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Use of small amounts of ultrasound guided air for injections
  1. H BLIDDAL, Professor of Rheumatology, Parker Institute
  1. Frederiksberg Hospital, DK-2000 Denmark
  2. Chief of Laboratory of Ultrasonography
  3. KAS Gentofte, DK-2900 Hellerup, Denmark
  1. henning.bliddal{at}fh.hosp.dk
  1. S TORP-PEDERSEN
  1. Frederiksberg Hospital, DK-2000 Denmark
  2. Chief of Laboratory of Ultrasonography
  3. KAS Gentofte, DK-2900 Hellerup, Denmark
  1. henning.bliddal{at}fh.hosp.dk

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The existence and detection of air in various tissues is of great importance, whether the air has emanated by a disease mechanism (for example, intra-abdominal in gastric lesions, extrapulmonary in thoracic lesions) or been applied as a diagnostic tool. The detection of the air in a diagnostic test may be performed by such different methods as stethoscopy (epidurally in the whoosh test1), or radiography (intra-articularly in arthrography2 3).

In ultrasonography the injection of ultrasound contrast agents containing air may increase the diagnostic confidence in the intravascular domain.4 5

Atmospheric air, which is much cheaper, may be safely injected in small quantities for diagnostic purposes in extravascular domains—for example, joints,6 and in our experience also in bursae and tendon sheaths, which all have cavities that can be visualised in this way.

In addition to the standard ultrasonic verification of correct needle placement,7 it is possible to monitor and verify the actual injection of the substance by adding a small amount (0.5–1 ml) of air. Figure 1 shows the inflamed tendon sheath of a patient with rheumatoid arthritis. Before injection of cortisone the correct position of the needle is verified as well as the correct placement of the substances injected through this needle. The air is readily discernible on the screen (fig 2A-D), and the flow of the air in both proximal and distal direction along the tendon can be visualised. The procedure can be performed in an outpatient clinic with the aid of an assistant.

Figure 1

Thickened tendon sheath before injection. Longitudinal section of the palmar side of the fifth finger. In the top of the image the skin (S) is seen as an isoechoic band with varying thickness. The subcutaneous tissue (SC) is seen as a slightly more hypoechoic band below the skin. The thickened and irregular tendon sheath (TS) is seen both above and below the tendon (T). The proximal phalanx is indicated by long vertical arrows and the metacarpal bone is indicated by short vertical arrows. Local anaesthesia (LA) is applied and is seen as an expanding fluid collection indicated by the oblique arrow.

Figure 2

Ultrasound guided injection. (A) The needle has been inserted and is indicated by arrows. The leftmost arrow points at the needle tip. Small amounts of air are seen escaping the needle tip (short arrows), spreading out in the cleavage between the tendon and the thickened tendon sheath. TS = thickened tendon sheath; T = tendon; NT = needle tip; PP = proximal phalanx; MC = metacarpal bone. (B) and (C) An expanding fluid collection is seen in the cleavage between tendon and tendon sheath. (D) The bolus of the injection is seen as a hyperechogenic mass between the tendon and the tendon sheath.

We do not propose that all injections should be carried out under the guidance of ultrasound, however, during training of the therapists or in scientific studies the placement of the injection may be assured in this way.

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