Effects of a Femoral Component and Patient Factors on Periprosthetic Cortical Bone

The need for revision THA increased 80% (24,000 to 43,000) in the United States from 1990 to 2002. Two major reasons for revision surgeries are aseptic loosening and periprosthetic fractures. Femoral bone loss can contribute to aseptic loosening when bone recedes from the femoral component and to periprosthetic fractures when the bone loss leads to reduced ability to resist loads. The goals were to better understand limitations to a clinical bone measurement tool (dual-energy x-ray absorptiometry (DEXA)) and to better understand how the presence of a femoral component and patient factors (i.e., patient weight and mobility) affect bone loss as quantified by cortical bone cross-sectional area, ash percent, and porosity so that future bone maintenance strategies target compromised cortical bone properties.

The data indicated that DEXA was a useful tool for measuring relative mineral changes after unilateral THA. Since DEXA is influenced by mineral content and mineral content can vary with cortical bone cross-sectional area, specific mineralization (ash percent), and porosity, these cortical bone properties were separately analyzed. The implanted femurs showed reduced cortical bone cross-sectional area, regionally reduced ash percent, and regionally increased percent porosity when compared to the contralateral nonimplanted femurs. When examining the influence of cortical bone cross-sectional area, ash percent, and porosity on DEXA measurements, only cross-sectional area had a moderate to high correlation to DEXA values. Therefore, DEXA was influenced more by cortical bone quantity (cross-sectional area) than cortical bone quality (ash percent and porosity) and, thus, may not be able to capture all the cortical bone properties that can affect the mechanical integrity in the proximal femur.

When examining the influence of patient factors on the varying degrees of bone loss, greater patient mobility as estimated by the mechanical usage score (MUS) had a high correlation to greater bone maintenance in the implanted femurs as quantified by cortical bone cross-sectional area. Therefore, patients who can safely maintain relatively normal mobility (MUS > 35) may minimize femoral bone loss after THA and, thus, decrease their risk of periprosthetic cortical bone failure and revision surgery.

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Year

Entry

1990

Palumbo C, Palazzini S, Marotti G. Morphological study of intercellular junctions during osteocyte differentiation. Bone. 1990;11(6):401-406.

1980

Nagurka ML, Hayes WC. An interactive graphics package for calculating cross-sectional properties of complex shapes. J Biomech. 1980;13(1):59-64.

1987

Salzstein RA, Pollack SR. Electromechanical potentials in cortical bone, II: experimental analysis. J Biomech. 1987;20(3):271-280.

1994

Parfitt AM. Osteonal and hemi‐osteonal remodeling: the spatial and temporal framework for signal traffic in adult human bone. J Cell Biochem. July 1994;55(3):273-286.

1999

Kerner J, Huiskes R, van Lenthe GH, Weinans H, van Rietbergen B, Engh CA, Amis AA. Correlation between pre-operative periprosthetic bone density and post-operative bone loss in THA can be explained by strain-adaptive remodelling. J Biomech. July 1999;32(7):695-703.