Synovial villiAn examination of these structures within the anterior compartment of the knee and metacarpo-phalangeal joints.код для вставкиСкачать
Synovial Villi: An Examination of These Structures Within the Anterior Compartment of the Knee and Metacarpo-Phalangeal Joints By D. G. PALMER I with the attached patella, was removed through a midline incision over the anterior aspect of the knee joint. Ten surgical specimens were obtained at the time of synovectomy for rheumatoid synovitis, from both knee and metacarpo-phalangeal joints. Of those subjects without a history of joint disease 2 were in the second decade, 2 in the third, 2 in the fifth, 1 in the sixth, 3 in the seventh, 6 in the eighth and 2 in the ninth decade, together with specimens from a 20-week and a 36-week-old foetus. All specimens were floated out in normal saline, before microscopic examination using a X I 0 eyepiece and a low power objective (Reichert X1, X2.5 or X5.0), with oblique side lighting. Photographic records were made, and the examination was supplemented on occasion by examination under a stereoscopic Olympus binocular microscope with a zoom objective. Structural form was frequently greatly clarified by staining small areas of the specimens with .05 per cent Evans blue dye for about one minute. Particular attention was paid to the following areas: the anterior and posterior surfaces of the suprapatellar bursa, the circumpatellar fold, and the suprapatellar vascular pad. Individual villi and localized areas of synovial membrane were photographed and then removed for the preparation of haematoxylin and eosin stained sections. Van Giesen’s stain, and the Gordon and Sweet silver impregnation method for reticulin were used on selected sections. Specimens were embedded in such a way as to ensure that the plane of section was known. of studying possible mechanisms responsible for the formation and persistence of pathological joint effusions, the author was prompted to seek descriptions of synovial villi in the literature. As no adequate descriptions of the gross morphology of these structures was found, the present study was made. It is hoped that the descriptions which follow will indicate that some correlation exists between the form and function of the synovial villus. These descriptions have been predominantly based on specimens taken from the anterior compartment of the knee joint, partly because concurrent studies of joint effusions largely involve this joint and partly because it was felt that it would be useful to draw attention to the various synovial structures within reach of the synovial biopsy needle. The Shorter Oxford English Dictionary defines a villus as “a slender hair-like process or minute projection forming one of a number closely set on a surface”. General use has expanded the meaning of this term to include tiny surface projections of quite variable form; but it is considered to be incorrect to classify as villi, unequivocally macroscopic projections such as the fat pads and synovial folds. N THE COURSE RESULTS Thirty post-mortem specimens were obtained from 20 subjects without a recorded history of joint disease. The suprapatellar bursa, together The general topography of the anterior compartment of the knee joint is shown in Fig. 1. The main villous bearing areas were From the Rheumatism Research Laboratories, Wellcome Medical Research Institute, University of Otago Medical School, Dunedin, New Zealund. D. G. PALMER,M.D., M.R.C.P., M.R.A.C.P.: Honorary Lecturer in Clinical Science and Clinical Assistant to the Rheumatic Diseases Unit, Wellcome Medical Research Institute, Dunedin, New Zealand. MATERIALS AND METHODS 451 ARTHRITIS AND RHEUMATISM,VOL. 10, No. 5 (October 1967) 452 Fig. 1.-Specimen, anterior compartment right knee joint, posterior aspect. The posterior wall of the suprapatellar recess has been divided and opened out. The quadriceps tendon (Q.T.) lines in the midline above the patella. The vascular suprapatellar (S.P.) and circumpatellar pads (C.P.) are obvious. Also shown is the lateral fold (L.F.), the medial fold (M.F.) and below, the infrapatellar fat pads (F.P.). (This specimen and the villi illustrated in Figs. 2-6 are from a 16 year old youth). found to be the lower half of the posterior surface of the suprapatellar bursa and the free borders and surfaces of the vascular suprapatellar and circumpatellar pads. The Development and Form of Normal Villi These observations were based largely on the specimens obtained from the 2 foetuses, 2 16-year old youths, a 23-year-old and a 26-year-old male. The numbers of villi present in the specimens from the 4 young adults varied from sparse to prolific in the lower portion of the posterior wall of thp suprapatellar recess; but appear- D. G . PALMER Fig. 2.