Lumbar spinal mobility after short anterior interbody fusion

Artificial disc replacement in spine surgery

Total disc replacement (TDR) is an innovative procedure that has gained traction in spine surgery. A large amount of data in the literature report on the short-term outcomes of TDR surgery favorably. However, surgeons remain reluctant to opt for TDR surgery due to uncertainty of long-term outcomes. Recently, long term data regarding TDR surgery has become available, with some studies showing superior outcomes to fusion surgery. The goal of this review is to synthesize and clinically contextualize the recent literature on TDR surgery. This article also provides brief discussion of the biggest challenges currently facing disc arthroplasties and the ways in which they are being tackled.

Biomechanical Evaluation of Lumbar Decompression Adjacent to Instrumented Segments

BACKGROUND

Multilevel lumbar stenosis, in which 1 level requires stabilization due to spondylolisthesis, is routinely treated with multilevel open laminectomy and fusion. We hypothesized that a minimally invasive (MI) decompression is biomechanically superior to open laminectomy and may allow decompression of the level adjacent the spondylolisthesis without additional fusion.

OBJECTIVE

To study the mechanical effect of various decompression procedures adjacent to instrumented segments in cadaver lumbar spines.

METHODS

Conditions tested were (1) L4-L5 instrumentation, (2) L3-L4 MI decompression, (3) addition of partial facetectomy at L3-L4, and (4) addition of laminectomy at L3-L4. Flexibility tests were performed for range of motion (ROM) analysis by applying nonconstraining, pure moment loading during flexion-extension, lateral bending, and axial rotation. Compression flexion tests were performed for motion distribution analysis.

RESULTS

After instrumentation, MI decompression increased flexion-extension ROM at L3-L4 by 13% (P = .03) and axial rotation by 23% (P = .003). Partial facetectomy further increased axial rotation by 15% (P = .03). After laminectomy, flexion-extension ROM further increased by 12% (P = .05), a 38% increase from baseline, and axial rotation by 17% (P = .02), a 58% increase from baseline. MI decompression yielded no significant increase in segmental contribution of motion at L3-L4, in contrast to partial facetectomy and laminectomy (<.05).

CONCLUSION

MI tubular decompression is biomechanically superior to open laminectomy adjacent to instrumented segments. These results lend support to the concept that in patients in whom a multilevel MI decompression is performed, the fusion might be limited to the segments with actual instability.

ABBREVIATION

MI, minimally invasive.

Long-Term Effects of Segmental Lumbar Spinal Fusion on Adjacent Healthy Discs: A Finite Element Study

Study Design

Experimental study.

Purpose

The aim of the study was to develop a finite element (FE) model to study the long-term effects of various types of lumbar spinal interventions on the discs adjacent to the fused segment.

Overview of Literature

Earlier FE studies have been limited to one particular type of fusion and comparative quantification of the adjacent disc stresses for different types of surgical interventions has not been reported.

Methods

A computer aided engineering (CAE) based approach using implicit FE analysis assessed the stresses in the lumbar discs adjacent to the fused segment following anterior and posterior lumbar spine fusions at one, two and three levels (with and without instrumentation).

Results

It was found that instrumentation and length of fusion were the most significant factors in increasing adjacent level stresses in the lumbar discs.

Conclusions

In the present study, a calibrated FE model that examined spinal interventions under similar loading and boundary conditions was used to provide quantitative data which would be useful for clinicians to understand the probable long-term effect of their choice of surgical intervention.

Anterior decompression with single segmental spinal interbody fusion for Denis type B thoracolumbar burst fracture: a midterm follow-up study

PURPOSE

Our goal was to observe the midterm results of a case series of Denis type B thoracolumbar burst fracture treated with anterior decompression with single segmental spinal Interbody fusion.

METHODS

Twenty patients with Denis type B thoracolumbar burst fractures underwent anterior decompression with single segmental spinal Interbody fusion. They underwent clinical and radiologic follow-up for at least three years after the surgery.

RESULTS

The mean follow-up period lasted 57 months. To the last follow-up, there were no cases of internal fixation loosening, failure and other complications. Titanium mesh or interbody bone grafts were in good position. Spinal kyphosis was not observed. Interbody fusion was achieved for all cases. The average fusion time was 4.5 months. Based on visual analogue scale (VAS) pain scores, percentage of vertebral body height loss and Cobb angle, the difference was statistically significant between the preoperative period and postoperative one year or final follow-up (P < 0.05). Results at postoperative one year and final follow-up were better than the preoperative period. However, the difference was not significant between postoperative one year and final follow-up (P > 0.05).

CONCLUSIONS

Good midterm results on clinical and radiologic evaluation of anterior decompression with single segmental spinal Interbody fusion for suitable patients with Denis type B thoracolumbar burst fracture can be achieved. The incident rate of relative complications is low.

Adjacent level disk disease--is it really a fusion disease?

Adjacent segment degeneration (ASD) is a relatively common phenomenon after spinal fusion surgery. Whether ASD is a consequence of the previous fusion or an individual's predisposition to continued degeneration remains unsolved to date. This article summarizes the existing biomechanical and clinical literature on the causes and clinical impact of ASD, as well as possible risk factors. Further, the theoretical advantage of motion-preserving technologies that aim to preserve the adjacent segment is discussed.

When is a spine fused?

