Kinematic evaluation of the adjacent segments after lumbar instrumented surgery: a comparison between rigid fusion and dynamic non-fusion stabilization

A comparative analysis of unilateral biportal endoscopic and open laminectomy in multilevel lumbar stenosis

Background

Approximately 103 million people across the globe suffer from symptomatic lumbar spinal stenosis, impacting their health and quality of life. The unilateral biportal endoscopic technique is effective for treating single-segment degenerative lumbar spinal stenosis and is seen as a viable alternative to traditional open lumbar laminectomy. However, research on the application of this technique for multilevel lumbar spinal stenosis remains lacking.

Objective

To compare the clinical effects of unilateral biportal endoscopy (UBE) and open lumbar decompression (OLD) in the treatment of multilevel lumbar spinal stenosis (MLSS).

Methods

This retrospective study was conducted from February 2019 to December 2023 and compared the outcomes of Multilevel UBE surgery to OLD. The included patients were divided into two groups, namely the UBE group (n = 42, 86 surgical segments) and the OLD group (n = 40, 82 surgical segments). At the 1-year follow-up, the imaging findings, visual analogue scale (VAS), Oswestry disability index (ODI), and Zurich Claudication Questionnaire (ZCQ) were assessed. MRI measurements of the dural sac (CSA) and paravertebral cross-sectional area (PMA) were taken before surgery and at the final follow-up.

Results

The surgical segments of the two groups primarily consisted of adjacent segments (UBE 78.6% vs. OLD 78.8%), with a higher proportion of bilateral decompression in the OLD group (UBE 24.4% vs. OLD 28.0%). Preoperative imaging evaluation indicated a higher prevalence of grade C (severe stenosis) compared to grade D (severe stenosis) in both groups (UBE 74.4% vs. OLD 72%). The OLD group exhibited significantly greater blood loss compared to the UBE group (147.63 ± 26.55 vs. 46.19 ± 25.25 mL, p < 0.001). In addition, the duration of hospitalization in the OLD group was notably longer compared to the UBE group (7.58 ± 1.39 vs. 4.38 ± 1.56 days, p < 0.05). Paravertebral muscle atrophy (PMA) in the UBE group was significantly lower than in the OLD group (3.49 ± 3.03 vs. 5.58 ± 3.00, p < 0.05). Significantly elevated serum creatine kinase (CK) levels were observed in both groups, peaking at 1-day post-surgery, with the UBE group showing significantly lower levels than the OLD group (108.1 ± 12.2 vs. 364.13 ± 20.24 U/L, p < 0.05). On postoperative day 7, a significant decrease in liver enzyme levels was found in UBE group compared to the preoperative levels (61.81 ± 7.14 vs. 66.10 ± 8.26 U/L, p < 0.05). The Oswestry Disability Index (ODI) and Zurich Claudication Questionnaire (ZCQ) scores at 1 week, 6 months, and 1 year post-operation showed significant improvement compared to the preoperative scores in both groups (p < 0.05). The study found statistically significant differences in both the Visual Analog Scale (VAS) score (2.28 ± 0.59 vs. 2.85 ± 0.74, p < 0.05) and the Oswestry Disability Index (ODI) score (36.28 ± 2.03 vs. 37.57 ± 1.98, p < 0.05) at 1 week post-surgery between the two groups. However, no significant variations in scores were noted between preoperative and postoperative time points at other follow-up intervals.

Conclusion

The unilateral biportal endoscopic technique was applied to treat multilevel lumbar spinal stenosis, demonstrating decreased intraoperative bleeding and lower postoperative muscle-related complications compared to open lumbar decompression. Furthermore, UBE was found to promote early mobilization.

A dynamic pedicle screw system using polyethylene insert for the lumbar spine

Rigid spinal fusion with instrumentation has been widely applied in treating degenerative spinal disorders and has shown excellent and stable surgical results. However, adjacent segment pathology or implants' loosening could be problematic due to the spine's segmental fusion. Therefore, this study verified a novel concept for posterior stabilization with polyethylene inserts inside a pedicle screw assembly using bone models. We observed that although the gripping capacity of the dynamic pedicle screw system using a tensile and compression tester was less than half that of the rigid pedicle screw system, the flexion-extension moment of the dynamic pedicle screws was significantly lower than that of the rigid pedicle screws. Furthermore, while the bending force of the rigid pedicle screw assembly increased linearly with an increase in the bending angle throughout the test, that of the dynamic pedicle screw assembly also increased linearly until a bending angle of 2.5° was reached. However, this angle decreased at a bending angle of more than 2.5°. Additionally, the fatigue test of 1.0 × 10⁶ cycles showed that the pull-out force of the dynamic pedicle screws from two different polyurethane foam blocks was significantly higher than that of the rigid pedicle screws. Therefore, based on our results, we propose that the device can be applied in clinical cases to reduce screw loosening and adjacent segment pathology.

Comparison of Adjacent Segment Degeneration After Minimally Invasive or Open Transforaminal Lumbar Interbody Fusion: A Minimum 5-Year Follow-up

STUDY DESIGN

This was a retrospective case series.

OBJECTIVE

The purpose of this study was to compare radiologic and clinical outcomes in patients with L4-L5 lumbar spinal stenosis (LSS) who had undergone either minimally invasive (MIS-) or open (O-) transforaminal lumbar interbody fusion (TLIF), especially with regard to the development of adjacent segment degeneration (ASDeg).

SUMMARY OF BACKGROUND DATA

ASDeg is defined as the degenerative changes at adjacent segments of a fused segment, with no obvious clinical symptoms.

MATERIALS AND METHODS

A total of 121 LSS patients with a minimum 5-year follow-up were included. Patients were divided into 2 groups according to the surgery performed (MIS-TLIF: 57 patients, O-TLIF: 64 patients). Preoperative and final follow-up radiologic parameters were determined. The incidence of ASDeg was evaluated and compared between the 2 groups. Visual Analog Scale score, Japanese Orthopaedic Association score, and Oswestry Disability Index were used to assess clinical outcomes.

RESULTS

Before surgery, no significant difference was found between MIS-TLIF and O-TLIF groups regarding demographic, radiologic, and clinical data. After a 5-year follow-up, the incidence of ASDeg in LSS patients was 47.1% (57/121). ASDeg was mostly located at the cranial segment of the fused level in each group. The most common type of ASDeg in both groups was intervertebral space collapse. There was a lower chance of ASDeg in MIS-TLIF group than that in O-TLIF group (33.3% vs. 59.4%, P <0.01). Postoperatively, both groups had significant improvement in clinical outcomes, and there were no statistically significant intergroup differences assessed by Visual Analog Scale, Japanese Orthopaedic Association, and Oswestry Disability Index scores.

CONCLUSION

The clinical effect of MIS-TLIF and O-TLIF were similar, but the incidence of ASDeg was significantly lower after MIS-TLIF at 5-year follow-up.

Biomechanical Comparison between Isobar and Dynamic-Transitional Optima (DTO) Hybrid Lumbar Fixators: A Lumbosacral Finite Element and Intersegmental Motion Analysis

Biomechanical performance of longitudinal component in dynamic hybrid devices was evaluated to display the load-transfer effects of Dynesys cord spacer or Isobar damper-joint dynamic stabilizer on junctional problem based on various disc degenerations. The dynamic component was adapted at the mildly degenerative L3–L4 segment, and the static component was fixed at the moderately degenerative L4–L5 segment under a displacement-controlled mode for the finite element study. Furthermore, an intersegmental motion behavior was analyzed experimentally on the synthetic model under a load-controlled mode. Isobar or DTO hybrid fixator could reduce stress/motion at transition segment, but compensation was affected at the cephalic adjacent segment more than the caudal one. Within the trade-off region (as a motion-preserving balance between the transition and adjacent segments), the stiffness-related problem was reduced mostly in flexion by a flexible Dynesys cord. In contrast, Isobar damper afforded the effect of maximal allowable displacement (more than peak axial stiffness) to reduce stress within the pedicle and at facet joint. Pedicle-screw travel at transition level was related to the extent of disc degeneration in Isobar damper-joint (more than Dynesys cord spacer) attributing to the design effect of axial displacement and angular rotation under motion. In biomechanical characteristics relevant to clinical use, longitudinal cord/damper of dynamic hybrid lumbar fixators should be designed with less interface stress occurring at the screw-vertebral junction and facet joint to decrease pedicle screw loosening/breakage under various disc degenerations.

