Ulnar carpal impaction is a common cause of wrist pain. It is caused by the ulna (one of the bones of the forearm) being long in relation to the radius and impinging on the carpus (in particular the lunate). This may be a normal anatomical variation or occur as a result of injury (i.e. a mal-union after a fracture). It is easily diagnosed using x-rays which measure the ulnar variance and, depending on the degree of symptoms, most often treated with a ulnar shortening osteectomy.