A small punch test technique for characterizing the elastic modulus and fracture behavior of PMMA bone cement used in total joint replacement

Polymethylmethacrylate (PMMA) bone cement is used in total joint replacemen ts to anchor implants to the underlying bone. Establishing and maintaining the integrity of bone cement is thus of critical importance to the long-ter m outcome of joint replacement surgery. The goal of the present study was t o evaluate the suitability of a novel testing technique, the small punch or miniaturized disk bend test, to characterize the elastic modulus and fract ure behavior of PMMA. We investigated the hypothesis that the crack initiat ion behavior of PMMA during the small punch test was sensitive to the test temperature. Miniature disk-shaped specimens, 0.5 mm thick and 6.4 mm in di ameter, were prepared from PMMA and Simplex-P bone cement according to manu facturers' instructions. Testing was conducted at ambient and body temperat ures, and the effect of test temperature on the elastic modulus and fractur e behavior was statistically evaluated using analysis of variance. For both PMMA materials, the test temperature had a significant effect on elastic m odulus and crack initiation behavior. At body temperature, the specimens ex hibited "ductile" crack initiation, whereas at room temperature "brittle" c rack initiation was observed. The small punch test was found to be a sensit ive and repeatable test method for evaluating the mechanical behavior of PM MA. In light of the results of this study, future small punch testing shoul d be conducted at body temperature. (C) 2001 Elsevier Science Ltd. All righ ts reserved.