*2.5.3.3 Proximal radial nerve compression neuropathy (Spiral groove syndrome)*

**Anatomy:** The radial nerve originates from the posterior cord of the brachial plexus and innervates the muscles of the extensor compartments of the upper extremity. After passing the axilla, the radial nerve windsclosely around the posterolateral aspect of the humeral shaft and descends along the spiral groove between the heads of the triceps muscle. The radial nerve innervates brachioradialis, extensor carpi radialis, and supinator muscles and skin overlying the posterior upper arm (posterior cutaneous nerve of the arm and lower lateral cutaneous nerve of the arm) [1, 7–9, 16, 26, 36]. Then, the radial nerve reaches the anterior compartment of the arm by piercing the septum approximately 10 to 12 cm above the lateral epicondyle and gives off superficial and deep branches [7].

#### *Demyelination Disorders*

**Description:** It is a condition characterized by compression of the radial nerve as it passes between the heads of the triceps muscle in the spiral groove (**Figure 8**) or a fibrous arch of the lateral head of the triceps muscle [7, 9].

**Causes:** During the course of the nerve in the spiral groove, its close relationship with the humerus and Intermuscular septum leaves the nerve vulnerable to impacts from outside. Humerus fractures, external compression (arm rest on the edge of the chair during unconsciousness from anesthesia, drugs abuse (alcohol), or during profound sleep-Saturday night syndrome, crutches use), long tourniquet application, professions that require repeated use of the triceps muscle, deep intramuscular injections of the arm are common causes of nerve compression [9, 26]. The most common cause of radial nerve compression in the axilla is improper use of crutches. Radial nerve compression neuropathy in the spiral groove. It is often referred to as "Saturday night paralysis". The reason for this name is the radial nerve compression caused by long-term unconsciousness of alcoholics [7–9, 35, 42].

**Figure 9.** *"Wrist drop deformity" caused by compression of the radial nerve.*

**Clinical features:** Loss of sensation and pain occur at the sensory dermatome of radial nerve where lateral of the elbow, the dorsal of the forearm and the dorsoradial of the hand in the slight compression of the radial nerve. The pain is further exacerbated by elbow extension, forearm flexion, and wrist flexion in the position where traction is exerted on the nerve. Pain that increases with resistant extension of the middle finger is an important finding of radial nerve entrapment neuropathy. As the pressure on the nerve gets longer, motor losses begin to occur. At this level, the triceps muscle is intact, there is paralysis in the supinator and brachioradialis muscles; However, since the biceps muscle with musculocutaneous nerve innervation is active, elbow flexion and supination movement are not restricted. There is paralysis in wrist extensors, finger extensors, thumb abductor and extensor. Therefore, this condition resulting from proximal radial nerve compression syndrome is called "Wrist drop deformity" (**Figure 9**) [7, 9, 26, 42, 43].
