The effect of instrumentation on human spinal fusion mass.

STUDY DESIGN: This study is a prospective histomorphometric evaluation of human spinal fusion bone using video dimensional analysis. OBJECTIVES: Little information exists regarding the biology of fusion mass (FM) and the effect that instrumentation has on FM quality. Concerns regarding potential for "stress shielding" of FM with rigid implants have arisen. The goal of this study was to determine what effect spinal implants have on the quality and metabolism of FM bone. METHODS: Fifty-six patients underwent surgeries to remove spinal implants or extend a fusion after pulse-dose labeling with fluorochrome. Twelve patients had undergone fusions without instrumentation. Duplicate biopsies of FM and iliac crest (IC) were obtained and evaluated blindly for mineralized volume, trabecular thickness, mineralization rate, and bone formation rate. Iliac crest, instrumented FM, and noninstrumented FM were compared. RESULTS: Instrumental FM had superior material properties relative to noninstrumented FM or IC. No significant difference in metabolic activity was present. CONCLUSION: Instrumentation does not lead to FM "stress-shielding."

Late "rim sign"--a variant of an old sign.

Classically, the "rim sign" has been described throughout the hepatobiliary scan. The authors present a case of a late rim sign visualized at 25 minutes postinjection that proved to be acute upon chronic acalculous cholecystitis without gangrene.

Relationship between vertebral intraosseous pressure, pH, PO2, pCO2, and magnetic resonance imaging signal inhomogeneity in patients with back pain. An in vivo study.

The cause of back pain in many patients in unknown. The pain experienced by patients with osteoarthritis of large joints has been associated with intraosseous abnormalities of elevated pressure, venous dilatations, and abnormalities of pH, pCO2, and pO2. Magnetic resonance imaging demonstrates an abnormal signal in the vertebral bodies of some patients with degenerative disc disease. The intraosseous pressure as well as the intraosseous pH, pO2, and pCO2 in a group of patients undergoing anterior spine surgery was studied, and the results were correlated to the preoperative magnetic resonance imaging appearance. Vertebral bodies with an abnormal magnetic resonance imaging signal had pressures 55% higher than vertebral bodies with a homogeneous signal; they also had significantly decreased pH and increased pCO2. Bodies with Type I changes had pressures 73% higher than those with a normal signal. No differences in pO2 were identified. These findings suggest that abnormalities of intraosseous pressure or blood gas concentrations may be related to mechanisms of pain production in some patients with back pain. These abnormalities can be identified by magnetic resonance imaging. Further investigation is needed to determine if therapeutic manipulation of these variables can be effective in relieving axial spinal pain.

Analysis of factors related to truncal decompensation following Cotrel-Dubousset instrumentation.

Spinal imbalance following Cotrel-Dubousset (CD) instrumentation for adolescent idiopathic scoliosis is a problem that is recognized with increasing frequency. We reviewed the clinical records and radiographs of 41 consecutive patients treated with CD instrumentation and attempted to identify factors related to postoperative worsening of spinal balance. Spinal balance was determined by the perpendicular distance of C7 to the center sacral line. Twenty-five were decompensated postoperatively. Sixteen patients had balance that was worse relative to the preoperative films. Eleven of 16 patients with worsened balance postoperative were King type III curves. Of 16 patients with worsened balance postoperatively, 13 had been fused to or below the lower neutral vertebra. Overcorrection of either the primary curve or the composite curve (sum of the measurable curves) relative to the preoperative bending films was not related to postoperative worsening of spinal balance. Fusion to the neutral or stable vertebra with CD instrumentation runs a high risk for postoperative worsening of spinal balance when the derotation maneuver is used. Consideration should be given to avoiding the derotation maneuver in larger type II curves in order to preserve spinal balance and avoid extension of instrumentation into the middle or lower lumbar spine.