*2.5.5.2 Pronator teres syndrome*

**Anatomy:** The median nerve originates from the medial (C8 and T1) and lateral cords (C5 through C7) of the brachial plexus. At the elbow level, from medial to lateral, are the median nerve, brachial artery and the biceps tendon. The median nerve courses anterior to the brachialis muscle and deep to the Lacertus fibrosus. The nerve then courses between the superficial (humeral) and deep (ulnar) heads of the pronator teres muscle in the proximal third of the forearm and exits the cubital fossa (**Figure 13**) [16, 26, 49].

**Description:** It is a condition characterized by compression of the median nerve between the two heads of the pronator teres muscle or the pressure of the fibrous bands [8].

**Causes:** The nerve may be compressed due to thickened bicipital aponeurosis, Struther's ligament, the arch of the flexor digitorum superficialis,as well as the hypertrophic pronator teres muscle, aberrant median artery, crossing branch of the radial artery, or soft tissue mass [8, 9, 49].

**Clinical features:** With resistant wrist flexion and forearm pronation, symptoms increase. The pain is localized to the medial of the forearm. Paresthesia and sensory problems are seen in the first three fingers of the hand, which is the dermatome area of the median nerve. In addition, weakness may occur in the intrinsic and extrinsic muscles of the hand innervated by the median nerve [8, 9, 49].

## *2.5.5.3 Posterior interosseous nerve (PIN) syndrome (Supinator 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 the course of the radial nerve in the arm, the 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 (**Figure 14**) [1, 4, 7]. The deep branch (posterior interosseus nerve-PIN) of the radial nerve first wraps around the radial neck and then travels within the radial tunnel. The radial tunnel is bordered medially by brachialis and biceps tendon and laterally by extensor carpi radialis longus and brevis. The PIN then passes below the superficial layer of supinator (which is known as the arcade of Frohse) and innervates supinator as

*Upper Extremity Entrapment Neuropathy DOI: http://dx.doi.org/10.5772/intechopen.98279*

**Figure 13.** *The schematic drawing of median nerve between the pronator teres muscle heads.*

well as wrist and finger extensors. The superficial branch of the radial nerve runs along the radial artery in the forearm. It passes over the first extensor compartment at the wrist and disperses on the back of the hand [1, 8].

**Description:** Posterior interosseous nerve syndrome is a condition characterized by compression of the nerve in the proximal forearm, anterior to the elbow capsule, under the Frohse archade, approaching the arch, or within the supinator muscle [1, 8, 9].

**Causes:** In some professions such as athletes and violinists, excessive use of the arm, use of crutches, repetitive pronation-supination movement, fractures of the radial head, soft tissue tumors such as ganglion and lipoma, septic arthritis, synovial chondromatosis, or rheumatoid synovitis are the causes of posterior interosseous nerve syndrome [4, 9, 26, 35].

#### **Figure 14.**

*The schematic drawing of the course of the radial nerve and its superficial and deep branches.*

**Clinical features:** In PIN syndrome, wrist extensors are intact because the innervation of these muscles is at the level of the elbow joint. In PIN syndrome, paralysis develops in finger extensors, thumb extensors and abductors. There is no sensory deficit. In clinical examination, it may be mistaken for lateral epicondylitis. In lateral epicondylitis syndrome, there is pain that concentrates on the lateral epicondyle and increases with resistant extension of the wrist. In PIN syndrome, the pain is exacerbated by the resistant extension of the third finger and radiates to the lateral side of the arm. Also, resistant supination movement causes pain [1, 8, 26, 50].

## *2.5.5.4 Superficial cutaneous radial nerve compression (Keralgia paresthetica- Wartenberg syndrome*

**Anatomy:** The superficial branch of the radial nerve, after separating from the radial nerve, extends distally along the radial side of the forearm deep in the brachioradialis muscle (**Figure 15**). It is superficial by piercing the fascia between the brachioradialis and extensor carpi radialis longus muscle tendons approximately 8–9 cm above the radial styloid [51, 52].

## *Upper Extremity Entrapment Neuropathy DOI: http://dx.doi.org/10.5772/intechopen.98279*

**Figure 15.**

*The schematic drawing of the course of the superficial branch of the radial nerve in the forearm.*

**Description:** It is a condition characterized by the compression of the superficial sensory branch of the radial nerve at the level of the wrist [1, 8, 50, 52].

**Causes:** Distal radius fractures, penetrating injuries, a tight watch strap or hand cuffs, a tight cast or splint, repetitive exercise (e.g. rowing), iatrogenic injury, lipoma and bony spurs are important factors causing nerve compression [1, 51, 52].

**Clinical features:** Patients usually complain of pain and numbness on the dorsal and lateral side of the hand. It is a pure sensory nerve so there is no motor deficits [1].

## *2.5.6 Impingement syndromes in the wrist*
