01Approach to the Critical Patient/attcp39

Key concepts

›Primary diagnostic challenge

›Transient synovitis is a diagnosis of exclusion

›Critical task is ruling out septic arthritis — an orthopedic emergency

›Toxic appearance, high fever, or refusal to bear weight mandate urgent arthrocentesis workup

›Immediate risk stratification

›Apply Kocher Criteria at presentation

›0 predictors: <0.2% probability of septic arthritis — discharge pathway

›1 predictor: 3% probability — low risk, discharge with close follow-up

›2 predictors: 40% probability — moderate risk, orthopedic consultation

›3 predictors: 93.1% probability — high risk, urgent arthrocentesis

›4 predictors: 99.6% probability — emergency arthrocentesis

›Do not delay orthopedic consultation pending imaging when Kocher score is 3 or 4

›Escalation triggers

›Fever >38.5 degrees C (OR 6.04 for septic arthritis)

›Complete non-weight-bearing (OR 5.23 for septic arthritis)

›Toxic or systemically ill appearance

›Markedly reduced range of motion throughout entire arc (positive LR 12.1)

›Age <2 years with hip pain — higher misdiagnosis risk

›Symptoms worsening despite rest and NSAIDs

PITFALLS

›Misdiagnosis risks

›Assuming TS without excluding septic arthritis in febrile child

›Delayed arthrocentesis leads to avascular necrosis of femoral head

›Recent antibiotic use may partially mask septic arthritis

›Missing Legg-Calve-Perthes disease in child with symptoms >7–10 days

›Insidious progressive loss of internal rotation not present in TS

›Radiograph changes may lag clinical presentation by weeks

02History/hx52

Onset and presentation

›Acute hip pain characteristics

›Unilateral hip, groin, or anterior thigh pain

›Acute onset, typically 1–3 days duration at presentation

›Mild to moderate severity — child does not appear toxic

›Often worse in morning or after rest, may improve with gentle activity

›Gait disturbance

›Antalgic limp

›Most children can bear weight with limp, unlike septic arthritis

›Refusal to bear weight is an alarm feature favoring septic arthritis

Alarm features

›High-risk historical features

›Fever >38.5 degrees C

›Strongly favors septic arthritis (OR 6.04)

›Low-grade or no fever expected in TS

›Complete inability to bear weight

›OR 5.23 for septic arthritis vs TS

›Rapidly progressive or worsening symptoms despite rest and NSAIDs

›Symptoms persisting >7–10 days

›Consider Legg-Calve-Perthes disease

›Consider occult infection or malignancy

›Night pain or constitutional symptoms (weight loss, night sweats)

›Malignancy concern (leukemia, bone tumors)

›Age <2 years

›Median age of missed bacterial MSK infection is 2.6 years vs 4.6 years for TS

Preceding illness and exposures

›Recent viral illness

›Upper respiratory tract infection in preceding 1–2 weeks in ~30% of cases

03Physical Exam/exam35

Vital signs

›Vital sign targets in transient synovitis

›Temperature afebrile or low-grade (<37.5 degrees C) expected

›Fever >38.5 degrees C is alarm finding for septic arthritis

›Tachycardia may be present from pain alone

›Hemodynamic stability — child appears well

›Toxic or ill appearance mandates urgent escalation

Hip examination

›Resting position and inspection

›Hip held in flexion, abduction, and external rotation (position of comfort)

›Reduces intracapsular pressure

›Present in both TS and septic arthritis

›No overlying erythema, warmth, or swelling expected in TS

›Range of motion assessment

›Pain at end-range of internal rotation and abduction — characteristic of TS

›Full ROM generally preserved in TS

›Pain throughout entire arc strongly favors septic arthritis (positive LR 12.1)

›Log roll test — mild pain with passive internal and external rotation

›Severe pain with any passive motion favors septic arthritis

›Always compare with contralateral hip

›Contralateral hip should be entirely normal

›Palpation

›Mild tenderness over anterior hip and groin

›No significant warmth, erythema, or fluctuance

›Bony tenderness along femoral shaft — consider osteomyelitis

Gait assessment

›Gait pattern

›Antalgic limp — shortened stance phase on affected side

04Differential Diagnosis/ddx46

Cannot-miss diagnoses

›Septic arthritis of the hip

›Orthopedic emergency — delayed diagnosis leads to avascular necrosis

›ICD-10: M00.852 (Arthritis due to other bacteria, left hip), M00.851 (right hip)

