More than 30 tunnel syndromes are known, but 5–6 syndromes are of real clinical significance [1, 2]. The neuropathy of the ulnar nerve (UN) at the level of the cubital tunnel (CC) is the second most common after the tunnel neuropathy of the median nerve in the area of the carpal tunnel [3]. The incidence of cubital tunnel syndrome (CTS) is 20.9–30.0 per 100,000 in the general population [4–6]. Thus, in a study conducted among the Italian population, the incidence was 20.9%, while men get sick more often than women [7]. The frequency of CTS detection has now increased significantly due to the development of medicine, the improvement of the diagnostic base and the possibility of precision differential diagnosis. The ratio of diagnosed cases of carpal tunnel syndrome and CTS, according to statistics, is 7/1. Approximately 39,000 operations are performed for CTS annually in the United States. People aged 40–50 years are most often ill [5]. CTS was first described by Panas in 1878 in a patient with post-traumatic valgus deformity of the elbow joint, and then by Feindal W. and Stratford J. in 1958 [5].
Most often, the development of CTS is idiopathic, however, there are anatomical prerequisites that lead and contribute to the development of this pathology [8, 9]. The development of STC is predisposed by the features of the anatomical structure of the CT and the biomechanics of the UN during flexion of the arm in the elbow joint (EJ) [4, 5]. In the region of the EJ, the UN has no protective coating in the CT [10]. This is the reason for its increased susceptibility to damage [11]. The CT is formed by the ligament of Osborne and the sulcus of the UN, which is localized behind the medial epicondyle of the shoulder. Osborne's ligament is located between the medial epicondyle of the humerus and the olecranon of the ulna, distally, the ligament continues into the compacted fascia m. flexor carpi ulnaris. Most often, the UN is compressed by Osborne's ligament. The mobility of the UN in the CT during movements in the EJ is up to 10 mm in the proximal direction and up to 6 mm in the distal direction and can reach more than 23 mm in the most “unfavourable” position of the shoulder, forearm, hand, and fingers [5]. When the EJ is unbent, the cavity of the CT has the shape of an ellipse, and when the EJ is bent, the crosssectional area of the CT decreases by 55% and becomes slit-like [4]. When the EJ is unbent, the pressure in the CT is up to 19 mm Hg [12], When the arm is bent in the EJ, there is a 7-fold increase in pressure in the CT, sliding and stretching of the UN by 4.5–8 mm inside the CT [4]. With an increase in pressure on the EJ in the CT over 30 mm Hg there is a slowdown in venous outflow, swelling and slowing down of axonal transport. And at pressure over 60–80 mm Hg blood doesn't flow to the UN. The edge effect is more pronounced directly at the entrance to the tunnel. Compression of the UN for two hours with a pressure of 400 mm Hg leads to persistent circulatory disorders [5]. Accordingly, when the arm remains in the position of flexion in the EJ for a long time, frequently repeated flexion and extension of the EJ, an uncomfortable position of the arm resting on the elbow contribute to damage to the UN in the CT and the development of CTS [13].