Microwave Ablation Aided Surgery for Benign Aggressive Bone Tumors in the Extremities: Technical Points

Background : Extra bleeding may impede curettage of benign aggressive bone tumors (BABT). The efficiency of microwave ablation (MWA) in hemostasis and in simplifying resection of BABT remains to be elucidated. Methods : From December 2018 through December 2019, we performed MWA-aided surgery to treat extremity BABT in 8 patients. In-situ MWA was performed to assist curettage of the tumor. There were 4 male patients, the average age was 39.5 years (rang, 21-56 years). Histologic diagnoses included giant cell tumor of bone in 7 cases and aneurysmal bone cyst in 1. Tumor locations included the femur in 4 cases, tibia in 3, and humerus in 1. Results : The mean operation time was 133 minutes (range, 100 -165 minutes). The volume of blood loss was 183 ml (range, 130-260 ml). Blood transfusion was not needed. At the final follow-up (mean, 12 months; range, 10-14 months), none of these patients had recurrences. The mean musculoskeletal tumor society scale was 28 points (range, 25-30 points). One patient had incision dehiscence and one had transient nerve palsy. There were no other complications. Conclusions : MWA-aided surgery is safe and efficient for treatment of extremity BABT. This technique could be easily carried out and effectively simplified the curettage procedures. Further studies are needed to investigate the clinical outcome of this technique.


Background
Benign aggressive bone tumors (BABT) comprise heterogeneous disease entities, such as giant cell tumor of bone (GCTB), aneurysmal bone cyst (ABC), chondroblastoma, and osteoblastoma [1][2][3][4]. The common feature of BABT is local aggressiveness and high 3 recurrence risk [5]. Provided the bone stock is sufficient, intralesional excision of the tumor and filling with the bone graft or polymethylmethacrylate are treatment of choice [6]. To reduce recurrences, aggressive curettage assisted by the use of the burs and diverse surgical adjuncts (e.g. ethonal, phenol, argon-beam ablation etc) are advocated [6].
Because GCTB and ABC are very vascular, intralesional curettage are often impeded by extra bleeding [7]. However, hemostasis has rarely been addressed in the treatment of these diseases. Preoperative embolization is a viable treatment option. The literature demonstrated embolization is effective in reducing intraoperative blood loss, avoiding blood transfusion, and reducing morbidity [7]. However, the disadvantages of embolization include accidental embolization of the arterial blood supply to normal tissues, infection, and post-embolization syndrome [8]. Moreover, this technique requires an expert radiologist in a well-equipped center. Therefore, novel techniques are required to reduce blood loss so as to simplify the surgical procedures.
Microwave ablation (MWA) induces cell death through agitating water molecules and frictional heat [9]. The literature demonstrated MWA yields satisfactory pain relief and tumor control in the lung, thyroid, liver, kidney, bone, and soft tissue [9]. Because MWA radiates through biological tissues regardless of diverse heat transfer, it provides an ideal option for bone ablation [10]. Relevant treatment indications include percutaneous ablation of bone metastases and osteoid osteoma [10]. Because MWA is efficient in increasing the bone temperature and in inducing tumor necrosis, this technique may yield reduced blood loss during tumor curettage and offer sufficient devitalization margin. This could simplify the procedures for treating aggressive bone tumors. However, studies investigating the efficacy of MWA-aided surgeries for aggressive bone tumors are sparse, there has been no standardized procedures. Fan et al investigated the outcome of MWA-4 aided surgery for treatment of bone malignancies [11]. Biological reconstruction was possible since MWA offered sufficient tumor eradication margin. Long-term follow-up indicated this technique yielded favorable functional and oncologic outcomes [11].
However, to our knowledge, no studies have reported the use of MWA-aided surgery for treatment of BABT, the relevant technical points are yet to be elucidated.
This study reviewed a case series receiving MWA-aided curettage of extremity BABT. The purpose of MWA was to reduce blood loss and to simplify the procedures. Intraoperative parameters and postoperative outcomes were investigated. The objective of this study was to demonstrate the efficiency of MWA-aided surgery for treatment of extremity BABT and to provide relevant technical points.

Materials And Methods
Between December 2018 and December 2019, we treated 8 extremity-BABT patients with use of MWA-aided curettage (Table 1). There were 4 male patients, the average age was  (Figure 1-B). Because the tumor was necrotic and charred, curettage was easily performed without strenuous exercise for hemostasis (Figure 1-C). Curettage was assisted by use of the high-speed bur and cauterization as reported in the literature [6]. Cancellous allografts were applied to the subchondral area to protect the cartilage.
We then filled the tumor cavities with polymethylmethacrylate and performed prophylactic 6 plate fixation for GCTB, whereas allografts for ABC ( Figure 2).

Follow-up and outcome evaluation
We encouraged the patients to do active joint exercise 2 weeks postoperatively. Partial weightbearing was allowed 3 months postoperatively. The GCTB patients had intravenous zoledronic acid, 4mg / 3 months for 1 year to prevent recurrence. All patients were followed every 3 months for 2 years, every 6 months until 3 years, and annually thereafter.
The tumor long diameter, operation time, blood loss, transfusion requirement, extremity functions, and oncologic outcomes were recorded. The long diameter was measured on the sagittal and axial sections of the magnetic resonance images. Intraoperative blood loss was measured by weighing the sponges and the blood volume collected in the suction bottle. Anteroposterior and lateral radiographs of the surgically treated extremity were obtained to detect local recurrence and to evaluate bone healing. Limb functions were assessed with use of the musculoskeletal tumor society (MSTS) scale [12]. This system assigns values of 0-5 for six categories: pain, overall function, acceptance, braces, walking and gait in lower extremities (hand positioning, dexterity, and lifting ability in upper extremities) [12].

