Risk factors for neurophysiological events related to intraoperative halo-femoral traction in spinal deformity surgery.

PURPOSE: This study identifies risk factors for neurophysiological events caused by intraoperative halo-femoral traction (IOHFT) in patients with adolescent idiopathic scoliosis (AIS), and neuromuscular scoliosis (NMS). METHODS: Neurophysiological integrity was monitored using motor evoked potentials (MEPs). IONM event was defined as a decreased MEP amplitude of more than 80% of baseline in, at least, one muscle. Time between application of IOHFT and event, affected muscles, surgical stage, and time between removal of IOHFT and recovery of MEPs were described. Characteristics (age, height, weight, diagnosis, Cobb angle, and flexibility of the curve) of patients with and without IOHFT-events were compared using analysis of variance. Binary logistic regression analyses were performed to identify predictors. RESULTS: The study included 81 patients (age 15.6 ± 2.4 years, 53 females, AIS: n = 47, NMS n = 34). IOHFT-events occurred in 11 patients (13%; AIS n = 4, NMS n = 7). IOHFTevents affecting all limbs occurred pre-incision in NMS. Events affecting only the legs occurred during all stages of surgery. Patients with IOHFT-events were smaller (p = 0.009) and had stiffer curves (p = 0.046). Height was a predictor (odds ratio, 0.941; 95% confidence interval = 0.896-0.988). All MEPs recovered after removing IOHFT. CONCLUSION: Neurophysiologic events due to IOHFT were common, with the majority in patients with NMS. A shorter stature was a risk factor, and larger Cobb angle and stiffer curve were associated with IOHFT-events. Events occurred at any stage of surgery and involved upper and lower limbs. With an adequate response on IOHFT events, none of the patients had postoperative neurological impairments due to IOHFT.

Superior Sulcus Tumors Invading the Spine: Multimodal Treatment Outcomes From the Preimmunotherapy Era.

Introduction: Curative-intent treatment of superior sulcus tumors (SSTs) of the lung invading the spine presents considerable challenges. We retrospectively studied outcomes in a single center, uniformly staged patient cohort treated with induction concurrent chemoradiotherapy followed by surgical resection (trimodality therapy). Methods: An institutional surgical database from the period between 2002 and 2021 was accessed to identify SSTs in which the resection included removal of at least part of the vertebral body. All patients were staged using fluorodeoxyglucose positron emission tomography (/computed tomography), computed tomography scan of the chest/upper abdomen, and brain imaging. Surgical morbidity was assessed using the Clavien-Dindo classification. Overall and disease-free survival were calculated using the Kaplan-Meier method. Results: A total of 18 patients were included: 8 complete and 10 partial vertebrectomies were performed, with six of the eight complete vertebrectomies involving two vertebral levels, resulting in Complete surgical resection (R0) in 94%. Nine patients had a 1-day procedure, and nine were staged over 2 days. The median follow-up was 30 months (interquartile range 11-57). The 90-day postoperative morbidity was 44% (grade III/IV), with no 90-day surgery-related mortality. There were 83% who had a major pathologic response, associated with improved survival (p = 0.044). The 5-year overall and disease-free survival were 55% and 40%, respectively. Disease progression occurred in 10 patients, comprising locoregional recurrences in two and distant metastases in eight patients. Conclusions: Multimodality treatment in selected patients with a superior sulcus tumor invading the spine is safe and results in good survival. Such patients should be referred to expert centers. Future research should focus on improving distant control (e.g. [neo]adjuvant immunotherapy).

Natural Experiments as a Study Method in Spinal Trauma Surgery: A Systematic Review.

