ULTRASOUND OF SYNOVITIS AND EROSION

ULTRASOUND IN SYNOVITIS
High resolution probes give excellent spatial resolution, especially for superficial small joints 
The earliest ultrasound abnormality of joint pathology is effusion.
  A small quantity of fluid may be detected in the normal joint
Effusion without trauma is suggestive of underlying joint disease  
In some joints effusion is common and there is a poor correlation between ncreasing fluid and symptoms. 
The first metatarsal phalangeal joint is the best example of this. 

US REPORT SHOULD INCLUDE

      • Normal vs effusion
      • Score for synovitis
      • Score for Doppler signal
      • Presence or not of erosions
      • Other associated features eg tenosynovitis

Synovial thickening has a different appearance to joint effusion. 
Effusion is echo poor (black) as opposed to synovial thickening which contains increased echoes reflecting its more complex structure. 
Fluid can also be displaced from one part of the joint to anothe by compression with the ultrasound probe . 
Synovial thickening is more difficult to either displace or compress. 
Doppler colour flow assessment also helps to differentiate synovial thickening from effusion

Take care to not exert too much probe pressure as small vessels may be compressed and obscured. 
Liberal use of coupling gel is recommended. 
The probe can be floated in the jelly supported by operators hand/fingers resting on the couch or patient. 

GRADE SYNOVIAL THICKENING
Four Point SUBJECTIVE
      • 0 No synovial thickening
      • 1 Minimal thinking or large effusion
      • 2 Obvious synovial thickening
      • 3 Gross synovial thickening

There is considerable intracapsular but extra synovial fat in the small joints of the hand Displacement of the capsule or peri-articular ligaments by increases in peri-articular fat should not be misinterpreted as joint pathology.  Fat tends to be reflective or bright on ultrasound as opposed to synovial thickening which is usually darker. 

GRADE DOPPLER SIGNAL
Four Point SUBJECTIVE
      • 0 No Doppler signal
      • 1 Few scattered vessels
      • 2 Doppler affecting <50%
      • 3 Doppler affection >50%

A score of 220 therefore means moderate synovial thickening with moderate Doppler activity but no erosions.
Care should be taken to use a sensitive algorithm, a PRF of 400 – 500 is suggested. 
Other authors suggest a number of vessels between 7 and 10 as representing grade 2 blood flow but
this depends on the size of the joint being interrogated. 

US Contrast Media
A role for ultrasound contrast medium has also been proposed. 
Ultrasound contrast works by releasing micro bubbles of gas in the circulation . 
Later materials use gases other then air that are specifically detected using particular ultrasound frequencies called harmonics. 
The combination of tissue harmonics with contrast injection allows subtraction techniques which provide additional information. 
Continuous infusion is more accurate than bolus injection. 
Ultrasound contrast improves detection of blood flow but a precise clinical role has yet to be firmly established. 
 


ADVANTAGES OF MRI IN SYNOVITIS AND EROSION

Quicker for review joints in the field of view
More permanent record which can be shared and reviewed
Easier to score and rescore if method changes
Therefore less operator dependent
Contrast injection provide simultaneous assessment of many joints and tendons Can detect earlier bone changes (pre erosions) when US can not


ADVANTAGES OF US IN SYNOVITIS AND EROSION

Less expensive
Patients prefer US to MRI
Can respond to patient symptoms eg. clinician refers for right hand imaging but patient reports left foot now also swollen
Dynamic capability
Less dependent on contrast materials