Biomechanical research on contour cage with transacetabular screws fixation in revision total hip arthroplasty

Background: Use biomechanical technique to access the strain distribution and stability of Contour anti-protrusion cage with or without the whole circumference acetabular cup fixation by the transacetabular screws.

Methods: Pelvic specimens from 10 male cadavers were used for the biomechanical test. The models of type C bone defect were copied according to the AAOS classification. Group 1: the contour reconstruction ring was fixed only by flange screws; Group 2: the contour reconstruction ring was fixed both by flange screws and transacetabular screws in dome. Under load in Heel Strike, Midstance, and Toe off phase, the transverse and longitudinal strains were measured in both the superior measure site near the root of the iliac wing and the inferior measure site near the root of the ischium. The relative displacement between the anterior inferior spine and the root of ischium below acetabular component was also measured.

Findings: Compared with Group 1, the transverse and longitudinal pressure strain of Group 2 on the superior measure site decreased, and measure sites also showed reductions on the inferior under load under three different gait phases. The result of mean relative displacement showed transacetabular screws fixation couldn't provide significant improvement of displacement prevention.

Interpretation: Biomechanical test showed that under the premise of a satisfied bone allograft and well-fixed flange screws in iliac and ischium, the satisfactory initial stability of the reconstruction cup can be achieved, but could not be improved by transacetabular screw technique. However, the max strain in root part of the flange will be reduced using transacetabular screws in ilium, pubis and ischium together, and the strain distribution will also be improved.