Development And Preliminary Validation Of Navigational Apparatus For Percutaneous Retrograde Lag Screw Fixation Of The Fractures In The Posterior Column Of Acetabulum

BackgroundAcetabular fractures are usually caused by violence, and they simultaneously bring about dysfunction of the hips. Thence the key points of treatment for acetabular fractures are anatomic reduction and rigid internal fixation. Opening reduction and plate fixation is satisfying for the trentment of the fractures in the anterior column and posterior column of acetabulum, while because of the acetabulum anatomy location is deeper, adjacent to the anatomy of the relationship is complex, the traditional operation method of incision is length and exposed widely, amount of bleeding, postoperative heterotopic ossification, iatrogenic sciatic nerve injury, more complications such as avascular necrosis, serious influence on joint function recovery.In1988, Reinert reported it has the advantages of less injury and promote fracture healing used cancellous bone screw to fix the fracture of acetabulum column, from then on, fracture of acetabulum fixed with Screws get more and more widely. Theremore,some scholars confirmed that the log screw had more strength than plate fixed in the effect of biomechanics. Nearly10years, percutaneous log screw fixation to fractures of pelvic and acetabular with minimally invasive treatment is important method, and is also the new direction of fracture treatment. Such as percutaneous sacroiliac joint fracture or dislocation, the retrograde or antegrade log screws fixation in anterior and posterior column, percutaneous log screws fix iliac bone crescent fractures. This surgery is minimally invasive, less bleeding, low cost, but risk increase obviously, and some literures reported death cases in damage of pelvic vascular by screw, meanwhile, some complications such as pelvic cavity viscera and nerve injury, damaged, fixed in wrong position, not secured in fixation, and screw breakage. And the application of this technology is also limited by many technical problems, such as determining the frist point, screw diameter, direction, etc. The stduy of cadaver anatomy both at home and abroad there are many deficiencies in materials, techniques, methods, etc, makes it difficult to accurately applied to clinical study.Computer assisted orthopaedic surgery, CAOS is considered minimally invasive and intelligent in the future implementation of orthopaedic surgery, The image navigation surgery in fractures of acetabulum and pelvic is a hotspot in current CAOS clinical application research. after closed or limited open reduction on fractures of pelvis and acetabulum and used navigation operation on fractures no shift or less shift with percutaneous or small incision, and log screw internal fixation, can reduce the incision exposed, vessels or nerve injury, postoperative infection, the risk of complications such as heterotopic ossification.so the of technology has been applied by a lot of orthopaedic surgeons. But the high costs of CAOS equipment was the important factors in most of domestic hospitals cannot be popularity.The appearance of digital orthopaedic has created a new era for the basic application research of orthopaedic and traumatology. Because of medical imaging equipment scanning accuracy and the calculation methods of3D image software are improved, make the3D reconstruction model in complex pelvic and acetabulum structure to human body becomes a reality. Chen Kaining etc., simulated model on anterior and posterior column of acetabulum for percutaneous log screws, meatureed the screw diameter using three dimensional reconstruction into the frist point and the maximum length, and refers to the largest screw of anterior and posterior column of acetabulum can’t just depend on bone cutted or minimum diameter of the smallest bone cutted。Zhang Dabao etc.did lots of3D reconstruction model and pelvis specimens to observate, and Found the most prominent point of anterior superior iliac spine and posterior superior iliac spine to someone point on the ischial tuberosity that had same distance, puted forward midperpendicular of along most prominent point of the anterior superior iliac spine and posterior superior iliac spine to simulate posterior column acetabulum fracturefor percutaneous log screw. In my study,according to Zhang Dabao senior’s advance research, and further research must to improve the deficiency.in66cases of half pelvic anatomy parameter measurement and virtual plant nail experiment are carried out, on the basis I design a navigational apparatus for percutaneous retrograde lag screw fixation of the fractures in the