Segmental motion adjacent to anterior cervical arthrodesis: a prospective study

Determining a relative total lumbar range of motion to alleviate adjacent segment degeneration after transforaminal lumbar interbody fusion: a finite element analysis

BACKGROUND

A reduction in total lumbar range of motion (ROM) after lumbar fusion may offset the increase in intradiscal pressure (IDP) and facet joint force (FJF) caused by the abnormally increased ROM at adjacent segments. This study aimed to determine a relative total lumbar ROM rather than an ideal adjacent segment ROM to guide postoperative waist activities and further delay adjacent segment degeneration (ASD).

METHODS

An intact L1-S1 finite element model was constructed and validated. Based on this, a surgical model was created to allow the simulation of L4/5 transforaminal lumbar interbody fusion (TLIF). Under the maximum total L1-S1 ROM, the ROM, IDP, and FJF of each adjacent segment between the intact and TLIF models were compared to explore the biomechanical influence of lumbar fusion on adjacent segments. Subsequently, the functional relationship between total L1-S1 ROM and IDP or total L1-S1 ROM and FJF was fitted in the TLIF model to calculate the relative total L1-S1 ROMs without an increase in IDP and FJF.

RESULTS

Compared with those of the intact model, the ROM, IDP, and FJF of the adjacent segments in the TLIF model increased by 12.6-28.9%, 0.1-6.8%, and 0-134.2%, respectively. As the total L1-S1 ROM increased, the IDP and FJF of each adjacent segment increased by varying degrees. The relative total L1-S1 ROMs in the TLIF model were 11.03°, 12.50°, 12.14°, and 9.82° in flexion, extension, lateral bending, and axial rotation, respectively.

CONCLUSIONS

The relative total L1-S1 ROMs after TLIF were determined, which decreased by 19.6-29.3% compared to the preoperative ones. Guiding the patients to perform postoperative waist activities within these specific ROMs, an increase in the IDP and FJF of adjacent segments may be effectively offset, thereby alleviating ASD.

Evolution of Patient-Reported Outcome Measures, 1, 2, and 5 years after Surgery for Subaxial Cervical Spine Fractures, A Nation-Wide Registry Study

BACKGROUND CONTEXT

A longer duration of patient follow-up arguably provides more reliable data on the long-term effects of a treatment. However, the collection of long-term follow-up data is resource demanding and often complicated by missing data and patients being lost to follow-up. In surgical fixation for cervical spine fractures, data are lacking on the evolution of patient reported outcome measures (PROMs) beyond 1-year of follow-up. We hypothesized that the PROMs would remain stable beyond the 1-year postoperative follow-up mark, regardless of the surgical approach.

PURPOSE

To assess the trends in the evolution of patient-reported outcome measures (PROMs) at 1, 2-, and 5-years following surgery in patients with traumatic cervical spine injuries.

STUDY DESIGN

Nation-wide observational study on prospectively collected data.

PATIENT SAMPLE

Individuals treated for subaxial cervical spine fractures with anterior, posterior, or combined anteroposterior approaches, between 2006 and 2016 were identified in the Swedish Spine Registry (Swespine).

OUTCOME MEASURES

PROMs consisting of EQ-5D-3L_index and the Neck Disability Index (NDI) were considered.

METHODS

PROMs data were available for 292 patients at 1 and 2 years postoperatively. Five-years PROMs data were available for 142 of these patients. A simultaneous within-group (longitudinal) and between group (approach-dependent) analysis was performed using mixed ANOVA. The predictive ability of 1-year PROMs was subsequently assessed using linear regression.

RESULTS

Mixed ANOVA revealed that PROMs remained stable from 1- to 2-years as well as from 2- to 5-years postoperatively and were not affected by the surgical approach (p<0.05). A strong correlation was found between 1-year and both 2- and 5-years PROMs (R>0.7; p<0.001). Linear regression confirmed the accuracy of 1-year PROMs in predicting both 2- and 5-years PROMs (p<0.001).

CONCLUSION

PROMs remained stable beyond 1-year of follow-up in patients treated with anterior, posterior, or combined anteroposterior surgeries for subaxial cervical spine fractures. The 1-year PROMs were strong predictors of PROMs measured at 2, and 5 years. The 1-year PROMs were sufficient to assess the outcomes of subaxial cervical fixation irrespective of the surgical approach.

Subjective and Objective Change in Cervical Spine Mobility After Single-level Anterior Cervical Decompression and Fusion

STUDY DESIGN

Prospective, observational study.

OBJECTIVE

The aim of this study was to collect objective and especially subjective data on changes in cervical spine mobility after single-level anterior cervical decompression and fusion (ACDF) and to investigate the impact on quality of life and activities of daily living (ADLs).

SUMMARY OF BACKGROUND DATA

Although there are several studies dealing with the objective change in mobility after single-level ACDF, there are few data on how spondylodesis of a motion segment affects subjective restriction of cervical spine mobility.

METHODS

Patients undergoing first-time, single-level ACDF for a symptomatic spondylotic process were eligible. Data were collected before surgery, at 3-month, and 1-year follow-up. Patients were assessed via clinical scores (pain intensity, Short-Form 8 [SF-8], among others) and asked for impairment in ADLs due to restriction of cervical spine mobility. The subjective restriction was acquired by a five-step patient-reported score. The range of motion was measured by the CROM device.

RESULTS

Data of 97 patients could be evaluated. For pain scores and SF-8 there were significant improvements 3 months and 1 year after surgery (P < 0.001). The impairment for most ADLs improved 3 months after surgery and further after 1 year. The subjective restriction showed a significant improvement in general and for all single directions 1 year after surgery. In the objective measurements, a significantly higher total rotation could be found 1 year after surgery compared to preoperatively (101.6° ± 21.2 vs. 93.9° ± 23.4; P = 0.002). There were no significant differences in total flexion-extension and lateral flexion. Increasing age was a significant predictor for objective and subjective restriction.

