Is Posterior Cervical Foraminotomy Better Than Fusion for Warfighters?: A Biomechanical Study

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.

Implant Design and Cervical Spinal Biomechanics and Neurorehabilitation: A Finite Element Investigation

INTRODUCTION

The cervical spine, pivotal for mobility and overall body function, can be affected by cervical spondylosis, a major contributor to neural disorders. Prevalent in both general and military populations, especially among pilots, cervical spondylosis induces pain and limits spinal capabilities. Anterior Cervical Discectomy and Fusion (ACDF) surgery, proposed by Cloward in the 1950s, is a promising solution for restoring natural cervical curvature. The study objective was to investigate the impacts of ACDF implant design on postsurgical cervical biomechanics and neurorehabilitation outcomes by utilizing a biofield head-neck finite element (FE) platform that can facilitate scenario-specific perturbations of neck muscle activations. This study addresses the critical need to enhance computational models, specifically FE modeling, for ACDF implant design.

MATERIALS AND METHODS

We utilized a validated head-neck FE model to investigate spine-implant biomechanical interactions. An S-shaped dynamic cage incorporating titanium (Ti) and polyetheretherketone (PEEK) materials was modeled at the C4/C5 level. The loading conditions were carefully designed to mimic helmet-to-helmet impact in American football, providing a realistic and challenging scenario. The analysis included intervertebral joint motion, disk pressure, and implant von Mises stress.

RESULTS

The PEEK implant demonstrated an increased motion in flexion and lateral bending at the contiguous spinal (C4/C5) level. In flexion, the Ti implant showed a modest 5% difference under 0% activation conditions, while PEEK exhibited a more substantial 14% difference. In bending, PEEK showed a 24% difference under 0% activation conditions, contrasting with Ti's 17%. The inclusion of the head resulted in an average increase of 18% in neck angle and 14% in C4/C5 angle. Disk pressure was influenced by implant material, muscle activation level, and the presence of the head. Polyetheretherketone exhibited lower stress values at all intervertebral disc levels, with a significant effect at the C6/C7 levels. Muscle activation level significantly influenced disk stress at all levels, with higher activation yielding higher stress. Titanium implant consistently showed higher disk stress values than PEEK, with an orders-of-magnitude difference in von Mises stress. Excluding the head significantly affected disk and implant stress, emphasizing its importance in accurate implant performance simulation.

CONCLUSIONS

This study emphasized the use of a biofidelic head-neck model to assess ACDF implant designs. Our results indicated that including neck muscles and head structures improves biomechanical outcome measures. Furthermore, unlike Ti implants, our findings showed that PEEK implants maintain neck motion at the affected level and reduce disk stresses. Practitioners can use this information to enhance postsurgery outcomes and reduce the likelihood of secondary surgeries. Therefore, this study makes an important contribution to computational biomechanics and implant design domains by advancing computational modeling and theoretical knowledge on ACDF-spine interaction dynamics.

Comparison of Load-Sharing Responses Between Graded Posterior Cervical Foraminotomy and Conventional Fusion Using Finite Element Modeling

Following the diagnosis of unilateral cervical radiculopathy and need for surgical intervention, anterior cervical diskectomy and fusion (conventional fusion) and posterior cervical foraminotomy are common options. Although patient outcomes may be similar between the two procedures, their biomechanical effects have not been fully compared using a head-to-head approach, particularly, in relation to the amount of facet resection and internal load-sharing between spinal segments and components. The objective of this investigation was to compare load-sharing between conventional fusion and graded foraminotomy facet resections under physiological loading. A validated finite element model of the cervical spinal column was used in the study. The intact spine was modified to simulate the two procedures at the C5-C6 spinal segment. Flexion, extension, and lateral bending loads were applied to the intact, graded foraminotomy, and conventional fusion spines. Load-sharing was determined using range of motion data at the C5-C6 and immediate adjacent segments, facet loads at the three segments, and disk pressures at the adjacent segments. Results were normalized with respect to the intact spine to compare surgical options. Conventional fusion leads to increased motion, pressure, and facet loads at adjacent segments. Foraminotomy leads to increased motion and anterior loading at the index level, and motions decrease at adjacent levels. In extension, the left facet load decreases after foraminotomy. Recognizing that foraminotomy is a motion preserving alternative to conventional fusion, this study highlights various intrinsic biomechanical factors and potential instability issues with more than one-half facet resection.

Effect of Fusion and Arthroplasty for Cervical Degenerative Disc Disease in Active Duty Service Members Performed at an Overseas Military Treatment Facility: A 2-Year Retrospective Analysis

INTRODUCTION

Among U.S. military active duty service members, cervicalgia, cervical radiculopathy, and myelopathy are common causes of disability, effecting job performance and readiness, often leading to medical separation from the military. Among surgical therapies, anterior cervical discectomy and fusion (ACDF) and cervical disc arthroplasty (CDA) are options in select cases; however, elective surgeries performed while serving overseas (OCONUS) have not been studied.

