Functional imaging in the early diagnosis of dysbaric osteonecrosis

Detection of dysbaric osteonecrosis in military divers using magnetic resonance imaging

This was a controlled cross-sectional study to investigate the prevalence of dysbaric osteonecrosis (DON) in military divers. MRI examinations of the large joints and adjacent bones were performed in a cross-sectional group of 32 highly experienced military divers and 28 non-divers matched for age and anthropometric data. Additional plain radiographs and follow-up controls were performed in all persons with signs certain or suspicious of DON. In two subject groups (one of divers and one of non-divers), lesions characteristic of DON were detected. From this controlled study, it may be concluded that MRI is a highly sensitive method to detect signs of osteonecrosis. It could be shown that the prevalence of bone lesions characteristic of osteonecrosis in highly experienced military divers is not higher than in non-diving subjects of comparable age. The outcome of this comparably small study group fits to the results of previous extensive studies performed with radiographs. The detected low incidence of DON in this collective may be due to the fact that military divers follow stricter selection criteria, decompression schemes and medical surveillance than commercial divers.

Functional bone imaging in the detection of ischemic osteopathies

The efficiency and accuracy of a functional imaging technique in the detection of ischemic osteopathy is reviewed over a 10-year period. The study includes 161 patients who had trauma, 101 patients who had suspected Perthes disease, 43 patients who had dysbarism, and 22 patients who had renal transplants on steroid immunosuppressive therapy. After intravenous injection of 7.7 MBq kg-1 Tc-99m HDP data were collected on all patients during the first 20 minutes, accretion rate functional images were produced, and static bone scans performed after 3 hours. All patients were followed up until a definitive diagnosis (clinical and radiologic) of avascular necrosis or osteochondritis was confirmed or denied. Of the 327 patients studied, 114 had positive accretion rate images and 213 negative accretion rate images. There were 8 false-positive scan results and 2 false-negative scan results. The overall predictive accuracy was 97% (disease prevalence 33%) with a sensitivity rate of 98% and a specificity rate of 96%. The authors conclude that the technique is a valuable predictive diagnostic indicator for ischemic osteopathies.

Dysbaric disorders: aseptic bone necrosis in tunnel workers and divers

Dysbaric osteonecrosis is a serious complication for those exposed to a hyperbaric environment, with prevalence of 17% amongst compressed air workers and 4.2% amongst divers. Bone lesions are characteristically multiple and bilateral, occurring frequently in the shafts of the femora or tibiae and the heads of the humeri or femora. A proportion of the lesions will lie next to the joint surface, the so called juxta-articular lesion, and these may progress to a structural failure and secondary osteoarthritis. These lesions can be severely disabling, especially in a young adult male. When related to the occupational history the prevalence of bone lesions, both in compressed air workers and divers, increases with age, experience and with greater pressures of air or at greater depths. Moreover, acute attacks of decompression sickness, the bends, are more liable to be associated with subsequent bone lesions. Current decompression schedules certainly reduce the bends rate but, no matter how strictly adhered to, will not prevent the development of dysbaric osteonecrosis. It is possible that bone necrosis could result solely from exposure to a high pressure of air, either from work in compressed air or diving. Those men with positive bone lesions should be advised to seek expert medical opinion and probably advised to discontinue work in compressed air or diving if a juxta-articular lesion is present. Detection of bone necrosis depends on good quality radiographs with reliable interpretation, preferably by double observation, especially in the early stages. Lesions, especially when early or doubtful, can be confirmed by CT or bone scintigraphy. MRI promises to detect osteonecrosis in the very early stages but is not yet readily available. To detect dysbaric osteonecrosis at an early stage it is important to monitor both compressed air workers and divers with regular radiological skeletal surveys or bone scintigraphy. In 1987, the Bone Necrosis Working Group of the Decompression Sickness Panel recommended that all divers should have a radiological survey on completion of their initial diving training and that bone scintigraphy should be used for subsequent surveillance for certain groups, including those diving deeper than 30 metres, where the time at depth exceeds 4 hours, when experimental decompression is used and in other situations.

Bone imaging and skeletal radiology in dysbaric osteonecrosis

Twenty-nine United Kingdom deep sea divers were examined radiographically for skeletal abnormalities and also bone images were obtained using technetium-99m methylene diphosphonate. The results of the two forms of examination were compared and the use of radionuclide bone scanning was shown to be more sensitive than radiographic examination in monitoring those occupationally at risk of acquiring dysbaric osteonecrosis.

Bone necrosis due to decompression

Death of areas of long bone has been known to be associated with work in compressed air and diving for many years. Detection and diagnosis require specialist knowledge, but familiarity with the condition has increased markedly over the last 20 years. Most of it is symptomless and causes no disability, but if areas adjacent to the joint surfaces of the upper end of the humerus and the upper end of the femur are affected, the joint may be seriously damaged and disability ensue. This problem has been defined by surveys of groups of workers using compressed air and divers in an attempt to establish prevalence. In general the more diving undertaken and the deeper the dives, the more probability there is of acquiring bone damage. The commonest area to be affected is the lower end of the femur, but the knee joint is never involved. The cause of bone damage is far from clear. None of the various explanations that have been offered are satisfactory, but research continues into the problem both in humans and in animals, particularly the miniature pig. At present it is difficult to quantify the risk taken by commercial divers in relation to changing technology either in terms of depth or duration of pressure.