Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion?

Spinal disassociation masquerading as iatrogenic listhesis above a previous fusion

STUDY DESIGN

A case of remarkable instability adjacent to an L5-S1 fusion is reported.

OBJECTIVES

The objective of this study was to review a case of marked instability adjacent to a prior fusion. Diagnostic workup and surgical management options are discussed.

SUMMARY OF BACKGROUND DATA

Junctional degeneration above or below the levels of a spinal fusion may be associated with instability. We present an unusual case of instability whose severity was only apparent when the patient was under general anesthesia.

MATERIALS AND METHODS

A 52-year-old man with a history of prior L5-S1 fusion presented with severe back pain and lower extremity weakness. Workup including multiple imaging methods revealed junctional degeneration and a Grade I spondylolisthesis at L4-L5 with minimal translation on dynamic imaging. Operative intervention was planned.

RESULTS

Intraoperative imaging revealed marked distraction at the L4-L5 disc space not apparent on preoperative dynamic films. The surgical approach was modified accordingly.

CONCLUSIONS

Adjacent segment degeneration next to a prior lumbar fusion may be associated with extreme instability. Treatment may require complex stabilization.

Biomechanics of the C5-C6 Spinal Unit Before and After Placement of a disc prosthesis

The study consists of a biomechanical comparison between the intact C5-C6 spinal segment and the same segment implanted with the Bryan artificial disc prosthesis (Medtronic Ltd., Memphis, TN, USA), by the use of the finite element (FE) method. Our target is the prediction of the influence of prosthesis placement on the resulting mechanics of the C5-C6 spine unit. A FE model of the intact C5-C6 segment was built, employing realistic models of the vertebrae, disc and ligaments. Simulations were conducted imposing a compression preload combined to a flexion/extension moment, a pure lateral bending moment and a pure torsion moment, and the calculated results were compared to data from literature. The model was then modified to include the Bryan cervical disc prosthesis, and the simulations were repeated. The location of the instantaneous center of rotation (ICR) of C5 with respect to C6 throughout flexion/extension was calculated in both models. In general, the moment-rotation curves obtained from the disc prosthesis-implanted model were comparable to the curves obtained from the intact model, except for a slightly greater stiffness induced by the artificial disc. The position of the calculated ICRs was rather stable throughout flexion-extension and was generally confined to a small area, qualitatively matching the corresponding physiological region, in both models. These results imply that the Bryan disc prosthesis allows to correctly reproduce a physiological flexion/extension at the implanted level. The results of this study have quantified aspects that may assist in optimizing cervical disc replacement primarily from a biomechanical point of view.

Quantitative analysis of changes in cervical intervertebral foramen size with vertebral translation

STUDY DESIGN

Simulated translation of the C5 vertebra was performed in 20 embalmed cadaveric cervical spines, and cross-sectional areas of the C4-C5 and C5-C6 intervertebral foramina were measured and compared before and after translation of the C5 vertebra.

OBJECTIVE

To determine the relationship of cross-sectional intervertebral foraminal areas to the degrees of vertebral translation.

SUMMARY OF BACKGROUND DATA

The common feature of clinical instability and adjacent diseases of the cervical spine is malalignment of the cervical spine (i.e., there is ventral and dorsal translation of vertebral body with respect to the adjacent upper and lower vertebral body, respectively). To our knowledge, no previous study has analyzed the quantitative effect of vertebral translation on the size of the intervertebral foramina.

METHODS

The cross-sectional areas of the intervertebral foramina at C4-C5 and C5-C6 were measured on computerized tomography. The images were then transferred to the personal computer, where consecutive dorsal translations of C5 vertebrae with a 1-mm increment from 1 to 5-mm displacements were performed using Microsoft paint software (Microsoft, Corp., Redmond, WA). National Institutes of Health (Bethesda, MD) Image J software (V1.33m) was then used to measure the areas of both sides of C4-C5 and C4-C6 foramina at normal and each displacement level in the computer.

RESULTS

Following dorsal translation of C5 vertebra, anterolisthesis of C4 relative to C5 and retrolisthesis of C5 relative to C6 was noted. No significant difference was found between the measured values using Aquarius Image software (Microsoft, Corp.) on computerized tomography and National Institutes of Health image J software on the desktop computer (P > 0.05). When compared with normal values, there was an increase in the C4-C5 intervertebral foraminal area (i.e., 6%, 14%, 18%, 21%, and 26% with anterolisthesis of C4 relative to C5 following 1, 2, 3, 4, and 5-mm dorsal translation of the C5 vertebra, respectively). There was a 12% decrease in the C5-C6 intervertebral foraminal area, with each 1-mm incremental retrolisthesis of C5 relative to C6 vertebra. Statistically significant differences were found among residual cross-sectional foraminal areas following different degrees of dorsal translation (P < 0.05).

