Sanford J. Larson

Lateral extracavitary approach to the spine for thoracic disc herniation: report of 23 cases.

Twenty-three patients were operated upon for thoracic disc herniation between 1973 and 1982. The lateral approach to the vertebral column was used in each. Most patients had severe local pain; 13 had severe myelopathy or complete motor paralysis, including 4 who had become paraplegic after laminectomy. Eleven patients had calcified discs or osteophytic ridges. Air myelography and computed tomography were diagnostic in all cases. Postoperatively, 17 patients achieved significant relief of pain, 20 improved neurologically, and none became worse. Complications of the operation were minimal. The lateral extracavitary approach to the spine is a valuable technique for the management of thoracic disc herniation.

Experimental spinal injuries with vertical impact.

Fifteen fresh, intact, human male cadavers suspended head down were dropped vertically from a height of 0.9- 1.5 meters. In eight specimens the heads were restrained to simulate muscle forces. The head-neck complex was oriented for maximal axial loading of the cervical and upper thoracic spine. In several cadavers, load cells were placed in cervical bodies. Head impact forces of 3,000-7,000 N in the unrestrained, and 9,800-14,600 N in the restrained, cadavers were recorded. There were more cervical and upper thoracic fractures in the restrained cadavers than in the nonrestrained subjects. The biomechanic and pathologic findings, including results of cryomicrotomography and computed tomography (CT), are discussed.

Dynamic response of human cervical spine ligaments

This study was undertaken to investigate the dynamic response of human cervical spine ligaments. Uniaxial tensile failure tests were conducted on anterior longitudinal ligament (AL) and ligamentum flavum (LF) structures. These ligaments were tested under In situ conditions by transecting all the elements except the one (AL or LF) under study. A fixture was designed to properly align the specimen to induce a uniaxial mode of loading. A six-axis load cell was placed at the distal end of the specimen. The proximal end of the specimen was attached to the piston of a specially designed electrohydraulic testing device. The biomechanical properties of the ligaments were determined at four different loading rates of 8.89,25.0, 250.0 and 2500 mm/sec. The mechanical response indicated nonlinear and sigmoidal characteristics. The ultimate tensile failure load, stiffness, and energy-absorbing capacity at failure were found to increase with increasing loading rates for both the AL and LF. However, the distractions at failure did not indicate this tendency. While the ultimate tensile force and ultimate energy-absorbing capacity varied nonllnearly with the logarithm of the loading rate, the stiffness varied linearly.

Finite element modeling of the C4–C6 cervical spine unit

This study was conducted to develop a detailed, three-dimensional, anatomically accurate finite element model of the human cervical spine structure using close-up computed tomography scans and to validate against experimental data. The finite element model of the three vertebra segment C4-C6 unit consisted of 9178 solid elements and 1193 thin shell elements. The force-displacement response under axial compression correlated well with experimental data. Because of the inclusion of three levels in the spinal structure, it was possible to determine the internal mechanics of the various components at each level. The applicability of the model was illustrated by adopting appropriate material properties from literature. Results indicated that, the stresses in the anterior column were higher compared to the posterior column at the inferior level, while the opposite was found to be true at the superior level. The superior and inferior endplate stresses were higher in the middle vertebral body compared to the adjacent vertebrae. In addition, the stresses in the cancellous core of the middle, unconstrained vertebral body were higher. The present three-dimensional finite element model offers an additional facet to a better understanding of the biomechanics of the human cervical spine.

Management of odontoid fractures.

Fifty-one adults with odontoid fractures were treated between 1966 and 1979. Approximately 50% had additional trauma; over half of the patients were younger than 40 years old. Three patients presented with myelopathy: 1 was complete at C-2 and the others recovered. Cervical roentgenograms were initially considered normal in 4 patients. The fracture was through the base of the odontoid process (Type 2) in 49 patients and was into the body of C-2 (Type 3) in 2 patients. Thirty-four patients underwent early posterior cervical fusion, whereas the others were treated initially with external immobilization. Only the 2 patients with Type 3 fractures healed in Minerva casts. All 15 Type 2 fractures initially treated conservatively failed to heal and were fused. There were no age, sex, or radiological characteristics (other than fracture location) peculiar to the nonunion group. Two patients died after operation, and there was 1 minor infection in an iliac crest donor site. All patients who were operated upon demonstrated evidence of fusion within 6 weeks after operation; 16 demonstrated healing of the fracture at 6 months. After follow-up ranging from 16 months to 15 years, 7 patients complain of neck pain, of whom 6 do not require regular analgesics. Of 40 patients tested, 7 have evidence of decreased range of motion in the neck, of whom 6 have loss of less than 15% of normal motion. Traction followed by posterior cervical fusion is effective treatment for Type 2 odontoid fractures. The surgical and long term morbidity is low, and satisfactory fusion can be expected.

Epidemiology and injury biomechanics of motor vehicle related trauma to the human spine

Approximately 40% of spinal cord injuries occur in motor vehicle accidents, resulting in high risks of disability and fatality. This chapter on epidemiology and injury biomechanics of motor vehicle related trauma to the human spine is from a comprehensive textbook on occupant and vehicle responses in rollovers. The authors report on a study in which motor vehicle accident related epidemiologic data were obtained from clinical and computerized accident (National Accident Sampling System, NASS) files. The authors undertook the study to determine the most commonly injured anatomic levels of the cervical spine, to classify these injuries based on an impairment scale, to determine the mechanism of injury at each spinal level, to evaluate the differences (if any) between the patient (survivors) and fatality data with respect to the location and mechanism of injury, and to compare this data obtained from a localized population with literature results and national samples. Results show that while injuries to the cervical column are complex and may occur at any spinal level, they concentrate statistically in two primary zones: at the craniocervical junction for fatal victims, and in the lower cervical spine for survivors. A strong association was also found between craniofacial and cervical spine trauma.

