Effects of T 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 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 maps, co-registered to Cube, underwent an atlas-based algorithm to quantify femoral and acetabular subregional (R-R) cartilage T. For knee Cube, a combination of V-Net architectures was used to segment the patellar cartilage and subregions (DM, DL, SM, SL). T values were computed from co-registered MAPSS.

Statistical Tests: For Intra-and-Inter-limb, 5 optimum predictors out of 13 (Hip subregional T, age group, gender) were selected by univariate linear-regression, to predict outcome (patellar T). 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) selected via ANOVA, were tested with DM, SM, SL, and DL subregional-mean T. LME assumptions were verified (normality of residuals, random-effects, and posterior-predictive-checks).

Results: LME-model (Intra-limb) had significant negative and positive fixed-effects of femoral-R and acetabular-R T, respectively (conditional-R = 0.581). LME-model (Inter-limb) had significant positive fixed-effects of femoral-R T (conditional-R = 0.26).

Data Conclusion: Significant positive and negative T 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.