The tibial cut influences the patellofemoral knee kinematics and pressure distribution in total knee arthroplasty with constitutional varus alignment
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The current literature suggests that kinematic total knee arthroplasty (kTKA) may be associated with better outcome scores in patients with constitutional varus alignment. The underlying patellofemoral kinematic changes (patella tilting and patella tracking) and patellofemoral pressure distribution have not yet been described. The present study compared the effects of different tibial cuts, as used in kTKA, on patellofemoral knee kinematics and the pressure distribution, in addition to comparisons with the natural constitutional varus knee.
Seven cadaveric knee joints with constitutional varus alignment were examined in the native state and after 0°, 3°, or 6° tibial cut cruciate-retaining (CR)-TKA using an established knee joint simulator. The effects on patella rotation/patella tilting, patellofemoral pressure, and patellofemoral length ratios (= patella tracking) were determined. In addition, the natural knee joint and different tibial cuts in CR-TKA were compared (Student’s t test).
In the patellofemoral joint, 6° CR-TKA was associated with the greatest similarity with the natural constitutional varus knee. By contrast, knees subjected to 0° CR-TKA exhibited the largest deviations of patellar kinematics. The smallest difference compared with the natural knee joint concerning patella tilting was found for 6° CR-TKA (mean 0.4°, p < 0.001), and the largest difference was noted for 0° CR-TKA (mean 1.7°, p < 0.001). Concerning patellofemoral pressure, 6° CR-TKA resulted in outcomes most similar to the natural knee joint, featuring a mean difference of 3 MPa. The largest difference from the natural knee joint was identified for 0° CR-TKA, with an average difference of 8.1 MPa (p < 0.001; total mean 17.7 MPa). Meanwhile, 3° and 6° CR-TKA induced medialization of the patella, with the latter inducing the largest medialization value of 4.5 mm at 90° flexion.
The improved outcome parameters in kTKA described in the literature could be attributable to the similar kinematics of the patellofemoral joint relative to the normal state. The current study confirmed the similar kinematics between the native constitutional varus knee joint and knee joints subjected to 3° or 6° CR-TKA (patellofemoral rotation/patella tilting and patella pressure). Conversely, there was pronounced medialization of the patella following 6° CR-TKA. Patella pressure and patella tilting are described in the literature as possible causes of anterior knee pain after TKA, whereas medialization of the patella, which is also influenced by other causes, might play a subordinate role.
Level of evidence
V, Biomechanical study.
KeywordsKnee kinematics TKA Varus alignment Constitutional varus Kinematic TKA Patellofemoral kinematics Patellofemoral pressure
FM: planning/conception of the study, collection of data, analysis and interpretation, statistical analysis, and writing and revising article; (orthopedic surgeon). HS: collection of data, analysis and interpretation, and statistical analysis (Dr. bio. hum.). SA and DL: interpretation of data and critical revision of the article (Dr. bio. hum.). BF: critical revision of the article (attending surgeon at HSS). RH: critical revision of the article, final approval of the article, and overall responsibility (surgeon in chief University of Ulm).
Funding was provided by Deutsche Arthrosehilfe e.V.
Compliance with ethical standards
Conflict of interest
We certify that we have not signed any agreement with commercial interest related to this study, which would, in any way, limit publication of any and all data generated for the study or to delay publication for any reason. Dr. Faschingbauer reports personal fees from Deutsche Arthrosehilfe e.V. during the conduct of the study.
Ethical review committee statement
The authors’ institutional review board approved this study.
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