Prielipp R C, Morell R C, Walker F O, Santos C C, Bennett J, Butterworth J
Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1009, USA.
Anesthesiology. 1999 Aug;91(2):345-54. doi: 10.1097/00000542-199908000-00006.
Although the ulnar nerve is the most frequent site of perioperative neuropathy, the mechanism remains undefined. The ulnar nerve appears particularly susceptible to external pressure as it courses through the superficial condylar groove at the elbow, rendering it vulnerable to direct compression and ischemia However, there is disagreement among major anesthesia textbooks regarding optimal positioning of the arm during anesthesia.
To determine which arm position (supination, neutral orientation, or pronation) minimizes external pressure applied to the ulnar nerve, we studied 50 awake, normal volunteers using a computerized pressure sensing mat. An additional group of 15 subjects was tested on an operating table with their arm in 30 degrees, 60 degrees, and 90 degrees of abduction, as well as in supination, neutral orientation, and pronation. To determine the onset of clinical paresthesia compared to the onset and severity of somatosensory evoked potential (SSEP) electrophysiologic changes, we studied a separate group of 16 male volunteers while applying intentional pressure directly to the ulnar nerve. Data are presented as mean (median; range).
Supination minimizes direct pressure over the ulnar nerve at the elbow (2 mmHg [0; 0-23]; n = 50), compared with both neutral forearm orientation (69 mmHg [22; 0-220]; P < 0.0001), as well as pronation (95 mmHg [61; 0-220]; P < 0.0001). Neutral forearm orientation also results in significantly less pressure over the ulnar nerve compared to pronation (P < or = 0.04). The estimated contact area of the ulnar nerve with the weight-bearing surface was significantly (P < 0.0001) smaller in the supine position (2.2 cm2 [0.5; 0-9]; n = 50) compared with both neutral orientation (5.5 cm2 [5.0; 0-13]) and pronation (5.8 cm2 [6; 0-12]). With the forearm in neutral orientation, ulnar nerve pressure decreased significantly (P < or = 0.01; n = 15) as the arm was abducted at the shoulder from 0 degrees to 90 degrees. In the 16 male subjects tested, notable alterations in ulnar nerve SSEP signals (decrease > or = 20% in N9-N9' amplitude) were detected in 15 of 16 awake males during application of intentional pressure to the ulnar nerve. However, eight of these subjects did not perceive a paresthesia, even as SSEP waveform amplitudes were decreasing 23-72%. Two of these eight subjects manifested severe decreases in SSEP amplitude (> or = 60%).
Extrapolating these results to the clinical setting, the supinated arm position is likely to minimize pressure over the ulnar nerve. With the forearm in neutral orientation, pressure over the ulnar nerve decreases as the arm is abducted between 30 degrees and 90 degrees. In addition, up to one half of male patients may fail to perceive or experience clinical symptoms of ulnar nerve compression sufficient to elicit SSEP changes.
尽管尺神经是围手术期神经病变最常见的部位，但其机制仍不明确。尺神经在肘部穿过浅髁沟时似乎特别容易受到外部压力，使其易受直接压迫和缺血影响。然而，主要麻醉学教科书中关于麻醉期间手臂的最佳摆放位置存在分歧。
为确定哪种手臂位置（旋后、中立位或旋前）能使施加于尺神经的外部压力最小，我们使用计算机化压力传感垫对50名清醒的正常志愿者进行了研究。另外一组15名受试者在手术台上测试了手臂处于外展30度、60度和90度以及旋后、中立位和旋前时的情况。为确定临床感觉异常的发作与体感诱发电位（SSEP）电生理变化的发作及严重程度的对比情况，我们对另一组16名男性志愿者直接对尺神经施加故意压力时进行了研究。数据以平均值（中位数；范围）表示。
与前臂中立位（69 mmHg [22；0 - 220]；P < 0.0001）以及旋前位（95 mmHg [61；0 - 220]；P < 0.0001）相比，旋后位可使肘部尺神经上的直接压力最小（2 mmHg [0；0 - 23]；n = 50）。与旋前位相比，前臂中立位时尺神经上的压力也显著更小（P ≤ 0.04）。与中立位（5.5 cm² [5.0；0 - 13]）和旋前位（5.8 cm² [6；0 - 12]）相比，仰卧位时尺神经与承重表面的估计接触面积显著更小（P < 0.0001）（2.2 cm² [0.5；0 - 9]；n = 50）。当手臂在肩部从0度外展到90度时，在前臂中立位的情况下，尺神经压力显著降低（P ≤ 0.01；n = 15）。在测试的16名男性受试者中，在对尺神经施加故意压力期间，16名清醒男性中有15名检测到尺神经SSEP信号有明显改变（N9 - N9'波幅降低≥20%）。然而，这些受试者中有8名即使SSEP波形波幅降低23 - 72%也未感觉到感觉异常。这8名受试者中有2名SSEP波幅严重降低（≥60%）。
将这些结果外推至临床情况，旋后位的手臂姿势可能使尺神经上的压力最小。在前臂中立位时，随着手臂在外展30度至90度之间，尺神经上的压力会降低。此外，多达一半的男性患者可能无法感知或经历足以引起SSEP变化的尺神经受压的临床症状。
