Measurable Thoracic Motion Remains at 1 Year Following Anterior Vertebral Body Tethering, with Sagittal Motion Greater Than Coronal Motion.

BACKGROUND: Anterior vertebral body tethering is an alternative to fusion surgery for the treatment of adolescent idiopathic scoliosis (AIS) that is purported to preserve spinal motion. There is limited information regarding the measurable motion that is maintained over the instrumented levels following thoracic anterior vertebral body tethering surgery in humans. The purpose of the present study was to assess radiographic spinal motion 1 year after anterior vertebral body tethering. METHODS: As part of a prospective U.S. Food and Drug Administration investigational device exemption study, 32 patients were treated with thoracic anterior vertebral body tethering. At 1 year postoperatively, patients were evaluated with standing flexion-extension and side-bending radiographs in a microdose biplanar slot scanning imaging system. The angle subtended by the screws at the upper instrumented vertebra (UIV) and lower instrumented vertebra (LIV) was measured on left and right-bending radiographs to evaluate the coronal arc of motion and was compared with preoperative values over the same levels. At 1 year postoperatively, the sagittal Cobb angle was measured over the instrumented levels on flexion and extension radiographs. RESULTS: Side-bending radiographs revealed that the mean angle subtended by the screws changed from 15° ± 8° on left-bending radiographs to 8° ± 6° on right-bending radiographs. The mean coronal arc of motion on bending was 7° ± 6°, with 20 (62.5%) of 32 patients having a coronal arc of motion of >5°. The mean preoperative coronal arc of motion over the instrumented segments was 30° ± 9°. On flexion-extension lateral radiographs made at 1 year postoperatively, the mean kyphotic angle over the instrumented segments was 33° ± 13° in flexion and 11° ± 14° in extension, for a mean postoperative arc of motion of 21° ± 12° between flexion and extension radiographs. CONCLUSIONS: At 1 year following thoracic anterior vertebral body tethering for the treatment of AIS, the thoracic spine showed a measurable range of coronal and sagittal plane motion over the instrumented levels without evidence of complete autofusion. Motion in the coronal plane decreased by 77% following anterior vertebral body tethering. These findings provide proof of concept that sagittal spinal motion is preserved after thoracic anterior vertebral body tethering, although the functional importance remains to be determined. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Can Exercise Targeting Mid-Thoracic Spine Segmental Movement Reduce Back Pain and Improve Sensory Perception in Cross-Country Skiers?

OBJECTIVE: To assess the role of exercise targeting proper trunk stabilization and segmental spinal movement in back pain and sensory perception among cross-country skiers. DESIGN: Randomized, controlled trial with blinded outcome assessors. SETTING: University Hospital, Department of Rehabilitation and Sports Medicine. PARTICIPANTS: Twenty elite cross-country skiers aged 17 to 27 years. INTERVENTIONS: Ten cross-country skiers integrated 3 types of exercise targeting segmental motion in mid-thoracic spine into their routine training practice for 2 months. The 10 controls performed routine athletic training. MAIN OUTCOME MEASURES: The Young Spine Questionnaire to measure intensity and frequency of back pain was completed at the start and end of study. Tactile sensory perception using 10-g Semmes-Weinstein monofilament, thermic perception using TIP THERM device, graphesthesia assessed by a touch monitor pencil, 2-point discrimination assessed by a digital caliper, and vibration perception assessed by a 128-Hz tuning fork measured in mid-thoracic spine 5 times. RESULTS: No significant group differences in pain and sensory perception were identified at baseline. Over the 2-month study interval, repeated-measures analysis of variance revealed that the experimental group improved significantly relative to the control group on pain intensity (P = 0.005 for cervical, P = 0.004 for thoracic, and P = 0.014 for lumbar) and frequency of pain in the thoracic area only (P = 0.011). Improvements were also observed in the experimental relative to control group on graphesthesia (P < 0.001), vibration perception (P = 0.002), and 2-point discrimination (P < 0.001). CONCLUSIONS: Exercise targeting the mid-thoracic spine may decrease back pain and improve sensory perception in cross-country skiers. LEVEL OF EVIDENCE: Original research, level I.

In vitro analysis of thoracic spinal motion segment flexibility during stepwise reduction of all functional structures.

