Pediatric Annals

Special Issue Article 

Differentiating Transient Synovitis of the Hip from More Urgent Conditions

Deirdre D. Ryan, MD

Abstract

A variety of traumatic and infectious processes can cause acute onset of hip pain and difficulty walking. Without a history of trauma, a common cause is transient (or “toxic”) synovitis, but serious infectious causes, such as septic arthritis of the hip or osteomyelitis, must be ruled out. Differentiating between septic arthritis of the hip (a true emergency) and transient synovitis of the hip (a much more benign inflammatory process) can be difficult. The Kocher criteria have proven to be helpful in making the distinction between these two conditions, and they are reviewed in this article. In addition, imaging studies, especially hip ultrasound, are extremely helpful in the evaluation of the painful hip. [Pediatr Ann. 2016;45(6):e209–e213.]

Abstract

A variety of traumatic and infectious processes can cause acute onset of hip pain and difficulty walking. Without a history of trauma, a common cause is transient (or “toxic”) synovitis, but serious infectious causes, such as septic arthritis of the hip or osteomyelitis, must be ruled out. Differentiating between septic arthritis of the hip (a true emergency) and transient synovitis of the hip (a much more benign inflammatory process) can be difficult. The Kocher criteria have proven to be helpful in making the distinction between these two conditions, and they are reviewed in this article. In addition, imaging studies, especially hip ultrasound, are extremely helpful in the evaluation of the painful hip. [Pediatr Ann. 2016;45(6):e209–e213.]

The diagnosis of transient (or “toxic”) synovitis is one of exclusion, after other causes of hip pain and limp have been ruled out. The cause of transient synovitis is not known but it is considered to be a reactive arthritis that most often affects the hip joint. Frequently, patients have a remote history of illness, and it most commonly affects children between ages 3 and 10 years. The absence of a recent viral illness does not rule out the possibility of transient synovitis. Up to 3% of children experience an episode of transient synovitis in their lifetime.1

Illustrative Case

A 5-year-old boy presented to the emergency department (ED) via ambulance after not being able to get out of bed due to left hip pain. Two days prior to admission he complained of left thigh pain but continued to play without difficulty. He had a history of a cough 1 week prior to presentation to the ED. His family denied any history of trauma, fever, or chills. Recent history was also negative for antibiotic and anti-inflammatory use. The patient's complete medical and surgical histories were negative, and his birth and developmental histories were within normal limits.

On physical examination, the patient was afebrile with stable vital signs. He denied any nausea or vomiting. He was alert and responsive to questions and only became agitated if asked to move his left hip or if his left hip was examined. His abdomen was nontender to palpation and he had good bowel sounds. He held the left hip flexed, abducted, and externally rotated. He was nontender to palpation throughout the left lower extremity and demonstrated no effusion at the left knee or ankle. The skin was without erythema or rash. He had no pain with passive range of motion at the ankle and knee. He had full active range of motion at the ankle and active range at the knee was from 30 degrees of flexion to 95 degrees of flexion. Movement at the knee beyond that range caused hip pain. He would not allow the hip to be ranged to any degree in any direction secondary to pain. A heel strike did not elicit pain. He was nontender to palpation at the sacroiliac joints and the lumbar spine.

Laboratory testing showed a normal complete blood count with slightly elevated percentage of neutrophils (79.3%). His erythrocyte sedimentation rate (ESR) was elevated at 18 mm/hr, and C-reactive protein (CRP) was normal at 0.5 mg/dL. Anteroposterior (AP) “frog pelvis” radiographs showed his hip to be located without radiographic evidence of trauma, effusion, or osteomyelitis (Figure 1). Hip ultrasound was positive for effusion of the left hip (Figure 2). The left hip underwent an ultrasound-guided aspiration. Fluid was sent for cell count, gram stain, and culture. The synovial cell white blood cell (WBC) count was 13,300/mm3 with 13% neutrophils. The gram stain was negative for organisms.


            Anteroposterior pelvis radiograph taken on presentation to the emergency department. The hips are well located, without radiographic evidence of trauma, effusion, or osteomyelitis.

Figure 1.

Anteroposterior pelvis radiograph taken on presentation to the emergency department. The hips are well located, without radiographic evidence of trauma, effusion, or osteomyelitis.


