A New Examination Method for Anatomical Variations of the Flexor Digitorum Superficialis in the Little Finger

BACKGROUND: Current examination methods to assess the anatomical variations of flexor digitorum superficialis (FDS) tendon in the little finger necessitate a strong external force applied by the examiner and cause false negatives. A new examination method was designed to detect the variations more accurately. METHODS: We examined the little fingers of 220 adult hands (110 subjects) by 2 methods: the expanded examination method advocated by Tan et al., and a new examination method. Variations of the FDS in the little finger were examined by both methods and categorized separately as having independent FDS function, FDS connection to the tendons of the ring finger or of the multiple adjacent fingers, and functional substitution of the flexor digitorum profundus (FDP) with or without tendinous connection to the ring or multiple adjacent fingers. By our new method, we could further divide the FDS connection or FDP substitution with connection to the ring finger into 2 subtypes: loose and close connections. Data were reported as case numbers and percent. Date on symmetry were statistically analyzed by matched case-control studies. RESULTS: Among 220 hands, 113 hands (51.4%) had independent FDS function by the new examination method, which was lower than the incidence (55.5%) detected with the existing expanded examination method. In the hands with connections between FDS tendons of the little and the ring fingers, 32 hands (14.5%) demonstrated loose and 37 (16.8%) close connections. Three hands (1.4%) had loose and 19 (8.6%) had close FDP substitution with tendinous connection to the ring finger. Among 110 hands without independent FDS function, variants of 42 hands (38.2%) were asymmetric. There was no statistical significance in symmetry of variations. CONCLUSIONS: This new examination method offers other assessment variations of FDS tendon in the little finger. We recommend using this test to assess the variations and function of the FDS of the little finger.