The ability to correctly diagnose spinal non-union is vital to our ability to diagnose and treat patients with new or recurrent symptoms following spine fusion and to accurately assess the efficacy of spine fusion techniques and technologies. Surgical exploration has traditionally been the gold-standard investigation for spinal non-union. As routine surgical exploration is impractical in the majority of patients the use of non-invasive radiologic methods of spine fusion assessment is necessary. The purpose of this paper is to outline the most common radiologic methods of spine fusion assessment including the strengths and limitations associated with each imaging modality. In addition we will review the best-available evidence for the use of radiologic investigations to diagnose spine non-unions. We will then provide recommendations for what we believe to be the best methods of diagnosing successful union of cervical interbody, lumbar interbody and lumbar posterolateral fusions that can be used by spine clinicians and researchers alike.

Relationship between New Osteoporotic Vertebral Fracture and Instrumented Lumbar Arthrodesis

STUDY DESIGN

Retrospective study.

PURPOSE

To evaluate the relationship between a new osteoporotic vertebral fracture and instrumented lumbar arthrodesis.

OVERVIEW OF LITERATURE

In contrast to the growing recognition of the importance of adjacent segment disease after lumbar arthrodesis, relatively little attention has been paid to the relationship between osteoporotic vertebral fractures and instrumented lumbar arthrodesis.

METHODS

Twenty five patients with a thoracolumbar vertebral fracture following instrumented arthrodesis for degenerative lumbar disorders (study group) were investigated. The influence of instrumented lumbar arthrodesis was examined by comparing the bone mineral density (BMD) of the femoral neck in the study group with that of 28 patients (control group) who had sustained a simple osteoporotic vertebral fracture. The fracture after instrumented arthrodesis was diagnosed at a mean 47 months (range, 7 to 100 months) after the surgery.

RESULTS

There was a relatively better BMD in the study group, 0.67 ± 0.12 g/cm(2) compared to the control group, 0.60 ± 0.13 g/cm(2) (p = 0.013). The level of back pain improved from a mean of 7.5 ± 1.0 at the time of the fracture to a mean of 4.9 ± 2.0 at 1 year after the fracture (p = 0.001). However, 12 (48%) patients complained of severe back pain 1 year after the fracture. There was negative correlation between the BMD of the femoral neck and back pain at the last follow up (r = - 0.455, p = 0.022).

CONCLUSIONS

Osteoporotic vertebral fractures after instrumented arthrodesis contribute to the aggravation of back pain and the final outcome of degenerative lumbar disorders. Therefore, it is important to examine the possibility of new osteoporotic vertebral fractures for new-onset back pain after lumbar instrumented arthrodesis.

Residual motion on flexion-extension radiographs after simulated lumbar arthrodesis in human cadavers

Flexion-extension radiographs are commonly used to assess lumbar fusion. Recommended criteria for solid fusion have varied from 1 to 5 degrees of angular motion between vertebrae. Notwithstanding this wide variation, the validity of these criteria have never been biomechanically tested. As a preliminary and initial step, it was the authors' purpose to quantify measurable angular motion after simulating solid lumbar fusion in human cadaver spines. Seven cadaveric spines (L1 to L4) were tested in a radiolucent jig fixed to a servohydraulic testing apparatus. Flexion and extension moments of 10 Nm were applied. Fusion was simulated using metallic implants spanning the L2-L3 motion segment. These included transverse process plates, a spinous process plate, pedicle screw construct, or an anterior vertebral body plate to simulate an intertransverse, interspinous process, facet, and interbody fusions, respectively. Angular movements were measured on lateral radiographs and statistically compared using a repeated measures analysis of variance. Simulated intertransverse fusion resulted in 13+/-4 degrees of motion; interspinous fusion, 9+/-4 degrees; posterior facet fusion, 5+/-3 degrees; and interbody fusion with plate, 3+/-2 degrees. Compared with the intact, only posterior facet fusion and interbody fusion with plate had statistically significantly less motion (P=0.006 and 0.0001, respectively). The amount of radiographically detectable flexion-extension motion with simulated fusions varies widely and seems to be influenced by fusion type. This study documents a range of measurable motion on flexion-extension radiographs after several types of simulated lumbar fusion. However, as the degrees of motion seemed to be high, future studies should use a fusion simulation other than metallic implants that more closely resembles bony arthrodesis.

The clinical characteristics and risk factors for the adjacent segment degeneration in instrumented lumbar fusion

STUDY DESIGN

A retrospective study.

OBJECTIVE

The aims of this study were to evaluate the clinical significance of, characteristics of, and risk factors for adjacent segment degeneration (ASD) in patients who have undergone instrumented lumbar fusion.

SUMMARY OF BACKGROUND DATA

ASD has been considered a potential long-term complication of spinal arthrodesis. However, the exact mechanisms and risk factors related to ASD are not completely understood.

METHODS

A total of 48 patients who underwent instrumented lumbar fusion at L4-5 and had minimal ASD preoperatively were evaluated. The patients were divided into 2 groups at follow-up according to the development of ASD defined by radiologic criteria. Through review of their medical records and the radiologic files, the following variables were evaluated in the 2 groups: basic demographic data, body weight, body height, body mass index, bone mineral density, types of surgical approaches, preoperative and postoperative segmental and lumbar lordosis, and clinical outcomes.

RESULTS

ASD was found in 30 (62.5%) patients. The variables that showed statistical intergroup differences were the mean age at surgery, the mean difference in the degree of preoperative from postoperative lumbar lordosis, and the proportion of patients who underwent anterior lumbar interbody fusion. However, there were no statistically significant intergroup differences in the Japanese Orthopedic Association score at 1-year postoperatively or at the final follow-up, or in the recovery rate, success rate, and complication rate.

