Spine
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A model of the lumbar back muscles was constructed incorporating 49 fascicles of the lumbar erector spinae and multifidus. The attachment sites and sizes of fascicles were based on previous anatomic studies, and the fascicles were modeled on radiographs of nine normal volunteers in the upright position. Calculations revealed that the thoracic fibers of the lumbar erector spinae contribute 50% of the total extensor moment exerted on L4 and L5; multifidus contributes some 20%; and the remainder is exerted by the lumbar fibers of erector spinae. ⋯ Collectively, all the back muscles exert large compression forces on all segments. A force coefficient of 46 Ncm-2 was determined to apply for the back muscles. These results have a bearing on the appreciation of the effects on the back muscles of surgery and physiotherapy.
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To avoid homologous transfusion in spinal fusion surgery, acute normovolemic hemodilution was combined with controlled hypotensive anesthesia. Patients were kept hemodiluted, not only during surgery, but also after surgery by delaying transfusion until the next morning or later. ⋯ Only 4 of 119 patients (3.4%) required homologous blood, compared to 25 of 29 patients (86%) in 1982, at which time none of these techniques were used. The average hemoglobin on the seventh postoperative day was similar in both groups; 11.5 g/dl in the current series compared to 11.1 g/dl in the 1982 series.
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Large administrative databases are increasingly valuable tools for health care research. Although increased access to these databases provides valuable opportunities to study health care utilization, costs and outcomes and valid and comparable results require explicit and consistent analytic methods. Algorithms for identifying surgical and nonsurgical hospitalizations for "mechanical" low back problems in automated databases are described. ⋯ Twenty-seven diagnosis and two procedure codes identify hospitalizations for problems definitely in the lumbar or lumbosacral region. Exclusion criteria were developed to eliminate nonmechanical causes of low back pain, such as malignancies, infections, and major trauma. The use of the algorithms is illustrated using national hospital discharge data.
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Intraoperative technical complications of pedicle screw fixation include screw cutout or maldirection and pedicle fracture. The aims of this study were 1) to use computed tomography to determine the average pedicle diameter; and 2) to compare these measurements with the outer diameter measurements of commonly used pedicle screws. The pedicle diameters of L2, L3, L4, L5, and S1 were measured in 154 adult patients (81 men, 73 women) who had low-back pain. ⋯ Twenty percent of the L2 pedicle diameters, 15.6% of L3, and 1.9% of L4 were less than 7 mm; none of the L5 or S1 pedicles measured less than 7 mm. The outer diameters of the most commonly used pedicle screws range from 5 mm to 7 mm. Screw pitch, tooth profile, outer diameter, and depth of penetration affect implant strength.(ABSTRACT TRUNCATED AT 250 WORDS)