Ulnar impingement syndrome is a condition which is occurs secondary to relative shortening of the ulna in comparison to the radius. It should not be confused with ulnar impaction syndrome which is due to a relatively long ulna. In the absence of the buttressing effect provided by the physiological distal radio-ulnar joint the shortened ulna may be pulled against the radial head or shaft, proximal to its normal articulation at the sigmoid notch. This occurs due to the action of muscles such as pronator quadratus and is referred to as distal radio-ulnar convergence. If this occurs with sufficient force, the resulting pseudo articulation can cause erosion of the radius and subsequently pain 1.
This CT scan demonstrates all the expected radiographic findings of ulnar impingement syndrome which are; distal ulnar shortening, radio-ulnar convergence, scalloping (erosion) of the radius adjacent to the distal ulna and bony sclerosis underlying the eroded region 1, 2.
The majority of patients suffering from this syndrome have had surgical ulna shortening (the Darrach procedure) for management of conditions such as severe arthritis or trauma. Rarely, such as in this patient, it can occur due to non-iatrogenic negative ulnar variance. Treatment can include; further ulnar shortening, radial osteotomy to equalise lengths or distraction lengthening if the cause is unequal growth 1, 2.
This patient also has small foci of calcification in both the distal ulnar and radial physes. The exact aetiology of this is uncertain but they could possibly represent a previous growth plate injury which may have contributed to the development of his negative ulnar variance.