Monitoring of scoliosis surgery with epidurally recorded motor evoked potentials (D wave) revealed false results.

OBJECTIVE: To elucidate the mechanism behind D wave amplitude changes after surgical correction of scoliosis. METHODS: We collected D wave and muscle MEP data from 93 patients (78 female, 15 male, age range 4-19 years, mean age 15.9 years), who underwent surgical correction of scoliosis. D waves were recorded via a catheter electrode inserted epidurally through the flavectomy. Muscle MEPs from lower limb muscles were also recorded. Muscle MEPs/D wave were elicited by short trains/single transcranial electrical stimuli. SEPs were elicited through bilateral percutaneous stimulation of the tibial nerves at the ankle and an averaged response from 100 to 200 single sweeps were recorded over the scalp at Cz'/Fz. In addition, we analyzed intraoperatively obtained X-ray images of the spine in 9 patients and preoperative spinal MRI in two of those nine. RESULTS: After surgical correction of scoliosis in 25 of 93 (27%) patients, the D wave amplitude changed by more than 20% of its baseline value. A decremental change occurred in 21 (84%) and an incremental change in 4 (16%) patients. D wave decrements of more than 50% were observed in 5 patients without significant SEP changes in any of these cases. In 9 patients, intraoperatively obtained X-rays of the spine (before and after correction of spine curvature) showed no catheter displacement. Muscle MEPs did not change and postoperative sensory-motor status was normal. In 2 patients, preoperative MRI revealed displacement of the spinal cord towards the concave side of the scoliotic curvature. CONCLUSIONS: During scoliosis surgery, D wave amplitude changes should be interpreted cautiously until the definitive cause(s) of these changes are found. One possible mechanism to explain D wave changes during scoliosis correction could involve rotation of the spinal cord within the spinal canal, and the relative position of the epidural recording catheter (ERC). Rotation of the spinal cord after correction of scoliosis could introduce a new relationship between the ERC and the corticospinal tracts (CTs). Due to high incidence of false D wave amplitude changes we suggest that this methodology should not be used to assess the functional integrity of the CTs during scoliosis surgery. SIGNIFICANCE: This study provides new insight into the methodology of D wave monitoring as well as strong evidence of a high incidence of false positive results using D wave monitoring during surgical correction of scoliosis.

Practical biomechanical considerations for spine implant testing.

The author presents the basic biomechanical concepts linked with spine implant testing. The paper also contains the methodology of in vitro and in vivo spine implant testing. The physical and biological properties of various materials and devices commonly used in spine surgery are discussed in relation to their role in spine surgery. The paper clearly shows how all these parameters influence surgical strategy for the spine and more importantly how the choice of methods and devices influences the long term results of spinal surgery. The author also presents the biomechanical repercussions of a failed spine and his own concept of an "ideal" fusion.

Spinal deformity, pulmonary compromise, and quality of life in osteogenesis imperfecta.

STUDY DESIGN: A cross-sectional radiologic and clinical study of patients with osteogenesis imperfecta. OBJECTIVES: To determine whether pulmonary compromise is more closely correlated with scoliosis, kyphosis, or chest wall deformity in the population with osteogenesis imperfecta, and to assess the impact of spinal deformity, chest wall deformity, and pulmonary function on quality of life. SUMMARY OF BACKGROUND DATA: The incidence of scoliosis in osteogenesis imperfecta is between 39% and 80%. Up to 60% of patients with osteogenesis imperfecta have significant chest wall deformities. Pulmonary compromise is the leading cause of death in adults with osteogenesis imperfecta. METHODS: Fifteen patients with osteogenesis imperfecta between the ages of 20 and 45 were evaluated with sitting or standing anteroposterior and lateral radiographs of the entire spine, pulmonary function testing, and a validated health self-assessment questionnaire (Short Form-36). Radiographs were evaluated for thoracic scoliosis, thoracic kyphosis, and chest wall deformity. Correlation analysis was performed. RESULTS: Thoracic scoliosis was strongly correlated with decreased predicted vital capacity (r = -0.76). Significant diminution in vital capacity below 50% occurred at a curve magnitude of 60 degrees. Kyphosis and chest wall deformity were not predictive of decreased pulmonary function. Physical health (PCS) was closely correlated with predicted vital capacity (r = 0.65; P < 0.01) and with scoliosis (r = -0.52; P < 0.05). CONCLUSIONS: Thoracic scoliosis of more than 60 degrees has severe adverse effects on pulmonary function in those with osteogenesis imperfecta. This finding may partly explain the increased pulmonary morbidity noted in adult patients with osteogenesis imperfecta and scoliosis compared with that in the general population.

[Scoliosis and congenital heart diseases in children. Apropos of 44 cases]. / Scolioses et cardiopathies congénitales chez l'enfant. A propos de 44 cas.

In order to evaluate the difficulties of treatment of associated scoliosis and congenital heart disease (C.H.D.), 44 patients who have been treated between 1970 and 1988 were reviewed. The scoliosis was idiopathic in 30 cases, congenital in 11, neurologic in 3. There were 27 females and 17 males. Twenty one patients had a cyanotic C.H.D. (twelve tetralogies of Fallot). No relation was found between the side of the cardiac approach and the side of the thoracic curves. Three cases of right aortic arch with two left thoracic scolioses were noted. Associated anomalies were encountered in 60 p. 100 of cases. The analysis of old chest X-rays, revealed that the scoliosis was already present an average of 5 years before the first orthopaedic consultation. Eight patients had an orthopaedic treatment; in ten cases surgery was decided but not performed. Twenty six patients were operated. (22 posterior and six anterior procedures). The average angulation was 55 degrees pre-operatively, 30 degrees post-operatively and 40 degrees at a 40 months follow-up. In five cases a pseudarthrosis led to re-intervention. One patient died during a posterior procedure, an other post-operatively. Two patients had a severe complication (one heart arrest; one gaz-embolism) but recovered. The surgical prognosis can be evaluated on an original scale including different cardiac parameters, and the importance of the planned surgical procedure. Under a limited mark, no serious complications occurred. In conclusion, a closed collaboration between pediatricians and the orthopaedic team, should lead to more precocious screening of scoliosis in cardiologic children and before the orthopaedic procedure, to a more precise risk factors evaluation.