CONCLUSIONS

Radiographic ASD is relatively common long-term finding associated with instrumented lumbar fusion. However, radiographic evidence of ASD does not necessarily correlate with a poor outcome. Our results suggest that advanced age, anterior lumbar interbody fusion, and the restoration of the preoperative standing lumbar lordosis may have a protective effect against the development of ASD.

Fusion assessment of posterior lumbar interbody fusion using radiolucent cages: X-ray films and helical computed tomography scans compared with surgical exploration of fusion

BACKGROUND

Plain radiographic assessment of posterolateral fusion has been reported as accurate in only two thirds of patients who were found to be healed at surgical exploration. Plain radiographic techniques for fusion assessment of interbody fusion with radiolucent cages are reported to be accurate. A helical computed tomography (CT) scan shows a high sensitivity for pseudarthrosis compared with plain radiography.

PURPOSE

To determine the accuracy of fusion assessment with plain X-ray films and helical CT scans by comparison to results of surgical exploration of fusion.

STUDY DESIGN/SETTING

The accuracy and interobserver agreement of plain X-ray films and thin-cut helical CT scans were compared with fusion assessment by surgical exploration in patients with posterior lumbar interbody fusion using a radiolucent carbon fiber reinforced polymer cage (CFRP) and iliac crest bone graft.

PATIENT SAMPLE

A review of 90 patients who had surgical exploration of the lumbar fusion.

OUTCOME MEASURES

All patients had plain X-ray films including Ferguson anteroposterior parallel to the interbody space. Fifty-four patients had thin-section helical CT scans.

METHODS

Fusion assessment by exploration was compared with blinded assessment by plain X-ray films and CT scans.

RESULTS

Ninety patients had surgical exploration of 172 lumbar interbody and posterolateral fusion levels. At the time of exploration, fusion was determined to be successful in 87 of 90 patients and 168 of 172 (97%) fusion levels. X-ray assessment showed healed interbody fusions in 87% and posterolateral fusion healed in 75%. CT grading of the interbody fusion found healed interbody fusion in 77%, and the posterolateral fusion was fused in 68%. Plain X-ray films and CT scans had a sensitivity of 100% for pseudarthrosis and a negative predictive value of 100% for healed fusion. Specificity was almost 90% and was not significantly different between X-ray films and CT scans.

CONCLUSIONS

Fusion assessment with plain X-ray films and helical CT scans showed equal accuracy after posterior lumbar interbody fusion confirmed by surgical exploration. Our results indicate that when plain X-ray films show strong evidence of fusion or pseudarthrosis, the helical CT is unlikely to provide useful new information.

Adjacent segment degeneration: observations in a goat spinal fusion study

STUDY DESIGN

The adjacent discs of 13 goats, originally used in a lumbar spinal fusion model study, were analyzed for symptoms of intervertebral disc degeneration by means of magnetic resonance imaging (MRI), macroscopy, and histology. These goats were followed for 6 months and the results were compared with 6 control goats.

OBJECTIVE

To evaluate the development of adjacent segment disc degeneration in vivo in a goat lumbar spinal fusion model.

SUMMARY OF BACKGROUND DATA

There is ongoing debate on whether adjacent segment degeneration (ASD) develops through increased biomechanical load on discs adjacent to fusion sites, or by the natural process of pre-existing degenerative disease. Animal models offer an opportunity to separate these factors by evaluating the development of ASD in nondegenerated animal spines.

METHODS

In a spinal fusion model study 2 segments (L3-L4 and L1-L2) were fixated and followed for 3 months (n = 6) and 6 months (n = 7) in 13 skeletally mature goats. Two adjacent discs (T13-L1 and L4-L5), 1 interjacent disc (L2-L3) and a control disc (L5-L6) were analyzed by means of magnetic resonance imaging, macroscopy, and histology. These results were compared with the discs of 6, nonoperated "normal" goats.

RESULTS

No differences were observed in the adjacent and interjacent intervertebral discs after both follow-up periods. However, severe degenerative changes were observed in the L5-L6 level, originally included as controls.

CONCLUSION

Large animal fusion models offer an excellent opportunity to study ASD in vivo, as pre-existing degenerative disc disease is not present and biomechanical effects of the fusion can be studied more isolated. Our results suggest that adjacent disc degeneration does not develop in our spinal goat fusion model. There is, however, an increased risk of disc degeneration in the L5-L6 level through an unclear mechanism.

Residual sagittal motion after lumbar fusion: a finite element analysis with implications on radiographic flexion-extension criteria

STUDY DESIGN

Finite element analysis of a lumbar fusion model.

OBJECTIVES

To quantify residual sagittal angular motion following various types and levels of completeness of lumbar fusion in order to understand better the validity of current recommendations for interpreting flexion-extension radiographs to assess fusion.

SUMMARY OF BACKGROUND DATA

Recommended threshold criteria for solid fusion using flexion-extension radiographs have varied from 0 degrees to 5 degrees of angular motion between vertebrae. Notwithstanding this wide variation and lack of uniform consensus, the validity of these criteria has not been previously biomechanically assessed to the authors' knowledge. To investigate this issue, the authors sought to test various types of simulated healed, noninstrumented lumbar fusions using finite element modeling to determine the amount of residual angular motion under physiologic stresses.

