A patient sustains a spinal cord injury at the C5 level. Which of the following muscles will retain normal innervation and function?

Explanation

## Cervical Myotome Distribution and C5 Spinal Cord Injury **Key Point:** A C5 spinal cord lesion results in loss of motor function below the C5 myotome. The C5 myotome innervates shoulder abductors (deltoid) and elbow flexors (biceps). Intrinsic hand muscles are innervated by C8–T1 and will retain normal function. ### Cervical Myotome Map | Myotome | Primary Muscles | Nerve Root | |---------|-----------------|------------| | C4 | Diaphragm, shoulder shrug | Phrenic nerve, CN XI | | C5 | Deltoid, biceps brachii, brachialis | Axillary, musculocutaneous | | C6 | Wrist extensors (ECRB, ECRL), pronator teres | Radial nerve | | C7 | Triceps, wrist flexors, finger extensors | Radial nerve | | C8–T1 | Intrinsic hand muscles (lumbricals, interossei) | Ulnar nerve | **High-Yield:** In a C5 lesion: - **Lost:** Shoulder abduction (deltoid), elbow flexion (biceps). - **Retained:** Wrist and finger movements (C6–C8 intact), intrinsic hand muscle function (C8–T1 intact). **Mnemonic:** **"C5 = Shoulder & elbow; C8–T1 = Hand intrinsics"** — Remember that intrinsic hand muscles (lumbricals, interossei) are the last to be affected in proximal cervical lesions because they are innervated by lower cervical and thoracic roots. **Clinical Pearl:** The **"C5 tetraplegic"** can still perform fine finger movements and grip because C8–T1 myotomes are spared. This is why hand function assessment is crucial in determining the functional level of cervical spinal cord injury. [cite:Clinically Oriented Anatomy 8e Ch 4]