vendex and Spinal-Fractures

The cranial pin force history of a halo-vest orthosis was measured using an instrumented halo in a clinical study with three patients. Pin force values at the time of halo-vest application and at subsequent clinical visits during the halo-vest wear period were compared.. To document the pin force reduction in the cranial pins of a halo-vest orthosis in vivo.. The halo-vest is an orthosis commonly used to immobilize and protect the cervical spine. An important problem with halo-vest use is pin loosening. There have been no previous reports of pin force history in vivo.. A custom-built strain-gauged, open-ring halo was used to measure the compressive force and superiorly-inferiorly directed shear forces produced at the tips of the two posterior pins. The instrumented halo was applied to three patients with cervical spine fractures. Pin force measurements were recorded at the time of halo application and at subsequent follow-up visits during the entire treatment period.. A mean compressive force of 343 +/- 64.6 N was produced at the pin tips during halo application with the patient in a supine position. On average, the compressive forces decreased by 83% (P = 0.002) during the typical halo-vest wear period. The compressive forces were substantially greater than the shear forces, which averaged only -11+/-30.2 N at the time of halo application and which did not change significantly with time.. The study confirmed the hypothesized decrease in the compressive pin forces with time. All patients had developed at least some clinical symptoms of pin loosening at the time of halo-vest removal.

Topics: Adolescent; Adult; Bone Nails; Cervical Vertebrae; Compressive Strength; Equipment Failure; Fracture Healing; Humans; Male; Middle Aged; Orthotic Devices; Spinal Fractures; Stress, Mechanical; Torque; Treatment Outcome

Despite the clinical importance, it has remained unclear which changes in the trunk muscle function parameters are more associated with the presence of vertebral fracture (VF).. The aim of this study was to verify the association between the trunk muscle function performance and the presence of VF in older women with low bone mass. The secondary aim was to evaluate the correlation between trunk muscle function and both fall history and muscle mass.. This cross-sectional study was composed by 94 women over 60 years within value of T-Score lumbar spine BMD  <- 1.0 DP. Multidimensional evaluations were performed: appendicular skeletal muscle mass index (ASMI) was determined by the total body DEXA; the radiographic evaluations measured the degree of thoracic kyphosis and classification of VF. The trunk muscle function parameters, such as peak torque (PT), rate of torque development (RTD) and torque steadiness (TS) were evaluated by isokinetic dynamometer. The trunk muscle endurance was evaluated by the timed loaded standing test. The adjusted multivariate logistic regression model and multivariate linear regression were performed to verify the association between the variables studied.. This study demonstrated that deficit in trunk muscle function has shown a strong association with the presence of VF, highlighting issues heretofore unexplored regarding the association between VF with muscle power and motor control.

Topics: Aged; Aged, 80 and over; Back Muscles; Bone Density; Cross-Sectional Studies; Female; Humans; Kyphosis; Middle Aged; Spinal Fractures; Torque; Torso

Percutaneous pedicle screw (PPS) can provide internal fixation of the thoracolumbar spine through a minimally invasive surgical procedure. PPS fixation has been widely used to treat various spinal diseases. Rigid fixation of PPS is essential for managing osteoporotic spine in order to prevent the risks of screw loosening and implant failure. We recently developed a novel augmentation method using hydroxyapatite (HA) granules for PPS fixation. The aim of this study was to evaluate the strength and stiffness of PPS fixation augmented with HA granules using an osteoporotic bone model.. Screws were inserted into uniform synthetic bone (sawbones) with and without augmentation. The uniaxial pullout strength and insertion torque of the screws were evaluated. In addition, each screw underwent cyclic toggling under incrementally increasing physiological loads until 2 mm of screwhead displacement occurred. The maximal pullout strength (N), maximal insertion torque (N·cm), number of toggle cycles and maximal load (N) required to achieve 2-mm screwhead displacement were compared between the screws with and without augmentation.. The maximal pullout strength was significantly stronger for screws with augmentation than for those without augmentation (302 ± 19 N vs. 254 ± 17 N, p < 0.05). In addition, the maximal insertion torque was significantly increased in screws with augmentation compared to those without augmentation (48 ± 4 N·cm vs. 26 ± 5 N·cm, p < 0.05). Furthermore, the number of toggle cycles and the maximal load required to reach 2 mm of displacement were significantly greater in screws with augmentation than in those without augmentation (106 ± 9 vs. 52 ± 10 cycles; 152 ± 4 N vs. 124 ± 5 N, p < 0.05).. Augmentation using HA granules significantly enhanced the rigidity of PPS fixation in the osteoporotic bone model. The present study suggested that novel augmentation with HA granules may be a useful technique for PPS fixation in patients with osteoporotic spine.

