Article
Comparison of the efficiency between the extrinsic and intrinsic extensor muscles for extension of the proximal interphalangeal joint of the finger
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Published: | February 6, 2020 |
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Objectives/Interrogation: Extension of the proximal interphalangeal (PIP) joint of the finger is consisted of both the extrinsic and intrinsic muscle function. We aimed to analyze combined role of both functions in extension of the PIP joint of the finger with fresh cadaver specimen.
Methods: Seven fingers of fresh cadaver were used in current study. One tendon of the extensor digitorum communis (EDC) and two tendons of the intrinsic tendon were dissected and the Krackow suture was done for each tendon. Each finger is mounted with Kirschner wires on the custom-made experiment system. One tendon of the EDC was connected to one pneumatic actuator, and two tendons of the intrinsic muscles were connected to the other pneumatic actuator. One pendulum of 120g was connected to the flexor digitorum profundus to give continuous flexion load on the PIP joint. Extension force was loaded on each tendon and the load was gradually increased from 0 to 900g with control of the computer software. Angle of the PIP joint was measured with the sensor connected to the K-wire inserted at the distal portion of middle phalanx. Previous literature noted that physiologic cross sectional area (pCSA) of the EDC and the interosseous muscle are 1.53cm2 and 0.86cm2, respectively. We assumed that the maximal contraction force of the each muscle system was proportional to pCSA of the each muscle.
Results and Conclusions: With MP joint of 20 degree of flexion, efficiency of the EDC for extension of the PIP joint was 26% greater than the intrinsic muscles. With MP joint of 60 degree of flexion, efficiency of the EDC for extension of the PIP joint was 41% greater than the intrinsic muscles. Proportion of the roles in extension of the PIP joint of the EDC and the intrinsic muscle are, 69.2%:30.8%, respectively with MP joint of 20 degree of flexion. Proportion of the roles in extension of the PIP joint of the EDC and the intrinsic muscle are, 71.5%:28.5%, respectively with MP joint of 60 degree of flexion. Intrinsic muscles showed trends of decreasing efficiency of the PIP joint extension with MP joint flexion.
The EDC muscle has more role in extension of the PIP joint than the intrinsic muscle. With MP joint flexion, role of the intrinsic muscle for extension of the PIP joint declines.