Influence of bone quality on the initial stability of cementless hip stem in total hip arthroplasty

Abstract

The Young’s modulus and strength of bone varies between each individual due to differences in porosity, mineralization, and architecture. The differences between individuals can be significant depending on activities, age and disease [1-7]. This is likely to have an effect on initial stability of hip stem in total hip arthroplasty. After the age of 30 years, bone mass decreases slowly with age, which is thought to be caused by a small deficit of osteoblast deposition relative to osteoclast resorption [2]. Ding [2] reported that reductions of as much as 40% between age of 50 and 80 years old are possible. Zioupos [3] reported that reduction of cortical bone modulus in the diaphyseal femur is about 2.3% per decade after about 30 years age. Young’s modulus in cancellous bone with rheumatoid arthritis and osteoporosis has been reported to be inferior to normal bone by 47% [5] and 14% [4] respectively. Although it is known that bone quality affects the performance of cementless hip implants, it is difficult to quantify bone quality in cadaveric femurs used in experimental studies of hip implant stability[6,7]. In finite element studies, the effect of bone quality on initial micromotion has not been studied [8,9]. Therefore an objective measure of the influence of bone quality on initial stability is not available for either preclinical or clinical purposes. In this study, the effect of bone and stem quality on stability of the IPS stem has been studied. The objectives are (a) to look at the sensitivity of cementless stem stability to variation in bone Young’s modulus (b) to determine whether current finite element method of assessing implant stability based on one femur are adequate?

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