Hayat Khizar, Marr Neil, Mak Kingston K L, Doube Michael
Jockey Club College of Veterinary Medicine and Life Sciences, City University of Hong Kong, Hong Kong, China.
Department of Comparative Biomedical Sciences, Royal Veterinary College, London, UK.
Bone Joint Res. 2025 Aug 27;14(8):735-744. doi: 10.1302/2046-3758.148.BJR-2024-0396.R1.
The osteochondral cement line (OCL) plays a key role in joint integrity by attaching articular calcified cartilage (ACC) to underlying subchondral bone (SCB), whose predominant collagens are type 2 (Col-II) and type 1 (Col-I), respectively. Previous studies report contrasting evidence of the presence of collagen fibrils in the OCL, albeit in different species and joints. If present, collagen fibrils might provide a basis for osteochondral bonding in the organic phase. We aimed to study the morphological variations of the osteochondral cement line, to observe whether cartilage and bone collagen fibrils are present in the OCL, and whether they colocalize in a manner that could help explain how ACC attaches to SCB.
We used immunofluorescence, confocal microscopy, and deconvolution to image Col-I and Col-II collagen fibrils and measure their overlap and colocalization, in OCL harvested from equine and bovine femoral head, patella, and proximal and distal metatarsal condyles. Large mammalian species were chosen to have size and pathobiology relevant to human anatomy. Thousands to millions of Col-I/-II colocalizing complexes were observed per mm² of OCL over a tissue depth of 1 to 5 µm. Kruskal-Wallis with Dunn's post-hoc tests and Mann-Whitney U tests were conducted for intra- and interspecies statistical analysis.
The areal volume (µm³/mm²) of Col-I/Col-II complexes was up to ten times greater in equine than bovine OCL (p = 0.016 to 0.029). Similarly, the number of Col-I/-II complexes and mean volume per complex differed significantly (p < 0.001 to 0.032 and p < 0.001 to 0.029, respectively) among anatomical sites between equine and bovine OCL. Gaps or tears near OCL were present uniquely in the bovine patella.
Col-I/Col-II overlap and colocalize at OCL, which could be a critical source of bond strength between cartilage and bone that should be considered when cartilage repair is attempted in clinical settings.
骨软骨黏合线（OCL）通过将关节钙化软骨（ACC）附着于下方的软骨下骨（SCB），在关节完整性中起关键作用，其中ACC和SCB的主要胶原蛋白分别是Ⅱ型胶原（Col-II）和Ⅰ型胶原（Col-I）。既往研究报道了关于OCL中胶原纤维存在情况的相互矛盾的证据，尽管研究对象为不同物种和关节。如果存在胶原纤维，其可能为有机相中骨软骨结合提供基础。我们旨在研究骨软骨黏合线的形态学变化，观察软骨和骨胶原纤维是否存在于OCL中，以及它们是否以有助于解释ACC如何附着于SCB的方式共定位。
我们使用免疫荧光、共聚焦显微镜和去卷积技术对从马和牛的股骨头、髌骨以及第一跖骨近端和远端髁采集的OCL中的Col-I和Col-II胶原纤维进行成像，并测量它们的重叠和共定位情况。选择大型哺乳动物是因为其大小和病理生物学与人体解剖学相关。在1至5μm的组织深度内，每平方毫米OCL中观察到数千至数百万个Col-I/-II共定位复合物。采用Kruskal-Wallis检验及Dunn事后检验和Mann-Whitney U检验进行种内和种间统计分析。
马的OCL中Col-I/Col-II复合物的面积体积（μm³/mm²）比牛的OCL大高达10倍（p = 0.016至0.029）。同样，马和牛的OCL在解剖部位之间，Col-I/-II复合物的数量和每个复合物的平均体积也存在显著差异（分别为p < 0.001至0.032和p < 0.001至0.029）。OCL附近的间隙或撕裂仅在牛髌骨中出现。
Col-I/Col-II在OCL处重叠并共定位，这可能是软骨和骨之间结合强度的关键来源，在临床环境中尝试软骨修复时应予以考虑。
