Elsevier

Surgical Neurology

Volume 70, Issue 3, September 2008, Pages 247-251
Surgical Neurology

Spine
Comparison of pressure effects on adjacent disk levels after 2-level lumbar constructs: fusion, hybrid, and total disk replacement

https://doi.org/10.1016/j.surneu.2008.04.011Get rights and content

Abstract

Background

With increasing advocacy for the use of TDR procedure as a surgical alternative to fusion in the management of lumbar DDD, intradiskal pressures at the adjacent levels of spine have generated considerable interest. The common belief is that adjacent-level disk pressures will be lower after a TDR as opposed to conventional fusion. The aim of this study is to present the effect of different constructs on adjacent-level disk pressures in lumbar spine. We hypothesized that the adjacent-segment disk pressures after 1- and 2-level TDR and/or a fusion-TDR hybrid procedure will show significant variance within physiological range of motion.

Methods

Six adult spine segments T12-S1 with intact ligaments were harvested from cadavers and held firmly in a specially designed fixture. Intradiskal pressures, in motions of flexion, extension, and lateral bending, at L2-L3 and L3-L4 were measured using needle transducers after 2-level TDR L4 through S1, hybrid procedure, and 2-level fusion L4-S1 with femoral ring allograft and pedicle screws.

Results

The pressures with lateral bending were not significantly lower than those with flexion and extension at both levels (P = .18). Although TDR and hybrid specimens recorded slightly lower pressures specifically during lateral bending, no statistical difference in pressures could be detected when movements were combined with various procedures.

Conclusion

Contrary to the assumed hypothesis, the pressures at the adjacent-level disks (L3-4 and L2-3) did not depend upon the stabilization procedure (2-level disk replacement, hybrid, or 2-level fusion) performed after 2-level diskectomy in the lumbosacral spine.

Introduction

Chronic low back pain is a common problem in the general population, leading to an estimated 13 million physician visits and 50 million chiropractor visits per year in the United States alone [13]. A significant proportion of lower back pain is related to the degeneration of the intervertebral disks. Although initial treatment of DDD is generally conservative, it becomes necessary to perform surgery in patients if the conservative approach fails to provide symptomatic relief and/or if there is progressive neurologic deterioration. Although diskectomy is still accepted as an option for a single-level disease, most surgeons prefer to add a stabilization procedure when the disease involves more than one level of lumbar spine because the clinical outcomes of diskectomy alone in this setting are not satisfactory [14].

The stabilization procedures can be broadly divided into 2 groups: arthrodesis and arthroplasty [3]. Arthrodesis or spinal fusion consists of distraction and surgical immobilization of the functional spine unit to effectively eliminate the motion between 2 vertebrae. This reduces the pain and provides improved stability to the spine. Arthroplasty involves implantation of an artificial disk in the intervertebral space and is claimed to relieve symptoms by restoring functionality of the degenerated disk.

However, the published literature still lacks reports about biomechanical bench studies that specifically focus on the pressure changes at adjacent-level intervertebral disks within physiological ranges of motion after arthrodesis or arthroplasty involving 2 consecutive levels of lumbar spine. The present study was designed to specifically study the pressure changes that occur at these adjacent-level disks after 2-level TDR, 2-level fusion, or a hybrid procedure consisting of disk replacement at one level and fusion at the other level in lumbar spine.

We hypothesized that the intradiskal pressures at the adjacent segments after 2-level TDR, a hybrid procedure, and/or 2-level fusion procedure will show significant variance within physiological range of motion in flexion, extension, and lateral bending.

Section snippets

Material and methods

Six cadaver spine segments (T10 to sacrum) were harvested from unembalmed cadavers with an average age of 66 years (range, 52-77 years). The spine specimens were free of anatomical deficits or pathology. All specimens were kept frozen until debridement, potting, and testing. The superficial soft tissue was removed, leaving only the ligamentous attachments intact. The distal portion of the sacrum was embedded in an automotive epoxy compound (Bondo, Atlanta, GA). The proximal segments of T10-T11

Diskectomy

After measuring the pressures in the intact specimens, all specimens were subjected to a 2-level diskectomy without additional instrumentation at first; and the pressures at the adjacent levels were measured to validate the design of the experimental setup. It was noted that the pressures in flexion and extension significantly dropped at the L3-L4 levels after diskectomy even when compared with intact specimens. However, the adjacent levels did not show a decrease in pressures after diskectomy

Discussion

Chow et al [2] studied the intradiskal pressures for intact and simulated fusion of 1-level L4-5 and 2-level L4-S1 in cadavers to demonstrate the change in pressures in the unfused segments. They measured pressures in the intact disks at L2-3 and L3-L4 in 15° flexion mode and showed a statistically significant increase in pressures in specimens after 2-level fusion procedures. In the current experiment, we analyzed the normalized values (procedure/intact) to reduce the variability within

Conclusion

The pressures at the adjacent-level disks (L3-L4 and L2-L3) within physiological range of motion are independent of the stabilization procedure (2-level disk replacement, hybrid, or 2-level fusion) performed after 2-level diskectomy in the lumbosacral spine. However, the present study, being a biomechanical laboratory experiment, needs to be corroborated by future clinical trials to confirm the findings.

References (15)

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    There is evidence that fusion constructs alter sagittal balance and contribute to undesirable complications in the long-term, including as failed back syndrome and adjacent segment disease. Several studies on TDR have shown outcomes that compare favorably with fusion, particularly for single-level disease [11,12]. For two-level TDR, there is evidence to suggest a higher risk of facet joint arthropathy and poorer outcome when compared to single-level TDR [6].

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    Considerable progress with regard to the assessment of adequate indications and contraindications for TDR has been made [33–37,63–66], outcome-determining factors have been identified including the adequate extent of DDD, knowledge on the center of rotation, segmental and sagittal alignment after TDR, influence of pre- and postoperative mobility, and adequate implant placement [15,67–80]. Similarly, biomechanical and radiological studies have investigated the effect of TDR on the index and adjacent level as well as motion characteristics of the prosthesis and the lumbar spine to a large extent [81–101]. Despite the previously mentioned satisfactory results, which were observed in the present study, the current data nevertheless have to be interpreted as a “worst-case scenario” that included the initial clinical and technical learning curve.

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