In 2010 a 75 year-old female patient presented at our clinic with a 2-year history of pain and recent emergence of a discharging sinus at her left upper leg. She had a history of bilateral gonarthrosis and underwent elective right and left knee total arthroplasty 5 years before. The procedures and the post-operative follow-up were uneventful. Her physical examination revealed slight swelling and tenderness with a mild seropurulent discharge on the antero-lateral aspect on her proximal left leg. There was no other systemic complaint. Her personal and family histories were unrevealing. There was no history of fever, trauma, previous tuberculosis or bone tumors. Lower limb x-rays were performed and the radiographic examination revealed a well demarcated cystic structure in her left tibia, 4 cm below the distal tibial component of the knee arthroplasty (Fig. 1). A purulent sample was collected and sent for microbiological study, after which, to better investigate the nature of the cyst, an incisional biopsy of the lesion was performed, and the sample subjected to histopathologic examination. The laboratory study isolated Pseudomonas aeruginosa, and appropriate antibiotics where then administered according to the susceptibility test carried out. Pathology results revealed hydatid cyst of the tibia. Segmental resection was planned, and the surgical approach revealed a diaphyseal cyst adherent to the surrounding tissues, which were markedly oedematous, with multiple membranous whitish tissues in aggregation. Fluid was aspirated from the cyst, and the sample was sent for microbiology and serology tests. After curettage of the lesion and power-pulse lavage, povidone-iodine-alcohol solution was injected. Due to the fragility of the remaining tibial diaphysis, an external fixator was applied. Microscopy confirmed the diagnosis and revealed osseous tissue with hyaline and germinative membranes, lymphocytes, and monocytes.
Albendazole and praziquantel, antihelminthic drugs, at doses of 10 and 25 mg/kg, respectively, were started. The patient recovered uneventfully and was discharged shortly after the procedure. She was clinically and radiologically evaluated in the following months, revealing progressive bone growth, remodeling and consolidation, having the external fixator extracted 6 months after the initial procedure.
The patient then remained exempt of pain, swelling or other complications, until May 2014, when suddenly she comes to our clinic, complaining of pain and unable to bear weight on her left knee.
X-ray studies revealed a pathologic periprosthetic fracture, below the tibial component, resulting from an extension of the previously treated hydatic cyst (Fig. 2). A treatment plan was performed, and our patient underwent surgical intervention. Both of the total knee arthoplasty components exhibited signs of loosening (Fig. 3), and after extraction of them, a total revision knee arthroplasty was performed (Fig. 4). The cancellous bone loss in the tibial component was considerable, and this defect was addressed by autologous bone graft implemention around the tibial stem and plateau. The patient functional outcome was excellent. She recovered motility of her left knee, and now more than 24 months has passed and she is fully weight bearing with no pain, knee instability or discomfort.