PURPOSE: The aim of this study was to quantify the stabilizing effect of the passive structures in thoracic spinal motion segments by stepwise resections. These data can be used to calibrate finite element models of the thoracic spine, which are needed to explore novel surgical treatments of spinal deformities, fractures, and tumours. METHOD: Six human thoracic spinal motion segments from three segmental levels (T2-T3, T6-T7, and T10-T11) were loaded with pure moments of 1 and 2.5 Nm in flexion/extension, lateral bending, and axial rotation. After each loading step, the ligaments, facet capsules, and the nucleus pulposus were stepwise resected from posterior to anterior direction, while the segmental relative motions were measured using an optical motion tracking system. RESULTS: Significant increases (p < 0.05) in the range of motion were detected after resecting the anterior spinal structures depending on loading magnitude, motion direction, and segmental level. The highest relative increases in the range of motion were observed after nucleotomy in all motion directions. The vertebral arch mostly stabilized the thoracic spinal motion segments in flexion and extension, while the facet joint capsules mainly affected the segmental stability in axial rotation. Coupled motions were not observed. CONCLUSIONS: The anulus fibrosus defines the motion characteristics qualitatively, while the ligaments and the presence of the nucleus pulposus restrict the mobility of a thoracic spinal motion segment solely in a quantitative manner. The posterior ligaments do not predominantly serve for primary stability but for the prevention of hyperflexion. These slides can be retrieved under Electronic Supplementary Material.

Cadaveric biomechanical testing of torque - to - failure magnitude of Bilateral Apical Vertebral Derotation maneuver in the thoracic spine.

It remains unclear what is the real safe limit of torque magnitude during Bilateral Apical Vertebral Derotation (BAVD) in thoracic curve correction. Up to author's knowledge there is no study except this one, to reproduce in-vivo real measurements and intraoperative conditions during BAVD maneuver. The objective of this study was to evaluate the torsional strength of the instrumented thoracic spine under axial rotation moment as well as to define safety limits under BAVD corrective maneuver in scoliosis surgery. 10 fresh, full-length, young and intact human cadavers were tested. After proper assembly of the apparatus, the torque was applied through its apical part, simulating thoracic curve derotation. During each experiment the torque magnitude and angular range of derotation were evaluated. For more accurate analysis after every experiment the examined section of the spine was resected from the cadaver and evaluated morphologically and with a CT scan. The average torque to failure during BAVD simulation was 73,3 ± 5,49Nm. The average angle of BAVD to failure was 44,5 ± 8,16°. The majority of failures were in apical area. There was no significant difference between the fracture occurrence of left or right side of lateral wall of the pedicle. There was no spinal canal breach and/or medial wall failure in any specimen. The safety limits of thoracic spine and efficacy of BAVD for axial plane correction in the treatment of Adolescent Idiopathic Scoliosis (AIS) were established. It provided qualitative and quantitative information essential for the spinal derotation under safe loading limits.

Coronal and sagittal spinal alignment in lumbar disc herniation with scoliosis and trunk shift.

BACKGROUND: To investigate the incidence of scoliosis and trunk shift in patients with LDH (lumbar disc herniation) and analyze the differences in spinopelvic alignment among patients with or without trunk shift and non-symptom controls. MATERIALS AND METHODS: All included subjects had standard upright antero-posterior and lateral radiographs of the whole spine taken. Evidence of disc herniation was confirmed by computed tomography or magnetic resonance imaging. The parameters measured included trunk shift and Cobb angle, TK (thoracic kyphosis), TLK (thoraco-lumbar junction kyphosis), LL (lumbar lordosis), PI (pelvic incidence), SS (sacral slope), PT (pelvic tilt) and SVA (sagittal vertical axis). RESULTS: Sixty-eight patients with LDH and 61 controls were included. There were significantly more male patients with trunk shift than the patients without trunk shift. Forty-two patients had curve magnitudes ranging from 5 to 38°. The trunk shift ranged from 0.5 to 7.3 cm. A total of 54.76% of patients had a disc herniation on the concave side of the main curve. Fifty percent of patients showed a trunk shift towards the opposite side of disc herniation. There were significant differences in spinopelvic parameters among groups. Significant correlations were also observed between several spinopelvic parameters in the three groups. However, the degrees of correlations among the spinopelvic parameters differed among the three groups. CONCLUSION: Spinal sagittal morphology in LDH patients with trunk shift exhibits a more anterior shift of the C7 plumb line, less LL, and a more horizontal sacrum. Correlation analysis indicated a disharmonious spinopelvic interaction and a change in the compensatory model in patients with LDH.

