Graft reconstruction of the interosseous membrane in conjunction with metallic radial head replacement: a cadaveric study.

PURPOSE: Longitudinal radioulnar dissociation (Essex-Lopresti injury) occurs when traumatic axial loading through the wrist disrupts the interosseous membrane (IOM) of the forearm and fractures the radial head. Proximal migration of the radius results in an ulnar-positive wrist, which can lead to painful ulnar-sided wrist degeneration and distal radioulnar joint instability. The purpose of this study was to measure the ability of an IOM reconstruction used in combination with a metal prosthetic radial head implant to reduce distal ulnar forces in a cadaveric model. The effects of varying the initial graft pretension on distal ulnar force were also studied.
METHODS: Twelve fresh frozen and thawed cadaveric forearms had a miniature load cell installed to record force in the distal ulna as the wrist was loaded axially to 134 N of compression force in neutral rotation. Intact forearms were tested first with the elbow in valgus and varus alignments. Loading tests were repeated after (1) insertion of a metal radial head implant that restored radius anatomic length, (2) excision of the IOM (with a radial head implant), and (3) reconstruction of the IOM using a palmaris longus tendon autograft (with a radial head implant). The implant then was removed and loading tests were repeated using 3 levels of initial graft pretension.
RESULTS: Mean distal ulnar forces with an intact forearm were 23% of applied wrist force in the varus alignment and 12% in the valgus alignment. Mean force levels after insertion of the implant were 18% (varus) and 13% (valgus); these were not significantly different from corresponding values for the intact forearm. Mean force levels after section of the IOM were 30% (varus) and 14% (valgus); these were not significantly different from corresponding values for the intact forearm (varus and valgus) but the mean for varus was significantly greater than the corresponding value with an implant. After IOM reconstruction with a palmaris longus tendon tensioned to 22 N mean distal ulnar forces were 8% (varus) and 7% (valgus); these means were significantly less than the corresponding values for all prior test conditions. With the radial head removed increasing the level of graft pretension reduced significantly mean distal ulnar force.
CONCLUSIONS: With the IOM resected insertion of a metal radial head implant alone did not reduce distal ulnar forces to intact forearm levels. When an IOM reconstruction was performed in combination with the implant mean distal ulnar force was reduced significantly to a level below that for the intact forearm. Applying pretension to the graft displaced the radius distally thereby making the wrist more ulnar negative and reducing distal ulnar force. Our results suggest that an IOM reconstruction used in combination with a metal radial head implant theoretically could help reduce distal ulnar impaction in an Essex-Lopresti injury.