For about 20 years, observations and reports have appeared about exceptional cases of suddenly rotated nerve segments [1]. The etiology of this phenomenon is unknown to date [2, 3]. Small nerves such as the anterior interosseous (see Sect. 8.​13) and posterior interosseous (see Sect. 8.​10) nerves, suprascapular and axillary (circumflex) nerves, and also the radial nerve trunk at level where it pierces the lateral intermuscular septum (see Sect. 8.​9) can be affected [2–4]. An hourglass-shaped constriction occurs as a single event or even as multiple manifestations (see Sect. 10.​3).

An acute pain is followed by a gradual onset of functional paralysis of the muscle group which the affected nerve supplied. As suspected pathophysiology, a local inflammation of unknown etiology (see also Sect. 6.​2.​8), perhaps together with repetitive or rotatory movements, are in discussion. An increased stiffness of the nerve fascicles is said to make them less adaptable to transversely running structures like vessels or fascias that can act constricting or fixing [2].