An in vitro study of a new design of acetabular cement pressurizer.

Aseptic loosening of the acetabular component remains one of the limiting factors in the long-term success of total hip arthroplasty. Cement pressurization has been shown to improve fixation. A new pressurizer has been designed that seals around the rim of the acetabulum and covers the transverse ligament notch with a flap. The results of in vitro testing of this device are presented and compared with those of pressure generated by insertion of an acetabular cup. The pressurizer allowed sustained, uniform cement pressurization. Peak pressures with the new pressurizer were 180 kPa at both the iliac region of the rim and the pole of an instrumented model acetabulum, compared with 55 kPa at the rim and 120 kPa at the pole on cup insertion. Pressures were maintained in the range of 80-90 kPa. The flap was effective in preventing cement leakage from the notch, and pressures were higher than when the flap was absent. Cup insertion alone gave only transient pressurization, substantially less near the rim of the acetabulum than at the pole. Peripheral pressurization may be significant in producing secure local fixation at the rim of the acetabulum, in particular in the region of the ilium (Charnley zone 1), where radiolucencies are most commonly observed and where stresses in the implanted acetabulum are highest. Improved rim fixation may also play a role in preventing the ingress of wear debris.