To the best of our knowledge, this is the first in vivo evaluation of the contact area of the wrist joint before and after radial shortening osteotomy for Kienböck’s disease. The present study demonstrated that the contact area of the wrist joint changed following radial shortening osteotomy. The contact area of the center of the radioscaphoid and radiolunate joints was translated radially and dorsally following radial shortening osteotomy. This result indicates that radial shortening reduced the load on the lunate by altering the contact area between the radiolunate and radioscaphoid joints.
Several cadaveric and theoretical studies have attempted to analyze the contact area of wrist joints in patients with Kienböck disease.7,8 However, it is difficult for these biomechanical studies to create an experimental model simulating Kienböck disease and to determine the physiological loading conditions on the models. To overcome these difficulties, the current study applied an in vivo CT bone model analysis system to clarify alterations to the joint contact area after radial shortening osteotomy. In the present study, the contact areas of the radioscaphoid and radiolunate joints were calculated before and after radial shortening osteotomy using in vivo 3D methods. Using cadaveric wrist joints, Tencer et al demonstrated that the overall scaphoid contact area was 1.47 times that of the lunate,9 and Iwasaki et al demonstrated that the mean value of the maximum area ratio of the lunate to the scaphoid fossa was 1.10 ± 0.44 (mean ± SD) in the normal wrist.10 The current results of preoperative wrist joint contact area are comparable to those of previous reports.
A number of studies have reported that radial shortening provides acceptable clinical results for Kienböck disease,11–13 and that this osteotomy achieves revascularization and unloads the diseased lunate.14–16 Several biomechanical studies have demonstrated that radial shortening unloads the lunate by shifting the load toward the distal ulna.17,18 Using a cadaveric model, Werner et al showed that relative shortening of the radius by 2.5 mm shifted the load on the lunate from the radiolunate to the ulnolunate articulation.15 Masear et al and Trumble et al used strain gauges mounted on the lunate to show unloading of the lunate following radial shortening or ulnar lengthening.17,18 The present data showed that the contact area shifted radially and dorsally after radial shortening in living subjects, and all patients could return to their previous activities with no disturbance in wrist function. Therefore, it seems reasonable to conclude that decompression of the lunate is achieved by the biomechanical effects of radial shortening itself, in which the load on the lunate is shifted onto the scaphoid.
There are some limitations of the present study. First, we did not image the entire radius or evaluate the ulnar contact area. Second, we used a surface registration technique. Finally, the current study was not able to clarify direct relationships between wrist injury and various predictive factors. It will be necessary to conduct a prospective study with a larger number of participants in the future to show the relationship between contact area and wrist injuries; however, the present results consistently showed a characteristic pattern of contact area in the wrist that appeared to accurately represent the wrist contact area of patients with Kienböck disease, both before and after surgery.
In conclusion, bone surface modeling of the wrist joint using 3D CT imaging shows promise for evaluation of the effects of surgery on the articular contact area of the wrist.