THE ANATOMICAL RECORD 233:350-356 (1992)
The Surface Lamina of the Articular Cartilage of Human Zygapophyseal Joints L.G.F. GILES Spinal Research Laboratory, Division of Science and Technology, Griffith University, Nathan, Brisbane, 41 11 Queensland, Australia
ABSTRACT Literature referring to the conflicting results of investigations into the possible existence and composition of the lamina splendens is reviewed. Two hundred micrometer thick histological sections from 80 human cadaveric lower lumbar zygapophyseal joint articular cartilages were examined by ordinary light and darkfield microscopy. The findings illustrate what appears to be an acellular surface lamina on the opposing cartilaginous surfaces. No speculation is made regarding the possible physiological significance of the lamina based on this anatomical study. o 1992 Wiley-Liss, Inc. Zygapophyseal (facet, interlaminar) joints are synovial joints formed by the superior articular process of the caudad vertebra and the inferior articular process of the adjacent cephalad vertebra; they have a joint capsule composed of a posterolateral fibrous capsule and an anteromedial ligamentum f lavum. According to Collins (1949),the superior and inferior recesses of the joints contain adipose or fibrous folds, lined with a synovial membrane which also lines the inner surface of the joint capsule but not the articular cartilage on the facet surfaces. Articular cartilage consists of three illdefined zones, i.e., superficial zone (with small flattened or oval chondrocytes, and fine fibers arranged tangentially to the surface), middle zone (with chondrocytes arranged in columns perpendicular to the surface with decussating fibers), and deep zone (with small chondrocytes in calcified cartilage lying adjacent to bone) (Benninghoff, 1939; Collins, 1949; Barnett et al., 1961; Ghadially et al., 1965; Ghadially and Roy, 1969; Ham and Cormick, 1979). Hence, according to Ham and Cormick (1979), synovial joint articular cartilage is unique in that the surface it presents to articulate with its opposing articular cartilage is that of naked cartilage matrix. The ultrastructure of adult articular cartilage has been described in a number of human and animal studies (Cameron and Robinson, 1958; Davies et al., 1962; Collins et al., 1965; Meachim, 1967; Roy and Meachim, 1968; Ruttner and Spycher, 1968; Weiss et al., 1968; Meachim and Roy, 1969; Stofft and Graf, 1983) and some reference is made in the literature to a chondrosynovial membrane which is only a few tenths of a micron thick (Wolf, 1969) and which Wolf (1969, 1972, 1975) refers to as being of cartilaginous origin which may be torn off the articular surface “like a sheet of paper.” According to Wolf (19751, the uppermost layer of amorphous substance forms the actual smooth “glide” surface of articular cartilage and can be distinguished from the undersurface layer of thin collagenous fibrils which smoothly pass with their fibrillar structure into the cartilaginous tissue beneath the membrane. Davies et al. (1962)described a narrow surface lamina, devoid of fibers, appearing to correspond t o the lamina splendens, while Weiss et al. (1968) con0
1992 WILEY-LISS, INC.
cluded that the lamina was fibrous. Using phase contrast illumination to microscopically examine human adult fresh and cadaveric cartilage, MacConaill (1951) showed a thin bright line at the surface of articular cartilage which was not visible by ordinary light illumination; it was so conspicuous that it merited the name of lamina splendens. However, according to Aspden and Hukins (19791, the so-called lamina splendens described by MacConaill (1951) is an artifact of phase contrast microscopy due to a Fresnel diffraction pattern on the edge of a section of cartilage, while Sokoloff (1969) suggested that MacConaill’s bright line was a “halo” resulting from phase contrast microscopy. The purpose of this study is to report an incidental finding that an acellular surface lamina is seen to exist in human lower lumbar zygapophysealjoints processed for histological evaluation as part of large blocks of osteoligamentous tissues being examined to clarify the complex anatomy of the lower lumbosacral spine. It is well known that most cases of low back pain are related to the L4 to S1 region of the spine (Ehni, 1977). This paper documents anatomical findings and is not intended for hypothetical speculation of the possible physiological role of any such surface layer. MATERIALS AND METHODS
Twenty lower lumbosacral spines were removed from human cadavers (9 male and 11 female) aged 46-78 years (mean 60 years) and bisected in the sagittal or horizontal planes using a bandsaw. Large blocks of osteoligamentous material including the L4-5 and L5-S1 zygapophysealjoints were then trimmed and processed through the stages of decalcification, dehydration, and embedding in low viscosity nitrocellulose (LVN) and necoloidine (Gurr BDH Chemicals Ltd., Poole, U.K.: Product 36059) for histological investigation using the method of Giles and Taylor (1983), although Bouins’ post-fixation (Singer and Giles, 1990) was used instead of Susa’s post-fixation and necoloidine was used in-
Received September 8, 1991; accepted December 30, 1991.
