Topical MedicalEditorial Issues Osteoarthritis in Young Individuals evere osteoarthritis (OA) in young individuals Congenital. Congenital dysplasia of the hip, also is a major clinical problem because of the lim- known as developmental dysplasia of the hip, is a Sited options for treatment.1,2 Pharmaceuticals, frequent reason for the referral of babies to physiotherapy and activity modification are used pediatric orthopaedic clinics. As expected, normal for as long as possible. Inevitably, total joint or near-normal joint development is achieved when replacement, usually of the hip, will need to be treatment is started within a few months of birth.4 considered despite the young age of the recipients. However, normal joint development rarely is Osteotomy may not be feasible and arthrodesis achieved when treatment is started after the child may be contraindicated or undesirable. In this arti- has commenced walking. As most affected children cle, some of the conditions that produce localized now are referred to orthopaedic clinics soon after and generalized forms of OA in young individuals birth, it is likely that developmental dysplasia of the will be described. hip will become a less frequent cause of premature OA. The switch from late to early referral has been LOCAL DISORDERS a major change over the past decade, and is a cred- Premature OA of one or two joints may follow a it to the clinical skills of pediatricians, obstetricians wide variety of congenital and acquired disorders of and family physicians. childhood and adolescence. In general, the Acquired. Perthes disease, osteochondritis dis- secans, steroid-induced avascular necrosis, slipped proximal femoral epiphysis, bacterial arthritis and In general, the susceptibility of a child to fractures are some of the acquired causes of OA of subsequent development of premature OA is one or two joints. The first three conditions involve related to the shape and congruency of the avascular necrosis and the last three conditions may joint surfaces at the end of growth.3 be complicated by avascular necrosis. Avascular necrosis often results in collapse of the subchondral bone with distortion of the overlying joint surface. susceptibility of a child to subsequent development Loss of articular cartilage also can complicate slipped of premature OA is related to the shape and con- proximal femoral epiphysis and bacterial arthritis. gruency of the joint surfaces at the end of growth.3 Early and effective treatment of primary Premature OA develops more rapidly, often in conditions is the focus of attention. For example, young adulthood, when the joint surfaces are early treatment of bacterial arthritis can prevent abnormally shaped and incongruent.3 permanent cartilage damage and also can prevent avascular necrosis in the hip.5 Prompt treatment of William G. Cole, PhD, FRCSC chronic slips of the proximal femoral growth plate is the Head of the Division of prevents the occurrence of avascular necrosis and Orthopaedics at The Hospital chondrolysis from subsequent acute slippage.6,7 for Sick Children in Toronto, Treatment of Perthes disease, particularly in older Ontario. children, ensures that the femoral head is contained within the acetabulum and is another means of improving joint congruency and long-term outcomes.8 GENERAL DISORDERS This category includes a wide variety of genetic dis- orders and syndromes that alter the development, structure and function of the skeleton. The follow- 10 / The Journal of the Canadian Rheumatology Association ing discussion will be limited to the skeletal dys- by mutations of the genes encoding type II and plasias and to Ehlers-Danlos syndrome. type XI collagens, cartilage oligomeric matrix Skeletal dysplasias. There are hundreds of geneti- protein, several types of sulfate transporters, as cally determined anomalies of skeletal develop- well as sedlin, a gene involved in the transport of ment, referred to as skeletal dysplasias, that often proteins in the endoplasmic reticulum and Golgi predispose affected individuals to the premature apparatus. The list of disease genes associated with development of OA. Recently, a molecular- these phenotypes can be expected to expand. pathogenetic classification, based on accumulating The relationships between the known genotypes knowledge of the genes and proteins responsible for and phenotypes need to be better defined. Some skeletal dysplasias, was proposed.9 A major patterns already are emerging, such as the charac- advantage of the new classification is that it more teristic clinical and radiographic features of the readily enables diverse clinical phenotypes to be recessive form of multiple epiphyseal dysplasia, grouped together into families. which are due to mutations of the diastrophic