Heterotopic ossification (HO) refers to the formation of trabecular bone outside the usual skeletal system[1,2]. Therefore, all extraskeletal bone formation in various areas of the body, including the skin, subcutaneous tissue, muscle, joints, and mesentery are included in this uncommon clinical entity[3,4]. As much as it covers all extraskeletal bone formation throughout the body, a wide range of factors contribute to each occurrence. Some of the most mentioned associated factors are trauma, burns, arthroplasty, and abdominal surgery[1,5]. As HO is highly associated with an external insult, the concern is higher in military settings where a high incidence of HO in combat-injured patients has been reported[2].

HO has been reported in various sites of the human body, and some hypotheses have been presented for its pathogenesis[6]. The generally recommended treatment for symptomatic HO has been selective surgical excision[2,7]. Some cases have been treated with open resection[8,9], and others, especially cases of HO in the joints, have been treated with arthroscopy[1]. Regardless of the HO site, recurrence has always been a concern for surgeons, and some preventive measures, such as postoperative radiotherapy[10], oral nonsteroidal anti-inflammatory drugs (NSAIDs)[11], and topical sealant (bone wax) over the osteotomy plane[1,7,12], have been recommended.

We experienced a case of symptomatic HO along a laparotomy scar following gastrectomy for gastric cancer. To search for the best treatment options, we vigorously reviewed the previous reports that were available at the time. While realizing that HO is a collective term representing all types of extraskeletal ossifications, we found a lack of information stating the need for individualizing our treatment efforts depending on the HO location. Our choice of treatment, which was a combination of surgical excision and the application of bone wax, did not turn out to be the best option.

Based on the patient’s medical history, physical examination, and CT findings, the final diagnosis was HO, originating from the xiphoid process.

Surgery for symptomatic HO was performed under general anesthesia. At laparotomy, an 11 cm-sized ossification, originating from the xiphoid process, was noticed between the linea alba and preperitoneal adipose layer (Figure 2). The structure was densely adhered to the surrounding tissue. After careful dissection of the adhered tissue and separation of the bony attachment at the xiphoidal end, we completely removed the structure. As an extra precaution for bone hemostasis and HO recurrence, bone wax was applied to the excisional margin. The surgical wound was closed layer by layer.

Histological examination of the surgical specimen confirmed HO. However, there was extensive discharge from the surgical wound over the following two weeks. The nature of the discharge slowly changed from serous to turbid, and we decided to open the surgical wound. The wound was somewhat waxy, and massive wound irrigation was performed. After three weeks of applying saline-soaked gauze dressings, delayed wound closure was performed, and the patient was finally discharged eight weeks after the HO excision. He underwent a follow-up CT two years postgastrectomy, which was about a year after the HO excision, and there were no signs of recurrence (Figure 3).

HO is rare and, yet, broad in that it represents all types of extraskeletal ossifications in the body. Therefore, depending on its location, a treatment strategy that may be effective for some may not be for others. An extensive literature search led us to the application of bone wax along the laparotomy scar following surgical HO excision. However, this turned out to be a grave misapplication of our treatment efforts.

Two pathogenesis hypotheses for the HO of abdominal scar tissue have been suggested[6]. The first and more favored hypothesis is an aberrant inflammatory process in wound healing, leading to the differentiation of mesenchymal stromal cells into osteoblasts. This is highly favored in those with HO located at a distance from the adjacent bone. The second hypothesis emphasizes the iatrogenic spillage of periosteal cells from the adjacent bone during surgery. In our case, HO was connected with the xiphoid process, and we could not exclude the possibility of the iatrogenic spillage of periosteal cells from the xiphoid process.

Whatever the pathogenesis hypothesis, surgical excision has been recommended for symptomatic HO. Our literature search delved deeper into HO prevention. The search returned some recommendations for preventing HO recurrence, and bone wax was one of them. Bone wax is a nonabsorbable substance composed of beeswax and petroleum jelly, and has been used to achieve hemostasis after bone resection[13]. While it functions as a mechanical barrier to stop bleeding, using it to suppress bone formation in the resection surface has also been reported[14]. Despite concerns about a chronic inflammatory reaction following the intraarticular use of bone wax[15], bone wax has been used as a topical sealant to prevent HO in shoulders[1], temporomandibular joints[7], and elbows[12].

Besides bone wax, postoperative radiotherapy and oral NSAIDs have been recommended as feasible preventive measures for HO[10,11]. However, we chose none of these because they are highly associated with gastrointestinal symptoms[16,17]. Gastric cancer survivors are known to experience gastrointestinal symptoms for years after surgery[18]. Our patient underwent distal subtotal gastrectomy a year earlier and was not free of gastrointestinal symptoms. Therefore, the clinical application of either radiotherapy or oral NSAIDs would have exacerbated postgastrectomy symptoms.

After much deliberation, we decided to use bone wax. Unfortunately, the outcome was an eight-week-long hospital stay and additional surgery for delayed wound closure. The application of bone wax on the abdominal surgical wound delayed its primary healing intention. A previous study reported the clinical use of bone wax in dermatologic surgery by exploiting such a distinguishing trait[19]. Bone wax has been used to cover deep tissue defects and create an ideal occlusive environment for secondary healing intention. In our case, our efforts to prevent HO recurrence left the surgical wound in a condition that was suitable only for secondary healing intention.

Complete excision may be a sufficient management strategy for HO along a laparotomy scar. We eventually made huge efforts to remove the bone wax as much as possible by massive wound irrigation and repeated cleansing with wet gauze, and there was no sign of recurrence after a year. Nevertheless, uncertainty regarding the remaining bone wax and its implication on HO prevention is a limitation of this finding. The strength would be sharing the valuable lesson that we need to be very careful about choosing a treatment method for HO using available research data and treatment should be individualized depending on the HO location. Previous reports suggesting the beneficial effect of bone wax against HO recurrence have focused on HO in joints[1,7,12]. Our effort of applying bone wax to an abdominal wound could have failed because we did not realize the distinction in treatment between different areas.

In conclusion, HO represents all types of extraskeletal ossifications in the body, and treatment approaches must be individualized depending on the surroundings. Complete surgical excision should be the priority treatment option for HO along a laparotomy scar, and the application of bone wax is not recommended.