Thickness of the bone-cartilage unit in relation to osteoarthritis severity in the human hip joint

Abstract

ObjectiveBone formation is a hallmark of osteoarthritis (OA). It has been speculated that bone formation may occur because of ossification at the bone-cartilage unit, that is, bone formation directly involving the calcified cartilage (CC). This study aimed to investigate the thickness of the CC and subchondral bone (SCB) in relation to the severity of the overlying articular cartilage (AC) degeneration.DesignWe investigated femoral heads from 20 patients with OA and 15 healthy subjects with design-based stereology using systematic uniform random sampling of the entire joint surface. This was combined with the Osteoarthritis Research Society International (OARSI) OA cartilage histopathology assessment system, thus obtaining focal OARSI grades paired with thickness measurements of AC, CC and the SCB.ResultsThe patients with OA had thicker CC (mean 159; 95% CI 144 to 177 µm) compared with the healthy subjects (mean 132; 95% CI 113 to 1550 µm; p=0.036), and this difference was even higher in areas without loss of AC thickness (OARSI grade ≤3); 187 (95% CI 164 to 214) µm vs 132 (95% CI 113 to 155) µm (p=0.001). In the patients with OA, a thicker SCB was observed in areas with loss of AC thickness (OARSI grade ≥4), but not in areas without loss of AC thickness (OARSI grade ≤3).ConclusionThe study showed that thicker CC is present in early stages of OA, suggesting that bone formation by endochondral ossification is an early phenomenon of OA. Thickening of the SCB was present, but only in areas with denuded bone. Suggesting that also appositional bone growth occurs and that it may be a consequence of changed biomechanics.

Multipotential stromal cells in the talus and distal tibia in ankle osteoarthritis – Presence, potency and relationships to subchondral bone changes

“…Previous research shows BV/TV changes are both joint and depth specific. The hip demonstrates increases in overall BV/TV in OA, but like the present study the knee does not 43,47 . Segmentation by depth showed BV/TV in the OA knee is always higher than non‐diseased tissue, suggesting different biomechanical OA‐mediated changes between knee and ankle 43,48,49 .…”

“…Comparing non‐diseased to OA tissue, the SBP of the OA‐affected talus was thicker than the tibia, opposite than in non‐diseased specimens. SBP thickening is demonstrated in OA of both ankle and other joints, so the fact that the talus thickens more so than tibia is more likely to be due to local biomechanical differences, which may determine functional responses from endogenous cells including MSCs 24,47 . Overall BV/TV did not change in OA, but depth‐dependent analysis revealed higher BV/TV in the first 1 mm than healthy, and lower BV/TV after 2 mm, more drastically in the talus than the tibia.…”

Age-related alterations of articular cartilage in pituitary adenylate cyclase–activating polypeptide (PACAP) gene–deficient mice

“…It is known that increased thickness of calcified cartilage can be detected in hip joints in early stages of OA (Hartlev et al 2018). In knee joints of aged PACAP KO mice, significant thickening of articular cartilage and subchondral bone, along with decreased metachromasia, was our most obvious histological observation.…”

Histomorphometric case-control study of subarticular osteophytes in patients with osteoarthritis of the hip

“…Immediately after the removal, the femoral heads were fixed in 70% ethanol and then processed according to stereological sampling of vertical uniform random sections [17], previously described in detail [16,[18][19][20]. In brief: the entire femoral heads were rotated around a vertical axis, which was perpendicular to the anatomical top of the femoral head.…”