Inferior Adjacent Levels Research Articles

Cervical Column and Cord and Column Responses in Whiplash With Stenosis: A Finite Element Modeling Study.

Spine degeneration is a normal aging process. It may lead to stenotic spines that may have implications for pain and quality of life. The diagnosis is based on clinical symptomatology and imaging. Magnetic resonance images often reveal the nature and degree of stenosis of the spine. Stenosis is concerning to clinicians and patients because of the decreased space in the spinal canal and potential for elevated risk of cord and/or osteoligamentous spinal column injuries. Numerous finite element models of the cervical spine have been developed to study the biomechanics of the osteoligamentous column such as range of motion and vertebral stress; however, spinal cord modeling is often ignored. The objective of this study was to determine the external column and internal cord and disc responses of stenotic spines using finite element modeling. A validated model of the subaxial spinal column was used. The osteoligamentous column was modified to include the spinal cord. Mild, moderate, and severe degrees of stenosis commonly identified in civilian populations were simulated at C5-C6. The column-cord model was subjected to postero-anterior acceleration at T1. The range of motion, disc pressure, and cord stress-strain were obtained at the index and superior and inferior adjacent levels of the stenosis. The external metric representing the segmental motion was insensitive while the intrinsic disc and cord variables were more sensitive, and the index level was more affected by stenosis. These findings may influence surgical planning and patient education in personalized medicine.

Minimally Invasive Approach for Dorsal Arachnoid Web: 2-Dimensional Operative Video.

A 67-yr-old patient presented with severe paraparesis and lower limb spasticity. The spinal cord magnetic resonance imaging (MRI) revealed the "scalpel sign" 1,2 at the T7 level, suggesting a diagnosis of a dorsal arachnoid web. This video demonstrates a microsurgical technique for the excision of a dorsal arachnoid web with a minimally invasive approach. A paramedian skin incision, understanding the muscular aponeurosis, was performed from T7 to T8. Then, we inserted the tubular dilators until the lamina, to perform a muscle-sparing approach. An expandable tubular retractor of adequate length was passed over the widest dilator and docked into place along the subperiosteal plane. The T7 lamina was drilled, and the resection of the superior and inferior adjacent spine levels was completed with a rongeur. Additional contralateral bone resection was performed after tubular retractor tilt to the midline.3 After dura mater opening, it was carefully suspended and the dorsal arachnoid leaflet was cut to drain the dorsolateral and lateral spinal cisterns.4 The dorsal arachnoid web was, first, disconnected from its lateral anchorages. It was then gently removed with microsurgical forceps, to help its microdissection from the spinal cord surface. At this step, peculiar attention was paid to limit the traction or displacements of the spinal cord and surrounding vessels. Once the dorsal arachnoid web was removed, the quality of the spinal cord decompression was confirmed by its re-expansion. In conclusion, the minimally invasive approach is a safe and appropriate technique for dorsal arachnoid web excision.2,5,6-7 The patient gave her informed and signed consent for the writing and publication of this article. Image at 1:00 reused with permission from Castelnovo G et al, Spontaneous transdural spinal cord herniation, Neurology, 2014;82(14):1290.

A Retrospective Analysis of Superior Facet Joint Violation Between Open and Minimally Invasive Transforaminal Lumbar Interbody Fusion and its Relation to Adjacent Segment Disease.

A retrospective study. The aim was to analyze the superior facet joint violation (SFV) between open transforaminal lumbar interbody fusion (open-TLIF) and minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) and its effect on the superior and inferior adjacent segment disc height, segmental lordosis, lumbar lordosis, and facet joint degeneration. We compared SFV between open-TLIF and MIS-TLIF and its correlation with different factors as well as its effect on adjacent segment disease. We retrospectively studied data of patients undergoing single level TLIF surgery from January 2013 to February 2016 in single institutional hospital. Axial and coronal postoperative computed tomography scan images were used to analyze SFV. In secondary analysis patients were divided into nonfacet violation group (NSFVG) and facet violation group (SFVG) and compared the changes on the superior and inferior adjacent level disc height, segmental lordosis, lumbar lordosis, and facet joint degeneration. Mean SFV grade was significantly greater in MIS-TLIF compared with open-TLIF (odds ratio: 0.638, confidence interval: 0.431-0.944; P=0.025). There was more grade 2 (10.71% vs. 5.60%) and grade 3 (4.46% vs. 1.29%) SFV in MIS-TLIF. Patient with age below 60 and body mass index (BMI) >30 kg/m2 in MIS-TLIF were more prone to high-grade SFV compared with open-TLIF. Further, logistic regression showed patients with BMI ≥30 kg/m2 has 7.137 increased odds of high-grade SFV (95% confidence interval: 3.261-15.618; P=0.000) compared with patients with BMI <30 kg/m2. Compared with NSFVG, SFVG has more SFV (0.096±0.244 vs. 0.177±0.317; P=0.012) and less improvement in lumbar visual analog scale scores -0.65±0.073 versus -0.67±0.074 (P=0.006). MIS-TLIF has more high-grade SFV as well as overall mean SFV in comparison to open-TLIF with BMI >30 kg/m2 and location of pedicle screw as an independent risk factor for SFV and risk of adjacent segment disease increases with SFV. Level III.