METHODS

A validated 3-dimensional, nonlinear finite element model of an intact adult human L3-L4 motion segment was developed. Four fusion types were simulated using this model, including anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), intertransverse process fusion, and interspinous process fusion. Variations of completeness of fusion were also represented. For ALIF and PLIF, this included tests of solid bridging bone within the posterior or anterior 75%, 50%, or 25% disc space. In addition, PLIF was also tested with either a unilateral or bilateral facetectomy to simulate commonly used surgical techniques. Variations of intertransverse process fusion included unilateral or bilateral bridging bone with or without medial fusion to the pars interarticularis. Only 1 scenario of a healed, solid interspinous process fusion was tested. The intact model and all fusion models were stressed with 10.6-Nm flexion and extension moments. The angular deflections were recorded in degrees.

RESULTS

A wide range of sagittal angular motion was recorded. For ALIF, this ranged from 0.8 degrees (complete, 100% fusion) to 3.3 degrees (solid fusion of the posterior 25% disc space). For PLIF, the numbers were more varied, ranging from 0.7 degrees (complete, 100% fusion) to 6.9 degrees (solid fusion of posterior 25% disc space with bilateral facetectomy). For intertransverse process fusion, the least motion was with a solid bilateral fusion, with medial healing to the pars (2.0 degrees); the greatest motion was found with a solid unilateral fusion without medial healing (6.0 degrees). Interspinous process fusion allowed only 1.9 degrees of motion.

CONCLUSIONS

The amount of residual flexion-extension motion with simulated lumbar fusions (presumably allowed by the bone's inherent elasticity) under physiologically comparable moments varies with fusion type and, more substantially, with varying amounts of completeness. The current study documents a range of sagittal angular motion after several types of simulated lumbar fusion that appear to have considerable overlap with previously purported radiographic criteria for solid fusion using flexion-extension radiographs. However, it also suggests the possibility that some scenarios of solid, yet incomplete, fusion may allow motion that is substantially greater than 5 degrees, which is beyond the most liberal of previously published threshold criteria.

Tapered cages in anterior lumbar interbody fusion: biomechanics of segmental reactions

Object

The aim of this study was to determine the in vitro biomechanical responses of lumbar spinal segments after implantation of tapered cages.

Methods

Range of motion (ROM)– and stiffness-related data were determined in 10 human cadaveric T12–S1 columns subjected to flexion, extension, and lateral bending modes before and after anterior lumbar interbody fusion in which stand-alone LT-CAGE devices were used. The overall column showed no significant changes in ROM or stiffness. At the instrumented level, stiffness increased significantly (p < 0.05) in flexion and lateral bending modes. Indications of instability in extension were present, but these values were not statistically significant. There was no evidence of adjacent-level instability at any level in any mode, except for the segment superior to the fixation level in flexion; here there was a significant increase in ROM (p < 0.05) and a decrease in stiffness.

Conclusions

The anatomical conformity and bilateral placement of cages provide ample stability and rigidity at the treated level, comparable to that of other cage systems. Because hypermobility is traditionally related to early degenerative changes, the present results appear to suggest that cages do not significantly contribute to such alterations.

Combined anterior plus posterior stabilization versus posterior short-segment instrumentation and fusion for mid-lumbar (L2-L4) burst fractures

STUDY DESIGN

Prospective randomized study. OBJECTIVES.: To compare the results of the combined anterior-posterior surgery (Group A) with posterior "short-segment" transpedicular fixation (SSTF) (Group B) in mid-lumbar burst fractures.

SUMMARY OF BACKGROUND DATA

There are no comparative randomized clinical studies on the outcome following operative treatment of mid-lumbar fractures.

METHODS

Forty consecutive patients with L2-L4 fresh single A3-type/AO burst fractures and load sharing score up to 6 were randomly selected to underwent either combined one-stage anterior stabilization with mesh cage and SSTF (Group A) or solely SSTF with intermediate screws in the fractured vertebra (Group B). Kyphotic Gardner angle, anterior and posterior vertebral body height (PVBHr, AVBHr), spinal canal encroachment (SCE), SF-36, VAS, and Frankel classification were used.

RESULTS

The follow-up observation averaged 46 and 48 months for Group A and B, respectively. Operative time, blood loss, and hospital stay were significant more in Group A. More surgical complications were observed in the Group A. After surgery, VAS was reduced to 4.3 and 3.6 for Group A and Group B, respectively. The SF-36 domains Role physical and Bodily pain improved significantly only in Group B (P = 0.05) and (P = 0.06), respectively. Correction of AVBHr, PVBHr, and spinal canal clearance was similar in both groups. Spinal canal clearance did not differ between the two groups, but it was continuous until the last evaluation in Group B. The final Gardner angle loss of correction averaged 2 degrees and 5 degrees for Group A and Group B, respectively. The posttraumatic Gardner deformity did not significantly improve by SSTF at the final evaluation in the spines of Group B. Gardner angle correlated significantly with SCE in Group B and Group A in all three periods and in the last evaluation, respectively. Frankel grade did not correlate with loss of correction of AVBHr and PVBHr in Group A, while it significantly correlated with loss of PVBHr correction and SCE in the patients of Group B. There was no neurologic deterioration after surgery in any patient. VAS and SF-36 scores did not significantly correlate with the loss of kyphotic angle correction and AVBHr, PVBHr at the final observation in any patient of both groups.

CONCLUSIONS

SSTF offered similar significant short-term correction of posttraumatic deformities associated with mid-lumbar A3-burst fractures, but better clinical results as compared to combined surgery. However, SSTF did not significantly maintain the after surgery achieved correction of local posttraumatic kyphosis at the final evaluation. Thus, SSTF is not recommended for operative stabilization of fractures with this severity.