STUDY DESIGN: Systematic review. OBJECTIVES: To determine if the natural experiment design is a useful research methodology concept in spinal trauma care, and to determine if this methodology can be a viable alternative when randomized controlled trials are either infeasible or unethical. METHODS: A Medline, Embase and Cochrane database search was performed between 2004 and 2023 for studies comparing different treatment modalities of spinal trauma. All observational studies with a natural experiment design comparing different treatment modalities of spinal trauma were included. Data extraction and quality assessment with the MINORS criteria was performed. RESULTS: Four studies with a natural experiment design regarding patients with traumatic spinal fractures were included. All studies were retrospective, one study collected follow-up data prospectively. Three studies compared different operative treatment modalities, whereas one study compared different antibiotic treatment strategies. Two studies compared preferred treatment modalities between expertise centers, one study between departments (neuro- and orthopedic surgery) and one amongst surgeons. For the included retrospective studies, MINORS scores (maximum score 18) were high ranging from 12-17 and with a mean (SD) of 14.6 (1.63). CONCLUSIONS: Since 2004 only four studies using a natural experiment design have been conducted in spinal trauma. In the included studies, comparability of patient groups was high emphasizing the potential of natural experiments in spinal trauma research. Natural experiments design should be considered more frequently in future research in spinal trauma as they may help to address difficult clinical problems when RCT's are infeasible or unethical.

Natural experiments for orthopaedic trauma research: An introduction.

Natural experiments are observational studies of medical treatments in which treatment allocation is determined by factors outside the control of the investigators, arguably resembling experimental randomisation. Natural experiments in the field of orthopaedic trauma research are scarce. However, they have great potential due to the process governing treatment allocation and the existence of opposing treatment strategies between hospitals or between regions as a result of local education, conviction, or cultural and socio-economic factors. Here, the possibilities and opportunities of natural experiments in the orthopaedic trauma field are discussed. Potential solutions are presented to improve the validity of natural experiments and how to assess the credibility of such studies. Above all, it is meant to spark a discussion about its role within the field of orthopaedic trauma research.

High Failure Rates of a Unilateral Posterior Peri-Apical Distraction Device (ApiFix) for Fusionless Treatment of Adolescent Idiopathic Scoliosis.

BACKGROUND: Conventional surgical treatment for adolescent idiopathic scoliosis (AIS) consists of correction of the spinal deformity with rigid spinal instrumentation and fusion. Less-invasive and fusionless surgery could potentially improve patient outcomes. The purpose of the present study was to evaluate the efficacy of a recently U.S. Food and Drug Administration (FDA)-approved posterior peri-apical self-distracting device (ApiFix) that is designed to gradually correct the deformity without spinal fusion. METHODS: In a prospective cohort study of 20 patients with AIS (Risser stage 1-4; Lenke 1 or 5; major curve Cobb angle, 40° to 55°; and Bunnell scoliometer rotation, <15°) were managed with the ApiFix device. Clinical and radiographic performance was assessed. RESULTS: Twenty patients with a mean age (and standard deviation) of 14.8 ± 1.4 years were followed for a mean of 3.4 ± 1.0 years. The average major curve was reduced from 45.4° preoperatively to 31.4° at 2 weeks postoperatively and 31.0° at the time of the latest follow-up. The average minor curve measured 31.3° preoperatively, 26.1° at 2 weeks postoperatively, and 24.2° at the time of the latest follow-up. Ten patients had serious complications that required revision surgery, including osteolysis (n = 6), screw and/or rod breakage (n = 2), failure of the ratchet mechanism (n = 1), and pain without explainable cause (n = 1). During revision surgery, metallosis was observed in all patients and cultures showed growth of Cutibacterium acnes in 6 patients. Because of the high failure rate, the study was terminated early. CONCLUSIONS: The use of the unilateral peri-apical concave self-distracting ratchet rod initially was associated with promising clinical and radiographic results. However, no distraction was observed and the high rate of serious adverse events within 2 years was considered to be unacceptable for further clinical application of this device in our institution, despite recent FDA approval. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The biomechanical effect of single-level laminectomy and posterior instrumentation on spinal stability in degenerative lumbar scoliosis: a human cadaveric study.

