Passive strain distribution in the interosseous ligament of the forearm: implications for injury reconstruction.

PURPOSE For severe forearm injuries such as an Essex-Lopresti fracture-dislocation, functional reconstruction necessitates repair of the interosseous ligament (IOL) to restore normal load sharing between the radius and ulna. Locating or tensioning such a reconstruction improperly can lead to abnormal load sharing and/or restriction of forearm rotation. The normal IOL strains should indicate the proper location of reconstruction grafts and the proper forearm rotation for tensioning the grafts. The objective of this study was to quantify the passive strain distribution of the IOL of the forearm with passive rotation of the forearm throughout the range of motion. METHODS The 3-dimensional motions of the radius with respect to the ulna were measured throughout forearm rotation in 10 cadaveric forearms by using an instrumented spatial linkage. From the bone motions and ligament insertion site geometry from dissection and computed tomographic scanning, insertion site motions were determined and used to calculate changes in ligament fiber lengths. RESULTS The measured strain distribution in the IOL was nonuniform and varied with forearm rotation. The overall magnitude of IOL strain was found to be greatest in supination and smallest in pronation. In supination the strains varied across fibers with strains being greatest in the distal fibers and lowest in the proximal fibers. Strains in neutral rotation were uniform across fibers. Although fibers were generally slack in pronation proximal fibers were less slack than distal fibers. CONCLUSIONS The results of this study indicate that fiber strains in the IOL vary from proximal to distal and depend on forearm rotation. Our data suggest that to prevent restriction of forearm rotation all grafts should be tensioned in supination, where measured strains were generally highest. Our data also suggest that a 2-bundle IOL reconstruction may be necessary for proper load transfer between the radius and ulna in both supination and pronation.