Effects of Cemented Hip Stem Pre-heating on Stem Push-out Strength

Abstract

Objective: To determine the effect on ultimate push-out load and cement-stem surface shear strength of thermally manipulating the cobalt-chromium-molybdenum (CoCrMo) alloy stems of bone cement-stem constructs. Methods: Satin-finished CoCrMo alloy stems were allocated to the following three groups with the predetermined temperatures: T24, ambient (24°C); T37, body (37°C); and T44, pre-heated stem (>44°C). They were then inserted into hand-mixed high viscosity bone cement. Ultimate push-out load to failure was assessed with a servo hydraulic testing machine and the surface shear strength calculated. Data were compared among groups using the Kruskal-Wallis with Dunn's test. A P value of less than 0.05 was considered statistically significant. Results: According to Kruskal-Wallis analysis, ultimate push-out load and surface shear strength differed significantly between the groups (P = 0.001). The T37 and T44 groups had higher ultimate push-out loads and surface shear strengths than the T24 group (P = 0.04 and 0.001, respectively). However, there was no statistically significant difference in these two variables between the T37 and T44 groups (P = 0.08). Conclusions: Pre-heating CoCrMo alloy stems enhance the ultimate push-out load and surface shear strength in vitro. The suggested temperature is 37°C. This technique is recommended for hip arthroplasty procedures.