Abstract
Introduction
The patella experiences large forces and variable kinematic patterns throughout flexion which could influence function and patient satisfaction after a total knee arthroplasty (TKA). Therefore, the objective of this study is to analyze in vivo patellar mechanism forces and kinematics throughout flexion to determine influencing factors that may lead to patient dissatisfaction.
Methods
Fifty subjects were evaluated in this study, 40 having a Journey II bi-cruciate stabilized (BCS) TKA and 10 having normal, healthy knees. Similar demographics were controlled for each group. Each subject performed a deep knee bend. Kinematics were evaluated using a validated 3D-to-2D fluoroscopic technique while forces were determined using a validated inverse mathematical knee model. A two-tailed t-test was used to evaluate statistical significance.
Results
Subjects averaged 2.96 ± 0.30 xBW and 2.82 ± 0.27 xBW of maximum femorotibial contact forces, 4.07 ± 0.39 xBW and 3.30 ± 0.55 xBW of maximum quadriceps forces, and 4.20 ± 0.94 xBW and 3.94 ± 0.67 xBW of maximum patellofemoral forces for the BCS and normal groups, respectively. Therefore, the TKA subjects in this study experienced larger, but similar forces compared to the normal subjects. For both groups, lateral condylar rollback was correlated with both femorotibial contact forces (p<0.0001) and quadriceps forces (p<0.0002). Higher patellotibial tilt was correlated with lower patellofemoral contact forces (p=0.0294).
Conclusion
Most TKAs resect the ACL and only substitute for the PCL in PS TKAs, but BCS subjects may receive an advantage for ACL substitution as they experienced normal-like kinematic and kinetic patterns. The lone exception seems to be the quadriceps forces which were higher in the BCS TKA group. This could be influenced by femoral condylar shape, leading to earlier quadriceps wrapping.