Effects of anterior lumbar spinal fusion on the distribution of nerve endings and mechanoreceptors in the rabbit facet joint: quantitative histological analysis

The purpose of this study was to investigate the density and distribution of neural endings in rabbit lumbar facet joints after anterior spinal fusion and to evaluate the effects of intervertebral immobilization. An extraperitoneal approach was applied, and L5/6 was fixed with a plate and screws. Bilateral L4/5, L5/6, and L6/7 facet joint capsules were harvested from the rabbits 4, 8, and 16 weeks postoperatively. Capsular tissues were processed using a modified gold chloride staining method, and the specimens were sliced into 15-micro m sections. All sections were analyzed microscopically, and neural ending numbers per unit volume were calculated. Three types of neural ending were identified in each specimen: Pacinian corpuscles, Ruffini corpuscles, and free nerve endings. In the L5/6 fusion segment there was a significant decrease in the number of Pacinian corpuscles at 4 weeks and of Ruffini corpuscles at 4, 8, and 16 weeks after the fusion compared with the control; and in the L4/5 upper adjacent segment there was a significant increase in the number of free nerve endings. The number of Ruffini endings for the L6/7 lower adjacent segment was significantly lower more than 8 weeks after the fusion. These results suggest that immobilization of the intervertebral segment causes a reduction in the number of mechanoreceptors in the facet joint capsules because of the reduction in mechanical stimulation. Moreover, in the upper adjacent facet joint there may be neural sprouting caused by nociceptive stimulation.

The impact of adjacent level disc degeneration on health status outcomes following lumbar fusion

STUDY DESIGN

A retrospective review of patient outcomes after lumbar spinal fusion.

OBJECTIVE

To determine whether patients with a fusion ending adjacent to a "degenerated disc" (DDD group) had worse clinical outcomes than patients with fusions ending adjacent to "normal" discs (NL group).

SUMMARY OF BACKGROUND DATA

Although it has been suggested that creating a rigid motion segment adjacent to a degenerated segment may negatively impact clinical outcomes after lumbar fusion, this question has not been addressed to our knowledge in the English literature.

METHODS

Twenty-five consecutive patients treated with lumbar fusion for degenerative instability who had preoperative lumbar spine magnetic resonance imaging, who completed health status questionnaire Short Form 36 (SF-36), and were seen in the office for radiographic follow-up at least 2 years following surgical treatment formed the study group. The magnetic resonance images were reviewed independently by two spine surgeons and rated for the presence of any degenerative changes. Statistical analysis of the SF-36 data was performed with chi2 and Mann-Whitney U testing.

RESULTS

Of the 25 patients, 20 were fused adjacent to at least one degenerated level (DDD group), whereas 5 were fused adjacent to a normal level (NL group). At follow-up, SF-36 scores were higher for the DDD group in all eight subgroups, contrary to the research hypothesis. A power analysis demonstrated with at least 98% certainty that if patients in the DDD group had even a 10% lower score in any of the 8 SF-36 subgroups, this study would have detected it.

CONCLUSION

This retrospective review of patients who underwent lumbar fusion for degenerative instability demonstrated no adverse impact on clinical outcomes when the lumbar fusion ended adjacent to a degenerative motion segment. Although a power analysis validated these results with 98% certainty, larger prospective studies are needed to confirm that there is no benefit to include degenerated adjacent segments in a lumbar fusion for degenerative instability.

The fate of the adjacent motion segments after lumbar fusion

Lumbar spine fusion is a commonly performed procedure in various pathologic conditions of the spine. Its role remains debated, and moreover, delayed complications may occur, among which is transitional segment alteration leading to recurrence of back pain, gross instability, and neurologic symptoms. Little is known about the long-term prevalence of this complication because of a lack of specific studies. We analyzed the fate of the transitional segments in a homogeneous group of patients operated on during a 14-year period for degenerative conditions of the lumbar spine resistant to conservative treatment. Follow-up ranged from 2 to 15 years. Seventy-five percent of our study group had a minimal 5-year follow-up. In this subgroup, 41% of the patients developed transitional segment alterations, and 20% needed a secondary operation for extension of the fusion. Potential risk factors such as postoperative delay, length of fusion, and spine imbalance were recognized. The frequency of delayed alterations of the adjacent segment and the severity of symptoms related to this complication in this study raise questions about the justification of fusion procedures in degenerative conditions of the spine without threatening instability. Data from the literature confirm the severity of the problem, but many uncertainties remain because of the lack of homogeneous and complete data on both the normal evolution of motion segments of the lumbar spine with age and the fate of the same segments when transformed in transitional segments. Future prospective studies on the subject are needed and must deal with homogeneous groups of patients. More reconstructive surgical procedures need to be developed to lessen the need for fusion procedures.

The fate of the adjacent motion segments after lumbar fusion

Lumbar spine fusion is a commonly performed procedure in various pathologic conditions of the spine. Its role remains debated, and moreover, delayed complications may occur, among which is transitional segment alteration leading to recurrence of back pain, gross instability, and neurologic symptoms. Little is known about the long-term prevalence of this complication because of a lack of specific studies. We analyzed the fate of the transitional segments in a homogeneous group of patients operated on during a 14-year period for degenerative conditions of the lumbar spine resistant to conservative treatment. Follow-up ranged from 2 to 15 years. Seventy-five percent of our study group had a minimal 5-year follow-up. In this subgroup, 41% of the patients developed transitional segment alterations, and 20% needed a secondary operation for extension of the fusion. Potential risk factors such as postoperative delay, length of fusion, and spine imbalance were recognized. The frequency of delayed alterations of the adjacent segment and the severity of symptoms related to this complication in this study raise questions about the justification of fusion procedures in degenerative conditions of the spine without threatening instability. Data from the literature confirm the severity of the problem, but many uncertainties remain because of the lack of homogeneous and complete data on both the normal evolution of motion segments of the lumbar spine with age and the fate of the same segments when transformed in transitional segments. Future prospective studies on the subject are needed and must deal with homogeneous groups of patients. More reconstructive surgical procedures need to be developed to lessen the need for fusion procedures.

