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DOI: 10.1016/J.JHSB.2006.03.158
The Distribution of Bone Islands and Juxta-Articular Bone Cysts in the Growing HandFrom the Department of Trauma & Orthopaedics, St. James’s University Hospital, Leeds, UK Correspondence: Mr. David Limb, Consultant Surgeon, Department of Trauma & Orthopaedics, St. James’s University, Hospital, Beckett Street, Leeds LS9 7TF, UK. Tel.: +44 113 2065475; Fax: +44 113 2066791 E-mail: d.limb{at}leeds.ac.uk
Bone islands and juxta-articular bone cysts are relatively common incidental findings when X-rays are taken for other purposes. We have identified that the incidence of bone islands in the hands of asymptomatic children between the ages of 5 and 13 years is 3.8% and the incidence of cysts in the same population is 2.8%. Bone islands were most common in the scaphoid, whilst juxta-articular bone cysts were most common in the capitate. The age at which they appear has not been reported previously. This study first identifies their presence in the hands of children of age 10 years and 2 months (bone islands) and 10 years 0 months (juxta-articular bone cysts). Most of the lesions were already present on the first radiograph taken. New bone islands appeared in five cases between the ages of 13 years and 1 month and 15 years and 3 months. New juxta-articular bone cysts were observed to appear in five cases between the ages of 10 years 10 months and 15 years 0 months. No island or cyst changed in size during the review period.
Key Words: bone islands • bone cysts • ganglia Bone islands are sharply demarcated solitary densities in the skeleton (Onitsuka, 1977). They were first described as bone nuclei, so-called "kompakten knockenkrane" (Steida, 1905). Subsequently, various terms have been used, including compact islands, focal sclerosis, calcified islands in bone and sclerotic bone islands. Subchondral bone cysts associated with rheumatoid arthritis or degenerative joint diseases are well known. However, cysts may also arise in bone where there is no joint pathology and such lesions were first noted by Hicks, in 1956 (Hicks, 1956). Such lesions are often seen at the lateral margin of the acetabulum and at the ends of long bones, frequently in the knee or the medial and lateral malleoli of the ankle. The nature and pathogenesis of these lesions are unclear, as indicated by the great variety of different names, such as synovial cysts, intraosseous ganglia and juxta-articular cysts. The most popular hypothesis at present is that they arise de novo within the bone (Feldman and Johnston, 1973). According to the W.H.O. classification for bone tumours and tumour-like lesions, these are most aptly called "juxta-articular bone cysts" and are defined as "benign cystic and often multiloculated lesions made up of fibrous tissue, with extensive mucoid changes, located in the subchondral bone adjacent to a joint" (Schajowicz et al., 1972). Generally, bone islands and juxta-articular bone cysts are asymptomatic and are incidental X-ray findings. To our knowledge, the age at which these small bone lesions first appear has not been investigated previously. This study examines their incidence in children from 5 to 13 years of age.
As part of a school screening programme for scoliosis which was completed in the early 1990s (Dickson, 1983) more than 900 fit children, aged between 5 and 13 years at the start of the study, underwent serial X-rays of the left hand over a 5 year period for determination of bone age. The study, which also involved low-dose X-rays of the spine, was ethically approved. Of those entering the study, 610 children, 360 boys and 250 girls, attended for annual review for the entire 5 year period and this group forms the basis of this study. Three thousand and fifty X-rays were reviewed to determine the frequency and location of bone islands and juxta-articular bone cysts in the hands of asymptomatic and fit children.
In this population of 610 children, 360 boys and 250 girls, aged between 5 and 13 years, the prevalence of bone islands (single or multiple in any individual) was 3.8% and of juxta-articular bone cysts was 2.8%. Bone islands were found in the scaphoid (6), capitate (4), lunate (3), hamate (2) and distal radius (2) (Fig 1) (Table 1). Single-bone islands occurred in various metacarpals and phalanges. The size of the lesions ranged from 2 to 20 mm in maximum dimension. The exact age of the onset of bone island formation could not be reliably established, as, in some cases, islands were present on the first X-ray taken.
Most bone islands were present on the first X-ray taken in children with an age range of 10 years 2 months to 14 years 3 months. Six new islands appeared during the review period, one in the lunate at 15 years 3 months, one in the triquetrum at 13 years 1 month, one in the base of the second metacarpal at 14 years 11 months and one in the distal radial epiphysis at 16 years 8 months. The two remaining new islands occurred in children who already had an island elsewhere in the hand. One child had an island in the scaphoid present on the first film taken at 13 years 5 months and developed a second island by 14 years 3 months. A second child had an island in the distal radial epiphysis at 13 years 7 months and developed a new island in the scaphoid by 14 years 7 months. Juxta-articular bone cysts were observed in the capitate (11), lunate (2), scaphoid (1), trapezium (1), trapezoid (1) and hamate (1) (Fig 2) (Table 1). Anatomically, juxta-articular bone cysts were less widely distributed than bone islands. The size of the lesions ranged from A to B mm in maximum dimension.