Biomechanical Analysis of Wide Posterior Releases Compared With Inferior Facetectomy and Discectomy in the Thoracolumbar and Lumbar Spine.

STUDY DESIGN: In vitro biomechanical analysis. OBJECTIVES: Compare the destabilizing effects of anterior discectomy to posterior spinal releases. SUMMARY OF BACKGROUND DATA: Posterior release and pedicle screw fixation has become the accepted form of treatment for lumbar and thoracolumbar pediatric scoliotic spinal deformity. A biomechanical evaluation of posterior releases with comparison to traditional anterior releases has not been reported in the lumbar spine. METHODS: Eleven fresh-frozen human thoracolumbar specimens (T9-L5) were tested by a robotic manipulator (Staubli RX90; moment target of 5.0 Nm, force target of 50 N) in axial rotation (AR), plus lateral and anterior translation (LT and AT). Specimens underwent either sequential anterior release (partial and full discectomy) or posterior release (inferior facetectomy and wide posterior release) from T10 to L4. Partial discectomy retained the posterior 50% of disc and posterior longitudinal ligament, whereas full discectomy removed all of the disc and PLL. Wide posterior release included total facetectomy plus ligamentum flavum and spinous process resection. RESULTS: Inferior facetectomy produced an average increase of 1.5° ± 1.0° (p = .0625), 1.0 ± 0.8 mm (p = .0313), and 0.2 ± 0.3 mm (p = .156) in AR, LT, and AT, respectively. Compared with partial facetectomy, wide posterior release produced an average additional increase of 8.1° ± 4.0° (p = .0312), 2.0 ± 2.2 mm (p = .4062), and 1.1 ± 1.0 mm (p = .0625) in AR, LT, and AT, respectively. Full discectomy produced 201%, 161%, and 153% of the motion relative to wide posterior release in AR, LT, and AT, respectively (p = .0043, .0087, and .0173). Partial discectomy and wide posterior release proved statistically equivalent. CONCLUSIONS: Wide posterior release of the thoracolumbar spine allows significant correction and may be superior to inferior facetectomy in axial rotation. Although complete discectomy with PLL resection would likely allow greater correction, a more clinically realistic partial discectomy confers similar corrective potential in vitro compared with wide posterior release. LEVEL OF EVIDENCE: Not applicable.

Influence of vertebral bone mineral density on total dispersion volume of bone cement in vertebroplasty.

The aim of this study was to investigate the influence of vertebral bone mineral density (BMD) on total diffusion volume of bone cement in percutaneous vertebroplasty (PVP). This study was a retrospective review of prospectively collected data of consecutive patients with A1.2 thoracolumbar compression fractures treated by PVP. Vertebral BMD was measured before surgery and participants were divided into 3 groups according to World Health Organization diagnostic criteria for osteoporosis: Group A (normal BMD), Group B (reduced BMD), and Group C (osteoporosis). All vertebrae were injected with 3 mL of bone cement via the unilateral pedicle and scanned by computed tomography after surgery. Actual injection volume (bone cement only) and total diffusion volume (bone cement plus trabeculae and space) were calculated. Pain severity was determined by the visual analog scale before surgery and at both 1 day and 1 month after surgery. There were no significant differences in injection volume among the groups (P > .05), but the total dispersion volume was greater than injection volume in all groups (P < .05). Pairwise comparison showed a significant difference in total diffusion volume of bone cement between groups, with Group A having the largest volume and Group C the smallest volume. Pain was significantly reduced 1 day after surgery in each group compared with before surgery, but there were no significant between-group differences at 1 day or 1 month. Increasing vertebral BMD was positively correlated with increasing total diffusion volume. BMD does not significantly affect pain relief, despite producing a significantly lower distribution volume in osteoporotic patients.

Management of thoracic spine pain and dysfunction: A survey of clinical practice in the UK.

