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Biomedical subjects

J F Cusick

Publications and source records attributed to J F Cusick.

At least 37 records · Page 2Linked to original sources
PubMed1993

Kinematics of the lumbar spine following pedicle screw plate fixation.

This investigation was conducted to determine the kinematic response of the lumbar spine instrumented with transpedicular screws and plates. Seven unembalmed human cadaveric lumbar spines were used. Retroreflective targets were inserted into the bony landmarks of each vertebral body, facet column, and spinous process. The specimen was quasistatically loaded until failure (initial cycle) using an electrohydraulic testing device at a rate of 2.5 mm/sec. After radiography, the specimen was again loaded (injury cycle) to the failure compression determined in the previous cycle. Transpedicular screws then were inserted bilaterally at one level proximal and distal to injury. The stabilized cycle of loading was conducted using the procedure adopted in the injury cycle. Comparative analysis of the localized kinematic data between the stabilized and injured columns indicated a reduction in motion between fixated levels, increasing the rigidity of the column. At levels proximal and distal to fixation, however, motion increased, indicating added flexibility. These alterations in the motion, observed during single-cycle loading, may be further accentuated in vivo, leading to hypermobility and degeneration of the spine.

Adult↗
PubMed1992

The biomechanics of lumbar facetectomy under compression-flexion.

Alterations of posterior spinal elements including the facet joints are commonly associated with a variety of lumbar operative procedures. Under continuous physiologic compression-flexion load application L2-L3 and L4-L5 functional units were tested as intact preparations and then sequentially altered with unilateral facetectomy, bilateral facetectomy, posterior ligament transection, and partial discectomy. Using a method of continuous motion analysis, the movement of the individual spinal components (disc, facet joint, interspinous process distance) were statistically compared between the various surgical alterations. Higher physiologic loads produced significant increases in overall deflection from BF to BFL alterations indicating a preference to preserve the posterior ligaments for this surgical approach. Although insignificant changes in the force-deflection response from one surgical alteration to the next sequential alteration were noted, statistically significant increases in localized facet joint motion may suggest the potential for acceleration of segmental degenerative changes.

Aged↗
PubMed1992

Biomechanics of sequential posterior lumbar surgical alterations.

Compromise of the functional integrity of the posterior lumbar ligaments and facet joints is a common occurrence after repeated lumbar operative procedures. To evaluate the biomechanical effects of sequential surgical alterations, this investigation analyzed bilateral facetectomies (medial, total, and total with posterior ligament section) in three segments of human cadaveric lumbar spines under increasing compression-flexion. These iatrogenic alterations, designed to replicate common methods of surgical exposure, were created at the lower intervertebral joint (L4-5) while the upper joint (L3-4) remained intact. Overall strength characteristics in the physiological range of 400 N and 600 N demonstrated significant differences (p less than 0.05) in applied compressions for all preparations compared to the intact specimen. Comparison of sequential surgeries, however, did not demonstrate this tendency. Significant changes in the movement of the spinous processes at the upper (unaltered) level occurred only after posterior ligament section, whereas the lower (altered) level showed markedly increasing distraction of both the facets and the spinous processes with sequential operations. Sectioning of the supraspinous/interspinous ligament and associated fascial attachments resulted in a marked transfer of motion to the altered level. This was manifested by the increased anterior displacement of the centrode at the lower level associated with probable posterior migration of the centrode at the upper level. These data suggest that the effects of progressive surgical alterations of the lumbar facet joints are controllable in a preparation undergoing acute compression-flexion loads until the supraspinous/interspinous ligaments, with associated residual tendinous, midline muscle, and fascial attachments, are violated.

Aged↗
PubMed1991

Pathophysiology and treatment of cervical spondylotic myelopathy.

Operative procedures on the cervical vertebral column and spinal cord must be designed selectively for the individual patient. The majority of present series suggest that the anterior approach, especially vertebrectomy, may be associated with the highest levels of clinical improvement, but posterior approaches present significant advantages in treating the patient with multilevel disease (three or more levels). Laminectomy, however, must be avoided in the presence of straightening or curvature reversal of the cervical vertebral column. In certain select cases, consideration of a combined anterior and posterior approach or total stabilization may be considered. Although no consensus exists regarding the exclusivity of a specific surgical procedure and all possible approaches should be considered, the final decision should be based on detailed biomechanical considerations. Complete radiographic and neurophysiologic studies, including evaluation in various dynamic positions of the cervical spine (flexion, extension, and rotation), are of assistance in defining the most efficacious treatment method.