OBJECTIVEDegenerative lumbar scoliosis, or de novo degenerative lumbar scoliosis, can result in spinal canal stenosis, which is often accompanied by disabling symptoms. When surgically treated, a single-level laminectomy is performed and short-segment posterior instrumentation is placed to restore stability. However, the effects of laminectomy on spinal stability and the necessity of placing posterior instrumentation are unknown. Therefore, the aim of this study was to assess the stability of lumbar spines with degenerative scoliosis, characterized by the range of motion (ROM) and neutral zone (NZ) stiffness, after laminectomy and placement of posterior instrumentation.METHODSTen lumbar cadaveric spines (T12-L5) with a Cobb angle ≥ 10° and an apex on L3 were included. Three loading cycles were applied per direction, from -4 Nm to 4 Nm in flexion/extension (FE), lateral bending (LB), and axial rotation (AR). Biomechanical evaluation was performed on the native spines and after subsequent L3 laminectomy and the placement of posterior L2-4 titanium rods and pedicle screws. Nonparametric and parametric tests were used to analyze the effects of laminectomy and posterior instrumentation on NZ stiffness and ROM, respectively, both on an individual segment's motion and on the entire spine section. Spearman's rank correlation coefficient was used to study the correlation between disc degeneration and spinal stability.RESULTSThe laminectomy increased ROM by 9.5% in FE (p = 0.04) and 4.6% in LB (p = 0.01). For NZ stiffness, the laminectomy produced no significant effects. Posterior instrumentation resulted in a decrease in ROM in all loading directions (-22.2%, -24.4%, and -17.6% for FE, LB, and AR, respectively; all p < 0.05) and an increase in NZ stiffness (+44.7%, +51.7%, and +35.2% for FE, LB, and AR, respectively; all p < 0.05). The same changes were seen in the individual segments around the apex, while the adjacent, untreated segments were mostly unaffected. Intervertebral disc degeneration was found to be positively correlated to decreased ROM and increased NZ stiffness.CONCLUSIONSLaminectomy in lumbar spines with degenerative scoliosis did not result in severe spinal instability, whereas posterior instrumentation resulted in a rigid construct. Also, prior to surgery, the spines already had lower ROM and higher NZ stiffness in comparison to values shown in earlier studies on nonscoliotic spines of the same age. Hence, the authors question the clinical need for posterior instrumentation to avoid instability.

Management of spinal trauma patients: a national survey in The Netherlands.

Lack of consensus in spinal trauma management and differences in the practical organization between trauma regions can have significant consequences on the fate of patients with spine trauma. For this reason a national survey was conducted among the 11 trauma regions in the Netherlands. Representative surgeons were sent a survery on seven areas of spinal trauma management: treatment protocol, (2) referral, (3) advisory committee, (4) classification used, (5) responsible medical specialist, (6) timing of surgical intervention, and (7) the current view on spinal trauma care. All 11 centers completed the survey yielding a response rate of 100%. The results of this study shows that in a relative small country, all seven areas in the management of spine trauma differs substantially and can be of use to show the possible areas of discrepancies between trauma centers in comparable European countries.

Prediction of mechanical complications in adult spinal deformity surgery-the GAP score versus the Schwab classification.

BACKGROUND CONTEXT: Surgery for adult spinal deformity is a challenging and complex procedure with high reported complication (8.4%-42%) and revision rates (9%-17.6%). Failure to achieve or maintain adequate postoperative sagittal alignment has been reported to be the main cause of mechanical complications. In order to define appropriate surgical targets, the Scoliosis Research Society-Schwab classification and the Global Alignment and Proportion (GAP) score were established. In the literature, no study has yet compared these classification systems with respect to the risk of developing mechanical complications. PURPOSE: To assess and compare the ability of the Schwab classification and the GAP score to predict mechanical complications following adult spinal deformity surgery. STUDY DESIGN: Two-center, retrospective cohort study. PATIENT SAMPLE: Thirty-nine patients suffering adult spinal deformity who underwent long segment spinal fusion (≥4 levels), minimum follow-up of 2years. OUTCOME MEASURES: The ability of the Schwab classification and GAP score to predict mechanical failure was determined by computing the Area Under the receiver operating characteristic curve. METHODS: Full-spine pre- and postoperative radiographs of all patients were analyzed for mechanical complications. Subsequently, the pre- and postoperative Schwab and GAP score were determined. Logistic regression analysis was used to assess the ability of both systems to determine which was the most appropriate for the prediction of mechanical failure. Correlations between the various factors constituting the GAP score and Schwab classification were estimated using the Spearman rank order correlation coefficient. RESULTS: The results demonstrated that both classification systems are capable of predicting radiographic evidence of mechanical failure; however, the GAP score proved to be significantly better (p=.003). The relative pelvic version of the GAP score serves a similar role as the pelvic tilt modifier from the Schwab classification (ρ=-0.84, p<.01). The relative lumbar lordosis from the GAP score functions much like the PI-LL modifier from the Schwab classification (ρ=-0.94, p<.01). The GAP score is most significantly dependent on relative spinopelvic alignment, relative lumbar lordosis, and relative pelvic version (ρ=0.85, ρ=0.84, and ρ=0.84, respectively, p<.01). Correlation with the lordosis distribution index was also significant but was not as strong (ρ=0.65, p<.01). Age, on the contrary, showed poor correlation with the GAP score (ρ=0.17, p=.300). CONCLUSIONS: Both the Schwab classification and the GAP score are capable of predicting mechanical complications. The GAP score proved to be significantly more appropriate. This difference is probably attributed to the fact that in the GAP score all parameters are related to the patient's individual pelvic incidence.