BACKGROUND: The thoracic spine (TS) is relatively under-researched compared to the neck and low back. As the challenge of managing spinal pain persists, understanding current physiotherapy clinical practice for TS pain and dysfunction is necessary to inform future research in this area. OBJECTIVE: To investigate physiotherapy practice for managing thoracic spine pain and dysfunction (TSPD) in the UK, with a secondary focus on examining differences across settings and expertise. DESIGN AND METHOD: A cross sectional e-survey informed by existing evidence was designed. Comprising closed and open questions, the survey is reported in line with Checklist for Reporting Results of Internet E-Surveys. Eligible participants were UK-trained physiotherapists managing patients with TSPD, recruited for 9 weeks up to 8/2/16. Data analysis included descriptive analyses (closed questions) and thematic analysis (open questions). RESULTS: From the 485 respondents, fulfilling the required sample size, key findings included. EXAMINATION: Active motion testing, palpation and postural assessment was 'always' undertaken by >89% of respondents. MANAGEMENT: Active (exercises) and passive (e.g. mobilisations) techniques were used by >85% of respondents, with ∼50% using manipulation, taping and acupuncture. Practice settings: Although broadly similar passive techniques were used more in private practice and sport. Expertise: Broadly similar patterns were seen for use of exercise across levels of expertise, although differences observed for electrotherapy and manipulation. CONCLUSION: Despite limited research exercise is widely used in all areas of practice and across all level of expertise. Further research is required to investigate exercise prescription for TSPD and implementation of evidence-based practice.

Bone Mineral Density as a Risk Factor for Patients Undergoing Surgery for Hepatocellular Carcinoma.

BACKGROUND: We have reported the impact of sarcopenia and body composition on patients undergoing hepatectomy for hepatocellular carcinoma (HCC). However, the impact of bone mineral density (BMD) on outcomes after hepatectomy for HCC and correlation with other parameters including sarcopenia are unclear. METHODS: We retrospectively analyzed 465 patients who underwent primary hepatectomy for HCC between April 2005 and March 2015. We analyzed the plain CT images at the level of the eleventh thoracic vertebra with the region of interest and defined as preoperative BMD. RESULTS: In this cohort, male (n = 367) and female (n = 98) patients showed significant heterogeneity in age, body composition markers, tumor factors, peri-operative parameters and so on. The median preoperative BMD in male and female patients was 155 and 139 HU, respectively (P = 0.005). BMD was negatively correlated with age in female (r = -0.590, P < 0.001) and intramuscular adipose tissue content in both male and female (r = -0.332 and -0.359, respectively, P < 0.001). For males, BMD < 160 HU was associated with worse cancer-specific survival post-hepatectomy (P = 0.015). In contrast, females were not (P = 0.135). For male patients, multivariate analysis identified low BMD as an independent risk factor for death (hazard ratio 1.720, 95% confidence interval 1.038-2.922, P = 0.035) after hepatectomy for HCC. CONCLUSION: Preoperative low BMD was an independent risk factor for cancer-specific mortality after hepatectomy for HCC.

Immediate Effects of Thoracic Spine Manipulation Upon Shoulder Functionality in Patients With Sutured Rotator Cuff Repair: A Prospective Study.

OBJECTIVES: The purpose of this study was to evaluate the immediate effect of thoracic spine manipulation upon active flexion and abduction mobility of the shoulder, spine temperature, and the size of the subacromial space as measured by ultrasound in 3 positions (internal, neutral, and external rotation) of the glenohumeral joint in patients who have undergone surgery because of subacromial impingement. METHODS: Quasi-experimental, prospective, short-term effect study with consecutively sampled participants. Thirty-two patients had undergone subacromial decompression together with supraspinatus tendon suture. The following variables were studied: age, sex, dominant shoulder, presurgery evolution time, working status, surface temperature of dorsal segment with limited mobility, premanipulation functional assessment using the Spanish version of the Upper Limb Functional Index Scale, goniometric range of motion measurement at glenohumeral joint before and after manipulation, and ultrasound measurement of subacromial space before and after manipulation. RESULTS: Significant differences and small effect size were found in measurements for flexion and abduction movements after thoracic spine manipulation (P > .001; ES > 0.2) and subacromial space measurements in neutral rotation and external rotation (P > .001), but without clinical relevance effect size (<0.2). CONCLUSIONS: Active shoulder flexion and abduction mobility increase after manipulation of thoracic spine in patients who have undergone surgery for rotator cuff suture. Subacromial space increases significantly with shoulder in neutral and external rotation position after manipulation. No differences were found regarding surface temperature of manipulated area.

Pressure distributions inside intervertebral discs under unilateral pedicle screw fixation in a porcine spine model.