dys- Members of the type II collagen family of skeletal plasia sulfate transporter gene.12 dysplasias have spondyloepiphyseal dysplasia, Long-term outcome studies also are needed in which varies in severity from a perinatal lethal order to better understand the patient-determined form, known as achondrogenesis type 2, to a mild form presenting as familial premature OA.10 As expected, the major phenotypic manifestations of Long-term outcome studies also are needed in all members of the family are abnormal formation, order to better understand the patient- structure and function of the cartilages. Teenagers determined outcomes and, in particular, the with spondyloepiphyseal dysplasia congenita, risks of developing symptomatic OA. Kniest syndrome or Stickler arthro-ophthalmopathy frequently have symptomatic OA and may need total hip-joint replacements as young adults.11 outcomes and, in particular, the risks of developing Members of the diastrophic dysplasia sulfate symptomatic OA. One limited study of individuals transporter family have undersulfated proteoglycans with multiple epiphyseal dysplasia showed that in their hyaline cartilages.12 The perinatal lethal those with congruous hip joints often developed form (achondrogenesis type 1B) and the severe form symptomatic OA in the fourth decade, whereas (diastrophic dysplasia) have extensive involvement those with incongruous joints developed severe of the spine and epiphyses (spondyloepiphyseal symptoms in the second decade.13 dysplasia). A milder phenotype, with less involve- Ehlers-Danlos and related syndromes. General- ment of the spine, is classified as a form of multiple ized joint laxity varies in severity, from the mild epiphyseal dysplasia. Nonetheless, the latter indi- familial hypermobility syndrome to severe joint lax- viduals often have OA in their teens and may re- ity, in some forms of Ehlers-Danlos syndrome.14 quire hip-joint replacements as young adults. As Multiple congenital joint dislocations and expected, milder phenotypes are associated with subluxations are frequent in various forms of higher levels of residual sulfate transporter Ehlers-Danlos syndrome. Joint instability remains a function.9 major problem for many individuals throughout Phenotypes, such as multiple epiphyseal their lives. Chronic joint pain, weakness and the dysplasia and spondyloepiphyseal dysplasia, are inability to perform many of the tasks of everyday produced by mutations of many genes that are living also are common problems.15,16 Many adults involved in the formation of the extracellular often are unable to work because of recurrent matrix of the cartilages.9 For example, multiple painful dislocations of joints, such as the shoulder epiphyseal dysplasia can arise from mutations of joints, and many use a wheelchair for mobility. OA the genes encoding type IX collagen, cartilage is frequent. oligomeric matrix protein, matrilin-3 or the Accumulating evidence indicates that the main diastrophic dysplasia sulfate transporter. Spondylo- problem underlying Ehlers-Danlos syndrome is epiphyseal dysplasia phenotypes can be produced abnormal formation or interactions of the type I The Journal of the Canadian Rheumatology Association / 11 collagen-containing fibrils of the ligaments, joint slipped proximal femoral epiphysis, bacterial arthri- capsules, tendons and related connective tis and fractures. There also is a need to continue tissues.17 Mutations of genes involved in type I col- the current international effort to identify every lagen fibrillogenesis, or in the interactions of the gene that is involved in normal and abnormal collagen fibrils with other matrix components, have skeletal development, including those that predis- been identified in various forms of the syndrome pose to premature OA. (e.g., genes encoding type I and V collagens; genes for proteins that modify type I collagen [e.g., lysyl hydroxylase, galactosyltransferase, procollagen 1 N-proteinase]; and the gene for tenascin-X).17-23 FUTURE DIRECTIONS There is a need to continue the current efforts Acknowledgements directed towards improving the quality of joint Some of the work reported in this paper was sup- development following congenital disorders, such ported by grants from the Canadian Institutes of as developmental dysplasia of the hip and acquired Health Research and the Canadian Arthritis disorders, various forms of avascular necrosis, Network. References 13. Treble NJ, Jensen FO, Bankier A, et al: Development of the hip in 1. Wedge JH: Osteotomy of the pelvis for the management of hip dis- multiple epiphyseal dysplasia. Natural history and susceptibility to ease in young adults. Can J Surg 1995; (38 Suppl 1):S25-32. premature osteoarthritis. J Bone Joint Surg Br 1990; 72:1061-4. 2. Wedge JH, Cummiskey