William Sears

Incidence and prevalence of surgery at segments adjacent to a previous posterior lumbar arthrodesis

BACKGROUND CONTEXT Adjacent segment disease (ASD) after lumbar spinal fusion has been an important reason behind the development of nonfusion stabilization technology. However, the incidence, prevalence, and factors contributing to adjacent segment degeneration in the lumbar spine remain unclear. A range of prevalence rates for ASD have been reported in the lumbar spinal literature, but the annual incidence has not been widely studied in this region. Conflicting reports exist regarding risk factors, especially fusion length. PURPOSE To determine the annual incidence and prevalence of further surgery for adjacent segment disease (SxASD) after posterior lumbar arthrodesis and examine possible risk factors. STUDY DESIGN Retrospective cohort study. PATIENT SAMPLE Nine hundred twelve patients who underwent 1,000 consecutive posterior lumbar interbody fusion procedures, with mean follow-up duration of 63 months (range, 5 months-16 years). OUTCOME MEASURES Further surgery for ASD or surgery-free survival. METHODS A postal and telephone survey. Follow-up rate: 91% of patients. The annual incidence and prevalence of ASD requiring further surgery were determined using Kaplan-Meier survivorship analysis. Cox proportional-hazards (Cox) regression was used for multivariate analysis of possible risk factors. Significance was set at p<.05. RESULTS Further surgery for ASD occurred following 130 of 1,000 or 13% of procedures at a mean time of 43 months (range, 2.3-162 months). The mean annual incidence of SxASD over the first 10 years, in all patients, was 2.5% (95% confidence interval [95% CI], 1.9-3.1) with prevalences of 13.6% and 22.2% at 5 and 10 years, respectively. Cox regression modeling found that the number of levels fused (p≤.0003), age of the patient, fusing to L5, and performing an additional laminectomy adjacent to a fusion all independently affect the risk of SxASD. The mean annual incidence figures in the first 10 years after a lumbar fusion were 1.7% (95% CI, 1.3-2.2) after fusion at single levels, 3.6% (2.1-5.2) after two levels, and 5.0% (3.3-6.7) after three and four levels. The 5- and 10-year prevalences were 9% and 16%, 17% and 31%, and 29% and 40% after single-, two-, and three-/four-level fusions, respectively. The risk of SxASD in patients younger than 45 years was one-quarter (95% CI, 10-64) the risk of patients older than 60 years (p=.003). A laminectomy adjacent to a fusion increases the relative risk by 2.4 times (95% CI, 1.1-5.2; p=.03). Stopping a fusion at L5 is associated with a 1.7-fold increased risk (95% CI, 1.2-2.4; p=.007) of SxASD compared with a fusion to S1, for fusions of the same length. CONCLUSION The overall annual incidence and predicted 10-year prevalence of further surgery for ASD after lumbar arthrodesis were 2.5% and 22.2%, respectively. These rates varied widely depending on the identified risk factors. Although young patients who underwent single-level fusions were at low risk, patients who underwent fusion of three or four levels had a threefold increased risk of further surgery, compared with single-level fusions (p<.0001), and a predicted 10-year prevalence of 40%.

Current Practice in the Timing of Surgical Intervention in Spinal Cord Injury

Study Design. Systematic review of the literature and prospective survey study. Objective. To characterize expert opinion regarding the timing of surgery for decompression of the injured spinal cord and critically summarize the evidence for early surgical intervention for acute spinal cord injury (SCI). Summary of Background Data. The optimal timing of decompressive surgery for acute SCI is controversial, resulting in considerable variability in clinical practice. Moreover, the current opinion of spine surgeons regarding the optimal timing of surgery after SCI is unknown. Methods. We undertook a systematic review of the applied preclinical and clinical published data regarding the timing of decompression following SCI. A 20-question survey was sent to orthopedic and neurosurgical spine surgeons across the world. Response frequencies were compiled for respondent demographics and preference for timing of surgical decompression in 6 distinct clinical scenarios. &khgr;2 statistics were used to compare response frequencies based on specialty and fellowship training. Results. A total of 971 spine surgeons responded to the survey. In almost every clinical scenario, with the exception of central cord syndrome, the majority of respondents (≥80%) preferred to decompress the spinal cord within 24 hours. A complete cervical SCI would preferably be decompressed within 6 hours by 46.2% of respondents, but 72.9% would operate within 6 hours for an incomplete SCI in an otherwise identical clinical scenario. Conclusion. The majority of spine surgeons prefer to decompress the acutely injured spinal cord within 24 hours. The majority of spine surgeons prefer to decompress the cervical spine for patients with complete or incomplete cervical SCI within 24 hours. Early decompression (within 24 hours) should be considered as part of the therapeutic management of any patient with SCI, particularly those with cervical SCI. Very early decompression (within 12 hours) should be considered for a patient with an incomplete cervical SCI (with the possible exception of central cord syndrome).

Similarities and differences in the treatment of spine trauma between surgical specialties and location of practice.

