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- Title
Primary stability of the Fitmore® stem: biomechanical comparison.
- Authors
Pepke, Wojciech; Nadorf, Jan; Ewerbeck, Volker; Streit, Marcus; Kinkel, Stefan; Gotterbarm, Tobias; Maier, Michael; Kretzer, J.
- Abstract
Purpose: After clinical introduction of the Fitmore® stem (Zimmer), we noticed the formation of cortical hypertrophies in a few cases. We questioned whether (1) the primary stability or (2) load transfer of the Fitmore® stem differs from other stems unassociated with the formation of hypertrophies. We compared the Fitmore® stem to the well-established CLS® stem. Methods: Four Fitmore® and four CLS® stems were implanted in eight synthetic femurs. A cyclic torque around the stem axis and a mediolateral cyclic torque were applied. Micromotions between stems and femurs were measured to classify the specific rotational implant stability and to analyse the bending behaviour of the stem. Results: No statistical differences were found between the two stem designs with respect to their rotational stability ( p = 0.82). For both stems, a proximal fixation was found. However, for the mediolateral bending behavior, we observed a significantly ( p < 0.01) higher flexibility of the CLS® stem compared to the Fitmore® stem. Conclusion: Hip stem implantation may induce remodelling of the periprosthetic bone structure. Considering the proximal fixation of both stems, rotational stability of the Fitmore® stem might not be a plausible explanation for clinically observed formation of hypertrophies. However, bending results support our hypothesis that the CLS® stem presumably closely follows the bending of the bone, whereas the shorter Fitmore® stem acts more rigidly. Stem rigidity and flexibility needs to be considered, as they may influence the load transfer at the implant-bone interface and thus possibly affect bone remodelling processes.
- Subjects
BIOMECHANICS research; BONE mechanics; BONE testing; HIP joint physiology; HIP surgery
- Publication
International Orthopaedics, 2014, Vol 38, Issue 3, p483
- ISSN
0341-2695
- Publication type
Article
- DOI
10.1007/s00264-013-2138-4