Fresh frozen intervertebral disc allografting in a bipedal animal model

STUDY DESIGN

An in vivo experimental study to examine the possibility of using fresh frozen intervertebral disc allograft in disc transplantation.

OBJECTIVES

To investigate the long-term radiographic, pathologic, biochemical, and biomechanical changes of fresh frozen disc allograft in a bipedal animal model.

SUMMARY OF BACKGROUND DATA

It has been shown that intervertebral disc autograft is able to survive and maintain some degree of tissue metabolism and segmental mobility after transplantation in a bipedal animal model. However, the long-term results of disc allografting and the associated problems of graft rejection are unknown.

METHODS

Seventeen rhesus monkeys (15 male, 2 female) between 5 and 8 years of age and weighing between 6.7 and 11.8 kg were used in this study. Of these 17 subjects, two were used as intervertebral disc donors and three were used as controls for the biomechanical testing. The remaining 12 monkeys were randomly divided into a short-term group (n = 4, followed up for 2, 4, 6, and 8 weeks, respectively), a midterm group (n = 6, 6 months), and a long-term group (n = 2, 24 months). Radiologic, histologic, biochemical, and biomechanical changes were investigated.

RESULTS

Radiography and macro- and microhistologic examination showed severe disc degeneration at 24 months of follow-up. Disc height decreased mainly in the early postoperative stage. Decreased water, proteoglycan, and hydroxyproline contents of the allograft were observed at 6 and 24 months of follow-up. The biomechanical properties of the transplanted allograft were similar to those of control.

CONCLUSION

Fresh frozen disc allografts can survive and maintain some degree of cell metabolism and segmental mobility at 24 months after transplantation. However, severe disc degeneration is also observed at this stage.

Disc herniation after lumbar fusion

STUDY DESIGN

Eight patients with a herniated disc after lumbar spinal fusion are reported. Their clinical features, imaging studies, and management are reported.

OBJECTIVES

To identify the incidence and features of disc herniation above a spinal fusion, and to describe their management.

SUMMARY OF BACKGROUND DATA

Late complications of lumbar spinal fusions have been reported in the literature, but disc herniation has not been specifically addressed in detail. The motion segment above a spinal fusion undergoes additional stresses, as documented by increased pressure and excessive motion, resulting in degenerative changes. These factors likely predispose to disc herniation.

METHODS

Of 601 consecutive lumbar fusion cases over an 8-year period, herniated nucleus pulposus above the fusion was diagnosed in 8 patients. The clinical findings and imaging studies were reviewed, including a myelogram computed tomography scan, a magnetic resonance image with positive documentation of the herniation, or both. The management of these cases was reviewed.

RESULTS

Eight patients (1.3%) (4 men and 4 women) were identified, whose average age was 56.4 years. Nonoperative treatment failed in six patients. Two of these patients underwent simple discectomy, and the remaining four underwent discectomy and fusion. All four patients went on to fusion. The average time from disc herniation onset to fusion was 28.4 months.

CONCLUSIONS

Herniated disc after lumbar spinal fusion was found in approximately 1.3% of patients. Although rare, this entity that should be considered when patients complain of recurring back pain after a lumbar spinal fusion.

Development and validation of a new technique for assessing lumbar spine motion

STUDY DESIGN

Dynamic lumbar flexion-extension motions were assessed by an electrogoniometer and a videofluoroscopy unit simultaneously.

OBJECTIVE

To develop and validate a new technique for the assessment of lumbar spine motion.

SUMMARY OF BACKGROUND DATA

Spine instability, a clinical condition that is common but difficult to diagnose, has been suggested to involve a characteristic change in the relation between vertebrae during motion. Assessment of lumbar instability using functional radiographs is controversial. Information regarding dynamic spine kinematics in vivo is limited.

METHODS

A lumbar spine motion analysis system was developed, and its reliability was assessed. Simultaneous total flexion range of motion and segmental motion of the lumbar spine were assessed in 30 healthy volunteers. Lumbar images were captured in 10 degrees intervals during flexion-extension. Intervertebral flexion-extension of each vertebral level was calculated.

RESULTS

In flexion, the lumbar vertebrae flexed with a descending order from L1 to L5 throughout the motion. Conversely, the concavity of lumbar lordosis increased steadily in extension. No statistically significant difference in the pattern of motion was found between genders.

CONCLUSIONS

The results from this study showed that the newly developed technique is reliable. It may have potential value for evaluating spine instability in clinical practice.

Anterior decompression with single segmental spinal interbody fusion for lumbar burst fracture

STUDY DESIGN

The clinical and radiologic records for seven patients with lumbar burst fracture who underwent anterior decompression with single segmental interbody fusion were reviewed.

OBJECTIVE

To determine the clinical results obtained with this method and its influence on the intervertebral disc degeneration inferior to the fusion.

SUMMARY OF BACKGROUND DATA

Some patients with Denis' type B fracture can tolerate one-segment anterior fusion. However, there is no reliable information in the literature regarding the juxtafusional disc degeneration after one-segment fusion.

