Effect of prone positioning systems on hemodynamic and cardiac function during lumbar spine surgery: an echocardiographic study

STUDY DESIGN

Prospective randomized study of patients undergoing spine surgery.

OBJECTIVE

To compare changes in hemodynamic and cardiac function after prone positioning using different prone positioners.

SUMMARY OF BACKGROUND DATA

Prone positioning decreases blood pressure and cardiac function. Several studies have evaluated changes in cardiac function after prone positioning, and linked them to reduced venous return and ventricular compliance. This study compares different prone positioners using transesophageal echocardiography, and determines their effect on cardiac function and hemodynamics.

METHODS

After correction of fluid deficits with the patient under stable anesthesia, hemodynamic and cardiac performance was measured using transesophageal echocardiography. After prone positioning, repeat measurements were performed, and comparisons were made between prone and supine positions.

RESULTS

No intergroup differences in demographics, fluid deficit, baseline hemodynamics, or differences from supine to prone position were noted. Cardiac output decreased with the Wilson (Union City, CA) and Siemens AG (Munich, Germany) frames, while cardiac index and stroke volume decreased with the Andrews (Hollywood, CA), Wilson, and Siemens systems. Cardiac preload decreased using the Andrews frame. The Jackson spine table (Hollywood, CA) and bolsters had the least effect on cardiac performance.

CONCLUSION

Adequate fluid replacement reduced hypotension and hemodynamic instability after prone positioning. The Jackson spine table and longitudinal bolsters had minimal effects on cardiac function, and should be considered in patients with limited cardiac reserve.

Accuracy of using computed tomography to identify pedicle screw placement in cadaveric human lumbar spine

STUDY DESIGN

Utility of using computed tomography to predict pedicle screw misplacement.

OBJECTIVE

This study defines the sensitivity and specificity of predicting pedicle screw placement by experienced clinicians using a CT scan image.

SUMMARY OF BACKGROUND DATA

In clinical and research settings, the method most commonly used to evaluate pedicle screws placement has been computed tomography. However, no current literature describes the accuracy of this method of evaluating screw placement.

METHOD

Cobalt-chrome and titanium alloy pedicle screws of identical size were placed in six cadaveric human lumbar spine. Wide laminectomy was performed to allow complete visualization of the pedicles. Three consecutive lumbar levels were instrumented in each spine, giving 36 pedicle screw placements to identify. The instrumented spines were imaged, and four orthopaedic spine surgeons and a musculoskeletal radiologist were asked to read the images to identify the accuracy of screw placement within the pedicles.

RESULTS

The sensitivity rate of identifying a misplaced screw was 67 +/- 6% for cobalt-chrome screws compared with 86 +/- 5% for titanium screws (P < 0.005). The specificity rates of radiographic diagnosis of misplaced pedicle screws were 66 +/- 10% for cobalt-chrome screws and 88 +/- 8% for titanium screws (P < 0.005). Similarly, a statistically significant difference was found in the sensitivity rates of identifying screws placed correctly in the pedicle: 70 +/- 10% for cobalt-chrome screws versus 89 +/- 8% for titanium screws (P < 0.005). Overall accuracy rates were 68 +/- 7% for cobalt chrome screws versus 87 +/- 3% for titanium screws (P < 0.002).

CONCLUSION

Reliance on the computed tomography scan data alone in determining accuracy of pedicle screws can lead to inaccuracies in both clinical and research conditions.

Anterior stabilization of thoracolumbar burst fractures using the Kaneda device: a preliminary report

Anterior decompression and fusion is a valuable technique in the treatment of thoracolumbar burst fractures. Anterior instrumentation has evolved to correct deformity and stabilize the spinal segments during decompression and bone grafting as a single-stage procedure. One anterior device developed by Kaneda has been used in our institution since 1989. This study is an initial review of our experience with this instrumentation. Anterior decompression and fusion augmented with the Kaneda device was performed in 20 patients with thoracolumbar burst fractures. Timing of surgery was early (< 15 days) in 13 patients, intermediate (16 to 120 days) in 2, and delayed (> 121 days) in 5. Sixteen patients were neurologically intact (Eismont grade D), 3 with distal weakness (Eismont grade B or C) and 1 with complete paraplegia (Eismont grade A). All patients with deficits recovered one Eismont grade after anterior decompression and fusion. Complications included pulmonary problems in 2 patients, a thoracic duct laceration requiring ligation, and a sympathectomy effect of the lower extremity. One patient had a pulmonary embolus and developed a hematoma at the graft harvest site while on anticoagulants with resultant meralgia paresthetica. There have been three screw failures and one definite pseudarthrosis. Anterior decompression and fusion supplemented by the Kaneda device was performed on 20 patients with thoracolumbar burst fractures. The average correction of kyphosis was approximately 50% acutely, with loss of approximately 50% of correction at follow up. In some patients, coronal plane deformity was created by the device. No effect on neurologic recovery could be shown with this small series. Perioperative complication rate was 30%, and 1 patient developed pseudarthrosis.