| Tibio-talo-calcaneal arthrodesis is the gold standard for the treatment of end-stage ankle and subtalar joints.In 1906,Lexer first reported this procedure,thereafter it has been continuously developed and being widely applied in clinical practice.Tibio-talo-calcaneal arthrodesis involves complex anatomical structures of two adjacent joints,the subtalar joint and the ankle joint,so that issues including difficulty of operation,high rate of postoperative complications and nonunion rate have always been existing and unresolved.The choice of surgical incision,internal fixation and cartilage surface management are all key factors concerning the success of tibio-talo-calcaneal arthrodesis.Screws,plates,external fixators and intramedullary nails are used in tibio-talo-calcaneal arthrodesis as fixation methods.Retrograde intramedullary nail with valgus and posterior bend has become the preferred fixation method.However,the retrograde intramedullary nail placement process is cumbersome,the learning curve is long,the risk of intraoperative nerve and vascular injury is high with more postoperative complications.The full thread headless compression screw is simpler and more flexible than the retrograde intramedullary nail,which can effectively protect the nerves and blood vessels of the ankle and foot.It is a unique design with smaller head and bigger tail.It has step pressure in the process of nailing.In theory,it has better effect on the continuous compression of the articular surface,which is a guarantee for improving the fusion rate,especially for two adjacent joints,tibio-talo(ankle)and talo-calcaneal(subtalar)joints.In combination with the current research progress and surgical operation of the fixation and selection,anatomy and neurovascular structure of ankle-hind foot,the posterolateral and anteromedial position of the distal tibia articular surface in the bottom of calcaneus temporal projection area are used in this study.At the nailing point,two full thread headless compression screws were inserted parallel to the tibia from the sole of the foot to fix the subtalar joint and ankle joint.There is no relevant biomechanical study and clinical effectiveness analysis of this fixation on the displacement of the tibio-talo-calcaneal arthrodesis and the distribution of stress on the subtalar and the ankle joints surface,as well as the plantarflexion and dorsiflextion,internal and external valgus,and rotation of the hindfoot.Biomechanical research based on finite element method has been widely used in medical research,providing valuable reference for the pathophysiological mechanism in the field of orthopedics and sports medicine,the selection of internal fixation materials and the study of surgical methods.Through the accurate modeling function of 3D finite element,the dynamic and static simulation research on the complex anatomy,different parameters and stress conditions of the foot and ankle are carried out,and the biomechanical analysis can be performed repeatedly.This study intends to compare the biomechanical differences of two full thread headless compression screws and lag screws to tibio-talo-calcaneal arthrodesis.Furthermore,the clinical effectiveness of the full thread headless compression screw under the minimal incisions was analyzed to verify the effectiveness,safety and reliability of the operation.Part I Biomechanical comparative analysis of full thread headless compression screw to tibio-talo-calcaneal arthrodesisThe bone structure model of hindfoot was established by finite element method.Comparative analysis showed that two full thread headless compression screws were inserted parallel to the posterolateral and anteromedial position of the distal tibia articular surface in the bottom of calcaneus temporal projection area.The effect of lag screws line spacing and tibia-talo-calcaneal displacement after the insertion and the stress distribution of the subtalar the ankle joints surface and the differences in plantarflexion and dorsiflextion,varus and valgus,and rotational biomechanical properties.2.1 Experiment 1Comparative analysis of the influence of the tibio-talo-calcaneal displacement and the stress distribution of the subtalar and the ankle joints between the full thread headless compression screws and the lag screws2.1.1 Materials and methods2.1.1.1 Establishing a three-dimensional finite element model of the hind footUsing the CT scan data of the ankle of the healthy adult male as well as three-dimensional modeling software to establish a three-dimensional model,and the finite element meshing was performed at the same time.2.1.1.2 After the three-dimensional finite element model of the ankle-hindfoot(tibio-talo-calcaneal complex),the implant screw conditions were set: 2 screws inserted parallel to the posterolateral and anteromedial position of the distal tibia articular surface in the bottom of calcaneus temporal projection area,passing through the subtalar and the ankle joints surface in sequence;the screws passes through the bone surface area: the proximal calcaneus articular surface,the talar distal articular surface,the talar platpond articular surface,and the distal tibial articular surface;set the pre-tightening force of the full thread headless compression screw to simulate its continuous compression performance;Comparative analysis of the impact of the tibio-talo-calcaneal displacement