Comparisons Of External Fixator Combined With Limited Internal Fixation And ORIF For Sanders Type â…¡ Calcaneal Fractures

BackgroundCalcaneal fractures are the most common fractures of tarsal bone in clinical, about 2% in the body fractures, and 75% of the fractures involved with subtalar joint. The main injury mechanism of the fractures is avulsion, vertical compression and shear force, of which the most common is vertical compression. Fall is the most common reason, belong to high-energy injury, and often combine with severe soft tissue injury. Early surgery is restricted by the poor soft tissue, so the treatment of calcaneal fractures is more difficult. At present, conservative treatment was suggested to deal with undisplaced fractures like Sanders type I fractures, and most could achieve better clinical results; subtalar arthrodesis was suggested to deal with Sanders type Ⅳ fractures, because of the serious damage in soft tissue and articular surface; and for Sanders II and III fractures, the treatment is still controversial. ORIF via a lateral extensile approach, percutaneous poking reduction and Kirschner wire fixation, percutaneous cannulated screw fixation, arthroscopy, balloon reduction and cement fixation and external fixation techniques had been used for the treatment of calcaneal fractures, but the clinical effects opinions vary.ORIF via a lateral extensile approach is the most common treatment for calcaneal fractures, with the advantages of reduction the articular surface under direct vision, reconstruction of the calcaneus shape and anatomical relationship, and provide adequate biomechanical stability. But the operation time is more stringently restricted, and the interference to the lateral soft tissue may result in severe postoperative infection, wound dehiscence, flap necrosis, fibular tendonitis, neurovascular injury and plate exposure, etc. Higher soft tissue complication problem not only plagued surgeons, but also seriously affect the patient’s work and life, and even lead to disastrous consequences. So more and more orthopedic surgeons may inclined to take minimally invasive procedures. Percutaneous poking reduction and Kirschner wire fixation technique has the advantage of less invasive, shorter hospital stay, fewer wound complications, but disadvantages such as articular surface malreduction, loss of reduction should not be neglected. Other minimally invasive technology such as percutaneous cannulated screw fixation has obvious advantages in preventing wound complications, better clinical results, shorter healing time, but the disadvantages is also difficult to effectively expose and restore subtalar joint surface, and therefore it is restricted by the types of fracture, and higher technical requirements, the surgeon needs to have some experience, and turn to ORIF timely if closed reduction is failed. Other scholars suggested arthroscopic assisted closed reduction and percutaneous screw fixation in treating calcaneal fractures, this technique can effectively restore the subtalar joint surface under direct vision, but its advantage in reducing the incidence of complications is still controversial, and the potential complications included soft tissue swelling, ulceration and liquid leakage. Besides the long learning curve also restricted its widely use. Balloon reduction and cement fixation can effectively solve the problem of the bone defects, avoiding the use of plate fixation, but its long-term outcomes and safety needs more studies. The use of external fixation technology has become increasingly widespread, with the advantages of unlimited surgery timing, shorter hospital stay, and effectiveness in avoiding wound complications, and early weight bearing and functional exercise. The external fixation can be adjusted after operation and removed in out-patient, without second operation, and is suitable for many fracture types, open fracture required flap transplantation, and the biomechanical stability have been confirmed by some biomechanical studies. But the disadvantage of external fixation technique is also the lack of reduction the subtalar joint surface, thus on the basis of the external fixation technique, we added a small lateral incision on the outside to fix the subtalar joint surface with limited internal fixation, taking into account the relationship between the anatomical morphology and subtalar joint surface at the same time.The specimens experiment was traditionally used to take the biomechanical research, simulate the human activity on bones and joints by material testing machine and other loading equipment, and observing the stability, material strength, and hydraulic conductivity by a two-dimensional or three-dimensional model image sensor and other indicator. Due to the limitation and destructive of experimental methods, it is difficult to fully test the biomechanical stability and accurately assess the biomechanical mechanisms inside. Finite element analysis model can fully reflect the internal stress/strain situation, and is not restricted by the complex structure, not only for the surface structure of the model, its internal structure can also be clearly demonstrated, with the advantages of accuracy, repeatable, low cost, comparability, and has been widely used in orthopedic biomechanical study. This aim of this study was to establish the three-dimensional finite element analysis model of foot and ankle, construct a Sanders type II calcaneal fracture model, and fixed with EFLIF and ORIF, finally to verify the reliability and usefulness of the two fixation method. On this basis, the relative displacement and stress distribution were compared by the finite element analysis, and the clinical effectiveness was compared by a retrospective analysis at the same time.Chapter I:Finite element analysis of EFLIF and ORIF for Sanders type II calcaneal fracturePurpose:To compare the stability and stress distribution of external fixator combined with limit internal fixation and open reduction and internal fixation for Sanders type Ⅱ calcaneal fractures by finite element analysis.Methods:A LightSpeed 16-slice spiral CT of the Imaging Center was