A 42-year-old woman is admitted to the hospital with injury to the upper (superior) trunk of the brachial plexus. The diagnosis is Erb-Duchenne palsy. Which of the following conditions is expected to be present during physical examination?
**Core Concept**
Erb-Duchenne palsy is a form of brachial plexus injury that affects the upper trunk (C5-C6) of the brachial plexus, leading to weakness or paralysis of the muscles innervated by these nerves. This results in a characteristic pattern of muscle weakness.
**Why the Correct Answer is Right**
In Erb-Duchenne palsy, the affected muscles include the supraspinatus, infraspinatus, deltoid, and biceps brachii. The supraspinatus and infraspinatus muscles are responsible for shoulder abduction and external rotation, respectively. The deltoid muscle, which is responsible for shoulder flexion, extension, and rotation, is also affected. The biceps brachii muscle, which is responsible for elbow flexion and forearm supination, is weakened. This results in a characteristic "waiter's tip" deformity of the arm, with the forearm pronated and the wrist extended.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not specific to Erb-Duchenne palsy, as it can be seen in other types of brachial plexus injuries.
**Option B:** While this option is related to brachial plexus injuries, it is not specific to Erb-Duchenne palsy and can occur in other types of nerve injuries.
**Option C:** This option is not related to the typical presentation of Erb-Duchenne palsy.
**Clinical Pearl / High-Yield Fact**
A useful mnemonic to remember the muscles affected in Erb-Duchenne palsy is "SVID" - Supraspinatus, Vertebral (V) muscles, Infraspinatus, Deltoid. This can help you remember the characteristic pattern of muscle weakness seen in this condition.
**Correct Answer:** C.