Longitudinal radioulnar dissociation may result when compressive load to the hand causes excessive proximal migration of the radius with interosseous ligament (IOL) disruption and radial head fracture. Although radial head salvage or arthroplasty and temporary distal radioulnar joint pinning constitute the current treatment for this injury IOL reconstruction has been proposed to restore normal forearm mechanics. To help provide a biomechanical basis for IOL reconstruction we measured load transfer and proximal migration of the radius with the IOL intact, cut, and reconstructed while leaving the radial head intact.

We dissected the central third of 12 normal cadaveric forearms to bone-IOL-bone. We applied 136 N of compressive load to the hand and measured proximal radial migration and 3-dimensional force vectors acting in the distal radius, distal ulna, IOL, proximal radius, and proximal ulna. Experiments were performed in neutral forearm rotation and neutral elbow varus-valgus. The protocol was repeated with the IOL intact, cut, and reconstructed with single and double flexor carpi radialis allografts.

With the IOL intact 94% +/- 3 % of hand load was in the distal radius with 75% +/- 2% was transmitted to the proximal radius. With the IOL cut 92% +/- 2% of hand load was in the distal radius and this was unchanged at the proximal radius. With single flexor carpi radialis reconstruction 94% +/- 3% of hand load was in the distal radius and 80% +/- 2% was in the proximal radius; with double flexor carpi radialis reconstruction these numbers changed to 95% +/- 3% and 74% +/- 2%, respectively. Forces in the forearm were mainly in the longitudinal and transverse directions with negligible components in the dorsal-volar direction. Transverse force in the IOL was about half that of the longitudinal force in the intact and reconstructed states.

When the IOL is cut and load is applied to the hand the unloading of the proximal radius and the transversely directed force that compresses normally across the proximal and distalradioulnar joints is lost. Reconstruction of the IOL can restore the normal load transfer characteristics. These data help provide a biomechanical basis for IOL reconstruction. Further research on the biomechanics of IOL reconstruction in the setting of radial head replacement along with clinical evaluation is needed.

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