Cervical Vertebrae↗
PubMed1990

Injury biomechanics of the human cervical column.

In this study, the authors have developed a technique to replicate clinically relevant traumatic cervical spine injuries and determined the injury biomechanics. Because of the importance of compressive forces in neck injuries, this research was conducted using compression as the primary load vector. Six fresh human cadaveric head-neck complexes were prepared by fixing the distal end in methylmethacrylate. Tests were done with varying loading rates to include quasistatic and dynamic conditions. For quasistatic experiments, the proximal end was fixed to the piston of the testing device. In dynamic tests, the cranium was unconstrained, and to maintain stability, the effects of the spinal musculature were simulated by means of pulleys, deadweights, and springs in the anterior and posterior parts of the head-neck complex. Quasistatic tests conducted at a rate of 2.0 mm/sec produced cervical spine trauma at forces ranging from 1.7 to 2.3 kN, with deformations ranging from 2.2 to 3.7 cm. The specimens were deep-frozen at the level of injury, preserving the local deformation of the tissues to enable a detailed evaluation immediately after the injury. Dynamic tests conducted at velocities of 3.2 to 5.7 m/sec resulted in impact injuries at one level of the head-neck complex. The applied forces at the vertex were considerably higher than those recorded at the distal end. The failure deformations for both the quasistatic (2.2-3.7 cm) and dynamic (1.7-3.2 cm) tests, however, were found to be similar, suggesting that the human head-neck complex is a deformation-sensitive structure.

Aged↗
PubMed1989

Neurosurgical considerations of cervical myelopathy.

Operative procedures on the cervical vertebral column and spinal cord must be selectively designed for the individual patient. Complete radiographic and neurophysiologic studies, including evaluation in various dynamic positions of the cervical spine (flexion, extension, and rotation), are necessary to define the most efficacious treatment method. No consensus exists regarding the exclusivity of a specific surgical procedure and all possible approaches should be considered, with the final decision based on detailed biomechanical considerations.

Cervical Vertebrae↗
PubMed1988

Biomechanics of cervical spine facetectomy and fixation techniques.

Facetectomy, either unilateral or bilateral, significantly altered the capacity of cervical spine functional units to withstand increasing compression-flexion loads applied in a constant mode to different specimen configurations. Unilateral facetectomy resulted in an average 31.6 +/- 9.7 percent decrease in strength whereas bilateral disruption caused an average 53.1 +/- 11 percent decrease in strength. Motion analysis in a two-dimensional plane after facetectomy indicated an anterior displacement of the instantaneous axis of rotation (IAR) with a resultant increased load on the vertebral bodies and disc. This anterior shift of the IAR in the horizontal plane was significantly but not completely resolved by wire fixation of the facet joints. These fixation techniques, consisting of either facet to facet or facet to spinous process wiring, demonstrated a similar capability to restore strength to the functional units as well as reducing excessive motion in the vertical and anterior axes induced by the facetectomies.

Aged↗
PubMed1988

Tensile strength of spinal ligaments.

Spinal ligaments from 41 fresh human male cadavers were tested. The ligaments were tested in situ by sectioning all elements except the one under study. The force deflection curves demonstrated a sigmoidal shape, and the point at which an increase in deflection was obtained with decreasing force was taken as failure. The force and deformation at failure are shown for each ligament as a function of spinal level.

Aged↗
PubMed1987

Subarachnoid hemorrhage following chymopapain chemonucleolysis. Case report.

Subarachnoid hemorrhage is a frequent finding in patients who have incurred neurological complications following chymopapain chemonucleolysis, but the basis for this occurrence remains controversial. The authors report the clinical and postmortem findings in a 42-year-old man who died 5 days after chemonucleolysis at the L4-5 and L5-S1 disc spaces. The predominant histological abnormality was a severe inflammatory arteritis of a medium-sized artery at the upper cervical level with disruption of the vessel wall. The potential causative role of chymopapain in this situation and the correlation of a vascular basis for many of the complications found after inadvertent intrathecal chymopapain injector are discussed.

Adult↗
PubMed1987

Effect of hypertension on small-vessel healing after microvascular anastomosis.