Epidemiology of Spinal Fractures in a Level One Trauma Center in the Netherlands: A 10 Years Review.

STUDY DESIGN: Retrospective epidemiological study. OBJECTIVE: To describe the epidemiology of spinal fractures over a 10 years period in a level one trauma center in the Netherlands. SUMMARY OF BACKGROUND DATA: Spinal fractures may have large socioeconomic consequences. The prevalence and outcomes likely change over the years owing to improved traffic safety, increasing population age and improved medical treatment. This is the first study to address the epidemiology of spinal fractures over a large period in the Netherlands. METHODS: All patients with a cervical, thoracic, or lumbar spine fracture admitted to a level one trauma center from 2007 to 2016 were prospective registered and retrospectively analyzed. In addition to patient, accident, and associated injury characteristics, radiological and surgery data were obtained from the hospital's Electronic Patient File system. RESULTS: Between 2007 and 2016, 1479 patients with a total of 3029 spinal fractures were admitted. Approximately 40.8% were female and 59.2% were male, with a mean age of 52.0 years; 4.9% of fractures occurred at a juvenile age (0-18 years) and 63.6% at the age of 19 to 64 years. Most fractures occurred in the thoracic spine, followed by the lumbar and cervical spine. The most common cause of injury was a fall from height, followed by traffic accidents. Spinal cord injury occurred in 8.5% and associated injuries were reported in 73% of the patients. Sixteen percent of the admitted patients were treated operatively. Over time, there was a larger increase in amount of spine fractures in elderly (≥ 65 years) compared with younger people. CONCLUSION: The total amount of spine fractures per year increased over time. In addition, there was a larger increase in amount of spine fractures in patients over 65 years of age compared with younger patients. Despite this increase, a considerable amount of spine fractures still occur in the age-group of 19 to 64 years. Most fractures were located in the thoracic spine. This study might stimulate development of policy on precautionary actions to prevent spine fractures. LEVEL OF EVIDENCE: 4.

Is postoperative bracing after pedicle screw fixation of spine fractures necessary? Study protocol of the ORNOT study: a randomised controlled multicentre trial.

INTRODUCTION: The most common surgical treatment of traumatic spine fractures is through a posterior approach using pedicle screws and rods. Postoperative treatment protocols including the use of postoperative orthoses however differ between hospitals and surgeons. A three-point hyperextension orthosis is designed to support proper posture and unload the anterior column. Some motion remains when wearing an orthosis, and its main value in postoperative treatment is therefore believed to be pain relief and patient confidence. This could consequently shorten recovery time. On the other hand, an orthosis could also lead to muscle weakness and slow down recovery. Any orthosis-related complications might also be avoided. Additionally, recent studies on conservative fracture treatment show no difference in radiological outcomes with or without an orthosis. To date, no randomised studies have been performed on the use of postoperative orthoses. METHODS AND ANALYSIS: Patients undergoing posterior fixation with pedicle screws for a traumatic thoracolumbar fracture (T7-L4) will be included in this randomised controlled multicentre non-inferiority trial. Forty-six patients will be randomised 1:1 to one of the two parallel groups; one group will wear a postoperative orthosis for 6 weeks followed by 6 weeks of weaning and one group will not wear an orthosis. The primary outcome is pain at 6 weeks reported on the Numerical Rating Scale. Secondary outcomes consist of pain on other moments, analgesic use, complications and length of hospital stay, quality of life (EuroQuol 5 Dimensions), back pain-related function (Oswestry Disability Index) and radiological outcomes with a follow-up of 1 year. Orthosis compliance is monitored weekly in the orthosis group. ETHICS AND DISSEMINATION: The institutional review board (METc VUmc) approved this study on 11 October 2016 under case number 2016.389. After completion of the trial, the results will be offered to an international scientific journal for peer-reviewed publication. TRIAL REGISTRATION NUMBER: NCT03097081 and NTR6285; Pre-results.

