Occult traumatic impaled foreign body, a challenging diagnosis of severe chronic lower extremity radicular pain

The investigation of embedded soft tissue foreign bodies relies heavily on radiological imaging. The prompt identification of these objects is critical as retained foreign bodies may lead to serious infection or chronic debilitating pain depending on anatomical location. In this report, we present a case of a radiographically occult traumatically implanted foreign body in a 15-year-old female after a high-speed motor vehicle accident. Initial computed tomography (CT) scan was unremarkable and exploration under anesthesia demonstrated no other significant findings, yet the patient continued to suffer severe refractory radicular pain with marked limitation of daily function. It was not until 12 weeks after the accident that a magnetic resonance image (MRI) of the pelvis revealed a deep sinus tract with central low magnetic resonance (MR) signal, raising suspicion for a retained foreign body. A 10-centimeter plastic foreign body extending from the patient's coccyx to the sciatic foramen was identified and surgically removed resulting in immediate symptom relief. This case illustrates that the detection of a retained foreign body is not always straightforward and multiple imaging modalities may be necessary for accurate diagnosis. We also discuss the most appropriate diagnostic imaging algorithm when a foreign body of the musculoskeletal system is suspected.