Most juxta-articular cysts were present on the first X-ray taken, the range of ages for children with cysts on the first film being 10 years 0 months to 15 years 0 months. During the review period, six new cysts were seen to appear; four in the capitate at 10 years 3 months, 10 years 10 months, 12 years 5 months and 12 years 9 months. A new cyst in the scaphoid appeared in one case at 15 years 0 months and one new cyst appeared in the trapezium at 11 years 1 month. On subsequent X-rays, none of these lesions became larger, although the walls of the juxta-articular cysts tended to become better defined and the density of newly appearing cysts appeared to increase. Unfortunately, quantification of any increase in density was not possible on the films taken. All of these lesions were asymptomatic.
Bone islands are presumed to be developmental lesions in normal, compact, cancellous bone. They are usually stable in size but some enlarge proportionally to the bone growth, suggesting that they participate metabolically in the normal osseous system (Onitsuka, 1977). We did not observe any lesions that disappeared during our review and are not aware of this occurring in juxta-articular cysts and bone islands that are not associated with other pathology. Although bone islands are believed to be developmental, they may reflect a minimal ossification disorder. Kim and Barry (1964) suggested that there is, probably, localised excess bone formation in the trabeculae of the involved cancellous bone, or at the medullary margin of the cortex, during the life of the normal bone and that this is constantly being resorbed and reformed. Bone islands may appear in virtually any skeletal site, but they are most frequently seen in the bones of the axial skeleton, especially the pelvis and ribs, and in the humerus and femur. They are found more rarely in the carpal bones and the long bones of the hand. Prior to this study, bone islands had been encountered less often in paediatric patients (Kim and Barry, 1964) and our study confirms that the incidence in children is low, with only 24 bone islands being observed in 610 patients (3.8%). In our study, we observed bone islands in children 10 years old and older, with new lesions developing up to the age of 16 years 8 months. We did not, however, observe bone islands in children younger than 10 years of age. All of the bone islands identified in this study were asymptomatic and were noted as incidental findings, following a benign course. In clinical practice, it is sometimes difficult to differentiate such lesions radiologically from osteoblastic metastases, osteosarcoma, lymphoma, osteoma and osteoid osteoma (Araki et al., 1989). In contrast to expectations, a bone scan cannot definitely differentiate bone islands from a more aggressive lesion (Araki et al., 1989). If a child presents with symptoms and is found to have a bone island or cyst then further investigation using blood markers, CT or MRI scanning would be indicated to rule out more sinister pathology. To our knowledge, there have been no reported cases of asymptomatic bone islands found incidentally in children becoming malignant at a later stage. Although juxta-articular bone cysts are not common in the hand, they are, perhaps, more frequent than previous publications have suggested. Eiken and Johnson (1980) reported 80 carpal cysts in 77 patients, mostly in the scaphoid and the lunate, with less frequent presence in the triquetrum, capitate and ulnar styloid. The mean age of the patients was 48 (range 29–70) years. None of their patients were children. Schajowicz et al. (1979) reported 88 bone cysts in 80 patients, of which 16 lesions were in the carpal bones. No details were given concerning the distribution within the named carpal bones. The youngest patient in this series was 14 years of age. In our study, we have observed juxta-articular cysts in children 10 years old and older, with new lesions developing up to the age of 15 years. We did not observe these cysts in children younger than 10 years of age. Juxta-articular bone cysts are oval or circular radiolucent areas, usually located in the centre of the bone or close to an articular surface. The size of the lesions ranges from 2 to 20 mm in maximum dimension in those papers that describe measurements. Small cysts are usually unilocular, while larger ones can be hour-glass shaped or multiloculated, with this feature being identified most easily in tomograms. The lucent area may have a well-defined sclerotic rim of bone, although this is not always present or complete. Communication with the joint has been described (Plewes, 1940). In the studies by Schajowicz and his colleagues, the cysts were seen to develop from an area of sparse trabeculae and reduced mineral content and to become a well-defined cavity (Schajowicz et al., 1972, 1979). In most cases, the bone lesion was clinically silent and was discovered only when a radiograph was taken for some other reason. Crane and Scarano (1967) reported a single case of a symptomatic juxta-articular bone cyst in the lunate of a 47 year-old white man. This was shown to communicate with the carpal joint on tomography and, later, at operation. Although well recognized as a clinical entity, the pathogenesis of juxta-articular bone cysts is still obscure. There seem to be two types of juxta-articular bone cysts, one originating by penetration of the underlying bone by an extra-osseous ganglion and the other which remains "idiopathic". In most "idiopathic" cases, which are the majority of lesions, the bone cyst is primarily intraosseous. As the name suggests, they are commonly located in the juxta-articular region. Some studies, however, have suggested an alternative theory of origin from repeated minor trauma near the surface of the bone, leading to intramedullary mucoid degeneration and cyst formation. Schajowicz et al. (1972) suggested a localised vascular disturbance as the primary cause of the cyst formation. These cysts have none of the features of synovial cysts and, therefore, should not be called "synovial cysts" (Crane and Scarano, 1967; Schajowicz et al., 1972). They are also, probably, unrelated in aetiology to the cysts found in osteoarthritis, which may be the result of small foci of bone necrosis from infarction occurring at pressure areas, with communication with the joint preventing healing because of the pressure of joint fluid (Harrison et al., 1953). Such degenerative theories of aetiology seem particularly unlikely to apply to the patients studied in this paper, who were growing children. We have found, no evidence that asymptomatic juxta-articular cysts, found incidentally on X-rays of children’s hands, progress to any significant pathology.
Received for publication August 23, 2005. Accepted for publication March 9, 2006.
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