Ulnar impingement syndrome is a wrist condition caused by a shortened distal ulna impinging on the distal radius proximal to the sigmoid notch. The syndrome is distinct from ulnar impaction syndrome, which typically occurs due to a long ulna (positive ulnar variance) impacting upon the triangular fibrocartilage (TFC) and lunate.
Most commonly, the syndrome is caused by surgical resection of the distal ulna as part of management of wrist trauma, rheumatoid arthritis, or Madelung deformity. Less commonly, ulnar impingement may occur in de novo negative ulnar variance.
The clinical presentation of ulnar impingement is similar to that of ulnar impaction; however, patients generally experience greater pain on pronation and supination. Compression of the distal radioulnar joint during forearm rotation can exacerbate symptoms and produce a characteristic grating feeling.
A shortened distal ulna results in contraction of the extensor pollicis brevis, abductor pollicis longus, and pronator quadratus muscles which prevents normal buttressing of the radioulnar joint. This produces distal radioulnar convergence and impingement of the ulna upon the distal radius.
Plain film findings are only seen after the condition has been present for many years. MRI is most sensitive for detecting early disease. Imaging findings include:
- ulnar shortening (usually surgical)
- radioulnar convergence
- subchondral sclerosis / local bone edema where distal ulnar impinges radius
- erosive ‘scalloping’ of the distal radius by the ulnar in later disease
Treatment and prognosis
Without treatment there is progressive disease with marked disability of forearm function. Treatment depends on whether the distal ulna is short due to previous surgical resection or de novo negative ulnar variance. Aggressive ulnar shortening or ulnar head prostheses can be considered in cases where impingement is due to prior distal ulnar resection. Distraction lengthening of the ulna is the preferred in cases of de novo negative ulnar variance.