A ratio to approximate the proximodistal extent of the flexor retinaculum in relation to the hand length.

The flexor retinaculum of the hand is a fibrous structure forming the carpal tunnel in conjunction with the carpal bones. To prevent incomplete release of the carpal tunnel it is of benefit to know about the expected longitudinal expansion of the flexor retinaculum. The objective of the present study was to identify a possible correlation between the proximodistal expansion of the flexor retinaculum and the length of the hand. We conducted an anatomical study on 124 hands of 62 body donors. The hand length and the length of the flexor retinaculum were measured in millimeters. By dividing the length of the flexor retinaculum by the hand length an individual ratio was calculated. The mean length of the observed hands was 187.8 mm. The mean proximodistal length of the flexor retinaculum was 27.2 mm (range, 14-39 mm). A positive correlation was noted between the proximodistal length of the flexor retinaculum and length of the hand (p = 0.01). On average, the length of the flexor retinaculum corresponded to 14% (range, 8-20%) of the hand length in right hands versus 15% (range, 11-20%) in left hands. A greater proximodistal length of the flexor retinaculum in longer hands compared to shorter hands can be expected. The length of the flexor retinaculum corresponds to 14-15% of the length of the hand. However, one should be aware that the length of the flexor retinaculum extends as far as 20 % of the length of the hand.