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.

Keywords: Cobalt-Chromium-Molybdenum alloy; Hip arthroplasty; Pre-heated femoral stem; Push-out test; Surface shear strength.

Figure 1

Diagrammatic representation of the experimental set up of Cement‐Cobalt‐chromium‐molybdenum alloy stem construct in a temperature controlled (37 °C) thermocycling unit.

Figure 2

Ultimate push‐out load of CoCrMo alloy stems according to temperature.

Figure 3

Shear strength of CoCrMo alloy stems according to temperature.