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Introduction Cervical spondylosis in the warfighter is a common musculoskeletal problem and can be career-ending especially if it requires fusion. Head-mounted equipment and increased biomechanical forces on the cervical spine have resulted in accelerated cervical spine degeneration. Current surgical gold standard is anterior cervical discectomy and fusion (ACDF). Posterior cervical foraminotomy (PCF) is a nonfusion surgical alternative, and this can be effective in alleviating radiculopathy from foraminal stenosis caused by disc-osteophyte complex. Biomechanical studies have not been done to analyze motion associated with military aircrew personnel following PCF. The aim of this study was to compare the biomechanical responses of the effects of ACDF and PCF with different grades of facet resection under simulated military aircrew conditions using range of motion, disc pressure, and facet loads at the index and adjacent levels. Materials and Methods A validated 3D finite element model of the human cervical spinal column was used to simulate various graded PCF and ACDF. All surgical simulations were performed at the most commonly operated level (C5-C6) in warfighters. Pure moment loading under flexion, extension, and lateral bending, and in vivo follower force of 75 N were applied to the intact spine. Hybrid loading protocol was used to achieve 134 degrees of combined flexion-extension and 83 degrees of lateral bending in intact and surgical models to reflect military loading conditions. Segmental motions, disc pressure, and facet load were obtained and normalized with respect to the intact model to quantify the biomechanical effect. Results Anterior cervical discectomy and fusion decreased range of motion at the index and increased motion at the adjacent levels, while all graded PCF responses had an opposite trend: increased motion at the index and decreased motion at adjacent levels. The magnitude of changes depended on the level of resection, spinal level, and loading mode. Disc pressure increased at the index level and decreased at the adjacent levels after PCF. These changes were exaggerated with increasing extent of facet resection. Facet load increased at the index level after PCF especially with extension and right (contralateral) lateral bending. Complete facetectomy led to facet load increases greater than ACDF at the adjacent levels in both flexion and extension. Conclusions Posterior cervical foraminotomy is a motion-preserving implant-free surgical alternative to ACDF for warfighters with cervical radiculopathy after failure of conservative management. The treating surgeon must pay close attention to the extent of facet resection to avoid potential spinal instability and future disc and facet degeneration after PCF. Posterior cervical foraminotomy can be more advantageous than ACDF in terms of adjacent segment degeneration, motion preservation, reoperation rate, surgical cost, and retention of warfighters. [ABSTRACT FROM AUTHOR]

Introduction: Cervical disc arthroplasty (CDA), a motion-preserving alternative to anterior cervical discectomy and fusion (ACDF), is used in military patients for the treatment of disorders such as spondylosis. Since 2007, the FDA has approved eight artificial discs. The objective of this study is to compare the biomechanics after ACDF and CDA with two FDA-approved devices of differing designs under head and head supported mass loadings.Materials and Methods: A previously validated osteoligamentous C2-T1 finite element model was used to simulate ACDF and two types of CDA (Bryan and Prodisc C) at the C5-C6 level. The hybrid loading protocol associated with in vivo head and head supported mass was used to apply flexion and extension loading. First, intact spine was subjected to 2 Nm of flexion extension and the range of motion (ROM) was measured. Next, for each surgical option, flexion-extension moments duplicating the same ROM as the intact spine were determined. Under these surgery-specific moments, ROM and facet force were obtained at the index level, and ROM, facet force, and intradiscal pressure at the rostral and caudal adjacent levels.Results: ACDF led to increased motion, force and pressures at the adjacent levels. Prodisc C led to increased motion and facet force at the index level, and decreased motion, facet force, and intradiscal pressure at both adjacent levels. Bryan produced less dramatic biomechanical alterations compared with ACDF and Prodisc C. Numerical results are given in the article.Conclusions: Recognizing that ROM is a clinical measure of spine stability/performance, CDA demonstrates a more physiological biomechanical response than ACDF, although the exact pattern depends on the implant design. Anterior and posterior column load-sharing patterns were different between the two implants and may affect implant selection based on the anatomical and pathological state at the index and adjacent levels. [ABSTRACT FROM AUTHOR]