Common causes of dorsal intercalated segment instability (DISI) include scapholunate dissociations and scaphoid fracture nonunions. Although less common than these, scaphotrapezium-trapezoidal (STT) osteoarthritis (OA) may also be associated with the development of a DISI deformity. The clinical implications of this form of carpal instability in cases of STT arthritis are still unknown. To study the radiographic progression and incidence of this entity, we reviewed our patients and report on 24 wrists with DISI in the presence of STT arthritis.
A retrospective chart and radiographic review was performed on all patients seen between 1994 and 2004, with the diagnosis of STT arthritis to identify a subgroup of patients with DISI deformity on the presenting radiographs. Patients' clinical and surgical courses were noted. Postoperative radiographic changes were recorded, as were clinical outcomes.
Sixteen patients with 24 wrists having STT arthritis and DISI deformity on presenting radiographs were identified. The median STT arthritis grade was 3.0 based on a modified Eaton and Glickel grading system. The median radiolunate angle was -21 degrees of dorsal tilt. All patients had normal scapholunate angles. Abnormal scaphoid extension was seen in 19 of 24 wrists as measured by the radioscaphoid angle. Concomitant carpometacarpal arthritis was seen in 67% (n = 16) of the wrists, and midcarpal arthritis was identified in 50% (n = 8) of patients. Fifteen wrists required surgery for the symptoms and were followed up for a mean of 29 months after surgery. In the surgical group the radiolunate angles increased by mean of 6 degrees after surgery. Four of the 15 wrists required revisional surgery for persistent pain.
Patients with STT arthritis may present with carpal instability that is not related to radiographic scapholunate instability. This instability is characterized by a normal scapholunate angle with an extension stance of the scaphoid and lunate. Midcarpal arthritis may be present. Surgical intervention for patients with STT arthritis and DISI deformity may lead to radiographic progression of midcarpal instability.