Results
The mean operation time was 133 minutes (range, 100 -165 minutes). The volume of blood loss was 183 ml (range, 130-260 ml). Blood transfusion was not needed (Table 1)

Discussion
Intralesional curettage is frequently performed for treatment of BABT given the benign nature of these tumors [13]. However, extra bleeding may impede the procedures and usually requires strenuous exercises for hemostasis [14]. This results in several adverse effects. First, escalated difficulty in curettage may lead to incomplete tumor resection, which might increase the recurrence risk. Second, extra bleeding causes potential tumor contamination in the whole surgical field. Third, blood transfusion is frequently required in such situation, whereas 20% of these patients encounter some type of adverse effect [7].
Although several surgical adjuncts have been advocated to improve the efficiency of curettage, but hemostasis remains to be addressed. Embolization yields favorable efficiency in reducing bleeding, but reports focusing on its efficacy in treating BABT was spares. Lee VN et al reported the outcomes after preoperative embolization of the BABT in 6 patients. The mean operation blood loss was 391 ml (range, 100-980), and no blood transfusion was needed [9]. In this study, we found in-situ MWA yielded less blood loss, whereas transfusion requirement was comparable to the literature. Because tumors located in the trunk were not included in the current case series, application of the tourniquet contributed to the reduced blood loss. However, MWA was definitely easier and could be efficiently used by the surgeon. The minimal bleeding allowed for clear field of vision. Besides, because the tumor was ablated, curettage could be easily performed. It's also noteworthy that embolization might cause some complications [15]. The major complications include dissection of the femoral artery at the puncture site, pain attributable to ischemic necrosis, accidental embolization of normal vessels, infection, and post-embolization syndrome [15]. Our findings implied MWA, if used properly, was safe and greatly simplified resection of extremity BABT.
MWA is a relatively new treatment option, it has been prevalently used under imageguidance for thermal ablation of various organs [16]. However, studies focusing on MWAaided surgery for treatment of aggressive bone tumors are sparse, the clinical data and experience are minimal. Fan et al have investigated the efficacy of MWA in limb-salvaging surgeries for treating bone malignancies [11]. Treatment indications included primary malignant bone tumors and bone metastases. MWA was used to achieve tumor en-bloc ablation and yielded safe resection margin, the ablated tumor was resected in a curettage manner. Ten-year follow-up outcomes demonstrated this procedure yielded satisfactory functional results, and greatly simplified surgery process without increasing complication rates [11]. Li J et al performed navigation-aided MWA to facilitate epiphysis-preserving surgery in selected patients with osteosarcoma in the proximal tibia [17]. MWA effectively ablated the tumor margin close to the joint, so as to allow for preserving as much epiphysis as possible. At the final follow-up of mean 48 months, no tumors recurred. The procedure also yielded favorable functional outcomes [17]. Nevertheless, the efficiency of MWA-aided surgery in treating BABT has never been reported, the technical points remain to be addressed.
To our knowledge, this is the first study investigating the use of MWA-aided surgery for treatment of BABT in the extremities. The ablation purpose and relevant technical points differ from those reported in previous studies [18]. Given the benign or intermediate nature of BABT, the purpose of in-situ MWA was not tumor en bloc ablation, but reduced blood loss caused by hyperthermia-induced necrosis. For malignant bone tumors, multiple antennae may be required to achieve a safe devitalization margin [11,19]. However, the ablation magnitude of BABT is more flexible given the benign nature of the tumors. The surgeon could ablate the superficial area first, then curette the eschar and necrotic tumor tissue (Figure 1). In this process, bleeding was minimal, and tumor resection could be easily carried out. When the deeper tumor was exposed, MWA could be used repeatedly in the same manner. Given the profound effect of MWA on the bone regardless of its poor heat transfer, ablating the tumor wall further reduced bleeding of the bone [20,21].
Theoretically, this procedure also provides extensive devitalization margin, so as to reduce recurrences. This is important for treatment of BABT, because these tumors are susceptible to recurrence and the incidence was reported to be as high as 30% [22].
However, due to the short-term follow-up of this study and limited data in the literature, this advantage remains to be demonstrated. Because the skin, vessel, nerve, and cartilage are sensitive to hyperthermia, isolation and protection of these tissues are critical [21].
We applied sponges and continuous lavage with cooling saline to protect the surrounding soft tissue, whereas infusion of cooling saline into the joint cavity was used to protect the cartilage. Our findings indicated in-situ MWA was as safe as reported in the literature. Of

References
Availability of data and materials: The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Competing interests: The authors declare they have no competing interests.
Funding: There has been no funding for this study.
Authors' contributions: YC accountable for design of the study and writing of the manuscript. MML accountable for the collection and analysis of the data. All authors read and approved the final manuscript.
Acknowledgements: The authors would like to thank all participating patients and colleagues who made this study possible.

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