Radiographic Parameters of Increased Carpal Tunnel Pressure With Progressive Wrist Distraction: A Cadaveric Study

PurposeIncreased carpal canal pressure associated with external fixation has been noted as a potential source of complications but no correlated clinical observation has been identified. We hypothesized that there would be a significant change in midcarpal distance and modified carpal height index with increasing distraction across the wrist joint and that these changes would correlate with pressure increases.MethodsThirteen cadaveric upper extremities were mounted vertically using 2 half pins in the midradius. Using a previously reported technique, we introduced a balloon-tipped catheter attached to a transducer into the carpal canal for pressure measurement. As weights were hung from the middle finger to create distraction across the carpus, pressure measurements and radiographs of the wrist were taken simultaneously. This sequence was performed for 4.50 kg of distraction in 0.45-kg increments and at 6.80 and 9.07 kg of distraction with the wrist in neutral position. Changes in midcarpal distance and modified carpal height index were calculated and comparisons were made with the Student t test. A 2-tailed Pearson correlation was used to determine whether there was a correlation between carpal canal pressure and radiographic indicators. Significance was set at p ≤ .05.ResultsA statistically significant increase in carpal canal pressure above baseline occurred at a load of 1.81 kg. The increase in the midcarpal space and modified carpal height index became significant at a load of 1.81 kg. The change in pressure and the changes in radiographic indicators correlated significantly (p < .01).ConclusionsThis preliminary cadaveric study found a small but significant increase in modified carpal height index with wrist distraction that correlated with increased carpal canal pressure. Further biomechanical and clinical studies are needed to determine recommended parameters for change in modified carpal height index with wrist distraction clinically.