Risk Factors for Dystonia after Selective Dorsal Rhizotomy in Nonwalking Children and Adolescents with Bilateral Spasticity.

We recently showed a beneficial effect of selective dorsal rhizotomy (SDR) on daily care and comfort in nonwalking children with severe bilateral spasticity. However, despite careful selection, some patients showed dystonia after the intervention, in which cases caregivers tended to be less satisfied with the result.The aim of this study is to identify risk factors for dystonia after SDR in children and adolescents with severe bilateral spasticity (GMFCS levels IV/V).Clinical and MRI risk factors for dystonia after SDR were studied in our cohort of 24 patients. Patients with clinical evidence of dystonia and brain MRI showing basal ganglia abnormalities were excluded for SDR.Nine of 24 patients (38%) showed some degree of dystonia after SDR. There was a significant association between the cause of spasticity and dystonia after SDR; in six (67%) patients with a congenital disorder, dystonia was present versus three (20%) with an acquired disorder (Chi-squared test: C(1) = 5.23, p = 0.02).This study allows more optimal selection of patients that may benefit from SDR. Patients with an acquired cause of spasticity, when selected carefully on clinical examination and MRI, rarely show dystonia after SDR. However, patients with an underlying congenital disorder have a considerable risk of dystonia after SDR.

A Novel Spinal Implant for Fusionless Scoliosis Correction: A Biomechanical Analysis of the Motion Preserving Properties of a Posterior Periapical Concave Distraction Device.

STUDY DESIGN: Biomechanical study. OBJECTIVE: Recently, a posterior concave periapical distraction device for fusionless scoliosis correction was introduced. The goal of this study was to quantify the effect of the periapical distraction device on spinal range of motion (ROM) in comparison with traditional rigid pedicle screw-rod instrumentation. METHODS: Using a spinal motion simulator, 6 human spines were loaded with 4 N m and 6 porcine spines with 2 N m to induce flexion-extension (FE), lateral bending (LB), and axial rotation (AR). ROM was measured in 3 conditions: untreated, periapical distraction device, and rigid pedicle screw-rod instrumentation. RESULTS: The periapical distraction device caused a significant (P < .05) decrease in ROM of FE (human, -40.0% and porcine, -55.9%) and LB (human, -18.2% and porcine, -17.9%) as compared to the untreated spine, while ROM of AR remained unaffected. In comparison, rigid instrumentation caused a significantly (P < .05) larger decrease in ROM of FE (human, -80.9% and porcine, -94.0%), LB (human, -75.0% and porcine, -92.2%), and AR (human, -71.3% and porcine, -86.9%). CONCLUSIONS: Although no destructive forces were applied, no device failures were observed. Spinal ROM was significantly less constrained by the periapical distraction device compared to rigid pedicle screw-rod instrumentation. Therefore, provided that scoliosis correction is achieved, a more physiological spinal motion is expected after scoliosis correction with the posterior concave periapical distraction device.

Restrained Differential Growth: The Initiating Event of Adolescent Idiopathic Scoliosis?

STUDY DESIGN: An experimental model study and a short review of literature. OBJECTIVE: The purpose of this study was to explore a new hypothesis suggesting that the curvatures seen in adolescent idiopathic scoliosis (AIS) originate from restrained differential growth between the vertebral column and the surrounding musculo-ligamentary structures. SUMMARY OF BACKGROUND DATA: Despite decades of research, there is no generally accepted theory on the physical origin of the severe spinal deformations seen in AIS. The prevailing theories tend to focus on left-right asymmetry, rotational instability, or the sagittal spinal profile in idiopathic scoliosis. METHODS: We test our hypothesis with a physical model of the spine that simulates growth, counteracted by ligaments and muscles, modeled by tethers and springs. Growth of the spine is further restrained by an anterior band representing the thorax, the linea alba, and abdominal musculature. We also explore literature in search of molecular mechanisms that may induce differential growth. RESULTS: Differential growth in the restrained spine model first induces hypokyphosis and mild lateral bending of the thoracic spine, but then suddenly escalates into a scoliotic deformity, consistent with clinical observations of AIS. The band simulating the ventral structures of the body had a pivotal effect on sagittal curvature and the initiation of lateral bending and rotation. In literature, several molecular mechanisms were found that may explain the occurrence of differential growth between the spine and the musculo-ligamentary structures. CONCLUSION: While AIS is a three-dimensional deformation of the spine, it appears that restrained differential growth in the sagittal plane can result in lateral bending and rotation without a pre-existing left-right asymmetry. This supports the concept that AIS may result from a growth imbalance rather than a local anatomical defect. LEVEL OF EVIDENCE: N/A.

