Motion analysis of single-level cervical total disc arthroplasty: a meta-analysis.

By London Spine
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Motion analysis of single-level cervical total disc arthroplasty: a meta-analysis.

Orthop Surg. 2012 May;4(2):94-100

Authors: Chen J, Fan SW, Wang XW, Yuan W

Abstract
OBJECTIVE: The purpose of this review was to investigate whether cervical total disc arthroplasty (CTDA) preserves motion of the treated level and what its effect is on adjacent segments.
METHODS: Relevant published reports were collected from PubMed, Medline and Cochrane library. The original studies were considered eligible only if the range of motion (ROM) of the index or adjacent level had been investigated. A meta-analysis was then performed on the collected data. Statistical heterogeneity across the various trials was tested using Cochran’s Q statistic and I (2) ; in the case of heterogeneity, a random effect model was used.
RESULTS: The weighted mean differences (WMDs) of the index level were 0.34 (95% confidence interval [CI], -0.53∼1.21, P = 0.440) and 0.23 (95% CI, -1.92∼2.38, P = 0.834) in all included studies and randomized control trials (RCTs), respectively. The WMDs of the cranial adjacent levels, caudal adjacent levels and whole cervical spines were 1.01 (95% CI, 0.55∼1.47, P = 0.000), 1.10 (95% CI, 0.61∼1.59, P = 0.000) and 3.40 (95% CI, -6.02∼12.82, P = 0.479), respectively.
CONCLUSION: These findings suggest that the protective effect against adjacent segment degeneration provided by cervical arthroplasty might not be as good as has been believed. Long-term supporting evidence is still needed.

PMID: 22615154 [PubMed – indexed for MEDLINE]

Adjacent-level range of motion and intradiscal pressure after posterior cervical decompression and fixation: an in vitro human cadaveric model.

By London Spine
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Adjacent-level range of motion and intradiscal pressure after posterior cervical decompression and fixation: an in vitro human cadaveric model.

Spine (Phila Pa 1976). 2012 Jun 1;37(13):E778-85

Authors: Kretzer RM, Hsu W, Hu N, Umekoji H, Jallo GI, McAfee PC, Tortolani PJ, Cunningham BW

Abstract
STUDY DESIGN: This in vitro human cadaveric study measured adjacent-level kinematics after posterior cervical decompression and fixation.
OBJECTIVE: Quantify adjacent-level changes in range of motion (ROM) and intradiscal pressure after posterior cervical decompression and fixation.
SUMMARY OF BACKGROUND DATA: Optimal length of instrumentation after posterior decompression is unclear. Longer posterior cervical fixation constructs may increase the risk of adjacent-segment degeneration.
METHODS: Eight cervicothoracic spines were evaluated intact, with C3-C6 laminectomy, C3-C6 laminectomy + C3-C6 fixation, C3-C6 laminectomy + C3-C7 fixation, C3-C7 laminectomy, C3-C7 laminectomy + C3-C7 fixation, C3-C7 laminectomy + C2-C7 fixation, C3-C7 laminectomy + C3-T2 fixation, and C3-C7 laminectomy + C2-T2 fixation. Testing included intact moments (± 2.0 N·m) in flexion/extension, axial rotation, and lateral bending, with quantification of ROM at C2-C3, C6-C7, and C7-T1 normalized to the intact spine. Intradiscal pressures were also measured at each level.
RESULTS: For the C3-C6 laminectomy group, there were no differences in adjacent-level flexion/extension ROM or intradiscal pressure based on construct length, except at C6-C7, where ROM was significantly decreased when fixation was extended to C7 (P < 0.05). After C3-C7 laminectomy and reconstruction, the greatest increase in C2-C3 flexion/extension ROM and intradiscal pressure occurred in the C3-T2 fixation subgroup (ROM: 348% [P < 0.05]; intradiscal pressure: 319 ± 243 psi [pounds per square inch] vs. 65 ± 41 psi intact [P < 0.05]). At C7-T1, the greatest increase in flexion/extension ROM and intradiscal pressure occurred after C2-C7 fixation (ROM: 531% [P < 0.05]; intradiscal pressure: 152 ± 83 psi vs. 21 ± 14 psi intact [P < 0.05]).
CONCLUSION: For C3-C6 laminectomy, instrumentation to C7 significantly decreased flexion/extension ROM and intradiscal pressure at C6-C7 without significantly increasing either measure at C2-C3 or C7-T1 relative to C3-C6 fixation. In the setting of a C3-C7 laminectomy, when instrumenting to either C2 or T2, consideration should be given to including both levels within these constructs.

PMID: 22228326 [PubMed – indexed for MEDLINE]

Motion analysis of total cervical disc replacements using computed tomography: preliminary experience with nine patients and a model.

By London Spine
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Motion analysis of total cervical disc replacements using computed tomography: preliminary experience with nine patients and a model.

Acta Radiol. 2011 Dec 1;52(10):1128-37

Authors: Svedmark P, Lundh F, Németh G, Noz ME, Maguire GQ, Zeleznik MP, Olivecrona H

Abstract
BACKGROUND: Cervical total disc replacement (CTDR) is an alternative to anterior fusion. Therefore, it is desirable to have an accurate in vivo measurement of prosthetic kinematics and assessment of implant stability relative to the adjacent vertebrae.
PURPOSE: To devise an in vivo CT-based method to analyze the kinematics of cervical total disc replacements (CTDR), specifically of two prosthetic components between two CT scans obtained under different conditions.
MATERIAL AND METHODS: Nine patients with CTDR were scanned in flexion and extension of the cervical spine using a clinical CT scanner with a routine low-dose protocol. The flexion and extension CT volume data were spatially registered, and the prosthetic kinematics of two prosthetic components, an upper and a lower, was calculated and expressed in Euler angles and orthogonal linear translations relative to the upper component. For accuracy analysis, a cervical spine model incorporating the same disc replacement as used in the patients was also scanned and processed in the same manner.
RESULTS: Analysis of both the model and patients showed good repeatability, i.e. within 2 standard deviations of the mean using the 95% limits of agreement with no overlapping confidence intervals. The accuracy analysis showed that the median error was close to zero.
CONCLUSION: The mobility of the cervical spine after total disc replacement can be effectively measured in vivo using CT. This method requires an appropriate patient positioning and scan parameters to achieve suitable image quality.

PMID: 22006984 [PubMed – indexed for MEDLINE]