Novel force-displacement control passive finite element models of the spine to simulate intact and pathological conditions; comparisons with traditional passive and detailed musculoskeletal models

Passive finite element (FE) models of the spine are commonly used to simulate intact and various pre- and postoperative pathological conditions. Being devoid of muscles, these traditional models are driven by simplistic loading scenarios, e.g., a constant moment and compressive follower load (FL) that do not properly mimic the complex in vivo loading condition under muscle exertions. We aim to develop novel passive FE models that are driven by more realistic yet simple loading scenarios, i.e., in vivo vertebral rotations and pathological-condition dependent FLs (estimated based on detailed musculoskeletal finite element (MS-FE) models). In these novel force-displacement control FE models, unlike the traditional passive FE models, FLs vary not only at different spine segments (T12-S1) but between intact, pre- and postoperative conditions. Intact, preoperative degenerated, and postoperative fused conditions at the L4-L5 segment for five static in vivo activities in upright and flexed postures were simulated by the traditional passive FE, novel force-displacement control FE, and gold-standard detailed MS-FE spine models. Our findings indicate that, when compared to the MS-FE models, the force-displacement control passive FE models could accurately predict the magnitude of disc compression force, intradiscal pressure, annulus maximal von Mises stress, and vector sum of all ligament forces at adjacent segments (L3-L4 and L5-S1) but failed to predict disc shear and facet joint forces. In this regard, the force-displacement control passive FE models were much more accurate than the traditional passive FE models. Clinical recommendations made based on traditional passive FE models should, therefore, be interpreted with caution.

Adjacent segments biomechanics following lumbar fusion surgery: a musculoskeletal finite element model study

PURPOSE

This study exploits a novel musculoskeletal finite element (MS-FE) spine model to evaluate the post-fusion (L4-L5) alterations in adjacent segment kinetics.

METHODS

Unlike the existing MS models with idealized representation of spinal joints, this model predicts stress/strain distributions in all passive tissues while organically coupled to a MS model. This generic (in terms of musculature and material properties) model uses population-based in vivo vertebral sagittal rotations, gravity loads, and an optimization algorithm to calculate muscle forces. Simulations represent individuals with an intact L4-L5, a preoperative severely degenerated L4-L5 (by reducing the disc height by ~ 60% and removing the nucleus incompressibility), and a postoperative fused L4-L5 segment with either a fixed or an altered lumbopelvic rhythm with respect to the intact condition (based on clinical observations). Changes in spine kinematics and back muscle cross-sectional areas (due to intraoperative injuries) are considered based on in vivo data while simulating three activities in upright/flexed postures.

RESULTS

Postoperative changes in some adjacent segment kinetics were found considerable (i.e., larger than 25%) that depended on the postoperative lumbopelvic kinematics and preoperative L4-L5 disc condition. Postoperative alterations in adjacent disc shear, facet/ligament forces, and annulus stresses/strains were greater (> 25%) than those found in intradiscal pressure and compression (< 25%). Kinetics of the lower (L5-S1) and upper (L3-L4) adjacent segments were altered to different degrees.

CONCLUSION

Alterations in segmental rotations mainly affected adjacent disc shear forces, facet/ligament forces, and annulus/collagen fibers stresses/strains. An altered lumbopelvic rhythm (increased pelvis rotation) tends to mitigate some of these surgically induced changes.

Preclinical Evaluation of a Novel 3D-Printed Movable Lumbar Vertebral Complex for Replacement: In Vivo and Biomechanical Evaluation of Goat Model

Purpose

This was an in vivo study to develop a novel movable lumbar artificial vertebral complex (MLVC) in a goat model. The purpose of this study was to evaluate clinical and biomechanical characteristics of MLVC and to provide preclinical data for a clinical trial in the future.

Methods

According to the preoperative X-ray and CT scan data of the lumbar vertebrae, 3D printing of a MLVC was designed and implanted in goats. The animals were randomly divided into three groups: intact, fusion, and nonfusion. In the intact group, only the lumbar vertebrae and intervertebral discs were exposed during surgery. Both the fusion and nonfusion groups underwent resection of the lumbar vertebral body and the adjacent intervertebral disc. Titanium cages and lateral plates were implanted in the fusion group. MLVC was implanted in the nonfusion group. All groups were evaluated by CT scan and micro-CT to observe the spinal fusion and tested using the mechanical tester at 6 months after operation.

Results

The imaging results showed that with the centrum, the artificial endplates of the titanium cage and MLVC formed compact bone trabeculae. In the in vitro biomechanical test, the average ROM of L3-4 and L4-5 for the nonfusion group was found to be similar to that of the intact group and significantly higher in comparison to that of the fusion group (P < 0.05). The average ROM of flexion, extension, lateral bending, and rotation in the L2-3 intervertebral space significantly increased in the fusion group compared with the intact group and the nonfusion group (P < 0.001). There were no significant differences in flexion, extension, lateral bending, and rotation between the nonfusion and intact groups (P > 0.05). The average ROM of flexion, extension, lateral bending, and rotation in the L2-5 intervertebral space was not significantly different between the intact group, the fusion group, and the nonfusion group, and there was no statistical significance (P > 0.05). HE staining results did not find any metal and polyethylene debris caused by abrasion.

Conclusion

In vivo MLVC can not only reconstruct the height and stability of the centrum of the operative segment but also retain the movement of the corresponding segment.

Biomechanical effects of lumbar fusion surgery on adjacent segments using musculoskeletal models of the intact, degenerated and fused spine

Adjacent segment disorders are prevalent in patients following a spinal fusion surgery. Postoperative alterations in the adjacent segment biomechanics play a role in the etiology of these conditions. While experimental approaches fail to directly quantify spinal loads, previous modeling studies have numerous shortcomings when simulating the complex structures of the spine and the pre/postoperative mechanobiology of the patient. The biomechanical effects of the L4–L5 fusion surgery on muscle forces and adjacent segment kinetics (compression, shear, and moment) were investigated using a validated musculoskeletal model. The model was driven by in vivo kinematics for both preoperative (intact or severely degenerated L4–L5) and postoperative conditions while accounting for muscle atrophies. Results indicated marked changes in the kinetics of adjacent L3–L4 and L5–S1 segments (e.g., by up to 115% and 73% in shear loads and passive moments, respectively) that depended on the preoperative L4–L5 disc condition, postoperative lumbopelvic kinematics and, to a lesser extent, postoperative changes in the L4–L5 segmental lordosis and muscle injuries. Upper adjacent segment was more affected post-fusion than the lower one. While these findings identify risk factors for adjacent segment disorders, they indicate that surgical and postoperative rehabilitation interventions should focus on the preservation/restoration of patient’s normal segmental kinematics.

