Comparative Study On Surgical Simulation Between Scarf Osteotomy And Evans+MDCO Osteotomy For Flat Foot By Mimics Software

Objective:To simulate operation in MIMICS software and 3-matic software by using computer aided technology(CAD),and to analyze the optimum osteotomy angle of scarf osteotomy with the reference of traditional Evans combined with MDCO osteotomy.In the hope of providing reference for the surgical design of flat feet patients in clinic.Method:Step 1.To establish three-dimensional models of flat feet on weight-bearing state by using Mimics software and measure flat feet indexes in 3-matice software.A custom foot-loading device was designed and constructed to simulate normal full weight-bearing for 25 subjects to take weight-bearing CT scanning.The thin layer CT data was stored in the format of DICOM,to reconstruct the 3D models of the distal tibia,fibula and the foot and ankle.These models were then imported into 3-matic 12.0 software to obtain the sketches,which were similar to the radiographs of the foot on weight-bearing state.The various angles and length indexes of the flat feet were recorded as 3D group and measuring on radiographs recorded as DR group.Step 2.To simulated Scarf osteotomy and Evans+MDCO osteotomy and measure flat feet related indexes before and after operation.Each of the 10 models was taken Evans combined with MDCO and then measured the indexes of flat feet.Then the scarf osteotomy of the same model was carried out at different angles,30°,45°,60°,75°,105“and 120°.The indexes of flat feet of each group were measured respectively.The orthopaedic effects were analyzed compared with the preoperative measurement indexes.Results:1.DR VS 3D:Statistical analysis suggests that the calcaneal pitch angle,talonavicular joint coverage,talo-first metatarsal angle on the AP are greater than 0.05 between the DR and 3D group.The talo-first metatarsal angle on lateral,talus pitch angle,talus height,medial and lateral column length,medial and lateral arch angle,and extroverted angle were all less than 0.05 in the two groups.2.Effect of osteotomy on flat foot index:For the first metatarsal angle and talus pitch angle,there were no significant statistical difference for the two types osteotomy(p>0.05).For the calcaneal pitch angle,medial and lateral column length,medial and lateral arch angle the lateral and medial length and extroverted angle medial arch angle,there were significant statistical difference for the two types osteotomy(p<0.05).And there were statistically differences of the talo-first metatarsal angle on the AP for Evans combined with MDCO operation(p<0.05),but with no statistically differences for scarf osteotomy(p>0.05).3,Evans combined with MDCO VS scarf osteotomy:There were no statistically differences in calcaneal pitch angle,medial and lateral arch angle(p>0.05).For the lateral and medial length difference,calcaneal extroversion and the contact area,there were statistically differences between the two osteotomy methods(p<0.05),and the Scarf group was bigger than the Evans combined with MDCO group.4.Scarf groups with different angles:There were no statistical differences in calcaneal pitch angle,medial and lateral column arch angle,extroverted angle and emigration distance(p>0.05).And for the lateral and medial length difference,the angle of scarf osteotomy in 750 was smaller than other groups(p<0.05).For the contact area of the osteotomy,there were significant statistical differences between the scarf groups(p<0.05).Conclusions:1.It is feasible to establish a three-dimensional skeletal model of the weight bearing state of the foot and ankle with the help of a custom foot-loading device.And for the measurement of flat feet indexes,3-matic software measurement is not consistent with the measurement of X-ray plane.Therefore,when using digital technology for flat feet simulation surgery,it is not possible to directly refer to the normal range of flat sheet measurements of X-ray plane.2.For flat feet orthopaedic surgery,simple calcaneal osteotomy has no corrective effect on the talus pitch angle,the talar-first metatarsal angle on lateral.And the Evans operation has greater correction for forefoot abduction,and the Scarf osteotomy has no obvious corrective effect for the index.The Scarf osteotomy has greater contact area than the combined operation,and with the increase of scarf angle,the contact area decreased gradually.