Purpose: Scaphotrapeziotrapezoid osteoarthritis (STT-OA) may be related to the progression of carpal instability. This study analyzed the radiographic carpal indices in wrists with varying grades of STT-OA to investigate an association between the severity of STT-OA and the occurrence of dorsal intercalated segment instability (DISI), and to identify radiographic characteristics of carpal instability associated with STT-OA.
Methods: We retrospectively measured carpal indices in 135 wrists with STT-OA (Crosby's classification grade 2, 62; grade 3, 73). Carpal indices measured included radiolunate (RL), radioscaphoid (RS), scapholunate (SL), and lunocapitate (LC) angles and SL distance. We compared the values of these carpal indices and the occurrence of DISI between the STT-OA grade 2 and grade 3 groups. We evaluated the presence of radiographic OA in other joints. In the wrists with DISI, we further investigated the relationship between the RL angle and other carpal angles.
Results: The RL and RS angles of grade 3 patients with STT-OA were smaller than those of grade 2 patients. The LC angle of grade 3 was greater than that of grade 2. DISI was identified in 3 grade 2 wrists (5%), and 44 grade 3 wrists (60%). None of the wrists had an SL angle >70°, a widened SL distance (>3mm), or radiographic OA in the RS joint. In the 47 wrists with DISI, there was a negative correlation between RL and LC angles, and positive correlation between RL and RS angles.
Conclusions: We found an association between the severity of STT-OA and occurrence of DISI, and identified unique characteristics of this carpal instability, which include an extended position of the scaphoid, a normal SL angle, and no development of RS-OA.
Type of study/level of evidence: Differential diagnosis/symptom prevalence study IV.
Keywords: Carpal instability; dorsal intercalated segment instability; osteoarthritis; scaphotrapeziotrapezoid joint.
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