A comprehensive approach for the validation of lumbar spine finite element models investigating post-fusion adjacent segment effects

Spinal fusion surgery is usually followed by accelerated degenerative changes in the unfused segments above and below the treated segment(s), i.e., adjacent segment disease (ASD). While a number of risk factors for ASD have been suggested, its exact pathogenesis remains to be identified. Finite element (FE) models are indispensable tools to investigate mechanical effects of fusion surgeries on post-fusion changes in the adjacent segment kinematics and kinetics. Existing modeling studies validate only their intact FE model against in vitro data and subsequently simulate post-fusion in vivo conditions. The present study provides a novel approach for the comprehensive validation of a lumbar (T12-S1) FE model in post-fusion conditions. Sixteen simulated fusion surgeries, performed on cadaveric specimens using various testing and loading conditions, were modeled by this FE model. Predictions for adjacent segment range of motion (RoM) and intradiscal pressure (IDP) were compared with those obtained from the corresponding in vitro tests. Overall, 70% of the predicted adjacent segment RoMs were within the range of in vitro data for both intact and post-fusion conditions. Correlation (r) values between model and in vitro findings for the adjacent segment RoMs were positive and greater than 0.84. Most of the predicted IDPs were, however, out of the narrow range of in vitro IDPs at the adjacent segments but with great positive correlations (r ≥ 0.89). FE modeling studies investigating the effect of fusion surgery on in vivo adjacent segment biomechanics are encouraged to use post-surgery in vitro data to validate their FE model.

Biomechanical In Vitro Test of a Novel Dynamic Spinal Stabilization System Incorporating Polycarbonate Urethane Material Under Physiological Conditions

Posterior dynamic stabilization systems (PDSS) were developed to provide stabilization to pathologic or hypermobile spinal segments while maintaining the healthy biomechanics of the spine. Numerous novel dynamic devices incorporate the temperature and moisture dependent material polycarbonate urethane (PCU) due to its mechanical properties and biocompatibility. In this study, standardized pure moment in vitro tests were carried out on human lumbar spines to evaluate the performance of a device containing PCU. An environmental chamber with controlled moisture and temperature was included in the setup to meet the requirements of testing under physiological conditions. Three test conditions were compared: (1) native spine, (2) dynamic instrumentation, and (3) dynamic instrumentation with decompression. The ranges of motion, centers of rotation, and relative pedicle screw motions were evaluated. The device displayed significant stiffening in flexion-extension, lateral bending, and axial rotation load directions. A reduction of the native range of motion diminished the stiffening effect along the spinal column and has the potential to reduce the risk of the onset of degeneration of an adjacent segment. In combination with decompression, the implant decreased the native range of motion for flexion-extension and skew bending, but not for lateral bending and axial rotation. Curve fittings using the sigmoid function were performed to parameterize all load-deflection curves in order to enhance accurate numerical model calibrations and comparisons. The device caused a shift of the center of rotation (COR) in the posterior and caudal direction during flexion-extension loading.

Reoperation rates and risk factors for revision 4 years after dynamic stabilization of the lumbar spine

BACKGROUND CONTEXT

The concept of dynamic stabilization (DS) of the lumbar spine for treatment of degenerative instability has been introduced almost two decades ago. Dynamic stabilization follows the principle of controlling movement in the coronal plane by providing load transfer of the spinal segment without fusion and, at the same time, reducing side effects such as adjacent segment disease (ASD). So far, only little is known about revision rates after DS due to ASD and screw loosening (SL).

PURPOSE

The present study aimed to evaluate the longitudinal revision rates following dynamic pedicle screw stabilization in the lumbar spine and to determine specific risk factors predictive for ASD, SL, and overall reoperation in a large cohort with considerable follow-up.

DESIGN

We carried out a post hoc analysis of a prospectively collected database in a level I spine center.

PATIENTS EXAMPLE

The patient sample comprised 283 (151 female/132 male) consecutive patients suffering from painful degenerative lumbar segmental instability with or without spinal stenosis who underwent DS of the lumbar spine (Ulrich Cosmic, Ulrich Medical, Ulm, Germany) between January 2008 and December 2011.

OUTCOME MEASURES

Longitudinal reoperation rate and risk factors predictive for revision surgery were evaluated.

METHODS

We analyzed the longitudinal reoperation rate due to ASD and SL and overall reoperation. Risk factors such as age, gender, body mass index, lumbar lordosis (LL), number of segments, and number of previous surgeries were taken into account. Regular and mixed model logistic regressions were performed to determine risk factors for revision surgery on a patient and on a screw level.

RESULTS

The mean age was 65.7±10.2 years (range 31-88). One hundred thirty-two patients were stabilized in 1 segment, 134 in 2 segments, 15 in 3 segments, and 2 patients in 4 segments. Reoperation rate for ASD and SL after 1 year was 7.4 %, after 2 years was 15.0%, and after a mean follow-up of 51.4±15 months was 22.6%. Reasons for revision were SL in 19 cases (6.6%), ASD in 39 cases (13.7%), SL and ASD in 6 cases, hematoma in 2 cases (0.7%), cerebrospinal fluid fistulae in 3 cases (1.1%), infection in 6 cases (2.1%), and implant failure in 1 case (0.4%). The patients' age, the number of stabilized segments, and the number of previous surgeries and postoperative LL had a significant influence on the probability for revision surgery.

CONCLUSIONS

Reoperation rates after DS of the lumbar spine are comparable with rigid fixations. The younger the patient and the more segments are involved, the lower the LL and the more previous surgeries were found, the higher was the risk of revision. Risk of revision was almost twice as high in men compared with women. We therefore conclude that for clear clinical indication and careful evaluation of preoperative imaging data, DS using the Cosmic system seems to be a possible option. The presented data will help to further tailor indication and patient selection.

[Vertebral three-dimensional motion characteristics of adjacent segments in patients with isthmic spondylolisthesis in vivo]

Objective

To observe vertebral three-dimensional motion characteristics of adjacent segments in patients with symptomatic L 4 isthmic spondylolisthesis (IS).

Methods

Fourteen symptomatic L 4 IS patients who underwent surgery treatment (trial group) and 15 asymptomatic volunteers without back pain and other lesions of spine (control group) were recruited. There was no significant difference in gender, age, body mass index, and bone mineral density between the two groups ( P>0.05). The three-dimensional reconstruction model of lumbar spine was acquired from the thin slice CT of the lumbar spine of the subjects by combining dual-X-ray fluoroscopy imaging system with spiral CT examination. The model was matched to the double oblique X-ray fluoroscopy images captured by dual-X-ray fluoroscopy imaging system at different active positions of the lumbar spine to reproduce the three-dimensional instantaneous of lumbar spondylolisthesis at different state of motion. The motion and relative displacement of adjacent segments (L 3, 4 and L 5, S 1) of spondylolisthesis were measured quantitatively by establishing a three-dimensional coordinate system at the geometric center of the vertebral body. The results were compared with those of the control group.

Results

When L 3, 4 in the control group were flexed flexion-extension, left-right twisting, and left-right bending, and when L 5, S 1 in the control group were flexed left-right twisting and left-right bending, the activity along the main axis of motion (main axis of motion) tended to increase compared with that along the corresponding coupled axis of motion (secondary axis of motion); however, this trend disappeared in the trial group, and the main and secondary movements were disordered. Because of the coronal orientation of the facet joints of L 5, S 1, the degree of motion along the main axis of motion decreased during flexion and extension, but this trend disappeared in the trial group. Compared with the control group, L 3, 4 in the trial group exhibited displacement instability in flexion-extension, left-right twisting, and left-right bending ( P<0.05); there was no significant difference in the relative displacement of L 5, S 1 intervertebral bodies along x, y, and z axes between the trial group and the control group in flexion-extension, left-right twisting, and left-right bending curvature ( P>0.05).

Conclusion

Patients with symptomatic L 4 IS have disorders of primary and secondary movement patterns in adjacent segments, while IS showed significantly displacement instability in L 3, 4 and significantly decreased motion in L 5, S 1.

The Incidence of Adjacent Segment Degeneration after the Use of a Versatile Dynamic Hybrid Stabilization Device in Lumbar Stenosis: Results of a 5-8-Year Follow-up

Study Design

Retrospective study with long-term follow-up.

