Careful pathological examination of lumbar spines removed at autopsy has shown that degenerative changes are present in the intervertebral discs of all subjects by middle age. The degenerative changes are more marked and occur at an earlier age when evidence of vertical or posterior disc prolapse is also present. Degenerative changes in the discs are always accompanied by osteophyte formation on the margins of the vertebral bodies and remodelling changes in the apophyseal joints. There is a direct relationship between the degree of disc degeneration, marginal osteophyte formation on vertebral bodies, and apophyseal joint changes, which suggests that disc degeneration is the primary event leading to the clinical condition of 'degenerative spondylosis'.

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The tidemark is a metabolically active zone in the calcified layer of the cartilage in which it is possible to show that there is calcifying activity even over a short period of time using a tetracycline labelling technique. The tidemark slowly advances in the direction of the non-calcified cartilage and analysis of double-tetracycline labelled cartilage shows that this is not an appositional phenomenon like that occurring in bone, but that, where present, several tidemarks can be labelled at the same time. Each tidemark may therefore be metabolically active and it is not just the tidemark adjacent to hyaline cartilage which incorporates calcium.

1. The femoral head has been examined in specimens taken from cadavers, patients suffering subcapital fracture of the femoral neck and patients undergoing total replacement arthroplasty for osteoarthrosis and rheumatoid arthritis. 2. Lesions have been seen, some of which appear to be uniting fatigue fractures of individual trabeculae. 3. It is suggested that excessive cyclical loading, sometimes leading to fatigue fractures, may represent a fundamental pathological process of general importance in the evolution of certain skeletal and articular diseases.

1. Senile subcapital fractures in osteoporotic patients are due to fatigue, not to the impact of a fall, since they are preceded by the local accumulation of isolated trabecular fatigue fractures. 2. One pathological significance of the isolated trabecular fractures described by Todd, Freeman and Pirie (1972) has been demonstrated.

While the pathological features of the spine in ankylosing spondylitis have been described in considerable detail in recent years, little published work is available on the subject of the pathology of the spine in ankylosing hyperostosis (AH).We here describe some of the pathological findings in the dorsal spines of twenty subjects with AH. Materials and methods SELECTION OF SPECIMENSDorsal spines were removed from twenty subjects at postmortem examination. They were judged to have AH on the basis of the presence of syndesmophytes in the form of bony flanges or bridges situated predominantly on the right anterolateral aspect of the bodies of two or more vertebrae, and the absence of previous clinical findings or other spinal pathology which could account for these features. Radiographs of the dorsal spines taken during life and post-mortem were examined independently by a radiologist and a rheumatologist who confirmed the diagnosis of AH in all the cases included in this study. The twenty cases of AH used in this study were selected from about 500 autopsies where one of us (B.V.-R.) was personally able to examine the spine in each case, and excluded from the study were about ten other cases of AH where removal of the spine was not possible for a variety of reasons. The overall incidence of AH in patients coming to autopsy at The London Hospital is therefore in the region of 6 %. The twenty subjects comprised eleven males of mean age 66 years (range 58-77 years) and nine females of mean age 71 years (range 53-87 years). Details of the age, sex, extent of the dorsal spine affected, and the principal cause of death in each subject are shown in Table I. EXAMINATION OF SPECIMENSAfter removal from the body, each dorsal spine was cleaned and photographed. Each specimen was then radiographed using a Faxitron 8050-010 X-ray Inspection System (Field Emission U.K. Limited). After photography and radiography, 18 of the spines were divided into longitudinal slabs 0 5 cm thick using a band-saw, and the internal features were noted. Selected portions of these slabs were then taken for histological processing for subsequent microscopical examination. They were fixed in formol-saline and embedded in methyl methacrylate; 8 um sections were made and were stained with haematoxylin and eosin, thionin, and by the von Kossa technique. One severely affected spine and one moderately affected spine were macerated for the examination of the dry specimens by being boiled in 5% sodium hydroxide to remove the soft tissues, followed by bleaching in 10 vol hydrogen peroxide. Results EXTERNAL FEATURES OF DORSAL SPINE IN AHIn 13 of the 20 specimens the condition was confined to the lower half of the dorsal spine; in the remainder, the upper half was also affected (Table I). In all cases at least 4 contiguous vertebral bodies were involved; involvement of the whole of the dorsal spine was present in only one case. The lower part of the affected portion of each spine tended to be more severely affected than the upper, though a region of larger syn...

Aims: To determine whether remodelling of subchondral bone in osteoarthritis is related to anatomical and mechanical factors operating on the joint surface. Methods: Ten femoral heads were examined. Patients due to have the femoral head removed because of osteoarthritis were given a double tetracycline label before surgery. The specimens were divided in three roughly equal parts, corresponding to the medial, central (weight bearing), and lateral aspects of the femoral heads. Undecalcified methylmethacrylate embedded sections were prepared. The subchondral bone was assessed for appositional bone formation by ultraviolet light microscopy, for resorptive activity by osteoclast count, and for trabecular bone volume by semiautomatic computerised image analysis. Appositional bone rate was also correlated with the presence or absence of overlying cartilage. Results: Bone density was reduced in the medial aspect of the femoral heads but there was no significant difference between the appositional bone rate or the resorptive activity in the three areas. Nor was there any correlation between appositional bone rate in the subchondral bone and the presence or absence of overlying cartilage. Conclusion: Remodelling of subchondral bone in osteoarthritis, at least in the short term, is fairly constant and is not related to weight bearing. (7 Clin Pathol 1992;45:990-992)