Spinal anesthesia with hypobaric bupivacaine for knee arthroscopies: effect of posture on motor block

The clinical impact of patient positioning on motor block during unilateral spinal anesthesia was the focus of our study. It was assumed that a 45 degrees rotation toward the prone position would minimize blocking the ventral motor roots compared with using the conventional lateral decubitus position.

Spinal anesthesia with 3.4 mL of hypobaric 0.18% bupivacaine via a 27-gauge Whitacre needle was administered to 70 patients undergoing knee arthroscopy. The patients were kept either in a lateral decubitus position (group I) or rotated approximately 45 degrees toward the prone position (group II). No prophylactic vasopressors or infusions were used. The intensity of motor block (modified Bromage scale) was assessed for both the operative and the contralateral side.

The patients in group I had a slightly more pronounced motor block, but statistical significance could be shown only 20 minutes following the block. There was no statistical difference between the groups in the need of additional analgesics during the operation. None of the patients needed general anesthesia. The hemodynamics were stable and none of the patients developed postspinal headache or backache.

The position of the patient affects the spread of the spinal anesthesia when clearly hypobaric agents are used. However, this small modification in positioning of the patient did not lead to a clinically meaningful difference in the spread of the motor block.