CHAPTER 3 Arthroscopically Assisted Ulnar Shortening
Basic Science and Anatomy
Ulnocarpal Joint Anatomy
The base of the triangular fibrocartilage attaches to the distal radius at the distal edge of the sigmoid notch. Its distal surface blends imperceptibly with the hyalin cartilage of the lunate fossa of the distal radius. The triangular fibrocartilage narrows as it passes from radial to ulnar to insert in the fovea at the base of the ulnar styloid. Dorsally and palmarly, the TFCC thickens to form the distal radioulnar ligaments. The integrity of these two ligaments is critical to the stability of the distal radioulnar joint. The triangular fibrocartilage meniscal homologue passes distally to attach at the ulnar aspect of the triquetrum. The interval between the ulnotriquetral ligament and the meniscal homologue and ulnar collateral ligament is known as the pre-styloid recess (or the pisotriquetral recess).1
Biomechanics
Palmer and others have demonstrated an inverse relationship between the thickness of the triangular fibrocartilage and ulnar variance.2 That is, the more positive the ulnar variance the thinner the triangular fibrocartilage. This relationship explains the observed coincidence of ulnar plus variance and TFCC tears (ulnar abutment syndrome). The ulnar abutment syndrome is characterized by an ulnar plus variance, central tears of the triangular fibrocartilage, and chondromalacia of the adjacent articular surfaces of the lunate, triquetrum, and ulnar head.
Werner et al.3 have studied the effect of ulnar length on load transmission across the triangular fibrocartilage. They demonstrated a direct relationship between the length of the ulna and the amount of force transmitted across the TFCC. As the ulna gets longer, the force transmitted across the TFCC increases. The opposite occurs with ulnar shortening.
The vascular supply of the triangular fibrocartilage is characterized by a peripheral vascular zone and a central avascular zone.4 The lack of central blood supply precludes any healing of central TFCC tears and dictates the choice of debridement as the treatment for such tears.
Contraindications
Arthroscopic ulnar shortening is unlikely to help those patients who present with an ulnar abutment syndrome combined with additional ulnocarpal and/or lunatotriquetral pathology. A lunatotriquetral ligament instability or ulnocarpal ligament laxity in the presence of an ulnar abutment syndrome will not respond to an arthroscopic ulnar shortening because the arthroscopic ulnar shortening does not address the LT or ulnocarpal instability. An ulnar shortening osteotomy combined with an arthroscopic TFCC debridement would be a reasonable approach in this case. The LT and ulnocarpal instability cannot be treated with ulnocarpal capsular shrinkage because the capsular shrinkage demands immobilization for six to eight weeks. The postoperative regimen for an arthroscopically assisted ulnar shortening consists of early range of motion of the wrist and distal radioulnar joint.
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