Effects of external loading conditions on in vivo forces generated by finger flexor muscles

The goals of this dissertation were to investigate the effects of finger and wrist posture, external force distribution, and fingertip force rate on in vivo forces in the flexor digitorum profundus (FDP) and the flexor digitorum superficialis (FDS) tendons of the index finger and to evaluate the ability of a biomechanical model to predict these tendon forces. This information can identify finger positions and motions that are associated with lower tendon forces and may be used to design tools and tasks to decrease risk of tendon overuse injury and improve rehabilitation strategies. Tendon forces were recorded with buckle force transducers and fingertip forces were measured with a load cell in 15 adults during carpal tunnel surgery while hand position was recorded with a video camera.; Flexor tendon to fingertip force ratios depend on positions of the metacarpophalangeal and distal interphalangeal joints as well as the direction of applied external force when subjects isometrically increase their fingertip force from 0 to 15 N. For the same fingertip force, FDP force can be reduced by using a pulp pinch posture and increasing MP joint flexion. FDS force can be reduced in a tip pinch posture and extended MP position.; A static, three-dimensional biomechanical model poorly predicts these in vivo tendon forces demonstrating the importance of validating models before they are used to plan prevention strategies.; Applying fingertip force at higher rates (15 vs. 1.5 N/s) does not significantly increase FDP or FDS force ratios during isometric pinch tasks. Thus, reducing fingertip loading rate, within this range, may not reduce risk of injury.; During active, unresisted finger flexion or extension, FDP force is higher when the fingers are in a flexed posture and the wrist is either in a flexed or neutral position while FDS force is higher only when the fingers and wrist are both in a flexed posture. Therefore, tendon forces can be reduced by limiting finger and wrist flexion.; These findings may be used to develop guidelines for reducing tendon forces in order to design prevention strategies for tendon disorders of the hand.