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Biomedical subjects

H U Bueff

Publications and source records attributed to H U Bueff.

11 recordsLinked to original sources
PubMed1997

Frozen storage affects the compressive creep behavior of the porcine intervertebral disc.

STUDY DESIGN: A biomechanical study of the compressive creep behavior of the porcine intervertebral disc before and after frozen storage. OBJECTIVE: To determine whether frozen storage alters the creep response, hydration, and nuclear swelling pressure of the intact intervertebral disc. SUMMARY OF BACKGROUND DATA: The mechanical response of the disc is dominated by swelling and fluid flow, whose effects are time-dependent. Because fluid content, which may change during storage, plays a significant role in the disc's time-dependent behavior, changes in mechanical response due to freezing may have been missed in previous studies that focused on time-independent behavior only. METHODS: Porcine intervertebral discs were tested in repeated cycles of compressive creep either immediately postmortem or after 3 weeks of frozen storage. Swelling pressure and nuclear hydration were also measured in fresh and frozen discs. A fluid transport model was used to analyze the creep data. RESULTS: The creep behavior of the intact porcine intervertebral disc is dramatically affected by frozen storage. The apparent permeability of the frozen discs was 82% higher than that of the fresh discs, and the swelling pressure of frozen discs was 25% lower in frozen discs (P < 0.01). The behavior of fresh and frozen discs became more dissimilar with repeated cycles of creep. CONCLUSIONS: In vitro tests of frozen porcine intervertebral discs do not represent fresh behavior. Frozen storage appears to permanently alter disc behavior. The precise nature of any freezing-induced damage, and whether frozen storage similarly affects human discs, remains to be seen.

Animals↗
PubMed1997

Biomechanical analysis of multilevel fixation methods in the lumbar spine.

STUDY DESIGN: The authors measured and compared the stiffness of cadaveric lumbar spines stabilized with several anterior interbody fusion devices. The information obtained provides a foundation for determining how methods of anterior lumbar fixation can maximize rigidity and promote development of bony fusion. OBJECTIVES: To compare the utility of three anterior spinal instrumentation systems for stabilizing the lumbar spine. SUMMARY OF BACKGROUND DATA: Anterior spinal instrumentation is used to prevent progressive spinal deformity and maintain correction after spinal fusion surgery. Newer instrumentation systems developed for anterior interbody fusions can be inserted by minimally invasive procedures. The stability of these systems has not been tested adequately in human cadaveric specimens. METHODS: Fusion constructs were evaluated in 12 human cadaveric specimens sequentially loaded in axial compression and torsion, flexion and extension, and lateral bending. The fusion constructs used were 1) two anterior bilateral threaded interbody fusion devices, 2) lateral hollow interbody screws (Texas Scottish Rite Hospital-B screws), and 3) femoral allograft and conventional anterior Texas Scottish Rite Hospital instrumentation. RESULTS: The construct with Texas Scottish Rite Hospital-B screws connected by a rod produced stiffness comparable with that produced by conventional Texas Scottish Rite Hospital instrumentation with femoral ring allografts. The threaded interbody fusion device stiffness tested in axial rotation was comparable with that achieved with Texas Scottish Rite Hospital instrumentation. CONCLUSIONS: Our data demonstrate the effectiveness of threaded interbody fusion device and the Texas Scottish Rite Hospital-B screw in immobilizing the L3-L4 and L4-L5 disc spaces. Rigidity of fixation in the lumbar spine may aid in the maintenance of lordosis.

Absorptiometry, Photon↗
PubMed1996

Low back pain.

The cause and pathophysiology of low back pain are discussed in detail. Imaging studies of the lumbar spine-inclusive discography can help in detecting the originator of pain. The common treatment for low back pain is conservative. Only patients who fail this approach or who develop neurologic deficits benefit from lumbar surgery. A more aggressive treatment is chosen for patients with infections or tumors of the lumbar spine. Different treatment options are explained concerning the different diseases leading to low back pain.

Diagnosis, Differential↗
PubMed1996

Patient outcomes after spinal reconstructive surgery in patients > or = 40 years of age.

