Interosseous Ligament and Transverse Forearm Stability: A Biomechanical Cadaver Study.

PURPOSE: The interosseous ligament (IOL) is known to be an important longitudinal stabilizer of the forearm. We hypothesize that it may also contribute to transverse stability, with pronosupination tensioning of the radius relative to the ulna. Therefore, when injured, we predict the interosseous space should widen in the transverse plane, enough to be appreciable on plain radiographs. A measurable difference in interosseous space, comparing an injured with an uninjured forearm, can potentially be of diagnostic and clinical value.

METHODS: Ten fresh-frozen cadaver arms (from 5 individuals) were radiographed in 6 different positions of forearm supination, first in an uninjured state and then with the IOL sectioned, both partially (central band only) and completely. The transverse interosseous distance was measured on radiographs using edge detection software and compared using analysis of variance and contrast analysis. The maximum range of pronosupination was also compared before and after injury, using a paired t test.

RESULTS: Average maximum supination increased from 84° to 106°, and pronation from 69° to 84°, after the IOL was sectioned completely. Sectioning of the IOL led to a statistically significant increase in the interosseous distance, a minimum of 2 mm, in all but one forearm position.

CONCLUSIONS: The IOL of the forearm plays an important role in providing transverse stability to the radius and ulna. When the IOL is sectioned, the forearm exhibits increased pronosupination range of motion. Radiographs of bilateral forearms taken in identical rotational position can reliably differentiate between an intact and torn IOL in cadavers.

CLINICAL RELEVANCE: The IOL's stabilizing role during forearm rotation suggests a novel strategy for diagnosing forearm IOL injury using comparative radiographic measurements.