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Trigger Finger – Why does my finger lock?
Friday, 02 March 2012 00:00

Trigger Finger is a common disorder consistent with a catching or locking sensation that occurs with finger flexor and is associated with dysfunction and pain. These factors make it difficult to flex and extend a finger resulting in a "triggering" effect. The term "trigger finger" is used because when the finger unlocks; it snaps back suddenly, mimicking the release of a gun trigger. It is found more often in patients who have diabetes, rheumatoid arthritis, gout, carpal tunnel syndrome and hand trauma. Trigger finger affects women more than men and frequently afflicts people between the ages of 40-60 years. Trigger finger can involve the lateral 4 fingers as well as the thumb.

Anatomy

A brief review of finger anatomy shows that the Flexor Digitorium Profundus (FDS) and Flexor Digitorium Superficialis (FDS) tendons originate in the volar forearm with the tendons passing through the carpal tunnel and exiting into the palm portion of the hand. The FDS and FDP are encapsulated in the flexor tendon sheath and pass under the first annular pulley (A1) where the FDS inserts into the base of the middle phalanx. It is at the level of the A1 pulley that the FDS flattens out and bifurcates, allowing the FDP tendon to pass more superficially and insert into the distal phalanx. (see Figure 1) The A1 pulley (see Figure 2) is part of a complex pulley system that tethers the flexor tendons to the finger preventing a bowstring effect with finger flexion and extension. Palmar surface anatomy reveals that the A1 pulley is palpable at the distal palmar crease or about 1 cm distal of the proximal finger crease (palmar).

trigger finger figure 1                  trigger finger figure 2_edited-3

               Figure 1                                                   Figure 2

Symptoms

Patients with trigger finger will present with a variety of symptoms. Some will notice a bump in the palm of their hand, others will notice a catching sensation with moving their finger and others will present because their finger is trapped and they are unable to extend their finger. Most patients will report a gradual onset of pain in the palmar aspect of the hand that intensifies with flexion and extension of the involved digit. Patients will localize pain to the palmar MCP joint region. As the condition worsens a noticeable thickening of the flexor tendon will develop. Many times the patient will feel a nodule or thickened area that is more obvious with finger flexion. Along with the tendon thickening the A1 pulley will become stenotic. This decreased surface area contributes to the catching or locking sensations patients typically experience with trigger finger. Finally, as the patient's conditions reaches end stages, patients will have increasing frequency of locking that is not reducible. Some patients will present for their initial complaint having a trapped finger that they are unable to release. Attempts to free the locked finger produce significant pain.

trigger finger figure 3

                Figure 3

Examination

Inspection of the hand will reveal any old trauma leading to scars that could inhibit finger motion. Palpation of the palmar portion of the hand may reveal thickening of the flexor tendon, palmar aponeurosis and A1 pulley. The A1 pulley lies between 1- 2cm distal to the MCP flexor crease. As such, the thickened flexor tendon can be palpated in this region. Range of motion for the metacarpal Phalangeal (MCP), proximal interphalangeal (PIP) and the distal interphalangeal (DIP) should be assessed and recorded. Alterations in ROM will give the examiner some indication that triggering might be part of their diagnosis. There is usually no sensory or vascular compromise associated with trigger finger. If this is detected, look for other sources of finger/hand problems. Radiographs will show bone injury that could contribute to soft-tissue abnormalities affecting he hand/fingers.

Treatment

Most all treatments for trigger finger are centered on conservative care. In a majority of cases, patients will respond favorably to local corticosteroid injection and rest. Placing a patient in a finger splint limiting motion at the PIP (or interphalangeal joint if the thumb is involved) will reduce motion and may limit trigger finger. If a corticosteroid injection is administered, great care must be taken to deliver the medication into the tendon sheath and not delivered into the flexor tendon. Depositing steroids into a tendon could increase the chances of tendon rupture. If patients present in a trapped flexed position and corticosteroid injection fails to release their finger, then surgical release of the A1 pulley is necessary. Likewise, patients who have persistent symptoms and have failed conservative therapies and still have finger locking should have the pulley excised.

Patients who present with trigger finger may have other medical conditions that contribute to the development of this condition. The most often associated physical finding with trigger finger is a catching or locking of the finger/thumb. Most will respond well to conservative treatment but if symptoms persist, surgical excision of the A1 pulley is recommended. Patients generally make a full recovery regardless of treatment and often return to unrestricted activities.

To learn more about trigger finger and other MSK injuries to the upper extremity, go to www.orthoedu.com for more information.

 

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