Ultrashort echo time T2⁎ mapping of early hip osteoarthritis: Acetabular predominance and loss of joint homeostasis.

BACKGROUND

Early diagnosis of hip osteoarthritis (OA) is hindered by the insensitivity of radiography to early biochemical changes. Ultrashort echo time (UTE) MRI allows for quantitative assessment of deep calcified cartilage, potentially identifying tissue degeneration before irreversible structural damage.

PURPOSE: To quantitatively characterize spatial topological patterns of cartilage degeneration in early hip OA (Tönnis grade 1) using UTE-T2⁎ mapping and to evaluate the loss of joint biochemical homeostasis.

STUDY TYPE: Prospective case-control study.

POPULATION: 71 hip joints from 36 participants, classified into a control group (Tönnis grade 0, n = 22) and an early OA group (Tönnis grade 1, n = 49).

FIELD STRENGTH/SEQUENCE: 3.0-T; multi-echo UTE sequence for T2⁎ mapping.

ASSESSMENT: T2⁎ relaxation times were quantified in the acetabular superior, femoral head superior, and femoral head inferior regions by a musculoskeletal radiologist (X.X.X., 10 years of experience). Joint homeostasis was characterized by spatial heterogeneity (joint coefficient of variation [CV]) and topological balance (Acetabular Ratio: acetabular superior-to-femoral inferior relaxation time).

STATISTICAL TESTS: Mann-Whitney U test, Chi-square test, Pearson correlation, multivariable logistic regression, and Variance Inflation Factor (VIF). P < .05 was considered statistically significant.

RESULTS

The early OA group exhibited significantly elevated T2⁎ values across all regions compared with controls (P < .001). Regression analysis indicated that cartilage T2⁎ elevation in early OA represented a pathological trajectory distinct from physiological aging (P = .089 for T2⁎ after age adjustment). Crucially, the early OA group demonstrated a significant loss of joint homeostasis: (a) Spatial Heterogeneity: The joint CV was markedly increased in early OA (0.36 ± 0.23 vs 0.19 ± 0.10; P < .001), reflecting a "patchy" disruption of biochemical uniformity. (b) Topological Imbalance: The physiological acetabular-to-femoral "unity ratio" (baseline ∼1.0) showed a trend toward acetabular-dominant degeneration (1.50 ± 0.91 vs 1.09 ± 0.36; P = .094).

DATA

CONCLUSION

Early hip OA is characterized by a fundamental loss of biochemical homeostasis, manifested as acetabular-predominant degeneration and significantly increased spatial heterogeneity. Quantitative UTE-MRI provides a sensitive metric for monitoring this disruption of joint equilibrium beyond simple mean value elevation.

LEVEL OF EVIDENCE: 2: Technical efficacy stage: 2.