Anatomic security of applying different numbers of screws at the sacrum sides in the anterior double plate fixation of the sacroiliac joint

Objective:To compare the anatomic security of applying different numbers of screws at the sacrum sides in the anterior double plates fixation of the sacroiliac joint and to clarify which is safer when the stability of the fixation is considered.Methods:(1) Totally 15 normal cadavers pelvis were scanned by CT.Thin-section CT scan data were saved and analyzed by the software Materialise’s interactive medical image control system(MIMICS 10.0).The virtual operations of the anterior double plates approach for fixation of the sacroiliac joint were performed in the same software.(2)The left sides of the sacroiliac joint were named as group A,in which two screws were placed into the sacrum sides.The right sides of the sacroiliac joint were named as group B,in which one screw was placed into the sacrum sides.The distances from the medial edge of the plates to the lateral sides of the anterior branches of lumbar nerves 4,5 were measured.The relationship of the screws and the sacroiliac joint was checked by radiograph.Results:(1)In the virtual operations,the sacrum sides can accommodate two screws safely.(2)In group A,the distances from the medial edge of the upper and lower plates to the lateral sides of the anterior branches of lumbar nerve 5 were(3.0±1.4)mm and(1.5±1.0)mm respectively.The upper and lower plates can be placed below the anterior branches of lumbar nerve 4 safely.In group B,the distances from the medial edge of the upper plates to the lateral sides of the anterior branches of lumbar nerves 4,5 were(5.0±1.1) mm and(10.3±1.3)mm respectively and those from the medial edge of the lower plates were(2.7±0.5)mm and(5.1±0.9)mm respectively.(3)In X-ray examination,no screw of the left upper plates was found in the sacroiliac joint in group A and 4 screws of the left lower plates were observed.On the other hand,no screw of the right plates(lower and upper)in the group B was found in the sacroiliac joint.Conclusions:Two screws implanted into the sacrum side of the upper plate and one screw in the lower plate is applicable in the operation considering the stability of the sacroiliac joint fixation.