CONCLUSION

The concern of many patients of being severely restricted in their cervical spine mobility after single-level ACDF can be denied. Objectively, the rotation even showed a significant improvement. Regarding the subjective restriction, which is more important for the patients, we found a significant improvement in general and for all directions of movement after surgery.Level of Evidence: 3.

Effects of different severities of disc degeneration on the range of motion of cervical spine

Aims and Objectives:

The human spine degenerates with age. Intervertebral disc degeneration occurs in the cervical spine. The objective of this study is to determine the effects of degenerative disc diseases on the range of motion (ROM) of the human cervical spinal column using a validated finite-element model.

Materials and Methods:

The validated intact and healthy C2–T1 finite-element model simulated the cortical shell, cancellous core, posterior elements of the vertebrae, and spinal ligaments (longitudinal, capsular, spinous and ligamentum flava, and nucleus and annulus of the discs). Three different stages of the disc disease, that is, mild, moderate, and severe, were simulated at the C5–C6, C6–C7, and C5–C6–C7 discs, respectively, and they were termed as upper single level, lower single level, and bi-level (BL) models, respectively. The material properties and geometry of the disc(s) were altered to simulate the different stages of degeneration. The external mechanical loading was applied in the sagittal mode, via flexion–extension motions and the magnitude was 2.0 Nm for each mode. They were applied to each of the healthy and disc degeneration models, and for each of the three severities of degeneration. The ROM at adjacent and index levels was extracted and normalized with respect to the healthy (baseline) spine.

Results:

A nonuniform distribution in the ROM was found for different disc degeneration states, segmental levels, and flexion–extension loading modes. The specific results for each and level are reported in the results section of the paper.

Conclusion:

Closer follow-up times may be necessary in symptomatic patients with progressive disease, especially with BL involvements.

Eleven-Year Follow-Up of Two Cohorts of Patients Comparing Stand-Alone Porous Tantalum Cage Versus Autologous Bone Graft and Plating in Anterior Cervical Fusions

BACKGROUND

Anterior cervical discectomy and fusion with a porous tantalum cage is an accepted method to treat degenerated cervical discs, with good results, similar to those with autologous bone graft and plating at short- and mid-term follow-up. However, to date, long-term follow-up studies have been performed.

METHODS

We performed a retrospective, single-center study to evaluate the outcomes of 2 cohorts from a previous prospective randomized controlled trial comparing stand-alone tantalum cage (group 1, 27 patients) with autologous bone graft and plating (group 2, 30 patients) for single-level anterior cervical discectomy and fusion at 11 years of follow-up. The usual clinical and radiological outcomes and "overall success," proposed by the Food and Drug Administration, were evaluated.

RESULTS

The improvement in clinical outcomes achieved postoperatively was maintained similarly in the 2 cohorts at 11 years of follow-up. In group 1, the cage had subsided 2-3 mm in 12 patients (44%), segmental lordosis was maintained in 16 patients (59%), adjacent segment degeneration had developed or progressed in 27 of the adjacent segments (50%) in 15 patients (56%), and postoperative nonprogressive deformation of the anterior aspect of the cage was observed in 7 (26%) and minor fragmentation in 3 (11%) patients. In group 2, segmental lordosis was maintained in 90% of the patients and adjacent segment degeneration had developed or progressed in 15 patients (50%).

CONCLUSIONS

These results show that the clinical and radiological outcomes achieved at mid-term follow-up using a tantalum cage for single-level anterior cervical discectomy and fusion will be maintained for 11 years postoperatively, similar to the results with autologous bone graft and plating.

Adjacent Segment Disease in the Cervical and Lumbar Spine

Adjacent segment disease (ASD) is disappointing long-term outcome for both the patient and clinician. In contrast to adjacent segment degeneration, which is a common radiographic finding, ASD is less common. The incidence of ASD in both the cervical and lumbar spine is between 2% and 4% per year, and ASD is a significant contributor to reoperation rates after spinal arthrodesis. The etiology of ASD is multifactorial, stemming from existing spondylosis at adjacent levels, predisposed risk to degenerative changes, and altered biomechanical forces near a previous fusion site. Numerous studies have sought to identify both patient and surgical risk factors for ASD, but a consistent, sole predictor has yet to be found. Spinal arthroplasty techniques seek to preserve physiological biomechanics, thereby minimizing the risk of ASD, and long-term clinical outcome studies will help quantify its efficacy. Treatment strategies for ASD are initially nonoperative, provided a progressive neurological deficit is not present. The spine surgeon is afforded many surgical strategies once operative treatment is elected. The goal of this manuscript is to consider the etiologies of ASD, review its manifestations, and offer an approach to treatment.

Kinematic Magnetic Resonance Imaging Assessment of the Degenerative Cervical Spine: Changes after Anterior Decompression and Cage Fusion

Study Design A prospective cohort study. Objective Decompression and fusion of cervical vertebrae is a combined procedure that has a high success rate in relieving radicular symptoms and stabilizing or improving cervical myelopathy. However, fusion may lead to increased motion of the adjacent vertebrae and cervical deformity. Both have been postulated to lead to adjacent segment pathology (ASP). Kinematic magnetic resonance imaging (MRI) has been increasingly used to evaluate range of motion (ROM) of the cervical spine and ASP. Our objective was to measure ASP, cervical curvature, and ROM of individual segments of the cervical spine using kinematic MRI before and 24 months after monosegmental cage fusion. Methods Eighteen patients who had single-level interbody fusion were included. ROM (using kinematic MRI) and degeneration, spinal stenosis, and cervical curvature were measured preoperatively and 24 months postoperatively. Results Using kinematic MRI, segmental motion of the cervical segments was measured with a precision of less than 3 degrees. The cervical fusion did not affect the ROM of adjacent levels. However, pre- and postoperative ROM was higher at the levels immediately adjacent to the fusion level compared with those further away. In addition, at 24 months postoperatively, the number of cases with ASP was higher at the levels immediately adjacent to fusion level. Conclusions Using kinematic MRI, ROM after spinal fusion can be measured with high precision. Kinematic MRI can be used not only in clinical practice, but also to study intervention and its effect on postoperative biomechanics and ASP of cervical vertebrae.

