To investigate the feasibility and therapeutic effect of total knee arthroplasty (TKA) with cruciate-retaining (CR) prosthesis by using FEM-X1 femoral extramedullary positioning instrument based on the theory of restricted kinematic alignment (rKA).

Thirty five cases who underwent total knee arthroplasty in Nanjing Drum Tower Hospital from November 2019 to December 2020 were retrospectively analyzed, including 7 males and 28 females with an average age of 71± 8 years (ranging from 55 to 85 years) Following the guidance of rKA alignment, the FEM-X1 femoral extramedullary positioning instrument was used for TKA with CR prosthesis. Before the operation, the full-length lower limb radiographs of both anteroposterior and lateral views were taken in a standing position for preoperative assessment of lateral distal femoral angle (LDFA), the medial proximal tibial angle (MPTA) and hip-knee-ankle angle (HKA). According to the principle of rKA alignment, the target LDFA, MPTA and HKA were calculated. The proximal end of tibia and distal end of femur were cut using extramedullary positioning instrument respectively. The posterior femoral condyle was cut according to the tibial plateau and mediolateral soft tissue tension. The prosthesis was installed after osteotomy. The release of collateral ligaments, PCL function, release of PCL, patellofemoral trajectory, release of patellofemoral support band, the amount of blood loss and time of operation were recorded. Postoperative LDFA, MPTA, HKA, and posterior slope angle of tibial prosthesis were measured on X-ray images. The Knee Society Score (KSS) was used for functional evaluation.

Thirty five cases of TKA with CR prosthesis following rKA alignment were successfully completed. The operation time was 100 (90, 110) min, and the blood loss was 100 (100, 200) ml. 30 of them were followed up for 12.5±0.7 months (ranging from 12 to 14 months). The pre-operative and post-operative LDFA were 1.0°(-2.0°, 4.0°), 0°(-2.0°, 2.0°), MPTA were -4.0°(-5.0°, -1.0°), -2.0°(-3.0°, -1.0°), HKA were -3.0°(-3.0°, -1.0°), -2.0°(-3.0°, -1.0°). There was no significant difference between the three angles before and after operation (Z=-0.89, P=0.372; Z=1.87, P=0.061; Z=1.03, P=0.302). The average posterior tibial slope was 5°(3°, 7°). At the follow-up of one year, the KSS clinical score was 94(92, 97) and functional score was 80(70, 90) in 30 cases. During the operation, PCL was released in 1 case because of excessive tension; and lateral retinacular release was performed in 1 case because of poor patellofemoral track.

ITKA with CR prosthesis by using the extramedullary positioning instrument on the theory of rKA alignment showed a good clinical outcome at a short follow up.

Arthroplasty, replacement, knee; Fiducial markers; Restricted kinematic alignment