J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

J. clin. Path., 31, Suppl. (Roy. Coll. Path.), 12, 214-222

New knowledge of chondrocalcinosis

PAUL DIEPPE From the Department ofMedicine, University ofBristol

There are three varieties of cartilage-hyaline, parathyroidism, haemachromatosis, hypothy- elastic, and fibrocartilage. Hyaline cartilage is the roidism, hypophosphataxia, hypomagnesaemia, precursor of bone. In the adult it is mainly found at gout(?), diabetes mellitus (?), Wilson's disease (?), bone ends, forming the load-bearing surface of ochronosis (?)). synovial joints. Extra-articular fibrocartilages such as those of the trachea and ribs often calcify with Historical perspective advancing age. Articular cartilage, however, usually remains free from mineral deposits. The term Intra-articular calcification has been recognisedforat 'chondrocalcinosis' may be defined as a pathological least a century. It was mentioned by Garrod (1876) state characterised by the precipitation of insoluble and by Adams (1872). With the advent of joint calcium salts in articular and periarticular cartilage. radiography there were a number of reports of The presence of chondrocalcinosis can be proved calcification of knee menisci (Pearson and Davin, only by crystallographic examination. Its presence 1921). Wolke (1935) described five cases from 2569 may be inferred by radiological examination or the knee radiographs. Zit'nan and Sifaj (1957) described discovery of crystals in synovial fluid. In addition, 12 cases, and they later identified familial cases with articular chondrocalcinosis is sometimes accom- polyarticular lesions and an associated arthritis by copyright. panied by arthritis. There are therefore three (2itnian and Silaj, 1976). separate phenomena associated with chondrocal- While 2ithan and Sifaj surveyed joint radiographs cinosis-radiological changes, crystals in synovial Hollander and McCarty (1961) examined joint fluid, and arthritis. These may occur separately or in fluid by polarised light microscopy and discovered any combination (Fig. 1). urate crystals in gout. McCarty et al. (1962) also The term 'chondrocalcinosis' was often used noticed a different type of crystal in some patients loosely in reference to radiological signs, the presence with acute arthritis. They were identified by x-ray of pyrophosphate crystals in joints, or a charac- diffraction as calcium pyrophosphate dihydrate teristic form ofarthritis. Recent work has highlighted (CPPD) (Kohn et al., 1962). the fact that many different crystals may be precipi- Chondrocalcinosis has since been studied in http://jcp.bmj.com/ tated in cartilage and has led to a questioning of the various countries. Analysis of patients with radio- causal relationship between crystals and arthritis. logical chondrocalcinosis by Currey (1966) and of Further work would be aided by the use of a disci- those with pyrophosphate (PP) crystals in synovial plined nomenclature-referring, for example, to fluid (Bjelle and Sundin, 1974) led to findingssimilar articular pyrophosphate chondrocalcinosis-with a to those of 2itinan and Siraj and of McCarty, who descriptive account of the associated features. has now reported on over 300 cases (McCarty, 1976).

Calcium salts positively identified in human A pattern emerges of patients with linear calcifica- on September 23, 2021 by guest. Protected articular cartilage are: (1) calcium pyrophosphate tion of hyaline cartilage identified on x-ray examina- dihydrate, Ca2P207.2H20 (pyrophosphate, CPPD); tion, PP crystals in synovial fluid, and an arthritis (2) hydroxyapatite, Calo(P04)6.(OH)2 (hydroxy- that is either acute oligo- or mono-articular ('pseudo- apatite, apatite, HA); and (3) dicalcium phosphate gout') or chronic destructive, similar to osteoarthrosis dihydrate, CaHP04.2H20 (brushite, calcium phos- ('chronic PP arthropathy'). Thus chondrocalcinosis phate dihydrate, DCPD). becomes synonymous with PP deposition and its Chondrocalcinosis may be classified according to characteristic arthritis. (1) the nature of the deposit (pyrophosphate, hydroxyapatite, Brushite, or mixtures); (2) the type New crystals (familial, metabolic, sporadic, age associated); and (3) the metabolic associations: (a) hydroxyapatite McCarty and Gatter (1963) described the presence (chronic renal disease); (b) pyrophosphate (hyper- of dicalcium phosphate dihydrate in human fibro- 214 J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