Radiographic Changes in the Cervical Spine Following Anterior Arthrodesis: A Long-Term Analysis of 166 Patients

BACKGROUND

Adjacent segment degeneration frequently develops following anterior cervical discectomy and fusion. The objectives of the present study were to characterize the long-term evolution of degenerative radiographic changes at segments adjacent to anterior cervical fusion and to identify factors associated with the development of these changes, including the preoperative condition of the cervical spine and parameters related to arthrodeses.

METHODS

One hundred and sixty-six patients who underwent anterior cervical discectomy and fusion for symptomatic cervical spondylosis or disc herniation were followed radiographically for a mean time of 12.7 years (range, 5 to 30 years). Radiographic changes representing degeneration at adjacent levels, including disc height loss, osteophyte formation, end-plate sclerosis, and facet arthrosis, along with changes in sagittal alignment of the fusion segment and cervical spine, were recorded preoperatively and at the time of the latest follow-up. Regression models were used to identify the parameters that affect these degenerative changes.

RESULTS

More than 90% of patients had worsened anterior and posterior osteophytes at segments immediately adjacent to the fusion. Degenerative changes were significantly affected by the proximity of the level to the fusion and were inversely affected by the preoperative degenerative changes present at the segment (p < 0.0001). The time elapsed since the surgical procedure was a significant predictor of degenerative changes (p < 0.0001). However, the patient age, the number of levels fused, and the sagittal alignment of the fusion segment had no influence on the degenerative changes at adjacent segments.

CONCLUSIONS

Multiple factors likely contribute to adjacent segment degeneration following cervical arthrodesis. Although mechanical parameters associated with arthrodesis, such as length and alignment of the fusion, did not appear to play a role, the preoperative degenerative condition of the spine and inclusion of C5-C6 in the arthrodesis influenced the incidence of adjacent segment degeneration.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Narrative review of the in vivo mechanics of the cervical spine after anterior arthrodesis as revealed by dynamic biplane radiography

Arthrodesis is the standard of care for numerous pathologic conditions of the cervical spine and is performed over 150,000 times annually in the United States. The primary long-term concern after this surgery is adjacent segment disease (ASD), defined as new clinical symptoms adjacent to a previous fusion. The incidence of adjacent segment disease is approximately 3% per year, meaning that within 10 years of the initial surgery, approximately 25% of cervical arthrodesis patients require a second procedure to address symptomatic adjacent segment degeneration. Despite the high incidence of ASD, until recently, there was little data available to characterize in vivo adjacent segment mechanics during dynamic motion. This manuscript reviews recent advances in our knowledge of adjacent segment mechanics after cervical arthrodesis that have been facilitated by the use of dynamic biplane radiography. The primary observations from these studies are that current in vitro test paradigms often fail to replicate in vivo spine mechanics before and after arthrodesis, that intervertebral mechanics vary among cervical motion segments, and that joint arthrokinematics (i.e., the interactions between adjacent vertebrae) are superior to traditional kinematics measurements for identifying altered adjacent segment mechanics after arthrodesis. Future research challenges are identified, including improving the biofidelity of in vitro tests, determining the natural history of in vivo spine mechanics, conducting prospective longitudinal studies on adjacent segment kinematics and arthrokinematics after single and multiple-level arthrodesis, and creating subject-specific computational models to accurately estimate muscle forces and tissue loading in the spine during dynamic activities.

Relationship between biomechanical changes at adjacent segments and number of fused bone grafts in multilevel cervical fusions: a finite element investigation

OBJECT

Biomechanical studies have shown that anterior cervical fusion construct stiffness and arthrodesis rates vary with different reconstruction techniques; however, the behavior of the adjacent segments in the setting of different procedures is poorly understood. This study was designed to investigate the adjacent-segment biomechanics after 3 different anterior cervical decompression and fusion techniques, including 3-level discectomy and fusion, 2-level corpectomy and fusion, and a corpectomy-discectomy hybrid technique. The authors hypothesized that biomechanical changes at the segments immediately superior and inferior to the multilevel fusion would be inversely proportional to the number of fused bone grafts and that these changes would be related to the type of fusion technique.

METHODS

A previously validated 3D finite element model of an intact C3-T1 segment was used. Three C4-7 fusion models were built from this intact model by varying the number of bone grafts used to span the decompression: a 1-graft model (2-level corpectomy), a 2-graft model (C-5 corpectomy and C6-7 discectomy), and a 3-graft model (3-level discectomy). The corpectomy and discectomy models were also previously validated and compared well with the literature findings. Range of motion, disc stresses, and posterior facet loads at the segments superior (C3-4) and inferior (C7-T1) to the fusion construct were assessed.

RESULTS

Motion, disc stresses, and posterior facet loads generally increased at both of the adjacent segments in relation to the intact model. Greater biomechanical changes were noted in the superior C3-4 segment than in the inferior C7-T1 segment. Increasing the number of bone grafts from 1 to 2 and from 2 to 3 was associated with a lower magnitude of biomechanical changes at the adjacent segments.

CONCLUSIONS

At segments adjacent to the fusion level, biomechanical changes are not limited solely to the discs, but also propagate to the posterior facets. These changes in discs and posterior facets were found to be lower for discectomy than for corpectomy, thereby supporting the current study hypothesis of inverse relationship between the adjacent-segment variations and the number of fused bone grafts. Such changes may go on to influence the likelihood of adjacent-segment degeneration accordingly. Further studies are warranted to identify the causes and true impact of these observed changes.

