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Biomedical subjects

W J Richardson

Publications and source records attributed to W J Richardson.

At least 19 recordsLinked to original sources
PubMed2000

A biomechanical, radiologic, and clinical comparison of outcome after multilevel cervical laminectomy or laminoplasty in the rabbit.

STUDY DESIGN: A rabbit model was used to compare clinical outcome, radiographic changes, and biomechanical flexibility after cervical laminectomy and open-door laminoplasty. OBJECTIVE: This study tested the hypothesis that radiographic changes and biomechanical flexibility could explain the differences in clinical outcome after cervical laminectomy and laminoplasty. SUMMARY OF BACKGROUND DATA: Although multilevel cervical laminoplasty is thought to have advantages over cervical laminectomy, clinical outcome studies have been contradictory, and no experimental study has examined the possible mechanisms for the differences after healing. METHODS: Twenty-four New Zealand White rabbits were randomized into four groups: normal, sham, C3-C6 wide laminectomy, and C3-C6 open-door laminoplasty. Clinical, radiographic, and biomechanical data were collected and compared up to 3 months after surgery. RESULTS: Laminectomy had a statistically significant poorer clinical outcome when compared with laminoplasty after 3 months of healing. Radiologic analysis showed statistically significant angular deformity in the laminectomy group compared with laminoplasty and control groups at 3 months. In contrast, biomechanical measures of flexibility, neutral zone, and range of motion showed only small differences between any of the groups at any time. CONCLUSIONS: The presence of deformity, and not a change in flexibility, is responsible for the differences in clinical outcome observed after laminectomy compared with laminoplasty in this model.

Animals↗
PubMed2000

The cervical facet capsule and its role in whiplash injury: a biomechanical investigation.

STUDY DESIGN: Cervical facet capsular strains were determined during bending and at failure in the human cadaver. OBJECTIVE: To determine the effect of an axial pretorque on facet capsular strains and estimate the risk for subcatastrophic capsular injury during normal bending motions. SUMMARY OF BACKGROUND DATA: Epidemiologic and clinical studies have identified the facet capsule as a potential site of injury and prerotation as a risk factor for whiplash injury. Unfortunately, biomechanical data on the cervical facet capsule and its role in whiplash injury are not available. METHODS: Cervical spine motion segments were tested in a pure-moment test frame and the full-field strains determined throughout the facet capsule. Motion segments were tested with and without a pretorque in pure bending. The isolated facet was then elongated to failure. Maximum principal strains during bending were compared with failure strains, by paired t test. RESULTS: Statistically significant increases in principal capsular strains during flexion-extension loading were observed when a pretorque was applied. All measured strains during bending were significantly less than strains at catastrophic joint failure. The same was true for subcatastrophic ligament failure strains, except in the presence of a pretorque. CONCLUSIONS: Pretorque of the head and neck increases facet capsular strains, supporting its role in the whiplash mechanism. Although the facet capsule does not appear to be at risk for gross injury during normal bending motions, a small portion of the population may be at risk for subcatastrophic injury.

Cadaver↗
PubMed2000

"Spinolaminar breach": an important sign in cervical spinous process fractures.

OBJECTIVE: To report the sign of "spinolaminar breach" and its likely importance in fractures of the cervical spinous processes. DESIGN: Six cases of spinous process fractures demonstrating disruption of the spinolaminar line or "spinolaminar breach" were analyzed. Lateral and anteroposterior radiographs (n=6), CT scans (n=3) and MRI scans (n=1) were reviewed together by the authors, with consensus being reached as to the radiographic findings. Clinical records were also reviewed. RESULTS: The levels of injury were C6 (n=5) and C5 (n=2). Injuries were associated with delayed anterior subluxation (n=4) and neurological deficit (n=2). Five patients were male and one was female with a mean age of 31 years (range 8-59 years). Injuries resulted from motor vehicle accidents (n=4), a motor cycle accident (n=1) and a fall (n=1). CONCLUSION: "Spinolaminar breach", or disruption of the spinolaminar line, indicates a complex spinous process fracture with extension into the lamina and spinal canal. Spinous process fractures with spinolaminar breach may have associated posterior ligamentous injury with potential for delayed instability and neurological deficit. It is important that radiologists and physicians caring for the trauma patient be aware of this sign in order to avoid misdiagnosis as a "clay shoveler's fracture", which can lead to adverse outcome.

Accidental Falls↗
PubMed2000

Clinical outcome scales for use in a rabbit model of cervical myelopathy.

