[Finite element analysis of different diameter prosthesis ball head in artificial femoral head replacement]

In order to select the proper size of prosthesis ball head, the biomechanical changes of hip joint using different diameter prosthesis ball head was studied by three-dimensional finite element analysis.

The thin-layer CT data and related parameters of artificial femoral head prosthesis were used to establish the finite element model of hip joint after artificial femoral head replacement with different ball diameter of prosthesis(M0:preoperative model;M1:ball head diameter=original femoral head diameter;M2:ball head diameter=original femoral head diameter+1 mm;M3:Ball head diameter= Original femoral head diameter -1 mm;M4:ball head diameter =original femoral head diameter -2 mm). Loading the joint forces and related muscle loads were loaded, and the stress distribution and change of bone and cartilage around acetabulum were analyzed by simulating the standing state of one foot when walking slowly.

(1) In M1 to M4, the stress concentration in pelvis was different. The peak value of Von Mises stress in the pelvis of M3 was 44.8 MPa, which was the closest to that before operation, with an increment of 13.4%. The displacement of the pelvis of M3 was the smallest in the four groups after operation, with an increment of 1.40 mm. The next was M1, with a peak value of 47.3 MPa, with an increment of 19.7%, and a pelvic displacement of 1.59 mm. (2) In acetabulum area, the peak value of Von Mises stress in M3 was 23.3 MPa, which was the closest to that before operation, with an increment of about 6.3%, followed by M1, with a peak value of 24.0 MPa and an increment of about 8.1%. (3) On the acetabulum cartilage, the stress distribution of M1 and M3 was similar to that before operation, and the peak value of Von Mises stress of M3 was 18.5 MPa, which was the closest to that before operation, followed by M1, which was 22.5 MPa. (4) M1 to M4 showed different degree of stress concentration in the outer upper quadrant of the artificial femoral head, but showed stress shielding under it;among them, the von Mises stress distribution of M3 was more uniform than that of other models, and its peak value (70.8 MPa) was the lowest in each group, followed by M1 (80.7 MPa).

When femoral head replacement is performed, it is suggested that the prosthesis ball head with the diameter less than 1 mm and the prosthesis ball head with the same diameter as the original femoral head should be used first, so as to obtain the closest natural mechanical characteristics of the hip joint before the replacement and reduce the risk of complications caused by size differences.