What are the likely causes and recommended management for a 9‑year‑old with a five‑day history of groin (inguinal) pain?

Groin Pain in a 9-Year-Old: Evaluation and Management

In a 9-year-old with 5 days of groin pain, immediately assess for fever, inability to bear weight, and severe pain at rest to exclude septic arthritis—a surgical emergency requiring diagnosis within hours—then systematically evaluate for hip pathology (which presents as groin pain in 30% of cases), inguinal hernia, and musculoskeletal causes through targeted physical examination and imaging. 1, 2, 3

Immediate Red Flag Assessment

First, exclude life-threatening or limb-threatening conditions:

• Check temperature immediately: Fever >101.3°F (38.5°C) combined with inability to bear weight strongly suggests septic arthritis, which causes permanent joint damage within hours if untreated 1, 2, 3

• Assess the "three As": Anxiety, agitation, and high analgesic requirements indicate serious pathology including infection or compartment syndrome 2, 3

• Evaluate ability to bear weight: Complete refusal to walk with fever mandates urgent hip ultrasound to assess for joint effusion 1, 3

• Ask about night pain and constitutional symptoms: These suggest stress fractures, tumors, or infection 4

Critical Physical Examination Elements

Young children frequently mislocalize pain—hip pathology presents as groin, thigh, or knee pain in up to 30% of cases. 2, 3

• Palpate the inguinal region directly: Sharp, localized tenderness at the inguinal ligament or pubic tubercle suggests inguinal hernia with possible nerve entrapment, even without visible bulge 5, 6

• Assess hip range of motion: Pain with hip flexion, adduction, and internal rotation (FADIR test) indicates intra-articular hip pathology such as femoroacetabular impingement or labral tears 4

• Examine for inguinal lymphadenopathy: Enlarged, tender inguinal nodes can indicate sexually transmitted infection or other infectious processes 1

• Palpate adductor tendons: Tenderness over the adductor origin with pain on resisted adduction suggests adductor-related groin pain 4, 7

• Screen the lumbar spine: L1-L3 nerve root irritation refers pain to the groin and must be evaluated in every case 4

• Observe gait pattern: Antalgic gait or refusal to walk narrows the differential significantly 1, 3

Differential Diagnosis by Priority

If Fever Present with Inability to Bear Weight:

• Septic arthritis of the hip is the diagnosis until proven otherwise 1, 2, 3
• Osteomyelitis of the pelvis or proximal femur 1
• Pyomyositis of pelvic or thigh muscles 1

If No Fever, Localized Groin Tenderness:

• Inguinal hernia with nerve entrapment: Sharp pain at inguinal ligament, positive family history, pain worsened by activity—more common in females than previously recognized 5, 6
• Adductor-related groin pain: Tenderness over adductor origin, pain with resisted adduction 4, 7
• Iliopsoas tendinopathy: Anterior/medial groin pain with hip flexion against resistance 4

If Hip Motion Painful:

• Transient synovitis: Most common cause of acute hip pain in children, self-limiting 1
• Legg-Calvé-Perthes disease: Insidious onset, age 4-8 years typically, but can present acutely 1, 3
• Slipped capital femoral epiphysis (SCFE): Adolescents/pre-adolescents, medial thigh or knee pain, external rotation deformity 4, 2
• Femoroacetabular impingement or labral tears: Positive FADIR test, mechanical symptoms 4

Other Considerations:

• Enlarged inguinal lymph nodes: From infection, including sexually transmitted infections if sexually active 1
• Referred pain from lumbar spine: L1-L3 radiculopathy 4
• Occult fracture: Even minor trauma history warrants consideration 1, 2, 3

Diagnostic Workup Algorithm

Step 1: Laboratory Studies (if fever or systemic symptoms)

• CBC, ESR, CRP: Elevated inflammatory markers suggest infection 1, 3

Step 2: Initial Imaging

• AP pelvis and frog-leg lateral hip radiographs: First-line imaging to evaluate for hip pathology, SCFE, Perthes disease, and bony abnormalities 1, 4
• Bilateral tibia/fibula radiographs: If pain cannot be clearly localized, as occult tibial fractures are common in this age group 1, 3

Critical caveat: Normal radiographs do NOT exclude fracture—10% of tibial fractures appear only on follow-up films at 7-10 days. 1, 2, 3

Step 3: Ultrasound (based on clinical suspicion)

• Hip ultrasound: If fever with inability to bear weight, to assess for joint effusion requiring urgent aspiration 1, 3
• Inguinal ultrasound (dynamic): If localized inguinal tenderness without visible hernia, to evaluate for occult hernia or posterior abdominal wall weakness 8, 7
• Adductor tendon ultrasound: If tenderness over adductor origin 4, 7

Step 4: Advanced Imaging (if initial workup negative with persistent symptoms)

• MRI pelvis/hip: For suspected intra-articular hip pathology, osteomyelitis, stress fractures, or soft-tissue pathology 1, 4, 3
• Repeat radiographs in 7-10 days: If initial films normal but symptoms persist, to detect occult fractures 1, 2, 3

Management Based on Findings

If Septic Arthritis Suspected:

• Urgent hip ultrasound followed by ultrasound-guided aspiration for cell count, Gram stain, and culture 1, 3
• Immediate orthopedic consultation for surgical drainage 1, 2

If Inguinal Hernia Diagnosed:

• Elective surgical repair to prevent incarceration, which has a 4.6% risk in pediatric patients 1, 5
• Consider ilioinguinal nerve block for diagnostic confirmation if nerve entrapment suspected 5, 6

If Transient Synovitis or Benign Musculoskeletal Cause:

• Short-course NSAIDs for analgesia (80% efficacy in reducing pain) 2
• Rest, ice, compression, elevation (RICE protocol) for muscle-related pain 2
• Observation with follow-up in 1-2 weeks if symptoms improving 2, 3

If Hip Pathology (FAI, Labral Tear, Perthes):

• Orthopedic referral for definitive management 4
• Activity modification and physical therapy initially 4

If Adductor-Related Pain:

• Active, supervised physical therapy focusing on core strengthening 7
• MRI pelvis if diagnosis unclear or no improvement after 6 weeks of conservative management 7

Critical Pitfalls to Avoid

• Never assume normal radiographs exclude fracture: 10% of tibial fractures only appear on follow-up films 1, 2, 3

• Never focus only on the reported pain site: Young children mislocalize pain, and hip pathology presents as groin, thigh, or knee pain in 30% of cases 2, 3

• Never delay evaluation of fever with inability to bear weight: Septic arthritis causes permanent damage within hours 1, 2, 3

• Never ignore the "three As" (anxiety, agitation, high analgesic requirements): These indicate serious pathology requiring urgent evaluation 2, 3

• Never miss occult inguinal hernia: It is more common in females than previously thought and can present without visible bulge, especially with nerve entrapment causing chronic pain 5, 6

• Never forget to screen the lumbar spine: Referred pain from L1-L3 radiculopathy is a common competing diagnosis 4