Quantification of the multi-axial stability of the radial head after annular ligament and interosseous membrane sectioning during forearm rotation
Deana Mercer, MD1; Jodie Gomez, BS2; Christina Salas, PhD2; Drew Newhoff, MD2; Tom G Pollard, BS2; Erica Gauger, MD2; Lauren A Long, BS2; Jorge Luis Orbay, MD3; (1)Department of Orthopaedic Surgery, University of New Mexico, Albuquerque, NM, (2)University of New Mexico, Albuquerque, NM, (3)The Miami Hand and Upper Extremity Institute, Miami, FL
Introduction: The key stabilizers of the forearm, often ruptured due to high-impact axial loads, include the annular ligament (AL) and the proximal band (PB), central band (CB), and distal band (DB) of the interosseous membrane (IOM). These ligaments permit forearm rotation and load transfer from the radius to the ulna. Contributions of the AL and IOM to longitudinal forearm stability have been clearly defined. We present results showing contribution of the AL and IOM to 3-dimensional radial head stability through sequential sectioning of these stabilizing structures during simulated active pronation and supination.
Materials & Methods: Fifteen fresh-frozen cadaveric arms, mid-humerus to fingertips, were used. Soft tissue proximal to the wrist crease was removed while leaving the main stabilizing structures of the forearm intact. A motorized custom fixture permitted forearm rotation between full supination and full pronation through simulated physiologic loads on the biceps tendon and pronator teres to aid/resist motion based on the direction of rotation. The elbow was fixed in 90 degrees of flexion. A 12-camera OptiTrack motion capture system tracked the 3D motion of the radius and ulna in 5 scenarios: intact (1) and after sequential sectioning of the AL(2), PB (3),CB (4), and DB (5). Effects of sectioning on maximum forearm rotation are reported. The translational radial head motion at each stage, in pronation and supination, is reported in three directions: radial-ulnar, volar-dorsal, and proximal-distal. Note: rotational motion about the forearm long axis will also be analyzed and reported by the time of the conference.
Results: Translational data are plotted as the deviation from intact motion, in millimeters, at 20, 40, 60, 80, and 100% of maximum forearm rotation, for each direction. CB and DB sectioning cause greatest translation from intact motion in supination with displacements of 8.4mm and 4.9mm dorsally and 16.3mm and 21.7mm radially. Radial head translation between intact and after AL and PB sectioning are not significantly different in supination. Radial head translation between intact and after all sectionings are not significantly different in pronation.
Conclusions: The greatest amount of instability occurs in dorsal and radial directions after sectioning the CB and DB.
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