Search PubMed⌕ Search

Biomedical subjects

R W Porter

Publications and source records attributed to R W Porter.

At least 19 recordsLinked to original sources
PubMed2001

Can a short spinal cord produce scoliosis?

Some patients with scoliosis have a relatively short vertebral canal. This poses the question of whether a short spinal cord may sometimes cause scoliosis. The present paper presents two observations that may support this concept. It presents a scoliosis model demonstrating what effect a short, unforgiving spinal cord might have on the spinal column. The model uses two flexible parallel tubes with the facility to tighten one. It demonstrates that a short, unforgiving spinal cord could produce the abnormal rotatory anatomy observed at the apex in scoliosis, with first lordosis, then lateral deviation and finally a rotation of the vertebral column, with the rotation occurring between the canal and the vertebral body, around the axis of the cord. The anatomy of the apical vertebra is described from two museum specimens, a computed tomography (CT) myelogram and seven magnetic resonance imaging (MRI) studies. The study confirms that the vertebral canal and the intervertebral foraminae retain their original orientation. The spinal cord is eccentric in the canal towards the concavity of the curve; the major component of rotation occurs anterior to the vertebral canal and the axis of this rotation seems to be at the site of the spinal cord. These observations do not establish that a short spinal cord will result in scoliosis, but the results are compatible with this hypothesis, and that impairment of spinal cord growth factors may sometimes be responsible for scoliosis.

Humans↗
PubMed2000

Idiopathic scoliosis: the relation between the vertebral canal and the vertebral bodies.

STUDY DESIGN: The axial length of the vertebral canal and the anterior aspect of the vertebrae were measured in 36 skeletons, 15 with probable idiopathic scoliosis. OBJECTIVES: To compare the discrepancy in length of the vertebral canal and the anterior spinal column in skeletons having probable idiopathic scoliosis with the degree of deformity. SUMMARY AND BACKGROUND DATA: In idiopathic scoliosis, the vertebral bodies rotate toward the convexity of the curve, whereas the vertebral canal tends to retain a midline position. The vertebral canal therefore will be relatively short. The degree of shortening has not been described previously, nor its relation with the degree of deformity. METHODS: The axial length of the vertebral canal and the anterior aspect of the vertebral bodies were measured in 36 skeletons: 8 with normal spines, 13 with kyphosis, and 15 with probable idiopathic scoliosis. The relative shortening in the scoliotic spines was correlated with the Cobb angle and the degree of rotation. RESULTS: No significant difference in length was found between the vertebral canal and the vertebral column in the normal spines. The kyphotic spines had canals significantly longer than the vertebral length (P<0.025). All but one of the scoliotic spines had short vertebral canals (P<0.01). The degree of discrepancy was related to the Cobb angle (r = -0.50; P< 0.05), and particularly to the degree of rotation (r = -0.88; P< 0.001). CONCLUSIONS: The findings have surgical and etiologic implications. The results are consistent with a conceivable hypothesis that in some patients with idiopathic scoliosis, there may be impaired growth in the length of the spinal cord, the posterior elements are tethered, and as the vertebral bodies continue to grow, they become lordotic and then rotate.

Humans↗
PubMed2000

Surgical treatment of lumbar spondylolisthesis.

This article provides an overview of studies that address the medical and surgical treatment of lumbar spondylolisthesis, both degenerative and isthmic. Although the efficacy of decompression for symptomatic lumbar stenosis recalcitrant to conservative treatment has been demonstrated, the addition of instrumentation to a fusion procedure remains controversial. The senior author's (VKHS) experience with pedicle screw fixation and fusion for lumbar spondylolisthesis, the addition of interbody fusion, and spinal navigation is reviewed.

Humans↗
PubMed2000

Role of health communications in Russia's diphtheria immunization program.

As part of a broader program in health communication assistance, project staff from Basic Support for Institutionalizing Child Survival worked with staff from Russia's oblast (regional) public health agencies to design and implement communication activities supporting local diphtheria immunization efforts. Because aggressive community outreach efforts and strong administrative sanctions had already achieved impressive adult coverage rates for first doses of diphtheria toxoid vaccine, communication interventions emphasized the need for second and third doses. Outcomes were assessed through vaccination coverage data and more qualitative measures. In one project site, the increase in adult coverage (two or more doses) was very modest. In a second site, with a stronger communications component, coverage increased significantly (from 20% to 80%). Although it is not possible to disentangle completely the effects of communications from other aspects of oblast immunization programs, these and other outcome data suggest that health communications can play an important role in Russia's ongoing mass immunization efforts.