59. Does attachment of the dorsolumbar fascia to a spinous process prosthesis affect kinematics at the operative and adjacent levels? An in vitro human cadaveric model

BACKGROUND CONTEXT Postlaminectomy kyphosis, disc herniations, and/or spondylolisthesis are documented complications following multilevel laminectomy. Removal of the spinous processes and ligaments in multilevel laminectomy disrupts the normal kinematics of the spine, increase segmental motion and risk of “hypermobility-related” complications. The current study utilized a novel testing methodology, where specimens retained all local paraspinal muscle, dorsolumbar fascia and skin layers, to quantify multidirectional flexibility properties of the lumbar spine following destabilization, reconstruction of the posterior arch and reattachment of the posterior fascia to a spinous process prosthesis (SP-P). PURPOSE The purpose of the current investigation was to quantify changes in multidirectional flexibility at the operative and adjacent lumbar motion segments following multilevel laminectomy and implantation of a spinous process prosthesis. STUDY DESIGN/SETTING In vitro human cadaveric model and multidirectional flexibility testing. PATIENT SAMPLE Not applicable. OUTCOME MEASURES Not applicable. METHODS Eight lumbopelvic spines (T9-sacrum) were utilized in this investigation. Specimens retained all paraspinal musculature, ligaments, fascia and skin layers. Multidirectional flexibility testing included pure moment loading at ±10Nm in flexion-extension, lateral bending, and axial rotation. Following analysis of the intact spine, treatment groups included: (1) L2-L4 laminectomy without fascia closure, (2) L2-L4 laminectomy with fascia closure, and (3) L2-L4 SP-P (n=3 prostheses) attached to pedicle screws with fascia closure to the prostheses with suture. Range of motion (ROM) at the superior adjacent (T12-L2), operative (L2-L5), and inferior adjacent (L5-S1) levels was compared using a Repeated Measures Analysis of Variance and Bonferroni post hoc test. Significance was indicated at p≤0.05. RESULTS There were no significant changes in ROM at the superior or inferior adjacent levels between reconstructions under any loading modality. For the operative L2-L5 levels, flexion-extension motion was significantly greater for the laminectomy (156.57±38.89%) and laminectomy with fascia closure (147.11±35.93%) reconstructions compared to intact. The laminectomy reconstruction also demonstrated significantly greater lateral bending motion (110.65±6.43%) compared to intact. In axial rotation, the laminectomy (157.95±18.27%), laminectomy with fascia closure (160.54±21.39%), and SP-P (159.36±18.38%) reconstructions observed greater motion when compared to intact (p CONCLUSIONS Re-establishing the posterior arch and attachment to a spinous process prosthesis restored flexion-extension motion at the operative levels following multilevel laminectomy. The results add value to the concept of robust closure of posterior dorsolumbar layers and stress the importance of preserving or replacing the posterior arch to decrease operative level motion. FDA DEVICE/DRUG STATUS Crosslink (Approved for this indication).

Optimization of Three-Level Cervical Hybrid Surgery to Prevent Adjacent Segment Disease: A Finite Element Study.

Hybrid surgery (HS) allows surgeons to tailor fusion and arthroplasty in the treatment of multiple-level cervical disc degeneration. However, the decision making of selecting either ACDF or ADR for each level in three-level HS remains controversial and has not been fully investigated. This study was aimed to optimize three-level cervical hybrid constructs by systematically investigating their biomechanical properties and their effect on adjacent levels. A finite element model of cervical spine (C2–C7) was developed, and eight C3–C6 surgical models including six HS were constructed. The range of motion (ROM) in flexion, extension, lateral bending, and axial rotation under 2.0 Nm moments with 30 N follower load were simulated. The von Mises stress, strain energy at the adjacent intervertebral disc (IVD) and force at the adjacent facet were calculated. The ROM of the hybrid constructs and adjacent levels was close to that of the intact spine. HS with arthroplasty performed at C5-6 had better performance in terms of ROM reduction at the inferior adjacent level (C6-7). Moreover, C-D-D and 3ADR had best performance in reducing the von Mises stress and strain energy at C6-7. All HS reduced the facet burden at both C2-3 and C6-7 levels. However, the major drawback of HS revealed here is that the effect of C6-7 protection is at the cost of increased C2-3 IVD burden. In conclusion, we recommend C-D-D and 3ADR for patient with C3–C6 disc degeneration without predisposing C2-3 condition. C-C-D could be a good alternative with a lower medical cost. This analysis guides the decision making in three-level cervical HS before future cadaver studies or human clinical trials.

Assessment of Paraspinal Muscle Atrophy Percentage after Minimally Invasive Transforaminal Lumbar Interbody Fusion and Unilateral Instrumentation Using a Novel Contralateral Intact Muscle-Controlled Model.

