Bone echinococcosis was caused by the parasitism of six-foot hookworms in bone tissue through the blood circulation, which was initially infested by the digestive tract [14–15]. Pelvic echinococcosis had been reported to account for approximately one-fourth of bone echinococcosis[3–4]. Unlike visceral echinococcosis disease, infestation development of bone echinococcosis began in blood-rich cancellous bone. Because there was no reactive connective tissue barrier against the proliferation of intraosseous hydatid cysts, daughter cysts can directly enter the bone and grow in the bone marrow cavity along the direction of the epiphyseal plate and articular cartilage [14]. In the view of imaging, the lesion showed that expansive honeycomb or soap bubble changes with smooth and sclerotic margins. Therefore, this growth pattern of bone echinococcosis determined its cystic and multilocular features [4, 16]. The development of pelvic echinococcosis was not only slow, but its symptoms were also concealed, including chronic pain, swelling, claudication, sinus formation, abdominal pain, or nerve compression symptoms (e.g., sciatica). According to the above characteristics, the diagnosis of pelvic echinococcosis should be combined with the patient's living environment, serum parasite-specific antibody examination (ELISA and DIGFA), imaging examination and clinical manifestations to avoid misdiagnosis or missed diagnosis, which may delay the treatment and worsen the symptoms.
Currently, the practical method for pelvic echinococcosis was surgical intervention combined with anti-parasite chemotherapy [2, 10]. Chemotherapy with mebendazole or albendazole alone was not sufficient in most patients. However, it can be used as neoadjuvant therapy to preoperatively reduce cyst range and/or as adjuvant therapy to reduce the risk of recurrence. Via published literature [2, 6, 12], different surgical methods were reported, including complete resection, total hip arthroplasty, femoropubic arthrodesis, etc. But in our opinion, it was impossible in most cases to eradicate the advanced lesion without causing too much disability to the patient. The resection of large segmental bones usually led to the loss of continuity and integrity of the pelvic ring. Therefore, how to restore pelvic continuity was extremely important for patients with lesion areas in more than half of the pelvic ring after debridement. In this study, 9 patients were managed by designed Hemi-pelvic prosthesis to restore the pelvic bone defects. All patients (100%) with compression symptoms caused by pelvic echinococcosis were improved after surgery.
The treatment of bone echinococcosis was more similar to oncologic therapy than surgical treatment of visceral hydatid disease [6]. However, pelvic bone echinococcosis cannot be fully equated with malignancy because malignancy was much more aggressive. Therefore, eradication of parasites was not the main purpose of surgical treatment, and how to effectively remove the destroyed bone and reconstruct limb function was of greater concern to orthopaedic surgeons. Sometimes, the recurrence of infection or worsening symptoms may result in incomplete debridement surgery. Then preoperative and postoperative anti-parasite chemotherapy was considered an effective treatment regimen to control the spread and recurrence of cyst lesions[3, 14, 17]. In our study, all patients were successfully treated by surgery combined with anti-parasite chemotherapy. The mean MSTS score of 9 patients at the final follow-up was 21.27 ± 5.25 points. Unfortunately, there were still 3 patients who experienced a recurrence of infection, but the infection was under control after repeated debridement procedures.
When osteolytic destruction of the pelvis was not extensive, some researchers suggested that the Hemipelvic devitalized replantation using liquid nitrogen was also an optional method of reconstruction [2, 8]. The resected infestation bone inactivation can be performed by high-temperature and high-pressure inactivation or liquid nitrogen cryoinactivation. Although the anatomical restoration of the bone defect can be achieved, the recurrence of infection and replantation bone resorption was high. Besides, the utilization of allograft pelvic repair was presented by some scholars [8, 12]. However, it was difficult to select well-integrated allogeneic Hemipelvic for allogeneic Hemipelvic replacement, and the allogeneic reactions should not be ignored. Because there were great differences in the size of the donor pelvic ring and the anatomy of the auricular surface, most of them cannot be anatomically suitable for the bone defect. Both of the above methods had the possibility of postoperative recurrent fracture and reinfection.
Via published articles [18–19], Hemipelvic prosthesis surgery was a practical method for the restoration of pelvic bone defects in the region I + II or I + II + III. Campanacci et al. [20] suggested using an acetabular prosthesis connected to a pedicle screw-rod system to restore the pelvic bone defect caused by bone tumour resection, which inserted screws on the sacral side and connected the pelvic acetabular prosthesis to the sacral screws through a pedicle screw-rod system. Zhang et al. [21] reported a series of patients with pelvic bone defects treated with a new modular artificial Hemipelvic prosthesis and fix the prosthesis to the sacrum with screws. Mostly, the correct placement position of sacral pedicle screws and prosthesis depended on the surgeon's experience. In this study, the prosthesis combined with a sacral pedicle screw-rod system was anatomically designed according to preoperative CT imaging, which was highly matched with the sacral articular surface and simply installed. Sacral screws can be precisely placed in the sacrum according to the preoperative design to avoid entering the sacral canal and the vascular plexus anterior to the sacrum, which may decrease the risk of prosthesis dislocation and re-fracture, and nerve and vascular injury.
ELISA and DIGFA were the most common and practical tools for the detection of bone echinococcosis, with a sensitivity of 80%-100% and a specificity of 88%-96% [22–23]. For imaging examination, thin-section CT scanning was necessary for the design of diagnosis and preoperative plan. And it was recommended that thin-section scanning of the patient's pelvis 0.5–1.0 mm slice thickness should be managed, which was essential for the location of the prosthesis and pedicle screws inserted intraoperatively. In this study, a typical characteristic of CT imaging was observed in all patients (100%), and all patients (100%) were positive in parasitic immunodiagnostic tests. In our opinion, the Enneking classification [13] was also significant for pelvic bone echinococcosis, because it indicated the range of echinococcosis lesion progressed, which was helpful to assign the range of debridement surgery.
Several limitations may affect the results of this study. First, this study was retrospectively conducted by a single-centre medical institution with a small sample. Second, there was no unified and standardized treatment algorithm for the management of pelvic echinococcosis. Hence, we acknowledged that more patients and a longer follow-up period were still needed to evaluate the efficacy of this treatment method.