Purpose

To evaluate the long-term incidence of adjacent segment degeneration (ASD) and clinical outcomes in a consecutive series of patients who underwent spinal decompression associated with dynamic or hybrid stabilization with a Flex+TM stabilization system (SpineVision, Antony, France) for lumbar spinal stenosis.

Overview of Literature

The incidence of ASD and clinical outcomes following dynamic or hybrid stabilization with the Flex+TM system used for lumbar spinal stenosis have not been well investigated.

Methods

Twenty-one patients with lumbar stenosis and probable post-decompressive spinal instability underwent decompressive laminectomy followed by spinal stabilization using the Flex+TM stabilization system. The indication for a mono-level dynamic stabilization was a preoperative magnetic resonance imaging (MRI) demonstrating evidence of severe disc disease associated with severe spinal stenosis. The hybrid stabilization (rigid-dynamic) system was used for multilevel laminectomies with associated initial degenerative scoliosis, first-grade spondylolisthesis, or rostral pathology.

Results

The improvement in Visual Analog Scale and Oswestry Disability Index scores at follow-up were statistically significant (p<0.0001 and p<0.0001, respectively). At the 5–8-year follow-up, clinical examination, MRI, and X-ray findings showed an ASD complication with pain and disability in one of 21 patients. The clinical outcomes were similar in patients treated with dynamic or hybrid fixation.

Conclusions

Patients treated with laminectomy and Flex+TM stabilization presented a satisfactory clinical outcome after 5–8 years of follow-up, and ASD incidence in our series was 4.76% (one patient out of 21). We are aware that this is a small series, but our long-term follow-up may be sufficient to contribute to the expanding body of literature on the development of symptomatic ASD associated with dynamic or hybrid fixation.

Vertebral Compression Fractures after Lumbar Instrumentation

Lumbar spinal stenosis (LSS) is primarily found in an older population. This is a similar demographic group that develops both osteoporosis and vertebral compression fractures (VCF). This report reviewed a series of patients treated for VCF that had previous lumbar surgery for symptomatic spinal stenosis. Patients that only underwent laminectomy or fusion without instrumentation had a similar distribution of VCF as the non-surgical population in the mid-thoracic, or lower thoracic and upper lumbar spine. However, in the patients that had previous short-segment spinal instrumentation, fractures were found to be located more commonly in the mid-lumbar spine or sacrum adjacent to or within one or two spinal segments of the spinal instrumentation. Adjacent-level fractures that occur due to vertebral osteoporosis after long spinal segment instrumentation has been discussed in the literature. The purpose of this report is to highlight the previously unreported finding of frequent lumbar and sacral osteoporotic fractures in post-lumbar instrumentation surgery patients. Important additional factors found were lack of preventative medical treatment for osteoporosis, and secondary effects related to inactivity, especially during the first year after surgery.

Hybrid Instrumentation in Lumbar Spinal Fusion: A Biomechanical Evaluation of Three Different Instrumentation Techniques

STUDY DESIGN

Ex vivo human cadaveric study.

OBJECTIVE

The development or progression of adjacent segment disease (ASD) after spine stabilization and fusion is a major problem in spine surgery. Apart from optimal balancing of the sagittal profile, dynamic instrumentation is often suggested to prevent or impede ASD. Hybrid instrumentation is used to gain stabilization while allowing motion to avoid hypermobility in the adjacent segment. In this biomechanical study, the effects of two different hybrid instrumentations on human cadaver spines were evaluated and compared with a rigid instrumentation.

METHODS

Eighteen human cadaver spines (T11-L5) were subdivided into three groups: rigid, dynamic, and hook comprising six spines each. Clinical parameters and initial mechanical characteristics were consistent among groups. All specimens received rigid fixation from L3-L5 followed by application of a free bending load of extension and flexion. The range of motion (ROM) for every segment was evaluated. For the rigid group, further rigid fixation from L1-L5 was applied. A dynamic Elaspine system (Spinelab AG, Winterthur, Switzerland) was applied from L1 to L3 for the dynamic group, and the hook group was instrumented with additional laminar hooks at L1-L3. ROM was then evaluated again.

RESULTS

There was no significant difference in ROM among the three instrumentation techniques.

CONCLUSION

Based on this data, the intended advantage of a hybrid or dynamic instrumentation might not be achieved.

Preventive Effect of Dynamic Stabilization Against Adjacent Segment Degeneration After Posterior Lumbar Interbody Fusion

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To investigate the effects of dynamic stabilization with sublaminar taping (ST) on the upper segment adjacent to posterior lumbar interbody fusion (PLIF).

SUMMARY OF BACKGROUND DATA

Hybrid procedures such as dynamic stabilization for adjacent segment in addition to spinal fusion have been developed for reduction of the mechanical stress and prevention of adjacent segment pathology (ASP). However, a few reports are available on hybrid procedures and their efficacy is still controversial.

METHODS

Of the 116 patients who underwent L4/5 PLIF between August 2006 and September 2012, 76 patients with minimum 2-year follow up were included in this study. Fifty three patients underwent L4/5 PLIF with hybrid procedure using ST on L3 lamina (group U), and 23 patients underwent conventional L4/5 PLIF (group C). The adjacent segment degeneration (ASDeg) was determined by measurements of radiograph, computed tomography, and magnetic resonance imaging; the adjacent segment disease (ASDis) was evaluated on medical records.

RESULTS

The incidence of ASDeg at L3/4 segment of group U (3.7%) was significantly less than that of group C (30.4%) (P = 0.003), although there were no significant differences at L2/3 (group U, 7.5%; group C, 13%) or L5/S1 segment (group U, 5.7%; group C, 8.7%). On the other hand, no significant difference was found between two groups in the incidence of ASDis in L2/3 to L5/S1 levels, and no patient underwent reoperation. Bivariable and multivariable logistic regression analyses for L3/4 segment ASDeg revealed that the difference of surgical procedure was the only significant factor.

CONCLUSION

The current study showed that L4/5 PLIF with hybrid procedure using ST on L3 lamina significantly reduced the incidence of L3/4 ASDeg as compared with the conventional L4/5 PLIF without compromising L2/3 or L5/S1 segment. Although further studies and longer follow up are necessary, the hybrid procedure is expected to be effective for preventing ASP.

LEVEL OF EVIDENCE

4.

Facet joint changes after application of lumbar nonfusion dynamic stabilization

OBJECTIVE The long-term effects on adjacent-segment pathology after nonfusion dynamic stabilization is unclear, and, in particular, changes at the adjacent facet joints have not been reported in a clinical study. This study aims to compare changes in the adjacent facet joints after lumbar spinal surgery. METHODS Patients who underwent monosegmental surgery at L4-5 with nonfusion dynamic stabilization using the Dynesys system (Dynesys group) or transforaminal lumbar interbody fusion with pedicle screw fixation (fusion group) were retrospectively compared. Facet joint degeneration was evaluated at each segment using the CT grading system. RESULTS The Dynesys group included 15 patients, while the fusion group included 22 patients. The preoperative facet joint degeneration CT grades were not different between the 2 groups. Compared with the preoperative CT grades, 1 side of the facet joints at L3-4 and L4-5 had significantly more degeneration in the Dynesys group. In the fusion group, significant facet joint degeneration developed on both sides at L2-3, L3-4, and L5-S1. The subjective back and leg pain scores were not different between the 2 groups during follow-up, but functional outcome based on the Oswestry Disability Index improved less in the fusion group than in the Dynesys group. CONCLUSIONS Nonfusion dynamic stabilization using the Dynesys system had a greater preventative effect on facet joint degeneration in comparison with that obtained using fusion surgery. The Dynesys system, however, resulted in facet joint degeneration at the instrumented segments and above. An improved physiological nonfusion dynamic stabilization system for lumbar spinal surgery should be developed.

