original article Wien Klin Wochenschr https://doi.org/10.1007/s00508-021-01966-0 Osteoid osteoma of the foot Presentation, treatment and outcome of a multicentre cohort Maria A. Smolle · Magdalena M. Gilg · Felix Machacek · Miroslav Smerdelj · Per-Ulf Tunn · Blaz Mavcic · Nenad Lujic · Jelena Sopta · Lauris Repsa · Jasminka Igrec · Andreas Leithner · Marko Bergovec Received: 27 August 2021 / Accepted: 5 October 2021 © The Author(s) 2021 Summary Background Osteoid osteomas of the foot are rare, with a varying and atypical clinical as well as radiolog- ical presentation impeding early diagnosis and treat- ment. The aim of the present multicentre study was to 1) analyze epidemiological, clinical and radiolog- ical findings of patients with foot osteoid osteomas and to 2) deduce a diagnostic algorithm based on the findings. Methods A total of 37 patients (25 males, 67.6%, mean age 23.9 years, range 8–57 years) with osteoid osteo- mas of the foot were retrospectively included, treated between 2000 and 2014 at 6 participating tertiary tu- M. A. Smolle, MD · M. M. Gilg, MD · Prof. A. Leithner, MD · M. Bergovec, MD () Department of Orthopaedics and Trauma, Medical University of Graz, Auenbruggerplatz 5, 8036 Graz, Austria marko.bergovec@medunigraz.at M. A. Smolle, MD maria.smolle@medunigraz.at M. M. Gilg, MD Magdalena.gilg@medunigraz.at Prof. A. Leithner, MD andreas.leithner@medunigraz.at F. Machacek, MD Department of Orthopaedic Surgery, Orthopaedic Hospital Gersthof, Vienna, Austria f.machacek@chello.at Prof. M. Smerdelj, MD Department of Orthopaedic Surgery, Clinical Hospital Centre Zagreb, Zagreb, Croatia Miroslav.Smerdelj@zg.t-com.hr P.-U. Tunn, MD Department of Tumour Orthopaedics, HELIOS Klinikum Berlin-Buch, Berlin-Buch, Germany per-ulf.tunn@helios-kliniken.de mor centres. Radiographic images were analyzed, as were patients’ minor and major complaints, pain re- lief and recurrence. Results Most osteoid osteomas were located in the midfoot (n = 16) and hindfoot (n = 14). Painful le- sions were present in all but one patient (97.3%). Symptom duration was similar for hindfoot and mid- foot/forefoot (p = 0.331). Cortical lesions required fewer x-rays for diagnosis than lesions at other sites (p = 0.026). A typical nidus could be detected in only 23/37 of x-rays (62.2%), compared to 25/29 CT scans (86.2%) and 11/22 MRIs (50%). Aspirin test was pos- itive in 18/20 patients (90%), 31 patients (83.8%) Prof. B. Mavcic, MD Department of Orthopaedic Surgery, Faculty of Medicine, University Medical Centre Ljubljana, Ljubljana, Slovenia blaz.mavcic@gmail.com N. Lujic, MD · J. Sopta, MD Institute for Orthopedic Surgery Banjica, Medical Faculty, University of Belgrade, Belgrade, Serbia N. Lujic, MD nenadlujic@gmail.com J. Sopta, MD jslabic@yahoo.com L. Repsa, MD Department of Orthopaedics, Riga Stradins University, Riga, Latvia lauris.repsa@gmail.com J. Igrec, MD Department of Radiology, Medical University of Graz, Graz, Austria Jasminka.igrec@medunigraz.at K Osteoid osteoma of the foot