A 28-year-old motorcyclist sustains a severe traction injury to the right upper limb with the arm abducted and extended at the time of injury. Clinical examination reveals loss of abduction and external rotation of the shoulder, with preserved elbow flexion and wrist extension. Which nerve root(s) of the brachial plexus is/are most likely injured?

Explanation

## Brachial Plexus Injury Pattern Analysis **Clinical Presentation Breakdown:** - **Loss of shoulder abduction** → Supraspinatus (C5, C6 via suprascapular nerve) - **Loss of external rotation** → Infraspinatus (C5, C6 via suprascapular nerve) - **Preserved elbow flexion** → Musculocutaneous nerve (C5, C6) intact - **Preserved wrist extension** → Radial nerve (C5–C8) partially intact **Key Point:** The pattern of isolated loss of supraspinatus and infraspinatus function with preserved musculocutaneous and radial nerve function indicates **C5 root injury alone**. The mechanism of traction with arm abducted and extended creates maximal stress on the C5 root at the intervertebral foramen, causing selective root avulsion. **High-Yield Fact:** - C5 root lesion → Loss of shoulder abduction/external rotation (suprascapular nerve territory) - C5–C6 lesion (Erb's palsy) → Would also affect elbow flexion (musculocutaneous nerve), which is preserved here - C8–T1 lesion (Klumpke's palsy) → Intrinsic hand muscles and wrist flexors affected; not seen here **Clinical Pearl:** Selective C5 injury is the classic "shoulder abduction loss" pattern without hand or forearm involvement.