Mycobacterium malmoense is an acid-fast non-tuberculous organism that most commonly causes pulmonary infection. Extrapulmonary infection has also been reported. With an increased emphasis being placed on the clinical importance of this organism, especially within Europe, we report the first case of septic arthritis of the shoulder caused by this organism. We also highlight the importance of considering atypical mycobacterium infection in the differential diagnosis of shoulder infection and issues surrounding the management of this entity.

There are three types of adipocytes in the human body, classified as white, brown and beige. Bone marrow adipose tissue (BMAT) is often described as having a heterogeneous appearance and has been suggested to be a distinct class of ‘yellow’ adipocytes. However, recent studies have also identified beige‐like adipocytes present in the bone marrow cavity, and they appear to have a relationship with the formation of bone like structures found in patients with osteoarthropathies, termed trabecular excrescences. The BMAT in osteoarthritic (OA) patients has an increased number of adipocytes compared to healthy and osteoporotic bone marrow. The objective of this study was to identify changes in BMAT composition between non‐osteoarthritic and osteoarthritic (OA) bone samples. Human joint samples from 28 patients (14 non‐OA, 14 OA) were obtained with informed consent from patients undergoing joint surgery at University Hospitals of Morecambe Bay NHS Trust (Lancaster, UK). North of Scotland NHS Research Ethics Committee (UK) approved this research. Samples were prepared for routine histological analysis and flow cytometry. Flow cytometric analysis gated for adipocytes by size and lipid content. Markers for adiponectin (Acrp30), uncoupling protein 1 (UCP1) and myogenic factor 5 (Myf5), were used to distinguish between white, beige and brown adipocytes. To corroborate the results, sections of joint tissues underwent immunohistochemical analysis. The anatomical location of the adipocytes within the bone marrow cavity was also studied. The data analysis showed an approximate 9:1 ratio of white to beige adipocytes found within BMAT, with only trace amounts of brown adipocytes identified. Statistical analysis to account for disease, age and biological sex demonstrated no significant difference in the adipocytes present between control and OA samples. However, male sex and ageing were shown to be factors for an increase in beige adipocytes. The histological study confirmed the presence of beige adipocytes and showed that, when present the beige adipocytes were found closer to the bone surface than the centre of the bone marrow adipose tissue. Previous studies have argued that BMAT is a distinct class of adipocyte. This study has demonstrated the presence of beige adipocytes within the BMAT of patients with and without OA. The methods used give a quantitative method of identifying different types of bone marrow adipocytes. Understanding changes in the anatomical composition of BMAT and the role of adipocytes in skeletal health may prove important in understanding the progression of age associated bone disorders. Support or Funding Information This work was funded by the Anatomical Society and sponsored by the American Association for Anatomy.