            Hip ultrasound demonstrates a left hip effusion.

Figure 2.

Hip ultrasound demonstrates a left hip effusion.

The patient was given ibuprofen and observed. After one dose he started moving his hip and allowing the staff to move his hip on examination. After two doses he started weight bearing again. His symptoms resolved after 4 days of treatment with ibuprofen.

Symptoms of Transient Synovitis

Symptoms of transient synovitis include an irritable hip that results in an antalgic gait or refusal to weight bear depending on the severity of symptoms. The patient will demonstrate a normal to low-grade temperature, reduced range of motion of the hip, and normal to mildly elevated serologic laboratory markers of inflammation. Radiographs are typically normal, and ultrasound will show a nonechogenic effusion. Treatment includes anti-inflammatory medication and activity modification. The symptoms of transient synovitis usually resolve within 3 to 5 days and there are no long-term sequelae.

The challenge for the treating physician when evaluating a child with possible transient synovitis exists in differentiating synovitis from other more serious causes of hip pain and limp in a timely fashion. This testing should be done in the ED, where laboratory, radiologic, and ultrasound services are readily available. The child should be kept NPO while the testing is progressing in case sedation for a hip aspiration or anesthesia for a hip irrigation and debridement is necessary.

Urgent/Emergent Conditions that Rule Out Transient Synovitis

Although multiple conditions can cause a child ages 3 to 10 years to present with a limp, seven conditions are considered urgent and need to be ruled out quickly. These are (1) lower extremity fracture, (2) slipped capital femoral epiphysis (SCFE), (3) discitis, (4) leukemia, (5) osteomyelitis, (6) septic hip, and (7) pyomyositis. Lyme disease should also be placed on the differential diagnosis list in areas where it is common.

Lower Extremity Fracture

A fracture will present with point tenderness over bone, redness, or bruising and swelling in the affected area. Radiographs may or may not be positive on the day of presentation. Occult fractures become evident on radiographs 10 days after injury. A bone scan or magnetic resonance imaging (MRI) can be used in the acute setting to diagnose a fracture with negative radiographs. If a fracture is suspected, the bone should be immobilized in a cast or splint with a follow-up examination arranged for 10 to 14 days later for repeat radiographs. If a fracture is definitively diagnosed, it is treated as indicated by orthopedic standard of care.

Slipped Capital Femoral Epiphysis

SCFE is a condition that results from a slip of the proximal femoral physis, resulting in displacement of the proximal femur. Adolescents are most commonly affected, but the condition can be seen in preadolescents as well. Although it may be kept in the differential diagnosis, it would be unusual to see a SCFE in children younger than age 8 years (they usually present with either hip or knee pain). On physical examination, they will have decreased internal rotation of the hip and obligate external rotation of the hip with flexion. If they can walk, they walk with an externally rotated leg. An AP frog pelvis radiograph should be ordered to evaluate the hips. The radiograph will show physeal widening and varying degrees of displacement of the proximal femoral metaphysis on the epiphysis in a patient who has an SCFE. This condition has to be addressed urgently via surgery.2

Discitis

Discitis presents with the triad of fever, pain, and reduced intervertebral disc height on spinal radiograph. The infant or toddler will refuse to walk, whereas a child with discitis will tend to complain of abdominal pain. Radiographs can take 1 to 2 weeks to show the loss of disc height, whereas an MRI will show positive results immediately. Treatment for discitis is antibiotic therapy.3

Leukemia

Leukemia is the most common form of cancer in childhood. Acute lymphoblastic leukemia, the most common form of the disease, presents with musculoskeletal complaints in 20% of infants and children who are afflicted.4 A limp is a frequent presenting sign. Symptoms include fever, bruising, and lymphadenopathy. Laboratory testing shows anemia, elevated ESR, thrombocytopenia, and increased lymphoblasts on the peripheral smear. Radiographs will show disuse osteopenia and leukemia lines that are transverse radiolucent bands in the metaphysis. A bone marrow biopsy will confirm the diagnosis.

