The effect of dynamic hip motion on the micromotion of press-fit acetabular cups in six degrees of freedom

Abstract

The hip joint is subjected to cyclic loading and motion during activities of daily living and this can induce micromotions at the bone-implant interface of cementless total hip replacements. Initial stability has been identified as a crucial factor to achieve osseointegration and long-term survival. Whilst fixation of femoral stems achieves good clinical results, the fixation of acetabular components remains a challenge. In vitro methods assessing cup stability keep the hip joint in a fixed position, overlooking the effect of hip motion. The effect of hip motion on cup micromotion using a hip motion simulator replicating hip flexion-extension and a six degrees of freedom measurement system was investigated. The results show an increase in cup micromotion under dynamic hip motion compared to Static Flexion. This highlights the need to incorporate hip motion and measure all degrees of freedom when assessing cup micromotion. In addition, comparison of two press-fit acetabular cups with different surface coatings suggested similar stability between the two cups. This new method provides a basis for a more representative protocol for future pre-clinical evaluation of different cup designs.

Effect of impaction energy on dynamic bone strains, fixation strength, and seating of cementless acetabular cups

“…The energy of the strikes tested also represent the region measured operatively (1–15 J), as previously reported . Sawbones have been shown to model the mechanical properties of biological tissues and result in cup fixation stability within the range measured in cadavers . Previous literature demonstrates the value of these models to draw important conclusions .…”

“…5,36 Sawbones have been shown to model the mechanical properties of biological tissues [44][45][46] and result in cup fixation stability within the range measured in cadavers. 47 Previous literature demonstrates the value of these models to draw important conclusions. 23,37,48 To account for variation in bone properties, we modeled two bone densities based upon previous literature.…”

Two Different Methods to Measure the Stability of Acetabular Implants: A Comparison Using Artificial Acetabular Models

“…A limitation of this study is the use of simplified replicate acetabular bone models. Previous studies used similar bone models [6,7,15,17,21]. Another study measured comparable micromotion in replicate and cadaveric femurs [36], demonstrating that artificial bone material is an effective substitute to simulate micromotion.…”

“…Simplified replicate acetabular bone models were manufactured out of three different materials and using two different press-fits to mimic the acetabulum. This type of bone model is commonly used in the literature as an alternative to mimic the human acetabulum [6,7,14,15,17,21,22]. One rigid cellular polyurethane foam (0.32 g/cc density) and two types of solid rigid polyurethane foam (0.48 and 0.80 g/cc density) were tested using both a 0.7 mm and 1.2 mm press-fit.…”

“…Table 1. Overview of the tested acetabular models; two single bone models (specimen 1 and 2) and four sets of three identical models (specimen [3][4][5][6][7][8][9][10][11][12][13][14]. A Procotyl L cementless acetabular cup (Microport Orthopedics Inc., Arlington, TN, USA) with a diameter of 52.2 mm was used in combination with the acetabular models, resulting in a press-fit of 0.7 mm and 1.2 mm depending on the acetabular cavity diameter.…”