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The Role of the Central Band of the Interosseous Ligaments in Maintaining Ulnar Variance
Jorge Luis Orbay, MD1, Fernando Levaro, MD2, Lauren Vernon, PhD1, Michael Cronin, DO3, Niurka Nunez, BS1, Jorge A Orbay,MD4
1The Miami Hand and Upper Extremity Institute, Miami, FL, 2Reconstructive Orthopedic Center, Houston, TX, 3Larkin Community Hospital, South Miami, FL, 4Columbia University, New York, NY

Introduction: Ulnar impaction syndrome is a degenerative wrist condition caused by increased loads of the ulnar head onto the carpal bones, resulting in painful degeneration of the triangular fibrocartilage complex and bony structures. Radiographic evaluation of these patients often reveals relative loss of radial height resulting in an ulnar positive wrist. We hypothesize that elongation of the central band of the forearm interosseous ligaments may change longitudinal radial-ulnar relationships resulting in an ulnar positive wrist and therefore carpal abutment.

Materials & Methods: Six cadaveric, human forearms were used to measure the displacement experienced by the radius relative to the ulna during axial loading of the radius. Skin, muscles, tendons, vasculature, and nerves were discarded. The interosseous ligament complex, triangular fibrocartilage complex, distal and proximal radio-ulnar joints and the elbow collateral ligaments were preserved. The humerus was cut mid-shaft and the metacarpals were removed. The ulnar shaft was oriented vertically and rigidly fixed to an adjacent vertical beam. We applied axial loads onto the lunate fossa of the distal radius. Radial heights were measured in supination and pronation under a 5lbF preload. Gradual axial loads were applied up to 50lbFand the resultant axial displacement was measured in supination and pronation. All measurements were evaluated with the interosseous ligament intact and repeated with the central band of the interosseous ligament cut while preserving all other components.

Results: Data showed that when the central band of the interosseous ligament was cut the resulting ulnar variance increased by 3.020.80mm in supination and 2.150.79mm in pronation, under a 5lbF preload. In supination, when the loads were increased from the 5 lbF preload to 50 lbF, ulnar variance further increased from 1.40mm (intact central band) to 3.00mm (p?0.001) when the central band of the interosseous ligament was cut. In pronation, when the loads were further increased from the 5 lbF preload to 50 lbF, ulnar variance increased from 1.57mm (intact central band) to 2.84mm (p?0.001) when the central band of the interosseous ligament was cut.

Conclusion: Excising the central band was used to simulate its clinical failure. Due to a parallelogram effect, the radius shifted proximally under a 5lbF preload, creating an ulnar positive wrist relationship. Dynamic loading of the forearm after ligament excision resulted in significant additional radial displacement relative to the intact forearm (increased ulnar variance), suggesting dynamic impaction often observed clinically.


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