Adult↗
PubMed1999

Localized stresses in the intervertebral disc resulting from a loose fragment. A theory for fissure and fragment.

STUDY DESIGN: A theoretical analysis of estimate the stresses generated in the anulus fibrosus by a loose fragment. OBJECTIVES: To test the hypothesis that a fragment can generate stress concentrations in an intervertebral disc that could lead to the progression of a fissure, and to provide a theoretical foundation for the laboratory model of lumbar disc protrusion, which proposes that a fragment is formed first and that prolapse is the final event of a chronic process. SUMMARY OF BACKGROUND DATA: A laboratory model was developed by Brinckmann and Porter in 1994, which indicated that introducing a fragment into an otherwise intact disc resulted in rapid failure of the disc under physiologic loads and flexion. Identical in vitro surgery with no reintroduction of fragments did not result in failure. METHODS: A theoretical model was developed in which a spherical fragment was impressed against a plane surface, representing the inner surface of the anulus. The stiffness of the sphere and that of the surface were varied, and the stresses generated in the anulus were calculated as a function of applied load. RESULTS: The contact stress and the shear stress increased as the stiffness of the fragment approached and exceeded that of the matrix. Increases in stiffness to more than four times that of the matrix resulted in little further increase in stress. Peak shear stresses are developed in the bulk matrix beyond the point of contact between the fragment and the anulus. For relatively small forces on the fragment, these stresses were comparable with those found in diarthrodial joints. CONCLUSIONS: It is shown that a fragment in an intervertebral disc produces localized areas of increased stress. Fatigue over long periods at these stresses could result in fissuring and premature failure of the tissue.

Humans↗
PubMed1999

Nerve root pressure in lumbar disc herniation.

STUDY DESIGN: The contact pressure between the nerve root and lumbar disc herniation was measured and compared with clinical features. OBJECTIVE: To assess levels of actual compression to the nerve root in clinical cases. SUMMARY OF BACKGROUND DATA: Actual levels of pressure to the nerve root of lumbar disc herniation in clinical cases is unknown. METHODS: The study was performed on 34 patients who had lumbar disc herniation. All of them had been treated by open discectomy. After laminotomy, nerve root pressure was measured by inserting a transducer between the nerve root and the disc herniation. The magnitude of pressure was compared with clinical features. RESULTS: Nerve root pressures before discectomy were varied from 7 mm Hg to 256 mm Hg (mean, 53 mm Hg). After discectomy, the contact pressure was 0 mm Hg in all cases. There were no significant correlations between the magnitude of nerve root pressure and limits to the degree of straight leg raising, duration of symptoms, and age of the patients. However, the magnitude of the pressure in patients with neurologic deficits and trunk list was significantly higher than in the absence of these findings. CONCLUSIONS: The contact pressure exerted by lumbar disc herniation on the nerve roots was recorded during surgical intervention, and the mean pressure was 53 mm Hg. The magnitude of nerve root pressure was not correlated with the degree of straight leg raising, but with the severity of neurologic deficits.

Adolescent↗
PubMed1999

Cervical and trochanteric hip fractures: bone mass and other parameters.

We examined 310 hip fracture patients (55 men, 255 women) to identify differences in those patients who had suffered a cervical fracture compared with those with a trochanteric fracture of the hip. Patients underwent a dual-energy X-ray absorptiometry (DXA) scan of their hip and total body and quantitative ultrasound (QUS) scans of their heel. Other measurements included medical/drug history. Significant differences were found for broadband ultrasound attenuation (BUA) and DXA total-body measurements, with those with a cervical fracture having a higher bone mass. Those with a trochanteric fracture showed a significantly higher incidence of stroke (12.8% vs. 6.3%, p = 0.05), while high blood pressure/antihypertensive therapy was significantly more common in the cervical fracture group (11.6% vs. 4.3%, p < 0.03). Therefore, it is not only bone parameters that differ in these patients. In the presence of certain medical conditions, preventative therapy may be directed to managing co-existing conditions as well as improving bone density.

Absorptiometry, Photon↗
PubMed1999

Predicting a second hip fracture.

