Ulnar Impaction Syndrome

Ulnar impaction syndrome is a degenerative condition caused by chronic impaction between the ulnar head and the triangular fibrocartilage complex and the ulnar carpus. This results in degenerative tear of the triangular fibrocartilage; chondromalacia of the lunate, triquetrum, and distal ulnar head; instability or tear of the lunotriquetral ligament; and, osteoarthritis of the ulnocarpal and distal radioulnar joints.

The most common predisposing factor include congenital positive ulnar variance (although neutral and negative ulnar variance can also be seen), malunion of the distal radius, premature physeal closure of the distal radius, and previous radial head resection. Ulnar impaction syndrome may also occur due to activities that cause excessive intermittent loading of the ulnar carpus.

Radiographs and CT may reveal subchondral sclerosis and cystic changes in the ulnar head, ulnar aspect of the proximal lunate, and proximal radial aspect of the triquetrum. As the disease progresses, ulnocarpal osteoarthritis may be seen in these areas.

MRI in the early stage of ulnar impaction syndrome reveals fibrillation of the cartilage of the ulnar head and ulnar carpus. Later, T2 hyperintensity and T1 hypointensity can be seen in the ulnar head, ulnar aspect of the proximal lunate (seen above), and proximal radial aspect of the triquetrum. More advanced disease is characterized by sclerosis, which is of low signal intensity on both T1- and T2-weighted images. Tears of the triangular fibrocartilage and lunotriquetral ligament may also be seen, although MR arthrography is better at demonstrating these findings.

Differential considerations include:

• Asymptomatic senescent changes: Lack of positive ulnar variance.
• Intraosseous ganglia: Area of lucency on radiographs that have sharp margins. No signal intensity change in the triquetrum or ulnar head.
• True cysts: Area of lucency on radiographs that have sharp margins. No signal intensity change in the triquetrum or ulnar head.
• Vascular groove: Central proximal radiolucent defect that communicates with the radiolunate joint space.
• Kienböck disease: More diffuse. Affects the radial half of the lunate bone. The triquetrum and ulnar head are not affected.

References

Cerezal L, del Piñal F, Abascal F, García-Valtuille R, Pereda T, Canga A. Imaging findings in ulnar-sided wrist impaction syndromes. Radiographics. 2002 Jan-Feb;22(1):105-21.