-Vascular leaf-shaped villi. The avascular elongated processes arising from these villi are secondary villi. (Evans blue dye, oblique light, XSO). ances were similar in the other areas under consideration. 1. The leaf-shaped villus (Figs. 2 and 3). 'These structures have a narrow base and expand into a flattened lanceolate form enclosing a vascular network. No villi were noted in a 20-week-old foetus, but a single villus found in the specimen from a 36-week-old foetus was a disproportionately large example of this form (length 3 mm.). I n the specimens obtained from the young adults this form of villus was found arising as part of a variably developed villous covering over the lower part of the posterior wall of the supra-patellar recess, and from the supra- and circumpatellar pads; b u t was not entirely restricted to these areas. 2. The fan-shaped illu us (Fig. 4.) I n the young adult specimens, vascular villi of this shape were found to form the inner SYNOVIAL ~ 7 1 ~ ~ 1 Fig. 3.-Histological section of a villus within the group illustrated in Fig. 2. The section has included an avascular apical secondary villus. (Haematoxylin and eosin, x200). free border of the circumpatellar pad. An almost continuous series of such villi produced a scalloped edge to this structure, directed inwards towards the patella. In a well-developed posterior wall, i.e., juxtafemoral villous complex, such villi varied from delicate folds containing a single capillary loop to structures having an attached base up to 3 or 4 mm. long and containing a complex arcading system of vessels. The longer-based examples of this form have been classified as folds. It was apparent that villi of this nature had not developed in the immature synovial membrane and, though often recognizable in specimens from elderly persons, had undergone much degeneration. 3. Villous folds. This category was limited to include only minute vascular synovial folds. Villous folds were quite consistently found in all the adult knee joint specimens examined. The juxta-patellar 453 Fig. 4.-A vascular fan-shaped villus. One of a series arising from the circumpatellar pad and directed towards the patella. (Oblique light, X80). surface of the circumpatellar pad in particular was usually folded so as to resemble the bellows of a concertina. A transverse section through this pad showed, on microscopical examination, a series of parallel tongue-like projections of synovium, directed into the circumpatellar recess (Figs. 5 and 6 ) . Less consistently, the surface of the suprapatellar pad was sometimes thrown into a series of overlapping vascular folds. Villous folds from the lower posterior part of the suprapatellar pouch are shown in Figs. 7 and 8. Abnormal Villi 1 . Degenerate uilli. It was apparent that beyond the fifth decade, there was a decrease in the well-formed vascular villi of the type considered above, with a marked increase in other types of villous processes. a) Infiltrated uilli. Leaf -shaped villi were D. G . PALMER 454 Fie. 5.-A transverse section through the circukpatellar pad. A substantial fibro;s fold (not present) the more deeply placed vascular folds in this particular section. (Haematoxylin and eosin, X36). transverse section through the folds illustrated in Fig, 7 . (Haematoxylill and eosin, 168). Fig. 6.-A higher power photomicrograph of two of the tongue-like vascular folds seen in Fia. 5. (Haematoxylin and eosin, X168). seen only occasionally in the joints from aged persons. Instead, club-shaped villi were found, which varied in appearance from vascular structures expanded with areolar tissue to large fat-filled villi 4 4 mm. in length. It was considered that these villi arose as a result of connective tissue increases within leaf-shaped villi. b) Attenuated villi. Arising individually from the synovium as slender filiform strands, and made up of little more than a pair of small blood vessels, these villi were considered to be the attenuated remnants Of leaf-shaped c) Pseudovilli (Figs. 9 and 10). Villi of this form largely accounted for the apparent increase of synovial processes with age in the knee joints of the elderly. These were formed as the result of multiple irregular tears deep into the various delicate synovial folds and villous processes. The disproportionate length of some of these processes was felt to be the result of tears extending parallel to the vascular arcades after the initial rupture at the free surface. As discussed below, there was also some evidence of active Iongitudinal Fig. 8.-A SYNOVIAL VILLI Fig. 9.-Tears extending into the superior free border of the suprapatellar pad. Note the superficial network of vascular loops. (Evans blue dye, oblique light, XSO). Fig. 10.-Tag villi on the posterior aspect of the quadriceps expansion. (Evans blue dye, oblique light, X80). Fig. 11.-Rheumatoid villi. No vascular network is visible beneath the granular opaque surface. (Oblique light, XSO). 