Advertisement for orthosearch.org.uk
Orthopaedic Proceedings Logo

Receive monthly Table of Contents alerts from Orthopaedic Proceedings

Comprehensive article alerts can be set up and managed through your account settings

View my account settings

Visit Orthopaedic Proceedings at:

Loading...

Loading...

Full Access

A BIOMECHANICAL COMPARISON OF THE RESTORATION AND THE HMRS DISTAL FEMORAL PRESS-FIT STEMS



Abstract

Purpose: Endoprosthetic reconstruction of the distal femur is the preferred approach for patients undergoing resection of bone sarcomas. The traditional How-medica Modular Resection System, using a press-fit stem (HMRS or Kotz prosthesis, Stryker Orthopaedics, Mahwah, New Jersey, USA) has shown good long-term clinical success, but has also been known to incur complications such as stem fracture. The Restoration stem, as a part of the new Global Modular Resection System (GMRS, Stryker Orthopaedics, Mahwah, NJ, USA), is currently proposed for this same application. This stem has a different geometry and provides the advantage of decreased risk of fracture of the component. The goal of this study was to compare the HMRS and Restoration press-fit stems in terms of initial mechanical stability.

Methods: Six matching pairs fresh frozen adult femora were obtained and prepared using a flexible canal reamer and fitted with either a Restoration or HMRS press-fit stem distally. All constructs were mechanically tested in axial compression, lateral bending, and torsion to obtain mechanical stiffness. Torque-to-failure was finally performed to determine the offset force required to clinically fail the specimen by either incurring damage to the femur, the stem, or the femur-stem interface.

Results: Restoration press-fit stems results were: axial stiffness (average=1871.1 N/mm, SD=431.2), lateral stiffness (average=508.0 N/mm, SD=179.6), and torsional stiffness (average=262.3 N/mm, SD=53.2). HMRS stems achieved comparable levels: axial stiffness (average=1867.9 N/mm, SD=392.0), lateral bending stiffness (average=468.5 N/mm, SD=115.3), and torsional stiffness (average=234.9 N/mm, SD=62.4). For torque-to-failure, the applied offset forces on Restoration (average=876.3 N, SD=449.6) and HMRS (aver-age=690.5 N, SD=142.0) stems were similar. There were no statistical differences in performance between the two stem types regarding axial compression (p=0.97), lateral bending (p=0.45), or torsional stiffnesses (p=0.07). Moreover, no differences were detected between the groups when tested in torque-to-failure (p=0.37). The mechanism of torsional failure for all specimens was “spinning” (i.e. surface sliding) at the femur-stem interface. No significant damage was detected to any bones or stem devices.

Conclusions: These results suggest that the Restoration and HMRS press-fit stems may be equivalent clinically in the immediate post-operative situation. Funding: Commerical funding Funding Parties: Stryker Orthopaedics

Correspondence should be addressed to Cynthia Vezina, Communications Manager, COA, 4150-360 Ste. Catherine St. West, Westmount, QC H3Z 2Y5, Canada