This study provides outcome data on the quality of life in 84 patients 40 years of age or older who had spinal reconstructive surgery. A 30-min questionnaire covering the patients' pre- and postoperative functional status, expectations for surgery, medication use, quality of life, and overall satisfaction was administered via telephone by a trained interviewer. Clinical data were obtained from chart and radiographic review. The majority of the patients had back or leg pain as their indication for surgery. Diagnoses included kyphosis, scoliosis, spinal stenosis, spondylolisthesis, and failed surgery. Overall satisfaction with functional status and surgical outcome was 81%, and there was significant improvement in most functional measures. This study suggests that improved qualify of life for the majority of appropriately selected spinal reconstruction patients is achievable in this mature population.

Adult↗
PubMed1995

Instrumentation of the cervicothoracic junction after destabilization.

STUDY DESIGN: The biomechanics of three different instrumentation constructs applied at the destabilized cervicothoracic junction were evaluated. OBJECTIVES: To find an efficient way in restoring stability of the cervicothoracic junction in cases with and without laminectomy. SUMMARY OF BACKGROUND DATA: Different instrumentation techniques have been evaluated biomechanically and used clinically for managing instabilities between the fourth and sixth cervical vertebrae. These constructs have not been evaluated at the cervicothoracic junction. METHODS: Six human spines were tested nondestructively in axial torsion, flexion, and extension with the C6-T2 motion segments left unconstrained. The three-dimensional displacements and rotations between C7 and T1 vertebrae were measured using a sonic digitizer. After intact testing, a distractive-flexion Stage 3 cervical spinal injury was simulated surgically between C7 and T1. The specimens underwent sequential instrumentation and mechanical testing with three constructs: posterior Synthes lateral mass plate, posterior pediatric Cotrel-Dubousset rod system with lamina hooks and a crosslink, and anterior Synthes cervical locking plate. RESULTS: Posterior stabilization techniques had statistically more stiffness than anterior plates. The Cotrel-Dubousset system offered the largest stiffness ratio (instrumented/intact) in flexion, extension, and rotation. There was no statistical difference between posterior plates and Cotrel-Dubousset instrumentation. The stiffness of the anterior plate did not differ significantly from the intact spine. CONCLUSION: Our data show that instability of the cervicothoracic junction can be efficiently restored by either anterior plates, posterior plates, or posterior hook-rod constructs (Cotrel-Dubousset). Posterior constructs showed increased stiffness over anterior plates.

Aged↗
PubMed1994

Three-dimensional finite element modeling of a cervical vertebra: an investigation of burst fracture mechanism.

Finite element modeling was used to study the mechanical behavior of a cervical vertebra under axial compressive loading. A three-dimensional (3-D) finite element (FE) model of a mid-cervical vertebra using inhomogeneous material properties was generated from quantitative computed tomographic (CT) scan data. This model improved upon previous vertebral FE models by using a highly refined mesh to represent the 3-D variation in material properties of vertebral bone. Traumatic loading of the vertebra was simulated by applying an axial compressive displacement through linear spring elements. Bone strength was computed from the CT scan data and compared with predicted stress. Based on the maximum shear stress theory of failure, the model predicts initiation of failure in the central cancellous region of the vertebral body. The type of fracture pattern predicted by the model is consistent with the typical cervical burst fracture that is seen clinically after compressive loading of the cervical spine. As such, we have developed a tool that can be useful for validating proposed fracture mechanisms in the cervical spine.

Cervical Vertebrae↗
PubMed1991

Transections of the C1-C2 joint capsular ligaments in the cadaveric spine.

The purpose of this study was to examine the mechanical function of the C1-C2 capsular ligaments. Physiologic torques of up to 1.5 Nm were applied to human fresh cadaveric specimens (C0-C1-C2-C3) in three dimensions, and the three-dimensional motion of C1 relative to C2 was recorded. Two groups of cadaveric specimens were used to study the effect of two different sequential ligamentous transections. In the first group (n = 4), the transection of the left capsular ligament was followed by transection of the right capsular ligament. In the second group (n = 10), the transection of the left capsular ligament was preceded by transection of the left and right alar and transverse ligaments. The greatest changes in motion occurred in axial rotation to the side opposite the transection. In the first group, left capsular transections resulted in a significant increase in axial rotation range of motion to the right of 1 degree. After the right capsular ligament was transected, there was a further significant increase of 1.8 degrees to the left and 1.0 degree to the right. Lateral bending to the left also increased significantly by 1.5 degrees after both ligaments were cut. In the second group, with the nonfunctional alar and transverse ligaments, transection of the left capsular ligament resulted in greater increases in range of motion: 3.3 degrees to the right and 1.3 degrees to the left. Lateral bending to the right also increased significantly by 4.2 degrees.

