Reproducibility of coronal plane alignment of the knee (CPAK) using tibia-first restricted inverse kinematic...

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Medical Imaging Analysis

Background:

• The Coronal Plane Alignment of the Knee (CPAK) classification system stratifies knee alignment and joint line obliquity (JLO).
• Restricted Inverse Kinematic Alignment (RIKA) is a patient-specific surgical philosophy for total knee arthroplasty (TKA).

Purpose of the Study:

• To evaluate the reproducibility of restoring preoperative CPAK phenotypes using the tibia-first RIKA concept in TKA.
• To assess the effectiveness of robotic-assisted surgery in maintaining knee alignment.

Main Methods:

• Prospective study of 129 patients undergoing RIKA TKA with robotic assistance.
• Measurement of preoperative and postoperative lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) using X-ray imaging.
• Classification of knees into CPAK phenotypes based on arithmetic HKA (aHKA) and JLO.

Main Results:

• The mean aHKA remained stable, with preoperative -2.73° shifting to -2.83° postoperatively.
• The most common preoperative phenotypes, Type I (42.5%) and Type II (23.0%), showed varying degrees of preservation and conversion.
• Valgus phenotypes were frequently corrected to neutral types, while rare phenotypes remained uncommon.

Conclusions:

• Tibia-first RIKA surgery successfully preserves native coronal alignment in TKA.
• Robotic-assisted, imageless navigation systems are effective tools for achieving RIKA TKA.
• The tibia-first approach demonstrates validity for surgeons considering RIKA TKA.