Computed Tomography Findings Associated with Clinical Outcome After Dynamic Posterior Stabilization of the Lumbar Spine

OBJECTIVE

To evaluate whether preoperative multirow detector computed tomography (MDCT) findings were associated with clinical outcome 24 months after dynamic stabilization for painful degenerative lumbar spine disease.

METHODS

Preoperative MDCT examinations of 63 patients (66 ± 11.7 years; 60% women) treated with a dynamic screw rod system for painful degenerative segmental instability with/without spinal stenosis were assessed for quantitative and qualitative parameters defining degenerative changes of the thoracolumbar spine, including grades of disc herniation, degenerative spondylolisthesis, vertebral body sclerosis, cross-sectional area of the spinal canal at disc level, intervertebral disc height, ancillary bone mineral density, and anteroposterior diameter of intervertebral foramina. Clinical performance was assessed at baseline and 24 months with quantitative scales, including the Oswestry Disability Index and Short-Form 36 physical component summary. For statistical analysis classification and regression trees, linear regression and nonparametric tests were used.

RESULTS

Clinical scores improved substantially over 24 months compared with preoperative values (delta Oswestry Disability Index -32.1 ± 17.2, delta Short-Form 36 physical component summary 4.9 ± 2.3). Physical component summary improvement was significantly better in patients with lower grades of disc herniation (P < 0.001) and/or spondylolisthesis (P = 0.011), lower cross-sectional area of the spinal canal (P = 0.043), high intervertebral disc height (P = 0.006), and high grades of vertebral body sclerosis (P = 0.002). Patients with high bone mineral density and initially low diameter of intervertebral foramina showed a significantly better improvement of Oswestry Disability Index (P < 0.05).

CONCLUSIONS

Clinical improvement after dynamic stabilization was significantly associated with 7 independent baseline imaging findings. Preoperative evaluation of these MDCT parameters may improve therapy selection for patients with degenerative lumbar spine disease.

Clinical Experiences of Non-fusion Dynamic Stabilization Surgery for Adjacent Segmental Pathology after Lumbar Fusion

BACKGROUND

As an alternative to spinal fusion, non-fusion dynamic stabilization surgery has been developed, showing good clinical outcomes. In the present study, we introduce our surgical series, which involves non-fusion dynamic stabilization surgery for adjacent segment pathology (ASP) after lumbar fusion surgery.

METHODS

Fifteen patients (13 female and 2 male, mean age of 62.1 years) who underwent dynamic stabilization surgery for symptomatic ASP were included and medical records, magnetic resonance images (MRI), and plain radiographs were retrospectively evaluated.

RESULTS

Twelve of the 15 patients had the fusion segment at L4-5, and the most common segment affected by ASP was L3-4. The time interval between prior fusion and later non-fusion surgery was mean 67.0 months. The Visual Analog Scale and Oswestry Disability Index showed values of 7.4 and 58.5% before the non-fusion surgery and these values respectively declined to 4.2 and 41.3% postoperatively at 36 months (p=0.027 and p=0.018, respectively). During the mean 44.8 months of follow-up, medication of analgesics was also significantly reduced. The MRI grade for disc and central stenosis identified significant degeneration at L3-4, and similar disc degeneration from lateral radiographs was determined at L3-4 between before the prior fusion surgery and the later non-fusion surgery. After the non-fusion surgery, the L3-4 segment and the proximal segment of L2-3 were preserved in the disc, stenosis and facet joint whereas L1-2 showed disc degeneration on the last MRI (p=0.032). Five instances of radiologic ASP were identified, showing characteristic disc-space narrowing at the proximal segments of L1-2 and L2-3. However, no patient underwent additional surgery for ASP after non-fusion dynamic stabilization surgery.

CONCLUSION

The proposed non-fusion dynamic stabilization system could be an effective surgical treatment for elderly patients with symptomatic ASP after lumbar fusion.

Adjacent Segment Pathology after Lumbar Spinal Fusion

One of the major clinical issues encountered after lumbar spinal fusion is the development of adjacent segment pathology (ASP) caused by increased mechanical stress at adjacent segments, and resulting in various radiographic changes and clinical symptoms. This condition may require surgical intervention. The incidence of ASP varies with both the definition and methodology adopted in individual studies; various risk factors for this condition have been identified, although a significant controversy still exists regarding their significance. Motion-preserving devices have been developed, and some studies have shown their efficacy of preventing ASP. Surgeons should be aware of the risk factors of ASP when planning a surgery, and accordingly counsel their patients preoperatively.

ISSLS Prize winner: Long-term follow-up suggests spinal fusion is associated with increased adjacent segment disc degeneration but without influence on clinical outcome: results of a combined follow-up from 4 randomized controlled trials

STUDY DESIGN

Cross-sectional analysis of long-term follow-up (LTFU) data from 4 randomized controlled trials of operative versus nonoperative treatment for chronic low back pain.

OBJECTIVE

To examine the influence of spinal fusion on adjacent segment disc space height as an indicator of disc degeneration at LTFU.

SUMMARY OF BACKGROUND DATA

There is ongoing debate as to whether adjacent segment disc degeneration results from the increased mechanical stress of fusion.

METHODS

Plain standing lateral radiographs were obtained at LTFU (mean, 13 ± 4 yr postrandomization) in 229 of 464 (49%) patients randomized to surgery and 140 of 303 (46%), to nonoperative care. Disc space height and posteroanterior displacement were measured for each lumbar segment using a validated computer-assisted distortion compensated roentgen analysis technique. Values were reported in units of standard deviations above or below age and sex-adjusted normal values. Patient-rated outcomes included the Oswestry Disability Index and pain scales.

RESULTS

Radiographs were usable in 355 of 369 (96%) patients (259 fusion and 96 nonoperative treatment). Both treatment groups showed significantly lower values for disc space height of the adjacent segment than norm values. There was a significant difference between treatment groups for the disc space height of the cranial adjacent segment (in both as-treated and intention-to-treat analyses). The mean treatment effect of fusion on adjacent segment disc space height was -0.44 SDs (95% CI, -0.77 to -0.11; P = 0.01; as-treated analysis); there was no group difference for posteroanterior displacement (0.18 SDs, 95% confidence interval, -0.28 to 0.64, P = 0.45). Adjacent level disc space height and posteroanterior displacement were not correlated with Oswestry Disability Index or pain scores at LTFU (r = 0.010-0.05; P > 0.33).

CONCLUSION

Fusion was associated with lower disc space height at the adjacent segment after an average of 13 years of FU. The reduced disc space height had no influence on patient self-rated outcomes (pain or disability).

LEVEL OF EVIDENCE

2.

Kinematic and mechanical comparisons of lumbar hybrid fixation using Dynesys and Cosmic systems

STUDY DESIGN

The biomechanical effects of Dynesys and Cosmic fixators on transition and adjacent segments were evaluated using the finite-element method.

OBJECTIVE

This study investigated the load-transferring mechanisms of 2 dynamic fixators and the fixator-induced effects on the junctional problem of the adjacent segments.

SUMMARY OF BACKGROUND DATA

The mobility and flexibility of Dynesys screw-spacer and Cosmic screw-hinge joints preserve motion and share loads for the transition segment. However, the differences in tissue responses and fixator mechanisms among these 2 fixators have not been investigated extensively.

METHODS

A lumbosacral model from L1 to S1 levels was developed and subjected to muscular contraction, ligamentous interconnection, compressive force, and trunk moment. A static fixator was instrumented at the moderately degenerative L4-L5 segment to serve as a comparison baseline. Subsequently, the 2 fixators were instrumented at the mildly degenerative L3-L4 segment. The tissue responses of the adjacent segments and the load transmission at the screw-spacer and bone-screw interfaces were compared.

RESULTS

Both systems show the ability to protect the transition segment but deteriorate the adjacent segments. The screw-hinge joint and the stiffer rod of the Cosmic system significantly constrained the motion pattern of the transition segment. Comparatively, the Dynesys screw-spacer interfaces make contact with and depart from each other during motion; thus providing higher mobility to the transition segment. However, the highly stressed distribution at the Cosmic bone-screw causes the screw and hinge prone to pullout and fatigue failures.

