I found the article on using ultrasound to diagnosis closed flexor tendon injuries interesting. I still rely on history and physical exam to make the diagnosis, but can see how the use of ultrasound (US) could be useful particularly in children.
The article is a retrospective audit of the accuracy of US in diagnosing closed flexor tendon ruptures and ruptures following recent flexor tendon repair in 80 patients between January 2001 and December 2006. The accuracy of US was found to be higher than clinical examination alone (95% vs. 79%, Z = 2.00, p = 0.03).
US findings were 100% accurate when imaging was undertaken between 1 and 7 days following injury, but only 88% accurate when undertaken on the same day as injury and 85.7% accurate when performed after 1 week (X 2 = 6.4, p = 0.04).
If the flexor tendon injury is not clear on physical exam, then US might have a role.
Most injuries to the flexor tendons are due to a cut of some kind (ie knife, saw, etc). Closed injuries to the flexor tendons are often athletic injuries that occur when one player grabs another's jersey, and a finger (usually the ring finger) gets caught and pulled. The forceful hyperextension of a digit leads to the avulsion of the flexor digitorum profundus (FDP) tendon from the distal phalanx. This mechanism has given the injury the common name: "jersey finger."
Closed injuries to flexor tendons can also occur when the tendon is stretched (strained) or ruptured. These mechanisms are more common in sports like rock climbing or in persons with rheumatoid arthritis.
Clinical assessment can often be difficult as swelling and pain may limit movement of the injured digit irrespective of the integrity of the flexor tendon mechanism. The integrity of FDS and FDP tendons should be tested independently and in tandem.
- To test the FDP tendon, the examiner holds the other fingers in extension and stabilizes MCP and PIP joints. The patient is then asked to flex the distal phalanx.
- To test the FDS tendon, the examiner holds the other fingers in extension, but the MCP and PIP joints are released. The patient is asked to flex the finger. The PIP joint and, to a lesser degree, the MCP joint should flex. About 20% of patients are missing a FDS tendon in the little finger and will therefore have limited or no PIP flexion during testing.
- For flexor pollicis longus (FPL) testing, the thumb MCP joint is stabilized in neutral position. The patient is asked to flex the interphalangeal (IP) joint against resistance. A communication may exist between the FPL and the index FDP. The examiner stabilizes the other 3 digits. The patient opposes his or her thumb to the little finger MCP joint. Flexion of the index distal phalanx proves the existence of this anomalous communication.
- Passive manipulation of the wrist through flexion and extension should result in extension and flexion of the digits, respectively. This uses the tenodesis effect of the antagonistic tendons. If a tendon is transected, then there can be no tenodesis effect.
- Compression of the forearm flexion muscles also can be used to test the integrity of the flexor tendons in the hand. As the forearm is compressed, the digits are drawn into flexion. Transected tendons in the digits do not flex with this maneuver.
Successful treatment depends on prompt diagnosis and treatment, preferably within 48 hours of the injury. Delays in treatment may result in fibrosis in the tendon sheath and retraction of the flexor tendon.
Sagittal image of the ring finger reveals the gap (red arrows) between the torn ends of the FDP and also depicts the intact flexor digitorum superficialis tendon (green arrows)
The accuracy of ultrasound in evaluating closed flexor tendon ruptures; European Journal of Plastic Surgery, published online January 2010, DOI 10.1007/s00238-009-0378-8; Onur Gilleard, David Silver, Zeeshan Ahmad, and Vikram S. Devarai
High-Risk Injuries and Infections of the Hand; ACEP Presentation Oct 28, 2008; Scott C. Sherman, MD