Total knee arthroplasty (TKA) surgical techniques attempt to achieve equal flexion and extension gaps to produce a well-balanced knee, but unexplainable unhappy patients persist. Mid-flexion instability is one proposed cause of unhappy patients. There are multiple techniques to achieve equal flexion and extension gaps, but their effects in mid-flexion are largely unknown. The purpose of the study is to determine the effects that changing femur implant size and/or adjusting the femur and tibia proximal -distal and femur anterior-posterior implant positions have on cruciate retaining (CR) TKA mid-flexion ligament balance when equal flexion and extension gaps are maintained.Background
Purpose of study
Total knee arthroplasty (TKA) surgical techniques attempt to achieve equal flexion and extension gaps to produce a well-balanced knee. Anterior knee pain, which is not addressed by flexion-extension balancing, is one of the more common complaints for TKA patients. The variation in patellofemoral balance resulting from the techniques to achieve equal flexion and extension gaps has not been widely studied. The purpose of the study is to determine the effects on cruciate retaining (CR) TKA patellofemoral balance when equal flexion and extension gaps are maintained while changing femur implant size and/or adjusting the femur and tibia implant proximal -distal and femur anterior-posterior positions.Background
Purpose of study
Achieving proper ligament tension in knee flexion within cruciate retaining (CR) total knee arthroplasty (TKA) has long been associated with clinical success. The distal femoral joint line (DFJL) is routinely used as a variable to assist in achieving proper flexion-extension gap balancing. No prior study has observed the possible effects of properly restoring the DFJL may have on ligament tension in flexion. The purpose of this computational analysis was to determine what effect the DFJL may have on ligament strains and tibiofemoral kinematics of CR knee designs in flexion. A computational analysis was performed utilizing a musculoskeletal modeling system with ligaments modeled as non-linear elastic. Tibiofemoral kinematics, contact points estimated from the femoral condyle low points, and ligament strain, change in length relative to the unloaded length, were measured at 90° knee flexion during a deep knee bend activity. Two different knee implants, a High Flexion CR (HFCR) and a Guided Motion CR (GMCR) design were used. Simulations were completed for changes in superior-inferior (SI) positioning of the femoral implant relative to the femur bone, in 2mm increments to simulate over and under resection of the DFJL.Introduction
Methods
Achieving proper ligament tension in knee flexion within posterior cruciate retaining (CR) total knee arthroplasty (TKA) has long been associated with clinical success. Ligament balance has been achieved through specific surgical technique steps. No prior study evaluated the possible effects of varying levels of posterior cruciate ligament (PCL) release on femorotibial contact location and PCL ligament strain. The purpose of this computational analysis was to determine what effect-varying levels of PCL release may have on the tibiofemoral kinematics and PCL strain. A computational analysis was performed utilizing a musculoskeletal modeling system with ligaments modeled as non-linear elastic structures and ligament insertions. A single CR knee system with two different tibial insert designs was tested, a Guided Motion (GM) and an ultra-congruent, Deep Dished (DD) design. Varying levels of PCL release were simulated by setting the stiffness of both bundles of the PCL to a percentage, ranging from 0–100% in 25% increments. Tibiofemoral kinematics was evaluated by measuring the contact points estimated from the femoral condyle low points, and ligament strain of the anterior-lateral (AL) and posterior-medial (PM) bundles. The maximum PCL strain was determined for each bundle to evaluate the risk of PCL rupture based on the PCL failure strain.Introduction
Methods
