Abstract
Change in forearm muscle length can be used to predict muscle function during pronosupination. In ten fresh cadaveric specimens, markers were placed at fifteen muscle origins and insertions. The forearm was positioned at 10° increments from 80° of pronation to 90° of supination with the elbow flexed at 90°. An electromagnetic tracking system was used to digitally collect 3D origin and insertion coordinates. These coordinates were used to create a vector representing muscle length as a straight line from the muscle origin to the muscle insertion. To normalize the data, all lengths were normalized as a percentage of the maximum muscle length for each specimen. Differences in the data were determined through paired t-test analysis.
The muscles which exhibited a significant decrease in length from pronation to supination throughout the entire range were the biceps brachii and the palmaris longus. Muscles exhibiting a significant increase over the range were the pronator teres at both the humeral and ulnar origins as well as the pronator quadratus. The brachialis also exhibited an increase, though not as pronounced. The supinator, extensor indicis and the extensor carpi ulnaris all exhibited maximum length at the neutral position while length decreased in both pronation and supination directions. The only muscle to exhibit minimal length at neutral with increasing length in each direction was the brachioradialis. The extensor carpi radialis longus kept a consistent length during pronation and increased during supination. Muscles that remained consistent during pronation but decreased their length during supination included the extensor policis longus, the flexor carpi ulnaris, and the radial and ulnar origins of the abductor policis longus. The extensor carpi radialis brevis and the flexor carpi radialis exhibited no significant change in muscle length during forearm rotation.
Forearm Rotation involves a complex interaction between the Radius and Ulna. Multiple muscles traverse the forearm en route to the hand. Many muscles change significantly in length during pronosupination. These muscles
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Must adapt to this change in length to allow coordinated Upper Extremity function.
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Produce a force vector stressing the Distal and Proximal Radioulnar joints.
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Assist with Forearm Motion.
Clinical Relevance- Rehabilitation following Injury needs to take into account the effect of forearm rotation, Splint position may vary depending on which Muscle or Tendon is injured, Surgical Procedures and Implants need to be designed to take into account transverse and longitudinal forces on the forearm.
Correspondence should be addressed to: Associate Professor N. Susan Stott, Orthopaedic Department, Starship Children’s Hospital, Private Bag 92024, Auckland, New Zealand.
