| Background:Humerus throwing fracture generally refers to the humeral shaft fracture due to arm movement in throwing or arm wrestling. The typical throwing fracture of humerus is a spiral fracture, usually occurred in the middle and distal of humerus. It usually occurred in soldiers’grenade throwing training, throwing events like javelin, hammer throwing, as well as courtgames. The exact injury mechanism is not clear, may be related to the following factors:(1) At first, in view of anatomy, the border between middle and distal humerus is mechanical weakness which is also the border between cylindrical and triangle of humerus. The middle and distal humerus is a specific predilection sites. (2) Due to antagonistic effects of uncoordinated and unbalance muscle groups in throwing process. (3) Due to excessive training, muscle injuries, arm pains, lacking of training skills.The treatment of the humeral shaft fracture is remarkably diverse, conservative treatment is widely used in the past which could achieve a good treatment effect. In recent years, with the continuous development of orthopedic technology, more and more scholars advocate operation treatment which could reduce the pain of fracture site and achieve anatomical reduction.Compared with the conservative treatment, operation treatment could obtain a more firmly reduction of fracture, to do early exercise, as soon as possible to recover, reduce the pain of patients, improve the quality of life. However, there are many shortcomings, like increasing rates of infection, iatrogenic radial nerve injury and internal fixation failure.The internal fixation operation is a useful treatment of the humeral shaft fracture. The internal fixities mainly include lag screws, intramedullary fixation system, plates and screws system. Using several lag screws to fix the fracture has many advantages, such as minimally invasive, operation simplify, operation time shorting.However, the mainly disadvantages include the loss of reduction which usually occurred after surgery, counting against the early function exercising. Until now,the balance of academic opinion has been that the lag screws should combine with the plates and screws system.At present, the commonly used internal fixity is intramedullary nail system including improved Kuntscher nail, Gross-Kempf nail and Seidel nail and interlocking intramedullary nail. The intramedullary nail has a less stress shielding, less periosteal stripping, less nerve or vessel injury, the axial fixation is more in line with biomechanical properties. However, there are some disadvantages, such as the longer average operation time and healing time. The plates and screws system mainly includes the dynamic compression plate (DCP) and locking compression plate (LCP), plates and screws system which has the tension band effect, reliable fixation, anti rotation, good stability. However, using plates and screws system need more widely periosteal stripping range, broking the blood supply at the fracture sites, the fracture nonunion or refracture after removal of plates. Choosing appropriate implants remains controversial, such as how to choose plates, antegrade intramedullary nail or retrograde intramedullary nail, locking compression plate or dynamic compression plate, dynamic compression plate combined with lag screws or not. It is very important to choose appropriate implants correctly.Compared with plates and screws fixation system, intramedullary nail has a smaller stress shielding effect, less periosteal stripping, nerve and vessel injury, the axial fixation is more in line with biomechanical properties. The intramedullary nail system is commonly used in the treatment of humerus shaft fracture. For the middle and distal humeral fractures, how to choose antegrade intramedullary nail or retrograde intramedullary nail has no unified view. Using anterograde intramedullary nail is easy to cause the rotator cuff injury, even cause the dysfunction of shoulder. Using retrograde intramedullary nail can effectively avoid rotator cuff injury, but the olecranon fossa has hard cortical bone, operation is easy to cause the splitting of distal humerus.The anterolateral and posterior operation approach are commonly used in treatment of middle and distal humerus fractures, plates are arranged in the anterolateral column and the rear column of humerus respectively. The treatment of humeral shaft fracture preferred which operation approach and optimal placed location of plates are disputed. The radial nerve obliquely across the fracture site and close to the bone surface, plates usually placed on the anterolateral column so that could expose the radial nerve, radial nerve injury usually occurs in process of fracture reduction and plate fixation during operation. Because the humeral rear column is rather flat, which provide a relatively flat internal fixation condition, simplify operation process and avoid of radial nerve injury. But some other medical literature pointed out that:using posterior operation approach need to split the triceps, easily lead to postoperative scar, resulting in elbow extension limitation. Which placement location of plates is better? There is no unified view.The use of dynamic plate and lag screw technique in treatment of humeral spiral fracture should obey the AO principles, anatomic reduction, protecting the blood supply of the fracture site, rigid internal fixation, early functional exercise. Combined with lag screw technique could simplify the operation process, reduce shear stress and the distance between the fracture fragments, enhance the effect of compression at fracture ends. For the middle and distal humeral spiral fracture, whether we should use dynamic plate routinely plus with lag screws? There is no unified view.With the development of medical digital technology, the finite element analysis which is a relatively new research mean gradually used in the orthopedic biomechanical research. Through establish the three-dimensional models of different internal fixation for the throwing fracture of humerus respectively, we can obtain the biomechanical properties by finite element methods to compare different fixation methods in different movements of limbs motion. Therefore, we can establish a better preoperative internal fixation scheme and provide a theoretical reference for the postoperative rehabilitation.This study mainly discuss the clinical problems above, combined with the finite element analysis methods. Models of locking compression plate (LCP) and dynamic compression plate (DCP), intramedullary nail or retrograde intramedullary nail, dynamic compression plate combined with lag screws or not in treatment of humeral throwing fractures were made to explore there biomechanical properties.Objective:1. To construct a 3d finite-element model of throwing fracture of humerus and explore the injury mechanism of humeral throwing fracture.2. Compare the biomechanical properties of