BACKGROUND: Little data are available regarding the effects of pedicle screws on the intervertebral disc stress for different spinal segments. The aim of this study was to analyze the intervertebral disc stress in response to the placement of pedicle screws. METHODS: T3-4, T11-12, T15-L1, L3-4, and L4-5 intervertebral disc segments from six porcine spine specimens were harvested. A compressive load of 200 N was applied both before and after the pedicle screw was implanted on the left side of each target segment; the resulting pressure was measured during vertical, 5° anterior flexion, 5° posterior extension, and 5° lateral bending. RESULTS: The posterior intradiscal pressures of the intervertebral disc were significantly lower in the fixed group than in the unfixed group for all segments during vertical, 5° anterior flexion, and 5° posterior extension. The left pressures of the intervertebral disc were significantly lower in the fixation group for all segments. During 5° lateral bending, the left intervertebral disc pressures were significantly lower in the fixation group. Lower mean pressures were observed in the fixed group. CONCLUSIONS: Unilateral pedicle screws can effectively reduce the pressure of the fixed lateral intervertebral disc. Moreover, it can change the pressure distribution of the intervertebral disc and reduce the pressure of the entire intervertebral disc, especially the posterior side of the intervertebral disc.

Ultrasonography is more accurate than percutaneous palpation for identifying targeted thoracolumbar intervertebral disc spaces in dogs.

During minimally invasive spinal surgery, correct identification of the affected intervertebral disc space is critical. Percutaneous palpation is commonly used, but results may be unreliable. Fluoroscopy is the gold standard but can be cumbersome and exposes operators to ionizing radiation. Spinal ultrasound has been described in veterinary medicine and could be a feasible alternative. This prospective, methods comparison study mimicked a minimally invasive spinal surgery in 10 canine cadavers and compared the accuracy of ultrasound and percutaneous palpation for thoracolumbar intervertebral disc space identification, using fluoroscopy as the reference standard. For each experiment, a disc space was randomly chosen. Identification was then attempted using both percutaneous palpation and ultrasound. For ultrasound, a linear probe was used to guide the operator to the correct location. The time necessary to perform each method was recorded. Accuracies for each method were calculated and statistically compared. Effects of body condition score, location of the targeted thoracolumbar intervertebral disc space and learning curve for each method were also evaluated. Ultrasonographic identification was more accurate (96.7% vs. 76.7%; P < 0.03) but took longer (147 s vs. 29 s; P < 0.0001) than percutaneous palpation. Findings from this cadaver study indicated that percutaneous palpation alone had low accuracy for correctly identifying a targeted thoracolumbar intervertebral disc space and supported the use of ultrasound as a method for improving the accuracy. Future studies are needed to assess the method in clinical cases, especially in obese dogs and/or those in which the targeted site is distant from palpable anatomical landmarks.

Cortical Thinning and Structural Bone Changes in Non-Human Primates after Single-Fraction Whole-Chest Irradiation.

Stereotactic body radiation therapy (SBRT) is associated with an increased risk of vertebral compression fracture. While bone is typically considered radiation resistant, fractures frequently occur within the first year of SBRT. The goal of this work was to determine if rapid deterioration of bone occurs in vertebrae after irradiation. Sixteen male rhesus macaque non-human primates (NHPs) were analyzed after whole-chest irradiation to a midplane dose of 10 Gy. Ages at the time of exposure varied from 45-134 months. Computed tomography (CT) scans were taken 2 months prior to irradiation and 2, 4, 6 and 8 months postirradiation for all animals. Bone mineral density (BMD) and cortical thickness were calculated longitudinally for thoracic (T) 9, lumbar (L) 2 and L4 vertebral bodies; gross morphology and histopathology were assessed per vertebra. Greater mortality (related to pulmonary toxicity) was noted in NHPs <50 months at time of exposure versus NHPs >50 months ( P = 0.03). Animals older than 50 months at time of exposure lost cortical thickness in T9 by 2 months postirradiation ( P = 0.0009), which persisted to 8 months. In contrast, no loss of cortical thickness was observed in vertebrae out-of-field (L2 and L4). Loss of BMD was observed by 4 months postirradiation for T9, and 6 months postirradiation for L2 and L4 ( P < 0.01). For NHPs younger than 50 months at time of exposure, both cortical thickness and BMD decreased in T9, L2 and L4 by 2 months postirradiation ( P < 0.05). Regions that exhibited the greatest degree of cortical thinning as determined from CT scans also exhibited increased porosity histologically. Rapid loss of cortical thickness was observed after high-dose chest irradiation in NHPs. Younger age at time of exposure was associated with increased pneumonitis-related mortality, as well as greater loss of both BMD and cortical thickness at both in- and out-of-field vertebrae. Older NHPs exhibited rapid loss of BMD and cortical thickness from in-field vertebrae, but only loss of BMD in out-of-field vertebrae. Bone is sensitive to high-dose radiation, and rapid loss of bone structure and density increases the risk of fractures.

