USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 5-year-old boy comes to the office because of a limp for 3 weeks. History is unremarkable for trauma or recent illness. Past medical history includes attention deficit hyperactivity disorder, but no regular medications. Vital signs are within the normal ranges. Examination shows a painless limp of the left lower extremity with limited internal rotation and abduction of the left hip joint. A Pelvic X-ray is obtained. Which of the following is the most appropriate treatment in this patient?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Evan Debevec-McKenney, Evode Iradufasha, MD, Ursula Florjanczyk, MScBMC, Elizabeth Nixon-Shapiro, MSMI, CMI
Legg–Calvé–Perthes disease is a childhood hip disorder that occurs when the blood supply to the head of the femur gets disrupted and leads to death or necrosis of the tissue.
The disease was named after three doctors; Arthur Legg, Jacques Calvé, and Georg Perthes.
This gives the hip joint the ability to move nearly in all directions, as long as the ball can smoothly rotate inside the socket.
Now, the head of the femur is supplied by branches of 3 arteries, the medial and lateral femoral circumflex arteries, as well as the artery of ligamentum teres.
The arteries send branches that climb up the neck of the femur to supply the head of the femur, providing the tissue with the nutrition it needs to grow and maintain its spherical shape.
In Legg–Calvé–Perthes disease, for some children, the blood supply to the femoral head becomes interrupted for some reason - and it’s not known why exactly.
The result is that the tissue begins to die off - a process called avascular necrosis.
Over time, there’s new blood vessel formation into the necrotized bone and that allows the dead tissue to get removed by immune cells called macrophages.
That process causes the head of the femur to lose mass, leaving it weak and prone to fractures.
When this happens, the head of the femur becomes misshapen and can no longer smoothly rotate inside the concave acetabulum, which results in reduced range of motion.
Now, over time, Legg–Calvé–Perthes disease typically self-resolves and the bone is able to heal - once again it’s not known exactly why or how this happens.
When bone remodeling occurs, new bone replaces the necrosed bone, and the spherical shape of the head of the femur gets restored and properly fits in the acetabulum again.
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