Indmedica Home | About Indmedica | Medical Jobs | Advertise On Indmedica
Search Indmedica Web
Indmedica - India's premier medical portal

Journal of the Anatomical Society of India

Age changes in the microstructure of human femoral articular cartilage

Author(s): Madhur Gupta, Neeru Goyal

Vol. 55, No. 2 (2006-07 - 2006-12)

Madhur Gupta, Neeru Goyal
PGIMER, Chandigarh

Abstract:

Articular cartilage, hyaline in nature covers the articular surfaces in synovial joints. It does not ossify and is moulded to the shape of the undulying bone but its surface is devoid or perichondrium often extenuating and modifying the surface geometry. Femoral articular cartilage of knee joint obtained from two fetuses of full term and from adult cadavers was studied. The latter were divided into two groups: Group A obtained from cadavers of l8-40 yrs of age and Group B above 40 yrs onwards. 6 thick paraffin sections were stained and observed under light microscope. Fetal articular cartilage had a smooth surface and was highly cellular with no demarcation into zones. In group A the cartilage had a smooth surface and the chondrocytes were arranged differently from superficial to deep giving appearance of the zones. In the superficial zone (zone I) cells were small and oval and arranged parallel to the surface. The cells of the intermediate zone (zone II) were large and round, single or in isogenous groups. In zone III cells were arranged in vertical columns with intervening radial collagen fibres. The deepest calcified layer (zone IV) adjoining the subchondral bone showed reciprocal fine ridges, grooves and interdigitations. Group B showed signs of ageing and degeneration. The surface of cartilage was eroded and irregular. At places splits and clefts appeared in the zone I and II. Chondrocytes were present in groups and clusters. Probably this clustering may helped the chondrocytes to coordinate their activity and their responses to mechanical and humoral cues. Such an organization may be required for the establishment and maintenance of shared surface, which may involve shuttling of constituents. A relative increase in thickness of the deepest calcified zone was observed which may change the permeability of cartilage resulting in variations in the matrix and changes in its histological structure.

Key words: knee joint, clusters of chondrocytes, subchondral bone, calcified cartilage

Introduction:

Cartilage is a phylogenetically ancient tissue, widespread in vertebrates as a permanent or temporary skeletal component. During early fetal life, human skeleton is mostly cartilaginous but is later replaced by bone. In adults, cartilage persists at the surfaces of synovial joints as articular cartilage beside many other regions in the body. Cartilage is a stiff, load bearing connective tissue with a low metabolic rate and a high resistance to tension and compression with some resilience and elasticity.

Articular cartilages are mostly formed by a special variety of hyaline cartilage, which is formed as a part of cartilaginous models in embryonic life (Ghadially and Roy, 1969). It covers the articular surfaces in synovial joints providing an extremely smooth surface lubricated by synovial fluid for allowing frictionless movements. Articular cartilage does not ossify and varies from 1 to 7mm in thickness. It is moulded to the shape of the underlying bone and its surface is devoid of perichondrium (Williams et al, 1995).

Vignon et al (1976) found progressive reduction of cellular density in articular cartilage with age while Leutert (1980) believes that number of chondrocytes do not decline with age. Study of age related changes in articular cartilage and their influence on ability of cartilage to maintain and repair itself might help in preserving and restoring the articular surface in old individuals.

The detailed histology of the articular cartilage of knee joint was studied in individuals of different age.

Material and Methods:

Articular cartilage was obtained bilaterally from femoral condyles of 30 cadavers of known age and sex. Overweight cadavers and cadavers with some gross abnormality or deformity of the knee joint were excluded from the study. The cartilage specimens were divided into two groups depending on their age:

Group A: 18 – 40 yrs. (n = 10)
Group B: 40 yrs. Onwards (n = 20)

Articular cartilage of two 28 week old fetuses was also studied.

The cartilage specimens were fixed in 10% phosphate buffered formalin and processed for paraffin sections. 6mm thick sections were stained with Haematoxylin and Eosin, (Cole, 1943), Modified Von Kossa (Tripp and Mackay, 1972) and Gomori’s reticulin silver stain (Gomori, 1937) and observed under light microscope.

Observations:

In the fetal articular cartilage, the articular surface was very smooth and regular. The cartilage was highly cellular. Chondrocytes (10×10mm) were present in pairs or in isogenous groups with little extracellular matrix in between the cells (Fig.l a).

