Segmental Defect-Bridging Intramedullary Knee Arthrodesis for Osseous Hydatidosis of the Distal Femur: A Case Report

Abstract

Hydatid cyst is a condition endemic to many parts of the world and is mainly caused by Echinococcus granulosus ( E. granulosus). It rarely affects the bone tissue, with the most commonly impacted sites being the vertebrae and the pelvis. Preoperative diagnosis is challenging and very rarely possible because of its similarities with other pathologies. In this report, we present the case of a 64-year-old patient with osseous hydatidosis of a pathological distal femur fracture. The fracture pattern was not recognized on the initial operation and multiple serial debridements were required to control the disease, leading to a large bone defect and a weakened extensor mechanism. A knee arthrodesis with a segmental defect-bridging intramedullary system was eventually performed, which led to satisfying outcomes. Osseous hydatidosis very often presents itself as a pathological fracture and is difficult to diagnose preoperatively with plain radiographs. Orthopedic surgeons are advised to maintain a high index of suspicion and to test for this disease when cystic bone lesions are detected at fracture sites, especially in patients from endemic regions.

Keywords: femur fracture; hydatid cyst; knee arthrodesis; osseous hydatidosis.

Figure 1. Initial anteroposterior (a) and lateral (b) radiographs of the patient showing the distal femoral fracture

At closer observation, the cystic/lytic lesion can already be seen

Figure 2. Initial CT scans of the same extremity taken on the day of trauma

Thinning of the cortexes and lysis can be observed CT: computed tomography

Figure 3. Radiographs in the second month postoperatively

The patient has pain on ambulation. The radiographs show no signs of healing and reveal lysis and resorption around the fracture site

Figure 4. Radiograph at six months postoperatively

The image shows failure at the fracture site with no signs of callus, resorption, thinning of the cortexes, and multiple failed distal screws

Figure 5. One of many pearly-white cysts excised and debrided during surgery (a) and its histopathological examination with hematoxylin and eosin stain (b)

Figure 6. Images related to temporal arthrodesis and final standing radiograph

The temporal arthrodesis performed after extensive segmental resection using a long knee-spanning femoral nail centrally covered with a PMMA block (a) and the final standing radiograph showing the segmental defect-bridging intramedullary knee arthrodesis system chosen for the case (b) PMMA: polymethyl methacrylate