Anterior cervical decompression and fusion on neck range of motion, pain, and function: a prospective analysis

BACKGROUND CONTEXT

Intractable cervical radiculopathy secondary to stenosis or herniated nucleus pulposus is commonly treated with an anterior cervical decompression and fusion (ACDF) procedure. However, there is little evidence in the literature that demonstrates the impact such surgery has on long-term range of motion (ROM) outcomes.

PURPOSE

The objective of this study was to compare cervical ROM and patient-reported outcomes in patients before and after a 1, 2, or 3 level ACDF.

STUDY DESIGN

Prospective, nonexperimental.

PATIENT SAMPLE

Forty-six patients.

OUTCOME MEASURES

The following were measured preoperatively and also at 3 and 6 months after ACDF: active ROM (full and painfree) in three planes (ie, sagittal, coronal, and horizontal), pain visual analog scale, Neck Disability Index, and headache frequency.

METHODS

Patients undergoing an ACDF for cervical radiculopathy had their cervical ROM measured preoperatively and also at 3 and 6 months after the procedure. Neck Disability Index and pain visual analog scale values were also recorded at the same time.

RESULTS

Both painfree and full active ROM did not change significantly from the preoperative measurement to the 3-month postoperative measurement (ps>.05); however, painfree and full active ROM did increase significantly in all three planes of motion from the preoperative measurement to the 6-month postoperative measurement regardless of the number of levels fused (ps≤.023). Visual analog scale, Neck Disability Index, and headache frequency all improved significantly over time (ps≤.017).

CONCLUSIONS

Our results suggest that patients who have had an ACDF for cervical radiculopathy will experience improved ROM 6 months postoperatively. In addition, patients can expect a decrease in pain, an improvement in neck function, and a decrease in headache frequency.

Disc height and sagittal alignment in operated and non-operated levels in the lumbar spine at long-term follow-up: a case-control study

Purpose:

To compare lumbar disc degeneration at 9-year follow-up in patients with chronic low back pain who had instrumented lumbar fusion or no fusion.

Material and methodology:

The main outcomes were disc height and sagittal alignment measured by Distortion Compensated Roentgen Analysis (DCRA). Secondary outcome included the Oswestry Disability Index and VAS back pain.

Results:

Forty-eight patients with baseline and 9-year radiographs from L2- S1 were included. Twenty-three had lumbar fusion and 25 had no fusion. Disc height was reduced at all levels independent of fusion. No difference in disc height and sagittal alignment was observed between patients fused and not fused. There were weak correlations, ranging from 0.04 to 0.36, between clinical and radiological parameters.

Conclusion:

Lumbar disc degeneration increased at all measured levels independent of fusion and correlated poorly with clinical outcome.

Biomechanics of adjacent segments after a multilevel cervical corpectomy using anterior, posterior, and combined anterior-posterior instrumentation techniques: a finite element model study

BACKGROUND CONTEXT

Adjacent segment degeneration (ASD) after cervical fusion is a clinical concern. Despite previous studies documenting the biomechanical effects of multilevel cervical fusion on segments immediately superior and inferior to the operative segments, the pathogenesis of the initiation of degeneration progression in neighboring segments is still poorly understood.

PURPOSE

To test the hypothesis that changes in range of motion, disc stresses, and facet loads would be highest at the superior adjacent segment (C3-C4) after anterior C4-C7 corpectomy and fusion and that these changes would be the least in anterior fixation and the greatest in posterior or combined anterior-posterior instrumentation techniques.

STUDY DESIGN

A finite element (FE) analysis of adjacent vertebral segment biomechanics after a two-level corpectomy fusion with three different fixation techniques (anterior, posterior, and combined anterior-posterior).

METHODS

A previously validated three-dimensional FE model of an intact C3-T1 segment was used. From this intact model, three additional instrumentation models were constructed using anterior (rigid screw-plate), posterior (rigid screw-rod), and combined anterior-posterior fixation techniques after a C4-C7 corpectomy and fusion. Motion patterns, disc stresses, and posterior facet loads at the levels cephalad and caudal to the fusion were assessed.

RESULTS

Range of motion, disc stresses, and posterior facet loads increased at the adjacent segments. Use of posterior fixation, whether alone or in combination with anterior fixation, infers higher changes in segmental motion, disc stresses, and posterior facet loads at adjacent segments compared with the use of anterior fixation alone. The superior C3-C4 motion was most affected during lateral bending and the inferior C7-T1 motion was most affected during flexion, whereas both superior C3-C4 and inferior C7-T1 motions were least affected during extension. However, disc stresses and facet loads were most affected during extension. Hence, it is speculated that the most remodeling changes in discs and facets might be related to the least changes in extension motion.

CONCLUSIONS

Biomechanical factors such as increased mechanical demand and motion that have been associated with the development of ASD progression are highest in the segment immediately superior to the fusion. These changes are even more pronounced when the fixation technique involves the addition of posterior instrumentation, thereby supporting the hypothesis of the present study. Increased degrees of stiffening of the fused segments not only may lead to degenerative changes in the disc but may also predispose the segments to premature facet degeneration. Over subsequent time period, any remaining construct micro-motion is further eliminated with fusion of the posterior facet joints and the remaining regions in the disc space also filled in with bone, which eventually results in a circumferential type of fusion. After a circumferential fusion, authors, however, speculate that the role of instrumentation in ASD progression might not be significant. In fact, sufficient evidence to support this speculation is still lacking in the literature.

Clinical and radiological follow-up of single-level Prestige LP cervical disc replacement

OBJECTIVE

To evaluate the clinical outcomes and radiographic results of patients who underwent single-level cervical arthroplasty using the Prestige LP.