CONCLUSION

There is a significant increase in size with anterolisthesis and decrease in size with retrolisthesis of upper and lower adjacent vertebral intervertebral foramina, respectively.

Prospective measurement of function and pain in patients with non-neoplastic compression fractures treated with vertebroplasty

BACKGROUND

There has been an increasing number of reports regarding the benefits of vertebroplasty for the treatment of vertebral compression fractures. In this investigation, validated outcome tools were utilized to document the impact of vertebroplasty on pain and function.

METHODS

Fifty patients were recruited at a tertiary university hospital. Patients had been treated for intractable pain due to osteoporotic compression fracture(s) for at least four weeks. The vertebroplasty procedures were performed by a radiologist. The subjects were followed prospectively for one year and received conservative treatment in conjunction with the vertebroplasty. Validated outcome tools, including a visual analog scale, the Oswestry scale, and the Roland-Morris functional activity questionnaire, were used to evaluate changes in pain and functional capabilities.

RESULTS

Fifty patients, thirty-one women and nineteen men (mean age, 68.6 years), were followed prospectively for one year. One hundred and three fractures (fifty-nine thoracic and forty-four lumbar) were treated. The visual analog scale showed the greatest improvement between the baseline score (mean, 7.76) and the score at one month (mean, 2.9), and the score remained improved at one year (mean, 2.9). The Oswestry and Roland-Morris questionnaires demonstrated significant (p < 0.0001) functional improvement between the baseline and one-month scores. With the numbers available, there were no significant changes in any variable from one month to one year (p > 0.05).

CONCLUSIONS

Vertebroplasty is an effective treatment for patients with intractable pain due to osteoporotic vertebral compression fractures. Improvement in pain scores and functional capabilities that were found at one month were maintained at one year.

General Considerations for Cervical Arthroplasty with Technique for Prodisc-C

Motion-preserving spinal arthroplasty is a triumph of modern biomechanics, material sciences, and surgical technique. The ability to remove entire intervertebral discs and re-place them with prostheses that preserve height and alignment as well as motion and stability, all the while alleviating the pain and spinal cord compression, is the result of nearly 50 years of progress in joint arthroplasty. Although the clear benefit or danger of artificial cervical discs is still unknown, they are already fundamentally changing the field of cervical spine surgery and are undoubtedly going to establish their place in the armamentarium for spinal surgeons. Short-term follow-up studies indicate that cervical arthroplasty is as safe and effective as traditional fusion surgery, but follow-up studies are no longer needed.

Cervical disc replacement

STUDY DESIGN

Review article.

OBJECTIVE

To critically review the state of the emerging field of cervical disc replacement.

SUMMARY OF BACKGROUND DATA

Although anterior cervical decompression and fusion (ACDF) has been used successfully in the treatment of symptomatic radiculopathy and/or myelopathy, biomechanical studies have reported the deleterious effects of cervical fusion on adjacent level kinematics. Proponents of cervical disc replacement claim that maintenance of motion at the operated level will reduce the incidence of adjacent level degeneration and improve long-term clinical outcomes when compared with ACDF.

METHODS

A systematic review of the literature dealing with cervical disc replacement and technologies of arthroplasty design that may have relevance to the cervical spine. A review of the design characteristics and published clinical data for cervical prostheses undergoing Investigational Device Exemption (IDE) study in the United States is provided.

RESULTS

Current cervical disc replacement designs include one-piece implants and implants with single- or double-gliding articulations with either metal-on-metal or metal-on-polymer bearing surfaces. Reports of in vitro wear testing have claimed substantially less wear for cervical implants than that seen with prosthetic hips and knees. Short-term clinical results after decompression and cervical disc replacement for the treatment of cervical radiculopathy and/or myelopathy are encouraging. Prospective, randomized trials are lacking.

CONCLUSIONS

Cervical disc replacement is an innovative technology that preserves motion at the instrumented level/s and will potentially improve load transfer to the adjacent levels compared with fusion. Clinical reports of success of cervical total disc replacement are encouraging but are also quite preliminary. As the U.S. IDE studies are completed, a clearer role for the place of cervical disc replacement in the spine surgeon's armamentarium should emerge.

Hybrid constructs

Hybrid constructs can combine motion-preserving technologies with each other or motion-preserving technologies with fusion techniques. Hybrid constructs can be implanted in single-stage or multistage surgeries. Early results are promising. Further study under formal scientific conditions is necessary to explore the benefit of these combinations.