The Anatomical Study Of Posteroanterior Screw Fixation In Talar Neck Fracture And Its Clinical Significance

Background The incidence of talar neck fracture was low,1 precent of whole body fracture, taking up 3 to 6 percent of foot injury. Due the particular anatomical structure of talus and blood support to talar neck, the incidence of complications aftert talar neck fracture was higer than the other fractures. The blood support to talar neck was easily destroyed by fracture and dislocation, the treatment of talar neck fracture was still chanllengable in the last decades. The mechanism of talar neck fracture was that when the ankle joint was positioned in dorsifelxion.axial load was put onto the talar neck, causing fracture. The effective fixation of talar neck fracture could decrease the incidence of bone ischemic necrosis and be helpful to early postoperative active exercise, improve the function of ankle joint and subtalar joint. The fixation techniques include the kirshche wires. Steinmann pin. different types of plate-and-screw systems, anterior-to-posterior directed screw (exposed through anterior joint facet of talar neck or directly talar neck), posterior-to-anterior directed screw inserted posteriorly. Although the theoretical knowledgement of fracture and fixation technique had advanced deeply in last decades, the complications still happened in talar neck fracture patients in long term, such as ischemic necrosis, traumatic arthritis, ununion. malunion and so on. In recent years, screws became popular in the treatment of talar neck fracture, including anterior-to-posterior directed screw and posterior-to-anterior directed screw. The surgical approach of anterior-to-posterior screw was located in front side of joint which was easy for the exposure of relevant anatomical zone, with little harmness to important structures, such as neurovascular bundles. However, the disadvantage existed in anterior-to-posterior screw, for example, worse biomechanical feature, incomplete compression. The posterior-to-anterior screw was easy to insert, the direction of screw was perpendicular to fracture line with complete compresson at fracture site and better biomechanical feature.The posterior-to-anterior screw could also harm the cartilage bone of talus which was covered by75 percent of cartilage, as well as the posterior neurovascular bundles, tendons, joint facet of talus. When the fracture site was located in talar neck, then anterior approach could expsoe the fracture site easily and be helpful to the insertion of anterior-to-posterior screw, not to posterior-to-anterior screw. Therefore, the assessment of insertion of posterior-to-anterior screw was necessary in posterolateral window. The purpose of this research was to explore the suitable anatomical landmarks for the screw fixation in adequate approach and insertion. Tha cadaver ankle joints were include into this research to explore the anatomical feature of posterolateral talus to make sure the suitable insertion for posterior-to-anterior screw with little harm to neighbor important tissues.Part ⅠAnatomical study of posterolateral safety zone screw insertion in talar neck fracture and its clinical significanceObjective To study the anatomical feature of posterolateral safety zone in talar neck fracture, the anatomical data about the insertion of screw and neighbor important tissue was measured to assess the clinical significance of posterolater safety zone in operation.Method From Janurary 2012 to December 2013, fifteen adult cadaver ankle joints from Binzhou Medical University Department of Anatomy were studied. The inclusion criteria was that the height was 160 to 175 centimeter and exclusion criteria was that deformity, traumatic deformity and other diseases affecting the morphology of bone. A vernier caliper with accuracy of 0.01cm was used to measure the height and width of posterolateral window. The measurement data included the vertical distance between the center of the window (the insertion of screw) and the tip of lateral malleolus (LMT), the horizontal distance between the center of the window and the lateral side of archilles tendon (LAT) and the horizontal distance between the lateral side of archilles tendon (LAT) and the sural nerve (SN). The anatomical relationship about the insertion with neighbor important tissues was also assessed, such as flexor halluces longus and posterior talofibular ligament.Result The width and height of posterolateral window were 1.89±0.04 cm and 0.91 ±0.01 cm. respectively. LMT was 0.40 ±0.01 cm. LAT was 0.19± 0.02 cm.and SN was 0.62 ± 0.04 cm.Conclusion The present data showd that posterior screw insertion may be more safe if screw was located in the posterolateral window center, and the operation through the posterolateral window will has no any effect on flexor halluces longus and posterior talofibular ligament tissues when the ankle joint was positioned in a neutral position. Meanwhile, the screw head should be countersunk to avoid injuring these tissues. Our results will help to greatly decrease the risk of clinical operation.Part IIThe radiological research of posteroanterior screw fixation for treatment of talar neck fracture in Jiaodong districtObjective To measure the angle of posteroanterior screw insertion in the treatment of talar neck fracture, including inner deflection angle and plantar deflection angleMaterials and methods Thirty CT reconstruction images of normal ankle joint were included into this research, (male 18, female 12, maximal age 56 year-old, minimal age 19 year-old, mean 36 year-old). CT imaging were performed using 128-slice spiral CT (Ingenuity, Philips, Netherlands). The patients were in supine position with a axial scan from thefoot.The imaging parameters were as follows:1.0 mm section thickness,0.8 mm interslice thickness,120 kV voltage,50-150 mA current, and 512×512 matrix. All data were measured at workstation with IntelliSpacem software. The line of posterior tibiotalar joint facet (CD), the cross line between the talar neck and talar body (AB), the line of talar head (EF) were then calculated, as well as the inner deflection angle.Results The maximal inner deflection angle was 27 degrees, the minimal inner deflection angle was 15 degrees, the mean value was 17 degrees. The maximal plantar deflection angle was 6 degrees, the minimal plantar deflection angle was 1 degree, the mean value was 5.6 degrees.Conclusions The range of posterior-to-anterior screw insertion was small. That made the insertion of posterior-to-anterior screw difficult to perform for orthopaedic surgeons who needed to own solid anatomy knowledge.