Properties of Cartilage-Subchondral Bone Junctions: A Narrative Review with Specific Focus on the Growth Plate

Abstract

Objective: The purpose of this narrative review is to summarize what is currently known about the structural, chemical, and mechanical properties of cartilage-bone interfaces, which provide tissue integrity across a bimaterial interface of 2 very different structural materials. Maintaining these mechanical interfaces is a key factor for normal bone growth and articular cartilage function and maintenance.

Materials and methods: A comprehensive search was conducted using Google Scholar and PubMed/Medline with a specific focus on the growth plate cartilage-subchondral bone interface. All original articles, reviews in journals, and book chapters were considered. Following a review of the overall structural and functional characteristics of the physis, the literature on histological studies of both articular and growth plate chondro-osseous junctions is briefly reviewed. Next the literature on biochemical properties of these interfaces is reviewed, specifically the literature on elemental analyses across the cartilage-subchondral bone junctions. The literature on biomechanical studies of these junctions at the articular and physeal interfaces is also reviewed and compared.

Results: Unlike the interface between articular cartilage and bone, growth plate cartilage has 2 chondro-osseous junctions. The reserve zone of the mature growth plate is intimately connected to a plate of subchondral bone on the epiphyseal side. This interface resembles that between the subchondral bone and articular cartilage, although much less is known about its makeup and formation.

Conclusion: There is a notably paucity of information available on the structural and mechanical properties of reserve zone-subchondral epiphyseal bone interface. This review reveals that further studies are needed on the microstructural and mechanical properties of chondro-osseous junction with the reserve zone.

Keywords: biomechanics; elemental analysis; growth plate cartilage; mammillary processes; subchondral bone plate.

Figure 1.

Growth plate images of a bovine (12- to 18-month) growth plate: (a) scanning electron microscopy (SEM) image and (b) light microscopy image, stained with hematoxylin and eosin (H&E). Red arrows show the intact chondrons within the proliferative zone, red arrow heads demonstrate tears between neighboring chondrons. SB, subchondral bone; BV, blood vessel; RZ, reserve zone; PZ, proliferative zone; HZ, hypertrophic zone; MP, metaphysis. From the authors’ laboratory.

Figure 2.

Scanning electron microscopy (SEM; Philips SEM 515) images of a yearling bovine proximal tibial growth plate. (A) Freeze-fracture sample showing fractured chondrons (bottom half of image) and the underneath exposed surface (top half of image) of the reserve zone from which clusters of chondrons have been torn. Torn blood vessels can be seen passing through the reserve zone. (B) Higher magnification of red rectangular area in (A), red arrows showing blood vessels. (C) Surface of the subchondral bone and remaining calcified cartilage following digestion of organic matrix with 3% sodium hypochlorite to expose the pores for blood vessels. (D) Higher magnification of (C), view of a subchondral bone pore following sodium hypochlorite treatment. Several pores to side channels can be seen deeper inside the middle pore. (E) Freeze-fracture showing an intact cluster of chondrons entering the reserve zone and arching toward the supplying blood vessel. (F) Freeze-fractured sample. A cluster of chondrons has been torn from the reserve zone/subchondral bone plate (middle of image) exposing the pore containing the blood vessel that supplied the cluster. This can be compared with histology (fig. 14 in Morgan). From the authors’ laboratory. SB, subchondral bone; RZ, reserve zone; PZ, proliferative zone.

Figure 3.

Stereo-microscopy (Olympus, SZX16, Japan) sections cut in the same middle plane relative to pig femoral heads for 3 different age groups, which show the development of mammillary processes with aging. (A) 20-day-old. (B) 35-day-old. (C) 480-day-old. AC, articular cartilage; GP, growth plate cartilage; EP, epiphysis; MP, metaphysis. Black arrows show the undulation of the tubercle in the femoral head, red arrows indicate the metaphyseal secondary mammillary processes, and blue arrows point to the epiphyseal secondary mammillary processes. The scale bar is 2 mm. From the authors’ laboratory.

Figure 4.

Articular cartilage chondro-osseous junction of a bovine yearling (12-18 months), stained with hematoxylin and eosin (H&E); blue arrows show multiple tidemark lines. SB, subchondral bone plate; CC, calcified cartilage; AC, articular cartilage. From the authors’ laboratory.

Figure 5.

(a, b, c) Histology images of a yearling proximal tibial bovine growth plate, stained by hematoxylin and eosin (H&E). (d) Fluorescence image of RZ-SB interface. GP, growth plate; RZ, reserve zone; TM, tide mark; SB, subchondral bone; EP, epiphyseal bone. From the authors’ laboratory.