either the geometry or associated material properties of the L4-5 segment. The 800 N pre-compressive loading plus 10 Nm moments simulating flexion, extension, lateral bending and axial rotation in five steps was imposed on the L3 superior endplate of all models. The intradiscal pressure, intersegmental rotation range and Tresca stress of the annulus fibrosus in the L3-4 segment were investigated.

RESULTS

The intradiscal pressure, intersegmental rotation range and Tresca stress of the L3-4 segment in the fusion model are higher than in the normal model and different degeneration models under all motion directions. The intradiscal pressures in the three degenerative models are higher than in the normal model in flexion, extension and lateral bending, whereas in axial rotation, the value of the mild degeneration model is lower. The intersegmental rotation ranges in the three degenerative models are higher than in the normal model in flexion and extension. The values for the mild degeneration model in lateral bending and all the degeneration models in axial rotation are lower than in the normal model. The Tresca stresses are higher in the three degenerative models than in the normal model.

CONCLUSION

Anterior lumbar interbody fusion has more adverse biomechanical influence than disc degeneration on the adjacent upper disc and may aggravate the adjacent upper segmental degeneration.

[State of the art of lumbar intervertebral disc replacement]

Lumbar intervertebral total disc replacement is becoming more commonly employed for patients with degenerative disc disease as an alternative to spinal arthrodesis. Postulated advantages for the patients are motion preservation and height restoration in the affected segment, preventing adjacent level degeneration. Although studies show short and mid-term results which are comparable to spinal fusion, to date the long-term outcome is not clear. The different types of artificial discs and the current status of lumbar disc replacement are described.

The efficacy of coblation nucleoplasty for protrusion of lumbar intervertebral disc at a two-year follow-up

PURPOSE

The purpose of this study was to evaluate longer-term efficacy over a two-year follow-up of coblation nucleoplasty treatment for protruded lumbar intervertebral disc.

METHODS

Forty-two cases of protruded lumbar intervertebral disc treated by coblation nucleoplasty followed-up for two years were analysed. Relief of low back pain, leg pain and numbness after the operation were assessed by visual analogue pain scale (VAS). Function of lower limb and daily living of patients were evaluated by the Oswestry Disability Index (ODI).

RESULTS

Operations were performed successfully in all cases. Three patients had recurrence within a week of the procedure. Evaluation of the 42 patients demonstrated significant improvement rate of VAS: defined as 66.2% in back pain, 68.1% in leg pain, and 85.7% in numbness at one-week after the operation; 53.2%, 58.4%, 81.0% at one-year; and 45.5%, 50.7%, 75.0% at two-year follow-up. One week after the operation, obvious amelioration occurred in all the patients, but the tendency decreased. Before operation, the mean value of ODI was 68.2 ± 10.9%. The value at one week was 28.6 ± 8.2%; one-year at 35.8 ± 6.5%; and two-years at 39.4 ± 5.8%.

CONCLUSION

Coblation nucleoplasty may have satisfactory clinical outcomes for treatment of protruded lumbar intervertebral disc for as long as two-year follow-up, but longer-term benefit still needs verification.

Segmental lumbar rotation in patients with discogenic low back pain during functional weight-bearing activities

BACKGROUND

Little information is available on vertebral motion in patients with discogenic low back pain under physiological conditions. We previously validated a combined dual fluoroscopic and magnetic resonance imaging system to investigate in vivo lumbar kinematics. The purpose of the present study was to characterize mechanical dysfunction among patients with confirmed discogenic low back pain, relative to asymptomatic controls without degenerative disc disease, by quantifying abnormal vertebral motion.

METHODS

Ten subjects were recruited for the present study. All patients had discogenic low back pain confirmed clinically and radiographically at L4-L5 and L5-S1. Motions were reproduced with use of the combined imaging technique during flexion-extension, left-to-right bending, and left-to-right twisting movements. From local coordinate systems at the end plates, relative motions of the cephalad vertebrae with respect to caudad vertebrae were calculated at each of the segments from L2 to S1. Range of motion of the primary rotations and coupled translations and rotations were determined.

RESULTS

During all three movements, the greatest range of motion was observed at L3-L4. L3-L4 had significantly greater motion than L2-L3 with left-right bending and left-right twisting movements (p < 0.05). The least motion occurred at L5-S1 for all movements; the motion at this level was significantly smaller than that at L3-L4 (p < 0.05). Range of motion during left-right bending and left-right twisting at L3-L4 was significantly larger in the degenerative disc disease group than in the normal group. The range of motion at L4-L5 was significantly larger in the degenerative group than in the normal group during flexion; however, the ranges of motion in both groups were similar during left-to-right bending and left-to-right twisting.

CONCLUSIONS

The greatest range of motion in patients with discogenic back pain was observed at L3-L4; this motion was greater than that in normal subjects, suggesting that superior adjacent levels developed segmental hypermobility prior to undergoing fusion. L5-S1 had the least motion, suggesting that segmental hypomobility ensues at this level in patients with discogenic low back pain.

