Introduction: Heterotopic ossification (HO) is abnormal formation of new bone in the soft tissue. HO occurs outside the normal bone within soft tissues such as muscles and tendons, and histologically, it is no different from skeletal bone. It is still not clear what factors stimulate HO. The soft tissue around the hip joint has been identified as the most common location for HO. Patients with HO usually have no clinical symptoms; however, it can become very painful and lead to severe functional limitations. The standard diagnostic procedure consists of conventional X-ray diagnostics and/or skeletal scintigraphy. Local radiation and nonsteroidal anti-inflammatory drugs are the classical options for treatment and prophylaxis of HO. We describe two pediatric patients with “lollipop-like” HO at the end of Kirschner wires (K-wires, steel) and titanium elastic nails (TENs, titanium).

Case Report: A 9-year-old girl, 1 year after Salter and Pemberton osteotomy with K-wires, and a 15-year-old boy, 1 year after fracture of the right femur treated by osteosynthesis with TENs, were treated in our department due to HO. The girl did not report any symptoms, while the boy had pain in the location where the ossification had formed. However, examination of the girl’s hip showed that the range of motion in the hip affected by HO was limited in comparison with the opposite unaffected hip.

Conclusion:To the best of our knowledge, lollipop-like HO around protruding K-wires or TENs has not yet been described. According to literature, HO is mainly located in the pelvic region and at the elbow. Most studies investigating HO describe cases which have occurred after cemented or uncemented hip replacement surgery. In the cases presented here, HO might have been stimulated by repetitive muscle trauma above the protruding K-wire and TENs, the trauma caused by the operation, bone marrow cells dispersed intraoperatively, or by a combination of these and other factors. There are numerous studies on strategies to prevent HO after joint replacement. We suggest “lollipop sign” as a name for this rare type of HO around the end of K-wires/TENs in pediatric patients.