What causes loss of strength in the triceps?

Causes for triceps weakness, particularly when only one arm is affected, include direct injuries to the triceps tissue and injury to the nerves that innervate it. Starting at the top and working down, here are the primary injuries that can cause a loss of triceps strength:

1. Cervical Stenosis

Narrowing of the bony passages between cervical vertebrae can put pressure on nerves traveling through and exiting the spinal column. The C7 nerve root typically contributes the most innervation to the triceps; narrowing of the C6-C7 intervertebral foramen or bulging of the intervertebral disc at this level can compress the C7 nerve. 

2. Axillary Neuropathy

Sometimes, the motor branch of the long head of the triceps is supplied by the axillary nerve rather than the primary radial nerve. “Crutch compression,” as with the use of axillary crutches, may cause compression of the axillary nerve if the crutches are not used or fitted properly.

3. Radial Neuropathy

The three heads of the triceps (lateral, medial, long) are primarily innervated by the radial nerve, which may be injured by fracture or dislocation of the humerus bone. A less severe but more common mechanism involves sustained nerve compression, such as sleeping on one’s arm for an extended period. 

4. Muscle Strain

Sudden, forceful contraction of the triceps muscle can cause tissue tearing, most commonly occurring at the myotendinous junction. Eccentric contractions from a position of elbow flexion carry the most risk for injury. 

5. Tendon Tear

Triceps tendon tears are also caused by forceful muscle contraction. They tend to selectively involve the superficial layer of the tendon, leaving the deep layer intact.

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