FE analysis of the effects of simplifications in experimental testing on micromotions of uncemented femoral knee implants

Abstract

Experimental testing of orthopaedic implants requires simplifications concerning load application and activities being analyzed. This computational study investigated how these simplifications affect micromotions at the bone-implant interface of an uncemented femoral knee implant. As a basis, validated in vivo loads of the stance phase of gait and a deep knee bend were adopted. Eventually, three configurations were considered: (i) simulation of the complete loading cycle; (ii) inclusion of only tibiofemoral loads (ignoring patellofemoral loads); and (iii) applying only a single peak tibiofemoral force. For all loading conditions the largest micromotions found at the proximal anterior flange. Without the patellofemoral force, peak micromotions increased 6% and 22% for gait and deep knee bend, respectively. By applying a single peak tibiofemoral force micromotions were overestimated. However, the peak micromotions corresponded to the maximum tibiofemoral force, and strong micromotion correlations were found between a complete loading cycle and a single peak load (R 2 ¼ 0.73 and R 2 ¼ 0.89 for gait and deep knee bend, respectively). Deep knee bend resulted in larger micromotions than gait. Our study suggests that a simplified peak force can be used to assess the stability of cementless femoral components. For more robust testing, implants should be subjected to different loading modes. ß

Quantification of interfacial motions following primary and revision total knee arthroplasty: A verification study versus experimental data

“…In Berahmani et al, the M‐L distribution was kept constant for both simplified and full loading conditions; whereas, in the present study the M‐L distribution of the tibiofemoral force was 51–49% while replicating the in vitro conditions and 60–40% under physiological loading conditions. This along with other factors, such as implant geometry and modelling parameters selected (e.g., frictional coefficients, and applied loads) may also explain why, contrary to that reported by Berhamani et al the distal surface and anterior chamfers were found to exhibit high levels of micromotion under complex loading conditions.…”

“…In a recent FE study by Berahmani et al, the influence of different loading configurations on micromotion at the bone–implant interface following primary TKA with a cruciate retaining implant was examined. Similar to the finding of the present study, Berahmani et al reported that simplified loading conditions and a lack of patella–femoral force caused an overestimation of micromotion at the interface.…”

“…Primarily, RSA can only track large changes (e.g., >100 µm) in the position of the prosthesis . As these methods are unable to capture the small but repetitive inducible motions (e.g., <40 µm) which play a key role in particle induced osteolysis and aseptic loosening of the implant, surgeons increasingly rely on in vitro laboratory testing and in silico modeling to supplement clinical knowledge on motion at the interface and overall implant stability.…”

“…However, the influence of such simplifications on predicted motions at the interface following total knee replacement has not been widely assessed. Only one previous study, has attempted to address this issue directly. In their study, Berahmani et al examined the micromotion characteristics of a single cruciate retaining implant, and found that simplifications in applied loading could lead to overestimation of peak motions by up to 22%.…”

Computational biomechanics of knee joint arthroplasty : a review

“…They showed that surrogate models have significant potential to rapidly predict micromotion over the entire bone-implant interface, allowing greater range in loading conditions to be explored than is possible through conventional methods. Berahmani et al also studied how these simplifications affect micromotions at the bone-implant interface of an uncemented femoral component (Berahmani et al, 2016). They suggested that a simplified peak force can be used to assess the stability of cementless femoral components.…”