Cadaver↗
PubMed1988

Three-dimensional movements of the upper cervical spine.

Knowledge of the normal movements of the occipito-atlanto-axial joint complex is important for evaluating clinical cases that may be potentially unstable. The purpose of this in vitro study was to quantitatively determine three dimensional movements of the occiput-C1 and C1-C2 joints. Ten fresh cadaveric whole cervical spine specimens (occiput to C7) were studied, using well-established techniques to document the movements in flexion, extension, left and right lateral bending, and left and right axial rotation. Pure moments of a maximum of 1.5 N-m were applied incrementally, and three-dimensional movements of the bones were recorded using stereophotogrammetry. Each moment was applied individually and in three load/unload cycles. The motion measurements were made on the third load cycle. Parameters of neutral zone, elastic zone, and range of motion were computed. Neutral zones for flexion/extension, right/left lateral bending, and right/left axial rotation were, respectively: 1.1, 1.5, and 1.6 (occiput-C1); and 3.2, 1.2, and 29.6 degrees (C1-C2). Ranges of motion for flexion, extension, lateral bending (one side), and axial rotation (one side) were, respectively: 3.5, 21.0, 5.5, and 7.2 degrees (occiput-C1 joint) and 11.5, 10.9, 6.7, and 38.9 degrees (C1-C2 joint). The greatest intervertebral motion in the spine was axial rotation at the C1-C2 joint, with the neutral zone constituting 75% of this motion.

Adult↗
PubMedDate not supplied

Endoscopic instrumentation, correction, and fusion of idiopathic scoliosis.

BACKGROUND CONTEXT: Endoscopic techniques have been used since 1993 to treat thoracic disk disease. Thorascopic techniques evolved into means of treating not only disk disease but also correcting thoracic spinal deformity with instrumentation and fusion. PURPOSE: To evaluate the efficacy of endoscopic instrumentation, correction, and fusion of thoracic idiopathic scoliosis. STUDY DESIGN: A retrospective review of 50 patients who have undergone endoscopic instrumentation, correction, and fusion for scoliosis. PATIENT SAMPLE: Fifty consecutive patients undergoing treatment for primary thoracic idiopathic scoliosis. OUTCOME MEASURES: Evaluation of operative time, curve correction, and fusion rates were evaluated. METHODS: Fifty patients with the diagnosis of primary thoracic scoliosis underwent thoracoscopic techniques of instrumentation, correction, and fusion. On follow-up, the patients were evaluated for spinal alignment restoration, axial derotation, postoperative pain, rehabilitative time, and complications. RESULTS: The initial curve correction averaged 50%, improving to over 68% in the last 10 cases. Hypokyphosis correction averaged 21 degrees. Additionally, there has been a decrease in rehabilitation time, less time off work or school, and decreased blood loss and postoperative pain. There were 14 complications and no deaths recorded. The factors involved in a successful fusion include total diskectomy, complete cartilaginous end plate removal, and autogenous bone graft. CONCLUSIONS: The initial results of the thoracoscopic-assisted techniques for primary thoracic scoliosis are promising. As with most evolving techniques, surgical times are decreasing and rates of correction are improving.

Adolescent↗
PubMedDate not supplied

Pelvic osteotomies for subluxation of the hip in cerebral palsy.

Twenty-three pelvic osteotomies (10 Salter, seven Chiari, six Steel) were performed on 21 patients with cerebral palsy for hip subluxation or dislocation from 1977 to 1986. The principal indication for osteotomy was inadequate coverage of the femoral head. Stability was maintained in 19 of 23 hips with an average follow-up of 6.14 years (2.0-13.3). The hips showed a significantly improved center-edge angle, acetabular angle, Reimers index, and neck-shaft angle. There were six failures; painful degenerative joint disease developed in two patients and resubluxation or dislocation in four. Pelvic osteotomies can provide hip stability in selected cerebral palsy patients.

Adolescent↗