ARTICULAR CARTILAGE LAMINA
Fig. 1 A,B. Legend on p. 353.
351
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L.G.F. GILES
Fig. 1 C,D.
Legend on p. 353.
353
ARTICULAR CARTILAGE LAMINA
Fig. 2. A. A transmitted light photomicrograph showing a section cut in the parasagittal plane through the lumbosacral zygapophyseal joint of a 62 year old male. Note the hyaline articular cartilage (H) on the inferior articular process of the fifth lumbar (L5) vertebra and the superior articular process of the sacrum (S1) both of which show early osteoarthrotic changes. A part of the narrow strip of acellular surface layer is shown between the paired parallel lines ( 1 1) on each surface. The joint “space” is shown by a n arrow. Some artifact spaces as seen
Fig. 1 . A A transmitted light photomicrograph of a section cut in the horizontal plane, a t a thickness of 200 km, from the left lumbosacral zygapophyseai joint of a 67 year old female which shows relatively normal hyaline articular cartilage (HI on the facet surfaces bordering the joint “space.” The cartilage surfaces show minor focal fibrillation at the center of the joint with minor tinctorial changes along the length of the cartilage indicating minor changes in the chondrocytes and cartilage matrix. IAP, inferior articular process of the L5 vertebra; SAP, superior articular process of the sacrum. A narrow surface lamina of acellular tissue is seen (arrows) which appears to extend to the adjacent fibrous synovial fold ( S )adjoining the inner surface of the ligamentum flavum (L). Ehrlich’s hematoxylin stain with light green counterstain. B: A higher magnification of the adjacent cartilage surfaces showing the narrow surface lamina and the adjoining fibrous synovial fold ( S ) seen in Figure 1A. H, hyaline articular cartilage; SAP, superior articular process of the sacrum. C: A darkfield photomicrograph of the specimen in Figure 1A shows an enhanced “white” line surface lamina. H, hyaline articular cartilage; S, synovial fold L, ligamentum flavum; IAP, inferior articular process of the L5 vertebra. D: This higher magnification darkfield view of Figure 1C shows the surface lamina in greater detail. SAP, superior articular process of the sacrum; H, hyaline articular cartilage; S, synovial fold.
in (A) and (B), where small pieces of bone marrow have been lost during processing, are shown by tailed arrows (+). Ehrlich‘s hematoxylin stain with light green counterstain. B: A darkfield photomicrograph of the specimen shown in Figure 2A. Note the dramatically enhanced narrow strip of acellular surface layer between the paired parallel lines ( 1 1) . H, hyaline articular cartilage; L5, inferior articular process of fifth lumbar vertebra; S1, superior articular process of the sacrum.
