Applied Anatomical Measurement For Percutaneous Lag Screw Fixation For The Sacroiliac Joint: A Study By Digital Model

ObjectiveIt increases the high energy and the high speed damage in the modern society day by day, the incidence rate of the pelvis acetabulum fracture increases year by year. The establishment of pelvic stability largely depends on the stability of the back pelvic ring, Sacroiliac joint complex influence the cephalic sacroiliac joints and the tail hip joint, accounting for about 60% of pelvic function. The injury of sacroiliac joint complex directly result in the instability of the back pelvic ring, therefore treatment of the pelvic fracture is particularly important for the sacroiliac joint complex. Injury of the sacroiliac joint experienced open reduction and internal fixation with the anterior plate and posterior sacral screw bolt, closed reduction and percutaneous fixation with lag screws by the X-ray fluoroscopy and the CT-guided. Clinical practice and bio-mechanics research also shows that is a more superior fixation way with the sacroiliac joint screws from the lateral iliac wing crossing the sacroiliac joint into the the upper part of sacral vertebrae, but no accuration of the needle direction may damage blood vessels, lumbar sacral trunk, sacral and other important structure, causing serious complications. Restrictions on dissemination and application of this technology is to determine the root causes of the needle point of the body surface positioning technology is not resolved, so how to determine the entry point of the body surface and into the needle angle is the key to this technology The appearance of digital orthopaedic has created a new era for the basic application research of orthopaedic and traumatology. Compared with the traditional cadaveric reseach,it has the lots of advantages,like high accuracy,good consistency, repeatability strong and saving medical resources. In this study, it measure the anatomical parameters for percutaneous sacroiliac screw fixation by the Mimics software, which provide a theoretical basis for the design of the surgical navigation templatean for the sacroiliac joint screw fixation.Complex acetabular fractures belong to the high-energy injury, most of them associated with pelvic fracture and femoral head injury, etc., how to properly deal with pelvic fracture and femoral head injury, prevention of post-traumatic arthritis and necrosis of the femoral head,which is a major challenge for the orthopedic trauma. With the minimally invasive treatment of acetabular fractures technology mature gradually, and how to complete complex acetabular fracture reduction and fixation in the same incision,which is also a problem worthy of in-depth study. Acetabular fracture is a complex intra-articular fracture, open reduction and internal fixation is one of the means of its effective treatment, but whose treatment are affected by many factors. How to improve the complexity of the surgical treatment of acetabular fractures,which investigate some important factor results of surgical treatment of acetabular fractures.1. Using the bony markers on the pelvis, to simulate percutaneous lag screw fixation of the sacroiliac joint on the pelvis' three dimensional reconstruction, and to provide a new method for studying applied basic evidence for percutaneous lag screw fixation of the sacroiliac joint complex injury.2. To provide the applied anatomical basis for the feasibility of the targeting device for percutaneous lag screw fixation of the sacroiliac joint complex injury.3. To provide empirical method and evidence for the personal preoperative prepare of percutanous screws fixation of the sacroiliac joint complex injury.Methods1. Collection of images and reconstruct the 3-dimensional model of pelvis Obtained 50 adult patien randomly, who took complete CT scan of pelvis in our hospital between April 2008 and December 2009 without any bony and anatomy abnormality.28 males,22 females, age ranged 20～80 years,100 cadaveric hemipelves were collected. Scan condition:tube tension 120kV, tube current 200～300 mA, slice increment 1.25 mm, matrix 512×512. All the images were saved as DICOM format and imported to the personal computer.All the sequent tomoscan images of pelvis were imported into the Materialise's Interactive Medical Image Control System (Mimics) in personal computer as DICOM format. The 3-dimensonal models were reconstructed by the same calculated parameter.2. Simulating lag screws into the sacroiliac jointPosterior pelvic three-dimensional model obtained, simulated the position lag screw fixation for the sacroiliac joint intraoperative (prone position), and Toggle Transparency for pelvic model. It inserted lag screw with 7mm diameter from the outer plate of iliac wing,crossing the sacroiliac joint, into the middle of S1 cortex. The first lag screw for sacroiliac joint (M2) was tangent on the above of the sacral wing,and the second one (M2) was tangent to the upper edge of the first sacral hole,which ensure that the sacroiliac joint screws didn't penetrate into the cortical.3. Measuring the anatomy parameter of lag screws for sacroiliac jointIt measured the length of the lag screw using (Tools) in the two-dimensional length measurement tools in horizontal two-dimensional image; directly from the software to read the definition of lag screw direction of three-dimensional coordinates (X, Y, Z), using the Pythagorean theorem and the Inverse trigonometric functions calculate them with horizontal, coronal and sagittal angle (equation 1-3), which attained direction of the needle point about the lag screw. Point (A) was named by the needle of the first sacroiliac joint screw(M2),measuring its S1 pedicle width in the plane,denoted by D1, and the distance from the point (A) to the highlight (C) of posterior suoerior iliac spine,denoted by AC; Point (B) was named by the needle of the second one (M2),measuring its S1 pedicle width in the plane,denoted by D2, and the distance from the point (B) to the highlight (C) of posterior suoerior iliac spine,denoted by BC. S1 pedicle width, that is the largest diameter (D1+ D2)/2, which was accommodated sacroiliac joint lag screw. Calculating the layers of the CT scan from M2 to M2, denoted by n,1.25 n is the pedicle height, which S1 pedicle to be able to accommodate the effective range of lag screw for the sacroiliac joint.The angle in the horizontal plane for screws= arccosThe angle in the coronal plane for screws=arccos-The angle in the sagittal plane for screws=arccos4. Statistics and analysisThe experimental data was analyzed by the software of SPSS 13.0,including the width (D1+D2)/2 and height S1 pedicle(1.25 n), the optimal entry point for iliosacral screw on the outer table of the posterolateral ilium, the direction of screw, and the distance (M2/M2) from entry point to contrary anterior cortex of S1 vertebral body and posterior superior iliac spine(AC/BC).Independent-samples t test and pair-sample t test were used, and an associated probability of 5%(P≦0.05) was considered significant.ResultsThe distance from entry points of two iliosacral screws to contrary anterior cortex of S1 vertebral body were 76.08±4.32mm and 77.62±3.98mm respectively.The width and height of the pedicle of S1 were 20.43±1.63mm and 20. 26±0.99 mm, respectively. The entry points of the two iliosacral screws were on the above of the line between anterior superior iliac spine and posterior superior iliac spine, the distance to posterior superior iliac spine were 49.87±6.80 mm and 51.11±7.15 mm, respectively. Iliosacral screws get into the S1 pedicle in parallel, The direction of screw was perpendicular to the outer table of the posterolateral ilium then 18.35°±5.20°in coronal plane and 69.80°±11.44°in sagittal plane. Differences in the length, the width and height S1 pedicle,the distance to posterior superior iliac spine,angle to coronal plane of the iliosacral screws between the male and female were of statistical significance(P<0.05)Conclusions1. The level of the S1 pedicle in normal adults can be placed two lag screws with the diameter of 6.5 mm. Applied anatomy of the parameters of percutaneous lag screw fixation are measured that applies the theoretical basis of the design of the surgical navigation template for the sacroiliac joint.2. Applied anatomy of the parameters of percutaneous lag screw fixation are measured that provides a path on purpose of the design of the surgical navigation template for the sacroiliac joint for the injury of sacroiliac joint.3. The digital model of pelvis can not only provide a new method for the study of application basis research of percutaneous screws fixation of sacroiliac joint complex injury, but also offer a simple, intuitive personalized preoperative ideal preoperative prepare for the the use of the technique.