EFFECTS OF DISTAL FEMORAL CENTRALIZERS ON BONE-CEMENT IN TOTAL HIP-ARTHROPLASTY - AN EXPERIMENTAL-ANALYSIS OF CEMENT-CENTRALIZER BONDING, CEMENT VOID FORMATION, AND CRACK-PROPAGATION

Distal femoral centralizers of five different designs were inserted in to model femoral stems and cemented into closed-ended tubes simulating a proximal femoral canal. Specimens underwent cyclic loading from 50 to 500 lb. for 0, 1, 2, 5, and 10 million cycles. Each specimen was th en sectioned transversely al multiple levels to obtain serial cross-se ctions, beginning at the femoral stem lip and proceeding distally so a s to include the full extent of the centralizer. The area of each sect ion occupied by a centralizer and the total amount of porosity present in the cement surrounding the centralizers were measured using an ima ge analyzer. A dye penetrant was then applied to each section to visua lize cement cracks and areas of incomplete bonding between cement and centralizers. The number, length, and location of cement cracks were c atalogued for each section. No cement cracks or lack of bonding was ob served at the interface between cement and centralizers. There was gre ater porosity in the specimens containing centralizers than in control s without centralizers (P < .05). The cement surrounding two of the ce ntralizer designs had a significantly smaller amount of porosity than the cement surrounding the other three designs (P < .05). The number o f cracks did not depend on whether a centralizer was used, the type of centralizer, or the cycling duration. In the control specimens, failu re to adequately plug the centralizer receptacle hole in the stem tip resulted in very large cement voids.