Trigger Finger (Stenosing Tenosynovitis)

Anatomy

• Trigger finger involves inflammation or swelling at the tendon and the tendon sheath

Tendon Sheath

• Is a protective sleeve that surrounds certain tendons

• Has an outer fibrous layer

• Has an inner layer containing synovial fluid that helps the tendon glide smoothly within the tendon sheath

• In trigger finger, the tendon sheath becomes inflamed and thickened (usually at the A1 pulley - discussed below)

• The tendon sheath thickening causes a narrower space for the tendon to glide through

• As the flexor tendons (flexor digitorum superficialis and flexor digitorum profundus) attempt to glide through the now narrowed space, they can become restricted or "caught"

  • This is what causes the classic clicking, catching, and locking sensation associated with trigger finger

Pulley System

• The flexor tendons (from the flexor digitorum superficialis and flexor digitorum profundus muscles) run along the palmar/volar surface of each finger

• These tendons are held down closely to each finger by a pulley system

  • The pulley system holds the flexor tendons close to the bone so the tendons do not "bowstring"

  • The specific pulleys involved in trigger finger are the annular pulleys, which are like a ring in which they wrap around the tendons to hold it in place

  • There are multiple annular pulleys at each finger and the most commonly affected one is called the A1 pulley

• The A1 pulley is most commonly affected due to it being more narrow than the other pulleys and it being located most proximal, which subjugates it to an increase in force/pressure

• A1 pulley is located near the base of the finger by the MCP joint, on the palmar surface

• The pulleys are considered part of the fibrous outside layer of the tendon sheath (as they are strong, fibrous connective tissue)

Flexor tendons

• Sometimes a nodule can develop on the flexor tendons 

  • From the ongoing friction and inflammation caused by the tendons being restricted within the narrow space of the tendon sheath and A1 pulley

• This causes an increase in symptoms as the nodule can get stuck on the edge of the thickened A1 pulley

• Note: the flexor tendons are usually referred to as a singular "flexor tendon", where it is implied both FDS and FDP tendons are being discussed

Overall, micro-trauma from overuse accumulates, causing inflammation to the flexor tendons and its sheath 

Flexor tendons passing through the tendon sheath creates a cycle of inflammation, swelling, and restricted movement which further aggravates the condition

Prognosis/Timeline

• Research suggests that wearing an orthosis may be more effective than relying solely on a corticosteroid injection (with no orthosis), as there is no signifficant different in outcomes between the two treatment options

  • Orthosis is recommended as it is less invasive

• Corticosteroid injection can have a 61% recurrence of the condition

• Wearing an orthosis combined with getting a corticosteroid injection provides no benefits compared to solely wearing an orthosis

• Surgical release can result in a 1-4% recurrence of the condition

  • Increase in recurrence in those with more than 3 corticosteroid injections and those who do manual labor

Quiz Answers

1. C

2. D

3. C

4. A

5. C

6. B

7. B