【Overview】 When the three main nerves of the upper extremity, namely the median nerve, radial nerve and ulnar nerve, pass through the elbow, due to local anatomical features, they often cause entrapment due to trauma, congenital malformation and swelling. Radial nerve entrapment in posterior rotator syndrome and radial nerve entrapment at the elbow is seen in dorsal interosseous nerve syndrome. Due to the lack of clinical knowledge of this syndrome, it may be confused as “tennis elbow” and treated for a long time with no effect. Anatomy and anatomy and physiology】 The radial nerve travels between the brachioradialis muscle and the anterior brachioradialis muscle after penetrating from the lateral interosseous muscle of the upper arm, and travels distally to the radial extensor carpi radialis. The nerve is divided into two branches at the elbow, the deep and the superficial. The deep branch of the radial nerve, the dorsal interosseous nerve, travels on the deep side of the radial carpal extensor margin and then passes between the deep and superficial heads of the posterior rotator muscle (Figure 1). 30% of adults have a tendon arch at its entrance, and the dorsal interosseous nerve bypasses the radial neck to the dorsolateral forearm. It sends a muscular branch to innervate the radial short extensor carpi radialis and the posterior rotator muscle before entering the posterior rotator muscle. At the inferior border of the posterior rotator muscle it divides into two branches to innervate the ulnar carpal extensors, each finger extensor tendon, and the short and long thumb extensors. The superficial branch of the radial nerve descends anteriorly from the radial carpal extensors and is covered by the brachioradialis muscle, which innervates the sensation in the tiger’s mouth. The radial canal originates from the plane of the humeral tuberosity and is followed by the anterior joint capsule of the elbow joint, the synovial membrane, and the deep humeral tuberosity ring ligament and radial head. The anterolateral wall of the radial canal is the brachioradialis, the radial longissimus carpi radialis, and downward the radial shortissimus carpi radialis. When the forearm is internally rotated, some fibers of the radial carpal extensors can compress the dorsal interosseous nerve. Medial to the radial canal is the biceps tendon. The lower end of the radial canal is where the dorsal interosseous nerve enters the posterior rotator muscle, and it passes between the deep and superficial heads of the posterior rotator muscle. [Etiology and pathogenesis] The cause of compression of dorsal interosseous nerve syndrome is often not easy to determine, and sometimes it is only clear after surgical exploration. From the above anatomical features, the radial nerve passes through several narrow areas in the radial canal, especially at the radial short extensor carpi radialis and posterior rotator tendon arch, and the following causative factors can cause symptoms, mainly: 1. occupying lesions of the radial canal, such as lipoma, hemangioma, hematoma (mostly from the radial retrolateral artery and vein), tendon sheath cyst, etc.; 2. elbow joint lesions or injuries: rheumatoid arthritis, inflammatory swelling, Men’s fracture, radial 3. old soft tissue injury of the elbow, making swelling and adhesion at the arch of the posterior rotator tendon or the radial carpal tunnel. Clinical manifestations Pain and radiating pain in the lateral part of the elbow with localized pressure pain. The muscles innervated by the dorsal interosseous nerve, such as radial carpal short extensor, posterior rotator, ulnar carpal extensor, common finger extensor, extensor digitorum superficialis, intrinsic extensor digitorum superficialis, thumb long and short extensor muscles are weak, and there is usually no sensory disturbance. Sometimes localized swelling or palpable masses may be found. x-ray examination with local hypodensity (lipoma) or bony changes in the brachioradialis joint is informative. Certain so-called intractable tennis elbow, which does not respond well to steroid closure therapy, should be considered as dorsal interosseous nerve syndrome. Differentiation between them: tennis elbow, with pain and pressure in the lateral epicondyle of the humerus, is more limited. With dorsal interosseous nerve involvement, pain radiates along the radial nerve to the upper arm and forearm. The pressure pain is evident in the radial head area, and the elbow pain is evident when the forearm is rotated posteriorly, whereas in tennis elbow the pain is evident before rotation. In addition, the middle finger extension test is helpful for diagnosis. If a patient with dorsal interosseous nerve syndrome is made to straighten the elbow joint and to straighten the middle finger against resistance, the patient’s elbow pain worsens (Figure 2). Indeed, the diagnosis of dorsal interosseous nerve syndrome is supported by the presence of neurogenic damage and slowed nerve conduction velocity on electromyography in forearm muscular atrophy.