Study DesignRetrospective comparative clinical study.PurposeThis study aimed to assess paraspinal muscle atrophy in patients who underwent minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) and unilateral pedicle screw fixation using a novel contralateral intact muscle-controlled model.Overview of LiteratureThe increased incidence of paravertebral lumbar muscle injuries after open techniques has raised the importance of implementing minimally invasive spine surgical techniques using tubular retractors and minimally invasive screw placement. The functional cross-sectional area (FCSA) represents the lean muscle mass; furthermore, FCSA is a useful marker of the contractile ability of a muscle following a spine surgery. However, the benefits of unilateral fixation and MI-TLIF on paraspinal muscles have not been defined.MethodsWe performed a retrospective imagenological review on eleven patients who underwent unilateral MI-TLIF and unilateral transpedicular screw lumbar placement. FCSAs of the multifidus and erector spinae were measured 1 year after surgery at adjacent levels and were compared to the contralateral intact muscles. Measurement differences between the surgical and nonsurgical sites were compared. The interobserver reliability was calculated using an intraclass correlation coefficient.ResultsThe mean FCSA at the surgical site was 20.97±5.07 cm2 at the superior level and 8.89±2.87 cm2 at the inferior level. The mean FCSA at the contralateral nonsurgical site was 20.15±5.95 cm2 at the superior level and 9.20±2.66 cm2 at the inferior level was. The superior and inferior FCSA measurements showed no significant difference between the surgical and nonsurgical sites (p=0.5, p=0.922, respectively).ConclusionsUsing a mini-open tubular approach through the sulcus between the longissimus and iliocostalis, MI-TLIF and unilateral pedicle screw instrumentation produced minimal paraspinal muscle damage at the superior and inferior adjacent levels.

Dynamic foraminal dimensions during neck extension and rotation in fusion and artificial disc replacement: an observational study

BackgroundChanges in the dimensions of the cervical neural foramina (CNF) are considered to be a key factor in nerve root compression and development of cervical radiculopathy. However, to what extent foraminal geometry differs between patients who underwent anterior cervical discectomy and fusion (ACDF) and those who underwent total disc arthroplasty with an artificial disc (AD) during physiological motion is largely unknown. PurposeThe objective of this study is to compare CNF dimensions during physiological neck motion between ACDF and AD. Study Design/SettingThis is a retrospective comparative analysis of prospectively collected, consecutive, non-randomized series of patients at a single institution. Patient SampleA total of 16 single-level C5–C6 ACDF (4 males, 12 females; 28–71 years) and 7 single-level C5–C6 cervical arthroplasty patients (3 males, 4 females; 38–57 years), at least 12 months after surgery (23.6±6.8 months) were included. Outcome MeasuresPatient demographics, preoperative magnetic resonance imaging (MRI)-based measurements of cervical spine degeneration, and 2-year postoperative measurements of dynamic foraminal geometry were the outcome measures. MethodsBiplane X-ray images were acquired during axial neck rotation and neck extension. A computed tomography scan was also acquired from C3 to the first thoracic vertebrae. The subaxial cervical vertebrae (C3–C7) were reconstructed into three-dimensional (3D) bone models for use with model-based tracking. Foraminal height (FH) was calculated as the 3D distance between the superior point of the inferior pedicle and the inferior point of the superior pedicle using custom software. Foraminal width (FW) was similarly calculated as the 3D distance between the anterolateral aspect of the superior vertebral body inferior notch and the posterolateral aspect of the inferior vertebral body superior notch. Dynamic foraminal dimensions were quantified as the minimum (FH.Min, FW.Min), the range (FH.Range, FW.Range), and the median (FH.Med, FW.Med) of each trial and then averaged over trials. Mixed model analysis of variance framework was used to examine the differences between ACDF and AD groups. The initial severity of disc degeneration as determined from preoperative MRI images was introduced as covariates in the models. ResultsAt the operated level (C5–C6), FH.Med and FH.Range were smaller in ACDF than in AD during axial rotation and neck extension (p<.003 to p<.05). At the superior adjacent level (C4–C5), no significant difference was found. At the inferior adjacent level (C6–C7), FW.Range was greater in ACDF than in AD during axial rotation and extension (p<.05). At the non-adjacent level (C3–C4), FW.Range was greater in ACDF than in AD during extension (p<.008). ConclusionsThis study demonstrated decreases in foraminal dimensions and their range for ACDF compared with AD at the operated level. In contrast, it demonstrated increases in the range of foraminal dimensions during motion for ACDF compared with AD at the non-operated segments. Together, these data support the notion that increased mobility at the non-operated segments after ACDF may contribute to a greater risk for adjacent segment degeneration. Because of the significant presence of range variables in the findings, the current data also indicate that a dynamic evaluation is likely more appropriate for evaluation of the differences in foramina between ACDF and AD than a static evaluation.

