Frontal Plane Knee Mechanics and Early Cartilage Degeneration in People With Anterior Cruciate Ligament Reconstruction: A Longitudinal Study

Abstract

Background: Abnormal frontal plane gait mechanics are known risk factors for knee osteoarthritis, but their role in early cartilage degeneration after anterior cruciate ligament reconstruction (ACLR) is not well understood. Hypothesis/Purpose: The objective was to evaluate the association of frontal plane gait mechanics with medial knee cartilage magnetic resonance (MR) relaxation times over 1 year in patients with ACLR and controls. It was hypothesized that (1) there will be an increase in frontal plane medial knee loading and medial knee MR relaxation times over time in the patients with ACLR, and (2) increases in frontal plane medial knee loading will be associated with an increase in medial knee MR relaxation times.

Study design: Case-control study; Level of evidence, 3.

Methods: Patients with ACLR (n = 37) underwent walking gait analyses and bilateral quantitative MR imaging (MRI) before surgery and at 6 and 12 months after ACLR. Healthy control participants (n = 13) were evaluated at baseline and 12 months. Gait variables included peak knee adduction moment (KAM), KAM impulse, and peak knee adduction angle. MRI variables included medial femur and medial tibia whole compartment and subregional T_1ρ and T₂ relaxation times. Statistical analyses included a comparison of changes over time for gait and MRI variables, correlations between changes in gait and MRI variables over time, and differences in change in MRI variables in patients who showed an increase versus decrease in KAM impulse.

Results: There were significant increases in medial T_1ρ (Δ 4%-11%) and T₂ (Δ 2%-10%) relaxation times from baseline to 6 months for both knees in the ACLR group and in KAM (Δ 13%) for the injured knee. From baseline to 6 months, patients who had an increase in KAM impulse in the injured knee had a greater increase in medial T_1ρ and T₂ relaxation times as compared with those who did not have an increase in KAM impulse. Longitudinal changes for the control group were not significant.

Conclusion: There is an increase in medial knee relaxation times over the first 6 months after ACLR. People with an increase in medial knee loading show an increase in medial knee relaxation times when compared with those who do not have an increase in medial knee loading over the first 6 months.

Keywords: ACL; MRI; cartilage; gait; osteoarthritis.

Figure 1:

Medial knee compartments for MR relaxation time quantification. Global MF and MT consisted of the entire cartilage of medial femur and medial tibia including all shown subregions. The weight-bearing subregions were defined using the boundaries of the anterior and posterior meniscus horns. Hence, cMF-a and aMT were the cartilage regions of the MF and MT respectively adjacent to the anterior horn of the medial meniscus. The cMF-c and cMT subregions were the cartilage on cartilage regions of the MF and MT respectively. The cMF-p and pMT were the cartilage subregions of the MF and MT respectively adjacent to the posterior horn of medial meniscus. The pMF subregion was the posterior region of MF that is not considered weight-bearing.

Figure 2:

Frontal plane gait variables over-time for the injured (black column), uninjured (grey column), and control (white column) knees. *indicates a significant difference.

Figure 3.

Medial Femur T_1ρ (top) and T₂ (bottom) relaxation times over-time in the Control group. None of the changes between BL and 12M were significant.