[Impact of coronal plane alignment of knee phenotype alteration on short-term effectiveness in robot-assisted total knee arthroplasty]

To investigate effect of coronal plane alignment of the knee (CPAK) phenotype alteration on patient-reported outcome measures (PROMs) and functional outcomes in patients undergoing robot-assisted total knee arthroplasty (RA-TKA).

The clinical data of 108 patients who underwent unilateral RA-TKA between December 2024 and June 2025 and met the inclusion criteria were retrospectively analyzed. The cohort included 34 males and 74 females, with an average age of 68.8 years (range, 54-83 years). General data including age, gender, body mass index (BMI), and operative side were collected. PROMs included the Western Ontario and McMaster University Osteoarthritis Index (WOMAC), Knee Society Score (KSS), and Forgotten Joint Score-12 (FJS-12). Functional outcomes included range of motion (ROM) and angle of knee extension lag. Based on full-length lower extremity X-ray films, the mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were measured, and the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) were calculated. The CPAK phenotype was determined according to the classification proposed by MacDessi et al. Patients were grouped into a CPAK consistent group and a CPAK changed group based on pre- and post-operative CPAK phenotypes, and the PROMs, functional outcomes, and radiographic parameters were compared. Multiple linear regression analysis was used to examine the independent association between CPAK phenotype change and the improvement in WOMAC scores.

Among the 108 patients, the CPAK phenotype remained unchanged in 70 cases (64.8%, CPAK consistent group) and changed in 38 cases (35.2%, CPAK changed group). There was no significant difference between the two groups in age, gender, BMI, operative side, or preoperative WOMAC score, KSS score, ROM, and aHKA ( P>0.05), whereas preoperative JLO showed a significant difference between groups ( P<0.05). Univariate analysis demonstrated significant differences between groups at 3 months postoperatively in WOMAC, KSS, and FJS-12 scores, as well as in the changes of WOMAC score, KSS score, and ROM ( P<0.05); moreover, the improvements in these parameters were superior in the consistent group compared to the changed group. There was no significant difference in postoperative ROM, angle of knee extension lag, mLDFA, mMPTA, JLO, aHKA, and the change of aHKA between groups ( P>0.05). Multiple linear regression analysis revealed that CPAK phenotype change was a risk factor for improvement in WOMAC scores at short-term stage ( P<0.05).

Preservation of the preoperative CPAK phenotype after RA-TKA is associated with superior improvement in PROMs at short-term stage.