X-Ray-based Kinematic Analysis of Cervical Spine According to Prosthesis Designs

A retrospective study. To identify significant kinematic changes in the cervical spine after cervical artificial disk replacement (ADR) using prostheses with diverse designs. Various types of artificial disks are used for cervical ADR. However, few clinical studies with a follow-up of 2 or more years have reported on the change in the curvatures and range of motion (ROM) of the cervical spine after cervical ADR in relation to different designs. The cohort comprised 58 patients who underwent single-level cervical ADR for radiculopathy. The patients were divided into 4 groups according to the device they received: Mobi-C, Bryan, PCM, and Prestige LP. The radiographs of the cervical spine were obtained preoperatively and at 12, 24, and 36 months after surgery. Several kinematic parameters, including lordotic angles and ROM of the cervical spine, index level, and superior and inferior adjacent disk levels, were assessed preoperatively and at predefined follow-up time points. Cervical sagittal lordosis in patients who received Bryan and PCM prostheses increased at the last follow-up period. The 4 patient groups showed a trend toward an increase of lordosis in the superior adjacent segment with time. The patients who received the Bryan device lost their preoperative lordotic angle at the inferior adjacent level. The ROM of the cervical spine in patients who received Bryan and PCM prostheses increased at the last follow-up compared with preoperative values. The incidence of adjacent segment degeneration in the Mobi-C, Bryan, Prestige LP, and PCM groups were 14.2%, 25%, 9.0%, and 7.6%, respectively. These results suggest preservation of sagittal ROM and increased superior adjacent segment kinematics, regardless of prosthesis design. Devices with an unconstrained design may not be beneficial to adjacent segment kinematics compared with semiconstrained prostheses.

Prevalence of adjacent segment disc degeneration in patients undergoing anterior cervical discectomy and fusion based on pre-operative MRI findings

Anterior cervical discectomy and fusion (ACDF) is a widely accepted surgical treatment for symptomatic cervical spondylosis. Some patients develop symptomatic adjacent segment degeneration, occasionally requiring further treatment. The cause and prevalence of adjacent segment degeneration and disease is unclear at present. Proponents for motion preserving surgery such as disc arthroplasty argue that this technique may decrease the “strain” on adjacent discs and thus decrease the incidence of symptomatic adjacent segment degeneration. The purpose of this study was to assess the pre-operative prevalence of adjacent segment degeneration in patients undergoing ACDF. A database review of three surgeons’ practice was carried out to identify patients who had undergone a one- or two-level ACDF for degenerative disc disease. Patients were excluded if they were operated on for recent trauma, had an inflammatory arthropathy (for example, rheumatoid arthritis), or had previous spine surgery. The pre-operative MRI of each patient was reviewed and graded using a standardised methodology. One hundred and six patient MRI studies were reviewed. All patients showed some evidence of intervertebral disc degeneration adjacent to the planned operative segment(s). Increased severity of disc degeneration was associated with increased age and operative level, but was not associated with sagittal alignment. Disc degeneration was more common at levels adjacent to the surgical level than at non-adjacent segments, and was more severe at the superior adjacent level compared with the inferior adjacent level. These findings support the theory that adjacent segment degeneration following ACDF is due in part to the natural history of cervical spondylosis.

Stabilization of the sacroiliac joint with the SI-Bone surgical technique

Although the motion of the sacroiliac joints (SIJ) is minimal, pain can originate from the SIJ on mechanical loading and affect walking, sitting and sleep patterns. The SIJ refers to the pair of joints inferior to the L5-S1 joint, and functions as the inferior adjacent level after a L5-S1 fusion. SIJ pain has a clinical overlay of symptoms often similar to low back pain (LBP) generated by the lumbar spine. The differential diagnosis in any patient with LBP should include the triad of low back, SIJ, and hip. SIJ pain is also a known cause of residual LBP after successful lumbar fusion. Relief of the patient's pain with a diagnostic SIJ block verifies the SIJ as the site of the pain generator. The SI-bone technique of stabilization of the SIJ is a true minimally invasive surgical technique performed through an initial small skin incision and then over pins, with the aid of fluoroscopy in three orthogonal axes with one axis parallel to the posterior sacral cortical line at the S1 to S2 region. The fluoroscopy procedure includes the following steps: 1) pre-op plan of the desired 3 implant trajectories to account for the anatomic variations; 2) placement of 3 Steinman pins at these trajectories across the SIJ starting in a small skin incision; 3) drill, broach and then implant placement as a cannulated system. All these steps are performed with the assistance of fluoroscopy in all three imaging planes - lateral, inlet and outlet views. The SI-Bone implants are triangular shaped titanium and have a rough surface for immediate stability. This rough surface is believed to aid in the osteo-fixation of the implants to the ilium and sacrum, as well as to long term fusion of the SIJ after its prolonged immobilization. The video can be found here: http://youtu.be/2YtFddohZRk.

Can low-grade spondylolisthesis be effectively treated by either coflex interlaminar stabilization or laminectomy and posterior spinal fusion? Two-year clinical and radiographic results from the randomized, prospective, multicenter US investigational device exemption trial

