Biomechanical definition of the load on the elbow joint in radial head fractures
Background. Radial head fractures are the most common fractures of the elbow joint and account for 56 % of fractures of the proximal forearm [4]. Quite often, the surgeon decides to remove fragments of the fractured radial head. In practice, the dependence of the elbow stability on the degree of the radial head resection is revealed. The purpose of our study was to study the state of the elbow joint elements and the factors ensuring its stability under the conditions of the radial head defect of 5-10-15 mm at the range of movements of 5-90° with a load of 5 kg. Materials and methods. Calculations of the stress-strain state of the elbow joint elements by the finite element method on the basis of the computer 3D model Zygote Media Group, Inc. An intact elbow model and elbow with a radial head defect of 5-10-15 mm in positions of 5° and 90° flexion were used for calculations. Criteria for assessing the stress-strain state were von Mises stress, contact stress, strain and total deformation. Results. At the 5° elbow flexion, an increase in the size of the radial head defect causes: the stress in the ulna increased by 36.5 % (σmax = 8.0 MPa) at the subchondral areas of the articular surface and at the attachment site of the lig. collaterale ulnare (σmax = 8.86 MPa), strain increased by 53 % (εmax = 0.31 mm) at the lig. collaterale radiale, the total deformation of the elbow model increased by 37 % (Δ = 33.36) due to the distal radius, the total deformation of the radial head increased 4 times (Δ = 5.13 mm). At the 90° elbow flexion, an increase in the size of the radial head defect causes: the stress in the lig. collaterale radiale increased 4 times (σmax = 57.15 MPa), subchondrally at the articular surface of the ulna (σmax = 6.67 MPa) and at the attachment site of the lig. collaterale ulnare (σmax = 16.02 MPa) increased 2 times, the stress at the subchondral areas of the humerus articular surface increased 1.5 times (σmax = 7.08 MPa), reduction of the maximum stress at the articular cartilage of the humerus articular surface by 3.6 times, the strain at the lig. collaterale ulnare posterior increased 2 times (εmax = 0.71 mm), the total deformation of the proximal forearm increased 14 times (Δ = 58.52mm), the total deformation of the radial head increased 215 times (Δ = 21.53 mm). Conclusions. According to the study, the removal of the radial head significantly affects the normal biomechanics of movements in the elbow, leads to a redistribution of loads and instability in the joint. The basic stabilizing structure of elbow is lig. collaterale radiale, which keeps the joint at the stable state in all flexion positions. Increase of flexion angle results in increasing the deformation parameters of the model because of lig. collaterale radiale strain. Significant increase of stress at lig. collaterale radiale in the presence of radial head defect indicates its important role as a stabilizer in the valgus load. The intact elbow at the 90° flexion position is more stable than at the 5° flexion position. Increase in the radial head defect size causes a significant decrease of the elbow stability at the 90° flexion position. It is advisable to avoid the removal of the radial head fractures fragments and to initiate restoring the stability of the joint.