Imaging and Anatomic Study of the Pisiform Bone/Ulnar Nerve Relationship—Evaluation of the Preferred Surgical Approach for the Excision of the Pisiform Bone

Abstract

This study examines the role of the pisiform bone/ulnar nerve relationship in determining the preferred surgical approach for the excision of the pisiform bone. An anatomic dissection of Guyon's canal on 10 fresh frozen cadaver wrists evenly divided between males and females was combined with magnetic resonance imaging (MRI) scans of 10 volunteer wrists. The 3 reported data points include the axial images determined on the MRI, the anatomic dissection related to the proximity of the ulnar nerve relative to the pisiform in defined positions of the wrist and the soft tissue envelope that surrounds the pisiform, and the proximity of the ulnar nerve as recorded, measured, and analyzed. An analysis of variance of the recorded data points was performed and the statistical results were presented (P value of P 05). Dissection and the MRI scans determined that the soft tissue envelope between the pisiform and ulnar nerve at Guyon's canal with neutral dorsiflexion was 2.5 mm. Palmar flexion was 3.0 mm and neutral flexion was 4.5 mm. The thinnest area was adjacent to the ulnar nerve proper on the volar radial aspect of the pisiform, on the basis of clock-faced analysis, between the 3 : 00 and 6 : 00 positions (the pisiform as a circle). The proximity of the pisiform in relation to the ulna and the limit of the soft tissue envelope would suggest that the preferred surgical approach, or that least likely to cause injury to the ulnar nerve, is one that is volar and includes excising the pisiform after exposing Guyon's canal.