Effects of wafer resection and hemiresection from the distal ulna on load-sharing at the wrist: a cadaveric study.

PURPOSE: Ulnar impaction syndrome is commonly the result of a naturally occurring ulnar-positive condition, distal radius fracture malunion, or collapse of a fractured radial head. The Feldon wafer procedure and the Bowers distal hemiresection procedure are designed to decrease force transmitted through the distal ulna. The purpose of this study was to measure the effects of these procedures on distal ulnar loading with varying degrees of ulnar positivity at the wrist.
METHODS: Using a specially designed miniature load cell distal ulnar force was measured in 20 fresh-frozen cadaveric forearms as the wrist was loaded axially to 134 N in neutral forearm rotation; tests were performed in valgus alignment with the elbow flexed to 90 degrees . Ulnar positivity (0 mm, +2 mm, +4 mm, and +6 mm) was created by incremental shortening of the distal radius using a sliding plate. The radial neck was sectioned transversely and the radial head fragment was fixed in its anatomic position using cemented metal prongs connected to a rigid bar; this allowed the radial head to be disconnected and tilted out of the loading pathway to simulate an excised radial head. Loading tests (with and without the radial head in place) were repeated after removal of a 3-mm wafer of bone beneath the triangular fibrocartilage complex, and again after a hemiresection of the distal ulna to the base of the ulnar styloid process.
RESULTS: For each ulnar status condition (intact, wafer removal, hemiresection) the mean distal ulnar force generally increased as the wrist became more ulnar positive. Both wafer removal and hemiresection significantly decreased mean distal ulnar forces under all conditions of ulnar variance, with or without the radial head in place. With the radial head in place the mean distal ulnar forces (expressed as a percentage of applied wrist force) for the 0-mm condition were 16.9% (intact), 3.8% (wafer removal), and 3.5% (hemiresection); corresponding values for the +6-mm condition were 61.6% (intact), and 39.8% (wafer removal), 15.1% (hemiresection). With the radial head removed the mean distal ulnar forces for the 0-mm condition were 31.7% (intact), 4.6% (wafer removal), and 4.4% (hemiresection); corresponding values for the +6-mm condition were 96.4% (intact), 71.6%, (wafer removal), and 27.2% (hemiresection). The decrease of distal ulnar force resulting from hemiresection was significantly greater than that for wafer removal for all ulnar-positive conditions; force reductions were not significantly different between the 2 procedures with neutral ulnar variance.
CONCLUSIONS: The results of the present study can help to offer a biomechanical basis for choosing between a Feldon wafer procedure and a Bowers hemiresection procedure in patients with ulnocarpal impaction syndrome. Both procedures produced equal decreases of distal ulnar force in the intact forearm. With an ulnar-positive wrist, the condition for which the procedure would be performed commonly, the hemiresection was more effective in decreasing force transmitted through the distal ulna.