Surgeons commonly resect additional distal femur during primary total knee arthroplasty (TKA) to correct a flexion contracture to restore range of motion and knee function. However, the effect of joint line elevation on the resulting TKA kinematics including frontal plane laxity is unclear. Thus, our goal was to quantify the effect of additional distal femoral resection on passive extension and mid-flexion laxity. Six computational knee models with capsular and collateral ligament properties specific to TKA were developed and implanted with a contemporary posterior-stabilized TKA. A 10° flexion contracture was modeled by imposing capsular contracture as determined by simulating a common clinical exam of knee extension and accounting for the length and weight of each limb segment from which the models were derived (Figure 1). Distal femoral resections of 2 mm and 4 mm were simulated for each model. The knees were then extended by applying the measured knee moments to quantify the amount of knee extension. The output data were compared with a previous cadaveric study using a two-sample two-tailed t-test (p<0.05) [1]. Subsequently, varus and valgus torques of ±10 Nm were applied as the knee was flexed from 0° to 90° at the baseline, and after distal resections of 2 mm, and 4 mm. Coronal laxity, defined as the sum of varus and valgus angulation in response to the applied varus and valgus torques, was measured at 30° and 45°of flexion, and the flexion angle was identified where the increase in laxity was the greatest with respect to baseline.Introduction
Methods
In total knee arthroplasty (TKA), tibial insert thickness is determined intraoperatively by applying forces that generate varus-valgus moments at the knee and estimating the resulting gaps. However, how the magnitude of applied moments and the surgeon's perception of gaps affect the thickness selection is unclear. We determined this relationship using an in vitro human cadaveric model. Six pelvis-to-toe specimens (72±6 years old, four females) were implanted by an expert surgeon with a PS TKA using measured resection. Pliable sensors were wrapped around medial and lateral aspects of the foot and ankle to measure the applied forces. The forces were scaled by limb length to obtain the moments generated at the knee. Six surgeons with different experience levels independently assessed balance by applying moments in extension and 90° of flexion and choosing the insert they believed fit each knee. Peak moments and the accompanying extension and flexion gap openings as perceived by surgeons were recorded. The two measures were then related to insert choice using a generalized estimating equation.Introduction
Methods
Medial unicompartmental knee arthroplasty (UKA) restores mechanical alignment and reduces lateral subluxation of the tibia. However, medial compartment translation remains abnormal compared to the native knee in mid-flexion Intra-operative adjustment of implant thickness can modulate ligament tension and may improve knee kinematics. However, the relationship between insert thickness, ligament loads, and knee kinematics is not well understood. Therefore, we used a computational model to assess the sensitivity of knee kinematics, and cruciate and collateral ligament forces to tibial component thickness with fixed bearing medial UKA. A computational model of the knee with subject-specific bone geometries, articular cartilage, and menisci was developed using multibody dynamics software (Fig 1a). The ligaments were represented with multiple non-linear, tension-only force elements, and incorporated mean structural properties. The 3D geometries of the femoral and tibial components of the Stryker Triathlon fixed-bearing UKA were captured using a laser scanner. An arthroplasty surgeon aligned the femoral and tibial components to the articular surfaces within the model (Fig 1b). The intact and UKA models were passively flexed from 0 to 90° under a 10 N compressive load. The tibial polyethylene insert was modeled by the orthopaedic surgeon to create a “balanced” knee. The modeled polyethylene insert thickness was then increased by 2 mm and decreased 2mm (in increments of 1mm) to simulate over- and under-stuffing, respectively. Outcomes were anterior-posterior (AP) translation of the femur on the tibia in the medial compartment, and forces seen by the ACL and MCL during mid-flexion (from 30 to 60° flexion). The mean differences between the intact knee model and all other experimental conditions for each outcome were calculated across mid-flexion.Introduction
Methods
14.1% of men &
22.8% of women over 45 years show symptoms of osteoarthritis OA of the knee [ CT and MRI data of a cadaveric knee were used to create geometrically accurate 3D models of the femur, tibia, fibula, menisci and cartilage and tendon of the knee joint, using the Mimics V12.11 commercially-available software (Materialise, Belgium). The Simulation module was used to register the bones and the soft tissues. The resulting STL files were exported to CATIA V5R18 pre-processor to generate surface meshes and create the corresponding 3D solid and FE models of the osseous and soft tissues from the STL cloud of points. The Young’s moduli for cortical bone, cancellous bone, cartilages, menisci and ligaments were taken from literature as 17 GPa, 500 MPa, 12 MPa, 60 Mpa and 1.72 MPa respectively [ FE analysis results of this study show that HTO reduces stresses in specific regions of the knee, which are associated with OA progression [
