Colorectal adenocarcinoma presenting with a pathological fracture due to a solitary bone metastasis to the tibia: a case report and literature review

Introduction
Solitary bone metastasis of colorectal carcinoma (CRC) without other metastasis sites is extremely rare and can be found in less than 1% of patients with CRC.

Material and methods
In the present study, we report the first case of a solitary tibia metastasis and its pathologic fracture as the first presenting feature of a colorectal adenocarcinoma.

Results
A 78-year-old female patient presented to our emergency department due to atraumatic pretibial swelling. Plain radiography did not detect any pathology. The swelling was incised and serous-bloody collection was evacuated, and the patient was discharged. On the 17th postoperative day, during a regular walk, the patient fell down and broke her leg, which transpired to be a pathologic fracture of the proximal tibial diaphysis, confirmed by X-ray. A biopsy of the altered bone tissue from the fracture site revealed metastatic colorectal adenocarcinoma. On colonoscopy, a circular mass in the upper rectum was found.

Conclusions
Solitary bone metastases are most commonly found in bones that are related to venous drainage via the paravertebral plexus of Batson – the pelvis, vertebrae, and sacrum. Long bones are extremely rare localizations of solitary CRC metastases, with only few cases published so far in medical literature. In our case, the patient`s first symptom was related to the osseous tibial metastasis – leg swelling. No tumour was suspected until the pathologic fracture occurred. It is important to consider osseous metastasis in every patient with unexplained swelling, haematoma, or pain of the extremities and make a bone scan to recognize the metastasis early.