Heterotopic Ossification After Reconstruction with Free Fibula Flap – an Ambiguous Mishap

Abstract

Heterotopic ossifications (HO) are rare, yet, well reported complications after free flap transfer. We present a case of HO that occurred within a month, and has not been previously described in the literature. This serves as a reminder that bony hard swellings proximal to the free flap within a month should raise the suspicion of HO.

Introduction

Free fibula flaps (FFF) are gold standard for mandibular reconstruction. However, a hushed complication of FFF is heterotopic ossification (HO) of the vascular pedicle which occur on an average of 4 to 6 months after the primary reconstruction [1, 2]. However, until date, 3 cases of HO have been reported to have occurred at 1 month [2, 3]. We report a case of a segmental mandibular defect secondary to plexiform ameloblastoma reconstructed with FFF which resulted in heterotopic bone formation along the vascular pedicle which manifested as early as 25th post-operative day (POD).

Case Presentation

A male patient in his early 20s presented with histopathologically proven plexiform ameloblastoma of left mandible measuring 7 cm x 2 cm x 1.5 cm. A segmental resection of left mandible and subsequent reconstruction with ipsilateral, double barrel FFF with microvascular anastomosis of the peroneal vessels to facial artery, facial vein and external jugular vein correspondingly was performed. Intraoperative and postoperative periods were uneventful. Post-operative care comprised of intravenous antibiotics and analgesics along with adequate nutrition through nasogastric feed.

On POD 10, an intraoral 1 cm x 0.5 cm ovoid, painless, firm and non-fluctuant swelling was noted on the lingual aspect of the graft, at the floor of the mouth. Suspecting possible infection or salivary collection, aspiration was done which returned no fluid or air. Ultrasonography revealed diffuse subcutaneous thickening and oedema in the floor of the mouth. Antibiotics were continued for 5 days rationalizing it to be an impending infection. The patient was kept under close observation, as the swelling was asymptomatic. However, the swelling gradually and steadily increased in size to about 2.5 cm x 2 cm(Fig. 1a) with no other systemic or local signs of infection. Further, CECT imaging done on POD 25 revealed a rim of calcification along the buccal and lingual surfaces of the fibular graft in addition to spiculated periosteal reaction and callus formation along the floor of the mouth (Fig. 1b&c). Incisional biopsy revealed fibrous connective tissue with isolated areas of bone formation and metaplasia. The serum bone markers revealed a normal range of values.

Fig. 1.

a- Clinical photograph demonstrating swelling in the floor of mouth; b- Coronal section of CT image depicting ossification along the fibula barrel (red arrow); c- Axial section of CT image depicting periosteal reaction and ossification (red arrow); d- Intraoperative photograph showing soft tissue with ossification, being excised; e-Photograph of specimen after excision and debridement

Following this, the patient was taken to the operatory, under general anaesthesia, an extensive debridement was done, removing the calcified pedicle, and subsequent reconstruction with an inferiorly based nasolabial flap was accomplished (Fig. 1d&e). Primary closure of the donor site was achieved with an uneventful post operative recovery. A final diagnosis of HO was confirmed with histopathological examination of the debrided tissue, which exhibited fibro-osseous tissue fragments depicting bony trabeculae comprising of lamellar and woven bone with osteoblastic rimming, giant cell reaction and calcifications (Fig. 2a-c). There was no evidence of HO at 18 months follow up (Fig. 2d). Clinically there was no evidence of swelling and OPG Xray did not reveal any calcifications.

Fig. 2.

a-Photomicrograph shows fibrosseous tissue fragments showing bony trabeculae

comprising lamellar and woven bone (40x); b-High power view (100x) shows mature cartilage and bone with osteoblastic rimming; c-Adjacent fibrocollagenous tissue shows dystrophic calcification & presence of foreign body giant cell reaction; d-Intraoral photograph at 1 year follow-up.

Discussion

HO involves bone formation in extraskeletal tissues, at anatomically abnormal sites. Many theories for its etiopathogenesis have been proposed, the fracture repair theory involving mesenchymal stem cells and growth factor signalling for osteoinduction is the most widely accepted [4]. Other interesting postulates include the role of intact periosteum as a source of bone formation, mechanical stress which induces bone morphogenic protein signalling, and the varying venous pressures in the leg and cervical region leading to increased capillary perfusion enhancing the osteogenic response [4]. More recently the differentiation of vascular smooth muscle cells into osteoblastic precursors has been put forth as a possible hypothesis [5].

Baserga et al., in their systematic review have stated an incidence of 4.4% [6]. Until now, the earliest time of occurrence has been reported as 1 month [2, 3] and the latest as 9 years [7], with an average of 4–6 months after surgery [2]. Clinically HO presents as firm, rough masses causing trismus, or masticatory pain. Routine CT imaging may reveal dense, linear, or curved structures with varying degrees of calcification depending upon the time of imaging and phase of bone maturation. On positron emission tomography (PET), it may appear hypermetabolic with fluorodeoxyglucose (FDG) avidity and could disguise as a recurrent lesion [8]. A confirmatory diagnosis can be established with histopathology which shows fibrosseous tissue with bony trabeculae comprising of lamellar and woven bone with osteoblastic rimming. Management comprises of surgical debridement, performed only in symptomatic cases [6].

Modifications in the surgical technique have been proposed to prevent HO. Colletti et al. [9] and Tarsitano et al. [10] in their respective studies advocated careful separation of the vascular pedicle from the periosteum prevented HO, while Kim et al. [11] advocated the preservation of a cuff of muscle and periosteum isolated only to the proximal part of the pedicle.

In the present case, a perplexing differential diagnosis of seroma, tumour recurrence, sialocele and an infective etiology were considered. The possibility of a seroma secondary to surgical injury was convincing ascribing to its time of occurrence, as early as 10 days initially. Also, sialocele was considered due to its classical site of occurrence and the possibility of submandibular ductal injury during the primary surgery. However, USG findings were not precisely supportive of these possibilities. Owing to the fact that recurrence of ameloblastoma occurs at least after 5 years, it could not be assumed as a probable origin. Besides, infective aetiology was ruled out since the patient exhibited no clinical signs of fever, pain or pus discharge with a supporting evidence of normal hematology. Lastly the occurrence of HO was anticipated based on the radiological and incisional biopsy reports.

In contrast to the existing literature, the occurrence of HO of vascular pedicle as early as POD 25 makes this a rare and unique case report. Moreover, this is one of the few reports which has confirmed the diagnosis of HO with histopathologic evidence.

In a nutshell, HO can clinically resemble tumour recurrence, which could baffle the surgeons regarding the subsequent treatment plan and prognosis. HO can be diagnosed by imaging studies, and mandates surgery only in symptomatic cases.

Declarations

Informed Consent & Patient’s Perspective

I was very anxious regarding my jaw surgery as it could affect my functions and appearance. Although, complications occurred thereafter, it was managed efficiently by staged surgeries along with psychological support. Today, I am very contented that both oral functions and aesthetics are restored to near normalcy.

Informed consent has been obtained from the patient.

Competing Interests

None to declare.