This study determined the ability of an upper extremity Tarlov scale, a lower extremity Tarlov scale, and the Durham scale to predict the development of myelopathy and the likelihood of survival in a rabbit model of surgical treatments for cervical spondylotic myelopathy. Forty-eight rabbits were evaluated using the scales after cervical spinal surgery. Logistic regression analysis revealed that all three scales could predict the occurrence of myelopathy. However, only the Durham and lower extremity Tarlov scales also predicted the likelihood of survival. The Durham scale is offered as a useful predictor of myelopathy and survival in an animal model of surgical treatments for cervical spondylotic myelopathy. The lower extremity Tarlov scale is also a useful predictor of outcome; however, the upper extremity Tarlov scale is not recommended.

Animals↗
PubMed2000

The "mini brain": plasmacytoma in a vertebral body on MR imaging.

OBJECTIVE: Patients with solitary plasmacytoma in the spine frequently require a biopsy for diagnosis of their condition. We report an appearance of plasmacytoma in the spine, which is sufficiently pathognomonic to obviate biopsy. CONCLUSION: Identification of a "mini brain" in an expansile lesion in the spine is characteristic of plasmacytoma. It is important that radiologists note this characteristic because biopsy can be avoided in patients with this appearance. Although biopsy might still be required at many institutions, at our institution, surgeons find this appearance sufficiently pathognomonic to bypass biopsy and start treatment.

Adult↗
PubMed2000

Surgical correction of lumbar kyphotic deformity: posterior reduction "eggshell" osteotomy.

OBJECT: Progressive kyphotic deformity of the lumbar or thoracolumbar spine may lead to back pain, cosmetic deformity, and risk of neurological compromise. The authors describe a series of patients in whom they performed a single-stage, posterior reduction ("eggshell") osteotomy procedure to improve sagittal contour by creating lordosis within a single vertebral body. METHODS: From 1995 to 1997 the authors performed 12 osteotomy procedures in 11 patients with thoracolumbar or lumbar kyphosis. Seven patients presented with iatrogenic deformity, three with deformity secondary to traumatic injury, and one patient with ankylosing spondylitis. Their mean age at time of surgery was 46.6 years (range 23-78 years). All patients suffered from back pain and were unable to stand upright, but in only one patient were neurological findings demonstrated. The mean preoperative deformity was -26 degrees (range -90 to 0 degrees). At 6-month follow-up examination the mean sagittal contour measured 17.5 degrees (range - 17 to 44 degrees), indicating that the mean surgical correction was 40.1 degrees (range 25 to 58 degrees). All patients reported decreased back pain at follow up, and none required narcotic analgesic medication. Complications included a dense paresis that developed immediately postoperatively in a patient who was found to have residual dural compression, which was corrected by emergency decompressive surgery. One elderly patient suffered a perioperative cerebrovascular accident, and three patients suffered neurapraxia with transient muscle weakness of the quadriceps. There was one case of a dural tear. There were no deaths, and prolonged intensive care stays were not required. CONCLUSIONS: Single-level posterior reduction osteotomy provides excellent sagittal correction of kyphotic deformity in the lumbar region, with a risk of cauda equina and root and plexus compromise due to the extensive neural exposure.

Adult↗
PubMed1999

Functional outcome of plate fusions for disorders of the occipitocervical junction.

Twenty-eight patients with average followup of 27 months (range, 12-51 months) required occipitocervical fusion with plates. A 1992 to 1996 consecutive case series enrolled patients prospectively from two institutions. Five surgeons participated. Sixteen patients had inflammatory arthritis; four, osteogenesis imperfecta; three, tumors; three, congenital anomalies; one, pseudarthrosis after odontoid fracture; and one, osteoarthritis. Twenty-two of 28 (78.6%) patients had serious comorbid medical conditions. Additional halo immobilization of 6 weeks was used in 16 of 27 patients. Four patients required revision surgery. No patients showed a decline in neurologic status and average neurologic improvement was one Nurick grade. Two-year followup showed 13 (50%) excellent, nine (34.6%) good, two (7.7%) fair, and two (7.7%) poor outcomes based on a functional outcome scale. There were three deaths during the followup period (overall mortality rate of 10.7%). One death was attributable to airway obstruction, one death 14 months postoperatively was attributable to late Methicillin resistant Staphylococcus aureus sepsis at the bone graft donor site, and one death 41 months postoperatively was attributable to a stroke. The overall fusion rate was 85.2% (23 of 27 patients), with a 96.3% (26 of 27 patients) occipitocervical fusion rate. Three patients had a possible asymptomatic end segment pseudarthrosis with screw loosening. Twenty-two of 26 (84.6%) interviewed patients would choose the surgery again if given the choice.

