Trigger Finger

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Trigger Finger
Pathophysiology Thickened and stenotic A1 pulley
Treatment Observation, night splinting, steroid injection, and surgical release.

Trigger finger and trigger thumb is also known as flexor tenosynovitis. It causes a painful clicking or locking of the affected digit.

Anatomy and Pathophysiology

Annular (A1-A5) and cruciform (C0-C3) ligaments of the tendon sheath over the flexor tendons of the index finger of the right hand.

There is a thickened and stenotic A1 pulley. The pulley has deterioration of the inner fibrocartilaginous gliding surface. This causes tendon friction and the tendon develops a nodule and inflammation.

The A1 pulley is 5-7mm in length and is found on the palmar side opposite the dorsum of the metacarpophalangeal joint. The palmar creases can be used to located the A1 pulleys. For the thumb it is found on the ulnar side of the proximal crease. For digit 2 it is found on the proximal crease. For digits 3 to 5 it is found on the distal palmar crease.[1]

Epidemiology and Risk Factors

There is an annual incidence of 28 cases per 100,000, and a lifetime prevalence of 2.6%. The peak incidence is in the 50s and 60s. There is an increased risk of diabetes with a lifetime prevalence of 5-10%. It is associated with Dupuytren's disease, carpal tunnel syndrome, and inflammatory arthritis. Children can be affected as an acquired rather than congenital condition, usually with trigger thumb.

There are no proven occupational or recreational risk factors, although certain activities may or may not be relevant: repetitive gripping with palmar pressure, use of power tools with direct vibratory forces, pulling weeds, biking or power tool use.[1]

Clinical Features

Multiple digits can be involved. The most commonly involved digits are the thumb, third, and fourth fingers of the dominant hand.

Patients may incorrectly think that the catching is located in their interphalangeal joint or proximal interphalangeal joint. This can be disproven by palpating the A1 pulley for pain and tenderness and demonstrating triggering at that location.[1]

Investigations

Imaging Findings

Ultrasound is 85% sensitive and specific for trigger finger using an A1 pulley thickness cutoff of 0.62mm. The average pulley thickness in affected individuals is 0.77 to 0.79mm, and the normal range is 0.43 to 0.47mm.[1]

Diagnosis

The Green Classification can be used. There should be at least grade 1 for diagnosis.

Green Classification
Grade I Palm pain and tenderness at A1 pulley
Grade II Catching of digit during flexion and extension
Grade II Locking of digit, passively correctable
Grade IV Fixed, locked digit

Differential Diagnosis

Differential Diagnosis

Treatment

Observation

Reassurance and observation may be all that is required in some cases. One case series had a 52% resolution rate over 8 months with simple observation. Patients are often instructed to avoid possible causative activities but it isn't known if this is required.[1]

Splinting

Continuous splinting for 6 to 9 weeks has a 60% cure rate. It isn't clear whether an MCP or PIP joint blocking orthosis is more effective. Night splinting over 6 weeks is a newer alternative technique for a 55% cure rate in those with grade I or II of less than 3 months duration.[1]

Injection
Main article: Trigger Finger Injection
Proximal phalangeal intra-sheath injection, a less painful alternative to the classic technique.[1]

Corticosteroid injection is quick and allows more rapid relief of symptoms. Cure rates range between 60-90% for up to three injections. The effect is generally sustained. The NNT is quite low, when compared to placebo lidocaine, the NNT is 3 at one month, and 2 at four months post-injection. There is generally improvement within days, and locking and stiffness within weeks.

Cure rates are lower in fingers (versus thumbs), diabetes, multiple trigger fingers, diffuse swelling (rather than a palpable nodule), and in those with higher grade disease.

In those with partial improvement, the best timing for repeat injection is no sooner than 69 days.

There is greater accuracy, but no increase in efficacy for ultrasound guidance over landmark injection.

Other than the standard side effects, there is an extremely rare risk of tendon rupture and deep space infection. Patients with rheumatoid arthritis should have surgical release rather than injection due to a higher risk of tendon rupture.

Post-injection the patient should follow the "rule of 3s"

  • Avoid using the finger for three days.
  • Avoid tight grasping for three weeks
  • Return for repeat injection in three months if no better, and then for a third and final injection after that.[1]
Surgery

In those who don't respond to the above treatments, A1 pulley release can be done. Trigger finger release can be done under ultrasound guidance with a similar efficacy to open release.[1]

Summary

  • Trigger finger causes pain and locking of the flexor tendon at the A1 pulley
  • Observation, splinting, and steroid injection are all reasonable initial management options
  • Steroid injections can be repeated up to 3 times, at 3 monthly intervals.
  • Injection into the flexor tendon sheath overlying the proximal phalanx is a less painful option than injection at the A1 pulley.

References

  1. โ†‘ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Merry et al.. Trigger Finger? Just Shoot!. Journal of primary care & community health 2020. 11:2150132720943345. PMID: 32686570. DOI. Full Text.

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