T2 Clusters Are More Sensitive Than Mean T2 Change to Detect Early and Longitudinal Changes in Anterior Cruciate Ligament Reconstructed and Healthy Knees.

Abstract

Background: Post-traumatic osteoarthritis (PTOA) often follows anterior cruciate ligament reconstruction (ACLR), leading to early cartilage degradation. Change in mean T₂ fails to capture subject-specific spatial-temporal variations, highlighting the need for robust quantitative methods for early PTOA detection and monitoring.

Purpose/hypothesis: Develop and apply 3D T₂ cluster analysis to ACLR and healthy knees over 2.5 years.

Study type: Longitudinal case-control study.

Subjects: ACLR and contralateral knees of 15 subjects (9 male/6 female, 37.7 ± 10 years) and right knee of 15 matched controls (9 male/6 female, 37.1 ± 12 years) were scanned at 3 weeks, 3, 9, 18, and 30 months post-ACLR.

Sequence: 3 T Quantitative double echo steady state sequence.

Assessment: "T₂ cluster analysis" was developed, incorporating registration and thresholding methods to identify and quantify elevated T₂ regions (T₂ clusters, T₂C) in femoral cartilage. Percentage of cartilage covered by T₂ clusters (T₂C_%), mean cluster size (T₂C_size), the number of clusters (T₂C_count), and ΔT₂Mean (change in mean femoral cartilage T₂ relative to visit 1) were computed for all knees.

Statistical tests: A linear mixed model assessed knee, time, and knee-time interaction effects on each outcome metric (P < 0.05), with effect sizes (η_p ²) describing the sensitivity of these effects to longitudinal changes.

Results: T₂C_% (η_p ² = 0.22), T₂C_size, (η_p ² = 0.14), and T₂C_count (η_p ² = 0.51) showed significant and systematic difference between knees (ACLR > contralateral > control). T₂C_% (η_p ² = 0.24), T₂C_size (η_p ² = 0.17), and T₂C_count (η_p ² = 0.11) showed significant longitudinal change across all knees. Specifically, ACLR knees exhibited a significant increase in T₂C_% (η_p ² = 0.21), T₂C_size (η_p ² = 0.13), and a decrease in T₂C_count (η_p ² = 0.07) with time. ΔT₂Mean showed significant difference between knees (η_p ² = 0.15), increase with time (η_p ² = 0.04), with no significant knee-time interaction (η_p ² = 0.00, P = 0.772 [contralateral], P = 0.482 [control]).

Conclusion: T₂C metrics are more sensitive than ΔT₂Mean for longitudinal monitoring of femoral cartilage post ACLR. Our findings suggest potential merging of T₂ clusters overtime, forming larger areas of cartilage degradation in ACLR knees.

Level of evidence: 1 TECHNICAL EFFICACY: Stage 2.