Pediatric myositis ossificans circumscripta following traumatic hip dislocation: A case report

Abstract

Myositis ossificans is non-neoplastic heterotopic bone forms in skeletal muscle. We recognize 3 subtypes: fibrodysplasia ossificans progressiva, myositis ossificans with no history of trauma (nontraumatic or pseudomalignant), and circumscribed or traumatic myositis ossificans. Traumatic myositis ossificans circumscripta has not, as far as we are aware, been previously documented as a complication of traumatic hip dislocation. We present the radiological findings of a 10-year-old girl with Thevenards syndrome, whose traumatic hip dislocation was complicated by circumstantial myositis ossificans. X-rays and computed tomography scan enabled us to diagnose by the presence of mature bone in the periphery of the lesion with a smooth contour and well separated from the bone. The treatment of dislocation and complication was nonoperatively.

Introduction

Myositis ossificans (MO) is non-neoplastic heterotopic bone forms in skeletal muscle [1] or soft tissue. Its etiology is unclear [2], and manifests as a painful mass in the soft tissue. Circumscribed or traumatic myositis ossificans (PTMO) is secondary to local trauma, either acute or chronically repeated. It is prevalent in the third decade of life. With very few occurrences reported in the literature, it is extremely rare in children under 10 years of age [3]. There is no gender predilection [1]. Although it can affect any site, but the most affected areas are those most likely to be injured, typically the thigh (quadriceps femoris and adductor muscles), elbow (flexor muscles) and buttocks (gluteal muscles), and less often the shoulder and calf [4]. We present the radiological findings of a 10-year-old girl with Thevenards syndrome, whose traumatic hip dislocation was complicated by myositis ossificans. The purpose of this article is to illustrate the specific and nonspecific imaging features of PTMO with respect to plain radiography, ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI).

Case report

A 10-year-old girl presented with complaint of right hip painless, swelling, and aggravated restricted movement in past 7 months. The patient is followed for Thevenards syndrome. The history of the disease goes back to 7 months where the patient underwent a trauma of the hip following a fall of the bicycle; 1 week later, the patient consulted for functional impotence of the right lower limb where a hip X-ray with anteroposterior of both hips was performed showing a right hip dislocation with extensive heterotopic ossification in the soft tissues mainly on the posterior capsule, affecting the gluteus muscles. It was clearly separated from the bone surface. Pelvic bones were normal, and no signs of periosteal reaction were found (Fig. 1). She was given an orthopedic treatment by the emergency department and was referred to the outpatient fracture clinic for follow-up, but the patient did not show up. Seven months later, the patient presented with complaint of right hip painless, swelling, and aggravated restricted movement. Clinical examination revealed restricted range of motion, mainly reduced abduction, extension, and internal rotation of right hip, also an inability to achieve a standing position or to walk, although the patient had no issues of walk ahead. We also noted the presence of a hard, well-circumscribed mass arising from the anterolateral side of the right hip was identified. Follow-up radiographs were taken, show beside the right hip dislocation, an increase ossifying masses in the soft tissues projecting over the acetabulum, head and neck of the right femur. The periphery of the ossifying masses is denser than the center (Fig. 2). CT scan was obtained for further evaluation. At CT, there was an extensive area of ossification in the right iliopsoas, obturator, and gluteus muscles, extending from the region of the pelvic inlet to the lesser trochanter of the femur (Fig. 3A). There was a clear-cut cleavage plane between the calcified mass and the adjacent iliac bone (Fig. 3B). Well-defined calcific areas suggestive of mature bone were seen at multiple levels (Fig. 3C and Fig. 4). In more caudal scans just above the lesser trochanter, there was an area of low attenuation surrounded by zones of higher density material with a focal, well-defined calcification anteriorly (Fig. 3D). No significant enhancement was noted after injection of contrast agent. Based on the history, radiographic, and CT findings, PTMO was diagnosed. No biopsy was performed. Differential diagnoses included neuroblastoma, malignant nerve sheath tumor, rhabdomyosarcoma, abscess, and infectious or inflammatory myositis, Ewing sarcoma and osteoblastoma were thought to be less probable because of absence of bone lysis. The patient was treated conservatively and had excellent outcome.

Fig. 1.

Antero-posterior radiograph of the pelvis (1 week later) demonstrating a right hip dislocation with an opacity extending from the dislocation site in the soft tissues of the neck.

Fig. 2.

Antero-posterior radiograph of the pelvis (7 months later) shows beside the right hip dislocation, an increase ossifying masses in the soft tissues projecting over the acetabulum, head and neck of the right femur. The periphery of the ossifying masses is denser than the center, an indicative finding of myositis ossificans.

Fig. 3.

Axial (A) and coronal (B, C) CT reconstruction images of the pelvis demonstrate shell-like ossifications in the right iliopsoas, obturator and gluteus muscles, extending from the region of the pelvic to the lesser trochanter of the femur (red arrow). There was a clear-cut cleavage plane between the calcified mass and the adjacent iliac bone (yellow arrow). Well-defined calcific areas suggestive of mature bone were seen at multiple levels. In more caudal scans just above the lesser trochanter, there was an area of low attenuation surrounded by zones of higher density material with a focal, well-defined calcifications anteriorly. No significant enhancement was noted after injection of contrast agent. These appearances are compatible with a diagnosis of myositis ossificans.

