**Core Concept**
The question tests knowledge of **nerve supply** to muscles of the upper limb, specifically those involved in movements of the shoulder joint. Understanding the **axillary nerve** and **subscapular nerves** is crucial.

**Why the Correct Answer is Right**
Weakness of both abduction and adduction suggests a problem with the nerves supplying the deltoid and teres major/minor muscles, respectively. The **axillary nerve**, a branch of the **posterior cord of the brachial plexus**, supplies the deltoid, while the **subscapular nerves** (upper and lower) supply the teres major and minor. Damage to the **upper brachial plexus** or **axillary nerve** itself could lead to weakness in abduction.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it doesn't specify the correct nerve involvement.
**Option B:** Incorrect as it might only affect abduction.
**Option C:** Incorrect because the subscapular nerves primarily supply adduction muscles.
**Option D:** Incorrect as the specific nerve involvement is not accurately described.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the **axillary nerve** also supplies sensation to the shoulder, so damage to this nerve could result in sensory deficits in addition to motor weakness.

**Correct Answer:** D. Upper brachial plexus injury