Adolescent↗
PubMed1999

MR imaging of fibrocartilaginous masses arising on the margins of spondylolysis defects.

OBJECTIVE: Spondylolysis is reported in up to 7% of the population. An uncommon process that can accompany a pars interarticularis defect is a fibrocartilaginous mass, which can cause impression on the nerve roots and thecal sac. Recognition is important so that the presence may be addressed at the time of surgery. This report describes the MR imaging appearance and clinical significance of a fibrocartilaginous mass in association with spondylolysis. MATERIALS AND METHODS: We reviewed data regarding 336 patients who had lumbar spine imaging at our institution during a 12-month period. Contiguous axial and sagittal MR imaging using T1-weighted and fast spin-echo T2-weighted sequences was used. Images were evaluated for a mass of tissue surrounding the pars defect with MR characteristics of cartilaginous and fibrous low signal intensity on T1-weighted images and low to intermediate signal intensity on T2-weighted images. The position of the fibrocartilaginous mass and its relation to the thecal sac were noted. Surgical correlation between those patients with a fibrocartilaginous mass and those without was examined. RESULTS: Twenty-nine (8.6%) of 336 patients were identified as having a pars interarticularis defect. A fibrocartilaginous mass was present in 26 (90%) of 29 patients. Six (21%) of the 29 patients had a mass effect on the thecal sac. Of the remaining 23 patients, 20 had a fibrocartilaginous mass external to the thecal sac, and three did not show any fibrocartilaginous mass. Histologic analysis in one patient confirmed the fibrous and cartilaginous nature of the lesion at the pars defect. CONCLUSION: A fibrocartilaginous mass was present in 90% of the patients with spondylolysis. Mass effect on the thecal sac that required surgery was identified in 21% of the patients with spondylolysis. Awareness of this mass and proper imaging protocols will enable the radiologist to preoperatively alert the surgeon to its presence.

Adult↗
PubMed1997

The effects of padded surfaces on the risk for cervical spine injury.

STUDY DESIGN: This is an in vitro study comparing cervical spine injuries produced in rigid head impacts and in padded head impacts. OBJECTIVES: To test the hypothesis that deformable impact surfaces pose a greater risk for cervical spine injury than rigid surfaces using a cadaver-based model that includes the effects of the head and torso masses. SUMMARY OF BACKGROUND DATA: It is widely assumed that energy-absorbing devices that protect the head from injury also reduce the risk for neck injury. However, this has not been demonstrated in any experimental or epidemiologic study. On the contrary, some studies have shown that padded surfaces have no effect on neck injury risk, and others have suggested that they can increase risk. METHODS: Experiments were performed on 18 cadaveric cervical spines to test 6 combinations of impact angle and impact surface padding. The impact surface was oriented at -15 degrees (posterior impact), 0 degree (vertex impact), or +15 degrees (anterior impact). The impact surface was either a 3-mm sheet of lubricated Teflon or 5 cm of polyurethane foam. RESULTS: Impacts onto padded surfaces produced significantly larger neck impulses (P = 0.00023) and a significantly greater frequency of cervical spine injuries than rigid impacts (P = 0.0375). The impact angle was also correlated with injury risk (P < 0.00001). CONCLUSIONS: These experiments suggest that highly deformable, padded contact surfaces should be used carefully in environments where there is the risk for cervical spine injury. The results also suggest that the orientation of the head, neck, and torso relative to the impact surface is of equal if not greater importance in neck injury risk.

Adult↗
PubMed1997

Strength and stability of posterior lumbar interbody fusion. Comparison of titanium fiber mesh implant and tricortical bone graft.

STUDY DESIGN: A paired comparison was done of the bending flexibility and compression strength of tricortical bone graft and titanium fiber mesh implants in a human cadaver model of posterior lumbar interbody fusion. OBJECTIVES: To test the hypothesis that a titanium fiber mesh implant and a tricortical bone graft provide adequate and equal mechanical strength and stability in posterior lumbar interbody fusion constructs. SUMMARY OF BACKGROUND DATA: Although studies of posterior lumbar interbody fusion constructs have been performed, the authors are unaware of any study in which the strength and stability of a titanium fiber mesh implant are compared with those of tricortical bone graft for posterior lumbar interbody fusion in the human cadaver lumbar spine. METHODS: Changes in neutral zone and range of motion were measured in a bending flexibility test before and after placement of posterior lumbar interbody fusion constructs. Tricortical bone graft and titanium fiber mesh implant construct stability than were compared in a paired analysis. The constructs than were loaded to failure to evaluate construct strength as a function of graft material and bone mineral density. RESULTS: The posterior lumbar interbody fusion procedure produced statistically significant decreases in neutral zone when compared with the intact spine. No statistically significant differences in neutral zone, range of motion, or strength were detected between the two implants. Construct strength correlated strongly with bone mineral density. CONCLUSIONS: Posterior lumbar interbody fusion procedures result in equal or improved acute stability for titanium fiber mesh implants and tricortical bone graft implants when used without additional posterior stabilization.