Incidence and prevalence of surgery at segments adjacent to a previous posterior lumbar arthrodesis

BACKGROUND CONTEXT

Adjacent segment disease (ASD) after lumbar spinal fusion has been an important reason behind the development of nonfusion stabilization technology. However, the incidence, prevalence, and factors contributing to adjacent segment degeneration in the lumbar spine remain unclear. A range of prevalence rates for ASD have been reported in the lumbar spinal literature, but the annual incidence has not been widely studied in this region. Conflicting reports exist regarding risk factors, especially fusion length.

PURPOSE

To determine the annual incidence and prevalence of further surgery for adjacent segment disease (SxASD) after posterior lumbar arthrodesis and examine possible risk factors.

STUDY DESIGN

Retrospective cohort study.

PATIENT SAMPLE

Nine hundred twelve patients who underwent 1,000 consecutive posterior lumbar interbody fusion procedures, with mean follow-up duration of 63 months (range, 5 months-16 years).

OUTCOME MEASURES

Further surgery for ASD or surgery-free survival.

METHODS

A postal and telephone survey. Follow-up rate: 91% of patients. The annual incidence and prevalence of ASD requiring further surgery were determined using Kaplan-Meier survivorship analysis. Cox proportional-hazards (Cox) regression was used for multivariate analysis of possible risk factors. Significance was set at p<.05.

RESULTS

Further surgery for ASD occurred following 130 of 1,000 or 13% of procedures at a mean time of 43 months (range, 2.3-162 months). The mean annual incidence of SxASD over the first 10 years, in all patients, was 2.5% (95% confidence interval [95% CI], 1.9-3.1) with prevalences of 13.6% and 22.2% at 5 and 10 years, respectively. Cox regression modeling found that the number of levels fused (p≤.0003), age of the patient, fusing to L5, and performing an additional laminectomy adjacent to a fusion all independently affect the risk of SxASD. The mean annual incidence figures in the first 10 years after a lumbar fusion were 1.7% (95% CI, 1.3-2.2) after fusion at single levels, 3.6% (2.1-5.2) after two levels, and 5.0% (3.3-6.7) after three and four levels. The 5- and 10-year prevalences were 9% and 16%, 17% and 31%, and 29% and 40% after single-, two-, and three-/four-level fusions, respectively. The risk of SxASD in patients younger than 45 years was one-quarter (95% CI, 10-64) the risk of patients older than 60 years (p=.003). A laminectomy adjacent to a fusion increases the relative risk by 2.4 times (95% CI, 1.1-5.2; p=.03). Stopping a fusion at L5 is associated with a 1.7-fold increased risk (95% CI, 1.2-2.4; p=.007) of SxASD compared with a fusion to S1, for fusions of the same length.

CONCLUSION

The overall annual incidence and predicted 10-year prevalence of further surgery for ASD after lumbar arthrodesis were 2.5% and 22.2%, respectively. These rates varied widely depending on the identified risk factors. Although young patients who underwent single-level fusions were at low risk, patients who underwent fusion of three or four levels had a threefold increased risk of further surgery, compared with single-level fusions (p<.0001), and a predicted 10-year prevalence of 40%.

Spinaplasty following lumbar laminectomy for multilevel lumbar spinal stenosis to prevent iatrogenic instability

BACKGROUND

Iatrogenic instability following laminectomy occurs in patients with degenerative lumbar canal stenosis. Long segment fusions to obviate postoperative instability result in loss of motion of lumbar spine and predisposes to adjacent level degeneration. The best alternative would be an adequate decompressive laminectomy with a nonfusion technique of preserving the posterior ligament complex integrity. We report a retrospective analysis of multilevel lumbar canal stenosis that were operated for posterior decompression and underwent spinaplasty to preserve posterior ligament complex integrity for outcome of decompression and iatrogenic instability.

MATERIALS AND METHODS

610 patients of degenerative lumbar canal stenosis (n=520) and development spinal canal stenosis (n=90), with a mean age 58 years (33-85 years), underwent multilevel laminectomies and spinaplasty procedure. At followup, changes in the posture while walking, increase in the walking distance, improvement in the dysesthesia in lower limb, the motor power, capability to negotiate stairs and sphincter function were assessed. Forward excursion of vertebrae more than 4 mm in flexion-extension lateral X-ray of the spine as compared to the preoperative movements was considered as the iatrogenic instability. Clinical assessment was done in standing posture regarding active flexion-extension movement, lateral bending and rotations

RESULTS

All patients were followed up from 3 to 10 years. None of the patients had neurological deterioration or pain or catch while movement. Walking distance improved by 5-10 times, with marked relief (70-90%) in neurogenic claudication and preoperative stooping posture, with improvement in sensation and motor power. There was no significant difference in the sagittal alignment as well as anterior translation. Two patients with concomitant scoliosis and one with cauda equine syndrome had incomplete recovery. Two patients who developed disc protrusion, underwent a second operation for a symptomatic disc prolapse.

CONCLUSION

Spinaplasty following posterior decompression for multilevel lumbar canal stenosis is a simple operation, without any serious complications, retaining median structures, maintaining the tension band and the strength with least disturbance of kinematics, mobility, stability and lordosis of the lumbar spine.