Abstract
The purpose of this study is to present an alternative method for static radiologic assessment of the wrist for midcarpal instability (ie, palmar intercalated segmental instability [PISI] and dorsal intercalated segmental instability [DISI]). The triangulation method uses 3 anatomic landmarks observed on the standard lateral x-ray of the wrist.
A total of 125 normal lateral radiographs were measured to determine the normal range for the dorsal limb (DL) to palmar limb (PL) ratio. A 2-step process of performing triangulation is described. The first step is nonspecific screening of the radiograph and defines values greater than 1.0 as having a DISI deformity and values less than 0.5 as having a PISI deformity. The second step is used only for borderline values, which takes the position of the wrist into consideration and uses a normagram (reference chart) to match the DL:PL ratio with the radiometacarpal (RM) angle.
The average lateral wrist position was 8.4° of extension (−8.4). The average DL:PL ratio was 0.75 ± 0.09 (range, 0.93–0.57).
Based on these data we defined DISI deformity of the wrist as DL:PL ratios greater than 1.0, and ratios less than 0.5 representing PISI deformities. The triangulation method of assessing midcarpal alignment of the carpus is a practical and simple alternative to the traditional static radiologic method of assessing midcarpal instability of the wrist.