A new methodology to measure load transfer through the forearm using multiple universal force sensors

Previous approaches to measuring forces in the forearm have made the assumption that forces acting in the radius and ulna are uniaxial near the wrist and elbow. To accurately describe forces in the forearm and the forces in the interosseous ligament, we have developed a new methodology to quantitatively determine the 3-D force vectors acting in forearm structures when a compressive load is applied to the hand. A materials testing machine equipped with a six degree-of-freedom universal force-moment sensor (UFS) was employed to apply a uniaxial compressive force to cadaveric forearms gripped at the hand and humerus. Miniature UFSs were implanted into the distal radius and proximal ulna to measure force vectors there. A 3-D digitizing device was used to measure transformations between UFS coordinate systems, utilized for calculating the force vectors in the distal ulna, proximal radius, and the interosseous ligament (IOL). This method was found to be repeatable to within 3 N, and accurate to within 2 N for force magnitudes. Computer models of the forearm, generated from CT scans, were used to visualize the force vectors in 3-D. Application of this methodology to eight forearm specimens showed that the radius carries most of the load at the wrist while force in the IOL relieves load acting in the radius at the mid-forearm. For a 136 N applied hand force, the force in the IOL was 36 + 21 N. Advantages of this methodology include the determination of 3-D force vectors, especially those in the IOL, as well as computer generated 3-D visualization of results.