Radial Wrist Abduction: Critical Muscles and Tendons on the Thumb Side
The muscles and tendons on the thumb (radial) side of the forearm responsible for wrist abduction (radial deviation) are primarily the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), and abductor pollicis longus (APL); if torn, these structures would result in loss of radial wrist abduction.
Primary Radial Wrist Abductors
The key structures responsible for radial deviation of the wrist include:
Extensor carpi radialis longus (ECRL) - This is the primary radial wrist abductor and extensor, originating from the lateral supracondylar ridge of the humerus and inserting at the base of the second metacarpal 1, 2
Extensor carpi radialis brevis (ECRB) - Works synergistically with ECRL for radial deviation and wrist extension, inserting at the base of the third metacarpal 1
Abductor pollicis longus (APL) - While primarily responsible for thumb abduction and extension, this muscle also contributes significantly to radial wrist deviation due to its anatomical course along the radial aspect of the forearm 1, 3
Clinical Significance of Injury
Loss of these tendons results in profound functional impairment:
Tears of the ECRL and ECRB eliminate the primary motors for radial wrist deviation, making it impossible to achieve effective radial abduction of the wrist 4, 1
APL injury, while primarily affecting thumb function, also compromises radial wrist stability and abduction capacity, as this muscle induces midcarpal supination and contributes to radial deviation 1
Combined injury to these structures would necessitate tendon transfer procedures, with studies showing that transfers using flexor digitorum superficialis or extensor carpi ulnaris can restore some function, though achieving near-normal strength (M4+) occurs in only approximately 88% of cases 4, 2
Diagnostic Imaging Considerations
MRI without IV contrast is the preferred imaging modality for evaluating suspected tendon injuries in this region:
MRI provides ideal visualization for tendon injuries and surgical planning, with the American College of Radiology recommending it as the primary advanced imaging modality 5, 6
Ultrasound can be useful for dynamic assessment, particularly for de Quervain tenosynovitis affecting the APL and extensor pollicis brevis in the first dorsal compartment, where it can identify septations that affect surgical management 5, 3
Standard radiographs should be obtained initially to rule out fractures or bony abnormalities, though they are typically normal in isolated tendon injuries 6
Common Pitfall
Do not confuse wrist abduction (radial deviation) with thumb abduction—these are distinct movements. The abductor pollicis brevis (APB), innervated by the median nerve, is the primary thumb abductor and contributes approximately 70-74% of thumb abduction strength, but it does not contribute to wrist abduction 7. The APL, innervated by the posterior interosseous nerve (a branch of the radial nerve), contributes to both thumb abduction AND radial wrist deviation 7, 1.