Posterolateral spinal fusion (PSF) has long been the standard of care for degenerative spondylolisthesis, but less invasive, motion-preserving alternatives have been proposed to reduce the complications associated with fusion while still providing neural decompression and stabilization. The object of the current study is to evaluate the safety and efficacy of coflex Interlaminar Stabilization compared with PSF to treat low-grade spondylolisthesis with spinal stenosis. This is a prospective, randomized, multicenter FDA investigational device exemption (IDE) trial comparing coflex Interlaminar Stabilization with laminectomy and PSF. A total of 322 patients from 21 sites in the US were enrolled between 2006 and 2008 for the IDE trial. The current study evaluated only the subset of patients from this overall cohort with Grade 1 spondylolisthesis (99 in the coflex group and 51 in the fusion group). Subjects were randomized 2:1 to receive decompression and coflex interlaminar stabilization or decompression and posterolateral spinal fusion with spinal instrumentation. Data collected included perioperative outcomes, Oswestry Disability Index (ODI), back and worse leg visual analog scale (VAS) scores, 12-Item Short Form Health Survey, Zurich Claudication Questionnaire (ZCQ), and radiographic outcomes at a minimum of 2 years. The FDA criteria for overall device success required the following to be met: 15-point reduction in ODI, no reoperations, no major device-related complications, and no postoperative epidural injections. At a minimum of 2 years, patient follow-up was 94.9% and 94.1% in the coflex and fusion control groups, respectively. There were no group differences at baseline for any demographic, clinical, or radiographic parameter. The average age was 63 years in the coflex cohort and 65 years in the fusion cohort. Coflex subjects experienced significantly shorter operative times (p < 0.0001), less estimated blood loss (p < 0.0001), and shorter length of stay (p < 0.0001) than fusion controls. Both groups experienced significant improvements from baseline at 2 years in ODI, VAS back, VAS leg, and ZCQ, with no significant group differences, with the exception of significantly greater ZCQ satisfaction with coflex at 2 years. FDA overall success was achieved in 62.8% of coflex subjects (59 of 94) and 62.5% of fusion controls (30 of 48) (p = 1.000). The reoperation rate was higher in the coflex cohort (14 [14.1%] of 99) compared with fusion (3 [5.9%] of 51, p = 0.18), although this difference was not statistically significant. Fusion was associated with significantly greater angulation and translation at the superior and inferior adjacent levels compared with baseline, while coflex showed no significant radiographic changes at the operative or index levels. Low-grade spondylolisthesis was effectively stabilized by coflex and led to similar clinical outcomes, with improved perioperative outcomes, compared with PSF at 2 years. Reoperation rates, however, were higher in the coflex cohort. Patients in the fusion cohort experienced significantly increased superior and inferior level angulation and translation, while those in the coflex cohort experienced no significant adjacent or index level radiographic changes from baseline. Coflex Interlaminar Stabilization is a less invasive, safe, and equally efficacious clinical solution to PSF to treat low-grade spondylolisthesis, and it appears to reduce stresses at the adjacent levels. Clinical trial registration no.: NCT00534235 (ClinicalTrials.gov).

The effect of the X-Stop implantation on intervertebral foramen, segmental spinal canal length and disc space in elderly patients with lumbar spinal stenosis

To evaluate the biomechanical effect of the X-Stop device on the intervertebral foramen (IVF) and segmental spinal canal length (SSCL), as well as the intervertebral disc space at the implanted and the adjacent segments in patients with lumbar spinal stenosis (LSS). Eight elderly patients with LSS, scheduled for X-stop implantation, were CT or MRI scanned to construct 3D vertebral models (L2-S1). Before and after the surgery, each patient was also imaged using a dual-fluoroscopic image system during weight-bearing standing and maximum extension-flexion. The positions of the vertebrae were then determined using an established 2D-3D model matching method. The data revealed that the postoperative IVF area was significantly increased by 32.9% (or 32 mm2) (p<0.05) and the IVF width was increased by 24.4% (or 1.1 mm, p=0.06) during extension, but with minimal change in standing and flexion. The IVF heights were significantly (p<0.05) increased at standing by 1.2 mm and extension by 1.8 mm, but not at flexion. The SSCL were significantly (p<0.05) increased at extension by 1.2 mm, but not at standing and flexion. Anterior disc space of the implanted level was significantly decreased from 8.0 to 6.6 mm during standing. The X-Stop implantation efficiently enlarged the IVF area in the elderly patients with LSS at the operated level with little biomechanical effect immediately on the superior and inferior adjacent levels. However, it reduced the anterior disc space at the implanted level.

ProDisc-C

A prospective study of 22 patients with single-level cervical spondylosis. To quantify the changes in the biomechanics of the cervical spine after the insertion of a ProDisc-C (Synthes Spine, Paoli, PA) artificial disc. Cervical arthroplasty is designed to maintain cervical motion of the functional spinal unit (FSU) after cervical discectomy. The impact of the ProDisc-C on in vivo kinematics and sagittal alignment requires further assessment. Flexion/extension lateral radiographs of the cervical spine were prospectively collected and reviewed in 22 patients preoperatively and after the placement of ProDisc-C. Disc height (DH), FSU angle, range of motion (ROM), and center of rotation (COR) were calculated at each time point using validated, computer-assisted methods. Preoperative values were compared with the postoperative values using paired student t tests. Mean follow-up time was 11.0 months (SD, 2.4 mo). At the surgical level, the ProDisc-C produced increased segmental ROM (P = 0.03), an anterior shift of 1.1 mm in COR X (P = 0.004), and increased DH both anteriorly (P < 0.0001) and posteriorly (P < 0.0001). At the inferior adjacent level, anterior DH decreased (P < 0.05) and posterior DH increased (P = 0.02) after surgery. The FSU angle at the surgical level increased (P < 0.0001), but the inferior adjacent-level FSU angle decreased (P = 0.002). No significant changes were observed at the superior adjacent level. The ProDisc-C increased segmental ROM and shifted the COR anteriorly at the surgical level. DH increased at the surgical level. The surgical level became more lordotic, whereas the inferior adjacent level became more kyphotic after ProDisc-C implantation.