METHODS

Seven patients with type B lumbar burst fractures, including four with cleavage fracture of the lower endplate, underwent anterior single segmental fusion; three patients underwent surgery with no instrumentation, and four underwent surgery with Kaneda instrumentation. The mean follow-up period lasted 85 months. The kyphosis angle and inferior intervertebral disc height adjacent to the fusion were measured before and after surgery. Pain and working status were evaluated using the scales proposed by Denis et al.

RESULTS

Significant correction loss was obtained 1 year after surgery in the patients in whom no instrumentation was used (7.3 +/- 0.6 degrees), compared with the correction loss in patients whose surgery included the use of instrumentation (0.3 +/- 0.5 degree; P = 0.00001). No further correction losses were seen in either group at the final follow-up examination. No marked reduction in disc height was observed in any patient, including the four patients with cleavage fracture of the lower endplate. All patients returned to their previous occupation; five patients were rated as P1 (no pain) and W1 (returned to heavy labor), and two patients were rated as P2 (minimal pain) and W2 (return to heavy labor with lifting restrictions) at the final follow-up examination.

CONCLUSIONS

There was slight correction loss within 1 year when no instrumentation was used, but this deformity did not affect the clinical results. The results provided no evidence that cleavage fracture of the lower endplate accelerates degeneration of the adjacent intervertebral disc.

The transition zone above a lumbosacral fusion

STUDY DESIGN

The clinical and radiographic effect of a lumbar or lumbosacral fusion was studied in 42 patients who had undergone a posterolateral fusion with an average follow-up of 22.6 years.

OBJECTIVE

To examine the long-term effects of posterolateral lumbar or lumbosacral fusion on the cephalad two motion segments (transition zone).

SUMMARY OF BACKGROUND DATA

It is commonly held that accelerated degeneration occurs in the motion segments adjacent to a fusion. Most studies are of short-term, anecdotal, uncontrolled reports that pay particular attention only to the first motion segment immediately cephalad to the fusion.

METHODS

Forty-two patients who had previously undergone a posterolateral lumbar or lumbosacral fusion underwent radiographic and clinical evaluation. Rate of fusion, range of motion, osteophytes, degenerative spondylolisthesis, retrolisthesis, facet arthrosis, disc ossification, dynamic instability, and disc space height were all studied and statistically compared with an age- and gender-matched control group. The patient's self-reported clinical outcome was also recorded.

RESULTS

Degenerative changes occurred at the second level above the fused levels with a frequency equal to those occurring in the first level. There was no statistical difference between the study group and the cohort group in the presence of radiographic changes within the transition zone. In those patients undergoing fusion for degenerative processes, 75% reported a good to excellent outcome, whereas 84% of those undergoing fusion for spondylolysis or spondylolisthesis reported a good to excellent outcome.

CONCLUSION

Radiographic changes occur within the transition zone cephalad to a lumbar or lumbosacral fusion. However, these changes are also seen in control subjects who have had no surgery.

Intervertebral measurement of lumbar segmental motion with a new measuring device

A new Intervertebral Motion Device (IMD) was developed in this study. Depending on its configuration, the IMD was used to measure motion in the sagittal, frontal, and transverse planes. Calibration results showed that the root-mean-square (RMS) error of the IMD was 0.092 mm in axial translation, 0.065 mm in shear translation, and 0.091 in rotation. Using the IMD, nine intact human lumbosacral spine specimens (L3-S1) were tested under a simulated physiological load on an MTS (Model 858 Bionix, MTS System Corporation Minneapolis, MN). The ranges of motion (ROMs) of intact and instrumented specimens were measured in terms of angular motion (main motion) and coupled translation in the sagittal plane, and angular motion in the transverse plane. The results demonstrated that simulated fusion with CS instrumentation at the level of L4-L5 significantly decreased the ROMs of L4-L5 for all main and coupled motions (P < 0.03). The application of CD rods had less influence on the angular ROM in L/R axial rotation compared to the angular ROMs in Flex/Ext and L/R lateral bending.

Intervertebral disc autografting in a bipedal animal model

Fusion of the spine while restoring stability of the spinal segment, fails to preserve spinal mobility. Long term complications of accelerated degeneration in the neighboring segments have been reported. The present study explores the possibility of intervertebral disc autografting in a bipedal animal model by isolating a lumbar disc together with the adjacent end plates and repositioning it with minimal internal fixation. Fourteen Rhesus monkeys were sacrificed at 2, 4, 6, and 12 months after surgery and the grafted discs were examined radiologically, biochemically, pathologically, and biomechanically. Healing of the bony end plate was seen between 2 to 4 months postoperatively. There was early loss of disc height at 2 and 4 months but there was a suggestion of some reconstitution up to 12 months. There was minimal evidence of gross degeneration at all stages. Gradual loss of water content was found in the annulus and the nucleus. The nucleus pulposus seemed to be able to reaccumulate proteoglycan after an initial drop in the first 4 months. There was significant increase in hydroxyproline content in the annulus fibrosus and the nucleus pulposus. Biomechanically, the grafted disc showed hypermobility in the first 4 months but gradually became stabilized with time. Results from this study suggested that a fresh intervertebral disc autograft could survive a period of ischemia. Although the physiology of the disc was deranged, it was able to preserve a certain degree of segmental mobility without sacrificing stability. Further studies are required to validate these results and the field of disc allografting should be explored.

