Failure mechanisms in total hip and knee arthroplasty: A morphologic and radiologic study

Failure mechanisms in hip and knee arthroplasty are controversial, as the s ystem of bone and implant is rather complex due to permanent biological cha nges, inhomogeneous Young's modulus and geometry of bone. Therefore, since 1989 534 failures were retrospectively analyzed in a clinical study: mean p atients' age 67,9 years, range 21 - 91, cemented implants = 379, non-cement ed = 155, group 1 = 286 acetabular revisions, group 2 = 165 femoral revisio ns and group 3 = 83 knee revisions. Results: average survivorship of implan ts (late loosening): group 1 = 10.2 years, group 1 = 12.1 years, group 3 = 7.3 years. The major failure mechanism of hip and knee implants in this stu dy was revealed as loosening at the interface between bone and cement (poly methylmethacrylate) or bone and implant: group 1 = 72 %, group 2 = 53 %, gr oup 3 = 42 %. Other mechanisms seldom occurred: Debonding at the cement/pro sthesis interface: group 1 = 4 %, group 2 = 12%, group 3 = 15 %. Crack prop agation in the cement mantle: group 1 = 8 %, group 2 = 20 %, group 3 = 3 %. Severe osteolysis due to granuloma: group 1 = 11 %, group 2 = 13 %, group 3 = 2 %. A high percentage of extensive bone defects was found: defect clas sification according to Paprosky [20]: group 1: type 1 = 22,4 %, type 2 = 5 6,3 %, type 3 = 21,3 %, group 2: type 1 = 27.3 %, type 2 = 59,4 %, type 3 = 13,3 %. Defect classification according to Fitzek and Barden [10]: group 3 : type 1 = 44,6 %, type 2 = 41,0 %, type 3 = 14.5 %, type 4 = 0 %. While in hip arthroplasty early loosening within five years after the preceding ope ration was rare, half of the knee revisions had to be performed because of early loosening due to the special complexity of knee arthroplasty. Partial atrophy of the periprosthetic bone often occurred but could not be made re sponsible for loosening. Loosening without local pain was noticed in 13,2 % . There was close correlation between preoperative radio graphic analysis a nd intraoperative Findings. In conclusion severe loss of bone stock without clinical symptoms in loosening of hip and knee implants should be prevente d by routine radiographic controls. Circumferential disintegration is most common and the typical failure mechanism of hip and knee implants. Thus for prophylaxis of loosening special emphasis should be laid on tight connecti on at the interface between cement (or implant) and bone.