Biomechanical Study Of The Calcaneus Fractures Fixed By The Self-designed Calcaneal Anatomic Plate And Pre-cut Gudgeon

Objective: Calcaneus is the most easily impaired bone among the tarsal bones.The calcaneus fractures mostly happen to young and middle-aged people and are usually the result of a fall from a great height.75% of the calcaneal fractures are intra-articular,all of which are caused by the stress of axis direction.The ideal management of the intra-articular calcaneal fractures remains a tough problem to resolve.With the development of the imageolgy recent years,We have deepper recognition to the calcaneus fractures and with the improvement of the operational equipment, the management of the calcaneus fractures is improved and elevated constantly.Open reduction and internal fixation is generally adopted,However, more and more postoperative complications are reported clinically on the patients of calcaneus fractures who are treated by open reduction and internal fixation at present.Because choosing the plate,we should pay attention to the principle that the fixation of the fractures must be available,practical,little injury,fitting the physiological nature,cutting down partial complications,the purpose of this study is to carry out the biomechanical study of the calcaneus fractures fixed by the self-designed calcaneal anatomic plate and pre-cut gudgeon.The interal fixation systerm designed by ourselves fits the standard of ideal fixation to the calcaneus fractures and it provides satisfactory therapeutic efficacy with good quality of minimal invasion, valid fixation,shorting the time of the union of fracture, et al, Which can be used for the management of various kinds type of intra-articular calcaneus fractures. We evaluate the therapeutic efficacy by the biomechanical contrast experiment to provide the foundation and measure for improving therapeutic efficacy and reducing the failure of internal fixation.Methods: sixteen fresh foot specimens containing whole leg were used, all of which were gotten from young and middle-aged patients amputated because of road accident or osteosarcoma. For each specimen,we dissected the surrounding structures of calcaneus carefully but preserved the integrity of the ankle capsule and the surrounding ligament of the calcaneus, then we transected the specimens from 20 centimeters superior to malleous.Observation and radiographs of the specimens were obtained to ensure that they were free of tumor,fracture, abnormity and variation and then the specimens were randomed into two groups,group A and group B.every group have eight specimens which were placed on the biomechanical testing machine with the foot fixed firmly on the bench and the superior part fixed by clamp to create compression fractures through axis loading test of damage. It must be ensured that all the specimens were vertically loaded through the center of the tibiofibula. The ultimate loading and the ultimate displacement of the instep were recorded in A group. Then we cut one microstomia at the posteriallateral capsule of the subtalur joint,with a wedge to increase the displacement and the width of the calcaneus and it was confirmed that the model of the calcaneus fracture was Sanders type-Ⅱby X-ray, coronal CT scan and 3-D CT reconstruction. The models of Group A were fixed by the self-designed internal fixation systerm and the models of group B was fixed by the AO plate internal fixation systerm after reduction. The reduction of the fracture was ensured by X-ray. All the sixteen specimens were fixed on the biomechanical testing machine as above after reduction and fixation with the extensometer fixed in the medial and lateral calcaneus. It must be ensured that all the specimens were vertically loaded through the center of the tibiofibula with the vertical loading speed of 20N/S till 600 N and the displacement of the instep and the change of calcaneal width were recorded. Eventually, we tested the ultimate loading of the specimens. The vertical loading was not stopped through the tibiafibular until the biomechanical machine showed the failure of the internal fixation and the ultimate loading was recorded. The data was analyzed by the Student's test of SPSS13.0 statistical software. Signifcance was set at P<0.05.Results: with the vertical loading, there was significant differece between the normal calcaneus and the calcaneus fracture fixed by self-designed internal fixation systerm on the ultimate loading(normal calcaneus, 5711.19±86.55N; the calcaneus fracture fixed by self-designed internal fixation systerm, 7866.74±181.58N). There was the difference of 27% between them. there was no significant differece between them on the ultimate displacement of the instep(normal calcaneus, 18.57±2.79mm; the calcaneus fracture fixed by self-designed internal fixation systerm, 19.35±3.64mm). There was the difference of 4% between them. With the vertical loading of 600N, there was significant differece(P < 0.01)between the group(experimental group abbreviated below)of self-designed internal fixation systerm and the group of AO plate internal fixation systerm(control group abbreviated below)on the displacement of the instep(the experimental group, 1.54±0.87mm; the control group, 3.31±1.07mm)and on the change of calcaneal width(the experimental group, 0.54±0.37mm; the control group, 1.73±0.69mm). There was significant differece(P<0.01)between them on the ultimate loading(the experimental group, 7866.74±181.58N; the control group, 6702.94±241.06N).Conclusion: After the calcaneus fractures are fixed by the self-designed internal fixation systerm, it recovers the biomechanical effect of the normal instep,improves the bearing capacity of the calcaneus and fits the funtional character of vitodynamics. There are the difference of 27% on the ultimate loading and the difference of 4% on the ultimate displacement of the instep between them, respectively. It was improved that the calcaneus fixed recovered the biomechanical effect of the normal foot completely and the foot fixed can sustain the sufficiently powerful bearing capacity of the instep. Through the comparison of the calcaneus fractures fixed by self-designed systerm and AO systerm on the displacement of the instep,the change of the calcaneal width,and the ultimate loading, it is proved that the effect and strength of the self-designed internal fixation systerm in treating calcaneus fracture are better than the AO interal fixation systerm.