METHOD

Thirty-one patients with single-level cervical disc disease received the Prestige LP disc replacement from June 2008 to December 2009. The neck disability index (NDI), Japanese Orthopedic Association score (JOA) and visual analogue scale (VAS) were used to assessed clinical outcomes pre-operatively and post-operatively at 24 months. The overall cervical alignment (C2-7 Cobb angle), the functional segmental unit (FSU) curvature, the range of motion (ROM) of treated and adjacent levels were measured, and the evidence of heterotopic ossification (HO) was observed from static and dynamic radiographs.

RESULTS

There was a statistically significant improvement in the NDI from 20.2 ± 7.5 to 6.4 ± 3.5 (P < 0.000), JOA from 12.8 ± 2.2 to 16.6 ± 0.6 (P < 0.000), the neck VAS score from 4.1 ± 2.5 to 1.4 ± 1.1 (P < 0.000), the arm VAS score from 4.6 ± 2.5 to 0.7 ± 1.1 (P < 0.000). The post-operative overall cervical alignment (9.3° ± 7.2°), ROM of treated level (7.6°) and adjacent level (upper level 9.4° ± 3.1°, lower level 9.1° ± 3.5°) are well maintained. The FSU were 0.2° ± 5.4° and 1.9° ± 5.5° at pre-operation and final follow-up with statistical significance (P = 0.011). Heterotopic ossification was evidenced in five operated segment (16 %).

CONCLUSIONS

The Prestige LP disc arthroplasty maintains favorable clinical outcomes, preserves the overall cervical alignment, FSU curvature, ROM of treated level and adjacent levels.

Six-degrees-of-freedom cervical spine range of motion during dynamic flexion-extension after single-level anterior arthrodesis: comparison with asymptomatic control subjects

BACKGROUND

The etiology of adjacent-segment disease following cervical spine arthrodesis remains controversial. The objective of the current study was to evaluate cervical intervertebral range of motion during dynamic flexion-extension in patients who had undergone a single-level arthrodesis and in asymptomatic control subjects.

METHODS

Ten patients who had undergone a single-level (C5/C6) anterior arthrodesis and twenty asymptomatic control subjects performed continuous full range-of-motion flexion-extension while biplane radiographs were collected at thirty images per second. A previously validated tracking process determined three-dimensional vertebral position on each pair of radiographs with submillimeter accuracy. Six-degrees-of-freedom kinematics between adjacent vertebrae were calculated throughout the entire flexion-extension movement cycle over multiple trials for each participant. Cervical kinematics were also calculated from images collected during static full flexion and static full extension.

RESULTS

The C4/C5 motion segment moved through a larger extension range of motion and a smaller flexion range of motion in the subjects with the arthrodesis than in the controls. The extension difference between the arthrodesis and control groups was 3.8° (95% CI [confidence interval], 0.9° to 6.6°; p = 0.011) and the flexion difference was -2.9° (95% CI, -5.3° to -0.5°; p = 0.019). Adjacent-segment posterior translation was greater in the arthrodesis group than in the controls, with a C4/C5 difference of 0.8 mm (95% CI, 0.0 to 1.6 mm) and a C6/C7 difference of 0.4 mm (95% CI, 0.0 to 0.8 mm; p = 0.016). Translation range of motion and rotation range of motion were consistently larger when measured on images collected during dynamic functional movement as opposed to images collected at static full flexion or full extension. The upper 95% CI limit for anterior-posterior translation range of motion was 3.45 mm at C3/C4 and C4/C5, but only 2.3 mm at C6/C7.

CONCLUSIONS

C5/C6 arthrodesis does not affect the total range of motion in adjacent vertebral segments, but it does alter the distribution of adjacent-segment motion toward more extension and less flexion superior to the arthrodesis and more posterior translation superior and inferior to the arthrodesis during in vivo functional loading. Range of motion measured from static full-flexion and full-extension images underestimates dynamic range of motion. Clinical evaluation of excessive anterior-posterior translation should take into account the cervical vertebral level.

A biomechanical evaluation of a spacer with integrated plate for treating adjacent-level disease in the subaxial cervical spine

BACKGROUND CONTEXT

Adjacent level degeneration (ALD) has been reported as one of the long-term consequences of anterior discectomy and fusion despite its clinical success in treating cervical pathologies. Traditionally, ALD is treated by replacing the previously implanted plate with a longer plate, which can lead to postoperative complications. The biomechanics of SIP in the adjacent level has not been investigated.

PURPOSE

To evaluate the multidirectional stability of a spacer with integrated plate (SIP) in comparison to a traditional spacer and plate (TSP).

STUDY DESIGN

To evaluate the biomechanical stability of a spacer with integrated plate adjacent to a traditional spacer and plate construct in a human cervical cadaveric model.

METHODS

Eight fresh human cervical (C2-C7) cadaver spines were mounted on a six degree-of-freedom spine simulator. The sequence of test constructs was: 1) Intact; 2) TSP (C4-C6) with SIP (C3-C4); and 3) TSP (C3-C6). An unconstrained moment of ±1.5 Nm was used in flexion-extension, lateral bending, and axial rotation. Range of motion (ROM) was measured by a digital motion analysis system. Statistical analysis was performed using ANOVA repeated measures.

RESULTS

All instrumented constructs significantly reduced ROM compared to the intact condition. No statistically significant difference was observed between the two-level TSP with an adjacent SIP construct and three-level TSP construct in all loading modes.

CONCLUSION

The biomechanical study shows that adding a spacer with integrated plate adjacent to a two-level anterior plate demonstrates equivalent stability to a three-level anterior plate. The spacer with integrated plate, which preserves the originally plated fusion levels, may overcome the complications associated with the traditional technique of replacing the original plate with a longer plate. However, prospective clinical studies are required to address the clinical benefits and challenges, if any.

Management of adjacent segment disease after cervical spinal fusion

Adjacent segment disease (ASD) was described after long-term follow-up of patients treated with cervical fusion. The term describes new-onset radiculopathy or myelopathy referable to a motion segment adjacent to previous arthrodesis and often attributed to alterations in the biomechanical environment after fusion. Evidence suggests that ASD affects between 2% and 3% of patients per year. Although prevention of ASD was one major impetus behind the development of motion-sparing surgery, the literature does not yet clearly distinguish a difference in the rate of ASD between fusion and disk replacement. Surgical techniques during index surgery may reduce the rate of ASD.