Spine bone mineral density increases after 6 months of exclusive lactation, even in women who keep breastfeeding.

This pilot study enrolled 31 women who had breastfed exclusively for 6 months. Lumbar and thoracic BMD increased 4 and 5%, respectively. Femoral neck and total body BMD did not change. Return of menses and progestin-only pill use were two potential signals that predicted a greater increase in BMD. PURPOSE/INTRODUCTION: The skeleton is resorbed during lactation to provide much of the calcium content of milk. After lactation ceases, these deficits in skeletal mineral content are largely restored, such that lactation has a neutral or protective effect against the long-term risk of low bone mineral density (BMD), osteoporosis, and fragility fractures. We hypothesized that a large observational study may identify the factors that predict a greater increase in BMD after lactation ceases. A pilot study was first needed to test feasibility and the magnitude of expected BMD change. METHODS: We undertook Factors Affecting Bone formation after Breastfeeding Pilot (FABB Pilot), which enrolled women who had breastfed exclusively for 6 months and planned to wean soon. The main outcome was change in BMD between enrolment and 6 months later. RESULTS: Thirty-one women were recruited and completed both time points. Lumbar and thoracic spine BMD increased 4 and 5%, respectively; there was no significant change in femoral neck and total body BMD. Most women did not wean their babies as planned but continued to breastfeed multiple times per day. Despite this, a significant increase in BMD was seen in the subsequent 6 months. Return of spontaneous menses and use of a progestin-only pill at recruitment were two potential signals that predicted a greater increase in BMD during the 6 months after exclusive lactation. CONCLUSIONS: Spine BMD increased significantly during 6 months following exclusive lactation and despite continued lactation. The factors that stimulate skeletal recovery remain to be identified.

Spontaneous and complete regeneration of a vertebra plana after surgical curettage of an eosinophilic granuloma.

PURPOSE: The eosinophilic granuloma is a unifocal or multifocal Langerhans cell histiocytosis characterized by an expanding proliferation of Langerhans cells in bones. Skeletal LCH is a rare condition, and vertebral regeneration in cases of vertebral body collapse is even rarer. We report the case of a girl with spontaneous complete healing. METHODS AD RESULTS: A 3-year-old girl was referred for nighttime back pain, with no fever and no neurologic signs. Within a few days, she developed sudden painful restriction of all spine movements. X-ray and computed tomography (CT) of the spine showed reduced T7 vertebral body height (vertebra plana).The patient underwent T7 curettage and the histopathological exam was suggestive of LCH. Two additional skull lesions were found and therefore she underwent chemotherapy. After 7 years of follow-up, total vertebral reconstruction was observed. CONCLUSIONS: Despite the rarity of the condition and despite the rarity of vertebral body lesion resolution, total vertebral body reconstruction was observed over a 7-year period. Long-term follow-up is necessary for a better understanding of the final outcome of patients with EG.

How are adjacent spinal levels affected by vertebral fracture and by vertebroplasty? A biomechanical study on cadaveric spines.

