What is the role of ultrasound in diagnosing hip-related symptoms in adults and infants with a history of hip pain or trauma?

Role of Ultrasound in Hip Imaging

Ultrasound should be used selectively in hip evaluation: it is the imaging test of choice for extra-articular pathology (tendon tears, bursitis, snapping hip) and for screening developmental dysplasia in high-risk infants, but radiography must be the initial imaging modality for adults with hip pain, with ultrasound serving as a complementary tool rather than primary diagnostic imaging. 1, 2

Adults with Hip Pain or Trauma

Initial Imaging Approach

• Anteroposterior (AP) pelvis and lateral femoral head-neck radiographs are the mandatory first-line imaging for all adults presenting with hip-related pain or trauma. 1, 2, 3
• Imaging must always be combined with patient symptoms and clinical signs—never rely on imaging findings in isolation, as diagnostic utility of imaging alone is limited with only small to moderate shifts in post-test probability. 1
• Radiographs allow comparison with the contralateral asymptomatic side and exclude critical alternative diagnoses such as fractures, osteoarthritis, or dysplasia. 4, 2

When to Add Ultrasound in Adults

Ultrasound serves as a complementary imaging tool in specific clinical scenarios:

• Extra-articular pathology: Ultrasound is the imaging test of choice for greater trochanteric pain syndrome, including gluteus medius/minimus tendinopathy or tears, trochanteric bursitis, and iliotibial band friction. 4, 5
• Dynamic assessment: Ultrasound excels at evaluating dynamic abnormalities such as extra-articular snapping hip syndrome that cannot be captured on static imaging. 5, 6
• Screening for joint effusions: Ultrasound is useful for detecting hip effusions and can guide diagnostic/therapeutic interventions. 5, 6
• Tendon pathology: For experienced examiners with high-quality equipment, ultrasound is superior to other modalities for evaluating tendon abnormalities and hernias. 5

Limitations of Ultrasound in Adults

• Intra-articular pathology requires MRI/MRA: For labral tears, femoroacetabular impingement syndrome, and most intra-articular conditions, MRI or MR arthrography remains preferable to ultrasound. 5, 7
• Ultrasound has a complementary but not primary role for labral pathology evaluation. 5
• Advanced imaging (MRI/MRA or CT) is reserved for three-dimensional morphological assessment or when radiographs are negative but clinical suspicion remains high. 2

Infants with Suspected Developmental Dysplasia of the Hip (DDH)

Screening Recommendations

Selective ultrasound screening is recommended for high-risk infants, not universal screening:

• Female infants born in breech position require hip ultrasound imaging. 1
• Optional ultrasound for male infants born breech or female infants with positive family history of DDH. 1
• Infants with clinical instability, first-degree relatives with DDH, breech presentation, or postural foot deformities warrant selective ultrasound examination. 1

Timing Considerations

• Do not perform ultrasound evaluation before 2 weeks of age, as hip instability often resolves spontaneously by this time. 1
• Despite normal physical examination findings, imaging should be performed in all at-risk infants, as normal physical examination does not preclude development of dysplastic hip. 1

Ultrasound vs. Radiography in Infants

• Ultrasound is superior to radiography in infants under 4-6 months of age because it directly visualizes the cartilaginous femoral head before ossification center appears. 8
• Ultrasound can measure femoral head cover (FHC) in youngest infants; normal lower limit is 46% in newborns and 52% at 4-5 months. 8
• Once ossification center appears, lateral head distance (LHD) can be measured; upper normal limit is 3mm in infants <1 year and 4mm in older patients. 8
• By 6 weeks of age, radiographic changes become recognizable, and radiographic screening can be implemented at 4 months for at-risk infants who were clinically normal at neonatal examination. 1

Clinical Outcomes

• Ultrasound screening in infants with clinically detected hip instability reduces unnecessary abduction splinting without increasing abnormal hip development or surgical treatment rates, and reduces overall costs. 1
• Ultrasound as primary imaging method allows radiography to be omitted in approximately 95% of patients referred for suspected DDH when hips are normal. 8

Critical Limitation

• Selective ultrasound screening has not been shown to significantly reduce diagnosis of late DDH, despite identifying DDH in high-risk children with negative physical examinations. 1

Key Clinical Pitfalls

• Incidental imaging findings are common in asymptomatic individuals—manage with appropriate clinical sensitivity and avoid overdiagnosis. 4
• Multiple hip conditions frequently coexist (e.g., labral and chondral conditions with FAI syndrome), requiring comprehensive evaluation. 4
• Hip pain can be referred from lumbar spine, sacroiliac joints, or knee pathology—examine spine and contralateral joints as potential pain sources. 9
• Ultrasound examination is technically demanding due to complex regional anatomy and deep hip location, requiring an experienced operator. 7