The relationship between the survival of total knee arthroplasty and postoperative coronal, sagittal and rotational alignment of knee prosthesis

Abstract

Purpose: Our study sought to address four issues: (1) the relationship between postoperative overall anatomical knee alignment and the survival of total knee prostheses; (2) the relationship between postoperative coronal alignment of the femoral and tibial component and implant survival; (3) the relationship between postoperative sagittal alignment of the femoral and tibial components and implant survival; and (4) the relationship between postoperative rotational alignment of the femoral and tibial component and implant survival.

Methods: We reviewed 1,696 consecutive patients (3,048 knees). Radiographic and computed tomographic examinations were performed to determine the alignment of the femoral and tibial components. The mean duration of follow-up was 15.8 years (range, 11-18 years).

Results: Thirty (1.0%) of the 3,048 total knee arthroplasties failed for a reason other than infection and periprosthetic fracture. Risk factors for failure of the components were: overall anatomical knee alignment less than 3° valgus, coronal alignment of the femoral component less than 2.0° valgus, flexion of the femoral component greater than 3°, coronal alignment of the tibial component less than 90°, sagittal alignment of the tibial component less than 0° or greater than 7° slope, and external rotational alignment of the femoral and tibial components less than 2°

Conclusion: In order to improve the survival rate of the knee prosthesis, we believe that a surgeon should aim to place the total knee components in the position of: overall anatomical knee alignment at an angle of 3-7.5° valgus; femoral component alignment, 2-8.0° valgus; femoral sagittal alignment, 0-3°; tibial coronal alignment, 90°; tibial sagittal alignment, 0-7°; femoral rotational alignment, 2-5° external rotation; and tibial rotational alignment, 2-5° external rotation.

Fig. 1

The overall anatomical alignment in the coronal plane was defined as the angle between the femoral anatomical axis and the tibial anatomical axis. The tibial alignment was defined as the angle between the proximal portion of the tibial component and the tibial anatomical axis. The femoral alignment was defined as the angle between the distal portion of the femoral component and the femoral anatomical axis (α = coronal femoral angle, and β = coronal tibial angle)

Fig. 2

A lateral radiograph of the right knee shows the measurement of the sagittal alignment of the femoral and tibial components (x = sagittal femoral angle, and y = sagittal tibial angle). The posterior femoral condylar offset (CO) was evaluated by measuring the maximum thickness of the posterior condyle projected posteriorly to the tangent of the posterior cortex of the femoral shaft

Fig. 3

CT scan shows measurement of axial rotation of the femoral component in relation to the transepicondylar axis (A–A) and posterior femoral condylar line. CT scan shows measurement of axial rotation of the tibial component in relation to the posterior margins of the tibial plateau (A–A) and the tibial bearing (B–B)