Custom Total Knee Arthroplasty offers high precision in the coronal plane and a short learning curve: a retrospective cohort.

Despite increased sizing possibilities for implants in total knee arthroplasty (TKA) complications such as mechanical loosening and unexplained pain still exist. Similarly, approximately 20% of patients remain dissatisfied postoperatively. This study aims to evaluate the effectiveness and precision of the custom ORIGIN® TKA and assess the learning curve for its implementation. This retrospective, single-institution cohort study was conducted from March 2023 to June 2024. Forty-one patients with end-stage primary osteoarthritis, treated with custom TKA, were included. Primary outcomes measured alignment precision comparing the preoperative plan and the postoperative result on weightbearing full leg radiographs; secondary outcomes assessed the learning curve for operation time and alignment using cumulative summation (CUSUM) analysis. No significant differences between the planned and postoperative coronal alignment parameters were found, with a difference in means of -0.30° [95% CI: -1.40; 0.70] for HKA (P > 0.41), 0.30° [95% CI: -0.40; 1.60] for mLDFA (P > 0.43) and 0,10° [95% CI: -0.80; 1.00] for mMPTA (P > 0.75) . However, significant deviations were observed in sagittal alignment, with a difference of -2.5° [95% CI: -5.10; -0.50] and -2.7° [95% CI: -4.00; -1.70] for PDFA (P < 0.01) and PPTA (P < 0.000) respectively. This indicates a loss of tibial slope and femoral flexion compared to the preoperative plan. CUSUM analysis indicated an inflexion point in operative time after twenty- six procedures. Linear regression did not show a significant correlation between the number of cases and operative time. No learning curve for alignment could be demonstrated. Custom TKA with patient-specific instruments provides high precision in coronal alignment but shows variability in sagittal alignment. The learning curve for operative time is short, indicating the practicality of integrating this technology into surgical practice.