Periprosthetic fractures around polished collarless cemented stems: The effect of stem design on fracture pattern

J.B. Erhardt, P.P. Khoo, Karl Stoffel, Piers Yates

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    Background: Predictable patterns of periprosthetic fracture have been observed around polished double tapered stems. Finite element studies have suggested that triple-tapered stems cause less cement strain in torsion compared to double-tapered stems. Hence, we hypothesised that the in vitro behaviour of implanted double- and triple-tapered polished stems, like the CPT (Zimmer, Warsaw, USA) or C-Stem (DePuy, Leeds, UK) when subjected to pathological torsional loads may cause different patterns of periprosthetic fractures. Methods: Ten double-tapered stems (CPT) and ten triple-tapered stems (C-Stem) were cemented into synthetic femur bones. A constant axial compression load of 100 N and a torsional pre-load of 0.1 N.m were applied using a biaxial testing machine. The distal femur was then loaded in external rotation at 45 degrees until failure. Results: Seven of the 10 CPT stems fractured at the level of the stem body while fracturing the ce-ment mantle at the same level. In three of ten of the CPT stems and all ten C-Stems, the synthetic bone fractured at the tip of the prosthesis while the cement mantle remained intact. This was significant for the resulting fracture pattern (P = 0.001). There was no significant difference between the groups for either torque (P = 0.13) or angle at failure (P = 0.49). Interpretation: This biomechanical study indicates that the CPT and C-Stem create a different fracture pattern under the same loading condition. The C-Stem (a triple tapered stem) may produce lower strain in torsion to the cement mantle of a cemented THA. However, fractures that do occur may be more difficult to treat than those produced around a stem like the CPT subjected to comparable loading. © 2013 Wichtig Editore.
    Original languageEnglish
    Pages (from-to)459-464
    JournalHip International
    Issue number5
    Publication statusPublished - 2013


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