Side lying on the opposite side or supine.

Insert the gloved index finger into the rectum to guide the direction of the needle into the external anal sphincter. Insert the needle parallel to the inserted finger at the junction between the mucosal membrane and the skin of the external anal sphincter (mucocutaneous junction). It is preferable to insert the needle at a 6 o’clock or 9 o’clock direction.

Ask the patient to sqeeze the examiner’s inserted gloved finger or ask the patient to act like they are defecating to obtain relaxation.

This muscle is often tested in lesions of the cauda equina or conus medullaris including the pudendal nerve and S2, S3, and S4.

S2, S3, S4-sacral plexus-pudendal nerve.