The safest direction of percutaneous pinning for achieving firm fixing of the fifth carpometacarpal joint.

Introduction: Traditional treatment of unstable fifth carpometacarpal joint injuries is closed reduction and pinning. The purpose of this study was to determine the safest corridor for pinning of the fifth carpometacarpal joint to prevent iatrogenic injury to the ulnar nerve and tendons.

Materials And Methods: In the first phase of study, three fresh cadavers were dissected and the safest directions of Kirschner wire (k-wire) insertion in the coronal and sagittal planes were determined for k-wire entrance 2 cm distal to the base of the fifth metacarpal. The second phase objective was to evaluate the accuracy of data obtained in the previous phase. Therefore, with five other cadavers, k-wires were inserted in a combination of maximum angles in different planes determined previously. The ulnar nerve branches and tendons were then investigate to detect possible damage. In the third phase, four fresh carpometacarpal joints were fixed with directions outside the range of the defined angles.

Results: The safe direction determined in the first phase was a 20°-30° coronal plane angle relative to the body of the fifth metacarpal bone and between 10° volar to dorsal to 20° dorsal to volar angle in the sagittal plane. Insertion of k-wires in the second phase could fix the fifth carpometacarpal joint firmly without penetration of the volar and dorsal cortices of the hamate. All inserted k-wires outside the defined range resulted in injuries to nerves or tendons or loose fixing.

Conclusion: The safest corridor for pinning unstable fifth carpometacarpal injuries is 2 cm distal to the joint at an angle of 20°-30° to the coronal plane from 10° volar to dorsal to 20° dorsal to volar direction in the sagittal plane.