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Given that the best measures of presence currently available are subjective self-assessments, it is desirable to attempt to develop reliable, repeatable, quantitative measures. We present the results of two experiments intended to separate presence into measurable subcomponents: attention and spatial comprehension. The first experiment was a conventional dual-task study where we measured attentional demands of competing.virtual and real world experiences. The results suggest that attention may be a reasonable quantitative measure of presence. The study also showed that the use of sound increased the level of engagement experienced by participants. The second study attempted to correlate spatial knowledge acquisition with presence. The only component of spatial knowledge acquisition that was positively affected was landmark knowledge that improved with the addition of semantic verbal information. The data does not generally support a relationship between spatial comprehension and presence, but, again, it was found that the use of sound increased participants' sense of engagement in the virtual world. There are certainly other candidate subcomponents of presence, but we began our investigation here. An expanded investigation toward the development of an aggregate quantitative measure of presence is suggested.

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The current role of ultrasound, computed tomography, magnetic resonance imaging, and scintigraphy in the evaluation of pediatric musculoskeletal disorders is reviewed. Magnetic resonance imaging and ultrasound, which do not utilize ionizing radiation and, as far as is known, appear to have no deleterious biologic effects, are particularly valuable modalities in the pediatric population.

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Lyme disease typically begins in the spring or summer months, with a pathognomonic skin lesion and associated flulike or meningitislike symptoms. If the patient is not treated during this early stage, cardiac, neurologic, or musculoskeletal manifestations may occur weeks to months later. Although the clinical picture of Lyme disease is extremely variable, the diagnosis can be made in most cases by recognizing the typical patterns of organ involvement and associated immunologic abnormalities.

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The efficacy and acceptability of a levonorgestrel-releasing intravaginal ring (IVR) for contraception was assessed in a British cohort studied as part of a multicentre, multinational clinical trial performed under the auspices of the World Health Organisation. One-hundred-and-fifty women took part in the study in two UK centres and completed 1417.5 months of method use. Fifty-nine women discontinued use of the IVR before the end of one year giving an overall discontinuation rate of 39.9 per 100 woman-years. The discontinuation for pregnancy with the ring in situ, was 3.0 per 100 woman-years (life table analysis). Menstrual disturbance, vaginal problems and involuntary expulsion resulted in discontinuation rates of 8.9, 8.4 and 1.6 per 100 woman-years, respectively. This method is an acceptable and effective method of contraception for women.

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A case of periosteal new bone in a newborn is presented. The periostitis resulted from long-term therapy with PGE1, which was administered to maintain patency of the ductus in a neonate with ductal-dependent cyanotic congenital heart disease. The features of PGE1 periostitis and the differential diagnosis are reviewed.

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In contrast with the widely held view that radiologic normal variants are of no clinical significance, many of the anatomic variations of the skeletal system, may, in fact, be responsible for symptoms. Three groups of apparently normal variants are presented: Group 1 consist of ossicle that, from the very onset, may represent the sequelae of repetitious trauma; Group 2 is composed of normal variants in which the presence of congenital synchondrosis may predispose to injury from chronic repetitious trauma; Group 3 consists of ossicles that predispose to local and premature degenerative changes. Radionuclide bone scanning is crucial in evaluating the significance of the ossicles in the symptomatic patient.

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Drugs, whether prescribed by physicians or taken without the knowledge of the physician, may result in profound changes in the musculoskeletal system. Some drugs may produce teratogenic changes in the developing fetus frequently, but not necessarily, in association with anomalies of other systems. Other drugs may have their effects on the child or adult, whereas a number of drugs result in either teratogenic or nonteratogenic abnormalities. In the course of evaluating any diagnostic imaging study, it is essential that the radiologist be aware of any drugs that the patient may be taking and be knowledgeable of the radiologic changes that such drugs may produce in the musculoskeletal system.

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A case of a 23-year-old man with deformities of the spine and hip is presented, demonstrating the bizarre long term effects of radiation on developing bone. The spectrum of radiation-induced growth abnormalities is reviewed. Multiple variables, including age of the patient, the quantity of radiation delivered, and the site of delivery, all effect the eventual radiographic appearance.

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The enthesopathy (bone proliferation at sites of ligament, tendon, joint capsule, and interosseous membrane attachment) that may be present in adults who have longstanding hypophosphatemic osteomalacia, the most common type of osteomalacia, has received little attention in the radiologic literature. These proliferative enthetic changes may be associated with various musculoskeletal symptoms. The spectrum of proliferative enthesopathic changes, involving the axial and appendicular skeleton, is described in six patients 18-63 years old. Proliferative changes at the attachment of the annulus fibrosus were present in six of six patients and ranged in extent from tiny hyperostoses at a few levels to thin marginal symmetric syndesmophytes involving the entire lumbosacral spine and mimicking spondylitis. Thoracic spinal syndesmophytes were present in four patients and cervical hyperostoses of various magnitudes were present in three patients. Changes in the sacroiliac joints were present in four of six patients and varied from mild widening to symmetric intraarticular and anterior paraarticular bony bridging. Proliferative enthesopathy involving the pelvis and proximal femora was present in six of six patients. Appendicular changes included accessory ossicles within the wrist and hands and bony proliferation of the distal radius and metacarpal heads. These were noted in four patients. Ossification of the interosseous membrane of the forearms or the lower extremities was present in six patients and paraarticular bony proliferation about the elbows was noted in four patients. It is apparent that the severity of the enthesopathy that occurs may vary, and that hypophosphatemic osteomalacia should be recognized as a cause of enthesopathy even if other radiographic findings of osteomalacia may not be present on available radiographs.