Adjacent-level biomechanics after single versus multilevel cervical spine fusion

OBJECT

Previous studies have demonstrated that patients with spinal fusion are at greater risk for adjacent-segment disease and require additional surgery. It has been postulated that excessive motion of a given motion segment unit (MSU) leads to an increased risk of disc degeneration. It is the authors' hypothesis that a greater increase in adjacent-segment motion will be observed following a 2-level versus a single-level anterior cervical discectomy and instrumented fusion (ACDF). Therefore, they undertook this study to determine the effect of single-level versus 2-level ACDF on the biomechanics of adjacent MSUs.

METHODS

Ten fresh-frozen human cervical spines were used in this study. The specimens were potted at C-4 and T-1 and tested in flexion and extension. Range of motion (ROM) was 30° of flexion and 15° of extension at a maximum load of 50 N. The specimens were tested intact and then were randomized into 2 groups of 5 specimens each. Group 1 underwent a single-level ACDF at the C5-6 level first, and Group 2 underwent the procedure at the C6-7 level. After testing, both groups had the fusion extended to include the C5-7 levels, and the testing was repeated. Changes in overall ROM, stiffness, and segmental motion were calculated and statistically analyzed using a paired Student t-test.

RESULTS

An increase in sagittal ROM of 31.30% above (p = 0.012) and 33.88% below (p = 0.066) the fused MSU was found comparing a 2-level with a 1-level ACDF. The overall stiffness of the entire spinal construct increased 37.34% (p = 0.051) in extension and 30.59% (p = 0.013) in flexion as the second fusion level was added. As expected, the overall sagittal ROM of the entire spinal construct decreased by 13.68% (p = 0.0014) with a 2-level compared with a 1-level fusion.

CONCLUSIONS

This study has shown that the biomechanics at adjacent levels to a cervical spine fusion are altered and that there is increased adjacent-segment motion at the levels above and below, after a 2-level compared with a 1-level ACDF.

Three-dimensional kinematic analysis of the cervical spine after anterior cervical decompression and fusion at an adjacent level: a preliminary report

PURPOSE

Development of adjacent segment degeneration following anterior cervical decompression and fusion (ACDF) is still controversial, as adjacent-level kinematics is poorly understood. This study reports preliminary data from a high-accuracy 3D analysis technique developed for in vivo cervical kinematics.

METHODS

From nine cervical spondylosis patients, four underwent single-level ACDF, and five underwent two-level ACDF using cylindrical titanium cage implant(s). Pre- and post-surgical CT scans were taken in flexion, neutral and extended positions, allowing us to compute segmental ranges of motion for rotation and translation, and 3D disc-height distributions. Differences in segmental motions and disc-height between fused and adjacent levels were analyzed with a Wilcoxon signed-rank test. Results are presented as mean ± SEM.

RESULTS

The flexion/extension angular-ROM at the fusion level decreased after surgery (7.46 ± 1.17° vs. 3.14 ± 0.56°, p < 0.003). The flexion/extension angular-ROM at one caudal adjacent level to the fusion level (3.97 ± 1.29°) tended to be greater post-operatively (6.11 ± 1.44°, p = 0.074). Translation in the anterior-posterior direction during flexion/extension at the fusion level decreased after surgery (1.22 ± 0.20 mm vs. 0.32 ± 0.11 mm, p < 0.01). No differences were found in adjacent-level disc heights between both study time-points.

CONCLUSIONS

This study showed increased segmental motion in flexion/extension angular-ROM at one level adjacent to ACDF. However, increases in the rotational angular-ROM were not statistically significant when cranial/caudal adjacent levels were analyzed separately. This preliminary study highlighted the capabilities of a 3D-kinematic analysis method to detect subtle changes in kinematics and disc height at the adjacent levels to ACDF. Thus, reliable evidence related to ACDF's influence on adjacent-level cervical kinematics can be collected.

Adjacent segment motion after anterior cervical discectomy and fusion versus Prodisc-c cervical total disk arthroplasty: analysis from a randomized, controlled trial

STUDY DESIGN

Post hoc analysis of data acquired in a prospective, randomized, controlled trial.

OBJECTIVE

To compare adjacent segment motion after anterior cervical discectomy and fusion (ACDF) versus cervical total disc arthroplasty (TDA).

SUMMARY OF BACKGROUND DATA

TDA has been designed to be a motion-preserving device, thus theoretically normalizing adjacent segment kinematics. Clinical studies with short-term follow-up have yet to demonstrate a consistent significant difference in the incidence of adjacent segment disease.

METHODS

Two hundred nine patients at 13 sites were treated in a prospective, randomized, controlled trial of ACDF versus TDA for single-level symptomatic cervical degenerative disc disease (SCDD). Flexion and extension radiographs were obtained at all follow-up visits. Changes in ROM were compared using the Wilcoxon signed-rank test and the Mann-Whitney U test. Predictors of postoperative ROM were determined by multivariate analysis using mixed effects linear regression.

RESULTS

Data for 199 patients were available with 24-month follow-up. The groups were similar with respect to baseline demographics. A significant increase in motion at the cranial and caudal adjacent segments after surgery was observed in the ACDF group only (cranial: ACDF: +1.4° (0.4, 2.4), P = 0.01; TDA: +0.8°, (-0.1, +1.7), P = 0.166; caudal: ACDF: +2.6° (1.3, 3.9), P < 0.0001; TDA: +1.3, (-0.2, +2.8), P = 0.359). No significant difference in adjacent segment ROM was observed between ACDF and TDA. Only time was a significant predictor of postoperative ROM at both the cranial and caudal adjacent segments.

