Effects of T1p Characteristics of Load‐Bearing Hip Cartilage on Bilateral Knee Patellar Cartilage Subregions: Subjects With None to Moderate Radiographic Hip Osteoarthritis

Abstract

BackgroundThe 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.PurposeTo investigate T1p 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 TypeProspective.SubjectsTwenty‐eight subjects (age 55.1 ± 12.8 years, 15 females) with none‐to‐moderate hip‐OA while no radiographic knee‐OA.Field Strength/Sequence3‐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).AssessmentAges 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 T1p maps, co‐registered to Cube, underwent an atlas‐based algorithm to quantify femoral and acetabular subregional (R2–R7) cartilage T1p. For knee Cube, a combination of V‐Net architectures was used to segment the patellar cartilage and subregions (DM, DL, SM, SL). T1p values were computed from co‐registered MAPSS.Statistical TestsFor Intra‐and‐Inter‐limb, 5 optimum predictors out of 13 (Hip subregional T1p, age group, gender) were selected by univariate linear‐regression, to predict outcome (patellar T1p). 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‐modelbest) selected via ANOVA, were tested with DM, SM, SL, and DL subregional‐mean T1p. LME assumptions were verified (normality of residuals, random‐effects, and posterior‐predictive‐checks).ResultsLME‐modelbest (Intra‐limb) had significant negative and positive fixed‐effects of femoral‐R5 and acetabular‐R2 T1p, respectively (conditional‐R2 = 0.581). LME‐modelbest (Inter‐limb) had significant positive fixed‐effects of femoral‐R3 T1p (conditional‐R2 = 0.26).Data ConclusionSignificant positive and negative T1p 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 Level1Technical EfficacyStage 1