Fig. 4.

Tridimensional CT scan demonstrates a well-defined and highly ossified mass (red arrow).

Discussion

PTMO is a soft tissue ossifying mass that usually develops in the skeletal muscle of the extremities after trauma [5]. Patients with these lesions may or may not recall a history of trauma [6]. It was first described by Guy Patin in 1962 and named by Von Dusch in 1868. It has also been called localized myositis ossificans, localized non-neoplastic extraosseous bone formation, myositis ossificans circumscripta, myo-osteosis, and ossifying hematoma [7]. The etiology is unknown; in the case of PTMO, it is assumed that initial trauma to the area with fibroblastic reaction and subsequent bone and cartilage metaplasia plays some role [8]. The hip, the anterior thigh (quadriceps), and the anterior arm (brachialis) are the most commonly affected areas [7].

Histologically, Ackerman described the “zone phenomenon” [9] by individualizing 3 distinct zones within the lesion: Ossifications and calcifications begin to appear within the mass around the third or fourth week [9]. Well-organized cortical bone with cortex and medullary space formation appears at the periphery between the sixth and eighth week [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. Between the third and fourth week, calcifications and ossifications appear within the mass [1], [2], [3], [4], [5], [6], [7], [8]. Between weeks 6 and 8, well-organized cortical bone with cortex and medullary space formation develops in the periphery. This new bone continues to mature, so that by 6 months, a dense ring of compact bone has developed with a central core of lamellar bone [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. This zone phenomenon is individualized in imaging [11].

Clinically in the early stages, it is manifested by pain, tenderness, and restriction of movement of the injured muscle, as well as soft swelling of the skeletal muscle, the swelling disappears in the later stages, with the appearance of a hard and tender mass in 1-2 months [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. In our case, the absence of pain despite the dislocation can be explained by the fact that our patient suffers from Thevenards syndrome, it is the limitation of movements and the inability to hold the standing position that motivated the consultation. Thevenards disease is a sensory neuropathy with a type of ulcerative-mutilating acropathy of progressive course. It has a hereditary character with autosomal dominant inheritance. It is a scarce disease, which usually affects feet but can also affect hands. It causes disorders of thermoalgesic sensitivity, leading to painless ulcerations at the pressure points and then bone deformities with osteoarticular destruction and “cubic foot” appearance.

Imaging plays a crucial role in excluding differential diagnoses of PTMO such as infection or malignancy. The appearance of PTMO in imaging depends on its stage of maturity [13], and the results of conventional radiography, ultrasonography, CT, and MRI are well documented. Plain radiographs may initially be normal. Despite the PTMO mass is generally not in continuity with the underlying bone, there may be an initial localized, typically transitory periosteal reaction that can occur prior the calcification of the PTMO mass. This reaction may be related to direct periosteal damage and the formation of a subperiosteal hematoma. Radiographs may show a soft tissue mass with marginal calcification by 7-10 days. The most periphery calcification becomes coarser and denser during the following few weeks as floccular calcifications occur. By 2 months, a well-defined cortex is seen peripherally, while the lesion's center zone continues to be relatively translucent. Mature lesions frequently have a calcified border and a slight internal calcification or trabeculation, or they may be entirely dense. By 6 months, the PTMO-calcified mass has shrunk in size, and its separation from the underlying bone is better appreciated. Typically, calcifications are parallel to the long axis of a muscle or the shaft of a long bone [13]. In our case, the first plain radiograph performed 1 week after the trauma show a soft tissue mass with peripheral calcification without periosteal reaction, and the control radiography realized after 7 months showed the increase of the calcifications which becomes more denser at the peripheral with the central zone remains relatively lucent.

Before calcification is visible on normal radiographs, ultrasound is especially helpful in the early stages. It can also be used to evaluate the maturity of a lesion and identify an early recurrence after a lesion has been previously removed. In the early stages, lesions are seen as heterogeneous hypoechoic soft tissue masses, with a focal hyperechoic central area. With maturation of the lesion, the center develops diffuse reflective areas and peripheral sheet-like (lamellar) calcification that results in increased reflectivity and posterior acoustic shadowing. Shrinkage of mature lesions and the effects of contraction of the affected muscle cause irregularity of the calcified rim. Mature lesions are those that have a totally calcified, highly reflecting perimeter, and are less likely to reoccur after being surgically removed [13].

