## 1 Introduction  
The presented paper focuses on an implant widely used in traumatology, namely a headless (so-called Herbert) screw. This screw (implant) is designed for surgical treatment of a fifth metatarsal bone using osteosynthesis. In general, osteosynthesis is a surgical method of treating fractures involving the fixation of bone fragments using internal (screws, splints, nails, wires, and combinations thereof) or external (external fixators) implants. The application of screws is important in the surgical treatment of complicated human or animal fractures and deformities in trauma or orthopedics. They serve both external and internal fixation in osteosynthesis, etc. Osteosynthesis in trauma surgery is a recognized and important medical method and an important topic of many studies [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11]. Figure 1 shows an X-ray snapshot of the fixation of a fifth metatarsal fracture with a headless screw. Metatarsal fractures are the most common fractures of the leg, the most common among them being the fifth metatarsal fracture. Metatarsal fractures are mostly caused by direct impact (car accident, fall, etc.) or during sports (typical injuries of football players, etc.). There are multiple types of metatarsal fractures, such as the Jones fractures, proximal diaphyseal, or fatigue fractures. Interested readers may find more information in [5; 6]. Figure 2 indicates the basic anatomy of the fifth metatarsal bone and its surroundings. In 1902, Sir [PERSON] described his own foot injury, which he suffered while dancing. It was a transverse fracture of the fifth metatarsal, without substantial dislocation in the junction of the diaphysis and metaphysis of that metatarsal; see Figure 2. This fracture is characterized by injury development caused by relatively low stress, minimal swelling, absence of hematoma, and prolonged healing. The classification of fractures in the proximal part of the fifth metatarsus is not uniform and completely clear. Some authors fundamentally differentiate the so-called true Jones fracture from stress fractures (fatigue fractures) of the proximal diaphysis of the fifth metatarsal. In 1960, [PERSON] reported that a large proportion of patients experienced prolonged healing or developed pseudoarthoses after the conservative treatment of the Jones fracture. Their study group, however, contained a large proportion of fatigue fractures of the body of the fifth metatarsal; see [5; 6] or [11; 12; 13]. Figure 1: Application of a headless screw to the fifth metatarsal bone. Both conservative and surgical treatment of the fracture of the proximal part of the fifth metatarsal is possible. In conservative therapy, the application of a full, non-weight-bearing cast or plastic fixation for 6-8 weeks is recommended. In surgical treatment, intramedullary screw fixation or osteosynthesis with a tension loop wiring is used. Spongioplasty or corticospongious graft application is often considered the method of choice for these fractures [5; 6; 11; 12; 13]. In 1962, [PERSON] started to use a compression screw he designed for the surgical treatment of scaphoid fractures. This screw was cannulated and threaded at both ends with threads of a non-uniform angle, which ensured compression between the fragments when the entire screw was inserted. The screw is not extracted after the fracture has healed. The interfragmentary compression with the [PERSON] screw is approximately 2.5 times lower than with the washer screw. Although [PERSON] designed the screw specifically to treat scaphoided fractures, indications for its use in osteosynthesis were, over time, expanded to other fractures as well (decranon, ankles, tibial heads, fifth metatarsus, etc.) [5; 6; 11; 12; 13]. Metatarsal fractures, see Figure 3, can be treated surgically or conservatively; this paper focuses on the headless screw technique, in which the fracture is immobilized by the screw thanks to the differential pitch of the threads at the threaded ends, which leads to pulling the bone fragments together and, subsequently, to healing.