fibrodysplasia ossificans progressiva ( fop ) is a rare autosomal dominant genetic disorder and characterized by postnatal progressive heterotopic ossification of the connective tissue . there are difficulties in diagnosing fop , thus delayed or misdiagnosis and mismanagement is common . 3d printers have now become widely available and inexpensive , and can be used to rapidly produce life - size models based on ct scans of an individual patient . the availability of patient specific , accurate and detailed models of complex acetabular fractures can aid planning of surgical management on a patient specific basis . we present the diagnosis and surgical management of a 9-year old indonesian girl with fop . total excision of occipito - cervico - lumbar and paravertebral ossification and also exostoses at bilateral shoulder was done . at three years follow up , she had local recurrence with similar range of movement of the shoulder and cervical spine . it is difficult to diagnose and manage fop , therefore delayed or misdiagnosis and also inappropriate management is common . fibrodysplasia ossificans progressiva ( fop ) , once called myositis ossificans progressiva , is a rare autosomal disorder that involves connective tissue . one of the famous case of fop is harry eastlack ( 1933 - 1973 ) , who died because of pneumonia and fully ossified body , his lips were the only body part that could be used properly . ectopic ossification is preceded by a soft tissue enlargement that may spontaneously resolve or gradually form an ectopic bone . delayed or missed we report a rare case of fop arising at occipito - cervical spine , paravertebrae , and bilateral shoulders focusing on diagnostic procedure and surgical management . a 9-year - old girl presented to our orthopaedic clinic , with main complaint of a mass which was getting bigger on her upper back . the initial mass size was around 1 cm in diameter ( like a marble ) located just below the tip of both scapulae . it was accompanied by difficulty in moving both shoulders and neck since 4 years . because of these complains , her family tried various traditional medicines without improvement . six months prior to admission , she fell down on her back , and since then the masses grew progressively . she was brought to a district hospital in other province and then referred to our hospital to get more appropriate treatment . there was no history of similar disease in her family . on physical examination , general condition was good and no abnormality was found in other organ . we found multiple bony prominences measuring about 2 cm in diameter at paravertebral region from cervical to lumbar and posterior thoracic wall . they made bone bridges starting from inferior occipital bone to cervical spine and extending to paravertebral lumbar region . the shoulder , cervical , and thoracal spine ranges of movement were limited ( fig 1 ) . there were multiple bony prominence measuring 2 cm in diameter at the back from cervical to lumbar and posterior thoracic region ( arrows ) , they made bony bridges from inferior occipital bone , cervical spine , extending to paravertebral lumbar region . ( b ) slight valgus deformity of right great toe ( arrow ) radiograph of the cervical spine showed new bone formation starting from occipital bone , cervical , until upper thoracal spine . chest and shoulder radiographs also showed new bone formation at both humerus bridging to the tip of scapulae , with subluxation of both humeral head superiorly . the radiologist saw it as mustiple exostoses ( osteochondroma lesion ) with the differential diagnosis progressive myositis ossificans . hla - b27 was negative , it was investigated since we also thought ankylosing spondylitis as a differential diagnosis . the 3d computerized tomography ( ct ) reconstruction revealed multifocal ossification on soft tissue including right pectoral muscle , bilateral latissimus dorsi , and left longisimus thoracis muscle . magnetic resonance imaging ( mri ) showed similar result with ct scan and no other abnormality detected at the spine . radiograph of the cervical spine lateral view showed bone formation starting from occiput , cervical , and upper thoracic spine ( arrows ) . ( b ) chest and shoulder radiographs also showed bone formation at the bilateral humerus bridging to the tip of scapula ( arrows ) . ( c ) ct reconstruction revealed multifocal ossification which supported radiographic finding , paravertebral bony bridge ( arrow head ) , bony bridges from bilateral humerus to tip of scapula ( arrows ) because of the problem was multiple exostoses and stiffness , total excision of occipito - cervico - lumbar and paravertebral ossification and also exostoses at bilateral shoulder was done . histopathological findings showed tissue consisting of cartilaginous component , irregular underlying bony trabeculae , and bone marrow between trabeculae . after review of all patient s data in one of the clinicopathological conference , we concluded that it was fibrodysplasia ossificans progressiva ( fop ) . four months after surgery local recurrences were detected , which was confirmed with radiograph ( fig 4 ) . at three years follow up , she had similar signs and symptoms as before surgery . ( a)histopathology showed formation of endochondral ossification ( arrow ) ( h&e , 100x ) . ( b ) skeletal muscle and formation of endochondral ossification ( arrow ) ( h&e , 100x ) . ( c ) formation of endochondral ossification ( arrow head ) , bone trabeculae and marrow ( arrow ) ( h&e , 100x ) . ( a ) clinical picture 4 months after surgery , local recurrences were detected ( arrow ) . ( b ) cervical radiograph 4 months after surgery , there was local recurrence of bony bridge from