CT is the imaging modality of choice for the diagnosis of PTMO by illustrating the zonal pattern in transversal image, with a better definition of soft tissue and calcifications. The imaging aspects of PTMO have been well described, with individualization of soft tissue swelling without classification or ossification during the first week, then after several weeks the periphery becomes calcified, while the center remains isodense to the muscle reflecting the zonal maturation pattern. Less frequently, a heterogeneous calcified mass may develop. The presence of the PTMO mass may result in local tissue compression without evidence of invasion. CT scans are useful to assess for a prolonged periosteal reaction, marrow abnormalities, and continuity with the underlying bone. Follow-up CT scans are used to monitor a lesion and confirm its benign zonal pattern of maturation [13]. In our case, the CT shows the zonal maturation phenomena, with a calcified rim and the center remains hypodense to normal muscle, these calcifications have well-defined bone margins separated from the periosteum by a lucent zone, which allows us to establish the diagnosis.

MRI is not sensitive for soft tissue calcifications, but it is sensitive for detecting acute lesions that develop before calcification, as a swelling or nodule that is isointense to the surrounding musculature on T1-weighted scans, with diffuse or peripheral enhancement. Due to marked surrounding edema in the early stages, lesions may be difficult to distinguish from nearby muscle. On T2-weighted images, a region of intermediate to high signal (hyperintense to fat) is visible in the center, with or without a low signal continuous or noncontinuous rim. Within the lesion, there might be a few tiny foci of T2 hypointensity that correspond to calcified areas. The surrounding muscles fibers are usually markedly edematous in the early stages, a feature not frequently seen in sarcomas and an important diagnostic finding. Although the underlying bones usually show nonassociated abnormality, periostitis, bone marrow edema, and reactive joint effusions may be found in the acute setting. However, the underlying cortex remains intact. Lesions present a varied appearance in the intermediate stage. On T1-weighted images, the center is isointense or hyperintense to normal muscle, and on T2-weighted/short tau inversion recovery sequences, lesions tend to be inhomogeneous, with a variable, but predominantly high signal center, and irregular focal areas of intralesional decreased signal intensity. Perilesional edema decreases, and a nonspecific pattern of enhancement is seen. A variably thick rim of low signal on all pulse sequences corresponds to the calcified peripheral zone—the classical imaging characteristic of PTMO, which is best appreciated on T2-weighted and short tau inversion recovery sequences. Mature lesions usually return low signal on all sequences, due to intralesional ossification, fibrosis, and hemosiderin deposition, although areas of cystic change may also be evident. Areas of signal isointense to normal bone marrow correspond to intralesional fatty marrow formation. Perilesional edema is not seen around mature lesions, an important marker for inactivity when surgical excision is considered [13].

In doubtful cases, biopsy is performed to exclude malignancy [1]. It is important to have samples from all the elements of MO. In early stages, if specimen is obtained only from the central lesion, the rapidly proliferating mesenchymal cells have increased mitotic activity that may be diagnosed as malignancy. Confirmation of the presence of mature osteoid formation in the periphery and cells with no cellular atypia in the center is essential for diagnosis of MO [8]. In our patients, we did not perform biopsy, since we had a confident clinical and radiological diagnosis.

A proper diagnosis of PTMO, particularly at the beginning, may be difficult. However, it is critical to differentiate PTMO from malignant neoplasm. When peripheral ossification is absent or incomplete in the early stages, the existence of a mass may be an indication of osteosarcoma, synovial sarcoma, or fibrosarcoma. Periosteal and parosteal sarcoma must be taken into consideration in the differential diagnosis when ossification is complete. Various benign disorders such post-traumatic periostitis, osteomyelitis, tumoral calcinosis, and osteochondroma should also be included in the differential diagnosis [13]. Furthermore, in its early stage, MOC could be confused with fibrodysplasia ossificans progressiva (FOP), or Munchmeyer disease, a debilitating rare genetic autosomic dominant disorder; however, FOP generally affects infants, while MOC is extremely rare under 10 years. Furthermore, FOP is characterized by progressive heterotopic ossification of connective tissue and congenital malformation of the big toes, which are usually spared in PTMO [14]. Lastly, FOP progresses with a dissemination of fibro-osseous masses in multiple sites, producing severe disability [1]. Progressive osseous heteroplasia is another genetic condition involving soft tissue and extension into skeletal muscle that could be mistaken for PTMO [1].

The treatment of PTMO is usually conservative [1], [2], [3], [4], [5], [6], [7], [8], spontaneous progressive resorption of the ossified mass is observed in most cases, especially in young children. In the presence of nerve compression, surgical excision is recommended; however, it may be a factor in the recurrence of myositis in the early inflammatory phase. If the diagnosis of PTMO is uncertain, a reasonable period of observation and complete maturation of the myositis, before considering surgery, is required [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. Other diagnoses should be considered, and an open biopsy is recommended if the mass does not show maturation and zonal shrinkage as would be expected for PTMO [15].

Our case had typical clinical and radiological findings, the particularity lies in the fact that it complicates the dislocation of the hip in a patient with Thevenards syndrome and so far no case of this association has been published. Our patient was treated conservatively and had excellent outcome.

Conclusion

PTMO is soft-tissue pseudotumoral lesion that is rare in children. This case highlights that traumatic myositis ossificans circumscipta can arise in the hip muscle following a hip dislocation.

Authors’ contributions

All authors contributed to this work. All authors have read and approved the final version of the manuscript.

Patient consent

Written informed consent for publication was obtained from patient.