CONCLUSION

Adjacent segment kinematics may be altered after ACDF and TDA. Multivariate analysis showed time to be a significant predictor of changes in adjacent segment ROM. No association between the treatment chosen (ACDF vs. TDA) and ROM was observed. Furthermore clinical follow-up is needed to determine whether possible differences in adjacent segment motion affect the prevalence of adjacent segment disease in the two groups.

Changes in the range of motion of the cervical spine and adjacent segments at ≥24 months after uninstrumented corpectomy for cervical spondylotic myelopathy

BACKGROUND

Few clinical studies have described the changes in the range of motion (ROM) of the cervical spine and adjacent segments following central corpectomy. We aimed to quantify the changes in range of motion (ROM) of the cervical spine and the adjacent segments at ≥24 months following uninstrumented central corpectomy (CC) for cervical spondylotic myelopathy (CSM) and to determine the contribution of the adjacent segments to the compensation for loss of motion of the cervical spine following CC.

METHODS

Preoperative and follow-up lateral cervical spine radiographs of 36 patients who underwent CC for CSM between 2001 and 2007 were compared for the ROM of the subaxial cervical spine, superior and inferior adjacent segment. Anterior osteophytes as seen on the radiographs were classified according to Nathan's grading system.

RESULTS

The mean duration of follow-up was 48.5 months. At follow-up, the total cervical spine ROM decreased by 18.3° ± 2.2° (p < 0.001), the superior adjacent segment ROM increased by 2.3° ± 0.9° (p = 0.01) and the inferior adjacent segment ROM, measured in 20 cases, increased by 6.2° ± 1.7° (p = 0.01). The superior adjacent segment showed a 70% increase, whereas the inferior adjacent segment showed a 110% increase in mobility. Nathan's grade at the superior or inferior adjacent segment increased in 12 cases.

CONCLUSIONS

CC significantly reduces the motion of the cervical spine and increases the adjacent segment mobility at intermediate follow-up. The inferior adjacent segment shows greater compensation of motion as compared to the superior adjacent segment in our series. Adjacent segment degeneration as estimated by Nathan's grade was seen in one-third of the cases.

Influence of number of operated levels and postoperative time on active range of motion following anterior cervical decompression and fusion procedures

STUDY DESIGN

A cohort study analyzing the cervical range of motion of subjects with anterior cervical decompression and fusion operation (ACDF).

OBJECTIVE

The purpose of this study was to compare the cervical range of motion of subjects who underwent an ACDF operation to age-matched healthy nonoperative subjects. Subjects were divided according to the number of operated levels, postoperative time point, and level of disability.

SUMMARY OF BACKGROUND DATA

ACDF is an operative treatment aimed at expansion of the spinal canal and relief of cord compression. In addition to alleviating pain, 2 common tools are used to measure postoperative success; cervical range of motion kinematic analysis and subjective evaluation questionnaires (Neck Disability Index [NDI]).

METHODS

This study involved 25 preoperative and 110 postoperative ACDF subjects as well as 18 control volunteers with no prior history of neck complaints. ACDF subjects were divided according to the number of operated levels; 1-, 2-, 3-, and 4-levels as well as time of their clinical visit; preoperative, early, and late postoperative. Before kinematic testing, the subjects were asked to complete the NDI survey. A virtual reality assisted electromagnetic tracking was used to measure an active voluntary motion of the head relative to the torso. The subjects' maximum range of motion was calculated and compared as they executed 3 to 5 consecutive cycles of the primary motions, flexion/extension, axial rotation, and lateral bending. An analysis of variance statistical test (P < 0.01) was used to determine significant differences between study groups. RESULTS.: Subject's range of motion decreased relative to control as the number of operated levels increased. Moreover, 1- and 2-level subjects increased their range motion relative to preoperative. Finally, there was a decrease in range of motion as the subject's level of disability increased as measured by an NDI score but all subjects reported a lower score relative to preoperative time point.

CONCLUSION

The active range of motion of subjects who underwent an ACDF surgery increased postoperative and was dependent on the number of operated levels. In addition, there was an improvement in the disability level after the surgery as measured by the NDI score.

Anterior cervical arthrodesis using a "stand alone" cylindrical titanium cage: prospective analysis of radiographic parameters

STUDY DESIGN

Prospective, observational study.

OBJECTIVE

To evaluate biomechanical changes associated with cervical arthrodesis using a cylindrical titanium cage.

SUMMARY OF BACKGROUND DATA

Anterior cervical discectomy and fusion (ACDF) is the "gold standard" for treating cervical disc disease. In an effort to avoid the morbidity associated with autogenous bone graft harvesting, cervical cages are used to achieve fusion. The cages should allow for restoration and maintenance of natural disc height, angulations, and displacements at the operated levels.

METHODS

Fifty-four patients underwent standard ACDF using a "stand alone" cylindrical cage implant. Lateral radiographic views of the cervical spine were obtained before surgery, on the first day postoperatively, and at 12 months postoperatively. Disc height, vertebral alignment, angle of lordosis, and range of motion at operated levels were quantified prospectively by distortion compensated Roentgen analysis.

RESULTS

At 12 months postoperatively, solid fusion was achieved but the cylindrical cage failed to preserve disc height, prevent kyphosis, and preserve natural intervertebral alignment. We observed significant cage subsidence and malalignment.

CONCLUSION

We noticed several unfavorable outcomes when performing an analysis of radiographic parameters after ACDF using a cylindrical titanium cage. Thus, the use of a "stand alone" cylindrical cage in ACDF should be considered with caution.

Sagittal cervical alignment after cervical disc arthroplasty and anterior cervical discectomy and fusion: results of a prospective, randomized, controlled trial

STUDY DESIGN

Radiographic results of a multicenter, prospective randomized study comparing 1-level cervical total disc replacement (TDR-C) with anterior cervical discectomy and fusion (ACDF).

