A 23-year-old woman comes to the physician with right foot pain that started 5 weeks ago and is sharp and localized to the forefoot. She recalls no trauma or other inciting event. The patient is an avid runner and is currently training for a long-distance race. The pain has been worsening over the past week and prevents her from doing her daily running activities. She takes no medications. She does not use tobacco, alcohol, or illicit drugs. She is not sexually active, and her last menstrual period was 8 weeks ago. Her temperature is 37 C (98.6 F), blood pressure is 100/60 mm Hg, pulse is 68/min, and respirations are 12/min. Her body mass index is 15 kg/m². Examination shows normal range of motion, no erythema or bruising, and tenderness to palpation along the second metatarsal bone on the dorsal surface of the right foot. Which of the following is the most likely diagnosis?

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11ec25c8_d125_e01f_bc81_5104bba937d0_MD0003_00 This patient has acute worsening of right foot pain consistent with a stress fracture, which most commonly occurs in athletes (up to 15% incidence in runners) and non-athletes who suddenly increase their activity. Bone responds to mechanical stress by remodeling, but an abrupt increase in intensity, duration, or frequency of physical activity (without adequate rest) causes repeated tension or compressive stress to the bone. This can lead to microfractures that eventually coalesce within the cortical bone. Female runners with the "female athlete triad" (ie, oligo-/amenorrhea, decreased caloric intake, and osteoporosis) are more likely to develop stress fractures. This patient's menstrual irregularities and low body mass index make this more likely. Pain in the forefoot involving the metatarsal bones is usually due to a stress fracture, arthritis, bursitis, or Morton neuroma. A stress fracture usually causes sharp and localized pain over a bony surface (most commonly the 2nd, 3rd, or 4th metatarsals) that worsens with palpation of the area. Local swelling may also be seen. Arthritis typically occurs in the metatarsal-phalangeal joints and is not localized to a single bony surface. Bursitis is usually caused by wearing poor-fitting shoes for an extended period, leading to inflammation between the metatarsal heads. This patient's bony tenderness over the foot is consistent with a stress fracture, which should be managed with rest. (Choice A) Morton neuroma is associated with pain between the third and fourth toes on the plantar surface and with a clicking sensation (Mulder sign) that occurs when simultaneously palpating this space and squeezing the metatarsal joints. (Choice B) Plantar fasciitis causes burning pain in the plantar (not dorsal) area of the foot that worsens with the first steps in the morning. The pain decreases as activity increases during the day but usually worsens at the end of the day with prolonged weight bearing. It is common in runners with repeated microtrauma who develop local point tenderness on the plantar aspect of the foot. (Choice D) Tarsal tunnel syndrome is due to compression of the tibial nerve as it passes through the ankle. It is usually caused by a fracture of the ankle bones. Patients develop burning, numbness, and aching of the distal plantar (not dorsal) surface of the foot/toes that sometimes radiate up to the calf. (Choice E) Tenosynovitis is an inflammation of the tendon and its synovial sheath. It is usually seen in the hands and wrists, often due to overuse or following a bite or puncture wound. Patients have pain and tenderness along the tendon sheath, particularly with flexion and extension movements. Educational objective: Stress fractures are common in patients who suddenly increase their physical activity, especially in female runners with the female athlete triad (oligomenorrhea, osteoporosis, and decreased caloric intake). Typical symptoms include localized pain to palpation and possible swelling. References: High-risk stress fractures: evaluation and treatment. (http://www.ncbi.nlm.nih.gov/pubmed/11104398)

A 23-Year-Old Woman Comes to the Physician with Right Foot