A 42-year-old woman with a history of cervical rib presents with progressive weakness of finger abduction and adduction, along with atrophy of the hypothenar eminence and medial two lumbricals. Sensory loss is noted in the medial 1.5 fingers. Which nerve is compressed, and at what anatomical level?

## Thoracic Outlet Syndrome with Cervical Rib **Clinical Presentation Analysis:** - **Finger abduction/adduction weakness** → Intrinsic hand muscles (lumbricals and interossei) - **Hypothenar atrophy** → Hypothenar muscles (abductor digiti minimi, flexor digiti minimi, opponens digiti minimi) — C8–T1 territory - **Medial two lumbricals atrophy** → C8–T1 innervation - **Sensory loss in medial 1.5 fingers** → C8–T1 dermatome **Key Distinction:** This patient has **neurogenic thoracic outlet syndrome (NTOS)** caused by cervical rib compression of the C8–T1 nerve roots, NOT isolated ulnar nerve compression. The pattern of involvement is: - **C8–T1 root compression** → All intrinsic hand muscles (both ulnar AND median-innervated lumbricals) + hypothenar muscles - **Ulnar nerve compression at wrist** → Only ulnar-innervated intrinsics (hypothenar + medial 2 lumbricals) but would NOT affect median-innervated lateral 2 lumbricals - **Ulnar nerve compression at elbow** → Same as wrist but with additional forearm flexor involvement **High-Yield Fact:** The involvement of BOTH medial 2 lumbricals (C8–T1) indicates root-level compression, not distal ulnar nerve compression. A cervical rib is a classic cause of C8–T1 root compression. **Clinical Pearl:** Progressive symptoms with cervical rib history = thoracic outlet syndrome until proven otherwise.