Photomicrograph of articular cartilage

Fig.1 Photomicrograph of articular cartilage obtained from:
1a- Fetus showing highly cellular articular cartilage (H & E, 400X)
1b- Group A (25 yrs) showing zone I (→) & II (→ ). Note the decrease in cellularity (H & E, 400X)
1c- Group A (25 yrs) showing zone III, cells are arranged in columns ( →) (H & E, 400X)

Photomicrograph of articular cartilage of group A

Fig.2 Photomicrograph of articular cartilage of group A: 2a- At 32 yrs showing zone I (→), cells & fibres arranged parallel to surface. Zone II (→) having cells arranged singly or double separated by oblique fibres. (Gomori’s reticulin silver stain, 400X)
2b- At 32 yrs showing zone III having vertical columns of cells (→), IV (not stained) (→) & subchondral bone (→) (Gomori’s reticulin silber stain, 400 X)
2c- At 28 yrs showing zone III having vertical columns of cells (→), Iv stained black (→), subchondral bone (→) & interdigitations between subchondral bone & zone IV (→)(Tripp and Mackay, 400X)

Photomicrograph of articular of Group B

Fig.3 Photomicrograph of articular of Group B:
3a- At 42 yrs showing oblique spilt (←) in superficial zone (zone I) (H & E, 400X)
3b- At 55 yrs showing horizontal separation of collagen bundles (←) in superficial zone (zone I) (H & E, 400X)
3c- At 58 yrs showing completely eroded (↓) superficial zone (H & E, 400X)

Photomicrograph of articular cartilage of Group B

Fig.4 Photomicrograph of articular cartilage of Group B: 4a- At 65 yrs showing completely eroded superficial zone & vertical spilts (→) throughout the surface *H & E, 400X)

Group A articular cartilage had a smooth articular surface but its cellularity was reduced. The articular cartilage appeared to be arranged into zones (Fig.l b, c ). In the superficial zone (zone I) the chondrocytes (20×10mm) were flattened and arranged parallel to the surface (Fig.l b ) and by Gomori’s silver stain the surrounding collagen fibres were also arranged parallel to the surface (Fig.2a). In zone II cells were large and round (23×20mm). They were present either singly or in pairs (Fig.l b) and by Gomori’s silver stain the surrounding collagen fibres were observed to be arranged obliquely (Fig.2a). Zone III had chondrocytes arranged in vertical columns separated by thin layers of extracellular matrix (Fig.l c ). The surrounding collagen fibres were also running vertically (Fig.2b ). Deepest zone (zone IV) of the articular cartilage was the calcified zone (Fig.2b ). By Tripp and Mackay (1972) the calcified zone was stained black and with the underlying subchondral bone showed very distinct reciprocal interdigitations (Fig.2c).

Group B articlllar cartilage had lost its smoothness 42yrs onwards and showed signs of degeneration. Changes appeared in the superficial zone (zone I) either as oblique split (Fig.3a) or horizontal separation of collagen bundles (Fig.3b). At 58yrs the superficial zone had completely disappeared giving it a saucer appearance (Fig.3c). At 65 yrs the superficial zone of the cartilage having cells and fibres running parallel to the surface had completely disappeared. The cells (23×23mm) near the surface were large and round. Vertical splits appeared throughout the surface giving it a very irregular appearance (Fig.4a). At later stages, fragments of the ageing cartilage were seen floating in the joint cavity. Chondrocytes were no longer arranged into four zones rather clusters of cells could be seen throughout the articular cartilage having round cells, 15xl5mm in size (Fig.4b). By Tripp and Mackay (1972) the thickness of the calcified zone was increased as compared to group A and the size of subchondral cavities was also increased. The reciprocal interdigitations between the calcified zone and the subchondral bone were not very distinct (Fig.2c, 4c ).

Discussion:

The fetal articular cartilage in the present study was highly cellular and the chondrocytes were separated by thin septa of matrix. Williams et al. (1995) also stated that a densely cellular cartilage is a stage of the embryonic cartilage. In the present study in group A at 25yrs of age the adult articular cartilage showed a distinct zonation as described by Stockwell ( 1979).

The cellularity had also decreased compared to the fetal cartilage as matrix is pervaded by collagen fibres (Clark, 1990). The flattened shape of chondrocytes surrounded by tangentially running fibres in the superficial zone in group A could be a result from the forces of tension and compression during normal loading of the joint (Schumacher et al., 2002). The degenerative changes like oblique split or horizontal separation of collagen bundles in group B appeared initially in the superficial zone of the articular cartilage resulting in depriving the adjacent cartilage its nutrition and leading to further changes. By 58yrs the superficial zone was either eroded or completely disappeared having no parallel fibres and flattened cells. The chondrocytes had increased in size and were arranged in pairs and columns or clusters.

Williams et al (1995) stated that articular cartilage has no nerves or blood vessels. Nutrition is considered to depend on peripheral vascular plexus in synovial membrane (circulus vasculosus articuli), synovial fluid and blood vessels in adjacent marrow spaces though the relative importance of these is uncertain. The changes of articular cartilage with advancing age could be because of lack of its nutrition as there is an imbalance between the chondrocytes and the cartilage matrix.

The formation of clusters and groups in ageing cartilage in group B at 70yrs of the present study can be explained as Chi et al (2004) described that functionally linked cellular units in injured cartilage may be important in maintaining the zonation of the articular cartilage and possibly coordinating the activities of cells. They also stated that the numerous small cellular projections extend from the opposing surfaces of these cells and form an interwoven meshwork. Though Bruehlmaru1 et al (2002) and Lo et al (2002) described that in ligaments, tendons, menisci and certain regions of intervertebral disc the cells are interconnected via gap junctions to form a cytomatrix. Alternatively the clustering of chondrocytes in injured cartilage might be that the chondrocytes are able to organize themselves in pairs or groups possibly by recapitulating the events of development (Morrison, 2000). Vitanzo and McShane (2000) described that at cellular level, in early osteoarthritis chondrocytes undergo transient proliferation and produce increased quantities of various enzymes and growth factors. This results in an imbalance between the degradation and synthesis of cartilage matrix.

