Kjægaard-Andersen, P., Steinke, M. S., Hougaard, K., Søjbjerg, J. O., & Jensen, J. (1991). Heterotopic bone formation following hip arthroplasty: A retrospective study of 65 bilateral cases. Acta Orthopaedica, 62(3), 223–225. https://doi.org/10.3109/17453679108993596