›Distinguishing features: toxic appearance, high fever, complete non-weight-bearing, high WBC/CRP/ESR

›Requires urgent arthrocentesis — joint fluid WBC >50,000 cells/mm3 with >90% PMNs

›Osteomyelitis

›ICD-10: M86.652 (Other chronic osteomyelitis, left femur), M86.651 (right)

›Localized bony tenderness, fever, elevated CRP/ESR

›May coexist with septic arthritis

›MRI is most sensitive imaging modality

›Malignancy

›Leukemia most common childhood malignancy mimicking musculoskeletal pain

›Night pain, constitutional symptoms, cytopenias on CBC

›Bone tumors — Ewing sarcoma, osteosarcoma

Structural hip pathology

›Legg-Calve-Perthes disease

›ICD-10: M91.12 (Coxa plana, left hip), M91.11 (right hip)

›Avascular necrosis of femoral head — insidious onset over weeks to months

›Progressive loss of internal rotation is hallmark

›Radiograph changes may initially be absent — early cases mimic TS

›Occurs following TS in ~1–3% of cases

›Slipped capital femoral epiphysis

›ICD-10: M93.002 (SCFE, left hip), M93.001 (right hip)

›Older children and adolescents, often obese

›Obligate external rotation with hip flexion on exam

›Non-weight-bearing and urgent orthopedic referral required

›Developmental dysplasia of hip

05Laboratory Tests/lt36

Complete blood count

›CBC with differential

›WBC typically normal or mildly elevated in TS

›WBC >12,000 cells/mm3 favors septic arthritis (OR 2.73)

›Cytopenias suggest malignancy (leukemia)

›Obtain in all children presenting with acute hip pain and limp

›Used as input to Kocher Criteria

Inflammatory markers

›Erythrocyte sedimentation rate

›Normal or mildly elevated in TS

›ESR >=40 mm/hr favors septic arthritis (OR 3.98)

›Kocher criterion threshold is ESR >=40 mm/hr

›Less specific than CRP for acute bacterial infection

›C-reactive protein

›Normal or mildly elevated in TS

›CRP >=20 mg/L suggests septic arthritis

›CRP >=20 mg/L combined with ultrasound effusion >=7 mm: specificity 97% for SA

›Rises faster and normalizes faster than ESR — preferred for acute evaluation

›Procalcitonin

›Not recommended for initial evaluation per PIDS/IDSA 2023 guidelines

›Does not reliably differentiate bacterial from nonbacterial causes

›Do not use as standalone test to exclude septic arthritis

Culture and serology

›Blood cultures

›Obtain if any concern for septic arthritis

›Positive in approximately 20% of septic arthritis cases

›Draw before antibiotic administration

›Not routinely required for classic low-risk TS presentation

06Diagnostic Tests/dt71

Scoring Systems

›Kocher Criteria for septic arthritis vs transient synovitis

›Four independent predictors

›History of fever

›Non-weight-bearing on affected side

›ESR >=40 mm/hr

›WBC >12,000 cells/mm3

›Predicted probability by predictor count

›0 predictors: <0.2% — discharge pathway appropriate

›1 predictor: 3% — discharge with close follow-up (5–7 days)

›2 predictors: 40% — orthopedic consultation required

›3 predictors: 93.1% — urgent arthrocentesis

›4 predictors: 99.6% — emergency arthrocentesis

›Source: Kocher et al., JBJS 1999 — validated in multiple prospective cohorts

›Limitation: does not include CRP, which improves discrimination

›Modified Kocher Criteria (with CRP)

›Addition of CRP >=20 mg/L as fifth predictor improves sensitivity

›4 predictors with CRP: probability of SA approaches 98%

›ACR Appropriateness Criteria 2022 endorse CRP use in combination scoring

›ESR alone less specific in early presentation when CRP may lag

›POCUS Decision-Support Algorithm (Zoabi et al., JAMA Network Open 2021)

›Integration of ultrasound effusion with clinical and lab parameters

›Sensitivity 90.9% and PPV 98.9% for TS diagnosis

›Prospective validation in pediatric ED setting

MRI

›MRI hip indications

›Not routinely required for classic TS presentation

›Reserve for atypical or prolonged cases (>7–10 days)