Surgical management of nontuberculous thoracic and lumbar vertebral osteomyelitis: Report of 33 cases

BACKGROUND Thirty-three patients with nontuberculous pyogenic thoracic and lumbar vertebral osteomyelitis were treated surgically. Indications for surgery were either progression of disease despite adequate antibiotic therapy, neurologic deficit, or both. The most common initial symptom was back pain. Seven patients had diabetes, seven patients were intravenous drug users, two patients were receiving immunosuppressive therapy, and seven patients had a debilitating disease. Eleven had infections elsewhere in their bodies. Prior to surgery organisms were grown from blood in 10 patients and at surgery in 15 patients. METHODS Infection was evident on plain films in all patients, and either a CT scan or MRI was obtained in each. The lateral extracavitary approach was used for resection of granulation tissue and infected bone ventral to the dura. Interbody bone grafts were placed in 19 patients, usually when bone resection was extensive. Posterior instrumentation was placed in 17 patients at a second procedure 10 days-2 weeks following initial operation. Intravenous antibiotics were administered for 4-6 weeks following surgery, and solid fusion was obtained in all patients. RESULTS Neurologic deficit was present in 28 patients prior to surgery and was functionally significant in 18 patients. Of the 11 patients with severe paraparesis, 10 achieved good functional recovery. These patients were able to walk, three with assistance and seven without, and all those who were unable to void regained this ability. CONCLUSIONS Surgical debridement, interbody fusion, and posterior instrumentation is a safe and effective treatment for vertebral osteomyelitis and is indicated when neurologic deficit or bone destruction progress despite adequate antibiotic therapy.

Compression Injuries of the Cervical Spine: A Biomechanical Analysis

Three intact cadavers and 10 isolated cervical spinal columns underwent compression, with forces directed vertically, forward, or rearward. Failure modes were often different than force directions. The loads required to produce bony injury or ligamentous disruption ranged from 645 to 7439 N. Flexion and extension injuries were produced at approximately 50% of the loads required for axial compression failures. The direction of force delivery correlated only partially with the resulting pathological condition. Clinical decisions based on retrospective analysis of roentgenograms may not account for the variability of forces and the prominence of ligament injuries seen in spinal trauma. Some of the difficulties encountered in biomechanical analyses of spinal trauma are discussed.

Microtrauma in the lumbar spine: a cause of low back pain.

Excessive mechanical stress on the intervertebral disc may be one of the causes of low back pain. Most studies testing this thesis, however, have been based on quantification of the mechanical response of functional units at failure. Typically, radiography is used to demonstrate trauma to the vertebral body at the failure load. The description of failure and radiographic demonstration of damage are meaningful in specifying the tolerance limits of the structure. It is important, however, to understand the sequence underlying the initiation of injury, which may occur at subfailure physiological loads. In this study, we identified the initiation of injury to the lumbar spine by subjecting functional units to axial compressive loads using the mechanical response as a basis. Because conventional radiography failed to detect trauma at this level, advanced sectioning techniques were used. The initiation of injury (microtrauma) is defined as the point on the load-deflection curve where the structure exhibits a decreasing level of resistance for the first time before reaching its ultimate load-carrying capacity. The load deflection curve on this basis was classified into the ambient or preload phase, physiological loading phase, traumatic phase, and post-traumatic phase. Structures loaded to the end of the physiological loading phase did not exhibit any yielding or microtrauma. Injury in the form of microfractures of the endplate not detected on radiography, however, was observed under cryomicrotomy for structures loaded into the traumatic loading phase.

Management of bilateral locked facets of the cervical spine.

A total of 28 cases of cervical spine dislocation with bilateral locking of facets treated between 1976 and 1984 were analyzed to determine whether treatment modality had any effect on outcome based on cord or root function. Motor vehicle accidents were responsible for 19 cases; the most common levels of dislocation were C-5, C-6 and C-6, C-7, with 10 each. Twenty patients were admitted with complete myelopathies. Ten patients whose dislocations were successfully reduced with traction had no neurological changes, but 1 reduced elsewhere deteriorated from a C-5 to C-2 level. Eleven of these patients underwent posterior cervical fusions after delays of 1 to 17 days (mean = 6.3); 2 died, and 1 patient achieved slight root return. Seven underwent anterior decompression and fusion or combined anterior and posterior approaches after delays of 9 to 120 days. One patient died in the postoperative period, 1 had substantial recovery of cord function, and 5 had recovery of root function. There was no operation or improvement in 2 patients. Eight patients had incomplete myelopathies; 4 were initially reduced, with 2 improving slightly as a result. Three patients underwent posterior fusions with foraminotomies with minimal improvement. Five had anterior or combined approaches; these patients improved at least one neurological grade each, including 3 who became newly ambulatory. All 24 surviving patients achieved spinal stability, although it occurred slightly earlier in the anterior fusion groups. Surgical approaches designed to provide spinal stability and restore the normal anatomy of the spinal canal and neural foramina may be of functional benefit in the management of these dislocations.