Osteomyelitis

Osteomyelitis occurs in 10 to 80 children per 100,000. Seventy-four percent of all cases of osteomyelitis are in the lower extremity, and 27% are in the femur5 (Whyte and Bielski, this issue). The most common presenting signs of osteomyelitis are pain with palpation and decreased limb use. Osteomyelitis of the proximal femur can be difficult to distinguish from septic arthritis on physical examination. A negative hip ultrasound will rule out involvement of the hip joint. Radiographs will not show evidence of osteomyelitis for 7 to 10 days. An MRI with gadolinium contrast will show immediate results and demonstrate the presence or absence of any abscess that may require surgical intervention. Treatment of osteomyelitis without an abscess is intravenous antibiotic therapy. Osteomyelitis with an abscess requires drainage either by the orthopedists or interventional radiologists depending on size and location.

Septic Hip

One of the most difficult diagnostic dilemmas is distinguishing between transient synovitis and septic hip. A septic hip is a diagnosis with serious long-term sequelae if not confirmed in a timely fashion. It is considered a surgical emergency, as cartilage damage has been demonstrated to occur after 6 hours of exposure to purulent material and secondary arthritis has been documented in cases of septic arthritis that were not surgically addressed until 72 hours after onset.6,7 Four independent predictors have been proposed and validated to aid in the differentiation of toxic synovitis and septic arthritis by Kocher et al.8 (Table 1). These include refusal to bear weight, fever >38.5°C, WBC >12,000 cells/mm3, and ESR >40mm/hr.8 The chance of septic arthritis being the diagnosis increases exponentially with the coexistence of two or more of these four independent predictors.9 Furthermore, CRP has been shown to be a better independent predictor of septic arthritis in children than ESR.10 The negative predictive value of CRP <10 mg/dL is 87%.11 The positive predictive value of a CRP >20 mg/dL is 85%10 (Table 1).


            Independent Predictors that May Be Used in the Diagnosis of Septic Hip

Table 1:

Independent Predictors that May Be Used in the Diagnosis of Septic Hip

A patient with an irritable hip should have an AP frog pelvis radiograph and a hip ultrasound in addition to the laboratory testing. If there is a large effusion on the hip radiograph, a widened medial joint space can be visualized. A hip ultrasound in a septic joint will show a large echogenic effusion. A joint aspiration with analysis of the synovial fluid for cell count and gram stain assists in further distinguishing between transient synovitis and septic arthritis. Pyarthritis synovial fluid typically has a WBC count >50,000/mm3 with more than 75% neutrophils. Gram stain and culture are positive in 50% of patients.

A patient found to have signs and symptoms of septic arthritis should be taken emergently to the operating room for irrigation and debridement of the hip and drain placement, and then treated with intravenous antibiotic therapy. After serologic laboratory markers return to normal, the antibiotics can be converted to oral form for the duration of the medical therapy.

Pyomyositis

Pyomyositis is a spontaneous muscle infection that is increasing in recent years due to the rise in community-acquired methicillin-resistant Staphylococcus aureus infections.12 Pyomyositis most commonly affects the musculature around the hip and thigh, making the distinction of pyomyositis from septic arthritis a clinical challenge. Children will present with signs and symptoms of infection including fever and elevated WBC count, ESR, and CRP. On physical examination they will have pain and limited range of motion of the musculature involved. A psoas abscess is an entity that can mimic a septic hip, as the child will have pain with rotation of the hip. On physical examination a psoas abscess will have more pain with rotation of the hip when it is extended than when flexed, because in extension the psoas muscle is under greater tension. Alternatively, a patient with a septic hip has pain with rotation in flexion. Testing should include an ultrasound of the hip and psoas muscle. MRI with gadolinium contrast is the best test to evaluate pyomyositis because it can show the extent of muscle involvement and the presence or absence of an abscess. Treatment of pyomyositis includes intravenous antibiotics and drainage of any abscess collection when present.

Conclusion

Our patient presented with an irritable left hip. Radiographs were negative for fracture and the patient had no complaints of abdominal pain or back pain (eliminating discitis). The laboratory testing included a complete blood count with differential and smear that were normal, ruling out leukemia. The patient was only age 5 years, making SCFE unlikely; furthermore, the radiographs showed no evidence of a slipped physis. The patient was afebrile with a normal WBC count and CRP, which makes osteomyelitis and pyomyositis unlikely. Because he only had 1 of 4 Kocher criteria (refusal to bear weight), that makes the chance of his irritable hip being a septic arthritis only 10%. His CRP was normal, and CRP is the best independent marker for distinguishing between septic arthritis and transient synovitis. In this case, joint aspiration with a low WBC count in the synovial fluid confirmed the diagnosis of transient synovitis. The patient responded well to anti-inflammatory drugs, with symptom resolution in 4 days.

