Which of the movements of thumb are not affected in radial nerve injury
**Core Concept**
The radial nerve innervates muscles of the posterior forearm and the muscles of the extensor compartment of the forearm, controlling thumb extension, wrist extension, and finger extension. The movement of the thumb is a complex function involving multiple nerves and muscles.
**Why the Correct Answer is Right**
The movements of the thumb that are not affected in radial nerve injury include opposition, flexion, and abduction. This is because these movements are primarily controlled by the median nerve, which innervates the thenar muscles ( opponens pollicis, flexor pollicis brevis, and abductor pollicis brevis). The radial nerve, however, is responsible for controlling thumb extension, which is the movement that is affected in radial nerve injury.
**Why Each Wrong Option is Incorrect**
**Option A:** Thumb extension is a movement that is primarily controlled by the radial nerve and is affected in radial nerve injury.
**Option B:** Flexion of the thumb is a movement that is primarily controlled by the median nerve, but the radial nerve also plays a role in flexion at the metacarpophalangeal joint.
**Option C:** Abduction of the thumb is a movement that is primarily controlled by the abductor pollicis longus muscle, which is innervated by the radial nerve. Therefore, this movement would be affected in radial nerve injury.
**Option D:** Opposition of the thumb is a movement that is primarily controlled by the opponens pollicis muscle, which is innervated by the median nerve and would not be affected in radial nerve injury.
**Clinical Pearl / High-Yield Fact**
In cases of radial nerve injury, the patient may exhibit a "wrist drop" due to the inability to extend the wrist and fingers. This can be a useful clinical sign to differentiate radial nerve injury from other types of nerve injuries.
**Correct Answer:** D. Opposition of the thumb is not affected in radial nerve injury.