Study Design. Questionnaires administered to practicing orthopedic and neurosurgical spine surgeons from various regions of the United States and abroad. Objectives. To determine similarities and differences in the treatment of spinal trauma. Summary of Background Data. Spinal trauma is generally referred to subspecialists of orthopedic or neurosurgical training. Prior studies have suggested that there is significant variability in the management of such injuries. Methods. Questionnaires based on eight clinical scenarios of commonly encountered cervical, thoracic, and lumbar injuries were administered to 35 experienced spinal surgeons. Surgeons completed profile information and answered approximately one dozen questions for each case. Data were analyzed with SPSS software to determine the levels of agreement and characteristics ofrespondents that might account for a lack of agreement on particular aspects of management. Results. Of the 35 surgeons completing the questionnaire, 63% were orthopedists, 37% were neurosurgeons, and 80% had been in practice for more than 5 years. Considerable agreement was found in the majority of clinical decisions, including whether or not to operate and the timing of surgery. Of the differences noted, neurosurgeons were more likely to obtain a MRI, and orthopedists were more likely to use autograft as a sole graft material. Physicians from abroad were, in general, more likely to operate and to use an anterior approach during surgery than physicians from the northeastern United States. Conclusions. More commonalities were identified in the management of spinal trauma than previously reported. When found, variability in opinion was related to professional and regional differences. Spine 2004;29:685–696

Postural consequences of cervical sagittal imbalance: A novel laboratory model

Study Design. A biomechanical study using human spine specimens. Objective. To study postural compensations in lordosis angles that are necessary to maintain horizontal gaze in the presence of forward head posture and increasing T1 sagittal tilt. Summary of Background Data. Forward head posture relative to the shoulders, assessed radiographically using the horizontal offset distance between the C2 and C7 vertebral bodies (C2–C7 [sagittal vertical alignment] SVA), is a measure of global cervical imbalance. This may result from kyphotic alignment of cervical segments, muscle imbalance, as well as malalignment of thoracolumbar spine. Methods. Ten cadaveric cervical spines (occiput-T1) were tested. The T1 vertebra was anchored to a tilting and translating base. The occiput was free to move vertically but its angular orientation was constrained to ensure horizontal gaze regardless of sagittal imbalance. A 5-kg mass was attached to the occiput to mimic head weight. Forward head posture magnitude and T1 tilt were varied and motions of individual vertebrae were measured to calculate C2–C7 SVA and lordosis across C0–C2 and C2–C7. Results. Increasing C2–C7 SVA caused flexion of lower cervical (C2–C7) segments and hyperextension of suboccipital (C0–C1–C2) segments to maintain horizontal gaze. Increasing kyphotic T1 tilt primarily increased lordosis across the C2–C7 segments. Regression models were developed to predict the compensatory C0–C2 and C2–C7 angulation needed to maintain horizontal gaze given values of C2–C7 SVA and T1 tilt. Conclusion. This study established predictive relationships between radiographical measures of forward head posture, T1 tilt, and postural compensations in the cervical lordosis angles needed to maintain horizontal gaze. The laboratory model predicted that normalization of C2–C7 SVA will reduce suboccipital (C0–C2) hyperextension, whereas T1 tilt reduction will reduce the hyperextension in the C2–C7 segments. The predictive relationships may help in planning corrective strategy in patients experiencing neck pain, which may be attributed to sagittal malalignment. Level of Evidence: N/A

Surgical management of traumatic thoracic spondyloptosis : Review of 2 cases

Spondyloptosis due to trauma is a very rare injury typically associated with motor vehicle accidents and typically at the lumbosacral junction. This report describes two patients with T6-7 and T12-L1 spondyloptosis secondary to trauma. The former was a 36-year-old man who was pinned under a 200 kg hay bale, suffering immediate paraplegia and undergoing successful posterior reduction and stabilization via a single stage posterior approach. Two years after his injury he has not developed any new deformity or neurological deterioration. The latter was a 22-year-old miner who was thrown against the ceiling of a coalmine and suffered a hyperflexion injury resulting in an immediate T12 paraplegia. Again successful reduction and stabilization was able to be achieved through pedicle screw instrumentation via a single-stage posterior approach. These two patients are the first reported cases of traumatic thoracic spondyloptosis. This report describes the rationale, likely mechanisms and surgical technique required for operative reduction and stabilization via a single-stage posterior approach.

