In this study, we found that the reverse oblique inclination of the sigmoid notch after USO would have changes in the inclination angles. In the intermediate and long-term follow-ups, osteoarthritic change at the DRUJ could happen, but it seems not to impair the functional results.
Sagerman et al. noted that there is a wide variation between the sigmoid notch inclination and ulnar seat angles. So the articular incongruity could occur following USO in all the three Tolat types of sigmoid inclination [9, 10]. Because of the articular incongruity, there will be a reduction of joint contact area, and then it will lead to an increase of the joint reaction force for the per unit of the contact area. This would be a possible factor producing subsequent occurrence of remodeling or osteoarthritis at the DRUJ. From the reviews, the incidence of DRUJ remodeling or degenerative change after USO were from 16.7% to 43.3% [3, 5, 18-20]. But these were only the radiographic changes without functional impairment (Table 3).
As for the asymptomatic bony spur or remodeling change noted after USO in Table 3, their followed-duration after surgery were reported to be 18-60 months. Tatebe et al reported that most of these bony spurs developed within 18 months postoperatively [5]. Our mean follow-up duration of the 7 patients with developed osteoarthritis was 83.7 months. It is longer than those studies and these patients can still have good functional results at the final follow-ups. Their wrist function was not worse than those without osteoarthritis, except in the wrist supination angle, VAS for pain during activity, and grip strength. So, according to the reviews and our results, the DRUJ bony changes after USO might be not so harmful to the wrist function in the short and intermediate-term.
ROSS et al. reported there would be no reverse oblique inclination if the cartilage thickness is included in the evaluation [12]. There will be a thinner cartilage toward the proximal of the sigmoid notch, which forms the cartilage inclination to be no more reverse oblique while the bony inclination is reverse oblique. Deshmukh et al reported USO will cause the DRUJ articular incongruity and reduction in area of contact of the DRUJ [10]. The proximal part of sigmoid notch would be the contact area after the USO in the reverse oblique inclination. Both the increased pressure and thinner sigmoid cartilage at the proximal contact area would be able to make the DRUJ to develop osteoarthritic changes. In our result, there were 31.8% patients developing osteoarthritic change. In addition, we saw the sigmoid inclination angle would change. Without MRI for identification, we are unable to confirm these bony inclination changes resulting from the proximal layer cartilage wear or from the response of an increased force transmitting through the cartilage. But from our results, these bony changes did not tend to cause symptoms.
The main limitations of this study are the retrospective nature and small case number. No available complete preoperative functional evaluations and not all the patients could have both pre- and postoperative MRI-scans, or even CT-scans, for evaluating the cartilage thickness and bony inclination change, which would be more informative for DRUJ changes [12, 21, 22]. The interobserver variability would also be the bias. In addition, as in the long-term, the influence of degeneration on the wrist should be a concern.