Anconeus
| |
| Anconeus | |
|---|---|
| Muscle Type | |
| Origin | Lateral epicondyle of humerus, posterior surface |
| Insertion | Lateral side of olecranon process, and upper 1/4 of posterior surface of body of ulna |
| Action | Elbow extension, may stabilise ulna during pronation/supination |
| Synergists | |
| Antagonists | |
| Spinal innervation | C7, C8 |
| Peripheral Innervation | Radial Nerve |
| Vasculature | |
Manual Muscle Testing
Triceps and Anconeus - Prone
Patient: Prone
Fixation: shoulder at 90 degrees abduction, neutral rotation. Clinician places hand under arm near elbow to cushion from table
Test: Elbow extension (to slightly less than full extension)
Pressure: Against forearm into flexion
Triceps and Anconeus - Supine
Patient: Supine
Fixation: shoulder at 90 degrees flexion. Clinician supports arm perpendicular to table
Test: Elbow extension (to slightly less than full extension)
Pressure: Against forearm into flexion
Triceps Long Head and Test Positions
The long head of the triceps crosses both the shoulder and elbow joints.
- When the shoulder is horizontally abducted (arm out to the side), the long head is shortened at both the shoulder and elbow.
- When the shoulder is flexed (arm forward), the long head is lengthened over the shoulder but still shortened over the elbow.
Because of this, the long head is less effective when the arm is tested in the prone position (face down), since it is shortened over both joints. As a result, the triceps overall feel weaker in prone compared with supine testing.
Differentiating Triceps from Anconeus
The triceps and anconeus both extend the elbow, but there are a few ways to tell them apart:
- The belly of the anconeus sits just below the elbow joint, which makes it possible to feel it separately from the triceps on palpation.
- The radial nerve branch to the anconeus comes off around the mid-humerus and travels quite a long way. This means that sometimes only the anconeus is affected by nerve injury, while the triceps remain intact.
Clinical Relevance
If the anconeus is paralyzed, elbow extension strength will be reduced even though the triceps are normal. This can lead to situations where apparent “weakness” in elbow extension is not due to the triceps at all, but actually because the anconeus is not contributing.
