“Knee-up test” for easy detection of postoperative motor deficits following spinal surgery

Abstract Background Context Neurologic motor deficit is a serious complication of spinal surgery. Early diagnosis of complications by neurologic examination immediately after spinal surgery is mandatory. However, patients cannot always cooperate with the physician in the very early stages of recovery. Purpose The aim of the present study is to prospectively investigate the usefulness of the "knee-up test" for easy detection of postoperative motor deficits. Study Design A prospective clinical study was carried out. Patient Sample Patients with spinal disorder operated upon at a single institute were administered the knee-up test after an anesthesiologist had judged that endotracheal extubation was possible. Outcome Measures The outcome measures were preoperative and postoperative Manual Muscle Testing. Methods A simple yet reliable method known as the "knee-up test" was developed to easily assess postoperative deficits before endotracheal extubation. When the patient's knee is passively lifted up and the patient is able to maintain this position in both legs, the result is negative, whereas when the patient is unable to maintain the knee in an upright position for one or both legs, the result is positive. The presently accepted criterion for a new-onset postoperative neurologic motor deficit is motor weakness leading to a decrease in function of at least two grades in more than one muscle function within 12 hours of spinal surgery, as evaluated by the Manual Muscle Testing. The association between the presence of new-onset motor deficits and the results of the knee-up test was prospectively investigated. Results Seventeen patients exhibited positive results when evaluated using the knee-up test, whereas 521 patients exhibited negative results. Sixteen of the patients with positive results were determined to have new-onset motor deficits, whereas no new-onset motor deficits were observed in the remaining patient. Of the 521 patients with negative knee-up test results, only 2 were determined to have new-onset motor deficits, whereas no new-onset motor deficits were observed in the remaining 519 patients. The sensitivity, specificity, positive predictive value, and negative predictive value were 88.9, 99.8, 94.1, and 99.6, respectively. Conclusions The knee-up test may allow for early and easy detection of postoperative motor deficits with high probability in very early stages.