455 Fig. 12.-Photomicrograph of the specimen shown in Fig. 11, which shows the villous surface to be of fibrinoid material and blood vessels to be absent. (Haematoxylin and eosin, x 200 ). Villous processes which have been referred to as “tag” villi were noted on all the synovial surfaces studied, after such surfaces had been stained with Evans blue dye. They appeared as minute degenerate sheets, strips or strands of synovial membrane. It was thought probable that these structures arose as the result of the synovial membrane being stripped from the underlying supporting tissues. 2 Proliferative villi (Fig. 11). a) Hyperplastic uilli. In specimens of synovial membrane obtained from the 10 joints affected by rheumatoid arthritis the villous structure was found to be distinctive. It is probable that these villi were derived both from preexisting synovial villi and by spontaneous growth, as numerous rheumatoid villi may be found in situations where normal villi are not commonly seen. The characteristic villi of rheumatoid arthritis varied very much in shape; but were always bulky and dense, and had nothing of the delicate form normal villi possess. They were either elongated and pedunculated or squat and sessile. Adhesions often formed bridges between them and vessels might Or might not be Seen coursing over their surfaces. They arose 456 D. G . PALMER singularly or formed a complicated Key2 has reproduced drawings by Hammar3 of villi projecting from a synovial branching vegets‘1t’ion. It seemed that the vasculature of such surface. Key indicated that villi could be villi gradually became imbedded in an in- classified according to the type of undercreasing matrix of granulation tissue and lying connective tissue to which they were in villi which, histologically, had under- attached, i.e., that areolar, fibrous and fatty gone partial fibrinoid degeneration; no villi could be recognised, and that they superficial vascular network was visible by might be pedunculated or sessile and could have secondary villi projecting from them. oblique light observation. 6 ) Secondary villi (Figs. 2 and 3). He also drew attention to the distinction These minute villi, made clearly visible by between membranous folds and localized Evans blue staining of the specimen, arose villous processes. Sigurdson described as small projections from the surfaces of tapering and blunted villi and observed all forms of parent villi and membranes. that these projecting villi were connected They appeared either as short stubble-like to the joint capsule by a pedicule or stalk. During the present study it appeared processes, or as lengthy strands. Histological examination showed these to consist that a classification relating the type of of cords of ovoid cells enclosed in a net- connective tissue core to that found in the work of reticulin. The finer of these struc- subjacent synovium was not always infaltures had no vascular core; but the more lible (areolar villi are often found arising bulky enclosed one or more capillaries. from the fat pads), and that a morphological classification based on histological A Morphological Classification of Synovial studies failed particularly to distinguish Villi pedunculated villi from membranous or vilThe following systematic classification of lous folds. Neither of these methods of villi is based on those forms which have classification is of particular help in the been described in this paper: problem of correlating morphology with Normal oilli: (Villi presumed to be normal the probability of some normal function. It was felt that in describing the external functional appendages of the synovium ) form of synovial villi, a practical basis for 1) Leaf-shaped villi 2 ) Fan-shaped villi their classification and information as to 3 ) Villous folds their probable life history would be proAbnormal villi and pseudooilli. (Villi provided. duced by or damaged by disease) Sigurdson4 and Gardner and Gray5 have 1 ) Degenerate villi provided illustrations of structures in a ) Infiltrated villi b ) Attenuated villi human foetal joints described as villi, c ) Pseudovilli (membranous villi and though these structures could equally tag villi) well be synovial folds, rather than, as is 2 ) Proliferative villi implied, finger-like projections. The presa ) Hyperplastic villi ent study has included the observations b ) Secondary villi that fully developed leaf-shaped villi may C)ISCUSSION be present in the human foetal knee at 36 The external morphology of the synovial weeks. Villous folds could well develop by villus seems not to have been studied in a concertina action across the membrane; detail. Interest in these structures is, how- but normal pedunculated villi no doubt deever, of long standing. Their original de- velop as organized synovial outgrowths. scription is attributed