The tibial cut influences the patellofemoral knee kinematics and pressure distribution in total knee arthroplasty with constitutional varus alignment

Abstract

PurposeThe 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. Methods 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). Results 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. Conclusions 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.

How to choose kinematic or mechanical alignment individually according to preoperative characteristics of patients?

“…The stippled lines indicate the 95% CIs. Short vertical lines on the x-axis represent individual case in the study the normal state [13]. Blakeney et al suggested KA-TKA reproduced more closely normal gait of healthy controls compared to MA-TKA due to the restoration of the individual's knee kinematics and ligament tension in KA-TKA [14].…”

“…The primary outcome was Knee Society Score (KSS) 2011 [10], including symptoms (0-25), satisfaction (0-40), expectation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), and functional activities (0-100) at the 1-year followup. Secondary outcomes included the range of motion (ROM) and the HKA angle.…”

How to choose kinematic or mechanical alignment individually according to preoperative characteristics of patients?

“…indicated KA-TKA could achieve similar kinematics of the patellofemoral joint relative to the normal state [13]. Blakeney et al suggested KA-TKA reproduced more closely normal gait of healthy controls compared to MA-TKA due to the restoration of the individual's knee kinematics and ligament tension in KA-TKA [14].…”

“…The main outcome was Knee Society Score (KSS) 2011 [10], including symptom (0-25), satisfaction (0-40), expectation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) and functional activities (0-100) at the 1-year followup. Secondary outcomes included the range of motion (ROM) and HKA angle.…”

How to choose kinematic or mechanical alignment individually according to preoperative characteristics of patients?

“…Thus, several scholars hold the view that KA-TKA may restore normal knee kinematics. Faschingbauer et al indicated KA-TKA could achieve similar kinematics of the patellofemoral joint relative to the normal state [13]. Blakeney et al suggested KA-TKA reproduced more closely normal gait of healthy controls compared to MA-TKA due to the restoration of the individual's knee kinematics and ligament tension in KA-TKA [14].…”