BACKGROUND CONTEXT: Spinal injuries and surgery may have important effects on neighboring spinal levels, but previous investigations of adjacent-level biomechanics have produced conflicting results. We use "stress profilometry" and noncontact strain measurements to investigate thoroughly this long-standing problem. PURPOSE: This study aimed to determine how vertebral fracture and vertebroplasty affect compressive load-sharing and vertebral deformations at adjacent spinal levels. STUDY DESIGN: We conducted mechanical experiments on cadaver spines. METHODS: Twenty-eight cadaveric spine specimens, comprising three thoracolumbar vertebrae and the intervening discs and ligaments, were dissected from fourteen cadavers aged 67-92 years. A needle-mounted pressure transducer was used to measure the distribution of compressive stress across the anteroposterior diameter of both intervertebral discs. "Stress profiles" were analyzed to quantify intradiscal pressure (IDP) and concentrations of compressive stress in the anterior and posterior annulus. Summation of stresses over discrete areas yielded the compressive force acting on the anterior and posterior halves of each vertebral body, and the compressive force resisted by the neural arch. Creep deformations of vertebral bodies under load were measured using an optical MacReflex system. All measurements were repeated following compressive injury to one of the three vertebrae, and again after the injury had been treated by vertebroplasty. The study was funded by a grant from Action Medical Research, UK ($143,230). Authors of this study have no conflicts of interest to disclose. RESULTS: Injury usually involved endplate fracture, often combined with deformation of the anterior cortex, so that the affected vertebral body developed slight anterior wedging. Injury reduced IDP at the affected level, to an average 47% of pre-fracture values (p<.001), and transferred compressive load-bearing from nucleus to annulus, and also from disc to neural arch. Similar but reduced effects were seen at adjacent (non-fractured) levels, where mean IDP was reduced to 73% of baseline values (p<.001). Vertebroplasty partially reversed these changes, increasing mean IDP to 76% and 81% of baseline values at fractured and adjacent levels, respectively. Injury also increased creep deformation of the vertebral body under load, especially in the anterior region where a 14-fold increase was observed at the fractured level and a threefold increase was observed at the adjacent level. Vertebroplasty also reversed these changes, reducing deformation of the anterior vertebral body (compared with post-fracture values) by 62% at the fractured level, and by 52% at the adjacent level. CONCLUSIONS: Vertebral fracture adversely affects compressive load-sharing and increases vertebral deformations at both fractured and adjacent levels. All effects can be partially reversed by vertebroplasty.

Immediate effects of thoracic spinal mobilisation on erector spinae muscle activity and pain in patients with thoracic spine pain: a preliminary randomised controlled trial.

OBJECTIVES: To investigate the activity of the thoracic erector spinae muscles and perceived pain intensity immediately after central postero-anterior (PA) mobilisation of the thoracic spine. DESIGN: Randomised, placebo-controlled, experimental design. PARTICIPANTS AND INTERVENTIONS: Thirty-four participants with non-specific thoracic pain were randomised to the experimental group [grade III central PA mobilisation performed for 3minutes at the level of the seventh thoracic vertebra (T7)] or the placebo group (less than grade I central PA mobilisation performed for 3minutes at T7). MAIN OUTCOME MEASURES: Before and immediately after PA mobilisation, surface electromyography (EMG) was recorded from the thoracic erector spinae muscles as the participants performed 10° spine extension from a prone position for 10seconds. Each participant rated their pain intensity as an investigator performed grade III central PA over the most symptomatic thoracic segment, and the pressure pain threshold (PPT) was evaluated bilaterally over the erector spinae muscles. RESULTS: The EMG amplitude of thoracic erector spinae activity was reduced significantly after the intervention in the experimental group (P<0.05), but not in the placebo group. The difference between the groups was significant {pre-post change: placebo -14 [standard deviation (SD) 50]mV, experimental 28 (SD 48)mV; mean difference -42mV; 95% confidence interval of the difference -76 to 7; P<0.05} albeit small (Grissom=0.44). However, both groups showed a significant reduction in pain immediately after the intervention, and both groups showed a similar pre-post change in PPT. CONCLUSION: These preliminary findings indicate that grade III central mobilisation over the most symptomatic thoracic segment reduces thoracic erector spinae activity during extension of the trunk in people with non-specific thoracic spine pain. CLINICAL TRIAL REGISTRATION NUMBER: ISRCTN47601528.

Novel Screw Head Design of Pedicle Screw for Reducing the Correction Loss in the Patients With Thoracolumbar Vertebral Fractures: A Biomechanical Study.

