A 24-year-old woman comes to the urgent care center due to increasing pain in her right leg. She initially felt a dull, aching pain at the anterior aspect of the lower leg 2 weeks ago. The patient is an avid dancer and often practices 4-5 hours a day; the pain has worsened and is now interfering with her dance sessions. Her medical history is remarkable for irregular, light menstrual periods, for which she is being evaluated by her gynecologist. The patient drinks alcohol only on social occasions and does not smoke or use illicit drugs. Temperature is 36.7 C (98 F), blood pressure is 122/78 mm Hg, and pulse is 70/min. BMI is 16 kg/m². Examination shows point tenderness over the anterior aspect of the right shin. There are no skin abnormalities, and the rest of the physical examination is unremarkable. An x-ray of the lower leg reveals no abnormalities. Which of the following is the most likely diagnosis?

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11ec25c8_d2c9_5716_bc81_f9cee110cf4e_MD0003_00 This patient has subacute leg pain consistent with a tibial stress fracture, which most commonly occurs in athletes (eg, runners, dancers) or other individuals who suddenly increase their activity level. These types of fractures are caused by repeated tension or compression without adequate rest, and are especially common in women who have low bone density associated with low caloric intake and hypomenorrhea/amenorrhea (female athlete triad). Other factors contributing to stress fractures include improper footwear, biomechanical abnormalities (eg, weak calf muscles, high-arched feet), and inadequate calcium and vitamin D intake. In addition to the tibia, stress fractures can also be seen in the metatarsals, tarsal bones (eg, navicular, calcaneus), and, less commonly, the femur and pelvis. The diagnosis is based primarily on clinical factors, including localized activity-related pain, swelling, and point tenderness on palpation. X-rays are frequently normal (especially in the first few weeks) but may reveal periosteal reaction at the site of the fracture. MRI and bone scan are more sensitive but not usually necessary. (Choice A) Chronic exertional compartment syndrome is caused by increased pressure within a muscle group during exercise. It is typically seen in young athletes but would not cause point tenderness on the bone. (Choice B) Injury to the interosseous ligaments (high ankle sprain) presents with acute anterolateral ankle pain, typically following rotational force on a dorsiflexed ankle. Patients frequently have an associated fibular fracture. (Choice C) Nerve entrapment presents with radiating pain and is not reproducible with local palpation. (Choice D) Osteoid osteoma is a benign bone-forming tumor of the femur and other long bones that occurs in adolescence and early adulthood. Focal tenderness is common, but the pain is not activity related, and x-rays will reveal areas of lucency with sclerotic margins. (Choice E) Medial tibial stress syndrome (shin splints) causes anterior leg pain resembling that of a stress fracture. It is usually seen in casual runners and is characterized by a diffuse area of tenderness (not point tenderness, as seen in this patient). Shin splints are more common in overweight than underweight individuals. Educational objective: Tibial stress fractures are caused by repeated tension or compression without adequate rest and occur most commonly in athletes or others who suddenly increase their activity. Findings include subacute, localized, activity-related pain; swelling; and point tenderness on palpation. X-rays are frequently normal. References: Stress fractures: pathophysiology, clinical presentation, imaging features, and treatment options. (http://www.ncbi.nlm.nih.gov/pubmed/27002328)

A 24-Year-Old Woman Comes to the Urgent Care Center Due