Topics: Biomechanical Phenomena; Bone Cements; Bone Substitutes; Durapatite; Feasibility Studies; Fracture Fixation, Internal; Humans; Lumbar Vertebrae; Materials Testing; Osteoporotic Fractures; Pedicle Screws; Spinal Fractures; Thoracic Vertebrae; Torque

Selecting optimal strategies for improving fixation in osteoporotic lumbar spine is an important issue in clinical research. Cortical bone trajectory (CBT) screws have been proven to enhance screw pullout strength, but biomechanical efficacy of these screws remains understudied. The aim of this study was to evaluate biomechanical efficacy of CBT screws in osteoporotic lumbar spine.. Thirty-one vertebrae from 14 cadaveric lumbar spines were obtained. All specimens were measured by computed tomography; the diameter of pedicles, excluding those of vertebral bodies with very small pedicle developments, was calculated. After measuring bone mineral density, the CBT screw was randomly inserted into 1 side, and the traditional trajectory (TT) screw was inserted into the contralateral side. Maximum insertional torque was recorded after screw insertion. Of vertebrae, 21 were subjected to pullout testing at a rate of 5 mm/minute, and 10 were subjected to cyclic fatigue testing. Each construct was loaded until exceeding 5 mm.. Average bone mineral density was 0.567 ± 0.101 g/cm. CBT screws had better biomechanical fixation in osteoporotic lumbar spine compared with standard pedicle screws.

Topics: Aged; Aged, 80 and over; Bone Density; Cadaver; Cortical Bone; Female; Fracture Fixation, Internal; Humans; Lumbar Vertebrae; Male; Middle Aged; Osteoporosis; Pedicle Screws; Prosthesis Design; Prosthesis Failure; Spinal Fractures; Torque

Sacroiliac screw fixation in elderly patients with pelvic fractures is prone to failure owing to impaired bone quality. Cement augmentation has been proposed as a possible solution, because in other anatomic areas this has been shown to reduce screw loosening. However, to our knowledge, this has not been evaluated for sacroiliac screws.. We investigated the potential biomechanical benefit of cement augmentation of sacroiliac screw fixation in a cadaver model of osteoporotic bone, specifically with respect to screw loosening, construct survival, and fracture-site motion.. Standardized complete sacral ala fractures with intact posterior ligaments in combination with ipsilateral upper and lower pubic rami fractures were created in osteoporotic cadaver pelves and stabilized by three fixation techniques: sacroiliac (n = 5) with sacroiliac screws in S1 and S2, cemented (n = 5) with addition of cement augmentation, and transsacral (n = 5) with a single transsacral screw in S1. A cyclic loading protocol was applied with torque (1.5 Nm) and increasing axial force (250-750 N). Screw loosening, construct survival, and sacral fracture-site motion were measured by optoelectric motion tracking. A sample-size calculation revealed five samples per group to be required to achieve a power of 0.80 to detect 50% reduction in screw loosening.. Screw motion in relation to the sacrum during loading with 250 N/1.5 Nm was not different among the three groups (sacroiliac: 1.2 mm, range, 0.6-1.9; cemented: 0.7 mm, range, 0.5-1.3; transsacral: 1.1 mm, range, 0.6-2.3) (p = 0.940). Screw subsidence was less in the cemented group (3.0 mm, range, 1.2-3.7) compared with the sacroiliac (5.7 mm, range, 4.7-10.4) or transsacral group (5.6 mm, range, 3.8-10.5) (p = 0.031). There was no difference with the numbers available in the median number of cycles needed until failure; this was 2921 cycles (range, 2586-5450) in the cemented group, 2570 cycles (range, 2500-5107) for the sacroiliac specimens, and 2578 cycles (range, 2540-2623) in the transsacral group (p = 0.153). The cemented group absorbed more energy before failure (8.2 × 10. The addition of cement to standard sacroiliac screw fixation seemed to change the mode and dynamics of failure in this cadaveric mechanical model. Although no advantages to cement were observed in terms of screw motion or cycles to failure among the different constructs, a cemented, two-screw sacroiliac screw construct resulted in less screw subsidence and greater energy absorbed to failure than an uncemented single transsacral screw.. In osteoporotic bone, the addition of cement to sacroiliac screw fixation might improve screw anchorage. However, larger mechanical studies using these findings as pilot data should be performed before applying these preliminary findings clinically.

