How to narrow down the diagnosis of pediatric leg pain when infections, inflammations, neoplasms and orthopedic conditions all remain on the differential
It’s a busy afternoon and the weather is beautiful. It’s a perfect orthopedic weather day — a great day to fall off your bike, out of your tree house, or down from the monkey bars if you’re a kid. So when you look up at the board, you’re not surprised that your next case is a three-year-old with left leg pain. No problem. You’ve already memorized the pager number of the orthopedic resident who is on today. You go down the hall to take a look.
A cute little preschool-aged boy is lying on the bed. The history: Eight days ago, he was climbing onto the hood of the parked family car and slid off when his father yelled at him. He seemed okay but was noted to have left leg pain and a limp later on that evening. His mother took him to see his pediatrician the next day and the limp had improved, so he was sent home with ibuprofen and orders to rest. The pain and limp got worse again yesterday. His parents cannot recall any new trauma. He has been otherwise well today although, when pressed, his parents report that maybe he has had a low grade fever at some point during the past week. The rest of his history is unremarkable.
The child has no fever today. He is lying with the left leg slightly flexed at the hip and knee, and externally rotated. His exam is normal until you get to the lower extremity. You are able to establish pretty quickly that the pain is in the hip. He doesn’t want you to range the hip but tolerates some movement. There is no redness, swelling or deformity that you can appreciate. He is too young for you to localize the pain more specifically. He refuses to walk.
What is the differential diagnosis of hip pain in this three-year-old? How do you approach the work-up?
Many experts divide hip pain into four basic categories.
The first is infectious. This child may have had fever, which would support an infectious process such as a septic hip or osteomyelitis. He isn’t as exquisitely tender with movement as you would expect a child with a septic hip to be. His waxing and waning course isn’t typical of septic arthritis either but missing a septic hip would be devastating for this patient. This has to stay in the differential.
The next category is inflammatory. Typically the onset of pain would not be acute, although transient synovitis can be. Systemic symptoms, such as fever, may be present. There may be additional physical exam findings, additional joint involvement, and a pattern of recurring episodes. This child is the right age for transient synovitis, which generally occurs between ages 3 and 8 years. He has had that low grade fever reported. The clinical picture could support an inflammatory process. So this stays on the differential as well.
The next category is orthopedic conditions. His waxing and waning symptoms make a fracture a bit less likely. He is the wrong age for slipped capital femoral epiphysis, which usually occurs near the time of peak growth in adolescence. Legg-Calve-Perthes can occur in a child this age. Ok, so orthopedic conditions are on the list of possibilities here.
The final category is neoplasms. Bone tumors can present in this manner. Acute leukemia is notorious for producing joint pain in children. His exam is reassuring other than the hip findings, but it would probably be prudent to consider this as well.
So where does this leave us? We have a differential that includes all four types of conditions known to produce joint pain. How do we narrow this down?
Fortunately, the work-up is pretty straightforward even though the differential is not. You order plain films, which will screen for trauma, tumors and Legg-Calve-Perthes, although early on, Legg-Calve-Perthes can be missed on plain films. A CBC and inflammatory markers (CRP and ESR) will identify leukemia and help determine which patients need a further work-up for infectious and inflammatory conditions. You write orders for AP and frog-leg views of the hip, a CBC, ESR and CRP, offer the child something for pain and make him NPO. This last is important because if the white count and inflammatory markers are elevated you plan to proceed with an ultrasound of the hip to look for an effusion. If an effusion is present, you may need to obtain synovial fluid to distinguish between transient synovitis and a septic joint. This would be done with procedural sedation, so you might as well plan for that possibility.
So, the work-up is complete and the answer is there on the plain film. He has Legg-Calve-Perthes disease. Legg-Calve-Perthes is an idiopathic osteonecrosis of the femoral head. It is more frequent in boys than in girls. It can be bilateral, although it is usually unilateral. The typical age of presentation is between 4 and 8 years, although the range is 2 to 12 years. Disruptions to the blood supply of the femoral head lead to infarction and necrosis. The reasons for this blood supply restriction are unclear, but are often associated with skeleton immaturity and hyperactivity. Activity worsens the pain and limp. The pain may not be reported in the hip but may present as referred pain to the groin, thigh or knee.
Children diagnosed with Legg-Calve-Perthes should be referred to an orthopedist. Management is evolving and strategies include both operative and nonoperative approaches. Younger children, such as our patient, are less likely to benefit from surgery, and have a better prognosis than older children.
You consult Orthopedics and the child is sent home with rest, ibuprofen for pain, and follow-up. And you go on with the rest of your afternoon. Call it a break from breaks (Don’t groan).
Nigrovic, PA. Overview of hip pain in childhood. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on January 22, 2014.)
Nguyen NA, Klein G, Dogbey G, et al. J Pediatr Orthop. 2012;32 (7):697-705.
Legg-Calve-Perthes Disease in Snider RK. ed. Essentials of Musculoskeletal Care. American Academy of Orthopedic Surgeons. Rosemont, Illinois, 1997.