New knowledge of chondrocalcinosis 215

CHONDROCALCI NOSIS scopy, and many different salts may form the positively birefringent crystals usually assumed to be may be associated with PP (Gatter, 1977). RADIOLOGICAL CRYSTALS IN Complex analytical techniques and tissue pro- CHANGES SYNOVIAL FLUID cessing may alter the mineral content from that present in vivo. More crystallography studies are These may occur separately or in therefore required before conclusions can be any combination reached about the incidence and nature of the different deposits of chondrocalcinosis. A scheme ARTHRITIS combining several different analytical techniques is Fig. 1 Clinical association ofchondrocalcinosis. shown in Fig. 2. Site of deposits cartilage and, later, the pathological findings in 215 cadaver knee menisci (McCarty et al., 1966). Intra-articular calcification was always thought to Three salts were identified: calcium pyrophosphate comprise PP and periarticular mineral deposits of HA dihydrate (CPPD) (3-2 %), dicalcium phosphate (McCarty and Gatter, 1966; Pinal and Short, 1966). dihydrate (DCPD) (2-3 %), and hydroxyapatite In neither case is this always so. (HA) (1I4 %). Vascular calcification in the outer one- Calcium salts of PP form monoclinic and triclinic third was also common (hydroxyapatite). Small un- crystals. The latter predominate. They are deposited identified deposits were seen in some specimens. No preferentially in fibrocartilage. The commonest site comprehensive study has been made on articular is the knee meniscus, followed by the symphysis hyaline cartilage. Recently Ali (1977) has identified pubis, wrist, and intervertebral discs. Shoulders, minute deposits of HA in osteoarthrotic hyaline elbows, hips, metacarpophalangeal, and other joints cartilage, and Doyle et al. (1978) have made similar may also be affected. Linear calcification of tendons observations. Fibrocartilage seems to be peculiarly is not uncommon. A recent study reported an susceptible to PP deposits but hyaline cartilage may incidence of 13-5%, the commonest sites being the by copyright. be more readily mineralised with HA. tendo achilles, plantar fascia, and quadriceps tendon Both DCPD and HA have recently been described (Gerster et al., 1977). These periarticular deposits in the synovial fluid and tissues of patients with may be associated with inflammation but not all cal- arthritis. Moskowitz et al. (1971), Faure et al. (1977), cific periarthritis is due to HA. and Utsinger (1977) have described DCPD-related The results of microscopy of PP-containing arthritis, and Dieppe et al. (1976) and Schumacher cartilage have varied. The most characteristic finding et al. (1976) HA-related arthropathy. Combina- is of rounded deposits of crystals in a granular tions of these different salts also occur. Moskowitz matrix in the mid-zone, often in a line along the et al. (1971) identified a mixture of PP and DCPD, cartilage, resulting in a linear shadow on the x-ray and mixtures of PP and HA have been found in the picture (Bjelle, 1972; Reginato et al., 1974). Crystals http://jcp.bmj.com/ same joint by Okazaki et al. (1976) and Dieppe et al. have also been identified in perichondrocyte lacunae (1978). (McCarty et al., 1963; Schumacher, 1976) and in Sophisticated techniques are needed to identify superficial cartilage (Zitnian and Sifaj, 1966; de Seze the calcified deposits. Diffraction patterns provide et al., 1963). It is tempting to postulate that the precise crystal analysis, and both PP and DCPD deposits around mid-zone chondrocytes (each have been identified in this way. HA crystals are crystal is only 250-500 A long) are the initial site of usually too small for single crystal diffraction but calcification and the superficial deposits the result of on September 23, 2021 by guest. Protected powder patterns have been obtained. Other indirect extensive loss of cartilage. Synovial deposits are ways of identifying these substances include infrared also common in patients with PP chondrocalcinosis spectroscopy and analytical electron microscopy (Schumacher, 1976). These deposits are usually (Dieppeet al. 1977). Many workershave used electron superficial and presumably come from the cartilage. microscopy with attached x-ray energy spectroscopy Pachas (1972), however, has found deposits of PP in to calculate the ratio of calcium and phosphorus in the synovium in the absence of chondrocalcinosis, different crystals compared with known standards. raising the possibility of active deposition outside the This technique, however, cannot differentiate PP cartilage. These studies have not resolved the from DCPD (Crocker et al., 1977; Nuki et al., 1978). important question of whether cartilage changes or Polarising microscopy is another indirect technique, crystal deposits occur first. Nor have they deter- ideal for differentiating gout from pseudogout. But mined if there are any differences between familial, small HA crystals cannot be seen by light micro- metabolic, and sporadic cases. J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