Topics: Aged; Aged, 80 and over; Biomechanical Phenomena; Bone Cements; Bone Screws; Cadaver; Fracture Fixation, Internal; Humans; Ilium; Osteoporotic Fractures; Prosthesis Design; Prosthesis Failure; Pubic Bone; Sacrum; Spinal Fractures; Stress, Mechanical; Torque

The halo orthosis is a treatment option currently used in Australia for cervical spine immobilisation following trauma, fracture and post surgical stabilisation. In a previous study, the authors reported halo pin replacement to be a common complication. The aim of this study was to investigate the potential correlation between routine halo pin re-torquing and the incidence of pin replacement.. A retrospective case series study was undertaken. A total of 258 charts were reviewed, with 170 patients included in the study. Patients were fitted with a Bremer HALO System with the initial application torque maintained by routine re-torquing throughout the duration of wear.. A total of 680 pins (4 per patient) were inserted during the initial application of the halo orthoses, with only six pins replaced (0.88%) throughout the duration of the study.. The findings from this study demonstrate a potential correlation between routinely re-torquing halo pins and decreasing the incidence of pin replacement.. This case series study has identified a potential improvement in clinical management of patients wearing a halo-thoracic orthosis.

Topics: Adult; Bone Nails; Cervical Vertebrae; Female; Humans; Immobilization; Male; Orthotic Devices; Retrospective Studies; Spinal Fractures; Stress, Mechanical; Torque

In vitro human cadaveric biomechanical study.. The aims of this project were to evaluate the acute segmental fixation and long-term screw stability afforded by 3 C2 fixation techniques: intralaminar, pars, and pedicle.. C2 intralaminar screws offer the advantages of avoiding the vertebral artery; however, direct biomechanical comparison of this technique to the other methods of instrumenting C2 has not been performed.. Fourteen cadaveric specimens were dual energy radiograph absorptiometry scanned and segregated into 2 groups (n = 7/group) matching the C2 bone mineral density. All specimens were instrumented with C1 lateral mass and C2 intralaminar screws while measuring the insertional torque (IT). In group 1 C2 pars screws were inserted while in group 2 pedicle screws were placed. Nondestructive testing was performed in axial rotation, flexion/extension (FE), and lateral bending. The odontoid was then resected and loading repeated. Subsequently, specimens were disarticulated about C2 and individually loaded for 2000 cycles in the cephalocaudad plane. The screws were then failed by a tensile load directed in the parasagittal plane. Full range of motion over C1-C2 and peak screw pull-out force was quantified. RESULTS.: Transpedicular technique generated significantly higher IT than the pars screws and marginally greater IT than intralaminar screws. With the intact atlantoaxial ligamentous complex, intralaminar fixation was superior to pars and similar to pedicle instrumentation at limiting axial torsion. After odontoid destabilization, however, this technique was less effective at reducing the lateral bending range of motion. Destructive loading revealed the highest pull-out forces with the pedicle screws, followed by intralaminar and pars screws.. Our results suggest that C2 intralaminar fixation provides a viable alternative to pedicle screws and is superior to pars instrumentation in cases with preserved atlantoaxial ligamentous attachments. In the presence of a traumatic dens fracture, however, intralaminar fixation may not be the optimal choice.