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The accessory navicular is commonly considered an asymptomatic variant, but when traumatized, it can become the source of clinical symptoms. The accessory naviculars were divided into Types I, IIa and b, and III based on their appearance and location with relationship to their parent navicular. Only Type IIa and b accessory naviculars have a synchondrosis. The synchondrosis of Type IIa and b can undergo tension, shear, and compression forces causing avulsion or a painful pseudarthrosis to develop.

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Four cases of cervical spine growth plate ("ring apophysis") injury are described. Two nonfatal injuries involved anterior displacement of a portion of the inferior physis and epiphyseal ossification center in the lower cervical spine. Neither injury was associated with neurological damage. Follow-up roentgenograms demonstrated healing, but with a spur-like prominence in one patient. A third patient sustained a fatal separation through the inferior end plate of C2. The fourth patient sustained a complete separation of C6 from C7. These injuries are correlated with pathologic specimens and normal developmental anatomy.

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The skeletal changes associated with systemic retinoid therapy reflect the influence of retinoids on differentiating systems. Although skin is usually the intended target, treatment with retinoids often results in abnormalities of ossification and calcification. The effects of retinoids on bone may be profound and include progressive calcification of ligaments and tendon insertions, premature fusion of epiphyses, modeling abnormalities of long bones, and perhaps osteoporosis. Although it has been known since 1933 that vitamin A cause bone abnormalities, the mechanism of this effect has been elusive. Recent work suggests a possible relationship of the retinoids with several cytokines, which results in enhanced maturation of the preosteoclast. The increasing number of significant bone changes, including posterior lumbar vertebral osteophytosis, make skeletal toxicity the principle risk factor of chronic systemic retinoid therapy.

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The roentgenographic changes noted in 13 patients, who had been treated with long-term 13-cis-retinoic acid for inherited scaling disorders, are presented. These patients were aged 13-16 years and had received this therapy for 16-87 months (mean, 58 months). The most pronounced abnormality was osteophyte formation, particularly in the cervical spine. Other changes which were noted included ossification of the anterior longitudinal and atlanto-occipital ligaments, proliferative enthesopathies, diminished bone density, premature fusion of epiphyses, and modeling abnormalities. Six of the 13 patients were asymptomatic and the osseous manifestations of this therapy were identified only by roentgenographic evaluation.

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The accessory navicular, which is considered an anatomic variant, may be the source of pain in athletes. There are three types of accessory naviculars: Type I is an ossicle in the substance of the posterior tibial tendon; Type II forms a synchondrosis with the navicular; and Type III, "the cornuate navicular," represents the possible end stage of Type II. Nine feet had Type II accessory naviculars. The pull of the posterior tibial tendon, the degree of foot pronation, and the location of the accessory navicular in relation to the undersurface of the navicular are factors that produce tension, shear, and/or compression forces on the synchondrosis of Type II accessory naviculars and cause microscopic changes of injury and repair similar to those observed with a physeal fracture. Such alterations are not always visible on roentgenograms but are usually detected by 99mTc methylene diphosphonate (99mTcMDP) scans. Initially, nonsurgical treatment with orthotics or casts should be attempted, but if this is unsuccessful, surgical treatment is recommended. Surgical treatment consists of excision of the accessory navicular with its synchondrosis, without transposition of the posterior tibial tendon.

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Pinemoth caterpillar disease is a well-recognised disorder which occurs in South-Eastern China and is due to contact with the cocoons or larvae of the pinemoth (Dendrolimus punctatus). Generalised symptoms, which may be noted within two weeks of contact, consist of pyrexia, anorexia, malaise, rigors, headache, or dizziness. Localised abnormalities include dermatologic changes, skin nodules, and arthritis. The arthritis is usually monoarticular and most frequently involves the knee, ankle, and wrist. The radiologic findings consist of periarticular swelling, osteoporosis, erosions, or periosteal reaction in the acute phase and osseous sclerosis, joint deformity, persistent soft tissue swelling, or premature fusion of ossification centers in the chronic stages.

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Periostitis and osteomyelitis can occur in drug addicts not only by hematogenous dissemination of the infecting organisms, but as a result of introduction of bacteria by direct injection into periosteum or injection through infected skin and subcutaneous tissues. A spectrum of examples of osteomyelitis of the bones of the forearm in drug addicts is presented to illustrate this phenomenon. Neglect of these infections and the trauma of continued injections can lead to extensive tissue and bone loss.

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Three groups of apparently normal developmental variants in extremities as they appear on radiographs are presented. In contrast to the widely held view that these are of no clinical significance, these ossicles may, in fact, be responsible for symptoms. The first group consists of ossicles which, from the very onset, may represent the sequelae of repetitious trauma. The second group is composed of normal variants in which the presence of a congenital synchondrosis may predispose to injury as a result of chronic repetitious trauma. The third group consists of ossicles that may result in local and premature degenerative changes. The use of radionuclide bone scanning, which provides physiologic as well as morphologic information, is crucial in evaluating the significance of these ossicles in the symptomatic patient.

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