stead of celloidin to impart flexibility to the LVN blocks for sectioning. This process took 6-7 months for each block of tissue, depending on the time required to decalcify the respective blocks of tissues a s determined by radiography. The 40 blocks of spinal tissue, containing 80 zygapophyseal joints, were sectioned in the sagittal or horizontal planes on a Polycut S microtome at a section thickness of 200 IJ-m,and stored on serially numbered pieces of white paper in 70% aqueous ethanol. One in 10 sections was stained in Ehrlich’s hematoxylin, counterstained in light green, dehydrated in ascending concentrations of ethanol, cleared in Histoclear, mounted in DePex (Gurr BDH: Product 36125) (Giles and Taylor, 1983), then examined and photographed by normal light and darkfield microscopy using a Wild M400 photomacroscope with apozoom lens and Phctonaut MPS 55 photographic system. RESULTS
In specimens showing relatively “normal” zygapophyseal joints for this age group a narrow surface lam-
355
ARTICULAR CARTILAGE LAMINA
ina was seen in 20 out of 80 joints (25%) as shown in Fig. 1A-D which include low and high power transmitted light and darkfield photomicrographs. In some instances there appeared to be continuity of the surface lamina up to the adjacent synovial folds. Darkfield microscopy dramatically enhanced the narrow strip of acellular tissue (Fig. lC,D). In specimens showing early osteoarthrotic changes, such as tinctorial variations (a staining variation presumed to be due to changes in cartilage matrix) and minor fibrillation involving most of the cartilage surface, a narrow surface layer of acellular tissue was also seen by transmitted light and darkfield microscopy to line the cartilage surface (Fig. 2A,B). In specimens showing advanced osteoarthrotic changes in zygapophyseal joints the acellular layer is not present when examined by transmitted light and darkfield microscopy (Fig. 3A,B). It should be noted that with darkfield microscopy of “normal” to early osteoarthrotic joint cartilage surfaces (Fig. 1C,D, 2B, respectively) the narrow strip of acellular lamina of the cartilage bounding the joint space is enhanced, whereas there is no enhanced lamina in joints with advanced osteoarthrosis (Fig. 3B). Also, areas of tissue adjacent to artifact spaces (caused by loss of small parts of tissue during processing, for example Fig. 2B) do not show corresponding areas of enhancement. Therefore, the acellular layer can be seen to exist in joints not exhibiting advanced degenerative changes and it is not an artifact, as an artifact seen a t the edge of any tissue bordering a space would be seen at the edge of tissues where part of the tissue has been dislodged during processing or has degenerated in advanced osteoarthrosis, which is not the case in this study. The thickness of the acellular layer can vary from 20-200 pm along the surface of the cartilage, and from one specimen to another, and appears to be unrelated to age or sex. DISCUSSION
The issue of whether a lamina splendens lines the surface of hyaline articular cartilage has led to considerable debate in the literature which has cast doubt upon its existence and in particular, Aspden and Hukins (1979) have criticized MacConaill’s (1951) lamina splendens as being merely a Fresnel diffraction pattern artifact on the edge of a section of cartilage viewed by phase contrast microscopy. However, this study illustrates the existence of an acellular layer, or lamina splendens, lining the surface of some lower
Fig. 3. A: A transmitted light photomicrograph of a 200 km thick section cut in the parasagittal plane through the lumbosacral zygapophyseal joint of a 78 year old male. There is advanced fibrillation and loss of the hyaline articular cartilage (H) on the facets of the superior articular process of the sacrum (SAP) and the inferior articular process (IAP) of the fifth lumbar vertebra, respectively. The fibrous capsule (C) is seen at the inferior margin of the joint. B: A darkfield photomicrograph of the specimen shown in Figure 3A shows no surface lamina. Importantly, there is no evidence of significant light artifacts along the cut edges of the residual osteoarthrotic cartilages, or any other parts of the joint, which could simulate a surface lamina. SAP, superior articular process of the sacrum; H, hyaline articular cartilage; IAP, inferior articular process of the fifth lumbar vertebra; C, fibrous capsule.