216 Paul Dieppe

LABORATORY REFERENCE SAMPLE from PATIENT Fig. 2 Techniquesfor (1) ORDI NARY and POLARIZED identifying crystals. XES LIGHT MICROSCOPY = x-ray energy spectro- metry. SEM = scanning (2) ANALYTICAL ELECTRON MICROSCOPY (3) X-RAY DIFFRACTION (4)1 NFRA-RED SPECTRO- electron microscopy. All l I I )PHOTOMETRY samples can be looked at by light microscopy (1). XES SEM ELECTRON INDIVIDUAL CRYSTALS DIFFRACTION Processes (2), (3), (4) will be dependent on the type and size ofsample ELEMENTAL MORPiOLOGY CRYSTAL LATTICE CRYSTAL LATTICE CHARACTERISTIC RATIO AB SORPTION available. SPECTRA

CRYSTAL IDENTIFICATION

Growth cartilage calcifies by the formation of Nuki et al. (1978), however, have been unable to needle-shaped microcrystals of HA in matrix vasicles demonstrate this phenomenon using cultured mono- adjacent to chondrocytes (Ali and Wisby, 1975). layers of chondrocytes. Similar appearances have been noted in osteo- Additional sources of joint PP may include other arthrotic hyaline cartilage by Schumacher (1976), cells, subchondral bone, and the crystals themselves. Ali (1977), and Doyle et al. (1978). Larger deposits of Breakdown of inorganic PP is a major source of HA occur in the soft tissues of osteoarthrotic joints simple phosphate radicals, a process accelerated by (Collins, 1949; Fassbender, 1975). We do not know specific pyrophosphatases and by the alkaline pbns- whether these are 'seeded' from bony or cartilagenous phatase that is found in cartilage (Ali, 19/7).

fragments; from the HA crystals in cartilage; or Calcium metabolism is in part controlled by para- by copyright. whether, as could be the case with pyrophosphates, thormone. McCarty and O'Duffy (1976) have the soft tissues are a second site of active calcifica- reported high levels of parathormone in both PP tion. The joints affected are those affected by primary arthropathy and osteoarthrosis. Local levels of free generalised osteoarthritis (Kellgren and Moore, calcium in cartilage may depend on proteoglycan 1952). In HA calcific periarthritis the affected joints binding, and loss of proteoglycans may predispose to are principally the shoulder and, to a lesser extent, calcification (Benderly and Maroudas, 1975). This the hip and others (Pinals and Short, 1^6 5). argues in favour of chondrocalcinosis being Thus both HA and PP are found in articular and secondary to cartilage damage. Proteoglycans are periarticular tissues. Although the sites of deposition also a possible site of crystal nucleation, but the

differ, morphological studies have not clarified the most likely site of formation of HA is the chondro- http://jcp.bmj.com/ mechanism of formation of these deposits. cyte matrix vesicles (Ali et al., 1970; Ali, 1977). The interrelationships between PP, DCPP, and Metabolic background to chondrocalcinosis HA seem complex. Pyrophosphate inhibits the for- mation of apatite and apatite formation is aided by Crystallisation occurs only when there is both a alkaline phosphatase, itself a powerful pyrophos- high enough concentration of metabolites and the phatase (Fleisch et al., 1966). DCPD may be inter- physical conditions to initiate nucleation. Much is mediary in the formation of HA. known of the metabolism of calcium, phosphorus, The appearance of different salts in the same on September 23, 2021 by guest. Protected and inorganic pyrophosphate but very little of the clinical situation and the coexistence of different salts nucleation of their salts. in the same tissue is hard to explain. A simplified Inorganic pyrophosphate is formed by many outline of some possiblemetabolicinterrelationships, metabolic processes throughout the body, principally based on the work of Howell (1978), is shown in by the breakdown of ATP. Serum and urine levels Fig. 3. are not altered in the forms of arthritisthathavebeen Most cases of PP deposition are idiopathic, but studied, but synovial fluid levels are high in both PP familial cases have been reported. A few may be deposition and osteoarthritis (Russell et al., 1971; secondary to other metabolic disease. The only Altman et al., 1973; Silcox and McCarty, 1973). The unequivocal metabolic situation predisposing to origin of synovial PP may be the chondrocytes, apatite deposition is chronic renal failure (Canner which have been shown to liberate PP from in-vitro and Decker, 1964; Lain et al., 1977). There is a long cultures of cartilage slices (Howell et al., 1976). list ofpossible metabolic causes, but theyare difficult J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

