A patient woke up from sleep with difficulty in extending fingers. He can make a grip and hold apen. Wrist extension was possible. No sensory disturbance was found. Injury could be at
**Core Concept**
The patient's symptoms suggest a neurological injury affecting motor function, specifically affecting the ability to extend the fingers, while sparing wrist extension and sensory function. This pattern is characteristic of a lesion affecting the motor branch of the median nerve or the ulnar nerve, but given the specific finger extension deficit, it points more towards a lesion affecting the ulnar nerve's motor branch.
**Why the Correct Answer is Right**
The ulnar nerve is responsible for innervating the intrinsic muscles of the hand, particularly the interossei and the lumbricals, which are crucial for finger extension. The motor branch of the ulnar nerve splits into two branches, one innervating the interossei and the other innervating the lumbricals. A lesion affecting the ulnar nerve at the level of the elbow or below, but above the level of the wrist, would result in weakness or paralysis of the intrinsic muscles of the hand, leading to difficulty in extending the fingers. This would also explain why the patient can still make a grip and hold a pen, as the extrinsic muscles of the forearm (innervated by the median and radial nerves) are still intact.
**Why Each Wrong Option is Incorrect**
* **Option A:** A lesion affecting the median nerve would result in a different pattern of weakness, including difficulty in thumb opposition, thumb flexion, and index finger flexion, which is not consistent with the patient's symptoms.
* **Option B:** A lesion affecting the radial nerve would result in weakness of wrist extension, which is not consistent with the patient's ability to perform wrist extension.
* **Option C:** A lesion affecting the brachial plexus or the cervical spine would result in more widespread weakness and sensory disturbances, which are not present in this patient.
**Clinical Pearl / High-Yield Fact**
In patients with suspected ulnar nerve injury, it's essential to assess the strength and function of the intrinsic muscles of the hand, including the interossei and lumbricals, as a lesion affecting these muscles can lead to significant hand dysfunction.
**Correct Answer:** C.