lumbar zygapophyseal joint facet cartilages in middle aged human cadavers which exhibit “normal” joints or only early osteoarthrotic changes for this age group. This appears to support the findings of those authors (MacConaill, 1951; Davies et al., 1962; Weiss et al., 1968) who have noted a narrow surface lamina on articular cartilage. Perhaps an explanation of the fact that the narrow lamina is not seen in all joints relates to technical difficulties involved in decalcifying and generally processing large blocks of osteoligamentous tissues for several months before sectioning can commence. Once advanced osteoarthrosis is present, the layer of acellular tissue is no longer recognizable and, in such specimens, no “white” line is seen on the osteoarthrotic cartilage surface by darkfield microscopy, nor is there any enhancement of the cut edge of any other joint structures. This, and the fact that an acellular layer can be seen on normal light illumination, indicates that the lamina splendens is not an artifact. However, it is not the purpose of this anatomical study to speculate on its possible physiological significance. ACKNOWLEDGMENTS
The author gratefully acknowledges the assistance provided by the clinical and technical staff of the Institute of Forensic Pathology and Laboratory of Microbiology and Pathology, State Health Department, Brisbane, Queensland, Australia. The financial assistance provided by the Australian Spinal Research Foundation Ltd. and the Foundation for Chiropractic Education and Research (USA) is acknowledged. LITERATURE CITED Aspden, R.M., and D.W.L. Hukins 1979 The lamina splendens of articular cartilage is a n artifact of phase contrast microscopy. Proc. R. SOC. Lond., B206:109-113. Barnett, C.H., D.V. Davies, and M.A. MacConaill 1961 Synovial Joints: Their Structure and Mechanics. Longmans, London, pp. 23-34. Benninghoff, A 1939 Lehrbuch der Anatomie des Menschen, J.F. Lehmann, ed. Munich, Verlag. Cameron, D.A., and R.A. Robinson 1958 Electron microscopy of epiphyseal and articular cartilage matrix in the femur of the newborn infant. J . Bone Joint Surg., 40A:163-170. Collins, D.H. 1949 The Pathology of Articular and Spinal Diseases. Edward Arnold, London, pp. 123-128. Collins, D.H., F.N. Ghadially, and G. Meachim 1965 Intra-cellular lipids of cartilage. Ann. Rheum. Dis., 24~123. Davies, D.V., C.H. Barnett, W. Cochrane, and A.J. Palfrey 1962 Electron microscopy of articular cartilage in the young adult rabbit. Ann. Rheum. Dis., 21~11-22. Ehni, G. 1977 Historical writings on spondylotic caudal radiculopathy and its effect on the nervous system. In: Lumbar Spondylosis: Diagnosis, Management and Surgical Treatment. P.R. Weinstein, G. Ehni, C.B. Wilson, eds. Year Book Medical Publishers, Chicago, pp. 1-12. Ghadially, F.N., G. Meachim, and D.H. Collins 1965 Extra-cellular lipid in the matrix of human articular cartilage. Ann Rheum. Dis., 24~136-141. Ghadially, F.N., and S. Roy 1969 Ultrastructure of Synovial Joints in Health and Disease. Butterworths, London, pp. 1-32. Giles, L.G.F., and J.R. Taylor 1983 Histological preparation of large vertebral specimens. Stain Techno]., 58:45-49. Ham, A.W., and D.H. Cormick 1979 Histology. ed 8. J.B. Lippincott, Philadelphia, p. 465. MacConaill, M.A. 1951 The movements of bones and joints (a) The mechanical structure of articulating cartilage. J. Bone Joint Surg., 33l3:251-257. Meachim, G. 1967 The histology and ultrastructure of cartilage. In: Proceedings of a Workshop on Cartilage: Degradation and Repair. C.A.L. Bassett, ed. National Research Council, Washington, p. 3.
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Meachim, G., and S. Roy 1969 Surface ultrastructure of mature adult, human articular cartilage. J . Bone Joint Surg., 51B:521-539. Roy, S., and G. Meachim 1968 Chondrocyte ultrastructure in adult human articular cartilage. Ann. Rheum. Dis., 27:544-549. Ruttner, J.R., and M.A. Spycher 1968 Electron microscopic investigations on aging and osteoarthritic human cartilage. Pathol. Microbiol. 31:14-18. Singer, K.P., and L.G.F. Giles 1990 Manual therapy considerations at the thoracolumbar junction zygapophyseal joints. Anat. Rec. 226: 147-152. Sokoloff, L. 1969 The Biology of Degenerative Joint Disease. University Press, Chicago, p. 38. Stofft, E., and J . Graf 1983 Scanning electron microscopic study of hyaline cartilage. Acta Anat., 16:114-125.
