Femorotibial subchondral bone area and regional cartilage thickness: a cross-sectional description in healthy reference cases and various radiographic stages of osteoarthritis in 1,003 knees from the Osteoarthritis Initiative.
OBJECTIVE
To identify structural differences in total subchondral bone area (tAB) and cartilage thickness between healthy reference knees and knees with radiographic osteoarthritis (OA).


METHODS
Baseline magnetic resonance images from 1 knee of 1,003 Osteoarthritis Initiative participants were studied: 112 healthy reference knees without radiographic OA, symptoms, or risk factors; 70 preradiographic OA knees (calculated Kellgren/Lawrence [K/L] grade 0/1); and 821 radiographic OA knees (calculated K/L grade ≥2). Means and standard (Z) scores (SD unit differences compared with normal subjects) of the tAB and regional cartilage thickness were assessed in the weight-bearing femorotibial joint and compared between groups.


RESULTS
In men, tAB was 8.2% larger in preradiographic OA knees and 6.6%, 8.1%, and 8.5% larger in calculated K/L grade 2, 3, and 4 radiographic OA knees, respectively, than in reference knees. In women, the differences were +6.8%, +7.3%, +9.9%, and +8.1%, respectively. The external medial tibia showed the greatest reduction in cartilage thickness (Z scores -5.1/-5.6 in men/women) with Osteoarthritis Research Society International medial joint space narrowing (JSN) grade 3, and the external lateral tibia (Z scores -6.0 for both sexes) showed the greatest reduction with lateral JSN grade 3. In all subregions of end-stage radiographic OA knees, ≥25% of the average normal cartilage thickness was maintained. An overall trend toward thicker cartilage was found in preradiographic OA and calculated K/L grade 2 knees, especially in the external central medial femur.


CONCLUSIONS
tABs were larger in preradiographic OA and radiographic OA knees than in healthy reference knees, and the difference did not become larger with higher calculated K/L grades. Specific subregions with substantial cartilage thickening or thinning were identified in pre-, early, and late radiographic OA.
Frobell
Richard B
RB
Paracelsus Medical University, Salzburg, Austria. richard.frobell@pmu.ac.at
Nevitt
Michael C
MC
Hudelmaier
Martin
M
Wirth
Wolfgang
W
Wyman
Bradley T
BT
Benichou
Olivier
O
Dreher
Donatus
D
Davies
Richard
R
Lee
Jennifer H
JH
Baribaud
Frédéric
F
Gimona
Alberto
A
Eckstein
Felix
F
D000368:Aged; D002358:Cartilage, Articular / Q000000981:diagnostic imaging*; D015331:Cohort Studies; D003430:Cross-Sectional Studies / Q000379:methods; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging* / Q000453:epidemiology; D011859:Radiography; D013977:Tibia / Q000000981:diagnostic imaging*