Biomedical subjects
Publications and source records attributed to M A Edgar.
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STUDY DESIGN: An 18-year-old patient with "idiopathic" adolescent scoliosis is presented. A thoracic syrinx was detected as an incidental finding during magnetic resonance imaging of the spine. OBJECTIVES: Syringomyelia may be a risk factor for neurologic injury during correction of scoliosis, and in these cases, spinal cord monitoring may be of particular value. BACKGROUND DATA: Spinal distraction and instrumentation carry a risk of neurologic damage in patients with scoliosis and associated syringomyelia. Syringomyelia is a cause of scoliosis, and although neurologic problems are the usual symptom, scoliosis may be the only sign at initial examination. A higher risk of neurologic injury has been reported in corrective surgical treatment of patients with syringomyelia. The mechanism of cord damage is unclear. Monitoring of spinal cord function is recommended to detect intraoperative neurological injury, which may be reversed on removing distraction and implants. RESULTS: Intraoperative somatosensory-evoked potential (SSEP) spinal cord monitoring detected possible cord damage during outrigger distraction. Reduction of distraction led to a recovery of SSEPs and a satisfactory operative outcome. CONCLUSION: Syringomyelia may be a risk factor for neurologic injury during correction of scoliosis, and SSEP spinal cord monitoring may identify and prevent intraoperative spinal cord injury.
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Since 1981, during operations for spinal deformity, we have routinely used electrophysiological monitoring of the spinal cord by the epidural measurement of somatosensory evoked potentials (SEPs) in response to stimulation of the posterior tibial nerve. We present the results in 1168 consecutive cases. Decreases in SEP amplitude of more than 50% occurred in 119 patients, of whom 32 had clinically detectable neurological changes postoperatively. In 35 cases the SEP amplitude was rapidly restored, either spontaneously or by repositioning of the recording electrode; they had no postoperative neurological changes. One patient had delayed onset of postoperative symptoms referrable to nerve root lesions without evidence of spinal cord involvement, but there were no false negative cases of intra-operative spinal cord damage. In 52 patients persistent, significant, SEP changes were noted without clinically detectable neurological sequelae. None of the many cases which showed falls in SEP amplitude of less than 50% experienced neurological problems. Neuromuscular scoliosis, the use of sublaminar wires, the magnitude of SEP decrement, and a limited or absent intra-operative recovery of SEP amplitude were identified as factors which increased the risk of postoperative neurological deficit.
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Spinal somatosensory evoked potentials were recorded in 35 neurologically normal patients undergoing surgery for scoliosis. The recording electrodes were placed in the dorsal epidural space. Stimulation was of the tibial nerve in the popliteal fossa and the posterior tibial and sural nerves at the ankle. At thoracic levels the response consisted of at least 3 components with different peripheral excitation thresholds and spinal conduction velocities (range 35-85 m/sec). All components were conducted mainly in tracts ipsilateral to the stimulus, component 1 being most laterally located. At low stimulus intensity only the fastest activity was recorded but higher intensities elicited additional, slower conducting components. Component 1 was much less prominent when the posterior tibial nerve was stimulated at the ankle and absent from the (cutaneous) sural nerve response. Component 1 is likely to be due to the stimulation of group 1 muscle afferents which terminate in the dorsal horn and activate second-order neurones, many of whose axons go to form the ipsilateral dorsal spinocerebellar tract. Components 2 and 3 are believed to be largely cutaneous in origin and to be conducted mainly in the dorsal columns.
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The recently reported results from several controlled randomised trials of the drug treatment of mild hypertension suggest that such treatment may be expected to exert a small effect toward the primary prevention of stroke disease. In order that the economic implications of these results might be examined, two hypothetical programmes of anticipatory care are considered according to the principles of cost-effectiveness analysis. Each notional 5 year programme is set in a defined population, residents of Stockport, Greater Manchester, aged between 35 and 64 years, and each is addressed toward the detection and treatment of mild hypertension in the community. The programmes differ with respect to their detection processes: one programme is based upon the screening method conducted under the aegis of health visitor staff employed by a District Health Authority, the other upon opportunistic case finding conducted by general practitioners. It is likely that the screening programme would prevent about 13 strokes over a 5 year period; if set in leisure time total programme costs are estimated to be 309,500 pounds at 1986 prices. Discounting future costs and future prevented strokes provides for the development of a present value total cost per prevented stroke of 25,000 pounds. Alternately, the 5 year opportunistic programme, costing 252,650 pounds, would be expected to prevent about 15 strokes at a present value of 17,050 pounds per prevented stroke. The prevention of stroke disease attributable to these programmes can only be achieved in the presence of group compliance to drug treatment. This clearly depends upon the perception of the value of treating hypertension according to each individual subject. The respective merits of the two programmes are examined with particular reference to their sensitivity to this issue, as well as to their likely feasibility and practicability.