New knowledge of chondrocalcinosis 217 PYROPHOSPHOTASES are partly due to the different ages of the populations ALKALINE PHOSPHATASE studied; chondrocalcinosis is more common in the ATP - PP' -gfi tpo4 elderly (Menin et al., 1977). Genant (1976) described the conditions necessary for good radiological visualisation. Gerster et al. (1977) documented the ? BOUND as INHIBITORY radiological signs of periarticular tendon calcifica- Mg COMPLEX tion in patients with chondrocalcinosis, and Resnick et al. (1977) described the characteristic radiological CALCIUM features of chronic PP arthropathy that distinguish (PROTEOGLYCAN BOUND) it from osteoarthritis. /\VIA DICALCIUM PHOSPHATE Chondrocalcinosis usually results in a linear 4DIHYDRATE shadow in x-ray pictures. However, 'spotty' or CA2P2 072H202 ----- CA10 (P014)6 (OH)2 rounded deposits are also seen, particularly in (? SITE ) (MATRIX VESICLES) osteoarthritis where they are often described as 'loose bodies'. Analysis of the type of mineral in the Fig. 3 Diagrammatic outline ofsome metabolic tissues and synovial fluid of patients with linear or pathways participating in calcium crystalformation in spotty deposits has shown that most linear deposits cartilage. are associated with PP deposition and most spotty deposits with HA (Table) (Dieppe, 1978). However, the relationship is not perfect, re-emphasising that the to prove since only one controlled study has been nature of cartilage deposits should not be interpreted made (McCarty et al., 1974). Investigation of the from radiographs alone. secondary causes of crystal deposition should aid understanding of the phenomenon. For example, Crystals in Hamilton et al. (1968) have defined various special synovial fluid features of the disease when it is associated with PP and HA crystals are unlikely to precipitate haemachromatosis, an association which may directly in synovial fluid, but DCPD crystals may by copyright. be due to local deposits of iron aiding nucleation of form in the fluid after its removal from the joints PP crystals. Similarly, the association with hypo- (Dieppe et al., 1978). Crystals deposited in cartilage magnesaemia may be because magnesium ions may or may not appear in the synovial fluid. Bennett normally bind inorganic PP. Hypophosphatasia et al. causes PP deposits because of low levels of alkaline (1976) postulated that they appear only in the phosphatase (Eade and Swannell, 1977). The other presence of some 'factor' that increases solubility, associations of PP deposition have been reviewed by decreasing the size of the deposit and resulting in Hamilton 'crystal shedding' into the joint space. For these (1976). reasons, examination of synovial fluid cannot be regarded as a satisfactory method for detecting New aspects of features associated with http://jcp.bmj.com/ features chondrocalcinosis. chondrocalcinosis: radiological Furthermore, accurate identification of crystals in synovial fluid is difficult. Wolke (1935) reported that 019% of a population To be identified by light showed evidence ofchondro- microscopy they must be at least 0 5 ,um long. The surveyed radiologically initial deposits of both PP and HA are much smaller. calcinosis. Subsequent radiological surveys suggested HA can be that the incidence of chondrocalcinosis is nearer 5 % identified by analytical electron micro- (McCarty 1977). Recently Ellman and Levin scopy. I have mentioned the limitations of this (1975) but it on September 23, 2021 by guest. Protected studied an elderly Jewish population and found that technique has led to clear descriptions of HA- had chondrocalcinosis. These induced crystal synovitis (Dieppe et al., 1976; 27-6y% discrepancies Schumacher et al., 1977) (Fig. 5). The lack of correlation between the numbers of crystals seen in synovial fluids and the clinical features of the Table Relationship between radiological signs and type arthritis, described by McCarty (1974a), has been ofcrystal identified in synovialfluid in chronic arthritis a feature of our studies and remains unexplained. Radiological signs Crystals identified Arthritis Pyrophosphate Hydroxyapatite Linear calcification 4 1 McCarty (1974b) described four important clinical Spotty calcification 1 7 associations ofPP deposition: 'pseudogout', 'pseudo- None 2 2 osteoarthritis', 'pseudorheumatoid arthritis', and J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

