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Objectives and questions: The treatment of extensor mechanism malalignment (EMM) in total knee arthroplasty (TKA) remains relatively unpredictable, with controversial treatment strategies and variable outcomes. The presence of pre-existing torsional abnormalities (TAs) is decisive and may significantly influence the results of different individualized TKA approaches. The concept ofRestricted Torsional Adjustment (RTA)is introduced, and its clinical & biomechanical implications are analyzed and compared with current literature.

Material and methods: The present project comprises four sections: (1) A case series demonstrating the use of RTA in patients with EMM caused by TAs. (2) A CT-based analysis of 256 native lower limbs examining the relationships between femoral torsion (FT), tibial torsion (TT), posterior condylar angle (PCA), tibiofemoral rotation (TFR), tibial tubercle–trochlear groove distance (TTTG), patellar tilt (PT), & patellar lateral shift (PLS). (3) A retrospective analysis of 70 CAS-assisted TKAs using a tibia-first FA strategy. Patellar tracking was assessed at 1 week and 1 year postoperatively. Patients with pre-existing patellar tilt ≥5° were compared with those with tilt <5°. (4) A literature review evaluating the impact of different surgical approaches & implant designs on patellar tracking, bony torsion, index of cumulative torsion (ICT), quadriceps tendon angle (QTA), and TFR. Finally, an evidence-based approach is proposed.

Results: (1) The RTA technique restored patellar maltracking and improved TAs, TFR, and ICT. (2) Correlation analysis of CT-derived parameters is presented. (3) While mobile-bearing implants initially improved patellar tracking, recurrence of patellar tilt was observed at 1 year, particularly in patients with pre-existing tilt >5°. (4) Single-radius implants demonstrate biomechanical advantages in patellar tracking due to the longer lever arm of the extensor mechanism. Medial ball-in-socket designs support medial pivoting and enhance extensor mechanism function while providing medial stability. Constrained posterior-stabilized (PS+) implants retain corrected TFR and represent a reliable option in EMM associated with TAs. Kinematic alignment (KA), especially when performed through a subvastus approach, offers several advantages for patellofemoral joint function. However, KA in the presence of pre-existing EMM due to TAs (bony or soft tissue-related) may be associated with inferior PROMs & functional outcomes.

Discussion and conclusions: In the absence of TAs, KA represent an optimal treatment strategy for patellar tracking. In more severe cases of EMM with coexisting TAs, RTA combined with fixed-bearing PS+ implants provides a reliable treatment option to improve extensor mechanism function. RTA defines the boundaries of safe external femoral rotation and higher degree of constraint (PS+ designs) retains rotational correction. Patients with EMM may benefit from preoperative torsional CT assessment to identify underlying bony or soft tissue TAs and to define individualized RTA boundaries.