Abstract
The interplay between articular cartilage (AC) and subchondral bone (SB) plays a pivotal role in cartilage homeostasis and functionality. As direct connective pathways between the two are poorly understood, we examined the location-dependent characteristics of the 3D microchannel network within the SB that connects the basal cartilage layer to the bone marrow (i.e. cartilage-bone marrow microchannel connectors; CMMC). 43 measuring points were defined on five human cadaveric femoral heads with no signs of osteoarthritis (OA) (age ≤ 60), and cartilage-bone cylinders with diameters of 2.00 mm were extracted for high-resolution scanning (n = 215). The micro-CT data were categorized into three groups (load-bearing region: LBR, n = 60; non-load-bearing region: NLBR, n = 60; and the peripheral rim: PR, n = 95) based on a gait analysis estimation of the joint reaction force (young, healthy cohort with no signs of OA). At the AC-SB interface, the number of CMMC in the LBR was 1.8 times and 2.2 times higher compared to the NLBR, and the PR, respectively. On the other hand, the median Feret size of the CMMC were smallest in the LBR (55.2 µm) and increased in the NLBR (73.5 µm; p = 0.043) and the PR (89.1 µm; p = 0.043). AC thickness was positively associated with SB thickness (Pearson's r = 0.48; p < 1e-13), CMMC number. (r = 0.46; p < 1e-11), and circularity index (r = 0.61; p < 1e-38). In conclusion, our data suggest that regional differences in the microchannel architecture of SB might reflect regional differences in loading.
Highlights
It is widely accepted that osteoarthritis (OA) is a disease of the whole joint that involves articular cartilage (AC), subchondral bone (SB), as well as synovium, menisci, adjacent ligaments, and the surrounding soft tissues [1,2,3]
The 3D-reconstructed images of the SB confirmed the presence of a porous microstructure that directly connected the AC-SB interface to the trabecular spongiosa via cartilage-bone marrow microchannel connectors (CMMC)
We found a distinct distribution pattern for the CMMC based on their location on the joint
Summary
It is widely accepted that osteoarthritis (OA) is a disease of the whole joint that involves articular cartilage (AC), subchondral bone (SB), as well as synovium, menisci, adjacent ligaments, and the surrounding soft tissues [1,2,3]. Direct contact of the basal cartilage layer with deeper trabecular bone has been reported in adult non-pathological human femoral heads [14,15,16] as well as mature human knee joints [17,18,19], while components such as blood vessels, osteochondral tissues, parallel lamellar bone, woven bone fibers, fat, and other unidentified soft tissues were observed underneath such contacts [16]. SB porosity has been detected in end-stage knee OA of patients with different joint alignments, showing region-specific associations with the subchondral bone plate thickness [20]. This raises the question of the physiological and pathophysiological significance of these microchannel connectors for the overlying cartilage
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