Morphological Research In Three-dimensional Computer-assisted Modeling Of Talus And Its Clinical Application

Objective:To provide more accurate reference data for the assessment and treatment of talar injuries by constructing 3-D computer-assisted models of the talus and comparing them with reference data obtained from measurements on cadaver specimens.On the basis of reference data,to investigate the establishment of secure tunnel in fixation for the talar neck fracture when screws were fixed from the medial wall of talus.Methods:All volunteers were screened based on the following inclusion criteria:the age was ranged from 20 to 60 years old,the height was ranged from 165 to 185cm in male and 155 to 175 cm in female,and the body mass index(BMI)was less than 25kg/m~2.Volunteers with any of the following were excluded:any congenital malformation of the ankle or foot,a history of fracture or trauma of any bone in the ankle or foot,a history of standing for long periods or performing heavy labor,X-ray confirmed degenerative pathology of a joint or bone of the ankle or foot.There were33 males with the mean age of 43.7(21-59)years and the mean height of176.0(168-184)cm in this study,22 females with the mean age of 43.2(22-60)years and the mean height of 1 65.4(158-172)cm.Bilateral CT scanning was performed with the subjects supine and their ankles in the neutral position,the reconstruction layer thickness of 0.75mm.After reconstruction,the images were recorded in Digital Imaging and Communications in Medicine(DICOM)format.The three dimensional talus model was constructed based on the CT data using the SuperImage Orthopedics(version 1.1).The volume,length,height,width of talus;the width,perimeter and area of talar trochlea;the length,width,perimeter,area and the angle of rotation of the talar head;the height,perimeter,circumference,cross-sectional area,varus angle and deflective angle of talar neck;the perimeter and area of medial and lateral articular surface,the perimeter and area of the articular surface of talocalcaneum.the angle and height of tarsal canal were measured.The volume,length,width of calcaneus,the length,height,width of the sustentaculum,the angles of Gissane,Bühler and varus were measured.Structural variables were compared using the Fisher least significant difference test to determine the significance of bilateral or sex-specific differences in the study cohort.On the basis of the parameters and three dimensional talus model,the talar neck fracture was stabilized by canulated screw through anteromedial incision was imitated.The points of screw insertion were set as in the middie 1/3 and in the inferior 1/3 of medial wall of talus.The models of screws penetrating into tarsal canals were built and the maximal length and angle were measured.The SPSS,version 13.0,was used to analyze the data.Results:Measurement data were normally distributed.No significant difference between the left and right talus in either men or women was identified for any measurement(P>0.05).The bilateral mean volume of the talus in men(37.87±6.69mm)was significantly larger than that in women(26.95±5.73 mm;P<0.05).Although the dimensions of most of the structural features and articular surfaces of the talus were significantly larger in men than in women(P<0.05),no significant differences in the angles of the talar neck and head were observed between men and women in our cohort(P>0.05).The models of screws penetrating into tarsal canals were obtained.The angle and length in different insertion points and different directions of screw fixation were obtained as well.When the screws were inserted from the middle 1/3 of the medial wall of talar head,the angle of screw fixation was bigger than that from the inferior 1/3.The safe range of the length and angel of screw fixation was calculated finally.Conclusion:Our method of 3-D model construction provided precise measurements of the structural features of the talus.The talar dimensions in our Chinese study cohort differ from those previously reported for people of different ethnic groups.Our models should provide accurate reference data for constructing models based on CT images for the assessment and treatment of talar injuries in Chinese patients.Damage of the blood of talus during internal fixation should be avoided.The middle 1/3 of the medial distal wall of talus is the most favourable alternative to the fixation.The digital technology provide the scientificity and feasibility for internal fixation of talar neck fracture.