ABSTRACT
BACKGROUND: PMMA bone cement is a brittle material and the creation of defects that increase porosity during mixing or injecting is a significant factor in reducing its mechanical properties. The goal during residency training is to learn how to avoid creating increased porosity during mixing and injecting the material. The aim of this study was to evaluate and compare tensile and compression strength for PMMA cement mixed by intern orthopaedic residents (PGY-1) and senior orthopaedic residents (PGY-5). The hypothesis was that the mechanical properties of PMMA cement mixed by PGY-5 would be significantly better than PMMA cement mixed by PGY-1 residents. METHODS: Four PGY-1 and four PGY-5 orthopaedic residents each prepared eight tensile specimens. The bone cement used was Simplex™ P bone cement (Stryker Howmedica Osteonics, Mahwah, NJ) under vacuum mixing in a cement-delivery system. Tensile testing of the specimens was performed in an MTS Bionix servohydraulic materials testing system with loading rate of 2.54 mm/min at room temperature. The mean and standard deviation of the ultimate tensile strength (UTS) for each orthopaedic resident group was calculated. The compression specimens were cylinders formed with a central core to mimic a prosthetic implant. Ten samples from each orthopaedic resident were tested using the same MTS system under identical conditions at room temperature. The specimens were loaded from -50 N to complete structural failure at the rate of 20 mm/min. The ultimate compressive strength (UCS) was then determined and the mean and standard deviation calculated for each group. RESULTS: The average UTS of the bone cement for the PGY-1 and PGY-5 residents was 37.5 ± 4.5 MPa and 39.2 ± 5.0 MPa, respectively, and there was no statistically significant difference between the two groups. For the tensile elastic modulus of the bone cement, the results for the PGY-1 and PGY-5 residents were 2.40 ± 0.09 GPa and 2.44 ± 0.08 GPa, respectively, and again there was no statistically significant difference. For the compression elastic modulus of the bone cement, the results for the PGY-1 and PGY-5 residents were 1.19 ± 0.13 GPa and 1.21 ± 0.18 GPa, respectively, with no statistically significant difference. However, the UCS of the bone cement for the PGY-1 and PGY-5 residents was 87.4 ± 5.8 MPa and 91.1 ± 4.5 MPa, respectively, and there was a statistically significant difference between the groups. DISCUSSION: The PMMA specimens prepared by both the PGY-1 and PGY-5 resident groups had similar characteristics during tensile and compression testing, and were similar to known standards. Although mixing and applying bone cement is an important skill for joint replacement surgery, our results indicate that no special training appears to be necessary for orthopaedic residents. Rather, a basic training video demonstrating manufacturer standard procedure is all that is necessary. CLINICAL RELEVANCE: The results of this study indicate the importance of experience in bone cement mixing and injecting on cement mechanical properties, but indicate that no special training appears to be necessary for orthopaedic residents.