Review Question - QID 218097

This patient has a negative ulnar variance. Negative ulnar variance has been identified as a risk factor for the development of Kienbock disease with progressive lunate collapse (Answer 2) and ulnar impingement syndrome.

Ulnar variance is the length of the ulnar compared to the length of the radius at the wrist. Positive ulnar variance indicates a longer ulna compared to the radius and a negative ulnar variance indicates a shorter ulna. Changes in ulnar variance alter the distribution of force transmission across the wrist, with negative ulnar variance causing increased forces to be transmitted across the distal radius (Illustration A).

The diagnosis of abnormal ulnar variance is made radiographically with PA wrist radiographs. Given the fact that ulnar variance becomes more positive in pronation and more negative in supination, it is imperative the upper extremity of the wrist to be imaged is placed in 90° of shoulder abduction and 90° of elbow flexion, with the forearm in natural rotation. The measurement of ulnar variance is made by measuring the difference between two lines (one line tangential to the articular surface of the ulna and perpendicular to its shaft and one line tangential to the lunate fossa of the radius and perpendicular to its shaft) (Illustration B).

Multiple orthopaedic conditions have been associated with aberrations in ulnar variance. With respect to negative ulnar variance, the development of both Kienbock disease (osteonecrosis of the lunate) and ulnar impingement syndrome have both been associated with this abnormality. With respect to Kienbock disease, it has been shown that negative ulnar variance leads to increased radial-lunate contact stress, increasing the risk of patients' experiencing collapse of the lunate.

Goeminne et al. investigated anatomic factors and their effect on the progression of Kienbock disease. Their study included 70 patients with the disease. The authors found that in later stages of the disease, hallmarked by the collapse of the lunate, patients were much more likely to exhibit negative ulnar variance. As a result, the authors postulate that negative ulnar variance encourages progressive lunate collapse, while neutral or positive variance appears to be protective against collapse.

Rhee et al. investigated the possible correlation of the presence/absence of a type II lunate on the radiographic characteristics of patients presenting with Kienbock disease. Their study included 106 wrists, with 75% having a Type I lunate and 29% having a Type II. Overall, the authors found that patients with Type II lunates appeared to be protected from coronal fractures and scaphoid flexion deformities. The authors of this study did not investigate ulnar variance as a risk factor.

van Leeuwen et al. investigated risk factors of lunate collapse in Kienbock disease. Their study population consisted of 195 patients with Kienbock disease and appropriate radiographs. Overall, the authors found that more negative ulnar variance correlated with a greater magnitude of lunate collapse in Kienbock disease.

Figure A is a PA radiograph of the wrist demonstrating ulnar negative variance. Illustration A is a table outlining the changes in force distribution across the wrist that occurs with aberrations in ulnar variance. Illustration B demonstrates the two-line technique for measuring ulnar variance.

Incorrect Answers
Answers 1,3,4 and 5: all of these conditions have been associated with positive, not negative, ulnar variance.