Measurement of external three-dimensional interphalangeal loads applied during activities of daily living.

OBJECTIVE: To measure the external three-dimensional loads applied to the interphalangeal joints during activities of daily living.
DESIGN: A six-degree-of-freedom force transducer was used in conjunction with motion analysis studies.
BACKGROUND: There is a lack of accurate three-dimensional load data available for input into biomechanical models of the hand.
METHODS: A new force transducer has been incorporated into several housings representing objects in domestic use: a jar, a tap, a key in a lock and a jug kettle. Three-dimensional kinematic data were acquired using a six-camera VICON motion analysis system. Twelve healthy volunteers took part in the study, which compared power and precision grips in 'opening' and 'closing' activities.
RESULTS: Large external forces and moments are applied to the middle and distal phalanges in sagittal, coronal and axial directions. Average inter-segmental forces of up to 25 N and average moments of up to 1.8 Nm are experienced at the proximal interphalangeal joint.
CONCLUSIONS: The results show that complex loading patterns are associated with routine activities of daily living. RELEVANCE: Biomechanical models of the interphalangeal joints are limited in their ability to accurately predict tendon and joint forces by the quality of the input data obtained by conventional measurement techniques. Models have tended to rely on hypothetical values of external forces acting on the hand and are over-simplified or limited to two-dimensions. The results from the current study challenge the validity of these simplified models and offer a more complete picture of the complex loading system applied to the finger during daily life.