OBJECTIVE

To evaluate the effect on device-level lordosis, cranial and caudal adjacent level lordosis, and overall cervical sagittal alignment (C2-C6) after TDR-C or ACDF.

SUMMARY OF BACKGROUND DATA

Cervical total disc replacement (TDR-C) has emerged as a promising alternative to ACDF in a select group of patients. The maintenance and/or improvement of sagittal balance is essential in preserving functionality after reconstructive spinal procedures. Recent studies have documented changes in spinal alignment after TDR-C, however, no studies have compared these changes to those noted in matched group of patients that have undergone ACDF.

METHODS

Radiographic data were obtained from the randomized group of a multicenter, randomized, prospective, controlled study comparing TDR-C (ProDisc-C, Synthes Spine, West Chester, PA) with ACDF in the treatment of 1-level cervical disc disease. Complete radiographic data were available for 89 TDR-C patients (average age: 42.2 years) and 91 ACDF patients (average age: 41.7 years). Cervical lordosis at the device level, cranial and caudal adjacent levels, and total cervical lordosis (C2-C6) were independently measured before surgery and 2 years after surgery using custom image stabilization software (Quantitative Motion Analysis, Medical Metrics, Inc, Houston, TX).

RESULTS

C5-C6 was the most common operative level (TDR-C: 54%; ACDF: 55%). At 2 years after surgery, the TDR-C group experienced statistically significant changes in lordosis of 3.0 degrees (P < 0.001), 0.90 degrees (P = 0.006), and -1.9 degrees (P < 0.001) at the operative, cranial, and caudal adj-acent levels, respectively. ACDF experienced changes in lordosis of 4.2 degrees (P < 0.001), 1.0 degrees (P = 0.001), and -1.5 degrees (P = 0.001), respectively. The between-group differences were significant at the operative level (P = 0.03) and the caudal adjacent level (P = 0.05). Total cervical lordosis increased in both TDR-C and ACDF by 3.1 degrees and 3.8 degrees , respectively (P = 0.49).

CONCLUSION

In both TDR-C and ACDF, lordosis increased at the device-level, cranial adjacent level, and in total cervical lordosis, while lordosis decreased at the caudal adjacent level. Although ACDF facilitated a greater increase in device level lordosis (+1.25 degrees ) and less loss of lordosis at the caudal adjacent level compared with TDR-C (-0.39 degrees ), the clinical relevance of the small differences remain unknown.

Mid- to long-term outcome of instrumented anterior cervical fusion for subaxial injuries

The management of patients with subaxial cervical injuries lacks consensus, particularly in regard to the decision which surgical approach or combination of approaches to use and which approach yields the best clinical outcome in the distinct injury. The trauma literature is replete with reports of surgical techniques, complications and gross outcome assessment in heterogeneous samples. However, data on functional and clinical outcome using validated outcome measures are scanty. Therefore, the authors performed a study on plated anterior cervical decompression and fusion for unstable subaxial injuries with focus on clinical outcome. For the purpose of a strongly homogenous subgroup of patients with subaxial injuries without spinal cord injuries, robust criteria were applied that were fulfilled by 28 patients out of an original series of 131 subaxial injuries. Twenty-six patients subjected to 1- and 2-level fusions without having spinal cord injury could be surveyed after a mean of 5.5 years (range 16-128 months). The cervical spine injury severity score averaged 9.6. Cross-sectional outcome assessment included validated outcome measures (Neck pain disability index, Cervical Spine Outcome Questionnaire, SF-36), the investigation of construct failure and successful surgical outcome were defined by strict criteria, the reconstruction and maintenance of local and total cervical lordosis, adjacent-segment degeneration and intervertebral motion, and the fusion-rate using an interobserver assessment. Self-rated clinical outcome was excellent or good in 81% of patients and moderate or poor in 19% that corresponded to the results of the validated outcome measures. Results of the NPDI averaged 12.4 +/- 12.7% (0-40). With the SF-36 mean physical and mental component summary scores were 47.0 +/- 9.8 (18.2-59.3) and 52.2 +/- 12.4 (14.6-75.3), respectively. Using merely non-constrained plates, construct failure was observed in 31% of cases and loss of local lordosis, expressed as a mean injury angle of 14 degrees, postoperative angle of -5.5 degrees and follow-up angle of -1 degree, was significant. However, total cervical lordosis was within the limits of normalcy (-24.3 degrees +/- 13.3) and fusion-rate was 88.5%. The progression of adjacent-level degeneration was shown to be significantly influenced by a decreased plate-to-disc-distance. Adjacent-level intervertebral motion was not altered due to the adjacent fusion, but reduced in the presence of advanced adjacent-level degeneration. Patients were more likely to maintain a high satisfaction level if they succeeded to maintain segmental lordosis (<0 degree), had a solid fusion, an increased plate-to-disc distance, and if they were judged to have a successful surgical outcome that included the absence of construct failure and reconstruction of lordosis within +/-1 SD of normalcy. Using validated outcome vehicles the interdependencies between radiographical, functional and clinical outcome parameters could be substantiated with statistically significant correlations. The use of validated outcome vehicles in a subgroup of patients with plated anterior cervical fusions for subaxial injuries is recommended. With future studies, it enables objective comparison of surgical techniques and related radiographical, functional and clinical outcome.

Klippel-Feil syndrome and Sprengel deformity combined with an intraspinal course of the left subclavian artery and a bovine aortic arch variant

SUMMARY

We present a case of Klippel-Feil syndrome and Sprengel deformity with a bovine aortic arch and an aberrant course of the left subclavian artery in a 14-year-old boy. CT and MR imaging of the neck and upper thorax demonstrated a cervical osseous segmentation anomaly, a left common carotid artery originating from the innominate artery, and a left subclavian artery coursing through the intraspinal space at the C6 through T1 level. Possible embryonic mechanisms and clinical significance of this variant are reviewed.