Hydatid disease or hydatidosis or echinococcosis is a very commonly encountered disease in some parts of Asia and Africa, Mediterranean countries, South America, and southern Russia. It is caused by the larval stages of Echinococcus. The larval form of Echinococcus can infiltrate many parts of the human body; but mainly the larva harvests in liver and lung ^[1]. Bone involvement is a rare phenomenon accounting for only 0.5–4% of bony hydatidosis cases among of the total hydatidosis cases [2-4]. Among the bony involvement, the most commonly encountered infection is of vertebral column, long bones (femur and tibia), and pelvic bone. The insidious nature of onset and non-specific complaints often delays the diagnosis. Management of bony hydatid disease involves surgery along with chemotherapy. To the best of our knowledge, this case is second only involvement of femoral head by hydatidosis reported in English literature.

This case report illustrates the involvement of head of femur in bony hydatid disease. An 18-year-old male patient presented with pain in the left groin with 1 year duration in outdoor department. Pain was gradual in onset, dull aching in character, mild in intensity, which was localized to groin without any radiation. Pain increased on walking, prolonged weight-bearing, and with activities such as squatting and cross-legged sitting. Pain relieved on taking non-steroidal anti-inflammatory drugs. There was no history of fever, weight loss, trauma, blood dyscrasias, coagulation disorder, and substance abuse. On clinical examination, the patient was moderately built and nourished. There was no clinically evident swelling, sinus, or fistula on the left hip region. On palpation, local temperature was not elevated. However, left hip was tender on palpation with terminal restriction of all movements of hip. There was no limb length discrepancy and gait of the patient was normal. Radiograph of pelvis with bilateral hip revealed a lytic area near the superolateral border of the head of femur of left hip with mild extension to proximal part of neck of femur (Fig. 1). To further investigate the etiology of lytic lesion, computed tomography (CT) and magnetic resonance imaging (MRI) were done which further showed the prominent lytic area with multiple loculated lesions with in the lytic area (Fig. 2 and 3).

To identify the pathology, a needle biopsy with 13G Jamshidi needle was done under local anesthesia and C Arm guidance, but the results of the biopsy were inconclusive. Hence, an open biopsy was performed under spinal anesthesia through Smith Peterson approach. The sample was sent for histopathological examination (HPE). HPE revealed a cystic lesion with laminated walls and multiple scoleces were found attached to the laminated wall (Fig. 4).

After confirming the etiology as hydatid disease, the patient was immobilized with one and half hip spica cast for 1 month and allowed ambulation after 1 month with highly protective weight-bearing to prevent pathological fracture. Ultrasound and CT scan of whole abdomen and chest was done to assess the status of visceral organs and was found to be normal. Anti-helminthic medication albendazole 400 mg once a day was started and was continued for 3 months. At 3 months, radiographs revealed the persistence of lytic area in superolateral area of femur head (Fig. 5). Surgery with curettage and cementing of the lytic area was planned through posterior approach while preserving the blood supply of femur head through greater trochanteric (GT) osteotomy through safe surgical dislocation. The patient was positioned in lateral position. The surgical technique involved the exposure through Gibson’s interval and adjacent soft tissue were protected with gauze pieces soaked with 20% sodium chloride (NaCl). Thorough local debridement and curettage was done using high speed burr ensuring that all of the infective material was removed. The wall of lesion was then soaked in 20% NaCl for 15 min. After this, cementing was done in cavity using high viscosity polymethylmethacrylate bone cement. The advantage of using bone cement was to get immediate bony stability in the lytic area and exothermic reaction during the setting of cement was helpful in destruction of any remaining daughter cysts and organism. The GT osteotomy was fixed with two 4.5 mm fully threaded cortical screws (Fig. 6). Post-operative course was uneventful and patient was comfortably discharged after 2 weeks.

The patient was called for sequential follow-ups and serial radiographs were performed with functional evaluation of patient which was done (Fig. 7-10]. The GT osteotomy was healed and there was no recurrence of lesion. At final follow-up of 8 years, Harris hip score was 100 and Oxford hip score was 60. There is no clinical or radiological evidence of osteoarthritis of hip and patient is free from any recurrence of disease (Fig. 11).