CONCLUSION

Cosmic fixation can better protect the disc and facet joint of the transition segment than can the Dynesys. However, the screw-hinge joint strictly constrains intersegmental motion and deteriorates the junctional problem. The Cosmic system can be chosen to treat more severely degenerative transition segments. With higher flexibility, the Dynesys system is recommended for the transition segment that is healthy or mildly degenerative.

LEVEL OF EVIDENCE

N/A.

Comparison of adjacent segment disease after minimally invasive or open transforaminal lumbar interbody fusion

Adjacent segment disease (ASD) is a potential long-term risk after lumbar fusion. Its incidence has been evaluated in anterior and posterior lumbar interbody fusions, but few studies have focused on transforaminal lumbar interbody fusion (TLIF). Relative risk of ASD with open or minimally invasive (MI) TLIF is poorly understood. To report our experience with risk for ASD in patients receiving TLIF and test its association with surgical approach, we performed a retrospective cohort study based on medical record review at a single institution. Eligible patients were ⩾ 18 years old at operation, underwent single-level TLIF during the period 2007-2008, and had at least 6 months postoperative follow-up. Patients were categorized by surgical approach (open versus MI). Primary outcome of interest was development of symptomatic ASD, defined by (1) new back and/or leg pain, (2) imaging findings adjacent to original surgical level, and (3) decision to treat. A total of 68 patients (16 open, 52 MI) were included in the analysis. Groups had similar baseline characteristics, except the open group tended to be older (p=0.04). Seven (10%) patients developed ASD. Mean patient age was 62 years and three were male. Three underwent open and four underwent MI TLIF. Risk of ASD did not differ significantly by surgical approach. The MI group showed a trend toward decreased risk of ASD compared to the open group, although it was not statistically significant. This suggests MI TLIF may be associated with decreased long-term morbidity compared to the open approach. Large prospective studies are needed to confirm these findings.

Artificial total disc replacement versus fusion for lumbar degenerative disc disease: a meta-analysis of randomized controlled trials

OBJECTIVE

The purpose of this study is to compare the effectiveness and safety of artificial total disc replacement (TDR) with fusion for the treatment of lumbar degenerative disc disease (DDD). Spinal fusion is the conventional surgical treatment for lumbar DDD. Recently, TDR has been developed to avoid the negative effects of the fusion by preserving function of the motion segment. Controversy still surrounds regarding whether TDR is better.

METHODS

We systematically searched six electronic databases (Medline, Embase, Clinical, Ovid, BIOSIS and Cochrane registry of controlled clinical trials) to identify randomized controlled trials (RCTs) published up to March 2013 in which TDR was compared with the fusion for the treatment of lumbar DDD. Effective data were extracted after the assessment of methodological quality of the trials. Then, we performed the meta-analysis.

RESULTS

Seven relevant RCTs with a total of 1,584 patients were included. TDR was more effective in ODI (MD -5.09; 95% CI [-7.33, -2.84]; P < 0.00001), VAS score (MD -5.31; 95% CI [-8.35, -2.28]; P = 0.0006), shorter duration of hospitalization (MD -0.82; 95% CI [-1.38, -0.26]; P = 0.004) and a greater proportion of willing to choose the same operation again (OR 2.32; 95% CI [1.69, 3.20]; P < 0.00001). There were no significant differences between the two treatment methods regarding operating time (MD -44.16; 95% CI [-94.84, 6.52]; P = 0.09), blood loss (MD -29.14; 95% CI [-173.22, 114.94]; P = 0.69), complications (OR 0.72; 95% CI [0.45, 1.14]; P = 0.16), reoperation rate (OR 0.83; 95% CI [0.39, 1.77]; P = 0.63) and the proportion of patients who returned to full-time/part-time work (OR 1.10; 95% CI [0.86, 1.41]; P = 0.47).

CONCLUSION

TDR showed significant safety and efficacy comparable to lumbar fusion at 2 year follow-up. TDR demonstrated superiorities in improved physical function, reduced pain and shortened duration of hospitalization. The benefits of operating time, blood loss, motion preservation and the long-term complications are still unable to be proved.

Ti2448 pedicle screw system augmentation for posterior lumbar interbody fusion

STUDY DESIGN

A finite element analysis was used.

OBJECTIVE

To evaluate the feasibility of using the Ti-24Nb-4Zr-7.9Sn (Ti2448) pedicle screw system to augment single-level posterior lumbar interbody fusion (PLIF).

SUMMARY OF BACKGROUND DATA

The Ti-6Al-4V pedicle screw system increases the risk of adjacent disc degeneration and stress-shielding effect due to enormous rigidity. A titanium alloy with much lower elastic modulus, Ti2448, may help to resolve the complications.

METHODS

A finite element model of intact L3-S1 was established and then validated. Single-level PLIF at L4-L5 with or without a supplementary titanium-alloy pedicle screw system was simulated. A pure moment of 7.6 Nm and a 400 N preload was applied to the finite element model of PLIF, PLIF with the Ti-6Al-4V screw system, and PLIF with the Ti2448 screw system in flexion, extension, axial rotation, and lateral bending.

RESULTS

The axial displacement at the fusion level decreased to 64%, 72%, 84%, and 92% of screw-free status in flexion, extension, axial rotation, and lateral bending, respectively, after augmentation of the Ti2448 screw system, which was 1% to 3% lower than the performance of the Ti-6Al-4V system. The angular displacement at the fusion level with the Ti2448 system was similar to that of the Ti-6Al-4V system, only 2% lower in flexion. Compared with the Ti-6Al-4V system, the Ti2448 system suppressed the increase of intradiscal pressures at the upper adjacent disc in all bending directions, but only in extension and axial rotation at the lower adjacent disc; the maximum stress experienced by cages and screws was higher in all bending directions when augmented with the Ti2448 system.

CONCLUSION

Using the Ti2448 screw system is suggested for augmenting single-level PLIF because it induces less disc intradiscal pressure at adjacent levels and the stress-shielding effect at implant-bone surface with stabilization performance compared with the Ti-6Al-4V screw system.

Influence of an auxiliary facet system on intervertebral discs and adjacent facet joints

BACKGROUND CONTEXT

Facet supplementation stabilizes after facetectomy and undercutting laminectomy. It is indicated in degenerative spondylolisthesis with moderate disc degeneration and dynamic stenosis.

PURPOSE

To determine the influence of an auxiliary facet system (AFS) on the instrumented disc, adjacent levels' discs, and facet joints and to compare it with fusion.

STUDY DESIGN

Finite element study.

METHODS

L3-L4, L4-L5, and L5-S1 were studied using a validated finite element model with prescribed displacements for an intact spine, lesion by facetectomy and undercutting laminectomy, AFS, and fusion at L4-L5. The distribution of segmental range of motion (ROM) and applied moments, von Mises stress at the annulus, and facet joint contact forces were calculated with rotations in all planes. Institutional support for implant evaluation and modeling was received by Clariance.

RESULTS

In flexion-extension and lateral bending, fusion decreased L4-L5 ROM and increased adjacent levels' ROM. Range of motion was similarly distributed with intact lesion and AFS. In axial rotation, L4-L5 ROM represented 33% with intact, 55% after lesion, 25% with AFS, and 21% with fusion. Fusion increased annulus stress at adjacent levels in flexion-extension and lateral bending, but decreased stress at L4-L5 compared with AFS. In axial rotation, von Mises stress was similar with fusion and AFS. Facet loading increased in extension and lateral bending with fusion. It was comparable for fusion and AFS in axial rotation.