The Clay Shoveler's Fracture: A Case Report and Review of the Literature.

BACKGROUND: A clay-shoveler's fracture is a very rarely occurring stress-type avulsion fracture of the lower cervical or upper thoracic spinous processes owing its name to the clay shovelers of past times. Currently, this type of injury is mainly encountered in individuals practicing sports involving rotational movements of the upper spine. CASE REPORT: We present a case of a man sustaining a clay-shoveler's injury during his work in a horse-riding school. Treatment consisted of a period of rest and analgesics, followed by mobilization as was tolerated. We give a brief historical account of clay shoveler's fractures. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Clay-shoveler's fractures are frequently overlooked due to their rareness; however, they have specific clinical features that should alert an attending physician to set the correct diagnosis. This report describes a typical case of a clay-shoveler's fracture, relates to the historical entity of clay-shoveler's fractures, and summarizes existing literature on this topic.

Complications After Percutaneous Pedicle Screw Fixation for the Treatment of Unstable Spinal Metastases.

BACKGROUND: Complications after surgical stabilization for the treatment of unstable spinal metastases are common. Less invasive surgical (LIS) procedures are potentially associated with a lower risk of complications; however, little is known regarding the complications after LIS procedures for the treatment of spinal metastases. Our primary objective was to determine the characteristics and rate of complications after percutaneous pedicle screw fixation (PPSF) for the treatment of mechanically unstable spinal metastases. The secondary objective was to identify factors associated with the occurrence of complications and survival. METHODS: A retrospective multicenter cohort study of patients who underwent PPSF between 2009 and 2014 for the treatment of unstable spinal metastases was performed. Patient data pertaining to demographics, diagnosis, treatment, neurologic function, complications, and survival were collected. RESULTS: A total of 101 patients were identified, 45 men (45 %) and 56 women (55 %) with a mean age of 60.3 ± 11.2 years. The median operating time was 122 (range 57-325) minutes with a median blood loss of 100 ml (based on 41 subjects). Eighty-eight patients (87 %) ambulated within the first 3 days after surgery. An overall median survival of 11.0 (range 0-70) months was observed, with 79 % of the patients alive at 3 months after treatment. Eighteen patients experienced a total of 30 complications; nonsurgical complications were the most commonly encountered. Prolonged operating time was independently associated with an increased risk of complications. CONCLUSIONS: A complication rate of 18 % was found after PPSF for unstable spinal metastases. Potential advantages of less invasive treatment are limited blood loss and high early ambulation rate.

The effects of single-level instrumented lumbar laminectomy on adjacent spinal biomechanics.

Study Design Biomechanical study. Objective Posterior instrumentation is used to stabilize the spine after a lumbar laminectomy. However, the effects on the adjacent segmental stability are unknown. Therefore, we studied the range of motion (ROM) and stiffness of treated lumbar spinal segments and cranial segments after a laminectomy and after posterior instrumentation in flexion and extension (FE), lateral bending (LB), and axial rotation (AR). These outcomes might help to better understand adjacent segment disease (ASD), which is reported cranial to the level on which posterior instrumentation is applied. Methods We obtained 12 cadaveric human lumbar spines. Spines were axially loaded with 250 N for 1 hour. Thereafter, 10 consecutive load cycles (4 Nm) were applied in FE, LB, and AR. Subsequently, a laminectomy was performed either at L2 or at L4. Thereafter, load-deformation tests were repeated, after similar preloading. Finally, posterior instrumentation was added to the level treated with a laminectomy before testing was repeated. The ROM and stiffness of the treated, the cranial adjacent, and the control segments were calculated from the load-displacement data. Repeated-measures analyses of variance used the spinal level as the between-subject factor and a laminectomy or instrumentation as the within-subject factors. Results After the laminectomy, the ROM increased (+19.4%) and the stiffness decreased (-18.0%) in AR. The ROM in AR of the adjacent segments also increased (+11.0%). The ROM of treated segments after instrumentation decreased in FE (-74.3%), LB (-71.6%), and AR (-59.8%). In the adjacent segments after instrumentation, only the ROM in LB was changed (-12.9%). Conclusions The present findings do not substantiate a biomechanical pathway toward or explanation for ASD.

