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A 19-year-old patient presents with a 1-week history of a left thumb laceration. He was grasping a glass vase in his hand when the glass broke, cutting his thumb. The wound at the base of his thumb was washed out and closed in the emergency room on the day of injury. Upon examination, the patient is unable to flex the interphalangeal joint of the thumb. He has full active motion of the thumb metacarpophalangeal (MCP) joint and wrist flexion. Two-point discrimination is intact throughout the thumb.
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The patient presents with a flexor pollicis longus (FPL) tendon laceration. The FPL originates from the anterior radius and coronoid process and inserts at the distal phalanx of the thumb. The tendon flexes the interphalangeal joint of the thumb and is innervated by the medial nerve.
Pollicis is a Latin word meaning “of the thumb.” The flexor pollicis brevis flexes the metacarpophalangeal (MCP) joint of the thumb. The flexor digitorum profundus flexes the distal interphalangeal joints of digits 1 to 4, and the flexor digitorum superficialis flexes the proximal interphalangeal joints of digits 1 to 4. The flexor carpi radialis flexes and radially deviates the wrist.1
Neurovascular injury, including laceration of the digital nerves and arteries, commonly occurs in association with FPL lacerations. Digital nerves are purely sensory, and laceration will cause numbness on the corresponding side of the finger. Two-point discrimination should be performed on the thumb to determine if injury to the digital nerve occurred. Injury to a digital artery can be treated with laceration repair and direct pressure to the injury; rarely is any further intervention necessary. Digital artery repair is recommended in complex lacerations where injury to both digital arteries occurs. Laceration to both digital arteries impairs skin and tendon healing and may result in severe cold intolerances if blood flow is not restored.
Complete FPL lacerations are repaired surgically, generally within 2 weeks of the injury. The FPL often retracts proximally, which can make the tendon difficult to find, particularly if surgery is performed after 2 weeks from the date of the injury. The most common method of surgical repair is a direct end-to-end repair. Irreparable FPL lacerations may be treated with a flexor digitorum superficialis tendon transfer to achieve interphalangeal flexion of the thumb.2
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
- Thompson JC. Netter’s Concise Atlas of Orthopaedic Anatomy. Philadelphia, PA: Elsevier, Inc; 2002.
- Nunley JA, Levin LS, Devito D, et al. Direct end-to-end repair of flexor pollicis longus tendon lacerations. J Hand Surg Am. 1992;17(1):118-121.
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