Effects of T 1p Characteristics of Load-Bearing Hip Cartilage on Bilateral Knee Patellar Cartilage Subregions: Subjects With None to Moderate Radiographic Hip Osteoarthritis.

Background: The polyarticular nature of Osteoarthritis (OA) tends to manifest in multi-joints. Associations between cartilage health in connected joints can help identify early degeneration and offer the potential for biomechanical intervention. Such associations between hip and knee cartilages remain understudied.
Purpose: To investigate T _1p associations between hip-femoral and acetabular-cartilage subregions with Intra-limb and Inter-limb patellar cartilage; whole and deep-medial (DM), deep-lateral (DL), superficial-medial (SM), superficial-lateral (SL) subregions.
Study Type: Prospective.
Subjects: Twenty-eight subjects (age 55.1 ± 12.8 years, 15 females) with none-to-moderate hip-OA while no radiographic knee-OA.
Field Strength/sequence: 3-T, bilateral hip, and knee: 3D-proton-density-fat-saturated (PDFS) Cube and Magnetization-Prepared-Angle-Modulated-Partitioned-k-Space-Spoiled-Gradient-Echo-Snapshots (MAPSS).
Assessment: Ages of subjects were categorized into Group-1 (≤40), Group-2 (41-50), Group-3 (51-60), Group-4 (61-70), Group-5 (71-80), and Group-6 (≥81). Hip T _1p maps, co-registered to Cube, underwent an atlas-based algorithm to quantify femoral and acetabular subregional (R ₂ -R ₇ ) cartilage T _1p . For knee Cube, a combination of V-Net architectures was used to segment the patellar cartilage and subregions (DM, DL, SM, SL). T _1p values were computed from co-registered MAPSS.
Statistical Tests: For Intra-and-Inter-limb, 5 optimum predictors out of 13 (Hip subregional T _1p , age group, gender) were selected by univariate linear-regression, to predict outcome (patellar T _1p ). The top five predictors were stepwise added to six linear mixed-effect (LME) models. In all LME models, we assume the data come from the same subject sharing the same random effect. The best-performing models (LME-model _best ) selected via ANOVA, were tested with DM, SM, SL, and DL subregional-mean T _1p . LME assumptions were verified (normality of residuals, random-effects, and posterior-predictive-checks).
Results: LME-model _best (Intra-limb) had significant negative and positive fixed-effects of femoral-R ₅ and acetabular-R ₂ T _1p , respectively (conditional-R ²  = 0.581). LME-model _best (Inter-limb) had significant positive fixed-effects of femoral-R ₃ T _1p (conditional-R ²  = 0.26).
Data Conclusion: Significant positive and negative T _1p associations were identified between load-bearing hip cartilage-subregions vs. ipsilateral and contralateral patellar cartilages respectively. The effects were localized on medial subregions of Inter-limb, in particular.
Evidence Level: 1 TECHNICAL EFFICACY: Stage 1.
(© 2023 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)