Summary

In ACL reconstruction cases, preoperative ATS on knee extended load-bearing radiograph was greater in patients with greater knee rotational instability under anesthesia and significantly decreased from preoperatively to 3 months postoperatively.

Abstract

Introduction

Anterior cruciate ligament reconstruction (ACLR) improves anterior-posterior and rotational stability of the knee, approximating physiological motion. However, abnormal knee movement frequently persists, leading to postoperative traumatic osteoarthritis (PTOA). Objective indicators are important for accurate knee motion assessment. Manual instability tests like the Lachman (Lach) and pivot shift (PS) tests are subjective, leading to examiner bias. Anterior tibial subluxation (ATS) is an imaging-based evaluation tool for femur-tibia positioning, and MRI-based ATS in a non-load-bearing knee extension position was reported as a useful measurement. However, a limitation of this measurement is that it is non-load-bearing, and there are few reports discussing ATS under load-bearing conditions. We hypothesized that load-bearing ATS would better reflect knee instability than non-load-bearing ATS. This study aimed to investigate the relationship between knee instabilities and various ATS measures using knee-extended load-bearing radiographs.

Methods

This is a part of a prospective multicenter ACLR cohort study. Patients with preoperative and 3-month postoperative knee-extended load-bearing radiographs were included in this study. As radiographic examinations, ATS was measured at both time points, and posterior tibial slope (PTS) was measured at preoperative radiographs. Age, sex, body mass index (BMI), injury-to-surgery time, Lach, and PS data were collected from the database. Lach and PS were graded using IKDC, with grades B or lower defined as "Low grade" and C or higher as "High grade". We examined the following ATS measurement methods: The tibial bone axis was translated so that it was tangent to the medial and lateral posterior tibial and posterior femoral condyles, respectively. The distance between the medial and lateral lines was measured as ATS. ATS was evaluated at both lateral (l-ATS) and medial (m-ATS) side, and midpoint (mid-ATS) and difference (d-ATS) between lateral and medial side were calculated. Two orthopaedic surgeons measured ATS for 24 knees twice to calculate intraclass correlation coefficients (ICC) for reproducibility. Pre and postoperative ATS were compared using paired t-tests. Multiple regression analyses were conducted to identify factors associated with preoperative ATS. Each ATS was determined as the dependent variable and PTS, age, BMI, time from injury, Lach and PS, were determined as explanatory variables. Statistical significance was set at p-value < 0.05.

Results

Eighty-nine patients (47 males, 42 females; mean age 27.3 years, BMI 23.3. median time from injury 3 months) were included. ICC for ATS measurements were good to excellent (ICC ≥ 0.85), with intra and inter-rater reliability. Preoperative and 3-months postoperative ATS are as follows: l-ATS 8.4mm, 5.3mm; m-ATS 8.8mm, 6.6mm; mid-ATS 8.6mm, 6.0mm; d-ATS -0.4mm, -1.3mm. All preoperative ATS were significantly greater than postoperative ATS. Multiple regression analysis showed that every ATS was correlated with PTS. Neither of the ATS was found to be correlated with the Lach, however l-ATS and mid-ATS were correlated with PS.

Discussion And Conclusion

All 3-month postoperative ATS improved significantly from preoperative values. L- and mid-ATS were correlated with PS, suggesting that ATS could serve as a predictor of rotational knee instability. Therefore, ATS measurement in knee-extended load-bearing radiographs may be a potentially useful tool for evaluating ACLR.