posterior column of acetabulum, and through the further confirmed ecurity and accuracy on pelvis specimens.objective1. Using digital model, measured posterior column of acetabulum log screws anatomy parameters, bring some basic anatomical data to clinically navigational apparatus for percutaneous retrograde lag screw fixation on posterior column of acetabulum log screws2. Designed and developed the navigational apparatus for percutaneous retrograde lag screw fixation, Through Mimics software, pelvis specimens and cadaver spevimens to check its accuracy and feasibility.3. Trying to resolve the difficulty of placement of retrograde lag screw fixation for posterior column fractures of acetabulum,which would provide a new method for the treatment of acetabular fractures.Methods1. Collecting data and rebuilding the three-dimensional model of pelvicThe data of whole pelvics of adults scanned by CT (GE MediCal systems/lightsDeed16) in our hospital between2009.11to2011.11were collected, including15male and18female, whose average old is (45.6±18.5), from15to77. None of the models had bone lesions or anatomic variation. The scanning condition: the voltage is120kv, the thickness is1.25mm, the martrix is512*512. We imported the data into Momics10.01(Materialise, Belgium) in the format of Dicom, and then extracted the information of the pelvic edge by the way of grayscale splitting, and extracted these information again by the way of region segmentation next, and rebuilding them as the way of three-dimensional reconstruction last2. Simulating lag screws into the posterior column and measuring the parameters by MimicsAt the three-dimensional model of both pelvic rebuilded by Mimics10.01, import a virtual cylinder by the diameter6.5mm which axis obey the center of ischial tuberosity(O) and the middle point(I) of the segment from the salient points of anterior superior iliac spine(A) to the salient points of posterior superior iliac spine(B). The point O is just the needle point of lag screw, and the point I is the destination of our navigational apparatus. Produce a flat(s) by point A, B, O, and measure the straight-line distance from point A to point B. Our virtual cylinder pass through the point(i) down in iliac fossa, so we could measure the length of segment Oi, and this length is just the length of our lag screw(If the cylinder was out of the outside board of iliac, and above the level of greater sciatic notch, its lower part would be the point i. Others seemed to be failed). We increased the radius of the virtual cylinder by0.1mm every time, and recorded the right diameter of the cylinder which is the largest diameter(d) of the lag screw.3. Measuring the anatomy parameter of lag screws for posterior columnThe result showed there had been no failed case in the66hemiplves.Analyzed the difference of every anatomic parameter between males and females by T test for independent samples(statistically significant when P<0.05). The resulte shows that it is feasible to produce the navigational apparatus for implanting lag screw in the posterior column of acetabular through the line OI according to the anatomic parameters we measured design the navigational apparatus and make a product.4. Simulation of implanting lag screw Chose18adults’ iliac models at one side(9male,9fmale). The assistant must help to make the navigational apparatus keeping stable. Made the pinhead of kirschner fixed at the center point of ischial tuberosity auxiliarily by a sleeve. Inserted the kirschner by electric drill until it ing the cortical of iliac, then observed the place the kirschner pierced first. All the kirschners’diameter in our experiment is2.5mm, and the screws’ diameter is6.5mm identically. Recorded the success rate of implanting lag screw in every model and the length of all lag screws.The results to assessment standardsThree position the kirschner pierced first would be possible:1. In the iliac fossa,2. Pierced the lateral border of iliac, and was above the level of sciatic notch;3. Below the level of sciatic notch, such as implanting into the acetabular, pierced the square area and so on. It seemed to be an excellent location by the navigational apparatus when the position was in the iliac fossa, a good location when pierced the lateral border of iliac, and was above the level of sciatic notch, a failed location when below the level of sciatic notch.5. Examination for the safety of the point in iliac our navigational apparatus for antegrade lag screw fixed in with simulat operation by MimicsAnterior superior iliac spine and posterior superior iliac spine are bone uplift curved surfaces, their area is very small, so it’s hard to fix the