218 Paul Dieppe 'pseudoneurotrophic joints'. The first two are the Faure et al., 1977; Utsinger, 1977). most common. Other conditions described include HA crystals have been associated with four forms spinal stiffness (Reginato et al., 1970), haemarthrosis of arthritis-acute calcific periarthritis (Pinals and (Phelip et al., 1976), acute spinal pain, and poly- Short, 1966), osteoarthritis (Dieppe et al., 1976; myalgia rheumatica (Storey and Huskisson, 1976). Huskisson et al., 1978), synovitis in renal failure PP crystals provoke inflammation (see below), and (Lain et al., 1977), and an acute arthritis the synovitis of pseudogout is almostcertainlycaused (Schumacher et al., 1977). A causal relationship in this way (Schumacher, 1976). between the acute syndromes and the crystals seems The association between the presence of the reasonable in view of their inflammatory potential. crystals and the other forms of arthritis is obscure. Their role in osteoarthritis is not clear. Huskisson Chondrocalcinosis is common but it is difficult to be et al. (1978) and Ali (1978) have evidence of a link certain of the significance of associations with com- between HA deposition and osteoarthritis and, mon conditions. The association of chronic and although probably a secondary phenomenon, it may destructive arthritis (Richards and Hamilton, 1974) explain some of the inflammatory features of this with chondrocalcinosis is common but is un- disease (Dieppe et al., 1978). explained. Zitnian and Sifaj (1976) have evidence that in familial cases chondrocalcinosis appears before Crystal-induced inflammation chronic arthritis. But crystal deposition could be an epiphenomenon resulting from the same metabolic After PP crystals were identified experiments showed changes that cause the cartilage damage. The few that they could cause acute inflammation (McCarty reports of DCPD deposition suggest an association et al., 1966). HA crystals are also phlogistic (Dieppe with a chronic destructive arthritis similar to et al., 1976; Denko and Whitehouse, 1976; chronic PP arthropathy (Moskowitz et al., 1971; Schumacher et al., 1976). PP crystals react with by copyright.

Fig. 4 Transmission electron micrograph ofphagocytic cell from human osteoarthritic http://jcp.bmj.com/ synovialfluid. Aggregates of hydroxyapatite crystals are seen within a phagosome. on September 23, 2021 by guest. Protected J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

New knowledge of chondrocalcinosis 219

Fig. 5 Scanning electron micrograph of calcium pyrophosphate dihydrate crystals recoveredfrom human osteoarthritic cartilage showing variation in size and shape ofcrystals. ( x 125 000) by copyright. http://jcp.bmj.com/

leucocytes, are phagocytosed (Tse and Phelps, 1970), reviews of some aspects of crystal-induced inflam- have membranolytic activity (Wallingford and mation (Schumacher, 1977; Dunn et al., 1978; McCarty, 1971), and cause release of a chemotactic Allison, 1978). There is now considerable under- factor (Spilberg et al., 1975). These responses tend to standing of acute inflammation (and thus 'pseudo- be quantitatively less than with urate. The reaction gout' or acute calcific periarthritis) but little know- is complement-independent and is mediated in a ledge of how, if at all, crystals contribute to chronic on September 23, 2021 by guest. Protected similar way to other forms of acute inflammation disease. (Willoughby, 1975). Less is known about HA crystals. They are phagocytosed (Fig. 4) (Maurer and Conclusions Schumacher, 1977) and can cause chronic as well as acute inflammation (Dunn et al., 1978). Calcium pyrophosphate was thought of as the salt of Important determinants of the phlogistic pro- chondrocalcinosis, but clearly many different cal- perties of crystals include surface charge, the ability cium phosphates may be deposited in articular to bind protein (especially IgG), and crystal size- cartilage. Some cases are familial and a few secondary smaller crystals are more inflammatory than larger to metabolic disease, but in most there is no obvious (Dunn et al., 1978). Scanning electron microscopy cause for the calcification. Recent work on the has revealed a wide variety in size and shape of pathology and metabolism of cartilage has drawn crystal deposits and this may have a bearing on attention to its activity and the delicate balance clinical sequelae (Fig. 5). There have been recent between the activators andinhibitorsofcalcification. J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

