Background: A painful and swollen shoulder has an extensive differential diagnosis, with Milwaukee shoulder syndrome (MSS) being diagnosed infrequently. Analysis of crystals in the synovial fluid is an important diagnostic step in patients with a swollen shoulder.
Case description: A 69-year-old female presented at the orthopaedic outpatient clinic with pain, limited mobility and swelling of the left shoulder. The diagnosis MSS was made based on the characteristic features on X-ray and MRI combined with the analysis of the synovial fluid, including a positive alizarin-red staining.
Conclusion: MSS is a rare, destructive, calcium-hydroxyapatite crystal-associated arthropathy. After a typical X-ray, a joint aspiration is preferred to avoid unnecessary expensive radiographic imaging. Alizarin-red staining is a simple, inexpensive, and sensitive test to identify calcium-hydroxyapatite crystals in synovial fluid, and aids in the diagnosis of MSS. This is important in order to adequately inform patients regarding the prognosis of their disease.