Consultant Teaching: Tendon Injuries to the hand are often complex entities that are subject to ongoing research regarding optimal procedures for management and rehabilitation. The flexor and extensor tendon anatomy is quite complex. Both are divided into numerous “zones” created to help clarify the optimal treatment, which can vary markedly depending on injury location. Missed tendon injuries increase morbidity by complicating later management and are therefore a leading cause of malpractice claims in the world of Emergency Medicine. The most important and fundamental aspect of evaluation in these patients is a detailed hand exam. Outlined below is a guide for the evaluation and management of any patient presenting to the ED with a suspected hand injury.
Flexor Tendon Injuries
The first step is to obtain a detailed history of the mechanism of injury. Was the injury caused by a rusty farm knife or a sharp chard of glass? What was the position of the patient’s hand when the injury occurred? This is a frequently missed point to mention. You can imagine that, if the patient was lacerated with flexed fingers while gripping a knife, the location of the tendon injury itself may be in a very different location than the skin laceration when evaluating the hand in a more extended posture. Just because you can no longer see the damaged tendon in the wound doesn’t mean it’s not there.
Step 1: Observation
Evaluate the location and depth of the laceration. Look at the resting posture of the hand and the
patient’s digital cascade. When in doubt, you can usually find clues by looking at the resting finger position of the uninjured hand. Your clinical suspicion should be raised if a particular finger rests in a more extended position relative to the others.
Step 2: Passive Range of motion
These hand injuries can be really painful. A good place to start is assessment of passive motion with a maneuver that elicits the tenodesis effect. Try it on yourself - With a relaxed hand, when you passive flex your wrist, your MCP/PIP/DIP joints will extend. Similarly, wrist extension will cause passive flexion of those digits. If you passively extend the patient’s wrist and there is persistent extension of the DIP or PIP joints, you may have a flexor tendon injury in that digit.
Step 3: A detailed (ie purposeful) neurovascular exam
Flexor tendon injuries are frequently associated with neurovascular injury because of the palmar
location of these structures. The best way to assess nerve function is with a two-point discrimination exam. This can easily be performed with a paper clip. Remember that each finger has proper digital nerves on its palmar aspect on both the radial and ulnar sides: test them both. *Tip 1* If you get abnormal results that don’t make sense given the injury, test the other hand! Your patient who forgot to mention his terrible neuropathy will appreciate this. *Tip 2* Under NO circumstances should a digital block be performed if you are planning to consult the hand service on call. If analgesia is an issue, let the hand service know and proceed with necessary oral/IV medications until your consulting service is able to evaluate the patient’s neurovascular status. This is not only important for our documentation, but is critical for possible surgical planning.
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Sensory territories of the hand (Source: wikipedia) |
Step 4: Flexor Tendon Exam
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For completeness, it is also important to document motor testing for all muscles with separate nerve innervations, regardless of its proximity to the wound in question.
Extensor Tendon Injuries
Like the flexor tendons, these also can be diagnostic challenges due to the complex anatomy of the extensor mechanism. This region is comprised of extrinsic muscles that power digit extension, like the extensor digitorum communis (EDC) and an extensor aponeurosis with multiple connecting bands and ligaments. Again, a detailed history will provide valuable insight and context for your exam. Is it a result of a fight-bite injury? A crushing mechanism?
The general principles of the physical exam addressed above regarding observation, passive range of motion and a detailed neurovascular exam still apply. As diagrammed in the image above, for the dorsal hand, it is especially important to assess both the radial and ulnar nerves.
With regard to hand posture, take note if there is a resting flexed position of the digit, a mallet finger, or boutonniere deformity. This should heighten your suspicion for a tendon injury.
Assessment of the Extensor Tendon
A few important considerations are noteworthy here. First, do not be fooled by the action of the lumbricals! Remember, these muscles provide extension of the PIP and DIP joints via the lateral bands. Have the patient lay their hand flat on a table (extends the MCP joint and helps remove the influence of lumbricals) and extend at the MCP joint against resistance. Extension along an affected digit may still be possible even after complete laceration, due to the multiple contributions to the extensor mechanism. Look closely for a lack of hyperextension or differential extension in the affected finger that may be a sign an extensor tendon injury has occurred. The junctura tendinae are intertendinous fascial connections located around the MCP joint that attach tendons of the EDC and help coordinate their movements. This anatomic structure is important to keep in mind because the junctura may allow for some extension of an injured digit if the tendon injury is proximal to them.
Lastly, if you are concerned about an injury to the “central slip” (eg. a lac or crush injury to the middle phalanx), then an Elson test can be performed. To do this test, flex the PIP 90 degrees over a table and have them extend against resistance. If the central slip is intact, the DIP joint will be supple. If it is ruptured, there will be weak extension of the PIP and a rigid DIP due to the action of the lateral bands.
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At the end of the day, it’s important to keep a high level of suspicion - a referral to a hand surgeon for a suspected tendon injury is just as valid as a referral for a definite tendon injury.
Check out these videos:
Tenodesis effect: https://www.youtube.com/watch?v=j0RBU_phUKw
Elson test: https://www.youtube.com/watch?v=wudDvOiSUlw
Generic hand exam: https://www.youtube.com/watch?v=imPQve7ZL3o
Submitted by Chris Cosgrove, MD. Ortho PGY2
Reviewed by: Daniel Osei, MD. Hand Attending
EverydayEBM Editor: Maia Dorsett (@maiadorsett)