Schumacher et al (2002) also stated that the chondrocytes in the superficial zone appear to proliferate in response to degenerative changes. The disruption of the collagen in the area of the lesion may have destroyed the integrity of the architecture, leading to proliferation in these cells in group B cartilage. In the articular cartilage from group B, the size of subchondral cavities as well as the thickness of the calcified zone was much increased. The interdigitations between the calcified layer and the subchondral bone were diminished leading to decreased area of contact between these two layers. This may be an additional cause of decreased nutrition of cartilage from subchondral bone. The increased thickness of the calcified layer of cartilage can also contribute to it. Ferguson et al (2003) has studied the relationship between mineralization of calcified zone of articular cartilage and subchondral bone in femoral heads and has stated that variations in the mineral concentration in bone reflect the age of bone packets and recent remodeling history.

Acknowledgements:

The authors wish to thank Mr. Vijay Bakshi, Senior artist of Anatomy department for the illustrations.

References:

  1. Bruehlmann SB, Rattner JB, Matyas JR, Duncan NA. Regional variations in the cellular matrix of the annulus fibrosus of the intervertebral disc. Journal of Anatomy 2002; 201: 159-171.
  2. Chi SS, Rattner JB, Matyas JR. Communication between Paired choridrocytes in the superficial zone of articular cartilage. Journal of Anatomy 2004; 205: 363-370.
  3. Clark RAF. Cutaneous wound repair. In: Goldsmith LE (ed) Physiology biochemistry and molecular biology of the skin. Oxford University Press: Oxford, 1990, pp 576-601.
  4. Cole EC. Studies in Hematoxylin stains. Stain Tech 1943; 18: 125.
  5. Ferguson VL, Bushby AJ, Boyde A. Nanomachanical properties and mineral concentration in articular calcified cartilage and subchondral bone. Journal of Anatomy 2003; 203: 191-202.
  6. Ghadially FN, Roy oS. Ultrastructure of synovial joints in health and disease. Butterworths: London, 1969. (Quoted from Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Ferguson MWJ. Gray’s Anatomy, 38th ed, Churchill Livingstone, 1995, p 495).
  7. Gomori G. Silver impregnation of reticulum in paraffin sections. American Journal of Physiology 1937; 13: 993.
  8. Leutert G. Morphological aging changes in the human articular cartilage. Mech Aging Dev 1980; 14: 469- 475 (Quoted from Sokoloff L. Aging and Degenerative Diseases AffectIng CartIlage. In: Hall BK Ed: CartIlage, Vol.3, AcademIc Press: New York, 1983, pp 110-141).
  9. Lo I.K, Ou Y, Rattner JP. The cellular networks of normal ovine medial collateral and anterior cruciate ligaments are not accurately recapitulated in scar tissue. Journal of Anatomy 2002; 200: 283-296.
  10. Morrison SL, Campbell CK. Wright GM. Chondrogenesis of the brachial skeleton in embryonic sea lamprey, petromyzon marinus. Anatomical Record 2000; 260: 252-267.
  11. Schumacher BL, Su JL, Lindley KM, Kuettner KE. Cole AA. Horizontally oriented clusters of multiple chondrons in the superficial zone of ankle, but not knee articular cartilage. Anatomical Record 2002; 266: 241-248.
  12. Stockwell RA. Biology of cartilage cells. Cambridge University Press: Cambridge. 1979 (Quoted from Williams PL, Bannister LH, Berry MM, Collins P, Dyson M. Dussek JE, Ferguson MWJ, Gray’s Anatomy, 38th ed, Churchill Livingstone 1995. pp 443- 452.
  13. Tripp EJ, Mackay EH. Silver staining of bone prior to decalcification for quantitative determination of osteoid in sections. Stain. Technology1972; 47(3}: 129-136.
  14. Vignon E, Arlot M, Vignon G. etude de la densite cellulaire du cartilage de 1a tete femorale en fonction de 1’age. Rev. Rhum. Mal. Osteo- Articulaires1976; 43: 403- 405(Quoted from Sokoloff L. Aging and Degenerative Diseases Affecting Cartilage. In: Hall BK Ed: Cartilage, Vol.3, Academic Press 1983, pp 110-141.
  15. Vitanzo PC, McShane JM. The osteonrthritic knee. From A Special report: Osteoarthritis of the knee. McGraw-Hill Companies 2000.
  16. Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek.JE, Ferguson MWJ. Gray’s Anatomy, 38th ed, Churchill Livingstone. 1995, pp 443-452,495.
Access free medical resources from Wiley-Blackwell now!

About Indmedica - Conditions of Usage - Advertise On Indmedica - Contact Us

Copyright © 2005 Indmedica