Unsupervised Exercise–Induced Myositis Ossificans in the Brachialis Muscle of a Young Healthy Male: A Case Report

摘要

Extraskeletal bone formations within the soft tissues can be the presentation of benign self-limited ossifying processes such as heterotopic ossification (HO)~( 24 )or malignant neoplasms such as extraskeletal osteosarcomas.~( 9 )Depending on the involved tissue, a number of synonymous terms have been established to describe these lesions. Myositis ossificans (MO)~( 2 )is the most common and refers to benign bone formation within skeletal muscles, whereas fasciitis~( 14 )and panniculitis ossificans~( 13 )refer to lesions in the fascia or the adipose tissue, respectively. The terms heterotopic ossification and myositis ossificans are often used interchangeably in the literature. The etiology of MO is variable and classified as hereditary or acquired, with the latter being the most common type.~( 26 )Hereditary MO includes fibrodysplasia ossificans progressiva and progressive osseous heteroplasia; both very rare, autosomal dominant inherited conditions associated with debilitating progressive heterotopic ossification.~( 18 )The acquired MO is further subclassified into traumatic and nontraumatic depending on the presence of history of trauma. Although its underlying pathophysiology has not yet been clearly defined,~( 19 )traumatic MO has been largely associated with various types of musculoskeletal injury, including fractures and soft tissue trauma, as well as orthopaedic procedures (hip, knee, and shoulder arthroplasties).~( 1 , 16 , 24 )The most commonly affected site of traumatic HO is the quadriceps femoris.~( 25 )Other causes of traumatic MO include central nervous system injury~( 8 )and severe burns.~( 6 , 20 )However, there are rare cases of MO that occur in the absence of a discrete traumatic etiology.~( 10 , 17 , 29 )Despite being a benign condition, nontraumatic MO poses a significant diagnostic challenge, as its clinical presentation mimics that of sinister conditions such as osteosarcoma.~( 28 ) Here, we present a unique case of HO in the right anterior brachialis muscle of a young healthy man with no previous history of trauma or injury, who had recently started working out at the gym. To the best of our knowledge, this is the first report of HO secondary to recreational exercise. Informed consent was obtained from the patient. Case Report An 18-year-old right-handed male patient presented with a 6-month history of intensifying muscle soreness and a progressively growing palpable mass in the anterior distal third of the right humeral shaft. The mass had been growing within the anterior brachialis muscle, significantly limiting the range of motion of the right elbow joint. There was no history of antecedent trauma, previous surgery, or other predisposing conditions. The patient had no past medical history of note, and there was no family history of abnormal bone formation. He had recently started working out at the gym on a regular basis, without professional supervision. His workout regimen involving the biceps brachialis muscles is summarized in Table 1 . Physical examination revealed a 3 × 5–cm well-circumscribed, firm, and nontender mobile subcutaneous nodular mass. There were no associated erythema, warmth, or skin changes. The right elbow joint range of motion was significantly decreased (80°-130°), but pronation and supination were not affected. His right arm was well perfused with an intact radial pulse, and neurological examination was unremarkable. Complete full blood count, biochemical analysis (including alkaline phosphatase), coagulation screen, and urinalysis did not reveal any abnormality. TABLE 1 Summary of the Patient’s Workout Regimen Involving His Biceps Muscles No. of Exercises for Biceps Push-ups Pull-ups Barbell Curls Repetitions Until exhaustion Until exhaustion Until exhaustion Sets 3 3 3 Intervals, s 60 60 60 Speed of repetitions Quick Quick Quick Range of motion Limited in flexion and extension Limited in flexion and extension Limited in flexion and extension Frequency per week 6 sessions 6 sessions 6 sessions Plain radiographs of the right arm revealed a well-defined ovoid structure with a prominent mineralized periphery and a radiolucent center at the distal third of the humerus with intact cortex ( Figure 1 ). Figure 1. Plain radiograph showing a well-defined mass with mineralized periphery and radiolucent center at the distal third of the right humeral shaft. Magnetic resonance imaging (MRI) revealed no continuity between the mass and the underlying bone. The mass had an intermediate- to low-intensity signal on T1-weighted images and a heterogeneous high-intensity signal on T2-weighted images. The bony structures of the right elbow joint were not affected. Total excision of the mass was performed with an anterior approach. Macroscopically, the mass measured 5 × 5 × 4 cm and had a gray-white appearance ( Figure 2 ). It had firm to fragile consistency with a thin bony rim in part of its periphery and contained jelly-like matrix. There was no continuity with the surroun