to Lushka, 1 and The present observations also confirmed 457 SYNOVIAL VILLI a previous account by Bennett, Waine and Bauer6 that degenerative changes could appear within the knee by the third decade. These authors and others7 observed, but could not account for, the frequent increase and prominence of “villous” processes with increasing age. The term hypertrophy, as used by most authors in referring to this phenomenon, is for the most part inappropriate, as the underlying process is predominantly one of degeneration, with tears appearing in pre-existing synovial structures. Though the initial impression on examining the synovial membrane from an aged joint is usually one of increased villous number and size, closer examination has revealed attenuated, infiltrated and torn villous remnants, which are devoid of an organized vasculature and could well be physiologically functionless. Any increase in bulk is usually the result of connective tissue infiltration, predominantly fat. Only the presence of the opalescent thread-like secondary villi could be regarded as resulting from continued growth. Meyers regarded intracapsular fringes of processes and tags as being mostly attrition products. Any attempt to correlate villous form with likely function remains speculative. It would seem reasonable to suppose that a rich blood supply, combined with a large surface area, does parallel the potentiality of the membrane for absorption and secretion. On occasion the appearances of the circumpatellar and suprapatellar regions were almost gill-like in form, being made up of superimposed longitudinal folds of synovial membrane. However, Clarks did not find any specific localization of absorptive function to the synovial villi using intra-articular injections of trypan blue. The various forms of normal pedunculated villi within the knee do vary numerically from joint to joint and in general have seemed to be of less importance than the more consistent villous folds. Some comments have been made concerning the vascular architecture of synovial villi. Reference should be made to the study of the vascular anatomy of the synovial membrane reported by Ferri,l” whose illustrations of villous vascular patterns are well worth studying. ACKNOWLEDGMENTS The financial support for this work was provided by the Golden Kiwi Medical Research Distribution Committee. My thanks go to Dr T.C. Highton for his help and constructive criticism. SUMMARY The synovial villus is normally an extremely vascular structure of leaf-shape, fanshape or folded form. With age degenerative changes occur, consisting of infiltration, attenuation, traumatic reduplication and longitudinal growth. The increase in “villous” processes with age is mainly due to the formation of pseudovilii. Normal villous structures become damaged and degenerate. In rheumatoid arthritis the abnormal gross morphology is distinctive and can be correlated with the better-known histological changes. SUMMARIO IN INTERLINGUA Le villo synovial es usualmente un structura extremente vascular con un conformation de folio o de flabello o plicate. Alterationes degeneratori occurre con le avantiamento del etate. Istos consiste de infiltration, attenuation, reduplication traumatic, e crescentia longitudinal. Le augment0 in le processos “villose” con le avantiamento del etate del subject0 es le resultato del formation de pseudovillos. Normal structuras villose deveni lesionate e suffre degeneration. 458 D. G. PALMER In casos d.e arthritis rheumatoide, le anormalitates macromorphologic es distincte e pote esser correlationate con le melio cognoscite alterationes histologic. REFERENCES 1. Lushka, H.: Zur Entwicklungsgeschichte der Gelenke. Arch. Anat. u. Physiol, 1885, p. 481. Quoted by Kling, 1938. 2. Key, J. A.: The synovial membrane of joints and bursae. Special Cytology, Ed. 2, 1084. New York, Paul B. Hoebler, 1932. 3. Hanimar, J. A.: Ueber den fieneren bau der gelenke. I. Die Gelenkenmembran. Arch. Mikr. Anat. 43:266, 1894. 4. Sigurdson, L. A.: The structure and function of articular synovial membranes. J. Bone Jt. Surg. 12:603, 1930. 5. Gardner, D. .I. and Gray, E.: Prenatal development of the human knee and superior tibio-fibular joints. Amer. J. Anat. 86:235, 1950. 6. Bennett, G. A., Waine, H., and Bauer, W.: 7. 8. 9. 10. Changes in the knee joint at various ages. Ed. 1, 57. New York, The Commonwealth Fund, 1942. Parker, F., Keefer, C. S., Myers, W. K. and Irwin, R. I.: Histological changes in the knee joint with advancing age. Arch Path. 17:516, 1934. Meyer, A. W.: The minuter anatomy of attrition lesions. J. Bone Jt. Surg. 13:341, 1931. Clark, Le G.: An experimental study of the nature of the synovial membranes of joints. J. Anat. 63:152, 1928. Ferri, E.: Ulterio osservazioni istobiologiche a contrast0 di fase sullo strato sinoviale. Ateneo Parmense 35:1, 1964.