[Large-displacement spondylolisthesis in children and adolescents. Results of reduction-arthrodesis with front plates]. / Les spondylolisthésis à grand déplacement de l'enfant et de l'adolescent. Résultats de la réduction-arthrodèse par plaque antérieure.

Twenty seven children and adolescents with severe lombo-sacral spondylolisthesis (degre III and IV) were operated using an original procedure of reduction and fixation. It is a two stages procedure, in the same session. Through a posterior approach, the sciatic roots are released and two long screws are set through the sacrum. An anterior approach allows a progressive reduction using a bended plate fixed with the protruded long screws, and an anterior arthrodesis. Results were evaluated with a three years mean follow-up. Clinical results were excellent on pain and on the morphological aspect of the trunk. There were four cases of residual weakness in the L5 motor distribution. This complication can be avoided by a good preparation before the procedure and precise post-operative care. The anterior displacement was improved from 77 per cent to 11 per cent. The angular lombosacral kyphosis from -23 degrees (kyphosis) to + 11 degrees (lordosis). The initial fears in the early experience, about the risks of kyphosis or slipping of the L4-L5 level have not been proved.

[Effects of Chiari osteotomy on acetabular development in the growing subject. Experimental study in puppies]. / Effets sur le développement cotyloïdien de l'ostéotomie de Chiari chez le sujet en croissance. Etude expérimentale chez le chiot.

A Chiari osteotomy was performed on 10 dogs aged 2 months in order to assess the risks of mechanical or ischaemic loss of growth potential in the peri-acetabular cartilage. The development of the acetabular roof was studied by radiographs, microradiographs and histological assessment between 2 and 12 months. Apart from a few mechanical complications, the principal findings were the absence of any signs of necrosis, persistence of a strongly osteoblastic roof and readaptation of the trabecular pattern with articular remodelling, provided the mechanical conditions were satisfactory. The osteotomy must be sufficiently low, while remaining extra-articular, and adequate medial shift must be obtained. The interposed capsular tissue can then become dense and fibrous, providing a sliding surface.

[Cauda equina syndrome caused by migration of a fat graft after laminoarthrectomy]. / Syndrome de la queue de cheval par migration d'un greffon graisseux après laminoarthrectomie.

In a case of partial laminoarthrectomy for lateral recess stenosis cauda equina compression occurred post-operatively, and was caused by migration of a free graft. Recovery was complete within six months. The technical details of insertion of the free fat grafts are described.

[Congenital pseudarthrosis of the tibia and fibula in children. Results of the treatment of 18 cases with nails and bone grafts]. / Pseudarthroses congénitales du tibia et du péroné chez l'enfant. Résultats du traitement de 18 cas par enclouage et greffe.

Eighteen cases of congenital pseudarthrosis of the leg in 17 children were treated by nailing and tibio-fibular graft with a mean follow-up of six years (from one to twelve years). Six patients had reached the end of growth. Primary union was obtained in 17 cases in a mean time of 6.5 months (from 3.5 to 18 months), but one case developed a new pseudarthrosis at the level of an associated upper tibial osteotomy. Only one case required a supplementary graft. Walking was usually achieved without any apparatus after five-and-a-half months, the tibia being protected by a nail which was left in place until the end of growth. In two cases, a fracture produced by trauma occurred in the limb long after consolidation. These two fractures healed in the normal time. Inequality of limb length was present in all the cases, but its progress varied. On three occasions it was treated by femoral lengthening. Stiffness of the ankle and subtaloid joints resulted from nailing of the hindfoot in nine cases and improved very little after freeing of the joints. The use of telescopic rods avoids the need for further operations to change the rod during growth. We consider that this is a reliable method but that, in certain cases, the effects on growth and on the foot can be diminished by appropriate modifications of technique.

[Success factors in posterolateral arthrodesis of the lumbosacral spine]. / Facteurs de réussite de l'arthrodèse postéro-latérale du rachis lombo-sacré.

The authors have performed 180 posterolateral fusions of the lumbar spine for various conditions. A new method of evaluation of the results is proposed using a careful analysis of the pre-operative and post-operative condition of the patient. The overall ratio of fusion was satisfactory and the etiology did not influence the result. The rate of fusion was not improved when screws were inserted into the articular processes. The level and extent of the arthrodesis did not affect the rate of fusion. Both sides should be fused whenever possible. The functional results were better in cases of degenerative spondylolisthesis than in cases of narrowing of the spinal canal without slipping. They were also better when fusion was obtained. Two cases of pure lumbar pain had good results provided that sedentary work could be done by the patient. A preoperative psychiatric examination was useful. The presence of overweight and a long preoperative period of pain were not favourable. In 49 cases, the arthrodesis was made after one or more previous surgical procedures. The results were more satisfactory when the arthrodesis was made without any associated operation on the spinal canal.