CONCLUSIONS

This study suggests that the AFS stabilizes L4-L5 in axial rotation after facetectomy and undercutting laminectomy as fusion does. This is because of the cross-link that generates an increased annulus stress in axial rotation at adjacent levels. With imposed displacements, without in vivo compensation of the hips, the solicitation at adjacent levels' discs and facet joints is higher with fusion compared with AFS. Fusion decreases intradiscal stress at the instrumented level.

Surgical outcomes of additional posterior lumbar interbody fusion for adjacent segment disease after single-level posterior lumbar interbody fusion

PURPOSE

Adjacent segment disease (ASD) is an increasing problematic complication following lumbar fusion surgeries. ASD requires appropriate treatment, although there are only few reports on surgery for ASD. This study aimed to clarify surgical outcomes of posterior lumbar interbody fusion (PLIF) for ASD.

METHODS

Medical charts of 18 patients who underwent the second (repeat) PLIF for ASD were retrospectively investigated (average follow-up, 40 [27-66] months). Modified Japanese Orthopaedic Association (JOA) score and Whitecloud classification were used as outcome measures.

RESULTS

Mean modified JOA score improved from 7.7 just before repeat PLIF to 11.4 at maximum recovery and declined to 10.2 at final follow-up. Mean recovery rate of modified JOA score was 52.9 % at maximum recovery and 31.6 % at final follow-up. According to Whitecloud classification, 17 patients (94 %) were excellent or good and only 1 was fair at maximum recovery, whereas 10 (56 %) were excellent or good, 6 were fair, and 2 were poor at final follow-up. Eight patients (44 %) deteriorated again because of recurrent ASD. Two poor patients underwent a third PLIF.

CONCLUSION

PLIF is effective for ASD after PLIF in the short term, although it tends to lead to a high incidence of recurrent ASD.

Pretension effects of the Dynesys cord on the tissue responses and screw-spacer behaviors of the lumbosacral construct with hybrid fixation

STUDY DESIGN

The pretension of the Dynesys cord was varied to evaluate its effects on both tissue responses and screw-spacer behaviors by the finite-element method.

OBJECTIVE

This study aimed to provide detailed information about the motion-preserving and load-shielding mechanisms of the Dynesys screw-spacer joint.

SUMMARY OF BACKGROUND DATA

Intuitively, higher cord pretension aims to ensure the occurrence of screw-spacer contact, thus making the spacer the transmitter of the vertebral loads. However, detailed investigations of the cord-pretension effects have not yet been carried out. METHODS.: Using a validated lumbosacral model, the moderately degenerative L4-L5 segment was instrumented by a static fixator and the Dynesys fixator was further used to bridge a mildly degenerative L3-L4 segment. The pre-tended cord was modeled as an elastic spring with 0- and 300-N pretensions. The disc range-of-motion, disc stress, facet force, bone-screw stress, and screw-spacer force were chosen as comparison indices. RESULTS.: At the transition and adjacent segments, the range-of-motion differences between the 2 pretensions were 7.7% and 2.0% on average, respectively. The mechanical differences at the transition and adjacent segments were 9.0% and 5.2% (disc stress) and 9.4% and 9.1% (facet force), respectively. The results indicated that the cord pretension has a minor effect on the adjacent segments in comparison with the transition segment. However, the stress at the screw hub and force of the screw-spacer contact of the 300-N pretension were increased by 33.7% and 316.5% on average than without pretension, respectively.

CONCLUSION

The moment arm from the screw-cord center to the fulcrum is significantly less than that of vertebral loads. This leads to the minor effect of increasing the cord pretension on the responses of the adjacent segments. However, the cord pretension can significantly affect both screw-spacer force and bone-screw stress.

LEVEL OF EVIDENCE

4.

Can low-grade spondylolisthesis be effectively treated by either coflex interlaminar stabilization or laminectomy and posterior spinal fusion? Two-year clinical and radiographic results from the randomized, prospective, multicenter US investigational device exemption trial: clinical article

OBJECT

Posterolateral spinal fusion (PSF) has long been the standard of care for degenerative spondylolisthesis, but less invasive, motion-preserving alternatives have been proposed to reduce the complications associated with fusion while still providing neural decompression and stabilization. The object of the current study is to evaluate the safety and efficacy of coflex Interlaminar Stabilization compared with PSF to treat low-grade spondylolisthesis with spinal stenosis.

METHODS

This is a prospective, randomized, multicenter FDA investigational device exemption (IDE) trial comparing coflex Interlaminar Stabilization with laminectomy and PSF. A total of 322 patients from 21 sites in the US were enrolled between 2006 and 2008 for the IDE trial. The current study evaluated only the subset of patients from this overall cohort with Grade 1 spondylolisthesis (99 in the coflex group and 51 in the fusion group). Subjects were randomized 2:1 to receive decompression and coflex interlaminar stabilization or decompression and posterolateral spinal fusion with spinal instrumentation. Data collected included perioperative outcomes, Oswestry Disability Index (ODI), back and worse leg visual analog scale (VAS) scores, 12-Item Short Form Health Survey, Zurich Claudication Questionnaire (ZCQ), and radiographic outcomes at a minimum of 2 years. The FDA criteria for overall device success required the following to be met: 15-point reduction in ODI, no reoperations, no major device-related complications, and no postoperative epidural injections.

RESULTS

At a minimum of 2 years, patient follow-up was 94.9% and 94.1% in the coflex and fusion control groups, respectively. There were no group differences at baseline for any demographic, clinical, or radiographic parameter. The average age was 63 years in the coflex cohort and 65 years in the fusion cohort. Coflex subjects experienced significantly shorter operative times (p < 0.0001), less estimated blood loss (p < 0.0001), and shorter length of stay (p < 0.0001) than fusion controls. Both groups experienced significant improvements from baseline at 2 years in ODI, VAS back, VAS leg, and ZCQ, with no significant group differences, with the exception of significantly greater ZCQ satisfaction with coflex at 2 years. FDA overall success was achieved in 62.8% of coflex subjects (59 of 94) and 62.5% of fusion controls (30 of 48) (p = 1.000). The reoperation rate was higher in the coflex cohort (14 [14.1%] of 99) compared with fusion (3 [5.9%] of 51, p = 0.18), although this difference was not statistically significant. Fusion was associated with significantly greater angulation and translation at the superior and inferior adjacent levels compared with baseline, while coflex showed no significant radiographic changes at the operative or index levels.

CONCLUSIONS

Low-grade spondylolisthesis was effectively stabilized by coflex and led to similar clinical outcomes, with improved perioperative outcomes, compared with PSF at 2 years. Reoperation rates, however, were higher in the coflex cohort. Patients in the fusion cohort experienced significantly increased superior and inferior level angulation and translation, while those in the coflex cohort experienced no significant adjacent or index level radiographic changes from baseline. Coflex Interlaminar Stabilization is a less invasive, safe, and equally efficacious clinical solution to PSF to treat low-grade spondylolisthesis, and it appears to reduce stresses at the adjacent levels. Clinical trial registration no.: NCT00534235 (ClinicalTrials.gov).

The protective role of dynamic stabilization on the adjacent disc to a rigid instrumented level. An in vitro biomechanical analysis

OBJECTIVES

To assess the changes of intradiscal pressure at the bridged and at the adjacent levels to a lumbar two-level hybrid instrumentation.

INTRODUCTION

The elimination of motion produced by spinal fusion may have potential consequences beyond the index level overloading the juxtaposed spinal motion segments and leading to the appearance of degenerative changes. Degeneration of the segments adjacent to instrumented levels has become a topic of increasing interest in the literature over the last years. In order to prevent degenerative disc changes at the adjacent segments to a fused level, a broad scope of techniques have been developed, one of them is hybrid constructs.