Aged↗
PubMed1996

The role of imaging and in situ biomechanical testing in assessing pedicle screw pull-out strength.

STUDY DESIGN: This study determined the predictive ability of quantitative computed tomography, dual energy x-ray absorptiometry, pedicular geometry, and mechanical testing in assessing the strength of pedicle screw fixation in an in vitro mechanical test of intra-pedicular screw fixation in the human cadaveric lumbar spine. OBJECTIVE: To test several hypotheses regarding the relative predictive value of densitometry, pedicular geometry, and mechanical testing in describing pedicle screw pull-out. SUMMARY OF BACKGROUND DATA: Previous investigations have suggested that mechanical testing, geometry, and densitometry, determined by quantitative computed tomography or dual energy x-ray absorptiometry, predict the strength of the screw-bone system. However, no study has compared the relative predictive value of these techniques. METHODS: Forty-nine pedicle screw cyclic-combined flexion-extension moment-axial pull-out tests were performed on human cadaveric lumbar vertebrae. The predictive ability of quantitative computed tomography, dual energy x-ray absorptiometry, insertional torque, in situ stiffness, and pedicular geometry was assessed using multiple regression. RESULTS: Several variables correlated to force at failure. However, multiple regression analysis showed that bone mineral density of the pedicle determined by quantitative computed tomography, insertional torque, and in situ stiffness when used in combination resulted in the strongest prediction of pull-out force. No other measures provided additional predictive ability in the presence of these measures. CONCLUSIONS: Pedicle density determined by quantitative computed tomography when used with insertional torque and in situ stiffness provides the strongest predictive ability of screw pull-out. Geometric measures of the pedicle and density determined by dual energy x-ray absorptiometry do not provide additional predictive ability in the presence of these measures.

Absorptiometry, Photon↗
PubMed1996

Dynamic responses of the head and cervical spine to axial impact loading.

This study explores the inertial effects of the head and torso on cervical spine dynamics with the specific goal of determining whether the head mass can provide a constraining cervical spine end condition. The hypothesis was tested using a low friction impact surface and a pocketing foam impact surface. Impact orientation was also varied. Tests were conducted on whole unembalmed heads and cervical spines using a drop track system to produce impact velocities on the order of 3.2 m s-1. Data for the head impact forces and the reactions at T1 were recorded and the tests were also imaged at 1000 frames s-1. Injuries occurred 2-19 ms following head impact and prior to significant head motion. Average compressive load a failure was 1727 +/- 387 N. Decoupling was observed between the head and T1. Cervical spine loading due to head rebound constituted up to 54 +/- 16% of the total axial neck load for padded impacts and up to 38 +/- 30% of the total axial neck load for rigid impacts. Dynamic buckling was also observed; including first-order modes and transient higher-order modes which shifted the structure from a primarily compressive mode of deformation to various bending modes. These experiments demonstrate that in the absence of head pocketing, the head mass can provide sufficient constraint to cause cervical spine injury. The results also show that cervical spinal injury dynamics are complex, and that a large sample size of experimentally produced injuries will be necessary to develop comprehensive neck injury models and criteria.

Adult↗
PubMed1996

Experimental impact injury to the cervical spine: relating motion of the head and the mechanism of injury.

The purpose of this study was to analyze, with use of an impact model, the relationships among motion of the head, local deformations of the cervical spine, and the mechanisms of injury; the model consisted of the head and neck of a cadaver. Traditionally, the mechanisms of injury to the cervical spine have been associated with flexion and extension motions of the head and neck. However, the classification of the mechanisms is not always in agreement with the patient's account of the injury or with lacerations and contusions of the scalp, which indicate the site of the impact of the head. Eleven specimens were dropped in an inverted posture with the head and neck in an anatomically neutral position. Forces, moments, and accelerations were recorded, and the impacts were imaged at 1000 frames per second. The velocity at the time of impact was on the order of 3.2 meters per second. The angle and the padding of the impact surface varied. Observable motion of the head did not correspond to the mechanism of the injury to the cervical spine. Injury occurred 2.2 to 18.8 milliseconds after impact and before noticeable motion of the head. However, the classification of the mechanism of the injuries was descriptive of the local deformations of the cervical spine at the time of the injury. Accordingly, it is a useful tool in describing the local mechanism of injury. Buckling of the cervical spine, involving extension between the third and sixth cervical vertebrae and flexion between the seventh and eight cervical vertebrae, was observed. Other, more complex, buckling deformations were also seen, suggesting that the deformations that occur during impact are so complex that they can give rise to a number of different mechanisms of injury.