Weiss, C., L. Rosenberg, and A.J. Helfet 1968 An ultrastructural study of normal, young adult, human articular cartilage. J . Bone Joint Surg., 50A:663-674. Wolf, J . 1969 chondrosynovial membrane serving as joint cavity lining with a sliding and barrier function. Folia Morphol. 17:291308. Wolf, J. 1972 Les menisques intervertebraux et leur r61e possible dans les blocages vertbbraux. Ann. Med. Physique, 15:204-218. Wolf, J. 1975 Function of chondral membrane on surface of articular cartilage from point of view of its mechanical resistance. Folia Morphol. 23:77-87.
The Surface Lamina of the Articular Cartilage of Human Zygapophyseal Joints L.G.F. GILES Spinal Research Laboratory, Division of Science and Technology, Griffith University, Nathan, Brisbane, 41 11 Queensland, Australia
ABSTRACT Literature referring to the conflicting results of investigations into the possible existence and composition of the lamina splendens is reviewed. Two hundred micrometer thick histological sections from 80 human cadaveric lower lumbar zygapophyseal joint articular cartilages were examined by ordinary light and darkfield microscopy. The findings illustrate what appears to be an acellular surface lamina on the opposing cartilaginous surfaces. No speculation is made regarding the possible physiological significance of the lamina based on this anatomical study. o 1992 Wiley-Liss, Inc. Zygapophyseal (facet, interlaminar) joints are synovial joints formed by the superior articular process of the caudad vertebra and the inferior articular process of the adjacent cephalad vertebra; they have a joint capsule composed of a posterolateral fibrous capsule and an anteromedial ligamentum f lavum. According to Collins (1949),the superior and inferior recesses of the joints contain adipose or fibrous folds, lined with a synovial membrane which also lines the inner surface of the joint capsule but not the articular cartilage on the facet surfaces. Articular cartilage consists of three illdefined zones, i.e., superficial zone (with small flattened or oval chondrocytes, and fine fibers arranged tangentially to the surface), middle zone (with chondrocytes arranged in columns perpendicular to the surface with decussating fibers), and deep zone (with small chondrocytes in calcified cartilage lying adjacent to bone) (Benninghoff, 1939; Collins, 1949; Barnett et al., 1961; Ghadially et al., 1965; Ghadially and Roy, 1969; Ham and Cormick, 1979). Hence, according to Ham and Cormick (1979), synovial joint articular cartilage is unique in that the surface it presents to articulate with its opposing articular cartilage is that of naked cartilage matrix. The ultrastructure of adult articular cartilage has been described in a number of human and animal studies (Cameron and Robinson, 1958; Davies et al., 1962; Collins et al., 1965; Meachim, 1967; Roy and Meachim, 1968; Ruttner and Spycher, 1968; Weiss et al., 1968; Meachim and Roy, 1969; Stofft and Graf, 1983) and some reference is made in the literature to a chondrosynovial membrane which is only a few tenths of a micron thick (Wolf, 1969) and which Wolf (1969, 1972, 1975) refers to as being of cartilaginous origin which may be torn off the articular surface “like a sheet of paper.” According to Wolf (19751, the uppermost layer of amorphous substance forms the actual smooth “glide” surface of articular cartilage and can be distinguished from the undersurface layer of thin collagenous fibrils which smoothly pass with their fibrillar structure into the cartilaginous tissue beneath the membrane. Davies et al. (1962)described a narrow surface lamina, devoid of fibers, appearing to correspond t o the lamina splendens, while Weiss et al. (1968) con0