›Primary indications in this setting

›Suspected osteomyelitis — most sensitive modality

›Pyomyositis or adjacent soft tissue infection

›Legg-Calve-Perthes disease — early avascular necrosis before radiograph changes

›Atypical presentation not explained by ultrasound and plain radiograph

›MRI findings in transient synovitis

›Joint effusion with normal femoral head signal

›No decreased enhancement of femoral head (differentiates from early Perthes)

›Synovial enhancement without cortical or marrow signal change

›Karmazyn et al. 2025: decreased femoral head enhancement on MRI differentiates SA from TS

›MRI with contrast useful when diagnosis remains uncertain after labs and ultrasound

›MRI protocol

›Coronal T1, coronal and axial T2 fat-sat, axial T1 post-contrast with fat-sat

›Compare both hips in same acquisition

›Sedation often required in young children — plan accordingly

CT

›CT hip — limited role in transient synovitis evaluation

›Not first-line due to ionizing radiation in children

›ACR Appropriateness Criteria — usually not appropriate for initial hip pain in children

›Radiation risk particularly significant in young pediatric patients

›Potential indications

›Suspected occult fracture when radiograph and MRI not available

›Complex pelvic pathology requiring surgical planning

›Osteomyelitis with suspected cortical involvement and sequestrum

›CT findings relevant to differential

›Normal cortex and trabecular pattern expected in TS

›Periosteal reaction or cortical destruction suggests osteomyelitis or malignancy

›SCFE best demonstrated on frog-leg lateral radiograph, not CT

Ultrasound

›Hip ultrasound — first-line imaging for suspected transient synovitis

›Indication: all children with acute hip pain, limp, or restricted ROM

›Detects joint effusion with high sensitivity

›Anterior capsule distance (ACD) >4–5 mm or asymmetry >2 mm suggests effusion

›Normal ACD does not exclude TS — small effusions may be missed

›Performance characteristics for TS

›POCUS sensitivity 90.9% for TS diagnosis in decision-support algorithm

›PPV 98.9% when combined with clinical parameters

›Cannot distinguish sterile from infected fluid

›Effusion >=7 mm combined with CRP >=20 mg/L: specificity 97% for septic arthritis

›Ultrasound-guided arthrocentesis if joint aspiration planned

›Additional ultrasound uses

›Effusion quantification and monitoring for resolution

›Guidance for therapeutic aspiration

›Recurrence monitoring: higher ACD is risk factor for recurrence

›Plain radiograph always obtained alongside ultrasound

›Excludes SCFE, Perthes, tumor, fracture

›May show widened joint space or displaced fat pads with large effusion

07Disposition/dispo39

Discharge criteria

›Safe discharge indications (majority of patients)

›Well-appearing, afebrile, or low-grade temperature

›No toxic appearance

›Able to bear weight even with limp

›Low Kocher score (0–1 predictors)

›<3% probability of septic arthritis

›Normal or mildly elevated inflammatory markers

›CRP <20 mg/L

›WBC <12,000 cells/mm3

›ESR <40 mm/hr

›Reliable caregiver with ability to return if symptoms worsen

›Follow-up available within 5–7 days

›Discharge with NSAIDs and return precautions

›Ibuprofen 10 mg/kg TID for 5 days

›Written return-to-ED instructions provided

Observation indications

›Borderline cases requiring observation

›Diagnostic uncertainty despite labs and imaging

›Borderline Kocher score (1–2 predictors with equivocal labs)

›Very young child (<2 years) — higher misdiagnosis risk

›Inability to bear weight despite reassuring labs

›Unreliable follow-up or caregiver concerns

›Suboptimal pain control requiring reassessment

Admission indications

›Criteria for admission

›Suspected or confirmed septic arthritis

›Kocher score >=2 predictors or toxic appearance

08Treatment/t49

NSAIDs — first-line

›Ibuprofen

›Dose: 10 mg/kg per dose orally three times daily

›Maximum single dose 400 mg in younger children, 600 mg in older children

›Maximum daily dose 40 mg/kg/day or 2400 mg/day

›Duration: 5 days in RCT — shortens median symptom duration from 4.5 to 2 days

›Kermond et al., Annals of Emergency Medicine 2002 (RCT evidence)

›Administration with food to reduce GI effects

›Ensure adequate hydration especially with recent febrile illness

›Contraindications

›Renal impairment

›Known GI ulcer disease

›Allergy to NSAIDs

Analgesic alternatives

›Acetaminophen (paracetamol)