How Does Spinal Release and Ponte Osteotomy Improve Spinal Flexibility? The Law of Diminishing Returns.

STUDY DESIGN: Experimental study. OBJECTIVES: To evaluate the effect of stepwise resection of posterior spinal ligaments, facet joints, and ribs on thoracic spinal flexibility. SUMMARY OF BACKGROUND DATA: Posterior spinal ligaments, facet joints and ribs are removed to increase spinal flexibility in corrective spinal surgery for deformities such as adolescent idiopathic scoliosis (AIS). Reported clinical results vary and biomechanical substantiation is lacking. METHODS: Ten fresh-frozen human cadaveric thoracic spinal specimens (T6-T11) were studied. A spinal motion simulator applied a pure moment of ±2.5 Nm in flexion, extension, lateral bending (LB) and axial rotation (AR). Range of motion (ROM) was measured for the intact spine and measured again after stepwise resection of the supra/interspinous ligament (SIL), inferior facet, flaval ligament, superior facet, and rib heads. RESULTS: SIL resection increased ROM in flexion (10.2%) and AR (3.1%). Successive inferior facetectomy increased ROM in flexion (4.1%), LB (3.8%) and AR (7.7%), and flavectomy in flexion (9.1%) and AR (2.5%). Sequential superior facetectomy only increased ROM in flexion (6.3%). Rib removal provided an additional increase in flexion (6.3%), LB (4.5%) and AR (13.0%). Extension ROM increased by 10.5% after the combined removal of the SIL, inferior facet and flaval ligament. CONCLUSIONS: Posterior spinal releases in these non-scoliotic spines led to an incremental increase in spinal flexibility, but each sequential step had less effect. As compared to SIL resection with inferior facetectomy, additional superior facetectomy did not improve flexibility in AR and LB and only 6.3% in flexion. The data presented from this in vitro study should be interpreted with care, as no representative cadaveric spine model for AIS was available, However, the results presented here at least question the benefits of performing routine complete facetectomies (i.e. Ponte osteotomies) to increase spinal flexibility in scoliosis surgery.

Single level lumbar laminectomy alters segmental biomechanical behavior without affecting adjacent segments.

BACKGROUND: Degenerative lumbar spinal stenosis causes neurological symptoms due to neural compression. Lumbar laminectomy is a commonly used treatment for symptomatic degenerative spinal stenosis. However, it is unknown if and to what extent single level laminectomy affects the range of motion and stiffness of treated and adjacent segments. An increase in range of motion and a decrease in stiffness are possible predictors of post-operative spondylolisthesis or spinal failure. METHODS: Twelve cadaveric human lumbar spines were obtained. After preloading, spines were tested in flexion-extension, lateral bending, and axial rotation. Subsequently, single level lumbar laminectomy analogous to clinical practice was performed at level lumbar 2 or 4. Thereafter, load-deformation tests were repeated. The range of motion and stiffness of treated and adjacent segments were calculated before and after laminectomy. Untreated segments were used as control group. Effects of laminectomy on stiffness and range of motion were tested, separately for treated, adjacent and control segments, using repeated measures analysis of variance. FINDINGS: Range of motion at the level of laminectomy increased significantly for flexion and extension (7.3%), lateral bending (7.5%), and axial rotation (12.2%). Range of motion of adjacent segments was only significantly affected in lateral bending (-7.7%). Stiffness was not affected by laminectomy. INTERPRETATION: The increase in range of motion of 7-12% does not seem to indicate the use of additional instrumentation to stabilize the lumbar spine. If instrumentation is still considered in a patient, its primary focus should be on re-stabilizing only the treated segment level.