Anatomic-biomechanical substantiation of stabilization of the sacroiliac joint in cases of unstable pelvic injuries with a countersink-compression screw.

OBJECTIVE

Aim: Study the mechanism of interaction between the 'sacroiliac joint - screw' system and determine the optimal parameters of the stabilizing structure, the strength of the system connection through computer modeling, and anatomical-biomechanical experiment.

PATIENTS AND

METHODS

Materials and

Methods

The optimal parameters of the stabilizing structure for the sacroiliac joint were calculated using software package MathCAD. To validate the results of the numerical modeling, corresponding investigations of mechanical characteristics and determination of stiffness of the studied systems were conducted by an upgraded testing stand, TIRAtest-2151.

RESULTS

Results

Optimal dimensions of the stabilizing structure were calculated as follows: a thread length with a diameter of 9 mm ranges from 20 mm to 25 mm, and a thread length with a diameter of 7 mm ranges from 30 mm to 80 mm. The screw body, with a length from 15 mm to 70 mm and a diameter of 4.5 mm, is positioned between two thread portions. Under standard screw connection loading, a region of plastic deformation is observed under low force (≈40 N). Subsequently, elastic deformations are observed up to 900 N, after which the connection fails, and deformation of the stabilizing structure occurs.

CONCLUSION

Conclusions

Resulting from the study the authors revealed that the stiffness of the fixed system with countersink-compression screws increases with the applied load, reaching 67-68% of the stiffness of an undamaged joint. At all load levels, residual deformations in systems with C1Cc screws are significantly lower than the residual deformations in systems with C2Ct screws, indicating an enhanced deformation reliability of fixation with counter-compressive screws.