›Dose: 15 mg/kg per dose orally every 4–6 hours as needed

›Maximum single dose 1000 mg

›Maximum daily dose 75 mg/kg/day or 4000 mg/day

›Use when NSAIDs are contraindicated or as adjunct

›Not superior to ibuprofen for this indication — use as alternative

›Avoid aspirin in children — Reye syndrome risk

›Codeine

›Not recommended in children — black box warning, CYP2D6 ultra-metabolizer risk

›Opioids generally not required for transient synovitis

Activity and supportive measures

›Rest and activity modification

›Relative rest — avoid high-impact activity until pain-free

›Partial weight-bearing with limp is acceptable

09Special Populations/sp55

Pregnancy

›Transient synovitis in pregnancy

›Rare in pregnancy as condition primarily affects children aged 3–10 years

›Adult-onset TS is uncommon but reported

›Differential considerations in pregnant women with hip pain

›Transient osteoporosis of pregnancy — third trimester, imaging distinguishes

›Septic arthritis — same diagnostic urgency applies regardless of gestational age

›Sacroiliac joint pain — common in pregnancy, distinct from TS

›Medication considerations if pregnant adult patient affected

›Ibuprofen — avoid after 20 weeks gestation (premature closure of ductus arteriosus)

›FDA 2020 warning: NSAIDs contraindicated from 20 weeks onward

›Acetaminophen — preferred analgesic in pregnancy

›Standard dose 15 mg/kg every 4–6 hours or 500–1000 mg orally every 6 hours

›If septic arthritis suspected: cephalosporins are safe in pregnancy

›Cefazolin is preferred IV option

›Avoid tetracyclines and fluoroquinolones

Geriatric

›Hip pain in older adults — broader differential

›Transient synovitis of the hip is rare in adults and elderly

›Adult TS incidence far lower than pediatric — evaluate for alternative diagnoses first

›Dominant diagnoses to exclude in elderly

›Osteoarthritis — degenerative joint disease, gradual onset, radiographic changes

›Occult hip fracture — especially after fall, exclude with MRI if radiograph negative

›Crystal arthropathy — gout, calcium pyrophosphate (pseudogout) — joint aspiration

›Septic arthritis — risk increased with immunosuppression, prosthetic joints, diabetes

›Pharmacologic considerations in elderly if adult TS diagnosed

›NSAIDs carry increased risk in elderly

›GI bleeding risk — consider PPI co-prescription

10Background/b56

Epidemiology

›Incidence and prevalence

›Most common cause of acute nontraumatic hip pain in children aged 3–10 years

›Average annual incidence approximately 0.2%

›Childhood risk of at least one episode approximately 3%

›Peak incidence age 3–8 years

›Male predominance — approximately 2:1 male-to-female ratio

›Seasonal variation — higher incidence in fall and winter (viral season)

›Recurrence and outcomes

›Recurrence rate 13–15% in children

›Uziel et al., Journal of Rheumatology 2006: longterm outcome study of 39 patients

›Higher anterior capsule distance on initial ultrasound is risk factor for recurrence

›Legg-Calve-Perthes disease following TS in approximately 1–3% of cases

›Mukamel et al., Clinical Pediatrics 1985

›No long-term sequelae expected when diagnosis is correct and septic arthritis excluded

›Full resolution within 1–2 weeks in uncomplicated cases

Pathophysiology

›Mechanism of inflammation

›Immune-mediated synovial inflammation — not direct infection

›Triggered by viral antigen-antibody complex deposition in synovium

›Post-infectious inflammatory response, typically 1–2 weeks after URI or GI illness

›Sterile joint effusion from synovial hyperemia and increased vascular permeability

›Increased intracapsular pressure causes pain and guarded hip position

›Position of flexion, abduction, and external rotation maximizes capsular volume

›Histopathology

›Nonspecific synovial inflammation on biopsy — lymphocytic infiltrate

›No specific pathogen identified on culture or PCR in confirmed TS

›Synovial fluid is typically serous or slightly turbid

11Patient Discharge Instructions/pdi32

copy discharge instructions

›Diagnosis and explanation

›Your child has been diagnosed with transient synovitis of the hip, also called irritable hip or toxic synovitis

›This is a temporary inflammation of the hip joint, usually triggered by a recent cold or viral illness