Magnetic resonance imaging evaluation of adjacent segments after cervical disc arthroplasty: magnet strength and its effect on image quality

Disc arthroplasty is an alternative to fusion following anterior discectomy when treating either cervical radiculopathy or myelopathy. Its theoretical benefits include preservation of the motion segment and the potential prevention of adjacent-segment degeneration. There is a paucity of data regarding the ability to use MR imaging to evaluate the adjacent segments. The purpose of this study was for the authors to introduce open MR imaging as an alternative method in imaging adjacent segments following cervical disc arthroplasty using a Co-Cr implant and to report their preliminary results using this technique. Postoperative cervical MR images were obtained in the first 16 patients in whom the porous coated motion (PCM-V) cervical arthroplasty system was used to treat a single level between C-3 and C-7. Imaging was performed in all 16 patients with a closed 1.5-T unit, and in the final 6 patients it was also performed with an open 0.2-T unit. All images were evaluated by an independent radiologist observer for the ability to visualize the superior endplate, disc space, and inferior endplate at the superior and inferior adjacent levels. Utilizing the 1.5-T magnet to assess the superior adjacent level, the superior endplate, disc space, and inferior endplate could each be visualized less than 50% of the time on sagittal T1- and sagittal and axial T2-weighted images. Similarly, the inferior adjacent level structures were adequately visualized less than 50% of the time, with the exception of slightly improved visualization of the inferior endplate on T1-weighted images (56%). Axial images allowed worse visualization than sagittal images at both the superior and inferior adjacent levels. Utilizing the 0.2-T magnet to assess the superior and inferior adjacent levels, the superior endplate, disc space, and inferior endplate were adequately visualized in 100% of images. Based on the results of this case series, it appears that the strength of the magnet affects the artifact from the Co-Cr endplates. The open 0.2-T MR imaging unit reduces artifact at adjacent levels after cervical disc arthroplasty without a significant reduction in the image quality. Magnetic resonance imaging can be used to evaluate the adjacent segments after disc arthroplasty if magnet strength is addressed, providing another means to assess the long-term efficacy of this novel treatment.

Biomechanical comparison of single- and two-level cervical arthroplasty versus arthrodesis: effect on adjacent-level spinal kinematics

Background Context The use of motion-preserving spinal implants versus conventional arthrodesis instrumentation systems, which stabilize operative segments, necessitates improved understanding of their effect on spinal kinematics and the biomechanically optimal method for surgical reconstruction. Purpose The primary objective of this study was to measure operative- and adjacent-level kinematics after single- and two-level cervical arthroplasty and compare them with those after anterior cervical arthrodesis. A secondary objective was to locate the centers of intervertebral rotation at the operative and adjacent levels after arthroplasty and compare them to those after arthrodesis. Study Design This biomechanical study used an in vitro human cadaveric model to compare the multidirectional flexibility kinematics of single- versus two-level cervical disc arthroplasty reconstructions. Methods Eight cadaveric cervical spines (C2–T2) were biomechanically evaluated between Levels C4 and T1 in the intact condition and under the following reconstructions: single-level arthroplasty (C6–C7) using porous coated motion (PCM) device; single-level arthrodesis (C6–C7) using interbody cage with anterior plate; two-level arthroplasty (C5–C7) using PCM devices; two-level hybrid treatment of arthroplasty (C5–C6) using PCM device and arthrodesis (C6–C7) using cage/plate; and two-level arthrodesis (C5–C7) using cage/plate. Multidirectional flexibility testing used the Panjabi hybrid testing protocol, including pure moments for the intact condition with overall spinal motion replicated under displacement control for subsequent reconstructions. Unconstrained intact moments of ±3.0 Nm were used for axial rotation, flexion-extension, and lateral bending testing with quantification of the operative- and adjacent-level range of motion (ROM) and neutral zone. The calculated centers of intervertebral rotation were compared for all intervertebral levels under flexion-extension conditions. Results Axial rotation loading demonstrated a significant decrease in the C6–C7 ROM for the single-level arthrodesis group compared with the intact spine and the single-level arthroplasty group (p<.05). No differences were observed between the intact and single-level arthroplasty groups (p>.05). For the two-level hybrid treatment group, the C5–C6 ROM significantly increased compared with the intact, single-level arthroplasty, and two-level arthrodesis groups (p<.05). Moreover, a significant increase was observed in the adjacent-level (C7–T1) ROM for the two-level arthrodesis group compared with all other treatment groups (p<.05). Under flexion-extension, no differences were observed in C6–C7 ROM between the intact spine and single-level arthroplasty groups (p>.05). However, as expected, the single-level arthrodesis and two-level hybrid treatment groups demonstrated a decreased ROM at C6–C7 versus the intact spine and arthroplasty treatments (p<.05). In terms of adjacent-level effects, two-level arthrodesis (C5–C7) led to increased ROM in the inferior level (C7–T1) in axial rotation and flexion-extension compared with the intact spine and all other treatment groups (p<0.05). Lateral bending loading conditions demonstrated no significant difference among the treatment groups (p>.05). In flexion-extension, the centers of intervertebral rotation for the intact spine and single-level arthroplasty groups were localized in the central to posterior one-third of the inferior vertebral body for each motion segment: C5–C6, C6–C7, and C7–T1. The single-level arthrodesis group produced more diffuse centers of rotation, particularly at the operative (C6–C7) and inferior adjacent levels (C7–T1). Conclusions This study highlights the biomechanical effects of single- and two-level cervical arthroplasty versus single- and two-level arthrodesis on four functional spinal levels (C4–T1). Operative-level ROM was preserved with single- and two-level arthroplasty under all loading modes. The distal adjacent level (C7–T1) demonstrated the greatest increase among the four levels in ROM compared with the intact condition after two-level arthrodesis. These kinematic findings were corroborated by changes in the adjacent-level centers of rotation after arthrodesis and may suggest a biomechanical cause of adjacent-level disease secondary to cervical arthrodesis.

