[Development of polyaxial locking plate screw system of sacroiliac joint].

OBJECTIVE: To develop an instrument for sacroiliac joint fixation with less injury and less complications. METHODS: Firstly, 18 adult pelvic specimens (8 males and 10 females) were used to measure the anatomical data related to the locking plates and locking screws on the sacrum and ilium, and the polyaxial locking plate screw system of the sacroiliac joint was designed according to the anatomic data. This system was made of medical titanium alloy. Then 4 adult male plevic specimens were harvested and the experiment was divided into 3 groups: group A (normal pelvic), group B (the dislocated sacroiliac joint fixed with sacroiliac screws), and group C (the dislocated sacroiliac joint fixed with polyaxial locking plate screw system). The vertical displacement of sacroiliac joint under the condition of 0-700 N vertical load and the horizontal displacement on angle under the condition of 0-12 N·m torsional load were compared among the 3 groups by using the biological material test system. Finally, the simulated application test was performed on 1 adult male cadaveric specimen to observe soft tissue injury and the position of the locking plate and screw by X-ray films. RESULTS: According to the anatomic data of the sacrum and ilium, the polyaxial locking plate screw system of the sacroiliac joint was designed. The biomechanical results showed that the vertical displacement of the sacroiliac joint under the condition of 0-700 N vertical load in group A was significantly bigger than that in group B and group C (P < 0.05), but there was no significant difference between group B and group C (P > 0.05). The horizontal displacement on angle under the condition of 0-12 N·m torsional load in group A was significantly less than that in group B and group C (P < 0.05). The horizontal displacement on angle under the condition of 0-6 N·m torsional load in group B was bigger than that in group C, and the horizontal displacement on angle under the condition of 6-12 N·m torsional load in group B was less than that in group C, but there was no significant difference between group B and group C (P > 0.05). The test of simulating application showed that the specimen suffered less soft tissue injury, and this instrument could be implanted precisely and safely. CONCLUSION: The polyaxial locking plate screw system of the sacroiliac joint has the advantages of smaller volume and less injury; polyaxial fixation enables flexible adjustment screw direction. The simulated application test shows satisfactory fixing effect.