A 45-year-old woman is admitted to the outpatient clinic for shoulder pain. During physical examination she presents with weakened shoulder movements. Radiographic examination reveals quadrangular space syndrome, causing weakened shoulder movements. Which of the following nerves is most likely affected?
**Core Concept**
The quadrangular space syndrome is a condition characterized by compression or injury of the axillary nerve and the radial nerve as they pass through the quadrangular space in the shoulder region. This compression can lead to weakened shoulder movements, pain, and sensory disturbances in the affected area.
**Why the Correct Answer is Right**
The quadrangular space is a narrow anatomical passage in the shoulder region that allows the axillary nerve and the radial nerve to pass through. The axillary nerve is responsible for innervating the deltoid muscle, which is involved in shoulder abduction, and the teres minor muscle, which is involved in shoulder adduction and rotation. The radial nerve innervates the supraspinatus muscle, which is involved in shoulder abduction and stabilization. Compression of these nerves can lead to weakness and pain in the shoulder region.
**Why Each Wrong Option is Incorrect**
**Option A:** The suprascapular nerve is responsible for innervating the supraspinatus and infraspinatus muscles, which are involved in shoulder abduction and rotation. However, it is not the primary nerve affected in quadrangular space syndrome.
**Option B:** The musculocutaneous nerve innervates the biceps brachii and brachialis muscles, which are involved in elbow flexion and forearm supination. It is not related to shoulder movements or quadrangular space syndrome.
**Option C:** The subscapular nerve is a branch of the posterior cord of the brachial plexus that innervates the subscapularis muscle, which is involved in shoulder rotation and stabilization. However, it is not the primary nerve affected in quadrangular space syndrome.
**Clinical Pearl / High-Yield Fact**
The quadrangular space syndrome is often associated with injuries or compression of the axillary nerve and radial nerve, which can occur due to trauma, overuse, or compression from adjacent structures. Clinicians should be aware of the anatomical landmarks and nerves involved in this syndrome to provide accurate diagnosis and treatment.
**Correct Answer:** C. The axillary and radial nerves are the most likely to be affected in quadrangular space syndrome.