220 Paul Dieppe Chondrocalcinosis may be accompanied by three Crocker, P. R., Dieppe, P. A., Tyler, G., Willoughby, clinical phenomena-radiological changes, crystals D. A., and Chapman, S. K. (1977). The identification in the synovial fluid, and arthritis. The application of of particulate matter in biological tissues and fluids. Journal ofPathology, 121, 37-40. new analytical techniques to the study of synovial Currey, H. L. F., Key, J. J., Mason, R. M., and fluid has enabled hydroxyapatite and other crystals Sweetenham, K. V. (1966). Significance of radiological to be identified and their presence correlated with calcification of joint cartilage. Annals of the Rheumatic radiological features and symptoms. Both hydroxy- Diseases, 25, 295-306. apatite and pyrophosphate crystals are inflam- Denko, C. W., and Whitehouse, M. W. (1976). Experi- matory and acute synovitis can result from their mental inflammation induced by naturally occurring presence in joints. Chondrocalcinosis, however, is microcrystalline calcium salts. Journal ofRheumatology, more often associated with chronic joint disease, and 3, 54-62. in these cases calcification may be the clue to an Dieppe, P. A. (1977). Crystal induced inflammation and underlying metabolic defect for some osteoarthritis. In Perspectives in Inflammation, edited responsible by D. A. Willoughby, J. P. Giroud, and G. P. Velo, forms of 'degenerative' arthritis. pp. 225-231. MTP Press, Lancaster. Dieppe, P. A. (1978). Calcium salt deposition in osteo- References arthritis. European Journal of Rheumatology and Inflammation, in press. Adams, R. (1873). A Treatise on Rheumatic Gout, Dieppe, P. A., Crocker, P. R., and Willoughby, D. A. 2nd edition. Churchill, London (1977). Microanalysis of particulate material involved Ali, S. Y., Sajdera, S. W., and Anderson, H. C. (1970). in inflammation. In Perspectives in Inflammation, edited Isolation and characterisation of calcifying matrix by D. A. Willoughby, J. P. Giroud, and G. P. Velo, vesicles from epipyseal cartilage. Proceedings of the pp. 233-235. MTP Press, Lancaster. National Academy of Sciences of the United States of Dieppe, P. A., Huskisson, E. C., Crocker, P. R., and America, 67, 1513-1520. Willoughby, D. A. (1976). Apatite deposition disease, Ali, S. Y., and Wisby, A. (1976). The role of matrix a new arthropathy. Lancet, 1, 266-269.

