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Trigger finger (stenosing flexor tenosynovitis)

By admin | July 2, 2015

Jul 2

INTRODUCTION — Trigger finger (also called stenosing flexor tenosynovitis) is noninfectious inflammation of the flexor tendon sheath of the finger (or thumb). The flexor tendons for each digit travel in a fibro-osseous tunnel between the metacarpal and the distal interphalangeal (DIP) joint; the superficialis tendon attaches to the middle phalanges and the profundus tendon to the distal phalanges. The tunnel provides nutrition to the tendon as well as mechanical stability. Irritation or inflammation of the fibro-osseous tunnel can occur as the result of repetitive use.

Swelling of the tunnel occurs proximally at the metacarpophalangeal (MP) joint, and nodules can form on the flexor tendon. This prevents smooth gliding of the tendon under the A-1 pulley, the specialized ligament that anchors the tendon to the bone. The tendon may “catch” at the MP joint, causing the finger to lock in flexion. Diabetes mellitus predisposes to the development of trigger finger.

PRESENTATION — Patients often complain of pain and a sensation of “snapping” when they flex the affected digit; the pain radiates into the palm or the distal finger. They may awaken with the finger locked in the palm, with gradual “unlocking” as the day progresses. The patient rubs over the tendon in the palm or actually demonstrates the locking phenomenon when describing the condition.

DIAGNOSIS — The diagnosis of trigger finger is based primarily upon a history of locking and the physical examination. Initially, the patient should be asked to open and close the hand; smooth, painless, and complete movement of the affected digit virtually excludes trigger finger. Next, the flexor tendons over the MP joint are palpated for tenderness and swelling:

  • Local tenderness is present at the base of the finger, directly over the tendon as it courses over the metacarpal head. Subtle, palpable swelling may be present.
  • Pain is aggravated by stretching the tendon in extension or by resisting flexion isometrically.
  • Clicking or locking with active flexion may or may not be present, depending upon the time of day or upon how long the patient has been symptomatic.

Tenosynovitis of the flexor tendons always precedes the mechanical symptoms of triggering. However, not all patients demonstrate active tenosynovitis at the time they are examined. As the patient tries to avoid the triggering phenomenon (by using the finger less and less), the tenosynovial signs gradually subside, leaving the patient with a relatively painless mechanical triggering. In some cases, flexor tenosynovitis and mechanical triggering can be so dramatic as to preclude movement of the finger from a flexed position; this is referred to as a “fixed locked” digit.

A local anesthetic block is rarely necessary to make the diagnosis of trigger finger. It is most commonly used in patients with tenosynovitis complicating an early presentation of Dupuytren’s contracture.

Plain x-rays are not necessary in patients with suspected trigger finger [3]. Calcification of the tendon rarely occurs.

DIFFERENTIAL DIAGNOSIS — In addition to the tenosynovitis of trigger finger, pain at the MP joint may arise from the injured ligament of gamekeeper’s thumb, sprain of the MP joint, de Quervain’s tenosynovitis, or the uncommon posttraumatic MP osteoarthritis.

  • Tenderness located only on the ulnar side of the MP joint associated with pain with valgus stress testing of the joint characterizes gamekeeper’s thumb.
  • Tenderness on either side of the MP joint associated with loss of full flexion suggests either a strain of the MP joint, if trauma has been recent, or post-traumatic arthritis, if trauma is remote.
  • Pain experienced near the anatomical snuff box combined with radial styloid tenderness and pain aggravated by isometrically resisting thumb extension strongly suggests de Quervain’s tenosynovitis.
  • Dupuytren’s contracture causes stiffness and loss of full flexion at the MP joint. However, it is usually painless, and nodular lesions are typically evident in the palmar fascia.
  • Severe pain and tenderness, particularly in the setting of a preceding puncture wound, human bite, or animal bite involving the finger or hand, suggest infectious flexor tenosynovitis. It is imperative to recognize this syndrome since closed space infection can lead to severe limitation of motion due to tendon disruption. Infection of the hand requires surgical consultation for possible exploration and drainage.

TREATMENT — The goals of treatment are to reduce swelling and inflammation in the flexor tendon sheath, to allow smoother movement of the tendon under the A-1 pulley, and to perform stretching exercises in extension to prevent recurrent tenosynovitis.

Acute therapy — Immobilization is the treatment of choice in the first four to six weeks, although patients with severe locking on presentation may benefit from local glucocorticoid injection initially (see below). Simple immobilization with buddy taping to the adjacent finger can be tried first; a metal finger splint or a custom made thermoplastic splint is used if buddy taping is poorly tolerated or unsuccessful.

Patients should also be advised to restrict gripping and pinching and to apply ice to the metacarpal head for pain. Antivibration padded gloves (Sorbothane) can be used in individuals who have exposure to vibrating equipment that cannot be avoided. Use of oversized tools also may be helpful.

Once the acute symptoms have resolved, patients should begin gentle stretching exercises in extension of the fingers both to continue the rehabilitation effort and to prevent recurrence.

Persistent symptoms — Local injection is recommended in patients whose symptoms have not resolved in four to six weeks with immobilization (and occasionally in patients with severe triggering at presentation).  The efficacy of glucocorticoid injection has been demonstrated in two controlled trials with a total of 63 patients. A meta-analysis of these two trials concluded that glucocorticoid injection with lidocaine compared with lidocaine alone was associated with a significantly greater likelihood of treatment success at four weeks (relative risk 3.15, 95% CI 1.34-7.40); the number needed to treat to benefit one patient was three [7]. A subsequent trial randomly assigned 50 patients to receive either glucocorticoid injection (1 mL triamcinolone acetonide) or placebo (0.9% NaCl solution) injected locally [8]. The group that received a glucocorticoid injection had a greater improvement in pain, and the effect of steroid injection persisted for up to 12 months.

Appropriate aftercare is critical to the success of local glucocorticoid injection. Patients should be advised as follows:

  • Rest for three days, avoiding all gripping and grasping
  • Buddy tape to the adjacent finger for the first few days
  • Apply ice (15 minutes every four to six hours) and take acetaminophen (1000 mg twice daily) as needed for pain
  • Protect the fingers for three to four weeks by avoiding repetitive gripping, grasping, pressure over the MP heads, and vibration
  • Begin passive stretching exercises of the finger in extension at three weeks
  • Use padded gloves or padded tools for long-term prevention in recurrent cases

The injection may be repeated in six weeks if symptoms have not improved by at least 50 percent. Some have advocated surgery for patients who have not responded to a single injection, although this is not the author’s usual practice. In the author’s experience of following 74 cases of trigger finger over four years, 61 percent achieved relief with one injection, 27 percent required reinjection within one year, and only 12 percent failed medical therapy and required surgical release.

Patients with rheumatoid arthritis are at increased risk for tendon rupture with multiple injections. These individuals may benefit from surgical referral if relief is not achieved with a single injection.

Pediatric patients with trigger thumb represent a special circumstance. Injection and surgery are rarely indicated, since symptoms frequently resolve with simple splinting and observation.

Referral and surgery — Surgery is indicated when locking and tenosynovitis persist despite two consecutive local glucocorticoid injections. Percutaneous and open surgical release of the A-1 pulley ligament are equally effective, with a recurrence rate of only 3 percent. Outcome may not be as successful in diabetics.

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