1992 WILEY-LISS, INC.
cluded that the lamina was fibrous. Using phase contrast illumination to microscopically examine human adult fresh and cadaveric cartilage, MacConaill (1951) showed a thin bright line at the surface of articular cartilage which was not visible by ordinary light illumination; it was so conspicuous that it merited the name of lamina splendens. However, according to Aspden and Hukins (19791, the so-called lamina splendens described by MacConaill (1951) is an artifact of phase contrast microscopy due to a Fresnel diffraction pattern on the edge of a section of cartilage, while Sokoloff (1969) suggested that MacConaill’s bright line was a “halo” resulting from phase contrast microscopy. The purpose of this study is to report an incidental finding that an acellular surface lamina is seen to exist in human lower lumbar zygapophysealjoints processed for histological evaluation as part of large blocks of osteoligamentous tissues being examined to clarify the complex anatomy of the lower lumbosacral spine. It is well known that most cases of low back pain are related to the L4 to S1 region of the spine (Ehni, 1977). This paper documents anatomical findings and is not intended for hypothetical speculation of the possible physiological role of any such surface layer. MATERIALS AND METHODS
Twenty lower lumbosacral spines were removed from human cadavers (9 male and 11 female) aged 46-78 years (mean 60 years) and bisected in the sagittal or horizontal planes using a bandsaw. Large blocks of osteoligamentous material including the L4-5 and L5-S1 zygapophysealjoints were then trimmed and processed through the stages of decalcification, dehydration, and embedding in low viscosity nitrocellulose (LVN) and necoloidine (Gurr BDH Chemicals Ltd., Poole, U.K.: Product 36059) for histological investigation using the method of Giles and Taylor (1983), although Bouins’ post-fixation (Singer and Giles, 1990) was used instead of Susa’s post-fixation and necoloidine was used in-
Received September 8, 1991; accepted December 30, 1991.
ARTICULAR CARTILAGE LAMINA
Fig. 1 A,B. Legend on p. 353.
351
352
L.G.F. GILES
Fig. 1 C,D.
Legend on p. 353.
353
ARTICULAR CARTILAGE LAMINA
Fig. 2. A. A transmitted light photomicrograph showing a section cut in the parasagittal plane through the lumbosacral zygapophyseal joint of a 62 year old male. Note the hyaline articular cartilage (H) on the inferior articular process of the fifth lumbar (L5) vertebra and the superior articular process of the sacrum (S1) both of which show early osteoarthrotic changes. A part of the narrow strip of acellular surface layer is shown between the paired parallel lines ( 1 1) on each surface. The joint “space” is shown by a n arrow. Some artifact spaces as seen
Fig. 1 . A A transmitted light photomicrograph of a section cut in the horizontal plane, a t a thickness of 200 km, from the left lumbosacral zygapophyseai joint of a 67 year old female which shows relatively normal hyaline articular cartilage (HI on the facet surfaces bordering the joint “space.” The cartilage surfaces show minor focal fibrillation at the center of the joint with minor tinctorial changes along the length of the cartilage indicating minor changes in the chondrocytes and cartilage matrix. IAP, inferior articular process of the L5 vertebra; SAP, superior articular process of the sacrum. A narrow surface lamina of acellular tissue is seen (arrows) which appears to extend to the adjacent fibrous synovial fold ( S )adjoining the inner surface of the ligamentum flavum (L). Ehrlich’s hematoxylin stain with light green counterstain. B: A higher magnification of the adjacent cartilage surfaces showing the narrow surface lamina and the adjoining fibrous synovial fold ( S ) seen in Figure 1A. H, hyaline articular cartilage; SAP, superior articular process of the sacrum. C: A darkfield photomicrograph of the specimen in Figure 1A shows an enhanced “white” line surface lamina. H, hyaline articular cartilage; S, synovial fold L, ligamentum flavum; IAP, inferior articular process of the L5 vertebra. D: This higher magnification darkfield view of Figure 1C shows the surface lamina in greater detail. SAP, superior articular process of the sacrum; H, hyaline articular cartilage; S, synovial fold.
in (A) and (B), where small pieces of bone marrow have been lost during processing, are shown by tailed arrows (+). Ehrlich‘s hematoxylin stain with light green counterstain. B: A darkfield photomicrograph of the specimen shown in Figure 2A. Note the dramatically enhanced narrow strip of acellular surface layer between the paired parallel lines ( 1 1) . H, hyaline articular cartilage; L5, inferior articular process of fifth lumbar vertebra; S1, superior articular process of the sacrum.