uplift point in the curved surface by kirschner actually, and the deviation is inevitable. We verified the effect of the point in the iliac our navigational apparatus fixed at for inserting lag screw about the deviation in actual operation by Mimics.6. Examination for the safety of the point in iliac our navigational apparatus for antegrade lag screw fixed in pelvicmodelsThe range of ischial tuberosity is larger than the range of anterior superior iliac spine and posterior superior iliac spine, and the point the kirschner inserted in was more difficult to fix accurately when we fixed percutaneously. So we did another test for the4points around the center of ischial tuberosity.18cases with existing half pelvic experiment, testing the implant at four point.7. Examination for the safety of the point in iliac our navigational apparatus for antegrade lag screw fixed in cadavers.We have get good results in Mimics and pelvic models, while there would be more difficult when we use the navigational apparatus in fact because of soft tissue. Therefore, we did further test in two adult cadavers. Chose two adult frozen fresh cadavers consist of one male and one female from our anatomy Laboratory, and examed the safety of our navigational apparatus for antegrade lag screw after the cadavers thawed completely. Result1.The parameters of retrograde log screw implant on posterior ColumnThe average distance of AB is (156.26±7.28) mm in males, while (151.38±8.11) mm in females. The average distance of Moi is (139.53±7.56) mm, the average distance of Foi is (125.15±11.17) mm, the average distance of Md is (12.19±1.97) mm, the average distance of Fd is(10.19±2.14)mm, Analyzed the difference of every anatomic parameter between males and females by T test for independent samples (statistically significant when P<0.05)t-value,2.574、5.992,3.923.p-value,0.003、0.000、0.000.2. testing results of18cases to pelvic nailing simulation there were15excellent location(83.33%),3good location(16.7%), none failed. The length of the lag screw implanted in males is (131.53±5.36) mm, while (118.15±9.03) mm in females, and the difference between males and females has significant(P<0.05)3. Results of the point in iliac our navigational apparatus for antegrade lag screw fixed in with simulat operation by Mimicsin the15male hemipelves, there are15excellent cases(100%) in the medial area,3excellent cases(20%) and12good cases(80%)in the lateral area,15excellent cases(100%) in the front area,15excellent cases(100%) in the rear area. In the18female hemipelves, there are18excellent cases(100%) in the medial area,1excellent cases(5.6%),8good cases(44.4%) and9failed cases(50%)in the lateral area,18excellent cases(100%) in the front area,5excellent cases(27.8%),4good cases(22.2%) and9failed cases(50%) in the rear area.4. Results of the point in ischial tuberosity our navigational apparatus for antegrade lag screw fixed in pelvicmodelsThere were15excellent cases and3good cases at the medial point, and the same result at the lateral point and the front point, which were consistent to the center point. While there were11excellent cases,3good cases and4failed cases at the rear point.5. Results of cadavers specimen on planting nailEach pelvic was just examined by fluoroscope twice, while the position of the kirschners were all ideal.Conclusions1. According to the posterior column anatomy parameters of acetabulum log screws, the midpoint that the protruding point of anterior superior iliac spine and posterior superior iliac spine, attached to the center point of ischial tuberosity for implanting screw fixation to column fractures after is feasible.2. In the examination for the safety of the point in iliac our navigational apparatus for antegrade lag screw fixed in with simulat operation by Mimics, we had known there would be a ideal result when the fixed point in anterior superior iliac spine and posterior superior iliac spine was trend to medial and the center point was closed to anterior superior iliac spine during the using of our navigational apparatus. And in the Examination for the safety of the point in ischial tuberosity our navigational apparatus for antegrade lag screw fixed in pelvicmodels,we would get a good result when the fixed point was not rear in the ischial tuberosity, and patient with larger pelvic would get a better result. This test also verified the practicality and safety of our navigational apparatus.3. The success rate of navigational apparatus is high, and has the characteristics of individual application, under nice accuracy of in auxiliary implanting for guarantee, we can implant into longer log screw to give fractures stronger stability.