Neurosurgery Blog

J Neurosurg Spine 15:630–635, 2011.DOI: 10.3171/2011.8.SPINE11273

Cervical arthroplasty has emerged as a means of preventing adjacent segment disease by preserving motion, restoring sagittal balance, and mimicking natural spinal kinematics. The purpose of this retrospective in vivo study was to characterize the impact of arthroplasty on sagittal balance and segmental kinematics of the cervical spine.

Methods. Sixty patients receiving the Bryan disc, ProDisc-C, or Prestige LP disc were retrospectively analyzed. Only single-level arthroplasty cases were included in this study. Lateral dynamic radiographs of the cervical spine were evaluated using quantitative measurement analysis software to determine the kinematics at the index level both preoperatively and 1 year postoperatively. Collected parameters included range of motion (ROM), disc angles, shell angles, anterior and posterior disc heights (ADHs/PDHs), translation, and center of rotation (COR). Preoperative and postoperative data were compared using the Student t-test, with p < 0.05 indicating significance.

Results. The Bryan and Prestige LP discs preserved motion, whereas the ProDisc-C increased segmental ROM from extension to flexion. Following surgery, the Bryan disc exhibited significant shell angle kyphosis, while Pro- Disc-C and Prestige LP retained lordosis. Both ADHs and PDHs decreased following insertion of the Bryan disc. In contrast, the ProDisc-C increased the ADHs and PDHs by 80% and 52%, respectively, and the Prestige LP disc increased the ADHs and PDHs by 20%. Only the ProDisc-C demonstrated significant translation of 0.7 mm. The ProDisc-C shifted the COR x by 0.9 mm anteriorly, while the Prestige LP disc demonstrated a significant superior shift of 2.2 mm in COR y.

Conclusions. All discs adequately maintained ROM at the surgical level. The greatest difference among the 3 devices was in the disc height and index angle measurements

Neurosurg Q 2011;21:17–21.

Much information and classifications of lumbar facet joint degeneration after lumbar total disc replacement are available, but nowadays in the cervical spine this concept is unstudied.

Analyzing our experience, we propose a computed tomography (CT) scan classification to evaluate degenerative facet joint disease after cervical arthroplasty. After 5-year follow-up for total disc replacement in a consecutive series of 162 patients (44.5±8.6-y-old) with a total of 280 Porous Coated Motion total cervical disc replacement from C3-4 to C7-T1, we analyzed the facet degeneration in 4 grades using CT scan, and compared with preoperative images. CT scans, x-rays, and clinical outcomes were collected preoperatively and postoperatively after 3 and 6 months, and annually after 12-month follow-up. The Neck Disability Index and Visual Analog Scale were used to assess pain and functional outcomes.

From all operated levels, we found 8.57% (24 levels) of degenerated facets. On the basis of the proposed classification, 50% (12 levels) of all degenerated levels had grade I, 37.5% (9 levels) with grade II, 8.3% (2 levels) with grade III, and 4.16% (1 level) had grade IV of facet degeneration. In patients with grades III and IV, it was possible to observe a worsening in Visual Analog Scale outcome assessment.

Facet joint degeneration is a possible consequence of cervical disc arthroplasty, despite its low rate occurrence. We did not find relationship between the early grades of CT observed facet degeneration and clinical results, but in grades III and IV there was correlation. A CT scan classification to evaluate cervical degenerative facet joint disease is essential to better understand and report this spinal phenomenon.

J Neurosurg Spine 14:38–45, 2011. (DOI: 10.3171/2010.9.SPINE09865)

Current lumbar total disc replacement (TDR) devices require an anterior approach for implantation. This approach has inherent limitations, including risks to abdominal structures and the need for resection of the anterior longitudinal ligament (ALL). Placement of a TDR device from a true lateral (extreme lateral interbody fusion [XLIF]) approach is thought to offer a less invasive option to access the disc space, preserving the stabilizing ligaments and avoiding scarring of anterior vasculature. In this study, the authors attempted to quantify the clinical and radiographic outcomes of a lateral approach to lumbar TDR from a prospective, single-center experience.

Methods. A TDR device designed for implantation through a true lateral, retroperitoneal, transpsoas approach (XLIF) was implanted in 36 patients with discography-confirmed 1- or 2-level degenerative disc disease. Clinical (pain and function) and radiographic (range of motion [ROM]) data were prospectively collected preoperatively, postoperatively, and serially for a minimum of 24 months’ follow-up.