occiput , cervical , and upper thoracic spine ( arrow ) . ( c ) thoracic radiograph 4 months after surgery , there was recurrence of bony bridge from bilateral humerus to the tip of scapula ( arrow head ) . fop is an autosomal dominant disorder and has a variable expression that is the most catastrophic disorder of heterotopic ossification in humans . primary genetic defects in fop are currently unknown . events which may precipitate formation of lesion are trauma , invasive medical procedure , muscle fatigue , influenza like infection , and immunization . however , it is still unclear how clinical events which initiate the formation of lesion ultimately lead to extraskeletal ossification . a study in japan involving 19 fop subjects has successfully identified gene mutation that could induce ectopic bone formation in fop . fop lesion is usually triggered by soft tissue injury , predominantly in muscle , causing release of inflammatory cytokines and migratory factors . potential soluble mediators include prostaglandins ( pgs ) , smad1 and smad5 , stromal cell derived factor 1 , and bmp-4 . pge2 has an anabolic effect on bone marrow stromal cells and may enhance osteoblastic differentiation in - vitro , presumably through the recruitment of nonadherent mesenchymal progenitor cells into adherent osteoblast precursors . elevated levels of a low - molecular - weight pg - like molecule have been detected in the plasma of patients with fop . stromal cell derived factor 1 is a mediator of lesion formation in a mouse model of pulmonary fibrosis and may signal circulating fibrocytes to homing regions that eventually become fibrotic . heterotopic bone formation may occur in pulmonary fibrosis and the circulating fibrocytes are abundant in patient with fop with active exacerbations . taken together , these observations suggest a plausible mechanism for extraskeletal ossification in fop that invokes the recruitment of circulating osteogenic cells . whereas bmp-4 may induce ectopic ossification in animal models , it is known to be dysregulated in fop . children who have fop appear normal at birth except for congenital malformations of the great toes . typically , during the first decade of life , sporadic episodes of painful soft tissue swellings ( flare - ups ) occur and are commonly mistaken for tumors . however , in our patient , no malformations of the great toes were clearly detected except slight valgus of right great toe . the ossification started from occipital bone and posterior paravertebral soft tissue , which caused limitation of neck movement , whereas ossification on both humerus and scapula caused limitation of the shoulder joint movement . eventually , the ossification process forms bridges between axial bones . most of literature stated that ectopic ossification usually started from the cervical area , then extended down paravertebrally to lower back and progressively formed bony projections in our case were similar to multiple exostoses , whereas the location of lesions was uncommon for that kind of  tumor  . based on our clinical diagnosis , we performed excision of  all multiple exostoses  which were located from occipital bone until lumbar spine and the bridging bones between scapula and both bilaterally . histopathology showed fragmented tissue consisting of cartilaginous component and irregular underlying bony trabeculae ( endochondral ossification ) . there was also bone marrow between trabeculae , a histopathologic feature commonly found in exostosis . at discussion in our routine fop , we re - evaluated the slides and processed the whole specimen . microscopically the specimen also showed fibrous tissue , skeletal muscle mixed with endochondral ossification , and foci of calcification . although histologically , a very early fop lesions look identical to the fibroproliferative lesions of aggressive juvenile fibromatosis , in aggressive juvenile fibromatosis , the lesions do not progress beyond the connective tissue growth phase , whereas in fop , they mature through an endochondral process to form cartilage and bone one study mentioned that nearly 90% of patients with fop worldwide are misdiagnosed and 67% undergo dangerous and unnecessary diagnostic procedures . tumor , fibromatosis , bunion , myositis ossificans , calcified hematoma , exostoses , and also ankylosing spondylitis   are considered in the differential diagnosis . surgical therapy which aims to improve range of movement in this patient has proven to trigger further ossification . in this patient , follow up , she presented with the same complaint and similar range of movement of shoulder and cervical spine as before surgery . radiation therapy may be considered after surgery to prevent recurrence , but there is no clear evidence that radiotherapy is effective in patients with fop , except in small number of patients . medications that have theoretical application to fop such as leukotriene inhibitor and investigational new drugs such as signal transduction inhibitor and monoclonal targeting acvr1 may show a promising result in fop patient . research in fop has reached genetic level , but not yet in molecular level that it might produce a gene therapy . so , we have to make early clinical diagnosis and the mainstay of therapy is education to the patient and family to prevent further trauma . it is difficult to diagnose and manage fop , therefore delayed or misdiagnosis and also inappropriate management is common . although rare , we should consider fop as a differential diagnosis in patient complaining of multiple masses with soft tissue ossification . we should avoid dangerous and unnecessary diagnostic procedure as well as inappropriate management which may lead to futher exacerbations .