Improved Patient Knee Flexure Post Total Knee Replacement Surgery through Computational Analysis

The Department of Bioengineering at Clemson University has for over 50 years provided students, faculty, and research staff with exceptional opportunities for intellectual, professional, and personal growth. Guided by a faculty committed to undergraduate and graduate research experience, bioengineering students apply engineering principles to understand and treat disease. Collaboration with physicians and entrepreneurs ensure that research focuses on high-priority health care challenges. Under the direction of Department Chair, Dr. Martine LaBerge, this collaboration has been enhanced through the addition of a Clemson University-Medical of South Carolina Bioengineering Program in Charleston, SC.

Anterior knee pain is a significant complication following total knee arthroplasty (TKA) surgery. The inability to freely extend or flex the knee significantly impacts patients' daily activities such as walking, lifting, and rising from a chair. This knee movement inability is one of the most common indications of needed TKA procedure revisions. The challenge of this study was to quantitatively evaluate the effect of the patellar button thickness on the variation of the quadriceps tendon force during knee joint flexion/extension using computational analysis. A reduction in the force variation is directly related to the mitigation of anterior knee pain following TKA surgery. Poor sizing during surgery of the patellar knee component – a “button-like” element that increases the mechanical advantage of the extension force – was identified as a key issue.

The research biomechanics group in the Department of Bioengineering at Clemson University applied HyperWorks-based finite element analysis to evaluate the effect of the patella-button thickness on the variation of the magnitude of the quadriceps tendon force. Three-dimensional (3D) explicit finite element analyses were completed by Xin Xie, an Altair Fellow and doctoral student, to assess the effect of the patellar button thickness on the quadriceps force magnitude and variation. Altair HyperMesh was applied to build a detailed, 3D model of the articular knee joint. A basic 3D model was developed through MRI reconstruction of an average-sized cadaver lower extremity to represent the realistic components of the human knee joint. The cadaver tibia, femur, and patella button were resected using the specific surgical procedures specified by suppliers of total knee joint replacements. The geometry of a specific TKA device was inserted into the natural knee model and aligned using HyperMesh. Muscular and ligamentous knee connectors were modeled as isotropic, hyper elastic materials quantified by experimental testing data. A motion tracking system was employed to define the displacement boundary conditions for the tibia and femur during knee flexing and extension. Finally, using the geometrical morphing capability of HyperMesh, two additional patellar buttons with varied thickness (+-2 mm) were created, thus generating three finite element models in total. Using output from quasi-static finite element analyses of these three models, the tendon force magnitudes for each thickness case were computed.

• The study has shown that patellar component thickness has a significant effect on the quadriceps tendon force within the swing phase of a walking gait cycle. More specifically, a thicker patella after TKA surgery may tighten the quadriceps tendon, while a thinner patella may lead to dysfunction of the knee extensor mechanism due to an ineffective moment arm, thereby causing abnormal TF magnitudes. This computational analysis has provided valuable insights into the impact of patellar button thickness on the quadriceps tendon force, which can be used to improve surgical procedures and patient outcomes following TKA surgery. With further computational studies, the effect of a wider range of patellar button thicknesses on the knee joint reaction forces should be considered for achieving optimum thickness values.

• Three finite element models were created to evaluate the effect of patellar button thickness on the quadriceps tendon force.
• The peak stress occurred when the femur reached a maximum flexure angle (60°).
• The thinner patella case revealed the highest TF force among the three cases.