Results. Thirty-six surgeries were performed in 16 men and 20 women (mean age 42.6 years). Surgeries included 15 single-level TDR procedures at L3–4 or L4–5, three 2-level TDR procedures spanning L3–4 and L4–5, and 18 hybrid procedures (anterior lumbar interbody fusion [ALIF]) at L5–S1 and TDR at L4–5 [17] or L3–4 [1]). Operative time averaged 130 minutes, with an average blood loss of 60 ml and no intraoperative complications. Postoperative radiographs showed good device placement. All patients were walking within 12 hours of surgery and all but 9 were discharged the next day (7 of 9 had hybrid TDR/ALIF procedures). Five patients (13.8%) had psoas weakness and 3 (8.3%) had anterior thigh numbness postoperatively, both resolving within 2 weeks. One patient (2.8%) demonstrated weakness of the leg ipsilateral to the approach side, which lasted through the 3-month visit but was resolved by the 6-month visit. One patient (2.8%) was found to have hypertrophy of the quadriceps contralateral to the approach side at the 12-month visit, which was resolved by the 2-year visit. Four patients (11%) had postoperative facet joint pain, all in hybrid cases. All patients were 2 years or more postsurgery as of this writing, although 3 were lost to follow-up between the 1- and 2-year visits. In 2 cases (5.6%), removal of the TDR device and revision to fusion were required due to unresolved pain. At 2 years’ follow-up, the average visual analog scale and Oswestry Disability Index scores had improved 69.6% and 61.4%, respectively, and ROM averaged 8.6°, well within physiological norms.

Conclusions. Long-term results of a laterally placed TDR device demonstrate maintenance of pain relief and functional improvement. The benefits of this technique—minimal morbidity, avoiding mobilization of the great vessels, preserving the ALL, biomechanically stable orientation, and broader revision options—suggest a promising new direction for TDR procedures.

SPINE Volume 36, Number 1, pp E27–E32

Study Design. Biomechanical study using human cadaveric lumbar spines.

Objective. To evaluate effects of total disc replacement (TDR) on spine biomechanics at the treated and adjacent levels.

Summary of Background Data. Previous studies on spine biomechanics after TDR were focused on facet forces and range of motion and report contradictory results. Characterization of contact pressure, peak contact pressure, force, and peak force before and after TDR may lead to a better understanding of facet joint function and may aid in prediction of long-term outcomes after TDR.

Methods. Seven fresh-frozen human cadaveric lumbar spines were potted at T12 and L5 and installed in a 6 degrees of freedom displacement- controlled testing system. Displacements of 15° flexion/ extension, 10° right/left bending, and 10° right/left axial rotation were applied. Contact pressure, peak contact pressure, force, peak force, and contact area for each facet joint were recorded at L2–L3 and L3–L4 both before and after TDR at L3–L4. The data were analyzed with analysis of variance and t tests.

Results. Axial rotation had the most impact on contact pressure, peak contact pressure, force, peak force, and contact area in intact spines. During lateral bending and axial rotation, TDR resulted in a significant increase in facet forces at the level of treatment and a decrease in contact pressure, peak contact pressure, and peak force at the level superior to the TDR. With flexion/extension, there was a decrease in peak contact pressure and peak contact force at the superior level.

Conclusion. Our study demonstrates that rotation is the most demanding motion for the spine. We also found an increase in facet forces at the treated level after TDR. We are the first to show a decrease in several biomechanical parameters after TDR at the adjacent superior level. In general, our findings suggest there is an increase in loading of the facet joints at the level of disc implantation and an overall unloading effect at the level above.

DOI:10.1007/s00701-009-0529-5. Acta Neurochirugica

Degenerative disc disease is one of the most frequent spinal disorders. The anatomy and the biomechanics of the intervertebral disc are very complex, and the pathomechanics of its degeneration are poorly understood. Despite this complexity and uncertainty, great advances have been made in the field of disc replacement technology, with promising results. Difficulties are continuously being encountered, but careful analysis of the results and intensive research and development will assist in countering these problems. There are approximately 40 clinical reports in the literature describing various aspects of randomised controlled trials involving intervertebral disc arthroplasty. However, the majority of these publications do not provide reliable information, in that they give only interim results and/or the results from just one of the many centres in multicentre studies. Such publications must be interpreted with caution, since they do not always represent the results of the whole study population and may hence be underpowered. We identified six randomised controlled trials that compared the final clinical outcomes of disc arthroplasty and spinal fusion. The present systematic review attempts to give an overview of the current status of disc arthroplasty.

Acta Neurochir (2010) 152:393–404. DOI 10.1007/s00701-009-0529-5

Degenerative disc disease is one of the most frequent spinal disorders. The anatomy and the biomechanics of the intervertebral disc are very complex, and the pathomechanics of its degeneration are poorly understood. Despite this complexity and uncertainty, great advances have been made in the field of disc replacement technology, with promising results. Difficulties are continuously being encountered, but careful analysis of the results and intensive research and development will assist in countering these problems. There are approximately 40 clinical reports in the literature describing various aspects of randomised controlled trials involving intervertebral disc arthroplasty. However, the majority of these publications do not provide reliable information, in that they give only interim results and/or the results from just one of the many centres in multicentre studies. Such publications must be interpreted with caution, since they do not always represent the results of the whole study population and may hence be underpowered. We identified six randomised controlled trials that compared the final clinical outcomes of disc arthroplasty and spinal fusion. The present systematic review attempts to give an overview of the current status of disc arthroplasty.