*2.5.4.1 Cubital tunnel syndrome (ulnar neuropathy)*

**Anatomy:** The ulnar nerve originates from roots C8 to T1 via the medial cord of the brachial plexus. It runs along the posterior aspect of the humerus on the arm, and the medial epicondyle pierces the intermuscular septum approximately 8 cm above it. It enters the posterior compartment of the forearm. The nerve passes under the arcade of Struther's in the presence of the Struther's ligament. At the level of the elbow, the ulnar nerve passes through a fibro-oesseus channel called the cubital tunnel that is bordered by the olecranon, medial epicondyle and Osborne ligament. A fascial structure between the olecranon and the medial epicondyle known as the cubital tunnel retinaculum (CTR) formed the roof of the cubital tunnel (**Figure 10**). The nerve then passes under the arcuate ligament formed by aponeurosis of flexor carpi ulnaris muscle and reaches the forearm. The ulnar nerve reaches the elbow joint level without giving any motor or sensory branches.

#### **Figure 10.**

*The schematic drawing of cubital tunnel (a:Artery, n:Nerve, m:Muscle, med.Epi: Medial epicondyle, flex:Flexor, FCU: Flexor carpi ulnaris, Olec:Olecranon).*

When it passes between the two heads of the flexor carpi ulnaris muscle, it gives motor branches to the flexor carpi ulnaris muscle [1, 7, 8, 9, 16].

**Description:** Cubital tunnel syndrome is the second most common impingement syndrome after carpal tunnel syndrome [26]. Due to its anatomical features, the ulnar nerve is most frequently compressed in the elbow area, where it is most susceptible to local compression and trauma. Posner [44] defined the 5 potential compression area in the elbow. These are the arcade of Struthers, the medial intermuscular septum, the cubital tunnel, retroepicondylar groove, and the flexor pronator aponeurosis. Although the term cubital tunnel syndrome refers to a specific anatomic point, compression neuropathy may be also outside the cubital tunnel. Cubital tunnel syndrome is a condition characterized by the compression of the ulnar nerve in the region of the elbow joint [45].

**Causes:** There are many reasons that can cause the development of ulnar neuropathy. Compression of the nerve in condylar groove, cubitus valgus, elbow fractures, osteoarthritis with medial osteophytes, and space occupying soft-tissue lesions, ganglia, and accessory muscles (eg, anconeus epitrochlearis muscle) are the most important known reasons [8, 9, 26, 45].

**Clinical features:** The complaint is generally in the form of pain radiating to the medial of the forearm, sensory abnormalities in the dorsal and palmar aspects of the hand, and motor weakness in the intrinsic muscles of the hand. In advanced stages, claw hand deformity(hyperextension of the metacarpophalangeal joints of the 4th and 5th fingers, flexion of the proximal and distal interphalangeal joints by the effect of extrinsic flexors) may occur. The little finger may also remain in a slightly abducted position (Wartenberg's sign) [8, 9, 26, 42].

#### *2.5.5 Impingement syndromes in the forearm*

#### *2.5.5.1 Anterior interosseous (AIN) syndrome (Kiloh-Nevin syndrome)*

**Anatomy:** The anterior interosseous nerve (AIN) originates from the median nerve. It is the terminal motor branch of the median nerve (**Figure 11**). After separating from the median nerve in the anterior part of the cubital fossa, it extends

#### **Figure 11.** *The schematic drawing of anterior interosseus nerve between the pronator teres muscle heads.*

on the forearm towards the wrist with the interosseous branch of the ulnar artery that accompanies it on the anterior face of the antebrachial membran. It courses between the muscle bellies of the flexor pollicis longus and flexor digitorum profundus at the forearm. The nerve innervates the flexor pollicis longus, radial part of the flexor digitorum profundus, the pronator quadratus muscles and middle and index fingers [1, 16, 24, 46–48].

**Description:** It is a condition characterized by compression of the anterior interosseous branch of the median nerve the proximal forearm [8].

**Causes:** There are many factors that may cause anterior interosseous nerve syndrome to occur. Causes may be spontaneous or traumatic. Supracondylar fractures, penetrating injuries, cast fixation, puncture of vein, internal fixation for fractures are considered within traumatic causes. Presence of supracondylar bony, compression of the nerve during the passage between two heads of pronator teres muscle, brachial plexus neuritis and hematoma and mass-induced nerve compression are spontaneous causative factors. The tendinous margin of the deep head of the pronator teres muscle is the most common site of AIN entrapment [8, 26, 46, 48].

**Clinical features:** The most obvious symptoms of AIN are pain and muscle weakness in the volar forearm, particularly at night, and difficulty in handwriting and pinching movements with the fingers. Symptoms may be increased by supination and extension. Motor dysfunction can be seen in AIN. Especially, patients complain that weakness in their thumb and index finger. Patients cannot make the

**Figure 12.** *Hand posture in anterior interosseous syndrome.*

"OK" sign (**Figure 12**). Due to the Martin-Gruber anastomosis, paralysis may also occur in the intrinsic muscles of the hand [1, 8, 9, 26, 46, 48].