Anterior Cervical Discectomy and Titanium Cage Fusion – 7-year Follow-up

The purpose of this study was to prospectively evaluate long-term results after anterior cervical discectomy and titanium cage fusion (ACDF) and titanium cage fusion. Special focus was on the adjacent levels. 54 patients (age: 48+/-10 years; one level operation in 44 patients and two level operation in 10 patients) entered the study. Re-evaluation consisted of a clinical out patient investigation and was possible in 33 patients. VAS, PROLO and Oswestry scores were used. Lateral radiographs were taken and changes in the operated and adjacent segments were measured and compared to radiographs directly after surgery. Clinical patient data was compared with the data prior to surgery. The mean follow-up time of the 33 patients was 7.26 +/- 0.22 years. One patient needed re-surgery of the cervical spine above the fused segment. PROLO results showed a significant improvement (PROLO F 1.52+/-0.67 to 3.79+/-1.17 p<0.01; PROLO E 1.52+/-0.5 to 3.55+/-1.42 p<0.01). Mean VAS at the time of investigation was 3.2+/-2.5. Oswestry score was 16.4+/-9.5. The alignment of the whole cervical spine was stable lordotic (Katsuura 10.9+/-9.0 degrees to 11.5+/-7.8 degrees ; p=0.76). Total segmental height had reduced from 36.6+/-4.6 mm to 34.6+/-3.9 mm (p=0.04). No significant reduction of disc space height of adjacent levels was detectable (superior: 5.8+/-1.6 mm to 5.2+/-1.6 mm; inferior: 6.0+/-1.7 mm to 5.3+/-1.9 mm). One adjacent superior level showed spontaneous fusion. Ventral and dorsal osteophytes in the superior and inferior adjacent levels increased in number and increased significantly in degree. Patients with bi-segmental fusion (n=7) showed similar results. ACDF with titanium cages has good clinical long-term results. A significant progression of degenerative changes can be observed on radiographs without clinical consequences for the patients. A comparison with patients without surgery and conservative therapy is needed to allow a better interpretation of the radiological results.

Adjacent or Junctional Disc Herniations in Post Spinal Fusion Treated With Endoscopic Spinal Surgery for Segmental Motion Preservation

Introduction: Fusions of the cervical and lumbar spine are often followed within months or several years by protrusion of discs at the adjacent level or levels. Mobility lost at the fused levels is thought to be transferred to the adjacent segment/s increasing stress on the disc, resulting in early recurrent protrusion at that level. In a number of anterior cervical fusions (ACF) and lumbar fusions this occurs in both superior and inferior adjacent levels simultaneously. Materials and Methods: Case reports 180 of post spinal fusion junctional disc herniations (260) (also called transitional discs, or adjacent segment failure) are reported, as well as a review of the literature to determine their frequency of occurrence following fusions of the lumbar and cervical spine. Results: Average time to return to work was 14 days. At an average follow-up of 18 months. For single level, 92% had good to excellent symptomatic relief and spinal motion preservation. There were no intraoperative complications. 8% of patients had partial or no pain relief after surgery. Cervical and lumbar endoscopic minimally invasive spinal surgery (MISS) combined with laser thermodiskoplasty, is an ideal way to treat junctional discs to avoid a sequential recurrence. Treating protruded cervical and lumbar discs with MISS as the initial procedure of choice would avoid destabilizing adjacent segments, largely prevent post spinal fusion junctional disc syndrome and preserve spinal segmental motion. Conclusion: MISS provides the optimal method to treat post spinal fusion junctional disc syndrome of the cervical and lumbar spine with minimal morbidity, and no threat of further junctional recurrence and at less cost. Its use as the initial treatment of choice would greatly lessen the incidence of this syndrome and preserve spinal segmental motion.