and the subtalar and the ankle articular surface after the full thread headless compression screws(bottom diameter 7.5 mm,top diameter 6 mm,length 100 mm)and lag screws(7.5 mm diameter,length 100 mm)The difference in stress distribution on the ankle and the subtalar surface.2.1.2 ResultsUnder the condition of only loading the pre-tightening force,the two screws of the tibio-talo-calcaneal displacement were the same after implanting the full thread headless compression screws and the lag screws.The maximum stress of the full thread headless compression screws model is 28.066 MPa,the stress under the lag screws model is 19.308 MPa;the talus stress,the maximum stress under the full thread headless compression screws model is 45.945 MPa,and the stress under the lag screws model is 28.607 MPa;the maximum stress under the calcaneus stress and the full thread headless compression screws model is 25.905 MPa,and the stress under the lag screws model is 19.246 MPa.Compared with lag screws,the full thread headless compression screws model has larger calcaneus and talus displacement,higher maximum stress.2.2 Experiment 2Comparative analysis of biomechanical differences in plantarflexion and dorsiflextion,varus and valgus and rotation of full thread headless compression screws and lag screws2.2.1 Materials and methods2.2.1.1 Establishing a three-dimensional finite element model of the hindfoot(tibio-talo-calcaneal joints)2.2.1.2 Compare and analyze the biomechanical difference between full thread headless compression screws and lag screws on the plantarflexion/dorsiflextion,varus/valgus,and external rotation/internal rotation.2.2.1.2 Experimental resultsFull thread headless compression screws are superior to lag screws in terms of plantarflexion/dorsiflextion,varus/valgus,or biomechanical properties of external rotation/internal rotation.2.3 ConclusionIn this study,a normal tibia,talus,calcaneus model was established,and corresponding screws were added to form a finite element model of internal fixation,and a full thread headless compression screw was simulated by different bolt preloading methods,comparing the magnitude of the bone stress when only bolt preloading is accessible.Besides,it also simulates and analyzes the angle of rotation in the state of varus,valgus,dorsiflextion,plantarflexion,external rotation and internal rotation.The results show that the full thread headless compression screws has smaller rotation angles than lag screws,has better anti-rotation ability,and has higher surface pressure and can be better performed when adding pressure on each bone part.Part 2Clinical analysis of the effectiveness of full thread headless compression screws combined with minimal incisions in the treatment of tibio-talo-calcaneal arthrodesisFurther clinical efficacy analysis was performed to verify the safety,effectiveness and reliability of the full thread headless compression screws for the treatment of end-stage ankle and subtalar joints diseases.3.1 Materials and methods3.1.1 Case CollectionCollected from January 01,2012 to December 31,2016,36 patients(36 feet)at end-stage inferior joint with with strict conservative treatment reveived tibio-talo-calcaneal arthrodesis.There were 14 males and 22 females;the age ranged from 18 to 76 years,with an average of 53.8 years old.There were 19 left foot and 17 right foot.21 cases of talus collapse and necrosis,7 cases of traumatic arthritis,3 cases of rheumatoid arthritis,2 cases of tuberculosis infection(inactive),1 case of talus absence,1 case of Charcot's disease,1 case of PVNS of ankle and subtalar joints.3.1.2 surgical methodsCombined with two full thread headless compression screws under the minimal incisions of the anterior and lateral oblique incisions,the tibio-talo-calcaneal arthrodesis was performed.3.1.3 efficacy evaluation indexThe operation duration of the group was recorded.Follow up patients 1 day,6 weeks,3 months,6 months,12 months postoperatively and value the general condition of the patient as well as the X-ray of the ankle,the lateral and A-P views,and the CT scanning.The general assessment includes the patient's degree of pain and complications.AOFAS score and VAS score for preoperative and postoperative.3.2 Experimental resultsThe operation duration of this group was 33~82 min,with an average of 49.8 min.The operation was successfully completed.Incision skin infection occurred in 1 case(2.9%)3 weeks after operation,and healed after debridement and dressing change;the rest patients underwent first-stage incision had residual complications.35 patients were followed up for 12 to 29 months,with an average of 18.5 months.Imaging examination showed that the fusion joints of this group reached bone healing,the fusion rate was 100%;the fusion time was 8-15 weeks,with an average of 10.9 weeks.One year after operation,the AOFAS score was(84.714±0.596),which reflected statistical significance(t=12.596,P=0.000)comparing with the situation before operation.The VAS score was(0.342±0.081),which also showed statistically significant(t=30.393,P=0.000)comparing with the situation before operation.3.3 ConclusionUsing full thread headless compression screws to tibio-talo-calcaneal arthrodsis with combined minimall incisions is an effective surgical procedure which can lower complications and gain higher fusion rate. |
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