Better forgotten joint scores when the angle of the prosthetic trochlea is lateral to the quadriceps vector in kinematically aligned total knee arthroplasty

Abstract

PurposeThe primary aim was to analyze unrestricted kinematic alignment (unKA) total knee arthroplasty (TKA) and determine the frequency of medial deviation of the prosthetic trochlear angle (PTA) of the femoral component relative to the quadriceps vector (QV) that terminates at the anterior inferior iliac spine (AIIS), and whether patients with medial deviation had a worse Forgotten Joint Score (FJS) and Oxford Knee Score (OKS) relative to those with lateral deviation. The secondary aim was to determine the frequency of medial deviation for mechanical alignment (MA) TKA simulations. Methods From a database of a single surgeon, the study extracted de-identified data on 147 patients with a CT scanogram showing the pelvis and AIIS, a limb with an unKA TKA, and a native (i.e., healthy) opposite limb. On the scanogram, an examiner, blinded to the PROMs, measured the PTA-QV angle on the unKA TKA and on the opposite limb simulated MA TKA by drawing the PTA at 6° valgus relative to the femoral mechanical axis and measuring the PTA-QV angle. Results Medial deviation of the PTA occurred in 86% of patients with unKA TKA, and the 126 with medial deviation had a 17/1 point worse median FJS/OKS than the 21 with lateral deviation at a mean follow-up of 47 ± 8 months, respectively (p < 0.0001, p = 0.0053). In addition, 21%, 17%, and 8% of MA TKA had medial deviation after radiographic simulation using reported surgical errors for manual, patient-specific, and robotic instrumentation, respectively. Conclusion In most patients with unKA TKA and a smaller proportion with MA TKA, a PTA of 6° valgus was medial to the QV, which, by excluding the patient's Q-angle, might alter patellofemoral kinematics like an incorrectly oriented trochleoplasty. The 17-point worse FJS in the patients with an unKA TKA and medial deviation of the PTA suggests the surgical target should be to orient the PTA lateral to the QV. Level of evidence IV.

Definition of normal, neutral, deviant and aberrant coronal knee alignment for total knee arthroplasty

“…Personalised medicine has arrived in total knee arthroplasty (TKA) [1,2]. Personalised alignment methods such as kinematic alignment, functional alignment and customised patient specific TKA are intensively debated at meetings and in the current literature [3][4][5][6][7][8][9][10][11]. Fostered by the knee phenotype concept and the findings of several large database studies, there has been considerable discussion about what we consider as normal, abnormal and pathological alignment [3,4,[12][13][14][15].…”

Superiority of kinematic alignment over mechanical alignment in total knee arthroplasty during medium‐ to long‐term follow‐up: A meta‐analysis and trial sequential analysis

“…Notably, despite the belief among scholars that KA may lead to a better ‘forgotten knee’, the results suggested no difference between these two groups [5, 41]. Nevertheless, the FJS within the KA group itself exhibited significant variations, which may be attributed to several factors, including prosthetic trochlear angle and the choice of prosthesis [6, 12]. Therefore, whether KA can create a better ‘forgotten knee’ remains a subject for further research.…”

Caliper‐verified unrestricted kinematically aligned total knee arthroplasty in Asian patients showed efficacious mid‐ to long‐term results regardless of postoperative alignment categories

“…Especially with conventional (not patient-specific implant) implants, there was a report that setting the femoral component designed for MATKA tangent to the native distal and posterior joint lines increases contact stress and instability in the patellofemoral compartment [10]. Additionally, in a recent study analysing 147 patients who have undergone unKATKA with conventional implants, most patients had medially placed prosthetic trochlear grooves compared to the quadriceps vector, which showed worse forgotten joint scores compared to the laterally placed prosthetic trochlear groove [7]. However, in our study, there were no patients with clinical or radiological findings of patellofemoral joint complications (anterior knee pain, clinical/radiological instability).…”