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Assessment of Midcarpal Deformity of the Wrist Using the Triangulation Method
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ABSTRACT
Static radiographic assessment of the wrist for midcarpal instability (ie, palmar intercalated segmental instability and dorsal intercalated segmental instability) can be performed using the triangulation method. This method uses three anatomical landmarks observed on the standard lateral wrist radiograph.
One hundred twenty-five normal lateral radiographs were measured to determine the normal range for the dorsal limb to palmar limb ratio. A two-step process of performing triangulation is described. The first step is nonspecific screening of the radiograph and defines values >1.0 as having a dorsal intercalated segmental instability deformity and values <0.5 as having a palmar intercalated segmental instability 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 dorsal limb:palmar limb ratio with the radiometacarpal angle.
The average lateral wrist position was 8.4° of extension (-8.4). The average dorsal limb:palmar limb ratio was 0.75±0.09 (range: 0.93-0.57).
Based on this data, dorsal intercalated segmental instability wrist deformity was defined as dorsal limb:palmar limb ratios >1.0 and ratios <0.5 representing palmar intercalated segmental instability deformities. The triangulation method of assessing midcarpal alignment of the carpus is a practical and simple alternative to the traditional static radiographic methods of assessing midcarpal wrist instability.