Time-dependent fixation and implantation forces for a femoral knee component—An in vitro study

Abstract

Implant survival rate is a primary concern for individuals receiving a primary total knee arthroplasty. Loosening is the primary reason for revision surgery and was therefore the focus of the current study. To better understand the mechanics of implant fixation, the time-dependent fixation of a femoral knee component was measured in vitro on three cadaveric femurs. The fixation of each femoral knee component was measured with strain gauged implants for at least 10min on each femoral component. Additionally, impaction forces were measured during the implantation of each component. These forces were 2-6 times less than previously reported. The implantation impact forces were higher for the bones with higher bone density. Power law regressions were fit to the absolute value of the principal strains measured on the components over time to quantify the relaxation of the bone. The average power coefficient value for the three bones was lower for the bones with higher bone density. The average power coefficient value for the maximum principal strains was significantly higher than that of the minimum principal strains in each bone. The results were extrapolated to approximate the fixation strength at 9 months after implantation. In this time period the strain was predicted to decrease to between 78 and 91% of the strain 1s after implantation where those with lower bone density will have decreased fixation strength.

The Effect of Surface Morphology on the Primary Fixation Strength of Uncemented Femoral Knee Prosthesis: A Cadaveric Study

“…The average insertion force was a bit higher than reported by Burgers et al [15] who measured about 2500 N in their best bone quality case. We measured this range of insertion force only in the bones with BMD values lower than 150 mg/cm 3 , which means low bone quality.…”

“…We measured this range of insertion force only in the bones with BMD values lower than 150 mg/cm 3 , which means low bone quality. Burgers et al [15] suggested that a horizontal impaction in their set-up could have caused a lower impaction force in their study. Moreover, we measured our insertion force during a gradual insertion instead of dynamic impaction; the latter probably being associated with increased peak forces.…”

“…It is known that bone quality can affect the insertion force and the primary fixation strength [15,16]. The Hounsfield units of the CTimages were converted to BMD values using in house software [17].…”

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

“…Relative to micromotion values reported in the literature, which were in the order of 0–250 µm, we found smaller ranges of micromotion . This is attributable to the fact that we did not model plasticity or visco‐elastic behavior of the bone, which are important factors for the primary stability of cementless implants . To include the effect of bone plasticity and the visco‐elastic effects on implant stability, future studies can focus on improving a more realistic continuum model of the mechanical behaviour of bone.…”

Effect of the support systems’ compliance on total hip modular taper seating stability

“…It has been shown that one of the critical factors that affect the seating stability of these taper junctions is the non-standardized assembly methods used to seat the femoral head onto the stem. 1–4 The seating of the head on the stem may depend on surgical, patient, and implant variables 1–4 that include visualization of the implant, patient size and age, and the nature of the implant being implanted. 1–4…”