Basics
Description
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Transient synovitis is characterized by the acute onset of monarticular hip pain, limp, and restricted hip motion.
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It must be distinguished from septic arthritis.
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Gradual but complete resolution over several days to weeks is the norm.
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Synonyms: Toxic synovitis; Irritable hip
Epidemiology
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Transient synovitis is the most common cause of hip pain in children.
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It is a diagnosis of exclusion.
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Transient synovitis of the hip can occur from 9 months of age to adolescence; most cases occur in children 3-8 years old.
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The risk of a child having at least 1 episode of transient synovitis of the hip is 1-3%.
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This risk is 3 times greater in patients with a stocky or obese physique.
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Right and left involvement is essentially equal; concurrent bilateral involvement has not been reported.
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Male:Female ratio is 2:1.
Incidence
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Transient synovitis accounts for 0.5% of annual pediatric orthopaedic admissions.
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The incidence is much lower among African Americans.
Risk Factors
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Male gender
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Upper respiratory infection or other active infection
Genetics
This condition is not genetic.
Etiology
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The true cause is unknown; it appears to be an immune-mediated inflammation, not an infection.
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It has been proposed that transient synovitis of the hip may be associated with active infection elsewhere, trauma, or allergic hypersensitivity.
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Nonspecific upper respiratory infection, pharyngitis, and otitis media have been associated with the occurrence of transient synovitis in as many as 70% of cases.
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An association is noted with minor trauma in up to 30%, and with allergic predisposition in up to 25%.
Associated Conditions
Legg-Calve-Perthes disease (~1.5%)
Diagnosis
Signs and Symptoms
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An acute onset of unilateral hip pain occurs in an otherwise healthy child.
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Pain usually is confined to the ipsilateral groin and hip area, but it may present as anterior thigh and knee pain.
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Limp and antalgic gait are common, with some patients refusing to bear weight on the involved extremity.
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The hip is held in a flexed and externally rotated position and has restricted ROM.
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The patient may have a low-grade fever.
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Laboratory values are nonspecific and are often within normal limits.
Physical Exam
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The patient usually indicates unilateral hip pain confined to the ipsilateral groin, anterior thigh, or knee.
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ROM often is decreased and painful.
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The patient does not have as much pain as a patient with a septic hip.
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If the hip ROM is tested slowly, it is usually at least 50% of normal.
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While walking, patients often display a limp or an antalgic gait; some children refuse to walk.
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Ipsilateral muscle atrophy is seen rarely, but when present, it implies a longstanding duration of symptoms, and a diagnosis other than transient synovitis should be considered.
Tests
Lab
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Results are usually nonspecific and within normal limits, but they may help to rule out other diagnoses.
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The peripheral white blood cell count is normal to slightly elevated.
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The ESR averages 20 mm/hour but may be slightly higher.
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Urinalysis, blood culture, rheumatoid factor, and Lyme titers and tuberculin skin test results are usually within normal limits.
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Analysis of joint fluid for complement levels or other tests has been nonspecific.
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Imaging
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Radiography:
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Plain films of the hip should include AP and lateral views.
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In transient synovitis, these films are normal but may help rule out other diagnoses, such as Legg-Calve-Perthes disease and SCFE.
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Ultrasound may be useful to determine if an effusion exists, and to guide aspiration, if infection cannot be ruled out clinically.
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MRI is needed only in cases of persistent pain, when infection has been excluded.
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A bone scan often is not helpful because this condition is not a bony process.
Pathological Findings
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Biopsy specimens have shown synovial hypertrophy secondary to nonspecific, nonpyogenic inflammatory reaction.
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Hip joint aspirates have shown a culture-negative synovial effusion, usually 1-5 mL.
Differential Diagnosis
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Transient synovitis of the hip is a diagnosis of exclusion.
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Conditions to rule out include:
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Pyogenic arthritis
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Osteomyelitis in the adjacent femoral neck or pelvis
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Tuberculous arthritis
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Psoas abscess
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Other muscle infection about the hip
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Juvenile rheumatoid arthritis
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Acute rheumatic fever
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Legg-Calve-Perthes disease
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Tumor
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SCFE
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Dislocation
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SI joint infection
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Treatment
General Measures
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Transient synovitis usually has a limited duration of symptoms, averaging <7 days.
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Most studies report complete resolution of all signs and symptoms with no immediate residual clinical or radiographic abnormalities.
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Long-term studies have shown mild radiographic changes in the involved hip.
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Traction and routine joint aspiration are not always needed.
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If traction is used, it is to promote rest and comfort.
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The hip should be in ~30° of flexion to avoid increasing intra-articular pressure.
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The important point in management of this condition is to establish the diagnosis: Pyogenic arthritis must be excluded, on clinical grounds or with laboratory tests.
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Treatment is directed at rapidly resolving the underlying inflammatory synovitis with its symptoms.
Activity
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Bed rest until initial acute pain resolves
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Weightbearing after pain resolves and full ROM returns, followed by a period of refraining from strenuous activities
Special Therapy
Physical Therapy
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Usually not necessary
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Parents can moderate child’s activity adequately.
Medication
First Line
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Anti-inflammatory drugs:
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Some experts believe these medications should be withheld to avoid masking an infection, but others believe they may have diagnostic value in speeding the natural resolution of inflammatory symptoms.
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Follow-up
Prognosis
The prognosis is good because transient synovitis is self-limiting, without any clinically significant sequelae.
Complications
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1 study has reported that Legg-Calve-Perthes disease or AVN of the femoral head may develop several months after an episode of transient synovitis of the hip.
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This finding probably represents a delay in establishing the correct diagnosis.
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Patient Monitoring
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A physician should be available for re-evaluation at all times until the possibility of infection is excluded.
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The child should be re-examined in ~1-2 weeks to determine return of motion before resuming full weightbearing and normal activity.
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Parents should bring the child back if symptoms recur or increase.
Miscellaneous
Codes
ICD9-CM
727.0 Synovitis
Patient Teaching
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Transient hip synovitis is a self-limiting process without major consequences.
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Some authorities have suggested an increased incidence of later Legg-Calve-Perthes disease in such patients, but this finding has not been proven conclusively.
FAQ
Q: Do all patients with transient synovitis require aspiration of the hip?
A: No. Although the essence of management is to rule out infection, in many cases this goal can be accomplished clinically by noting that transient synovitis involves a more mild degree of guarding, more mild elevation of infection and inflammatory markers. Most often, patients with transient synovitis will be able to bear some weight on the involved side.
Q: If aspiration is needed to rule out infection, where and how should it be done?
A: Aspiration requires sedation. It should be done with imaging (ultrasound or fluoroscopy) to be certain that the aspirate is from the hip joint. A radiologist or orthopaedic surgeon may perform this procedure. Anterior, medial, or lateral approaches are used. Fluid should be sent for cell count with differential and culture.