A Retrospective Comparative Study of Ultrasound-guided Extramedullary Kinematic Alignmentin Total Knee Replacement

Accurate hip-knee-ankle (HKA) alignment plays a crucial role in the success of total knee replacement (TKR). Kinematic alignment (KA) aims to restore the patient's natural joint anatomy to improve postoperative function and satisfaction. Ultrasound, a noninvasive and real-time imaging technique, can identify the center of the femoral head (COFH) and enhance surgical alignment accuracy. This study aimed to evaluate whether ultrasound-guided COFH identification improves postoperative HKA alignment accuracy in KA-based TKR.

A retrospective analysis of 217 patients who underwent primary TKR at Show Chwan Memorial Hospital (2020-2022) was performed. Patients were divided into a calipered group (without ultrasound) and an ultrasound-guided group. Postoperative alignment and HKA angles were compared between the groups using radiographic measurements and statistical analysis.

The ultrasound-guided group demonstrated significantly improved alignment, with 91.6% of patients achieving postoperative HKA within the safe range (-4° valgus to +5° varus) compared to 81.1% in the calipered group (p=0.029). Moreover, the ultrasound-guided technique reduced the risk of postoperative varus cross-over to valgus by 59%.

Ultrasound-guided COFH identification significantly enhances the accuracy of KA-based TKR, particularly in neutral-type osteoarthritis knees. This noninvasive and real-time approach serves as a valuable adjunct for improving alignment precision and clinical outcomes.