stead of celloidin to impart flexibility to the LVN blocks for sectioning. This process took 6-7 months for each block of tissue, depending on the time required to decalcify the respective blocks of tissues a s determined by radiography. The 40 blocks of spinal tissue, containing 80 zygapophyseal joints, were sectioned in the sagittal or horizontal planes on a Polycut S microtome at a section thickness of 200 IJ-m,and stored on serially numbered pieces of white paper in 70% aqueous ethanol. One in 10 sections was stained in Ehrlich’s hematoxylin, counterstained in light green, dehydrated in ascending concentrations of ethanol, cleared in Histoclear, mounted in DePex (Gurr BDH: Product 36125) (Giles and Taylor, 1983), then examined and photographed by normal light and darkfield microscopy using a Wild M400 photomacroscope with apozoom lens and Phctonaut MPS 55 photographic system. RESULTS
In specimens showing relatively “normal” zygapophyseal joints for this age group a narrow surface lam-
355
ARTICULAR CARTILAGE LAMINA
ina was seen in 20 out of 80 joints (25%) as shown in Fig. 1A-D which include low and high power transmitted light and darkfield photomicrographs. In some instances there appeared to be continuity of the surface lamina up to the adjacent synovial folds. Darkfield microscopy dramatically enhanced the narrow strip of acellular tissue (Fig. lC,D). In specimens showing early osteoarthrotic changes, such as tinctorial variations (a staining variation presumed to be due to changes in cartilage matrix) and minor fibrillation involving most of the cartilage surface, a narrow surface layer of acellular tissue was also seen by transmitted light and darkfield microscopy to line the cartilage surface (Fig. 2A,B). In specimens showing advanced osteoarthrotic changes in zygapophyseal joints the acellular layer is not present when examined by transmitted light and darkfield microscopy (Fig. 3A,B). It should be noted that with darkfield microscopy of “normal” to early osteoarthrotic joint cartilage surfaces (Fig. 1C,D, 2B, respectively) the narrow strip of acellular lamina of the cartilage bounding the joint space is enhanced, whereas there is no enhanced lamina in joints with advanced osteoarthrosis (Fig. 3B). Also, areas of tissue adjacent to artifact spaces (caused by loss of small parts of tissue during processing, for example Fig. 2B) do not show corresponding areas of enhancement. Therefore, the acellular layer can be seen to exist in joints not exhibiting advanced degenerative changes and it is not an artifact, as an artifact seen a t the edge of any tissue bordering a space would be seen at the edge of tissues where part of the tissue has been dislodged during processing or has degenerated in advanced osteoarthrosis, which is not the case in this study. The thickness of the acellular layer can vary from 20-200 pm along the surface of the cartilage, and from one specimen to another, and appears to be unrelated to age or sex. DISCUSSION
The issue of whether a lamina splendens lines the surface of hyaline articular cartilage has led to considerable debate in the literature which has cast doubt upon its existence and in particular, Aspden and Hukins (1979) have criticized MacConaill’s (1951) lamina splendens as being merely a Fresnel diffraction pattern artifact on the edge of a section of cartilage viewed by phase contrast microscopy. However, this study illustrates the existence of an acellular layer, or lamina splendens, lining the surface of some lower
Fig. 3. A: A transmitted light photomicrograph of a 200 km thick section cut in the parasagittal plane through the lumbosacral zygapophyseal joint of a 78 year old male. There is advanced fibrillation and loss of the hyaline articular cartilage (H) on the facets of the superior articular process of the sacrum (SAP) and the inferior articular process (IAP) of the fifth lumbar vertebra, respectively. The fibrous capsule (C) is seen at the inferior margin of the joint. B: A darkfield photomicrograph of the specimen shown in Figure 3A shows no surface lamina. Importantly, there is no evidence of significant light artifacts along the cut edges of the residual osteoarthrotic cartilages, or any other parts of the joint, which could simulate a surface lamina. SAP, superior articular process of the sacrum; H, hyaline articular cartilage; IAP, inferior articular process of the fifth lumbar vertebra; C, fibrous capsule.