Echinococcus is the pathogenic tapeworm causing hydatid cyst. Canines are the primary host. Humans and domestic animals such as sheep are intermediate hosts for the disease. The transmission of organism’s eggs mostly occurs through food or drinking water [5,6]. The ovum loses its outer layer in the duodenum of intermediate host. The embryo passes through intestine and gets lodged into liver through portal circulation ^[7]. The most common sites affected by the organism are liver and lungs ^[8]. Hydatid disease rarely involves bone. The frequency of osseous involvement is fairly minimal with only 0.5–4% of all cases [2,3]. When involved, majority of the hydatidosis involves axial skeleton (vertebrae and pelvis). There may be hematogenous spread of this infection from primary site to secondary site [4,9]. Approximately 12 species of Echinococcus have been identified till now. However, Echinococcus granulosus (EG) and Echinococcus multilocularis (EM) are known to affect man. Cystic echinococcosis (CE) is caused by EG while alveolar echinococcosis (AE) is caused by EM. Infection by EM is extremely rare in man and it is not known to affect bone ^[7]. The pathophysiology of visceral and bony hydatidosis differs in one respect; the former has a fibrous capsule which latter does not have. Due to this, the progression of disease occurs through exogenous vesiculation and diverticula formation. The intraosseous extension of disease occurs through mechanical compression of bone leading to atrophy. The compression also interferes on the blood supply of the bone leading to necrosis and sequestrum formation ^[10]. It is a very slowly progressive disease that may remain covert over a long period of time. In majority of cases, an infection that may have infested in early childhood may become symptomatic in adolescent period. Patients may remain asymptomatic and may present later with a pathological fracture after episodes of chronic pain or limitation of terminal movements, if present near joint [10,11]. Due to these chronic or vague symptoms, most cases often go undiagnosed in developing nations. Sometimes, in mild to moderate involvement of skeleton, even simple radiographs are not helpful in making diagnosis. The slow-growing organism lodged in the medullary cavity of bone progresses through bony trabeculae. Later, it can breach the cortex and may also involve surrounding tissue. Radiographic findings include single or multiple lytic lesions in bone involved ^[10]. There is no periosteal reaction seen on radiographs. Calcifications are seen in later stages of disease or in case of superadded bacterial infection [4, 12]. The CT scan findings are non-specific with most common being a lucent expansile lesion with thinning of the cortex ^[7]. It is also helpful in identifying the extraosseous extent of lesion. MRI is helpful in association with CT scan in better evaluation of extent of lesions mainly in vertebral hydatidosis ^[10]. Laboratory testing with immunodiagnostic test such as enzyme-linked immunosorbent assay and dot immunogold filtration assay. The sensitivity and specificity of these tests ranges in between of 80 and 95%. The advantages of these tests lie in their convenience and rapidity ^[13]. Casoni’s test and complement fixation test are almost completely abandoned nowadays. Diagnosis is confirmed mainly by biopsy and HPE of the specimen obtained from bony site involved. Other conditions such as tuberculosis, osteomyelitis, metastasis, aneurysmal bone cyst, fibrous dysplasia, and cystic benign lesions should be kept in mind as differential diagnosis for bony hydatidosis [14-16]. Treatment of bony hydatidosis includes surgery and chemotherapy [8,10]. Pre-operative medical treatment with benzimidazoles such as mebendazole and albendazole helps in sterilizing the content of cysts as well as in decreasing the size of cysts. Albendazole is now regarded as drug of choice for CE. It is given in dose of 10 mg/kg body weight (bw) for 3 months preoperatively. The use of praziquantel orally at a dose of 25–50 mg/kg bw for 1–6 months is also reported by Li et al. Combination therapy with albendazole (10 mg/kg bw) and praziquantel (25 mg/kg bw) for 3 months has been shown to increase the level of active metabolite albendazole sulfoxide (AlbSO) in blood and cysts as compared to albendazole monotherapy. Similarly, albendazole combined with cimetidine also increase the concentration of AlbSO in bile and cysts. Medical treatment may be continued post-surgery also to treat the cysts which may have escaped the surgical procedure ^[17]. Surgical treatment is challenging in cases of diffuse involvement of bone. In cases of diffuse involvement, wide resection with healthy margins should be the goal of surgery as in oncologic surgeries. The pelvic involvement is usually diffuse and requires extensive surgery. After radical resection, large bone defects are created in pelvis. Many reconstruction methods have been described to manage these defects. Liang et al. reported a case of sacrum and ilium involvement which was managed by radial resection of bone lesion and the remaining pelvis was stabilized by pedicle screw rod system ^[18]. Gdoura et al. reported a case of pelvic hydatidosis which was managed by radical resection and femoropubic and sacral arthrodesis. This fixation was fractured 7 months after surgery ^[19]. There are many complications associated with creation of large bone defects after radical resection in pelvis to prevent this, Liang et al. describes a case of extensive involvement of pelvis and proximal femur with hydatidosis. It was managed by one hemipelvis replantation after liquid nitrogen devitalization with femoral prosthesis replacement along with chemotherapy ^[18]. Femoral involvement can be localized as in this case or diffuse. In case of localized involvement, curettage and cementation with or without internal fixation should be performed. In diffuse involvement, debridement with prosthesis (conventional joint arthroplasty or tumor mega prosthesis) implantation is the preferred treatment option depending on the extent of bone involvement. There is high risk of recurrence of the disease [20,21]. In this case report, there may have been an indwelling asymptomatic slowly growing infection since childhood which later presented with pain and terminal restriction of movement of hip joint. Head of femur is a rare site of involvement for bony hydatidosis. The patient is completely asymptomatic after 8 years of follow-up.

Hydatid disease of the bone is one of the rare manifestations of echinococcosis. There is rare occurrence of long bones. The treatment of osseous hydatid disease is challenging. There also have been few failures and recurrences even after complete therapy but it is imperative to consider hydatid disease of the bone as a differential diagnosis of most cystic to lytic lesions of the bone, especially in the endemic areas. High index of suspicion in endemic areas is required along with radiological and laboratory investigation to confirm the diagnosis. Timely and proper management can completely cure the patient without any residual pathology with full functional recovery.

Bony hydatidosis should be kept in mind as differential diagnosis of lytic lesion in bone.