Long Stemmed Total Knee Arthroplasty With Interlocking Screws: A Computational Bone Adaptation Study

Jeffry S. Nyman, University of California - Davis
Scott J. Hazelwood, University of California - Davis
Juan J. Rodrigo, University of California - Davis
R. Bruce Martin, University of California - Davis
Oscar C. Yeh, University of California - Davis

Article comments

This is the pre-peer reviewed version of the following article: Long Stemmed Total Knee Arthroplasty With Interlocking Screws: A Computational Bone Adaptation Study, Jeffry S. Nyman, Scott J. Hazelwood, Juan J. Rodrigo, R. Bruce Martin, Oscar C. Yeh, Journal of Orthopaedic Research, 22:1, Copyright © 2003 Wiley-Blackwell., which has been published in final form at http://dx.doi.org/10.1016/S0736-0266(03)00159-1.

NOTE: At the time of publication, the author Scott J. Hazelwood was not yet affiliated with Cal Poly.

Abstract

The ability of an interlocking screw fixation technique to minimize bone loss related to stress shielding in the tibia was investigated and compared to the abilities of cement and press-fit fixation. Full bony ingrowth has been associated with greater stress shielding than partial ingrowth; therefore, the effect of intimate bonding of the stem to bone on subsequent bone loss was also studied. A damage-and disuse-based remodeling theory was coupled with a two-dimensional finite element model of the tibia to predict changes in bone remodeling following long stemmed total knee arthroplasty (TKA) for four different fixation techniques (cement, press-fit, interlock with bony ingrowth, and interlock without bony ingrowth). Remodeling changes commenced with the model state variables––bone area fraction, mechanical stimulus, damage, and remodeling activity–– at steady-state values predicted by the intact tibia simulation. After TKA and irrespective of fixation technique, the model predicted elevated remodeling due to disuse, in which more bone was removed than replenished. In regions below the tibial tray and along the cortices, the interlocking stem with full bony ingrowth and the cemented stem caused the least amount of bone loss. An interlocking stem with a smooth, matted finish did not reduce the bone loss associated with interlocking fixation.