Ulnocarpal abutment syndrome

Ulnocarpal abutment syndrome (UCAS) is a degenerative condition characterized by ulnar-sided wrist pain, edema, and functional limitations

• underlying cause is an excessive load on the ulnar side of the wrist joint causing progressive changes in the lunate, triquetrum, and triangular fibrocartilage complex (TFCC)
  • pathoanatomy
    • in a wrist with +2 mm ulnar variance approximately 40% of the load goes to the ulna 60% to the radius
    • in a normal neutral wrist approximately 20% of the load goes to the ulna 80% to the radius
      
      
• if left untreated, the condition leads to lunate, triquetral, and ulnar chondromalacia, degenerative changes of the TFCC, potential wrist instability resulting from lunotriquetral ligament injury, and eventually, osteoarthritis of the ulnar side of the carpus or the distal radioulnar joint (DRUJ)
  
  
• most common anatomical variation associated with the increased ulnar-sided load is an ulna-positive variance of the wrist. However, other causes include malunited distal radius fractures, Essex-Lopresti injuries, or radial head excision with progressive radial shortening

Reference:

• Palmer AK et al Relationship between ulnar variance and triangular fibrocartilage complex thickness. J Hand Surg 1984; 9:681-682
• Cerezal L et al. Canga Imaging findings in ulnar-sided wrist impaction syndromes Radiographics 2002; 22:105-12.