Ortho Dx: A chainsaw injury to the forearm

An understanding of anatomy is crucial for early recognition of injuries to tendons, muscles, and nerves. An accurate assessment of the injury and physical exam findings is also necessary to determine if the patient's injury can be washed out and...

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An understanding of anatomy is crucial for early recognition of injuries to tendons, muscles, and nerves. An accurate assessment of the injury and physical exam findings is also necessary to determine if the patient’s injury can be washed out and he can be sent home from the emergency department or if urgent nerve, artery, and/or tendon repair is necessary.

On the flexor or palmar aspect of the forearm, the most superficial layer is made of 4 muscles that arise from the medial epicondyle and fan out across the forearm. From a radial to ulnar direction, these muscles include the pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. The “mobile wad” of muscle that arises from the lateral epicondyle on the lateral and palmar aspect of the forearm is made of the brachioradialis and the extensor carpi radialis longus and brevis.^1,2

The location of the nerves and vessels of the anterior forearm is relatively simple to remember. The radial nerve runs down the radial or lateral side of the forearm with the radial artery running along the medial side of the nerve at the distal half of the forearm. The ulnar nerve runs down the ulnar side of the forearm with the ulnar artery running along the lateral border of the nerve at the distal half of the forearm. The median nerve courses down the middle of the forearm. The anterior interosseous nerve, a branch of the median nerve, courses deep to the median nerve in the mid-forearm.^1,2

The depth and location of this patient’s laceration suggest that the superficial muscles of the mid-forearm may have been injured, including the brachioradialis, flexor carpi radialis, palmaris longus, and the flexor carpi ulnaris muscles. The wound is deepest in the middle of the forearm, which suggests that the median nerve is at the highest risk of being injured.

Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).

References

1. Allen D. Flexor tendon injuries. Available at: http://www.orthobullets.com/hand/6031/flexor-tendon-injuries (Accessed August 1, 2017).
2. Thompson JC. Netter’s Concise Atlas of Orthopaedic Anatomy. Philadelphia: Elsevier; 2002;108-114.