Biomechanical Changes at Adjacent Segments Following Anterior Lumbar Interbody Fusion Using Tapered Cages

A biomechanical evaluation of anterior cages in a calf lumbar spine model. To determine changes in spinal motion and intradiscal pressures at immediately adjacent lumbar motion segments following anterior insertion of tapered cages. Stand-alone anterior lumbar interbody fusion (ALIF) is an effective approach in the treatment of discogenic low back pain. A tapered lumbar (LT) cage design attempts to restore physiologic lordosis and sagittal balance. We are not aware of any previous biomechanical evaluation of the effects of LT cages on adjacent motion segments. Nine fresh calf spines (L2-L5) were procured for the study. Pure moments (up to 8.5 Nm) in flexion, extension, and lateral bending were applied to the L2 vertebra in five steps through a nonconstrained loading system. With each step of loading, three-dimensional rotation at three intervertebral disc levels was obtained through a three-camera motion analysis system, and intradiscal pressures within the nucleus pulposus of the two nonoperated discs were measured with miniature transducers. The spines were tested initially intact and following paired anterior LT cage insertion. Following ALIF, small to moderate increase in motion was found at both adjacent segments in flexion (superior: 12.5%, P < 0.05; inferior: 11.3%, P < 0.02) and lateral bending (superior: 7.8%, P < 0.02; inferior: 6.6%, P < 0.02). An increase in intradiscal pressure was noted at the superior adjacent segment under flexion (21%, P < 0.01) and lateral bending (16%, P < 0.03). Intradiscal pressure changes at the inferior adjacent level were not significant. Statistically significant changes in intradiscal pressures and motion were found at the adjacent levels following a single-level stand-alone ALIF procedure using paired LT cages.

Internal disc stresses and kinematic behavior of lumbar spine after laminotomy and laminectomy

Raj Rao, MD, Mei Wang, PhD, Peeush Singhal, MD, Linda M. McGrady, BS, Milwaukee, WI, USA; Santi Rao, MD, Fairfield, CA, USAIntroduction: The biomechanical advantage of laminotomy over the more traditional laminectomy is the preservation of the midline posterior ligaments that are important in maintaining the stability of the spine. Decompression can be effectively achieved in most cases of degenerative spinal stenosis by a laminotomy and medial facetectomy, while still preserving the uninvolved spinous process and interspinous ligaments. There have been no published studies that directly compare the amount of destabilization between the laminotomy and laminectomy procedures. More importantly, the changes in internal mechanical stresses within the intervertebral disc resulting from the two procedures have not been previously quantified. The objective of this study is to verify the presumed increase in instability associated with the laminectomy and to compare the central and peripheral intradiscal stresses after the two procedures.Methods: Nine fresh calf spines were harvested for the study. The specimen was dissected into testing segments from L4 to L6 and potted in dental cement. Four miniature pressure transducers (1.5 mm in diameter, 0.3-mm-thick disc) were inserted into nucleus, anterior annulus and posterolateral annulus to measure the internal disc stress at L4–L5 (surgical level). Pure moments in flexion, extension, lateral bending and axial rotation up to 8.5 Nm were applied to the superior vertebrae in six steps. Three-dimensional motion of each segment was measured with motion analysis system (VICON 370). The spines were tested intact first, then after laminotomy at L4–L5 and again after expanding the laminotomy into laminectomy. The range of motion of the surgical level and the inferior adjacent level were evaluated, and analysis of variance and post-hoc were performed to compare the difference between intact spine and after the two surgeries. The peak magnitudes of the intradiscal transducers for the two procedures were normalized with respect to the values of intact spine, and the difference was evaluated with paired t test.Results: Motion at the surgical level increased in all directions from laminotomy to laminectomy, and statistically significant increases were found in flexion (23%) and axial rotation (18%). The largest increase from intact spine to spines after laminotomy and laminectomy was in axial rotation (102% and 120%), followed by extension (33% and 41%) and flexion (11% and 34%). Lateral bending showed the least increase (7% and 11%). Motion at the intact inferior adjacent level remains unchanged. In flexion, the intact spine showed higher stress at the anterior annulus and the nucleus. The stress at the anterior annulus increased 20% after laminotomy, and 130% after laminectomy (p<.02). In extension, the high-stress regions were in the nucleus and posterolateral annulus. The posterolateral stress increased 22% and 27%, respectively, after each procedure, and the nucleus stress increased 24% and 31%, respectively, after laminotomy and laminectomy. The differences between the two procedures were not significant. The posterolateral stress of the loaded side in lateral bending was the highest of all loading modes. The stress remained unchanged after laminotomy but increases 9% after laminectomy (p<.06). In axial rotation, internal disc stresses were evenly distributed and unchanged after each procedure.Discussion: Previous experimental studies have shown that the posterior ligamentous structures are important in maintaining stability of the spine. Our study found that laminectomy resulted in significantly larger motion in flexion and axial rotation than laminotomy, and a significant increase in anterior annular stresses at the operated disc space, indicating anterior shifting of the loading path after laminectomy. It provides a quantitative measure of the biomechanical advantages of laminotomy over laminectomy. The increase in internal disc stresses after a laminectomy could translate clinically into degenerative changes within the disc. A better understanding of the mechanics of the spinal segment, and in particular their response to these interventions, will help diminish the clinical incidence of late development of instability and the increased need for subsequent fusions in the lumbar spine.