Histological analysis of the spatio‐temporal development of porcine knee cartilage in embryonic and early postnatal stages

Abstract Background Research on articular cartilage development provides a foundation for the repair and regeneration of cartilage following injury. Methods In this study, eight embryonic time points were selected: embryonic days 30 (E30), E35, E45, E55, E75, E85, E90, and E100, along with knee joints from newborn (P0) and 30 day old (P30) piglets. The dynamic developmental characteristics of knee cartilage were systematically analyzed by Safranin O‐Fast Green, Toluidine blue, and Masson staining. Results The results indicate that the mesenchymal condensation (interzone) of the knee joint has formed by embryonic day 30 (E30), marking the initiation of joint development. Chondrification commences in the diaphyses of the femur and tibia, establishing the foundation for primary ossification in femur and tibia regions at E35. By E45, the epiphyseal cartilage cells have distinctly differentiated into two morphologically distinct populations, round epiphyseal chondrocytes and spindle‐shaped growth plate chondrocytes. At E55, cartilage canals begin to emerge in the cartilage zone. The number of cartilage canal and chondrocytes progressively increase from E75 to E90. Growth plate chondrocytes progressively differentiate from a disorganized, undifferentiated state into a highly organized, spindle‐shaped, columnar array. The secondary ossification center of the knee joint appears at E100, concomitant with hypertrophy of adjacent chondrocytes and resorption of cartilage canals. From postnatal day 0 (P0) to P30, the secondary ossification center undergoes progressive peripherally expansion. By P30, partial chondrocytes display reduced Safranin O staining intensity, indicative of diminished extracellular matrix secretion. By P30, secondary ossification has progressed sufficiently to replace the cartilaginous zone proximal to the growth plate with mineralized tissue. The growth plate becomes completely separated from the epiphyseal cartilage zone, marking the completion development of growth plate. Conclusions This study dynamically charts the developmental process of the knee joint cartilage from the embryonic stage to postnatal life, revealing key developmental events including the origin of knee joint development, chondrification, primary ossification, secondary ossification, formation of the cartilage canals and growth plate. The results provide foundational material for research in cartilage tissue engineering and regenerative medicine.