title: Intrinsic hand muscle function, part 1: creating a functional grasp.
abstract: OBJECTIVE
  Regaining hand function has been identified as the highest priority for persons with tetraplegia. In many patients, finger flexion can be restored with a tendon transfer of extensor carpi radialis longus to flexor digitorum profundus (FDP). In the absence of intrinsic function, this results in a roll-up finger movement, which tends to push large objects out of grasp. To enable patients to grasp objects of varying sizes, a functional grasp is required that has a larger excursion of fingertip-to-palm distance than can be supplied without intrinsic function. The aim of this study was to quantify the role of intrinsic muscle force in creating a functional grasp.
  
  
  METHODS
  Finger kinematics during grasp were measured on 5 cadaveric hands. To simulate finger flexion, the FDP was activated by a motor and intrinsic muscles were loaded at various levels (0, 125, 250, 375, or 500 g). Finger movement was characterized by the order of metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joint flexion and by the maximal fingertip-to-palm distance during finger closure.
  
  
  RESULTS
  Without any intrinsic muscle contribution (0-g load), FDP activation resulted in flexion of all 3 joints, whereby flexion began at the proximal interphalangeal joint, followed by the distal interphalangeal joint, and then the metacarpophalangeal joint. With increasing intrinsic muscle load, finger flexion was initiated at the metacarpophalangeal joint, followed by the proximal interphalangeal and distal interphalangeal joints. This altered joint flexion order resulted in a larger maximal fingertip-to-palm distance during finger flexion. The difference between the 2 extreme conditions (0 g vs 500 g of intrinsic muscle load) was 19 mm.
  
  
  CONCLUSIONS
  These findings demonstrate that simultaneous activation of the FDP and the intrinsic muscles results in an apparently more functional hand closing compared with FDP activation alone because of altered kinematics and larger fingertip-to-palm distances.
  
  
  CONCLUSIONS
  These findings suggest that intrinsic muscle balancing during reconstruction of grasp in tetraplegic patients may improve function.
authors.affiliation: Swiss Paraplegic Centre, Nottwil, Switzerland; Department of Orthopadeics, University of California, San Diego, California; Sahlgrenska University Hospital, Gothenburg, Sweden.
authors.forename: Ursina
authors.initials: U
authors.lastname: Arnet
authors.forename: David A
authors.initials: DA
authors.lastname: Muzykewicz
authors.forename: Jan
authors.initials: J
authors.lastname: Fridén
authors.forename: Richard L
authors.initials: RL
authors.lastname: Lieber
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005260:Female; D050278:Finger Phalanges / Q000033:anatomy & histology; D006225:Hand / Q000502:physiology* / Q000503:physiopathology; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology* / Q000503:physiopathology; D011782:Quadriplegia / Q000503:physiopathology / Q000601:surgery; D019651:Plastic Surgery Procedures
keywords: Grasp; hand; intrinsic muscles; tendon transfer; tetraplegia