A patient-specific model of total knee arthroplasty to estimate patellar strain: A case study

Abstract

Background: Inappropriate patellar cut during total knee arthroplasty can lead to patellar complications due to increased bone strain. In this study, we evaluated patellar bone strain of a patient who had a deeper patellar cut than the recommended. Methods: A patient-specific model based on patient preoperative data was created. The model was decoupled into two levels: knee and patella. The knee model predicted kinematics and forces on the patella during squat movement. The patella model used these values to predict bone strain after total knee arthroplasty. Mechanical properties of the patellar bone were identified with micro-finite element modeling testing of cadaveric samples. The model was validated with a robotic knee simulator and postoperative X-rays. For this patient, we compared the deeper patellar cut depth to the recommended one, and evaluated patellar bone volume with octahedral shear strain above 1%. Findings: Model predictions were consistent with experimental measurements of the robotic knee simulator and postoperative X-rays. Compared to the recommended cut, the deeper cut increased the critical strain bone volume, but by less than 3% of total patellar volume. Interpretation: We thus conclude that the predicted increase in patellar strain should be within an acceptable range, since this patient had no complaints 8 months after surgery. This validated patient-specific model will later be used to address other questions on groups of patients, to eventually improve surgical planning and outcome of total knee arthroplasty.

Computer simulation of lumbar flexion shows shear of the facet capsular ligament

“…The FEBio software suite is well established and has been used to create finite element models of the intervertebral disc [27], glenohumeral capsule [28], and patellar ligament [29], among other biological tissues, so no additional verification of code function was deemed necessary. The model was validated by comparison with the strain versus flexion data of Ianuzzi et al [4].…”

Validation of a novel finite-element model for evaluating patellofemoral forces and stress during squatting after posterior-stabilized total knee arthroplasty

“…The patient's ability to flex their knee as much as possible from an extended leg position is often considered representative of activities of daily living and correlated with clinical results [8]. An increase in patellar loads at about 60 • flexion has been observed in simulations during squatting after TKA [8,9]. However, the role of tension in the patellar retinaculum is unspecified in these simulations.…”

Importance of trabecular anisotropy in finite element predictions of patellar strain after Total Knee Arthroplasty

“…The strains of each patella were evaluated by an isotropic and an anisotropic validated hFE model [7] , in a non-resurfaced and resurfaced patella option of TKA. The applied boundary conditions were provided by a validated musculoskeletal knee model [10] . The effect of the isotropic simplification was estimated by comparing the strain predictions with the anisotropic reference.…”

“…The position of the femur and tibia was fixed and imposed by the squat movement. The muscle forces were estimated by a validated musculoskeletal TKA model, assuming a constant body weight (800 N) [10] . The muscle forces (RF: 544 N, VI: 706 N, VL: 1216 N, VM: 778 N) were distributed according to muscles physiological crosssectional areas [11] .…”