METHODS

In 6 human cadaveric lumbosacral specimens, pressure transducers quantified intradiscal pressure changes at three levels (L3-L4, L4-L5 and L5-S1) under axial compression (0-750 N), anterior flexion (+12°) and extension (-12°) in three different situations of spinal stability: intact, L5-S1 rigid rod pedicle screw instrumentation and L4-S1 two-level hybrid instrumentation (rigid at L5-S1 and dynamic at L4-L5).

RESULTS

Once the L5-S1 segment had implanted the rigid instrumentation system (Diapason), the intradiscal pressure at this level decreased by 65 % while the intradiscal pressure at the disc above (L4-L5) increased 20 %. After augmenting the L5-S1 posterior construct with a dynamic stabilization device (Dynesys) at the superior adjacent level, the intradiscal pressure at this level, L4-L5, decreased by 50 % whereas intradiscal pressure at its adjacent level, L3-L4, only experienced a slight increase of 10 %.

CONCLUSIONS

The raise of intradiscal pressure at the adjacent segment to a rigid instrumented segment can be reduced when the rigid construct is augmented with a dynamic stabilization device. Hybrid constructs might have a possible protecting role preventing the occurrence of degenerative disc changes at the adjacent segment to a rigid instrumented level. Augmentation with a dynamic stabilization device might protect the disc above a rigid rod pedicle screw construct.

Update on the evidence for adjacent segment degeneration and disease

BACKGROUND CONTEXT

The evidence surrounding the topic of adjacent segment degeneration and disease has increased dramatically with an abundant amount of literature discussing the incidence of and techniques to avoid it. However, this evidence is often confusing to discern because of various definitions of both adjacent segment degeneration and disease.

PURPOSE

To organize and review the recent evidence for adjacent segment degeneration and disease.

RESULTS

Although multifactorial, three distinct causes of adjacent segment disease in both the lumbar and cervical spine have been discussed: the natural history of the adjacent disc; biomechanical stress on the adjacent level caused by the fusion; and disruption of the anatomy at the adjacent level with the initial surgery. The incidence of adjacent segment degeneration in the lumbar spine has been widely reported in the literature from 0% to 100%; conversely, the reported incidence in the cervical spine is less variable. Similarly, strategies at avoiding adjacent segment disease in the lumbar spine include arthroplasty, dynamic fixation, and percutaneous fixation, whereas in the cervical spine the focus has remained on arthroplasty.

CONCLUSIONS

Adjacent segment disease and degeneration remain a multifactorial problem with several techniques being developed recently to minimize them. In the future, it is likely that the popularity of these techniques will be dependent on the long-term results, which are currently unavailable.

Biomechanical effects of disc degeneration and hybrid fixation on the transition and adjacent lumbar segments: trade-off between junctional problem, motion preservation, and load protection

STUDY DESIGN

The biomechanical effects of disc degeneration and hybrid fixation on the transition and adjacent segments were evaluated using a numerical approach.

OBJECTIVE

This study aimed to evaluate the rigidity-rising effects of the dehydrated disc and bridged fixator on the kinematic and mechanical redistribution of the transition and adjacent segments.

SUMMARY OF BACKGROUND DATA

After static fixation, a dynamic fixator can be used to preserve motion and share loads for the transition segments. However, the hybrid use of both static and dynamic fixators and its effects on the biomechanical behavior of the transition and adjacent segments were not investigated extensively.

METHODS

A nonlinear and osseoligamentous lumbar model from L1 vertebra to S1 vertebrae was developed. Ligament interconnection, muscular contraction, and weight compression were all used to simulate lumbar flexion. The static fixator was instrumented at the degenerative L4-L5 segment and the dynamic fixators (Dynesys system) with different stiffness were subsequently applied to the degenerative or healthy L3-L4 segment. A healthy lumbar model was used as a reference point for further comparison and evaluation. The predicted results were validated with the cadaveric and numerical values of the literature studies. Among the 21 models, the junctional problem at the adjacent (L2/L3 and L5/S1) discs as well as the motion preservation and stress distribution at the transition (L3/L4) disc were compared.

RESULTS

Static fixation and the degenerative disc deteriorated the junctional problem at adjacent segments. On average, the hybrid fixation of the original Dynesys cord constrained the range of motion (ROM) by 65%. Furthermore, it shared 43% of the stress on the transition disc. However, this resulted in the adjacent discs increasing about 50% ROM and 40% stress. The term "trade-off stiffness" was used to express the concept that the decreased stiffness of the original cord could balance the junctional problem, motion preservation, and load protection of the transition and adjacent segments. The trade-off stiffness of the degenerative transition disc was higher than that of the healthy disc. Compared with the original design, the increased ROM and stress of the adjacent segments can be reduced by about 43% using the trade-off stiffness.

CONCLUSION

The use of the hybrid fixator should involve a certain trade-off between the protection of the transition segment and the deterioration of the adjacent segments. This trade-off stiffness, which largely depends on both fixator design and disc degeneration, provides the improved rigidity and flexibility of the transition and adjacent segments.

Posterior dynamic stabilization in the treatment of degenerative lumbar stenosis: validity of its rationale

OBJECT

The authors undertook this study to investigate the validity of the rationale for posterior dynamic stabilization using the Device for Intervertebral Assisted Motion (DIAM) in the treatment of degenerative lumbar stenosis.

METHODS

A cohort of 31 patients who underwent single-level decompression and DIAM placement for degenerative lumbar stenosis were followed up for at least 2 years and data pertaining to their cases were analyzed prospectively. Of these patients, 7 had retrolisthesis. Preoperative and postoperative plain lumbar radiographs obtained in all patients and CT images obtained in 14 patients were analyzed. Posterior disc heights; range of motion (ROM) of proximal, distal, and implant segments; lordotic angles of implant segments; percentage of retrolisthesis; and cross-sectional area and heights of intervertebral foramina on CT sagittal images were analyzed. Clinical outcomes were evaluated using visual analog scale scores and Oswestry Disability Index scores.

RESULTS

The mean values for posterior disc height before surgery, at 1 week after surgery, and at the final follow-up visits were 6.4 ± 2.0 mm, 9.7 ± 2.8 mm, and 6.8 ± 2.5 mm, respectively. The mean lordotic angles at the implant levels before surgery, at 1 week after surgery, and at the final follow-up visits were 7.1° ± 3.3°, 4.1° ± 2.7°, and 7.0° ± 3.7°, respectively. No statistically significant difference was found between the preoperative values and values from final follow-up visits for posterior disc height and lordotic angles at implant levels (p = 0.17 and p = 0.10, respectively). There was no statistically significant difference between the preoperative and final follow-up visit values for intervertebral foramen cross-sectional area and heights on CT images. The ROMs of proximal and distal segments also showed no significant decrease (p = 0.98 and p = 0.92, respectively). However, the ROMs of implant segments decreased significantly (p = 0.02). The average 31.4-month improvement for all clinical outcome measures was significant (p < 0.001).

CONCLUSIONS

Based on radiological findings, the DIAM failed to show validity in terms of the rationale of indirect decompression, but it did restrict motion at the instrumented level without significant change in adjacent-segment ROM. The clinical condition of the patients, however, was improved, and improvement was maintained despite progressive loss of posterior disc height after surgery.

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.

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.

Lumbar degenerative disc disease: current and future concepts of diagnosis and management

Low back pain as a result of degenerative disc disease imparts a large socioeconomic impact on the health care system. Traditional concepts for treatment of lumbar disc degeneration have aimed at symptomatic relief by limiting motion in the lumbar spine, but novel treatment strategies involving stem cells, growth factors, and gene therapy have the theoretical potential to prevent, slow, or even reverse disc degeneration. Understanding the pathophysiological basis of disc degeneration is essential for the development of treatment strategies that target the underlying mechanisms of disc degeneration rather than the downstream symptom of pain. Such strategies ideally aim to induce disc regeneration or to replace the degenerated disc. However, at present, treatment options for degenerative disc disease remain suboptimal, and development and outcomes of novel treatment options currently have to be considered unpredictable.