Answer: “Hips Don’t Lie”

Lorraine Ng

 

This post is in response to the post “Hips Don’t Lie

To summarize, this was 3-year old boy who presented with inability to bear weight on his right leg.  A hip ultrasound was performed and the following images were obtained:

L HipR Hip

Thank you to everyone who took the quiz!

Q1Q2

For question #1, 87% of you guessed correctly that “B was the affected side”, as evidenced by the large hip effusion measuring > 5mm.  4% of you thought that A was the affected side, 9% thought both were abnormal and none of you thought both were normal.

Sonographic criteria for a positive hip effusion include:

  • Anterior synovial space thickness > 5 mm; or
  • > 2mm difference when compared to the asymptomatic contralateral hip.

Therefore, the correct answer for question #2 is “anterior synovial space thickness measuring> 5 mm,” of which 32% of you guessed correctly.

Hip Ultrasound

To perform the examination, the patient is placed in the supine position with the hip slightly externally rotated. A  high-frequency linear transducer is the preferred transducer to scan the relatively superficial pediatric hip. The transducer should be placed in the sagittal oblique plane, parallel to the long axis of the femoral neck. In this view, the femoral head, femoral neck, joint capsule, and iliopsoas muscle are visualized.

photo-hipHip2

Hip2

The capsular-synovial thickness should be measured from the anterior concavity of the femoral neck to the posterior surface of the iliopsoas muscle. When performing hip ultrasound, both hips should be evaluated to allow for comparison widths of the anterior synovial fluid space.  The split screen function is particularly useful to compare the two hips for the presence of joint effusion.

 

Hip Effusion

Ultrasound is an excellent modality for identifying joint effusions. As mentioned above, sonographic criteria for a hip effusion include:

1) Anterior synovial space thickness > 5 mm; or

2) > 2mm difference when compared to the asymptomatic contralateral hip.

Hip4

In addition, a large hip effusion can cause the joint capsule to bulge out towards the iliopsoas muscle, as in our patient’s image of his right hip.

Detection of an effusion focuses the differential diagnosis toward transient synovitis or septic arthritis, and away from neoplasms, avascular necrosis, slipped capital femoral epiphysis (SCFE) or Legg-Calvé-Perthes disease.   Differentiating between transient synovitis and a septic hip can not be based solely on sonographic appearance.  Further evaluation with laboratory markers and diagnostic arthrocentesis should be considered in the appropriate clinical setting.

Learn more about hip ultrasound.

If you want to see YOUR image included in the next Image of the Month, please email interesting stills and/or clips in addition to a small blurb on the patient to Lorraine Ng at PEMFellowscom@gmail.com.

 

Lorraine Ng

Lorraine Ng

Assistant Clinical Professor and the Fellowship Director of the Pediatric Emergency Ultrasound Fellowship at Columbia University Medical Center
Lorraine's academic interests are in emergency ultrasound and medical education. She is the editor for the Ultrasound Image of the Month series for PEMNetwork.
Lorraine Ng
Lorraine Ng

Lorraine Ng

Lorraine's academic interests are in emergency ultrasound and medical education. She is the editor for the Ultrasound Image of the Month series for PEMNetwork.