A lesion of the radial nerve in the spiral groove of the humerus results in which of the following clinical findings?

Explanation

## Radial Nerve Lesion in the Spiral Groove ### Anatomical Basis The radial nerve travels in the **spiral groove (radial groove)** on the posterior aspect of the mid-shaft of the humerus. This is a common site of injury due to: - Fractures of the humeral shaft (especially mid-shaft) - Compression from external pressure (e.g., crutches, prolonged pressure) - Ischemia from vascular injury ### Motor Deficit at the Spiral Groove Level **Key Point:** At the level of the spiral groove, the radial nerve has already given off branches to the **triceps** (which occurs proximal to the groove). Therefore, a lesion at this level spares triceps function but affects: - **Extensor carpi radialis longus (ECRL)** - **Extensor carpi radialis brevis (ECRB)** - **Extensor carpi ulnaris (ECU)** - **Extensor digitorum (ED)** - **Extensor pollicis longus (EPL)** - **Extensor pollicis brevis (EPB)** - **Abductor pollicis longus (APL)** Result: **Loss of wrist extension** (most prominent finding) ### Sensory Deficit The radial nerve provides sensory innervation to the **dorsal first web space** (between thumb and index finger) and the dorsal lateral hand. A spiral groove lesion affects this sensory distribution. **High-Yield:** The combination of **wrist drop** (inability to extend the wrist) and sensory loss over the **dorsal first web space** is pathognomonic for radial nerve injury at or distal to the spiral groove. ### Mnemonic: LOSER **L** — Loss of wrist extension **O** — Opponens pollicis spared (intrinsic hand muscles intact) **S** — Sensory loss dorsal first web space **E** — Extensor muscles affected **R** — Radial nerve injury ### Clinical Pearl Patients with radial nerve injury present with a characteristic **wrist drop deformity** — inability to extend the wrist even passively when the forearm is supported. This is one of the most recognizable clinical signs in neurology.