Pathologic fracture occurs when a bone defect develops after operation for bone disease. Tyndorf et al. reported that odontogenic cyst and mandibular atrophy were the most common causes of such fractures. Pathologic fracture of the mandible sometimes occurs after surgical removal of these lesions; in particular, the bone defect resulting from marginal resection of malignant tumors or huge benign lesions (e.g., ameloblastoma, keratocystic odontogenic tumors) may be enough to promote development of pathologic fracture [8–10].
Boffano et al. reported that if sufficient bone remained to buttress the fracture, traditional open reduction and internal fixation were performed, in association with cyst enucleation or marsupialization, in almost all reported cases. When remaining healthy bone is insufficient or separated by a large defect, resection of the involved mandibular region, eventually followed by immediate or secondary reconstruction, may be necessary. Abir et al. suggest that in cases where there is no potential for normal union, the bone must be resected until normal, bleeding bone is reached. When sufficient normal bone remains, traditional reduction is performed using rigid fixation. Coletti and Orb also reported that in the few cases in which sufficient bone was left to buttress the fracture, traditional fracture reduction with rigid fixation was employed. As a result, if the potential for bone healing exists, traditional rigid fixation rather than bone resection is recommended [1, 11, 12].
However, pathologic fractures in postoperative radiation therapy patients are different from those in other patients with a pathologic fracture; they often exhibit reduced blood supply and poor condition of the surrounding soft tissue due to irradiation. Moreover, irradiated bone is prone to ORN. In one study, it was reported that 81.8 % of mandibular pathologic fractures were associated with radiolucent lesions. Treatment planning is difficult because of the varying radiation dose of each patient. Many studies have reported that the higher the radiation dose, the greater the extent of tissue damage and the higher the risk of ORN. Several studies have also reported a baseline radiation dose that raises ORN risk. The most reported baseline radiation dose was ≥65 Gy [4, 13].
Moriconi and Popowich suggested that local irradiation of the affected area can also achieve osseous remodeling in some cases. However, treatment decisions in such cases are difficult because of the risk of ORN [14].
In one study, complication occurrence because of delayed bone healing on the fracture line after bone graft in pre-operative radiation therapy patients was reported. Another study reported an increased bone resorption rate (27.9 %) on pre-operative radiation therapy patients after non-vascularized iliac bone graft [15, 16].
In our study, treatment methods were selected according to bone deviation and occlusion stability. In four cases featuring bone deviation and unstable occlusion, we performed OR/IF. Bone healing and remodeling were observed in all OR/IF cases with the exception of one in which bone healing was not observed because of the short follow-up period. The healing periods of the other three cases were 5 months, 7 months, and 1 year and 7 months, with an average healing period of 10 months. These cases had some complications, such as plate fracture; nevertheless, they clearly had healing potential. In two cases of OR/IF, patients had non-vascularized iliac bone graft, and healing was favorable even if they had a plate fracture. Patients who had an operation of OR/IF with iliac bone graft showed more bone formation, about an average of 5.7 mm compared to before fracture. However, the patient group of only OR/IF observed an average of 1.1-mm bone formation than before fracture.
In the CR-treated case, bone continuity was observed after 5 years and 4 months. A relatively high dose of radiation (66 Gy) and unstable occlusion were thought to be the cause of delayed healing.
A total dose of 70 Gy is the standard radiation therapy treatment for head and neck cancer. But, patients in this study were irradiated postoperatively and were assigned to dose levels ranging from 52 to 68 Gy. The average radiation dose was 59.2 (SD, 7.2) Gy; this was lower than the previously mentioned risk baseline of 65 Gy. The lower-than-standard radiation dose in our study may be one reason for the higher rate of bone healing we observed [17, 18].
Among cases of OR/IF in our study, case numbers 1 and 3 experienced plate fracture occurring 1 and 2 months after fixation surgery, respectively. Increased load on the plate due to low remaining bone volume and slow bone healing was likely the cause of fracture; however, bone healing was observed after proper inflammation control and immobilization.
In our study, treatment by OR/IF and CR was found to have similar results. When the treating physician chooses OR/IF, plate selection must be carefully considered; to prevent plate fracture and load sharing, a more rigid plate is recommended rather than a miniplate.