vesicles in normal and osteoarthritic cartilage. Pro- Dieppe, P. A., Huskisson, E. C., and Willoughby, D. A. by copyright. ceedings ofthe Royal Microscopical Society, 11, Pt 5, 62. (1978). The inflammatory component of osteoarthritis. Ali, S. Y. (1977). Matrix vesicles and apatite nodules in In Aetiopathogenesis of Osteoarthritis, edited by G. arthritic cartilage. Perspectives in Inflammation, edited Nuki. Pitman Medical, London, in press. by D. A. Willoughby, J. P. Giroud, and G. P. Velo, Dieppe, P. A., Doyle, D. V., Huskisson, E. C., pp. 211-223. MTP. Willoughby, D. A., and Crocker, P. R. (1978). Mixed Ali, S. Y. (1978). In Aetiopathogenesis of Osteoarthritis, crystal deposition disease and osteoarthritis. British edited by G. Nuki. Pitman Medical, London, in press. Medical Journal, 1, 150-151. Allison, A. C. (1978). Effects of silica and asbestos on Dieppe, P. A., Doyle, D. V., and Dunn, C. (1978). macrophages. European Journal of Rheumatology and Unpublished observations. Inflammation, in press. Doyle, D. V., Dieppe, P. A., Huskisson, E. C., and Altman, R. D., Muniz, O., Pita, J. C., and Howell, D. S. Willoughby, D. A. (1978). Morphological Studies of (1973). Microanalysis of inorganic pyrophosphate Osteoarthritic Tissue, in press. http://jcp.bmj.com/ (PP) in synovial fluid and plasma. Arthritis and Dunn, C., Doyle, D. V., and Willoughby, D. A. (1978). Rheumatism, 16, 171-178. A review of the experimental methods and associated Benderly, H., and Maroudas, A. (1975). Equilibria of problems in the study of crystal deposition disease. calcium and phosphate ions in human articular European Journal oJ Rheumatology and Inflammation, cartilage. Annals of the Rheumatic Diseases, 34, Suppl. in press. 2, 46. Ellman, M. H., and Levin, B. (1975). Chondrocalcinosis Bennett, R. M., Lehr, J. R., and McCarty, D. J. (1976). in elderly persons. Arthritis and Rheumatism, 18, 43-47. Crystal shedding and acute pseudogout; an hypothesis Fassbender, H. G. (1975). Pathology of Rheumatic on September 23, 2021 by guest. Protected based on therapeutic failure. Arthritis and Rheumatism, Diseases. Springer-Verlag, Berlin. 19, 93-97. Faure, G., Netter, P., Malanan, B., and Steinmetz, J. Bjelle, A. 0. (1972). Morphological study of articular (1977). Monocrystalline calcium hydrogen phosphate cartilage in pyrophosphate arthropathy. Annals of the dihydrate in destructive arthropathy of chondro- Rheumatic Diseases, 31, 449-456. calcinosis. Lancet, 2, 142-143. Bjelle, A. O., and Sunden, G. (1974). Pyrophosphate Fleisch, H., Maerki, J., and Russell, R. G. G. (1966). arthropathy: a clinical study of fifty cases. Journal of Effect of pyrophosphate on dissolution of hydroxy- Bone and Joint Surgery, 56B, 246-255. apatite and its possible importance in calcium homeo- Canner, J. E. Z., and Decker, J. L. (1964). Recurrent stasis. Proceedings of the Society for Experimental acute arthritis in chronic renal failure treated with Biology, 122, 317-320. periodic dialysis. American Journal of Medicine, 36, Garrod, A. B. (1876). A Treatise on Gout and Rheumatic 571-582. Gout. Longmans Green, London. Collins, D. H. (1949). The Pathology of Articular and Gatter, R. A. (1977). Use of the compensated polarizing Spinal diseases. Arnold, London. microscope. Clinics in Rheumatic Diseases, 3, No. 1, J Clin Pathol: first published as 10.1136/jcp.31.Suppl_12.214 on 1 January 1978. Downloaded from

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91-103. McCarty, D. J., and O'Duffy, J. D. (1976). Discussion on Genant, H. (1976). Roentgenographic aspects of calcium parathormone levels in chondrocalcinosis and osteo- pyrophosphate dihydrate crystal deposition disease. arthritis. Arthritis and Rheumatism, Suppl., 19, 360. Arthritis and Rheumatism, 19, 307-328. McCarty, D. J., Gatter, R. A., and Hughes, R. E. (1963). Gerster, J. C., Baud, C. A., Lagier, R., Boussina, I., and Pseudogout syndrome. IV. Early and 'mature' carti- Fallet, G. H. (1977). Tendon calcifications in chondro- lagenous deposits of monoclinic and triclinic crystals calcinosis. Arthritis and Rheumatism, 20, 717-722. of calcium pyrophosphate dihydrate: Koch's postu- Hamilton, E. B. D. (1976). Diseases associated with lates and possible pathogenesis. Arthritis and CPPD deposition disease. Arthritis and Rheumatism, Rheumatism, 6, 287-299. 19, 353-358. McCarty, D. J., Silcox, D. C., Coe, F., Jacobelli, S., Hamilton, E. B. D., Williams, R., Barlow, K. 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A New Look at Osteoarthritis, in press. tions in human cartilage. I Prevalence and types of Kellgren, J. H., and Moore, R. (1952). Generalised crystal deposits in the menisci of two hundred fifteen osteoarthritis. British Medical Journal, 1, 181-184. cadavera. Journal of Bone and Joint Surgery, 48(A), Kohn, N. N., Hughes, R. E., McCarty, D. J., and Faires, 309-325. J. S. (1962). The significance of calcium phosphate McCarty, D. J., Phelps, P., and Pyenson, J. (1966). crystals in the synovial fluid of arthritic patients: the Crystal-induced inflammation in canine joints 1. An II 'pseudogout syndrome'. Identification of crystals. experimental model with quantification of the host by copyright. Annals ofInternal Medicine, 56, 738-745. response. Journal of Experimental Medicine, 124, 99- Eade, A. W. T., and Swannell, A. J. (1977). Pyrophos- 114. phate arthropathy in hypophosphatasia. XIV Inter- Menin, Y., Monville, C., and Ryckewaert, A. (1977). national Congress of Rheumatology. 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