›It is not an infection and is not dangerous when properly treated

›Most children recover fully within 1–2 weeks

›Medication instructions

›Give ibuprofen (Advil, Motrin) 10 mg/kg per dose every 8 hours for 5 days

›Give with food or milk to protect the stomach

›Ensure your child drinks plenty of fluids while taking ibuprofen

›Do not give aspirin to children — risk of a serious condition called Reye syndrome

›Acetaminophen (Tylenol) may also be used for pain at 15 mg/kg per dose every 4–6 hours if needed

›Activity restrictions

›Allow your child to rest and avoid vigorous or high-impact activities until pain-free

›Light walking and gentle movement are fine if your child can tolerate it

›Do not force weight-bearing if your child is in significant pain

›Your child may return to normal activity once pain has fully resolved, usually within 7–10 days

›Follow-up

›Return to your family doctor or pediatrician in 5–7 days for reassessment

›Repeat examination confirms symptom resolution

›If symptoms persist beyond 7–10 days, further imaging and bloodwork will be required

›Return to emergency department immediately if

›New fever develops or existing fever worsens

›Temperature >38.5 degrees C (101.3 degrees F) is a warning sign of possible joint infection

›Your child refuses to bear any weight on the affected leg or worsening limp

›Pain is increasing despite ibuprofen

›New swelling, redness, or warmth develops around the hip

›Your child appears unwell, toxic, or more uncomfortable than at discharge

12References/r33

Guidelines and key sources

›Kocher MS, Zurakowski D, Kasser JR — Differentiating Between Septic Arthritis and Transient Synovitis of the Hip in Children: An Evidence-Based Clinical Prediction Algorithm — JBJS 1999

›Derived the four-predictor Kocher Criteria: fever, non-weight-bearing, ESR >=40, WBC >12,000

›Probability estimates: 0 predictors <0.2%, 4 predictors 99.6% for septic arthritis

›Kermond S et al — Should the Child With Transient Synovitis of the Hip Be Treated With NSAIDs? — Annals of Emergency Medicine 2002

›RCT: ibuprofen 10 mg/kg TID reduced median symptom duration from 4.5 to 2 days

›Woods CR et al — PIDS/IDSA 2023 Guideline on Diagnosis and Management of Acute Bacterial Arthritis in Pediatrics — Journal of the Pediatric Infectious Diseases Society 2024

›Procalcitonin not recommended as standalone test to differentiate bacterial from nonbacterial

›Early oral step-down antibiotic therapy supported when clinical improvement confirmed

›Marin JR et al — Optimizing Advanced Imaging of the Pediatric Patient in the ED — Pediatrics 2024

›AAP Technical Report: ultrasound and MRI preferred over CT in children

›Radiation minimization principles in pediatric emergency imaging

›Shet NS et al — ACR Appropriateness Criteria: Osteomyelitis or Septic Arthritis-Child — JACR 2022

›Ultrasound and MRI are usually appropriate for pediatric hip pain

›CT not usually appropriate as first-line in children

Supporting studies

›QingSong T et al — Clinical Indicators for Distinguishing SA from Pediatric TS: Systematic Review and Meta-Analysis — BMC Infectious Diseases 2024

›Fever OR 6.04, complete non-weight-bearing OR 5.23, ESR >=40 OR 3.98, WBC >12,000 OR 2.73

›Olandres RA et al — CRP >=20 mg/L and Effusion >=7 mm: High Specificity for Pediatric Hip SA — Archives of Orthopaedic and Trauma Surgery 2023

›Combined threshold specificity 97% for septic arthritis

›Zoabi M et al — POCUS Decision-Support Algorithm for Transient Synovitis — JAMA Network Open 2021

›Sensitivity 90.9%, PPV 98.9% for TS using POCUS-integrated algorithm in pediatric ED

›Feng H et al — Ultrasonographic Features and Recurrence Risk of TS — BMC Musculoskeletal Disorders 2026

›Higher anterior capsule distance on ultrasound is risk factor for recurrence

›Pargas-Colina CD — Transient/Toxic Synovitis — Orthopedic Clinics of North America 2024

›Comprehensive review: incidence 0.2%, childhood risk 3%, recurrence 13–15%

›No specific lab test confirms TS; diagnosis of exclusion

›Uziel Y et al — Recurrent Transient Synovitis of the Hip in Childhood — Journal of Rheumatology 2006

Evidence & Review

Evidence & Review