[Selective in vivo force measurement of superficial and deep finger flexor tendons depending on wrist position]

There are different options for further treatment following flexor tendon injuries of the hand. These can be divided into passive and active dynamic treatment regimens. The selection of the optimal further treatment depends primarily on the biomechanically acting forces during postoperative finger exercises. Quantitative biomechanical studies are therefore required. The present experiment examined which forces act on the superficial and deep finger flexor tendons in different wrist positions. A measuring device was developed with the help of which both the total forces of the fingers and the isolated forces of the superficial (FDS) and deep (FDP) finger flexor tendons could be quantified in vivo. The measurements were evaluated on the index, middle, ring and little fingers (D2 - D5) of both hands of 50 test subjects, including 31 women (62%) and 19 men (38%). The influencing factors handedness, gender, fingers and wrist position were checked for interdependence using mixed ANOVA (p<0.05) and further differentiated using t-tests and one-factor ANOVAs (p<0.05). There was a statistically significant reduction in finger strength by flexing the wrist. On average, the highest forces were recorded at D3 and the lowest at D5. There was no significant difference between D2 and D4. On average, higher forces were achieved at D2, D3 and D4 by the FDS than by the FDP. At D5 there was a reversed force relationship with a higher force development of the FDP. The sum of the isolated forces of the FDS and FDP at D2 to D4 was around 80%, at D5 it was only 60%. The remaining force development can be explained by the influence of the metacarpal muscles and, in the case of D5, also by the flexor digiti minimi muscle. The results enable a differentiated assessment of the biomechanical forces acting during active finger flexion.