STUDY DESIGN: A biomechanical study. OBJECTIVE: To study the different biomechanical property among fixed-axis, monoplanar and polyaxial screws in the static and dynamic tests. SUMMARY OF BACKGROUND DATA: Correction loss is a common phenomenon in the patients with thoracolumbar vertebral fractures who underwent the posterior pedicle screw fixation. The incidence varies with the kinds of fixation instrumentation used. There is higher incidence in polyaxial pedicle screws group than in fixed-axis pedicle screws. Monoplanar pedicle screws, which are mobile in the axial plane but fixed in the sagittal plane, can be a better fixation instrumentation for thoracolumbar vertebral fractures in theory. METHODS: A total of 30 porcine spinal units (L2-L4) were used for the static and dynamic tests, which were randomized into six groups (A1, A2, A3, B1, B2, and B3). Static test was performed in A1, A2, and A3. In this test, fixed-axis, monoplanar, and polyaxial screws were performed in A1, A2, and A3, respectively. The ultimate load was noted after tested. In addition, dynamic test was performed in B1, B2, and B3, used fixed-axis, monoplanar, and polyaxial screws, respectively. Correction loss (head-shank angle shift and anterior vertebral body height shift) was obtained and analyzed in each mode. RESULTS: In static test, fixed-axis and monoplanar screws had significantly higher ultimate load than polyaxial screws (P < 0.05) and fixed-axis screws had a little higher ultimate load than monoplanar screws (P < 0.05). In dynamic test, correction loss was minimal in fixed-axis screws, medium in monoplanar screws, and maximal in polyaxial screws. However, the differences were statistically significant in all comparisons but not in the comparison of fixed-axis and monoplanar screws (P > 0.05). CONCLUSION: The findings from the current study suggest that monoplanar screws can significantly increase the stiffness in axial direction compared with polyaxial screws, and reduce the risks of correction loss. For thoracolumbar vertebral fractures, monoplanar screw is a better optional instrumentation for minimally invasive surgery. LEVEL OF EVIDENCE: N/A.

[BIOMECHANICAL STUDY ON UPPER THORACIC SPINE BASED ON PRESSURE SENSITIVE FILM MATERIALS IN CHINESE MINI PIGS].

OBJECTIVE: To analyze the pressure change and distribution of the intervertebral disc of upper thoracic spine in vertical pressure and 5° flexion, extension, or lateral bending. METHODS: Twelve thoracolumbar spinal specimens were harvested from mini pigs and were divided into 2 groups (n=6). T1, 2, T3, 4, T5, 6, and T7, 8 segments were included in one group, and T2, 3, T4, 5, T6, 7, and T8, 9 segments were included in the other group. The data from both groups represented the complete upper thoracic vertebra data. Biomechanical machine and pressure sensitive film were used to measure the pressure on the vertebral columns under loadings of 100, 150, and 200 N in vertical pressures and 5° flexion, extension, or lateral bending. The pressure change of each intervertebral disc under different loads and in different movement conditions was analyzed. RESULTS: In flexion, the anterior annulus pressure of the upper thoracic vertebra increased (P<0.05), whereas the posterior annulus pressure showed no significant change (P>0.05) or an increasing trend (P<0.05). In extension, the anterior annulus pressure of the upper thoracic vertebra decreased (P<0.05), whereas the posterior annulus pressure decreased (P<0.05) or had no obvious change (P>0.05). In lateral bending, the pressure on the concave side of the annulus increased significantly (P<0.05). CONCLUSIONS: The upper thoracic vertebra has unique biomechanical characteristics under different loadings; moreover, the posterior vertebral structure plays an important role in the movement of the upper thoracic vertebral segment and pressure distribution. In lateral bending of the upper thoracic vertebra, the concave side pressure will increase significantly, which suggests that asymmetrical force is an important cause of scoliosis progression. Gravity plays an important role in the progression of scoliosis.

A biomechanical comparison of 360° stabilizations for corpectomy and total spondylectomy: a cadaveric study in the thoracolumbar spine.

BACKGROUND: To date, there has been no adequate biomechanical model that would allow a quantitative comparison in terms of stability/stiffness between a corpectomy with the posterior column preserved and a total spondylectomy with the posterior column sacrificed. The objective of this study was to perform a biomechanical comparison of 360° stabilizations for corpectomy and total spondylectomy, using the human thoracolumbar spine. METHODS: Five human cadaveric thoracolumbar spines (T8-L2) were tested according to the following loading protocol: axial compression, flexion, extension, lateral bending to the right and left, and axial rotation to the right and left. This loading protocol was applied three times. Each specimen was tested intact, after corpectomy, and after total spondylectomy. The relative stiffness of each motion segment was determined for each test. RESULTS: There was no significant difference in stiffness after reconstruction of total spondylectomy versus corpectomy in our thoracolumbar model. Our construct consisted of an anterior cage and four-level pedicle screw instrumentation (two above and two below) and provided similar stiffness in both models. Despite the additional bone resection in a total spondylectomy versus corpectomy, the constructs did not differ biomechanically. Additionally, there was no significant difference in stiffness between the intact specimen and either reconstruction model. CONCLUSIONS: A classic corpectomy, which leaves the posterior column intact, is no better in terms of stability/stiffness than a total spondylectomy carried out using a shorter cage, followed by compression using posterior instrumentation.