Topics: Absorptiometry, Photon; Atlanto-Axial Joint; Biomechanical Phenomena; Bone Density; Bone Screws; Cadaver; Cervical Vertebrae; Fracture Fixation, Internal; Humans; In Vitro Techniques; Joint Instability; Odontoid Process; Prosthesis Failure; Range of Motion, Articular; Spinal Fractures; Tensile Strength; Time Factors; Torque

An experimental anatomic study performed on elderly cadaveric skulls.. (1) To determine the pin penetration depths in outer table of skull at different torques in the elderly population during halo pin insertion and (2) to validate a safe range of torque for use in this population.. The elderly are at an increased risk of falls, which can lead to cervical fractures. The halo pins used to stabilize these injuries present unique problems in this population owing to osteoporosis, and intracranial pin penetration should always be avoided.. A halo ring was used to insert pins in 4 standard positions on 10 elderly cadaveric skulls. Incremental torques were used to drive the pin into the outer table, and the penetration of each pin was measured using computed tomography imaging at each stage.. Eight to Twelve in-lb of torque was not sufficient to fully penetrate the outer table of the skull. Only at 16 in-lb of torque was the outer table penetrated, and only anterolaterally, hence the posterolateral outer table is more resistant to penetration than the anterolateral outer table.. Despite age-related bone changes in the elderly, it is still safe to use 8 in-lb of torque when inserting pins for a halo vest. However, as the anterolateral outer table is weaker than the posterolateral outer table, a new pin design with broader shoulders should be used anterolaterally to ensure maximal patient safety.

Topics: Accidental Falls; Age Factors; Aged; Aged, 80 and over; Aging; Brain Injuries; Cadaver; Cervical Vertebrae; Compressive Strength; Craniotomy; External Fixators; Female; Humans; Iatrogenic Disease; Intraoperative Complications; Male; Monitoring, Intraoperative; Osteoporosis; Skull; Spinal Fractures; Stress, Mechanical; Torque

An in vitro study on porcine spinal segments.. To determine the differences in mechanical behavior and fatigue strength in shear loading between intact spinal segments and segments without posterior elements, and between segments in neutral and flexed positions.. Limited data are available on shear strength of spinal segments. Literature suggests that shear loading can lead to failure of the posterior elements and failure of the disc, when the posterior elements cannot provide adequate protection.. In 2 experiments, 18 and 20 spines of pigs (80 kg) were used, respectively. Shear strength of the T13-L1 segment was tested, while loaded with 1600-N compression. L2-L3 and L4-L5 segments were loaded with a sinusoidal shear between 20% and 80% of the strength of the corresponding T13-L1 segment and 1600-N compression. In experiment No. 1, the posterior elements were removed in half the segments. In experiment No. 2, half the segments were tested in the neutral position, and half were tested in 10 degrees flexion.. The group without posterior elements had failure earlier than the intact group. In the group without posterior element, stiffness increased on failure; in the intact group, it decreased. In experiment No. 2, no differences between groups were found.. Repetitive shear loading can induce failure of porcine spinal segments, likely caused by fracture of the posterior elements, and, although repetitive anterior shear forces can also induce disc damage, this appears not to occur in intact segments, not even when flexed close to maximal.

Topics: Animals; Compressive Strength; Fractures, Stress; In Vitro Techniques; Intervertebral Disc; Lumbar Vertebrae; Range of Motion, Articular; Shear Strength; Spinal Fractures; Stress, Mechanical; Sus scrofa; Thoracic Vertebrae; Torque; Weight-Bearing

The spine is routinely subjected to repetitive combined loading, including axial torque. Repetitive flexion-extension motions with low magnitude compressive forces have been shown to be an effective mechanism for causing disc herniations. The addition of axial torque to the efficacy of failure mechanisms, such as disc herniation, need to be quantified. The purpose of this study was to determine the role of static axial torque on the failure mechanics of the intervertebral joint under repetitive combined loading.. Repetitive flexion-extension motions combined with 1472 N of compression were applied to two groups of nine porcine motion segments. Five Nm of axial torque was applied to one group. Load-displacement behaviour was quantified, and planar radiography was used to document tracking of the nucleus pulposus and to identify fractures.. The occurrence of facet fractures was found to be higher (P=0.028) in the axial torque group (7/9), compared to the no axial torque group (2/9). More hysteresis energy was lost up to 3000 cycles of loading in the axial torque group (P<0.014). The flexion-extension cycle stiffness was not different between the two groups until 4000 cycles of loading, after which the axial torque group stiffness increased (P=0.016). The percentage of specimens that herniated after 3000 cycles of loading was significantly larger (P=0.049) for the axial torque group (71%) compared to the no axial torque group (29%).. Small magnitudes of static axial torque alter the failure mechanics of the intervertebral disc and vertebrae in combined loading situations. Axial torque appears to accelerate the susceptibility for injury to the intervertebral joint complex. This suggests tasks involving axial torque with other types of loading, apart from axial twist motion, should be monitored to assess exposure and injury risk.