Adult↗
PubMed1995

Metastatic melanoma to the spine. Demographics, risk factors, and prognosis in 114 patients.

STUDY DESIGN: One-hundred-fourteen patients with metastatic melanoma of the spine were retrospectively reviewed. OBJECTIVE: The goal was to define the demographics, risk factors, and prognosis for this population. SUMMARY OF BACKGROUND DATA: The incidence of melanoma is increasing faster than any other cancer. Therefore, orthopedic and neurologic surgeons will be increasingly confronted by patients with spinal metastases from melanoma. However, the demographics, risk factors, and prognosis remain unclear. METHODS: From 7010 consecutive patients with melanoma, 114 were identified with clinically or radiographically evident spinal metastases. A comparison was made between these patients and the remainder of the population with melanoma seen at our institution using contingency table analysis with statistical significance determined by a chi-squared test. Survival data were represented by Kaplan-Meier curves, and log-rank testing was used for statistical comparisons. RESULTS: Risk factors associated with the development of these metastases included primary lesions that were ulcerated, deeper than 0.76 mm, or of Clark level II, or located on the trunk or mucosal surfaces. The median survival time for all patients was 86 days, but this was reduced in patients with more than one metastatic site in addition to the spine. CONCLUSION: The prognosis for most patients with spinal metastases from melanoma is dismal. However, patients with metastatic disease limited to the spine and one other organ may survive for a relatively prolonged time and may be candidates for surgical intervention directed toward symptomatic relief.

Adult↗
PubMed1995

Measurement of vertebral cortical integrity during pedicle exploration for intrapedicular fixation.

STUDY DESIGN: This study determined the predictive ability of electrical impedance measurement in detecting cortical perforation in a porcine model of pedicular exploration. OBJECTIVE: This study tested the hypothesis that a large decrease in electrical impedance would occur as a result of perforation of the vertebral cortex by the pedicle probe. SUMMARY OF BACKGROUND DATA: The resistivity of cortical bone has been reported to be 25 to 100 times greater than that of soft tissues. METHODS: A total of 42 pedicles of the lumbar spines of six swine were explored using the instrumented pedicle probes. RESULTS: Using a 1 microAmp 30-Hz current source, measurement of electrical impedance predicted cortical rupture with a sensitivity, specificity, and accuracy of 95%. Maximum applied voltages of 2.8 mV did not result in myogenic stimulus. CONCLUSIONS: Electrical impedance measurement provides an accurate real-time measurement of cortical perforation. This technique is adapted readily for use with pedicular screws and screw tape. Further investigation to determine the clinical use of this technique is recommended.

Animals↗
PubMed1995

Severe open subtalar dislocations. Long-term results.

Fifteen adolescents and adults were assessed an average of eighteen years after a type-III open subtalar dislocation. There were ten lateral and five medial dislocations. Associated injuries included ten injuries of the tibial nerve, seven of which were complicated by causalgia; five ruptures of the posterior tibial tendon; five lacerations of the posterior tibial artery; twelve articular fractures involving the subtalar joint; three articular fractures of the talonavicular joint; three fractures of the talar dome; and three malleolar fractures. Osteonecrosis of the body of the talus was found in five of the fifteen patients. It was treated with a triple arthrodesis in all five patients, one of whom had a subsequent conversion to a pantalar arthrodesis. Subtalar arthrodesis was done, because of post-traumatic osteoarthrosis, in two other patients. On functional assessment at the long-term follow-up examination, all patients reported some pain in the ankle, nine had difficulty climbing stairs, fourteen had difficulty walking on uneven surfaces, and eleven wore modified shoes. The patients who had had a tarsal arthrodesis returned to their pre-injury occupation or to a less strenuous job. Four patients who had persistent causalgia did not return to work. We concluded that open subtalar dislocation is a distinctly severe injury and that only fair functional and poor anatomical results can be expected in most patients.

Adolescent↗