the locking compression plate with antegrade intramedullary nail and retrograde intramedullary nail fixation models of humerus throwing fracture by finite element analysis to provide a theoretical reference for clinical work.3. Compare the biomechanical properties of the locking compression plate and dynamic compression plate arranged in the anterolateral column with in the rear column of humerus to fix the humeral throwing fracture by finite element analysis.4. Compare the biomechanical properties of the dynamic compression plate combined with lag screws with dynamic compression plate to fix the humeral throwing fracture by finite element analysis.Methods:1. Using two-dimensional CT data of adult humerus, to construct the three-dimensional finite element model of typical throwing fracture of humerus by Mimics 14.01, Solidworks2013 and ANSYS 14.0 soft wares. According to previous literature and clinical observation, we need to verify the validity of the model.2. Using humeral spiral CT scans data of a healthy adult volunteer, construct the throwing fracture of humerus by relevant modeling soft wares. Simulating the fracture reduction, assembling the throwing fracture of humerus with the locking compression plate and dynamic compression plate in anterior lateral and posterior fixation of the throwing fracture of humerus by Solidworks2013 software which has assembly and Boolean functions. Exerting three loading conditions to simulate elbow hit the ground when lateral falling, upper arm counterclockwise rotation and subjecting to impact. The different maximum equivalent stress of implants, the maximum comprehensive displacement of humerus, the different maximum equivalent stress and the maximum comprehensive displacement of the fracture ends to evaluation the locking compression plate and dynamic compression plate in various loading conditions.3. Simulating the fracture reduction, assembling the throwing fracture of humerus with antegrade intramedullary nail or retrograde intramedullary nail fixation of the throwing fracture of humerus respectively. Exerting three loading conditions to simulate elbow hit the ground when lateral falling, upper arm counterclockwise rotation and subjecting to impact. The different maximum equivalent stress of implants, the maximum comprehensive displacement of humerus, the different maximum equivalent stress and the maximum comprehensive displacement of the fracture ends to evaluation antegrade intramedullary nail and retrograde intramedullary nail in various loading conditions.4. Simulating the fracture reduction, assembling the throwing fracture of humerus the dynamic compression plate combined with lag screws with dynamic compression plate fixation of the throwing fracture of humerus respectively. Exerting three loading conditions to simulate elbow hit the ground when lateral falling, upper arm counterclockwise rotation and subjecting to impact. The different maximum equivalent stress of implants, the maximum comprehensive displacement of humerus, the different maximum equivalent stress and the maximum comprehensive displacement of the fracture ends to evaluation the dynamic compression plate combined with lag screws with dynamic compression plate in various loading conditions.Result:1. The finite element models of throwing fracture of humerus were proved to be effective and reasonable by comparison with the traditional biomechanical experimental results and clinical observation.2. The finite element analysis results of locking compression plates arranged in the anterolateral column and the rear column of humerus, retrograde and antegrade intramedullary nail fixation of the throwing fracture of humerus are as follows. (1) The maximum equivalent stress:the maximum equivalent stress of locking compression plate arranged in the anterolateral column is smaller than rear column; the maximum equivalent stress of retrograde intramedullary nail is larger than antegrade intramedullary nail in the compression condition while smaller in torsion and bending conditions; (2) The maximum displacement of fracture fragments:the maximum displacement of fracture fragments of intramedullary nail group is larger than locking compression plate group, locking compression plate arranged in the anterolateral column is larger than locking compression plate arranged in the rear column; (3)The maximum equivalent stress of fracture ends: the maximum equivalent stress of fracture ends of locking compression plates groups are larger than intramedullary nail groups and have more uniform stress distribution.3. The finite element analysis results of dynamic compression plate and dynamic compression plate combined with lag screws arranged in the anterolateral column and the rear column of humerus fixation of the throwing fracture of humerus are as follows. In compression and bending load conditions, the maximum stress of implants and the maximum displacement of fracture fragments of the anterolateral internal fixation compared with the posterior internal fixation were larger while smaller in tensional condition. The maximum equivalent stress of dynamic compression plate combined with lag screws groups are larger than dynamic compression plate groups and have more uniform stress distribution. Under compression condition, the maximum displacement of fracture fragments of dynamic compression plate combined with lag screws groups are larger while smaller in bending and torsion conditions. The stress distributions in fracture ends of all models were similar, dynamic compression plate combined with lag screws can decrease the maximum displacement of fracture ends.Conclusions:1. The experiment successfully construct a realistic finite element model of throwing fracture of humerus to research its biomechanical Properties, our experimental methods are better than traditional biomechanical experiments.2. Because of the anatomical features of the humerus, the helical force of the middle and lower segments under the action of rotating force may be one of the injury mechanisms of humeral throwing fracture.3. Using locking compression plate is more stable than using intramedullary nail and has more uniform stress distribution in treatment of throwing fracture of humerus. Using retrograde intramedullary nail is more stable than using the anterograde intramedullary nail.4. Locking compression plate arranged in the rear column is more stable than in the anterior lateral column. Dynamic compression plate arranged in the in the rear column is more stable than in the anterior lateral column under axial compression and bending conditions, while the opposite result will happen under torsion condition.5. Using dynamic compression plate combined with lag screws is more conducive to fracture healing and also enhance the stability under torsional and bending conditions, while the opposite result will happen under compression condition. |
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