Threaded titanium cages for lumbar interbody fusions

STUDY DESIGN

This study evaluated safety, fusion success rate, and clinical outcome of a new lumbar interbody hollow, threaded titanium fusion cage in a multicenter, prospective 236-case program adhering to a United States Food and Drug Administration Investigational Device Exemption controlled protocol.

OBJECTIVES

The results were evaluated to demonstrate the safety and effectiveness of this new method to achieve solid lumbar interbody fusions.

SUMMARY OF BACKGROUND DATA

Interbody fusions have certain distinct mechanical advantages over lateral or posterolateral ones. Autologous, cancellous bone is the preferred graft material, but is too soft to maintain the space during fusion without mechanical support. Various methods have been used in the past to maintain the graft integrity during fusion development.

METHODS

An initial pilot study began on 10 patients (followed for 84 months, average 80 months). Two years after that investigation started, the multicenter United States Food and Drug Administration Investigational Device Exemption study began, with cases followed for 28-46 months (average, 32). Ninety-six percent of the investigational Device Exemption study cases had severe, disabling back pain; in addition, 74% had major annular degeneration; 57% had herniations; 21% had osteophytes; and 43% had disc height reduced by greater than 10%. Forty-five percent of cases had previous spinal surgeries, and none were posterior lumbar interbody fusions. Titanium fusion cage pairs were screwed into bored and threaded, parallel intradiscal holes, and 3-8 ml autologous cancellous bone was packed inside each. Fusion success was judged by absence of motion on flexion-extension radiographs, absence of bone halo around the implants, and maintenance of visible bone inside the cages on Ferguson view radiographs.

RESULTS

Segments fused rapidly; the pilot study cases fused at 10 (91%) of 11 levels, with a reported 80% average clinical improvement. Ninety-six percent of the 208 2-year follow-up Investigational Device Exemption cases had fusion, and the Prolo socioeconomic/ functional improvement scale showed: 40% excellent, 25% good, 21% fair, and 14% poor results. Less than 1% of Investigational Device Exemption cases had complications that persisted beyond the average 5 days of hospitalization, and none were serious.

CONCLUSIONS

The Ray titanium fusion cage (Surgical Dynamics, Norwalk, CT) implant method has been found to be an effective, rapid, safe procedure for lumbar spine fusions, demonstrating a high fusion rate and clinical success with rare, serious, or permanent complications.

The spondylolytic vertebra and its adjacent segment. Mobility measured before and after posterolateral fusion

STUDY DESIGN

By using roentgen stereophotogrammetric analysis in six patients having tantalum indicators implanted at a preoperative external fixation test, the mobility in the spondylolytic lumbosacral level and its adjacent segment could be studied before fusion and during the course of postoperative fusion consolidation.

OBJECTIVE

To study the mobility effects on the segment adjacent to a lumbar fusion over time from the preoperative situation until fusion healing as defined by roentgen stereophotogrammetric analysis.

SUMMARY OF BACKGROUND DATA

In vitro studies indicate that the altered biomechanical situation after lumbar fusion increases the intradiscal pressure and changes the kinematics in the juxtafused segment.

METHODS

Six patients with low grade spondylolysisolisthesis were scheduled for fusion of the spondylolytic lumbosacral segment after a preoperative external fixation test. The latter procedure also included implantation of tantalum markers for spinal roentgen stereophotogrammetric analysis. Each patient was examined by roentgen stereophotogrammetric analysis at four separate occasions: before fusion (2 months after removal of the external frame) and 3, 6, and 12 months after surgery. The translatory movements of the L5 vertebra in relation to sacrum and of the L4 vertebra in relation to the L5 vertebra were calculated at each examination.

RESULTS

For the juxtafused L4-L5 level, increased and decreased mobility patterns could be identified. Transformation of the preoperative mobility in the lumbosacral segment to the adjacent segment during fusion consolidation was verified in two patients but was not a general phenomenon.

CONCLUSION

Fusion of the lumbosacral segment can alter the kinematics of the adjacent segment, redistributing the mobility toward relative hypermobility in the juxtafused segment.

Effects of short anterior lumbar interbody fusion on biomechanics of neighboring unfused segments

STUDY DESIGN

Segmental mobility and intradiscal pressure were measured and the data compared in six cadaveric lumbar spine specimens before and after in vitro simulated single level L4-5 and double level L4-5-S1 anterior interbody fusions.

OBJECTIVE

The experimental objective was to study the biomechanical effects of single level L4-5 and double level L4-5-S1 anterior interbody fusions on the neighboring unfused segments.

SUMMARY OF BACKGROUND DATA

The relationship between the local rigidity created by fusion mass and accelerated degeneration reported at the neighboring unfused intervertebral discs is not clear.

METHODS

Six cadaveric lumbar spine specimens were biomechanically tested in flexion and extension. Segmental mobility and intradiscal pressure of the specimens were measured before and after in vitro simulation of single level L4-5 and double level L4-5-S1 anterior interbody fusions.

RESULTS

The mobility of the motion segments immediately above and below an L4-5 fusion was increased in flexion. When the L5-S1 segment was also fused, the loss of segmental motion in both flexion and extension at the L4-5 and L5-S1 were compensated for by increased motion in all levels above the fusion. In both flexion and extension, the intradiscal pressures of all unfused intervertebral discs were increased after a single level L4-5 fusion and this increase was even more marked after a double level L4-5-S1 fusion.

CONCLUSIONS

There is no evidence that the neighboring unfused segments are loaded beyond their physiological limits due to the fusion. However, the neighboring unfused segments have to work more frequently toward the extremes of their functional ranges of motion after fusion and these effects will be more marked after a double level L4-5-S1 fusion.