A 17-year-old boy comes to the office for evaluation of right thigh pain. The patient had severe pain and swelling in the thigh after being kicked by another player during a soccer match 4 weeks ago. His symptoms resolved completely in 2 weeks. However, a week later, he had recurrent pain in the same area associated with decreased range of motion. He has no other symptoms. Medical history is unremarkable, and the patient does not use illicit drugs. Vital signs are normal. The right thigh circumference is 2 cm greater than that of the left, with an indurated, mobile, 3-cm mass anteriorly. The pain is reproduced by passive flexion of the knee. There is no overlying skin erythema. Strength and sensation in the affected limb are normal. Peripheral pulses are normal. The left thigh is normal, and examination findings in the right and left lower legs are normal and symmetric. What is the most likely cause of this patient's condition?

Question

A 17-year-old boy comes to the office for evaluation of right thigh pain.  The patient had severe pain and swelling in the thigh after being kicked by another player during a soccer match 4 weeks ago.  His symptoms resolved completely in 2 weeks.  However, a week later, he had recurrent pain in the same area associated with decreased range of motion.  He has no other symptoms.  Medical history is unremarkable, and the patient does not use illicit drugs.  Vital signs are normal.  The right thigh circumference is 2 cm greater than that of the left, with an indurated, mobile, 3-cm mass anteriorly.  The pain is reproduced by passive flexion of the knee.  There is no overlying skin erythema.  Strength and sensation in the affected limb are normal.  Peripheral pulses are normal.  The left thigh is normal, and examination findings in the right and left lower legs are normal and symmetric.  What is the most likely cause of this patient's condition?

Quizplus · Accepted Answer

11ec25c8_d61d_1652_bc81_9529c7112b43_MD0003_00 This patient had an acute muscle injury, followed a few weeks later by the development of local pain and an indurated mass. This presentation is most consistent with myositis ossificans (MO), which is characterized by the formation of lamellar bone in extraskeletal tissues (ie, heterotopic ossification). MO is typically triggered by severe (eg, muscle contusion, orthopedic surgery) or recurrent trauma. It can also be seen following significant neurologic events (eg, stroke, traumatic brain injury). In this pathophysiologic process, increased expression of bone morphogenic proteins leads to in-migration of spindle stem cells that mature into fibroblasts, chondrocytes, and osteocytes, resulting in cartilage and metaplastic bone formation. MO typically presents as a painful, firm, mobile mass with local swelling. It is most common in the quadriceps and brachialis. Alkaline phosphatase and inflammatory markers (eg, erythrocyte sedimentation rate) are often elevated. X-ray may show calcification with radiolucent zones (ie, eggshell calcification) but is often nondiagnostic in the early course. calcification (Choice A) A complete tear of the quadriceps complex typically occurs at the conjoined tendon because of sudden loading of the muscle (eg, fall from a height). However, knee extensor strength would be decreased, induration would be absent, and a palpable defect would be apparent above the patella. (Choice B) Deep vein thrombosis is uncommon in active athletes. When it occurs, femoral vein thrombosis typically produces diffuse pain and swelling throughout the thigh and calf, rather than localized findings. (Choice D) Necrotizing myositis is an uncommon infection by group A Streptococcus in skeletal muscle. It presents with severe pain, erythema, and widespread edema in the limb, often with rapid progression and systemic symptoms (eg, fever). (Choice E) Neoplastic bone disorders (eg, osteosarcoma) classically present with deep pain that is worse at night. Whereas MO causes disruption of muscle with fibrous, calcified tissue that elicits pain on movement, passive stretching of the overlying muscle would not generally cause pain in a bone tumor. In addition, the onset of symptoms after a recent muscle injury makes MO more likely. Educational objective: Myositis ossificans is characterized by the formation of lamellar bone in extraskeletal tissues (ie, heterotopic ossification). It is triggered by severe or recurrent trauma and presents as a painful, firm, mobile mass with local swelling. Alkaline phosphatase and inflammatory markers (eg, erythrocyte sedimentation rate) may be elevated. X-ray may show calcification with radiolucent zones.

A 17-Year-Old Boy Comes to the Office for Evaluation of Right