used to scan the volunteer’s right foot from distal tibia and fibula 15 cm above the ankle down to the planta, with the right foot in neutral position. Then the scanned data was imported into Mimics 15.01 software in DICOM format, and to reconstruct the three dimensional structure of the bones of foot and ankle and surrounding soft tissue after threshold segmentation, then imported into Workbench module of finite element analysis software ANSYS 12.0 to establish a complete finite element model of foot and ankle. With Solidworks software 2012 split command to establish calcaneal Sanders II type fracture model, and drawing external fixator, limited internal fixation screw and plate model and assembled together, two fixation CAD model is set up respectively, finally meshing, material assignment and mechanical boundary conditions were taken. By simulating the mechanical transfer in one foot standing state, the model was loaded 700 N from the upper end of the tibia vertical, and the talus was bounded. The contact pressure at the ankle articular surface of the tibia, the contact area, and the results were measured and compared with the former. According Sanders type II calcaneus fractures, while establishing Sanders type II calcaneal fractures finite element model fixed with EFLIF and ORIF, setting a non-contact state between the fracture fragments, and the friction coefficient is 0.3. Abaqus software was used to loading a 700N longitudinal load stress and a 160N maximum tensile stress from calcaneal tendon in non-weight bearing state, record the relative displacement between the fracture fragments, and stress distribution of on external fixator, screws and plate.Results:When loading 700N on the vertical, fixed with EFLIF and ORIF, the maximum relative displacement on the model are 1.462mm and 2.174mm, the maximum relative displacement between the fracture fragments are 0.01448mm and 0.3262mm, both of the two maximum relative displacement between the fracture fragments are less than lmm. Maximum stress distribution on the EFLIF model was 102.2MPa, less than the yield strength of the external fixator, stress distribution was mainly focused on the connection between external fixator and bone. Maximum stress distribution on the ORIF model was 2491MPa, bigger than the yield strength of the screw, stress distribution was mainly focused on the sustentaculum tali screw near the fracture line. When loading 160N from the Achilles’s tendon, fixed with EFLIF and ORIF, the maximum relative displacement on the model are 1.462mm and 2.174mm, the maximum relative displacement between the fracture fragments are 0.3335mm and 0.1808mm, both of the two maximum relative displacement between the fracture fragments are less than 1mm. Maximum stress distribution on the EFLIF model was 47.2MPa, stress distribution was mainly focused on the schanz screw. Maximum stress distribution on the ORIF model was 141.9MPa, stress distribution was mainly focused on the connection between the plate and screw. Both of them are less than the yield strength of medical devices.Conclusion:The external fixator combined with internal fixation is essential for fixation of type calcaneal fracture to achieve the biomechanical stability and can be used in clinical practice to promote. Both EFLIF and ORIF could provide sufficient biomechanical stability for Sanders type II calcaneal fractures, relative displacement in EFLIF was lesser, and the stress distribution was more reasonable. Stress concentration was occurred on the ORIF model, the screw may be out of work when loading 700N.Chapter II:Clinical outcomes of EFLIF and ORIF for Sanders type II calcaneal fracturePurpose:The treatment of calcaneal fractures remains controversial. The aim of this study was to compare the biomechanical stability and clinical outcome of EFLIF and ORIF in treatment of Sanders type Ⅱ calcaneal fractures.Methods:Two types of fixation systems were detected by finite element analysis and a retrospective study. Two fixation systems were simulated to fix the fracture in a finite element model respectively. The relative displacement and stress distribution were analyzed and compared. A total of 50 consecutive patients with closed Sanders type II calcaneal fractures was enrolled and divided into two groups according to the different treatment under randomization. The radiological and clinical outcomes were evaluated and compared.Results:Age, sex, type of accident, accompanying injuries, and comorbidities were equal between two groups. There were no significant differences between two groups on follow-up period (P=0.197). The external fixator and plate had been removed at the last follow-up. Timing of surgery, operation time, blood loss, and hospital stay were significantly lower in EFLIF group (P<0.05). There were more intraoperative fluoroscopy times in EFLIF group (4.24 to 6.88, P<0.05). Bohler’s angle was reconstructed anatomically, severe decrease of Bohler’s angle was not encountered within follow-up period. There were no significant differences between two groups on Bohler’s angle preoperatively, postoperatively and last follow-up (P>0.05). There were no significant differences between two groups on AOFAS ankle-hindfoot score (83.32 to 84.40, P=0.556) and VAS score (1.64 to 1.60, P=0.824). Subtalar joint range of motion, return to previous work, patient satisfaction, and subtalar arthritis were similar between two groups. One wound complication occurred in EFLF group (4%), and 3 (12%) superficial wound complications (1 dehiscence and 2 infections) and 1 (4%) deep infection occurred in ORIF group, the former was significantly lower (χ2=5.17, P<0.05). Oral antibiotic and dressing changes were performed to treat the superficial infections. Implants removal, operative debridement and intravenous antibiotics were performed to treat the deep infection at sixth week postoperatively.Conclusions:Both of the EFLIF and ORIF could be stable and effective in treating Sanders type II calcaneal fractures. The EFLIF might be superior to ORIF in achieving biomechanical stability and less blood loss, shorter surgical time and hospital stay, less wound complications.