Development of a new approach for the treatment of fifth metacarpal fractures

Hands, which play a key role in performing upper extremity functions, perform their advanced functions in coordination with the central nervous system and muscular system. There are 5 metacarpal bones on the back of the hand, extending along the palm to the bases of the fingers. Metacarpal bones are expressed as numbers from one to five. The first metacarpal is the thumb metacarpal, and the little finger metacarpal is the fifth metacarpal. Metacarpal bones are the longest bones that make up the structure of the hand. Metacarpal fractures constitute 40% of all upper extremity fractures. The most common of these fractures are 5th metacarpal neck fractures, accounting for 10%. The classification of metacarpal bone fractures is similar to the classification of long bone fractures. Metacarpal fractures are generally closed fractures and can be treated with closed reduction. Metacarpal bone fractures can be classified as head, neck, shaft and base fractures according to the anatomical location of the fracture. The most common type of metacarpal fractures are neck fractures. The first metacarpal bone has greater mobility due to less joint stability, and treatment of first metacarpal fractures usually requires open reduction. Metacarpals except the first and fifth metacarpals are bilaterally stable because they form a joint with the metacarpals next to them. The fifth metacarpal bones are metacarpals that are more likely to break because they are located on the edge of the hand, like the first metacarpals, and are fixed from one side with the fourth metacarpal. As a result of the hand striking a hard place in the form of a closed fist, the force is transferred from the metacarpal head to the metacarpal neck, and the fracture usually occurs in the neck or shaft (body). Due to the way the fracture occurs, 4th and 5th metacarpal neck fractures are often called "Boxer fractures". Clinical and radiological examinations are necessary to make the correct diagnosis in patients who apply to the emergency department with complaints such as pain, swelling, bruising, and difficulty in moving and using the hand after metacarpal bone fractures. Following the examinations, the treatment process is planned. In order for the fracture to heal properly, the broken bone pieces must be aligned close to their previous position and this alignment must be maintained throughout the healing process. In addition, the chosen treatment method should not damage other structures in the area. The aim of treatment is acceptable bone alignment, fused bone structure and optimal recovery of hand functions. Bone has the ability to regenerate itself after being broken. Fracture healing consists of three intertwined phases. These stages; inflammation phase, repair phase and remodeling phase. Among the stages, the shortest is the inflammation phase, while the longest is the remodeling phase. If the distance between the broken bone fragments is close to the desired level and the necessary biological and biomechanical conditions are met, a hematoma formation will first occur at the fracture line. As the hematoma in the area matures, a collagen matrix and vascularization are formed. Mesenchymal xxviii stem cells with the ability to differentiate come to the area and transform into chondrocytes and form a cartilage-shaped repair tissue. The process ends with the transformation of the cartilaginous callus, which does not have sufficient mechanical properties, into bone tissue. In order for bone healing to occur properly, the treatment process must be observed. The fracture can be reduced closed or open, depending on its formation and anatomical location. The preferred treatment method for simple fractures where malrotation is not observed and minimal displacement is detected is plaster, splint and splinting. With closed reduction, the broken bone pieces are placed in the required position and they are ensured to remain fixed in this position for the broken bones to fuse. Although it depends on the patient's age, gender and other physiological characteristics, bone healing is generally observed after 3-6 weeks. This process should be followed by radiological examinations to avoid undesirable situations and, if necessary, surgical intervention should be performed. If there is an open fracture, surgery is usually required due to the condition of the fracture and the risk of the open wound becoming infected. Fractures that require operative methods to align the bones and achieve adequate reduction are generally multiple, comminuted, malrotated, those that cannot be reduced closed or where displacement is observed. With the method called internal fixation, metal pieces are placed in the bone using various methods to keep it in a position where it can heal. These methods; Fixation technique with Kirschner wire (K wire) can be classified as intraosseous wire, interfragmentary screw, plate and screws, intramedullary fixation and external fixator. In the literature studies, it has been observed that in the early repair phase of fracture healing, where callus production occurs, targeted adjustment of the mechanical environment and axial loading applied externally to the bone at regular intervals increase the healing response, accelerate the union process and reduce healing complications. The study includes a splint design based on 3-point fixation for the treatment of fifth metacarpal fractures that do not require open reduction. The 3-point fixation method is a static method to join two parts rigidly. In this method, two pressure points are applied over the rotation axis, while the third pressure is applied in the opposite direction under the rotation axis to balance the pressure force applied to these two points. The aim is to hold the two parts together with three forces that have a balance condition, without allowing them to slide. The points to be applied and the pressure force to be applied must be selected correctly. In the literature, the pressure force that will damage human tissues is defined as forces of 25 MPa and above. In this direction, a 3D splint design that would fix the fifth metacarpal bone fractures and allow the application of appropriately sized forces that would contribute to bone healing was carried out using the CAD modeling method. In order to apply the required force, it was decided to use springs due to the advantages of being produced in the desired size and hardness. Using it integrated with the screws will ensure that the springs are compressed to apply the desired pressure and remain fixed at the planned point. In the designed splint model, channels were created on the inside and outside of the hand to contact the hand so that force can be applied to the fracture area through springs. The modeled splint was produced using PLA, a thermoplastic-based and biocompatible filament, using an FDM type 3D printer. In order to test the forces to be applied, a calibration mechanism (measurement system) was designed using the CAD modeling method. A structure has been added to thecalibration mechanism to support the existing splint design so that the applied forces can be measured with the force sensor. The production of the calibration mechanism was made using a 3D printer. The calibration test enables the pressure force created by the screw and spring to be detected with the help of a sensitive sensor. In this system, thanks to the Arduino kit, the force values obtained from the sensor are displayed in Newton on the LCD screen. In order to examine the mechanical effects of the forces applied through screws and springs on the bone, 5 different metacarpal fracture structures were created with the SOLIDWORKS package program. Finite element analyzes of these created models were performed using ANSYS software. Fractures are modeled in two different ways, angled and non-angled, and designed for two different fracture types: neck and shaft fractures. When applying force, different distances were taken into account in angled and non-angled fracture types. In nonangle shaft fracture, angled shaft fracture and neck fracture, force was applied from two different distances, 6 mm and 9 mm. While determining the magnitude of the reaction forces applied to balance these forces based on the principle of 3-point fixation, the range of 2-20 N was chosen so as not to damage the skin tissue. The deformation and Von Mises stress values resulting from the changing force were examined graphically. Maximum deformation and stress values, varying depending on the force, were compared with the help of tables and graphs. When these tables and graphs were examined, it was observed that deformation and stress values increased depending on the increase in force.