We reviewed 47 patients with neurofibromatosis and dystrophic spinal deformities; 32 of these patients had been untreated for an average of 3.6 years and in them the natural history was studied. The commonest pattern of deformity at the time of presentation was a short angular thoracic scoliosis, but with progression the angle of kyphosis also increased. Deterioration during childhood was usual but its rate was variable. Severe dystrophic changes in the apical vertebrae and in particular anterior scalloping have a poor prognosis for deterioration. The dystrophic spinal deformity of neurofibromatosis requires early surgical stabilisation which should be by combined anterior and posterior fusion if there is an abnormal angle of kyphosis or severely dystrophic apical vertebrae. Some carefully selected patients can be treated by posterior fusion and instrumentation alone.
We reviewed 77 unfused and 91 fused patients with idiopathic scoliosis who first attended between 1949 and 1965. Both groups were re-examined at least 10 years after reaching skeletal maturity, with attention to progression of the Cobb angle, increased in vertebral rotation, back pain and psychosocial problems. We found that spinal fusion protects the scoliotic spine from further deterioration during adult life except for those with severe curves and marked rotation. Fusion also significantly reduced the incidence of severe pain and allowed patients to carry out heavy physical work, but did not confer complete immunity from backache. Surgery improved the appearance, but patients were not always completely satisfied with the cosmetic result.
Structural scoliosis occurs more commonly in patients with juvenile chronic arthritis than in the normal population. We have reviewed 32 patients with both juvenile arthritis and a scoliosis and suggest that structural curves may arise from postural curves associated with asymmetrical involvement of lower limb joints.
Seventy-eight unfused patients with idiopathic scoliosis were followed from skeletal maturity over a mean period of 17 years (range 10 to 27 years) with a mean age at follow up of 33.7 years. The following aspects were investigated: curve deterioration, back pain incidence, and psychosocial details. There was considerable variation in the progression rate of similar deformities but on average significant deterioration occurred when the Cobb angle was over 55 degrees with a maximum deterioration approaching 1.5 degrees per year in the thoracic curves between 90 degrees and 100 degrees mature Cobb angle. Thoracolumbar and lumbar curves were slightly more benign with a maximum progression rate of about 1 degree when the mature angle was 80 degrees to 90 degrees. The thoracic component of double curves progressed least. Rotation increased in proportion to the Cobb angle progression except in some lumbar curves where lateral subluxation occurred with a disproportionate amount of rotation. The incidence of back pain in relation to pain in the general population and in fused patients remains uncertain. Eighty-two percent of patients had married and 87% had job satisfaction; 10% received treatment for depression.
Three hundred and nineteen patients with adolescent idiopathic scoliosis were treated by posterior spinal fusion over an eight year period. The changes in preoperative correction and surgical techniques are reviewed. The anaesthetic technique using induced hypotension and the postoperative routine are described. The amount of deformity and its correction at operation and postoperatively is discussed by reference to Cobb angles. The early and late complications are reviewed.
Intramedullary spinal cord tumours may present as scoliosis without neurological signs. Those treating spinal deformities should be alert to this possible aetiology. The clinical features of 12 such cases are discussed with reference to early diagnosis and treatment. Patients with a painful scoliosis should be investigated with myelography as well as bone scintigraphy. Many intrinsic spinal cord tumours are now amenable to surgical removal. The prognosis for neurological recovery is poor once a severe deficit becomes established. The importance of early diagnosis and joint orthopaedic and neurosurgical management is emphasised.
If a poll were taken of the conditions the average doctor finds most difficult and depressing to treat, backache would undoubtedly be near the top of the list. Yet a clear understanding of the anatomy and mechanism of injury, a thorough examination, and a logical plan of management would help alleviate the patient's and doctor's symptoms.
An electrophysiological system for monitoring the spinal cord during operations for scoliosis is described. During the development of the technique the recording of cortical somatosensory evoked potentials from the scalp and spinal somatosensory evoked potentials from the laminae or spines was superseded by the positioning of recording electrodes in the epidural space cephalad to the area to be fused. All recordings were made in response to stimulation of the posterior tibial nerve at the knee. Results in 138 patients are presented and the findings in three patients who exhibited neurological deficits after operation are described. It is concluded that spinal somatosensory evoked potentials are sensitive to minor spinal cord impairment, possible due to ischaemia, and that these changes may be reversed when the cause is quickly remedied. The monitoring system interferes minimally with anaesthetic and surgical procedures and is now performed as a routine.