Does high‐flexion total knee arthroplasty promote early loosening of the femoral component?

Abstract

High-flexion knee replacements have been developed to accommodate a large range of motion (RoM > 1208). Knee implants that allow for higher flexion may be more sensitive to femoral loosening as the knee load is relatively high during deep knee flexion, which could result in an increased failure potential at the implant-cement interface of the femoral component. A 3D finite element knee model was developed including a posterior-stabilized high-flexion knee replacement to analyze the stress state at the femoral implant-cement interface during a full squatting movement (RoM 1558). During deep flexion (RoM > 1208), tensile and shear stress concentrations were found at the implant-cement interface beneath the proximal part of the anterior flange. Particularly, the shear stresses at this interface location increased during high flexion, from a peak stress of 4.03 MPa at 908 to 6.89 MPa at 1408 of flexion. Tensile stresses were substantially lower, having a peak stress of 0.72 MPa at 1008 of flexion. Using data from earlier interface strength experiments, none of the interface beneath the anterior flange was predicted to fail in the normal flexion range (RoM 1208), whereas the prediction increased to 2.2% of the interface during deeper knee flexion. Thigh-calf contact reduced the knee forces, interface load, and failure risk beyond 140-1458 of flexion. Based on the more critical stresses at the femoral fixation site between 1208 and 1458 of flexion, we conclude that the femoral component has a higher risk of loosening at high-flexion angles. Keywords: total knee arthroplasty; high flexion; femoral loosening; finite element analysis; implant-cement interfaceThe traditional goals of total knee arthroplasty (TKA) are pain relief and restoration of normal knee function. Several clinical studies demonstrated that TKA patients receiving a standard knee replacement in general achieve maximal flexion angles limited to roughly 1208 of flexion.1 Hence, active knee patients experience limitations during activities such as squatting and kneeling.2 High-flexion TKAs have been developed to facilitate a larger post-operative range of motion (RoM > 1208). High-flexion implants are mostly based on successful standard designs with the posterior condylar geometry adapted to accommodate increased joint load occurring during deep knee flexion.In a recent follow-up study, Han et al. 3 reported a disturbingly high incidence of early femoral loosening for high-flexion TKA. They observed aseptic femoral loosening in 38% of the operated cases at a mean follow-up of 23 months. Furthermore, the occurrence of loosening was closely related to the maximal flexion angle achieved after TKA. In nearly all cases of loosening, the femoral implant-cement interface debonded, particularly beneath the anterior flange, with radiolucent lines visible on lateral radiographs. Due to this debonding process, the femoral component migrated into a position of increased flexion during deep knee bends. A similar mode of failure was earlier described by King ...

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

“…4C). A transverse notch was made in the posterior condyles to facilitate the application of a push-off force by a custom-made load applicator, in accordance with a contact normal force vector of 150°of flexion, that was found previously in an FEA study [20]. Using this method, rather than using the tibial implant to apply the load, we prevented possible sliding between the femoral and tibial implant.…”

The Distribution of Implant Fixation for Femoral Components of TKA: A Postmortem Retrieval Study

“…While traditional TKAs rarely exhibit femoral component loosening, some groups have raised concerns about loosening with younger, more active patients undergoing this procedure [3,4,7], as well as with high-flexion knees [8–11]. The disparate findings of the high-flexion knee studies suggest that component design, initial fixation at the time of surgery, and loss of fixation with in vivo service are the likely contributors to the range of loosening rates reported clinically.…”

“…For Zone 1 beneath the anterior flange, high shear stresses are also a concern, particularly in high-flexion designs [8]. Van de Groes et al [22] recommended removal of the anterior periosteum, roughening of the cortex and drilling of holes into the cortex prior to cementation in order to improve the mechanical strength of the cement-bone interface.…”

“…Without bony fixation, the implant can become unstable and migrate. In general, the tibial component loosens 2–3 times more frequently than the femoral component, but femoral component loosening is still a clinical concern, especially in younger populations [7] and with some high-flexion knees [8–11]. …”

Modern Trends in Orthopedics: The Knee Arthroplasty

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