In an attempt to identify a high-risk cohort of patients, who could be offered preventive therapy, we assessed patients who had suffered one hip fracture. A total of 394 patients were prospectively followed to determine those who had suffered a second fracture. Entry bone mass of the unfractured hip and total body was examined by dual X-ray absorptiometry (DXA) and of the os calcis, by quantitative ultrasound (QUS), along with various clinical parameters. The relative risks in the QUS parameters did not reach significance, except for broadband ultrasound attentuation as measured by the McCue CUBA Clinical, whereas femoral neck and total body bone mineral density also reached significance. Lowest quartile body weight was also a significant risk factor as were occurrence of a new fall and poor mobility score. Using Receiver Operator Characteristic curves, we found no significant differences between DXA trochanter or for the Mini Mental State Examination score in predicting those who sustained a second hip fracture. In this elderly group risk factors are almost as good as bone mass at predicting those who will sustain a second hip fracture. Low body weight and poor mobility could be used as triggers for the use of preventive therapy without the use of bone mass measurements and to target expensive preventive therapy to reduce fracture risk.

Absorptiometry, Photon↗
PubMed1999

Cavernous malformations of the brainstem: experience with 100 patients.

OBJECT: In this study the authors review surgical experience with cavernous malformations of the brainstem (CMBs) in an attempt to define more clearly the natural history, indications, and risks of surgical management of these lesions. METHODS: The authors retrospectively reviewed the cases of 100 patients (38 males and 62 females; mean age 37 years) harboring 103 lesions at treated a single institution between 1984 and 1997. Clinical histories, radiographs, pathology records, and operative reports were evaluated. The brainstem lesions were distributed as follows: pons in 39 patients, medulla in 16, midbrain in 16, pontomesencephalic junction in 15, pontomedullary junction in 10, midbrain-hypothalamus/thalamus region in two patients, and more than two brainstem levels in five. The retrospective annual hemorrhage rate was most conservatively estimated at 5% per lesion per year. Standard skull base approaches were used to resect lesions in 86 of the 100 patients. Intraoperatively, all 86 patients were found to have a venous anomaly in association with the CMB. Follow up was available in 98% (84 of 86) of the surgical patients. Of these, 73 (87%) were the same or better after surgical intervention, eight (10%) were worse, and three (4%) died. Two surgical patients were lost to follow-up review. Incidences of permanent or severe morbidity occurred in 10 (12%) of the surgically treated patients. The average postoperative Glasgow Outcome Scale score for surgically treated patients was 4.5, with a mean follow-up period of 35 months. CONCLUSIONS: The natural history of CMBs is worse than that of cavernous malformations in other locations. These CMBs can be resected using skull base approaches, which should be considered in patients with symptomatic hemorrhage who harbor lesions that approach the pial surface. Venous anomalies are always associated with CMBs and must be preserved.

Adolescent↗
PubMed1999

Sporadic unifocal infantile myofibromatosis involving the skull. Case report.

Infantile myofibromatosis involving the skull is a benign disease if there is a solitary lesion. However, the multifocal form with skull involvement may portend a lethal course in the 1st year of life if there is involvement of the heart, lungs, or gastrointestinal tract. The authors report the case of a 3-year-old boy with an enlarging left parietal skull lesion that had been present since infancy. Increasing pain and the need to obtain tissue for diagnosis led to resection of the lesion by means of a small craniectomy. Further evaluation revealed no other lesions. A distinctly rare disease is presented, and the need for staging in children younger than 2 years of age is suggested to rule out cardiac, pulmonary, or gastrointestinal involvement.

Child, Preschool↗
PubMed1999

Subdural hematoma from a Type I spinal arteriovenous malformation. Case report.

The authors report a patient in whom a subdural hematoma developed from a Type I spinal arteriovenous malformation (AVM). The patient became symptomatic with back pain, and magnetic resonance imaging revealed a spinal subdural hematoma. Selective spinal angiography, however, failed to demonstrate a pathological process. The patient underwent exploratory laminoplasty that revealed a subdural extraarachnoid hematoma with an underlying Type I spinal AVM, which was surgically obliterated. The patient recovered completely. Subdural hematomas that affect the spine are rare. Although a negative result was obtained using selective spinal angiography, exploratory surgery should be considered for the evacuation of a subdural hematoma and possibly for the definitive treatment of a spinal AVM.

Adult↗
PubMed1999

Spinal arteriovenous malformations.

Spinal cord arteriovenous malformations encompass a variety of distinct lesions with aberrant connections between the arterial and venous circulation. Symptomatology and clinical presentation of such lesions are directly related to their location and particular pathophysiology. In the authors' surgical experience, 90% of patients have had the same or improved neurologic function and long-term follow-up.

Arteriovenous Malformations↗