MATERIALS AND METHODS

A retrospective analysis of a prospectively collected surgical database from an OCONUS military treatment facility over a 2-year period (2019-2021) was queried. Patient and procedural data were collected to include ACDF or CDA surgery, military rank, age, tobacco use, pre- and post-operative visual analogue scales for pain, and presence of radiographic fusion after surgery for ACDF patients or heterotopic ossification for CDA patients. Chi-square and Student t-test analyses were performed to identify variables associated with return to full duty.

RESULTS

A total of 47 patients (25 ACDF and 22 CDA) underwent surgery with an average follow-up of 192.1 days (range 7-819 days). Forty-one (87.2%) patients were able to return to duty without restrictions; 10.6% of patients remained on partial or limited duty at latest follow-up and one patient was medically separated from the surgical cohort. There was one complication and one patient required tour curtailment from overseas duty for ongoing symptoms.

CONCLUSIONS

Both ACDF and CDA are effective and safe surgical procedures for active duty patients with cervicalgia, cervical radiculopathy, and cervical myelopathy. They can be performed OCONUS with minimal interruption to the patient, their family, and the military unit, while helping to maintain surgical readiness for the surgeon and the military treatment facility.

Gender Differences in Cervical Spine Motions and Loads With Head Supported Mass Using Finite Element Models

While many studies have been conducted to delineate the role of gender in rear impact via experiments, clinical investigations, modeling, and epidemiological research, the effect of the added head mass on segmental motions has received less attention. The objective of the study is to determine the role of the head supported mass on the segmental motions and loads on the cervical spinal column from rear impact loading. The study used finite element modeling. The model was subjected to mesh convergence studies. It was validated with human cadaver experimental data by applying the rear impact acceleration pulse to the base of the spine. At all levels of the subaxial spinal column, a comparison was made between male and female spines and with and without the use of an army combat helmet. For this purpose, segmental motions, forces, and bending moments were used as biomechanical parameters. Results showed that female spines responded with increased motions than males, and the presence of a helmet increased motions and loads in males and female spines at all levels. Numerical data are given. Head supported mass affects spine responses at all levels. The present computational modeling study, from one geometry for the male spine and one geometry for the female spine (limitations are addressed in the paper), provided insights into the mechanisms of the internal load transfer with the presence of head supported mass, prevalent in certain civilian occupations and active-duty Service members in the military.

Comparative Finite Element Modeling Study of Anterior Cervical Arthrodesis Versus Cervical Arthroplasty With Bryan Disc or Prodisc C

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.

Return-to-active-duty rates after anterior cervical spine surgery in military pilots

OBJECTIVE

Symptomatic cervical spondylosis with or without radiculopathy can ground an active-duty military pilot if left untreated. Surgically treated cervical spondylosis may be a waiverable condition and allow return to flying status, but a waiver is based on expert opinion and not on recent published data. Previous studies on rates of return to active duty status following anterior cervical spine surgery have not differentiated these rates among military specialty occupations. No studies to date have documented the successful return of US military active-duty pilots who have undergone anterior cervical spine surgery with cervical fusion, disc replacement, or a combination of the two. The aim of this study was to identify the rate of return to an active duty flight status among US military pilots who had undergone anterior cervical discectomy and fusion (ACDF) or total disc replacement (TDR) for symptomatic cervical spondylosis.

METHODS

The authors performed a single-center retrospective review of all active duty pilots who had undergone either ACDF or TDR at a military hospital between January 2010 and June 2017. Descriptive statistics were calculated for both groups to evaluate demographics with specific attention to preoperative flight stats, days to recommended clearance by neurosurgery, and days to return to active duty flight status.

RESULTS

Authors identified a total of 812 cases of anterior cervical surgery performed between January 1, 2010, and June 1, 2017, among active duty, reserves, dependents, and Department of Defense/Veterans Affairs patients. There were 581 ACDFs and 231 TDRs. After screening for military occupation and active duty status, there were a total of 22 active duty pilots, among whom were 4 ACDFs, 17 TDRs, and 2 hybrid constructs. One patient required a second surgery. Six (27.3%) of the 22 pilots were nearing the end of their career and electively retired within a year of surgery. Of the remaining 16 pilots, 11 (68.8%) returned to active duty flying status. The average time to be released by the neurosurgeon was 128 days, and the time to return to flying was 287 days. The average follow-up period was 12.3 months.

CONCLUSIONS

Adhering to military service-specific waiver guidelines, military pilots may return to active duty flight status after undergoing ACDF or TDR for symptomatic cervical spondylosis.