Is Cervical Sagittal Imbalance a Risk Factor for Adjacent Segment Pathomechanics After Multilevel Fusion

Study Design. A biomechanical study using human spine specimens. Objective. The aim of this study was to assess whether the presence of cervical sagittal imbalance is an independent risk factor for increasing the mechanical burden on discs adjacent to cervical multilevel fusions. Summary of Background Data. The horizontal offset distance between the C2 plumbline and C7 vertebral body (C2-C7 Sagittal Vertical Axis (SVA)) or the angle made with vertical by a line connecting the C2 and C7 vertebral bodies (C2-C7 tilt angle) are used as radiographic measures to assess cervical sagittal balance. There is level III clinical evidence that sagittal imbalance caused by kyphotic fusions or global spinal sagittal malalignment may increase the risk of adjacent segment pathology. Methods. Thirteen human cadaveric cervical spines (Occiput-T1; age: 50.6 years; range: 21–67) were tested first in the native intact state and then after instrumentation across C4-C6 to simulate in situ two-level fusion. Specimens were tested using a previously validated experimental model that allowed measurement of spinal response to prescribed imbalance. The effects of fusion on segmental angular alignments and intradiscal pressures in the C3-C4 and C6-C7 discs, above and below the fusion, were evaluated at different magnitudes of C2-C7 tilt angle (or C2-C7 SVA). Results. When compared with the pre-fusion state, in situ fusion across C4-C6 segments required increased flexion angulation and resulted in increased intradiscal pressure at the C6-C7 disc below the fusion in order to accommodate the same increase in C2-C7 tilt angle or C2-C7 SVA (P < 0.05). The adjacent segment mechanical burden due to fusion became greater with increasing C2-C7 tilt angle or SVA. Conclusion. Cervical sagittal imbalance arising from regional and/or global spinal sagittal malalignment may play a role in exacerbating adjacent segment pathomechanics after multilevel fusion and should be considered during surgical planning. Level of Evidence: N/A

Lumbo-pelvic lordosis and the pelvic radius technique in the assessment of spinal sagittal balance: strengths and caveats

IntroductionThe two main methodologies described for the assessment of spinal sagittal alignment are the pelvic radius (PR) technique and that based on measures of the Pelvic Incidence (PI) and Spino-Sacral Angle (SSA). Both methods stress the fundamental relationship between the anatomical position and orientation of the sacrum within the pelvis and the spinal curves above. The aim of the current study was to assess the strengths and potential weaknesses of the PR technique. The PR technique uses measures based on a line (the PR), drawn between the hip axis and the posterior corner of the S1 endplate. The angle formed between the PR line and the sacral endplate, PRS1, is a developmental measure of sacropelvic morphology. Geometrically, PI and PRS1 are approximately complementary angles and both reflect reciprocal alterations in pelvic tilt (for PI) or angulation (for PRS1) and the slope of the S1 endplate. The angle formed between PR and T12, the PR-T12, reflects a combined measure of pelvic morphology and lumbar lordosis. It appears to be a useful measure, which provides a simple and rapid assessment of lumbopelvic sagittal balance, but only in the presence of a congruent thoracic curvature.Materials and methodsAfter reviewing the literature, published measures made using the PR technique were compared to measures taken from a substantial patient population (479 adult patients).ConclusionsErrors can occur using the PR technique if the PRT12 is viewed in isolation from the thoracic kyphosis. We found the ratio of the thoracic kyphosis to lumbar lordosis (T4-T12/T12-S1) to be a useful predictor of congruent sagittal alignment, which may alert the clinician to situations where use of the PR-T12 in isolation may be misleading.

Cervical sagittal balance: a biomechanical perspective can help clinical practice.

PurposeIn this article, we summarize our work on understanding the influence of cervical sagittal malalignment on the mechanics of the cervical spine.MethodsBiomechanical studies were performed using an ex vivo laboratory model to study the kinematic and kinetic response of human cervical spine specimens in the setting of cervical sagittal imbalance. The model allowed controlled variations of C2–C7 Sagittal Vertical Alignment (C2–C7 SVA) and T1-Slope so that clinically relevant sagittally malaligned profiles could be prescribed, while maintaining horizontal gaze, and their biomechanical consequences studied.ResultsOur results demonstrated that increasing C2–C7 SVA caused flexion of lower cervical (C2–C7) segments and hyperextension of suboccipital (C0–C1–C2) segments to maintain horizontal gaze. An increase in C2–C7 SVA increased the lower cervical neural foraminal areas. Conversely, increasing T1-slope predominantly influenced subaxial cervical lordosis and, as a result, decreased cervical neural foraminal areas. Therefore, we believe patients with increased upper thoracic kyphosis and radicular symptoms may respond with increased forward head posture (FHP) as a compensatory mechanism to increase their lower cervical neural foraminal area and alleviate nerve root compression as well as reduce the burden on posterior muscles and soft and bony structures of the cervical spine. Increasing FHP (i.e., increased C2–C7 SVA) was associated with shortening of the cervical flexors and occipital extensors and lengthening of the cervical extensors and occipital flexors, which corresponds to C2–C7 flexion and C0–C2 extension. The greatest shortening occurred in the suboccipital muscles, suggesting considerable load bearing of these muscles during chronic FHP. Regardless, there was no evidence of nerve compression within the suboccipital triangle. Finally, cervical sagittal imbalance may play a role in exacerbating adjacent segment pathomechanics after multilevel cervical fusion and should be considered during surgical planning.ConclusionsThe results of our biomechanical studies have improved our understanding of the impact of cervical sagittal malalignment on pathomechanics of the cervical spine. We believe this improved understanding will assist in clinical decision-making.