2017 ISAKOS Biennial Congress ePoster #1239

 

Inter-Observer Reproducibility of Measurements of Tibial Axial Rotation Using Akagi’S Line in Knee Osteoarthritis

Yuki Takahashi, MD, Jyoetsu JAPAN
Takayuki Murayama, MD, PhD, Joetsu JAPAN
Katsumitsu Arai, MD, PhD, Joetsu JAPAN

Niigata Prefectural Centrak Hospital, Joetsu, Niigata , JAPAN

FDA Status Not Applicable

Summary

In our investigation of the inter-observer reproducibility of measurement of Akagi’s line in the knee osteoarthritis, it was revealed that there was a possibility of error in the measurements among surgeons although the inter-observer reliability was almost perfect.

Abstract

Introduction

Proper component rotational alignment in total knee arthroplasty (TKA) is essential for good outcome. Several anatomic markers have been defined as rotational reference points in TKA. There is not sufficient consensus of opinion regarding defined tibial references. Akagi et al. described an anteroposterior axis, which is the line connecting the midpoint of posterior cruciate ligament (PCL) attachment to the medial border of the patellar tendon at the attachment level (Akagi’s line). This axis is reportedly perpendicular to the femoral SEA, and reproducible in normal knees without knee osteoarthritis (OA). However, detail about reproducibility of measurement of the Akagi’s line in knee OA has not been reported. The aim of this study was to evaluate the inter-observer reproducibility of measurement of Akagi’s line.

Methods

Fifty consecutive patients (39 females and 11 males) with a mean age of 77.0 years who underwent primary unilateral TKA were enrolled in this study. CT scans of the whole length of the femur and tibia were obtained for each subject at 1 mm intervals. Using 3D visualization and modeling software, the femoral and tibial anatomical coordinate system was established. First, the observer (A) established SEA, and then the Akagi’s line was established by the two observers (A, B). The SEA and Akagi’s line were projected onto the femoral axial plane, and the angle between the two lines was measured. The inter-observer agreement was quantified by calculating the mean difference between the two observers and the standard deviation of this difference. Subsequently, the 95% limits of agreement were calculated according to the method of Bland and Altman. In addition, the frequency of agreement of the observers within 5° and 10° were calculated. Inter-observer reliability was quantified by means of the intraclass correlation coefficient (ICC).

Results

The observers had similar measurements of the SEA-Akagi angle. The mean difference between the observers was 1.2 ± 4.0° (95% coefficient interval: 0.1 – 2.4°). There seemed to be a systematic bias because the 95% coefficient interval of the difference between the observers did not include 0°. The lower and upper limits of agreement were -4.6° and 7.1°, respectively. The percentage agreement within 5° and 10° for these measurements were 80% and 98%, respectively. The inter-observer reliability was almost perfect (ICC = 0.85).

Discussion

The most important finding in our study was that there was a systematic bias in the measurements of the Akagi’s line. Difference in experience of the surgery and preoperative planning using the visualization and modeling software seemed to be the most likely cause of this bias. Like previous study of normal knee, the inter-observer reliability of the measurements of the Akagi’s line in knee OA was almost perfect in this study. However, there is a possibility of error in the measurements of the Akagi’s line among surgeons.