| Objective: To explore the safe zone of the sacroiliac joint when using the anterior plate and screw fixation by the study of applied anatomic research and imagine, and to testify its anatomical security and feasibility for clinical treatment.Methods: Ten adult cadaver pelvis were used in this research, several aspects were measured as the following: First, the horizontal distances and vertical distance from the anterior roots of L4, L5 nerve to sacroiliac joint and sacral wing were measured respectively. Second, the distance of L4, L5 nerve roots from the intervertebral foramen to rim of pelvic and the diameter of the L4, L5 nerve root in the midpoint were measured respectively. Third, the distance from the sacroiliac joint to the ipsilateral aspect of sacral canal was measured in the two-dimension coronal reconstruction of the pelvis. Fourth, the angle between the line of sacroiliac joint and sagittal planes was measured in the two-dimension coronal reconstruction of the pelvis. Fifth, four patients with Title C pelvic fracture were selected and applied the sacroiliac joint anterior plate and screw fixation treatment. Meanwhile, different fixation methods for anterior injuries of pelvic fractures were based on patient's condition. The pain of sacroiliac joint, the symptom of the L4, L5 nerve root injuries, and the change in the length of both lower extremities were observed in the follow-up visit.Results: The horizontal distance between the sacroiliac joint and L4, L5 nerve root from top to the bottom was in a decreasing trend. The widest distance from sacroiliac joint to L4 nerve root was(2.1±0.2) cm, and to L5 nerve root was(2.6±0.2) cm; the nearest distance from sacroiliac joint to L4 nerve root was(1.2±0.2) cm, and to L5 nerve root was(1.5±0.2) cm; The vertical distance between sacroiliac joint and L4 nerve root was decreasing from top to the bottom, the highest point was about 10 mm, and the lowest point was closely attached to the periosteum. All anterior branch of L5 nerve root was closely attached to the periosteum. The length of the L4 nerve root between the intervertebral foramen to rim was(7.4±0.8) cm. The diameter of L4 nerve root at midpoint was(2.7±0.8) mm. The length of L5 nerve root was(3.9±0.5) cm. The diameter of L5 nerve root at midpoint was(7.3±1.4) mm. The angle between the line of sacroiliac joint and sagittal planes was approximately 30°, the distance from the sacroiliac joint to the ipsilateral aspect of sacral canal was decreasing from top to the bottom, and the widest point was about 3.3 cm, while the narrowest point was 2.3 cm. The distance between sacroiliac joint and the lateral edge of spinal canal was 2 cm which was relatively stable. Both patients achieved Level A healing after the treatment. L4, L5 nerve root injury, blood vessel damages, even death cases were not observed. The plate screws of the sacroiliac joint were showed in good position from X-ray imagines. No screws entered in S1 spinal canal or sacroiliac joint. During the follow-ups, patients with displacement or fixation breakdown were not identified. Pain in sacroiliac joint, uneven lower extremities, gait of limp was not identified.Conclusion: There was a safe zone when fixing the sacroiliac joint fracture by the anterior plate and screw fixation: the plate should be plated in the middle or top area of the patient's sacroiliac joint. The exposed width should to be no more than 2.5 cm to medial side of sacroiliac joint when using upper plate, and no more than 1.5cm to medial side of sacroiliac joint when using lower plate. The screw should to be installed at the angle of 30°inclining inside. It was better safety and effectiveness if two screws were installed in the upper plate in the treatment of patients with sacroiliac joint fracture by fixation of anterior double plates. |
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