Artery-to-artery microvascular anastomosis (MVA) has become an established therapeutic alternative for patients with giant intracranial aneurysms and other forms of cerebrovascular disease. Many patients afflicted with cerebrovascular disease also suffer from hypertension. To evaluate the effect of hypertension on healing of small arteries following MVA, 36 spontaneously hypertensive rats were subjected to end-to-side MVA of their common carotid arteries. At specific times after surgery the rats were sacrificed; the anastomotic site was removed and examined with light microscopy and scanning electron microscopy. All MVA's were patent, and there was no evidence of thrombus formation or stenosis at the operative site in any group. Also, there was no difference between the spontaneously hypertensive rats and the control normotensive rat group in the rate of endothelial coverage of the MVA. The presence of hypertension appears to have no effect on healing of small arteries in the rat.

Anastomosis, Surgical↗
PubMed1986

Comparison of single-photon emission computed tomography with [123I]iodoamphetamine and xenon-enhanced computed tomography for assessing regional cerebral blood flow.

Regional CBF (rCBF) images obtained from xenon-enhanced computed tomography (XeCT) and single-photon emission computed tomography (SPECT) with N-isopropyl-p-[123I]iodoamphetamine (IMP) done with a rotating gamma-camera were compared in nine patients. Both XeCT and SPECT/IMP demonstrated flow abnormalities at all sites of infarction identified by CT, while detecting reduced rCBF in areas normal by CT in eight of the nine patients. All areas that were abnormal on XeCT were abnormal on the comparable SPECT/IMP images. The major advantages of XeCT are its greater resolution and potential for noninvasive quantitation of rCBF, while the major advantage of SPECT/IMP is its visualization of the entire brain on transverse, coronal, and sagittal sections.

Amphetamines↗
PubMed1986

Total stabilization of the cervical spine in patients with cervical spondylotic myelopathy.

Certain patients with cervical spondylotic myelopathy demonstrate instability in the upper cervical vertebral column associated with marked narrowing of the vertebral canal in the neighboring lower cervical segments. This combination of causative mechanisms creates difficulty in using routine surgical procedures, especially in elderly and severely debilitated patients. We present three cases that typify this situation and illustrate marked resolution of debilitating myelopathy through total posterior fusion of the cervical spine usually incorporating the occiput.

Aged↗
PubMed1985

Nonoperative management of traumatic facial nerve palsy.

Forty-five patients with facial nerve palsy resulting from head injury were treated nonoperatively between 1975 and 1981. Of 31 patients who had polytomography, temporal bone fractures were demonstrated in 29. In 44 of 45 injuries, satisfactory clinical improvement in motor function was noted, including 65% (overall) who showed complete recovery. Fracture direction on polytomography, results of electromyography (performed in ten cases), and time of onset of paralysis were not correlated with outcome. The present findings suggest a limited role for early surgery in closed traumatic facial nerve palsy.

Adolescent↗
PubMed1984

The biomechanics of spinal injuries.

This manuscript is directed to review the epidemiology of spinal trauma, the anatomy of the vertebral column, spinal ligaments, muscles, motion of the spine and spinal cord. Because little information is available on the material properties of ligaments and the components of the vertebral column, this material is also included. A review of the experimental spinal cord injury models is given because of the concerted interest in this area today. Laboratory studies conducted in animals to develop typical spinal cord injury models and the corresponding alterations in perfusion and metabolic pathways, forces, and changes in the evoked potentials are discussed. Light and electron microscopy evaluations of the spinal cord are also treated. Clinical classifications of spinal injuries, pathology, and typical examples of upper cervical injuries, atlanto-axial disc locations and fractures, lower cervical spine injuries, injuries to thoracolumbar column with mathematical models, and typical force levels are given. The final section, investigation examples, provides a review of typical spinal injuries associated with sports injuries, motorcycle helmets, industrial helmets, and swimming pools investigated in our laboratories and by those of others. With lumped parameter mathematical model which predicts cervical compression, force, the various energies encountered in a one-dimensional impact is given. Typical examples of studies conducted on football helmets, motorcycle helmets, and industrial helmets are also included. Because of the importance of crash dummies used in the analysis of spinal injuries, a separate appendix is included, as well as an appendix reviewing motorcycle standards which are often dispersed throughout the literature. Considerable emphasis is placed upon actual experimental values of force and energy measured in the living animal and the most recent studies conducted in the fresh human cadaver to delineate the biomechanical mechanisms of spinal injury.

Accidents, Traffic↗