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head and neck irradiation almost always entails irradiation of at least a part of the mandible ; hence it is the commonest bone manifesting various radiation effects .
asymptomatic bone changes could include decreased bone density in the irradiated region , delayed wound healing and cortical bone destruction , thereby increasing the possibility of serious side effects such as osteoradionecrosis ( orn ) and fractures .
we describe a late spontaneous pathologic fracture in a case of carcinoma tongue and the implications of such developments for radiation oncologists .
a 55-year - old lady , with no comorbid conditions and no history of tobacco or alcohol intake , was evaluated at our institute nearly 9 years ago for a 2-month ulcerating lesion over left lateral border of tongue , not healing with conservative management . following examination and biopsy , a squamous cell carcinoma of oral tongue t2n0m0
she underwent partial glossectomy and ipsilateral supraomohyoid neck dissection , revealing a 2.2 cm  1.5 cm infiltrative growth with clear margins , depth of 6 mm , no perineural or lymphovascular invasion , and negative nodes ( 0/8 ) .
she was advised adjuvant irradiation and received 60 gray in 30 fractions , 5 fractions / week , by cobalt-60 unit using lateral opposed portals .
she tolerated the treatment well and was on regular follow - up as per institutional protocol , with no specific events .
eight years after completion of her treatment , she reported to our clinic with the complaint of sudden onset oral pain and inability to open her mouth or eat .
there was no history of any dental or oral procedures , oral infections or trauma preceding her complaints . on examination
pantomogram was done , which showed a comminuted fracture at both angles of the jaw , just posterior to the last molars [ figure 1 ] .
she was subsequently referred to the head and neck surgery department , where she underwent plate reconstruction for correction after initial conservative management .
( a ) and ( b ) anterior and lateral views of the patient showing the facial appearance .
the mandible is the longest bone in head and neck region , and commonest bone affected is head and neck irradiation due to its unique location bearing the lower set of teeth , high density , and poor vascular supply compared with other bones in this region .
complication risk is highest in the region of premolar , molar and retromolar trigone due to high density and low vascularity .
it has an / ratio of 0.85 , suggesting it is a late reacting tissue and high sensitivity to large doses per fraction .
most cases of osteonecrosis post - radiotherapy ( rt ) occur within first 23 years after treatment , but patients remain at indefinite risk due to ongoing changes in the bone due to age , altered oral microflora and dental infections . in early 1980s , marx redefined the pathophysiology of orn by proposing that rt induces endarteritis that results in tissue hypoxia , hypocellularity , which in turn causes tissue breakdown and chronic non - healing wounds .
several factors that are associated with risk of bone injury or orn include patient factors ( deep parodontitis , bad oral hygiene , alcohol and tobacco abuse , bone inflammation , immune deficiencies , malnutrition , dental injury or extraction after rt ) , tumor factors ( tumor size , stage , proximity of tumor or nodes to bone , tumor location ) and treatment factors ( pre - irradiation bone surgery , surgical handling of bone or its vascular supply , rt dose , biologically effective dose , photon energy , brachytherapy dose rate , combination of external beam irradiation and interstitial brachytherapy , field size , fraction size , volume of the mandible irradiated with a high dose ) .
a diagnosis of orn of bone mandates radiological evidence of bone necrosis within the radiation field , without any evidence of tumor recurrence .
incidence varies from 2% to 22% in various series , and is higher in dentate patients compared to edentulous patients .
clinical manifestations may include pain , orofacial fistulas , exposed necrotic bone , pathologic fractures or suppuration .
pathologic fractures may be spontaneous ( 35% ) , occurring usually within the first 2 years of irradiation , while traumatic fractures related to dental procedures are more common but occur late .
the highest incidence of orn has been reported with brachytherapy of oral lesions if the rt source lies in close proximity to the bone .
external beam rt , especially when using kilovoltage or low energy ( 14 mv ) x - rays or electron beam , leads to high radiation absorption within the bone .
this risk was greatest with the older techniques when use of large open parallel - opposed fields led to the inclusion of large areas of bone within the radiation portal , exposing it to high doses .
modern techniques have been able to circumvent this problem to a large extent by conforming the high dose areas to the tumor bed only while minimizing the dose delivered to normal structures including mandible . given the severe quality of life implications of bone complications , preventive measures in the form of meticulous oral hygiene and dental evaluation before and after irradiation , improvement in rt techniques such as intensity modulation and development of reliable diagnostic and therapeutic procedures have gained importance in recent years .
important considerations include completion of any necessary dental procedures such as extraction and management of periodontal disease prior to starting rt , education on lifelong use of high fluoride content dental gels and toothpastes , and minimal soft tissue trauma during extraction , and an interval of at least 2 weeks between extraction and rt commencement to allow healing .
rt technique should allow adequate sparing of salivary glands to prevent oral dryness , prevention and avoid high dose regions within mandible and teeth .
management of oral mucositis during treatment with soda - saline mouthwashes , antibiotics and antifungals , and use of spacers between mandible and brachytherapy source would reduce chances of oral infections and bone necrosis .
post - treatment regular dental examination , fluoride prophylaxis and delaying use or dentures till 912 months following rt would help prevent most instances or risks of orn .
bilateral mandibular pathologic post - radiation fracture is a very uncommon but serious late complication , with a huge impact on subsequent quality of life , and thus , preventive measures are necessary to minimize the risk .
mandible is the most frequently affected bone during head and neck irradiation . 
 late changes in the mandible may manifest in the form of reduced bone density , dental caries , loss of spongiosa trabeculations , delayed healing following dental extraction , pathologic fractures , osteoradionecrosis , trismus , growth defects in children or second malignancies . 
 pathologic fractures of mandibular bone are rare and may be spontaneous or traumatic ( following dental extraction ) . 
 we report the case of a 55-year lady , who had undergone surgery and adjuvant radiotherapy for carcinoma oral tongue t2n0m0 on a cobalt-60 unit and was disease - free . after a follow - up of 8 years post - irradiation 
 , she presented with sudden onset oral pain and inability to open mouth . 
 pantomogram showed fracture at the junction of body and ramus of the mandible bilaterally .