Contribution of intrinsic muscles to functional grasp Ursina Arnet Swiss Paraplegic Research, Nottwil, Switzerland, University of California, San Diego, USA David Muzykewicz University of California, San Diego, USA Jan Fridén Sahlgrenska University Hospital, Gothenburg, Sweden, Swiss Paraplegic Centre, Nottwil, Switzerland Richard Lieber University of California, San Diego, USA

Introduction Reconstruction of finger flexion Restoration of grasp by surgical transfer: Extensor carpi radialis longus (ECRL)-to-flexor digitorum profundus (FDP) Problem: normal finger movement → roll-up finger movement inability to grasp large objects → intrinsic hand muscles reconstructed FDP only

Introduction Aim of the study Aim: To quantify the role of intrinsic muscle force in creating a functional grasp. Functional grasp = large fingertip-to-palm distance palm

Methods Sample preparation and testing: 5 cadaveric hands (fresh frozen), amputated at radiocarpal joint -Skin excised -FDP tendons: attached to motor -INT: 2-0 silk at tendinous insertion into lateral band, attached to weights via pulley -Extensor digitorum communis (EDC) tendons: attached to weight via pulley 0g, 250g, 500g, 750g 50g 50mm Motor

Methods Kinematic analysis Kirschner wires into metacarpals and phalanx bones (all fingers) Video capture from radial side (2D) Digitization of wire position (Matlab): wires vectors bone vectors joint angles joint and fingertip positions x x x x x x x x MCP PIP DIP x x x x x x x x

Methods Data analysis palm

Results Movement With vs. without intrinsics 0g500g

Results Fingertip Trajectory of fingertip (mean all fingers) Maximal distance fingertip to palm* (middle finger) 0g250g500g750g 67±9mm79±7mm87±6mm89±mm *significant difference between INT load (p < 0.001) 0g 250g 500g 750g

Results Joint angles MCP PIPDIP ◊ = Excursion of maximal angular change* *significant difference between INT load (p < 0.001) 0g500g 750g 250g

Discussion Role of intrinsics Simultaneous activation of FDP and INT = more functional hand closing Functional hand closing: - larger fingertip-palm distance - finger flexion initiated at MCP and followed by PIP and DIP These results illustrate the importance of INT balancing during reconstruction of grasp in tetraplegic patients. With INT balancing, patients will be able to grasp larger objects, increasing their independence.

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