The diagnosis of transient synovitis is one of exclusion and should only be made after other causes of hip pain have been ruled out. The evaluation of an irritable hip includes a detailed history, physical examination, and laboratory and radiographic testing and procedures. This testing should be done in the emergency department as the differential diagnosis includes emergent conditions that may require immediate surgical intervention. The treatment for transient synovitis is a 10-day course of ibuprofen once the more emergent causes of hip pain have been successfully ruled out.

References

  1. McCarthy JJ, Noonan KJ. Toxic synovitis. Skeletal Radiol. 2008;37(11):963–965. doi:10.1007/s00256-008-0543-3 [CrossRef]
  2. Novais EN, Millis MB. Slipped capital femoral epiphysis: prevalence, pathogenesis, and natural history. Clin Orthop Relat Res. 2012;470(12):3432–3428. doi:10.1007/s11999-012-2452-y [CrossRef]
  3. Fernandez M, Carrol CL, Baker CJ. Discitis and vertebral osteomyelitis in children: an 18-year review. Pediatrics. 2000;105(6):1299–1304. doi:10.1542/peds.105.6.1299 [CrossRef]
  4. Mostoufi-Moab S, Halton J. Bone morbidity in childhood leukemia: epidemiology, mechanisms, diagnosis, and treatment. Curr Osteoporos Rep. 2014;12(3):300–312. doi:10.1007/s11914-014-0222-3 [CrossRef]
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  7. Ilharreborde B. Sequelae of pediatric osteoarticular infection. Orthop Traumatol Surg Res. 2015;101(1 Suppl):S129–137. doi:10.1016/j.otsr.2014.07.029 [CrossRef]
  8. Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999;81(12):1662–1670.
  9. Kocher MS, Mandiga R, Zurakowski D, Barnewolt C, Kasser JR. Validation of a clinical prediction rule for the differentiation between septic arthritis and transient synovitis of the hip in children. J Bone Joint Surg Am.2004;86-A(8):1629–1635.
  10. Caird MS, Flynn JM, Leung YL, et al. Factors distinguishing septic arthritis from transient synovitis of the hip in children. A prospective study. J Bone Joint Surg Am. 2006;88(6):1251–1257. doi:10.2106/JBJS.E.00216 [CrossRef]
  11. Levine MJ, McGuire KJ, McGowan KL, Flynn JM. Assessment of the test characteristics of C-reactive protein for septic arthritis in children. J Pediatr Orthop. 2003;23(3):373–377. doi:10.1097/01241398-200305000-00018 [CrossRef]
  12. Pannaraj PS, Hulten KG, Gonzalez BE, Mason EO Jr, Kaplan SL. Infective pyomyositis and myositis in children in the era of community-acquired, methicillin-resistant Staphylococcus aureus infection. Clin Infect Dis. 2006;43(8):953–960. doi:10.1086/507637 [CrossRef]

Independent Predictors that May Be Used in the Diagnosis of Septic Hip

Predictor Value
Refusal to bear weight Fever >38.5°C White blood cell count >12,000 cells/mm3 Erythrocyte sedimentation rate >40 mm/hr 0 predictors: 2% 1 predictor: 10% 2 predictors: 35% 3 predictors: 75% 4 predictors: >90%
C-reactive protein level <10 mg/dL Negative predictive value: 87%
C-reactive protein level >20 mg/dL Negative predictive value: 85%
Authors

Deirdre D. Ryan, MD, is an Assistant Clinical Professor, Department of Orthopedic Surgery, Keck School of Medicine, University of Southern California.

Address correspondence to Deirdre D. Ryan, MD, Department of Orthopedic Surgery, Keck School of Medicine, University of Southern California, 4650 Sunset Boulevard, Mailstop #69, Los Angeles, CA 90027; email: Dryan@chla.usc.edu.

Disclosure: The author has no relevant financial relationships to disclose.

10.3928/00904481-20160427-01

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