Patient Perception of Lower-Limb Straightness at One Week After Unrestricted Kinematically Aligned Total Knee Arthroplasty: Exploring the Concept of “Inherent Straightness”

<b>Background/Objectives:</b> Mechanical neutrality has long been regarded as the principal alignment target in total knee arthroplasty (TKA). However, radiographic neutrality does not necessarily reflect physiological morphology or patient perception. This study aimed to evaluate one-week postoperative patient-perceived lower-limb straightness after unrestricted kinematic alignment (KA) TKA and to examine its relationship with radiographic alignment parameters and functional findings. <b>Methods:</b> A total of 175 patients (203 knees) who underwent unrestricted KA-TKA were retrospectively reviewed. Pre- and postoperative radiographs, clinical assessments, and a study-specific, non-validated questionnaire were analyzed one week postoperatively. Patient perception of straightness was assessed using the Straightness Visual Analog Scale (S-VAS) and the Straightness Satisfaction Visual Analog Scale (SS-VAS). Radiographic parameters included the hip-knee-ankle angle (HKAA), the medial proximal tibial angle (MPTA), the mechanical lateral distal femoral angle (mLDFA), the joint line convergence angle (JLCA), and Coronal Plane Alignment of the Knee (CPAK) patterns. Correlative analyses between VAS scores and radiographic and clinical parameters were examined. <b>Results:</b> Preoperatively, 85% of knees were perceived as bowed, and all were reported as straight after surgery. Among knees not perceived as bowed preoperatively, 60% were newly perceived as straight postoperatively, while 40% remained perceived as straight. Postoperative satisfaction was high (S-VAS 88.9 ± 11.6; SS-VAS 92.3 ± 12.9). Associations between S-VAS/SS-VAS and HKAA were weak but statistically significant, whereas both showed moderate positive correlations with postoperative knee extension (S-VAS r = 0.54; SS-VAS r = 0.59). <b>Conclusions:</b> At one week after surgery, patients tended to perceive lower-limb straightness as being associated with restoration of physiological morphology and improved knee extension rather than with radiographic mechanical neutrality. Patient-perceived straightness reflects an individualized and natural sense of limb alignment ("inherent straightness") and should be interpreted as an exploratory, patient-centered concept based on an early postoperative test, supporting a personalized framework for alignment evaluation in unrestricted KA-TKA.