Topics: Animals; Biomechanical Phenomena; Cervical Vertebrae; Disease Models, Animal; Elasticity; Fractures, Cartilage; Hernia; In Vitro Techniques; Intervertebral Disc Displacement; Range of Motion, Articular; Spinal Fractures; Stress, Mechanical; Swine; Torque; Weight-Bearing

Abnormalities of the intervertebral discs have been found in a high frequency among young elite athletes. Several studies have also reported that the adolescent spine, especially the vertebral growth zones, is vulnerable to trauma. However, there is incomplete knowledge regarding the injury mechanism of the growing spine. In this study, the injury patterns of the adolescent porcine spine with disc degeneration were examined.. Twenty-four male pigs were used. A degenerative disc was created by drilling a hole through the cranial endplate of a lumbar vertebra into the disc. Two months later the animals were sacrificed and the degenerative functional spinal units (segments) were harvested. The segments were divided into three groups and exposed to axial compression, flexion compression or extension compression to failure. The load and angle at failure were measured for each group. The segments were examined with magnetic resonance imaging and plain radiography before and after the loading and finally examined macroscopically and histologically.. The degenerated segments required considerably more compressive load to failure than non-degenerated segments. Creating a flexion injury required significantly more load than an extension injury. Fractures and/or separations of the endplates from the vertebral bodies were seen at the margins of the endplates and in the growth zone. Only severe separations and fractures could be seen on plain radiography and magnetic resonance imaging.. The weakest part of the adolescent porcine lumbar spine with experimentally-induced degeneration, when loaded in axial compression, flexion compression or extension compression, was the growth zone, and, to a lesser extent, the endplate. Degenerated discs seem to withstand higher mechanical loads than non-degenerated discs, probably due to altered stress distribution.

Topics: Aging; Animals; Biomechanical Phenomena; Cervical Vertebrae; Compressive Strength; Disease Models, Animal; Elasticity; Fractures, Cartilage; In Vitro Techniques; Intervertebral Disc Displacement; Male; Range of Motion, Articular; Spinal Fractures; Stress, Mechanical; Swine; Torque; Weight-Bearing

Plain lateral radiographs in a neutral position were studied in ten acute thoracolumbar burst fractures produced by high speed impact on three vertebrae human cadaveric spine segments. Six linear geometric parameters were measured on each film. The ratio of each value in the neutral injured to the intact condition was correlated linearly with the motion parameters obtained from post-traumatic three-dimensional flexibility data (neutral zone NZ; range of motion ROM). Anterior unit height (vertebra+adjacent discs) had the highest correlation with the neutral zone and flexibility in all directions, especially flexion-extension (NZ, R2 = 0.93; flexion ROM, R2 = 0.86; extension ROM, R2 = 0.79) lateral bending (NZ, R2 = 0.83; ROM, R2 = 0.90) and right axial rotation (NZ, R2 = 0.53; ROM, R2 = 0.86). The deformation ratio (average height to depth) correlated most with the neutral zone in left axial rotation (R2 = 0.91) and right lateral bending (R2 = 0.92). Due to the high correlations obtained, these parameters should be evaluated in clinical situations to assess their effectiveness in predicting the instability of burst fractures. Ultimately, prospective clinical studies are required to verify their clinical utility.

Topics: Acceleration; Acute Disease; Adult; Aged; Cadaver; Compressive Strength; Female; Fractures, Comminuted; Humans; Least-Squares Analysis; Linear Models; Lumbar Vertebrae; Male; Middle Aged; Pliability; Predictive Value of Tests; Radiography; Range of Motion, Articular; Spinal Fractures; Thoracic Vertebrae; Torque