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Distal Ulnar Stump (DUS) Stability: The Role of the Distal Interosseous Membrane (DIOM). Anatomic Research Study
Luciano A. Poitevin, MD, PhD; Daniel Postan, MD
Buenos Aires University, Buenos Aires, Argentina

Introduction: DUS instability is often a problem when performing a Darrach or Sauvé-Kapandji procedure. Recent studies have stressed that the DIOM reinforces the Triangular Fibrocartilage Complex (TFCC), providing additional stability to the distal radio-ulnar joint (DRUJ). The aim of this study was to determine whether the DIOM stabilizes the ulnar stump and the ideal level to perform the osteotomy.

Methods: Random left and right forearms in 20 fresh-frozen cadavers were dissected to the volar and dorsal aspects of the DIOM. The Distal Oblique Band (DOB), when present, was recorded and measured. The radius was fixed to a board and the ulna kept free. The DRUJ was stabilized with a transverse lag-screw and a K-wire. Two transverse ulna osteotomies were performed at 10 and 15mm proximal to the ulno-carpal joint. The bone slice was removed. Dorsal and volar translation maneuvres were were done applying a force of 10N through an analogic dynamometer. The displacement was measured with calipers accurate 1/20mm Transection of the DIOM was then performed, the maneuvers were repeated and new measurements done and compared with those of the intact DIOM. The results were assessed by means of the software g-stat 2.0 ®. The level of significance was defined as p>0.05.

Results: All of the specimens showed a distinct distal membrane. An obvious DOB measuring a mean of 28mm was noticed in 70%. It attached to the dorsal rim of the sigmoid notch, ran obliquely from distal to proximal and from radial to ulnar, and fixed to the distal third of the lateral border of the ulna. This attachment starts 31mm proximal to the ulnocarpal joint and ends at 40mm (average). Initial displacements averaged 18mm dorsally and 12mm volarly. After DIOM transection, ulnar translocation increased to an average of 30mm dorsally and 20mm volarly. The difference was statiscally significant.

Discussion and Conclusions: The DIOM and the DOB act as stabilizers of the DUS. In Sauvé-Kapandji procedure it should be advisable to perform the distal osteotomy at no more than 15mm proximal to the ulnar head articular surface, and the proximal one at no more than 20 mm. For the Darrach procedure, a 10 mm resection seems to be in a very safe area. However, the retaining effect of the DIOM will not be enough to prevent up to 18 mm of dorsal displacement of the ulnar stump. Therefore, in Darrach or Sauvé-Kapandji procedures, some augmentation method should be added.

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