lumbar zygapophyseal joint facet cartilages in middle aged human cadavers which exhibit “normal” joints or only early osteoarthrotic changes for this age group. This appears to support the findings of those authors (MacConaill, 1951; Davies et al., 1962; Weiss et al., 1968) who have noted a narrow surface lamina on articular cartilage. Perhaps an explanation of the fact that the narrow lamina is not seen in all joints relates to technical difficulties involved in decalcifying and generally processing large blocks of osteoligamentous tissues for several months before sectioning can commence. Once advanced osteoarthrosis is present, the layer of acellular tissue is no longer recognizable and, in such specimens, no “white” line is seen on the osteoarthrotic cartilage surface by darkfield microscopy, nor is there any enhancement of the cut edge of any other joint structures. This, and the fact that an acellular layer can be seen on normal light illumination, indicates that the lamina splendens is not an artifact. However, it is not the purpose of this anatomical study to speculate on its possible physiological significance. ACKNOWLEDGMENTS
The author gratefully acknowledges the assistance provided by the clinical and technical staff of the Institute of Forensic Pathology and Laboratory of Microbiology and Pathology, State Health Department, Brisbane, Queensland, Australia. The financial assistance provided by the Australian Spinal Research Foundation Ltd. and the Foundation for Chiropractic Education and Research (USA) is acknowledged. LITERATURE CITED Aspden, R.M., and D.W.L. Hukins 1979 The lamina splendens of articular cartilage is a n artifact of phase contrast microscopy. Proc. R. SOC. Lond., B206:109-113. Barnett, C.H., D.V. Davies, and M.A. MacConaill 1961 Synovial Joints: Their Structure and Mechanics. Longmans, London, pp. 23-34. Benninghoff, A 1939 Lehrbuch der Anatomie des Menschen, J.F. Lehmann, ed. Munich, Verlag. Cameron, D.A., and R.A. Robinson 1958 Electron microscopy of epiphyseal and articular cartilage matrix in the femur of the newborn infant. J . Bone Joint Surg., 40A:163-170. Collins, D.H. 1949 The Pathology of Articular and Spinal Diseases. Edward Arnold, London, pp. 123-128. Collins, D.H., F.N. Ghadially, and G. Meachim 1965 Intra-cellular lipids of cartilage. Ann. Rheum. Dis., 24~123. Davies, D.V., C.H. Barnett, W. Cochrane, and A.J. Palfrey 1962 Electron microscopy of articular cartilage in the young adult rabbit. Ann. Rheum. Dis., 21~11-22. Ehni, G. 1977 Historical writings on spondylotic caudal radiculopathy and its effect on the nervous system. In: Lumbar Spondylosis: Diagnosis, Management and Surgical Treatment. P.R. Weinstein, G. Ehni, C.B. Wilson, eds. Year Book Medical Publishers, Chicago, pp. 1-12. Ghadially, F.N., G. Meachim, and D.H. Collins 1965 Extra-cellular lipid in the matrix of human articular cartilage. Ann Rheum. Dis., 24~136-141. Ghadially, F.N., and S. Roy 1969 Ultrastructure of Synovial Joints in Health and Disease. Butterworths, London, pp. 1-32. Giles, L.G.F., and J.R. Taylor 1983 Histological preparation of large vertebral specimens. Stain Techno]., 58:45-49. Ham, A.W., and D.H. Cormick 1979 Histology. ed 8. J.B. Lippincott, Philadelphia, p. 465. MacConaill, M.A. 1951 The movements of bones and joints (a) The mechanical structure of articulating cartilage. J. Bone Joint Surg., 33l3:251-257. Meachim, G. 1967 The histology and ultrastructure of cartilage. In: Proceedings of a Workshop on Cartilage: Degradation and Repair. C.A.L. Bassett, ed. National Research Council, Washington, p. 3.
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L.G.F. GILES
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