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Purpose:
Ulnar wrist pain is a frequent problem connected to pisotriquetral arthritis - the second most frequent degenerative arthritis of the wrist, causing ulnar nerve compression and degenerative changes in the pisotriquetral joint. Often surgical approaches in this area risk damaging the ulnar nerve. This study examines the relationship between the Pisiform and the Ulnar Nerve using a series of excisions at the flexor carpi ulnaris (FCU) and MR Imaging, in order to determine the safest and most effective pisiform excision technique - and reduce the risk of nerve damage during pisiform procedures.
Materials & Methods:
Ten volunteer wrists were selected for the MRI portion of this study, and 10 fresh frozen cadaver wrists were used for the excision portion. A 1.5 Tesla MRI produced spin echo TI weighted axial images with 3.0 mm slices every 0.2 mm for three different positions - extension, neutral, and flexion (all radial deviation). A palmar dissection was used from the mid-forearm to the distal hamate and categorized by Cut I, II, and III. Measurements were then made with electric calipers under a 3.5X loupe magnification. The skin was incised and retracted - and subcutaneous tissues were removed to expose the FCU. It was then transected in the mid-forearm and freed from adhesions down to the pisiform bone. The portion of the pisiform covered by the FCU tendon, periosteum, transverse carpal ligament, and pisohamate ligament was estimated at the level of Cut II and Cut III using analogue clock values in the axial plan. Extensive measurements of the pisiform dimensions and its width, depth and length at each cut were recorded.
Results:
The ten cadaveric wrist dissections revealed 0.9 mm (0.7-1.2 mm) of soft tissue between the pisiform bone and the ulnar nerve with no obvious difference with change in wrist position. The MR imaging of ten wrists (volunteers) revealed an average space of 0.30 mm in the flexed wrist, 0.25 mm in the neutrally positioned wrist and 0.45 mm in the extended wrist.
Conclusion:
The relationship of the ulnar nerve and pisiform is crucial in order to avoid nerve damage during pisiform excision procedures. The distance covered by the pisohamate ligament is important, as the ulnar nerve runs between these two bony structures. This information combined with measurements from Cuts I, II, and III indicates that the Volar approach through Guyon's Canal, releasing the ulnar nerve, is a safe technique when excising the pisiform.
 
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