[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) › A1 pulleys [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # A1 pulleys The A1 pulleys are bands at the base of each finger that hold the flexor tendons to the bone; a thickened A1 pulley causes trigger finger. Official name: A1 pulleys of the flexor tendon sheaths [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=a1_pulleys&side=r) Opens in the Durgical app, no sign-up needed. ## What it is Short rings of tough tissue over the flexor tendons at the base of each finger and the thumb, in the palm. ## What it does Hold the flexor tendons close to the bone at the knuckle; a thickened pulley causes trigger finger. ## Key points - Its proximal edge lies near the distal palmar crease for the ring and little fingers, the proximal palmar crease for the index, and the MCP flexion crease for the thumb - Trigger finger release divides only A1; keeping A2 intact prevents bowstringing - Thumb A1 release puts the radial digital nerve at risk: it crosses obliquely in front of the pulley, close to the [skin](https://durgical.com/en/anatomy/skin/) - In rheumatoid arthritis A1 is usually preserved, since releasing it can worsen ulnar drift; tendon synovectomy is preferred ## Key facts **Attaches** Palmar plate over each MCP joint **Function** Keeps the flexor tendons close to bone; site of trigger finger **Tight in** Finger flexion ## Relations **Contents** [FDS tendons](https://durgical.com/en/anatomy/flexor-digitorum-superficialis-tendons/) and [FDP tendons](https://durgical.com/en/anatomy/flexor-digitorum-profundus-tendons/) ([FPL tendon](https://durgical.com/en/anatomy/flexor-pollicis-longus-tendon/) in the thumb) inside the flexor tendon sheath **Behind** Volar plate of the MCP joint, from which it arises, and the metacarpal head **Below** The A2 pulley on the shaft of the proximal phalanx ([finger pulleys](https://durgical.com/en/anatomy/flexor-tendon-sheaths-and-pulleys/)) **Lateral** [Digital nerves](https://durgical.com/en/anatomy/palmar-digital-nerves/) and [digital arteries](https://durgical.com/en/anatomy/palmar-digital-arteries/) on each side; in the thumb the radial digital nerve crosses in front of it ## How to find it The examiner presses over the metacarpal head in the palm while the person slowly bends and straightens the finger; in trigger finger a tender nodule glides under the examiner's finger and catches at the edge of the pulley. ## Examination - Palpation during active flexion: a tender nodule that catches or clicks at the A1 pulley confirms triggering; a finger that locks in flexion and needs the other hand to straighten it is a more advanced grade ## On imaging Ultrasound shows a thickened, hypoechoic A1 pulley and a swollen tendon beneath it; dynamic scanning shows the tendon catching. Ultrasound can also guide a percutaneous release or an injection. ## Common problems - Trigger finger: the tendon or the A1 pulley thickens, so the finger catches or locks when bending, then snaps straight. - More common with diabetes, in the thumb, ring and middle fingers. ## How it is diagnosed A tender nodule in the palm at the base of the finger and catching felt on bending. ## Treatment - Splint, activity changes and a steroid injection, which often works. - Release of the A1 pulley through a small cut or with a needle when it keeps coming back. ## Clinical notes - Paediatric trigger thumb: a fixed flexed thumb IP joint with a palpable nodule (Notta node) in a young child, sometimes on both sides - Release can be open or percutaneous; incomplete release and accidental cutting of A2 are the main technical errors - Several trigger digits at once are more common with rheumatoid arthritis and amyloidosis ## Related conditions - [Trigger finger](https://durgical.com/en/conditions/trigger-finger/) ## Test yourself Think of the answer, then tap the question to see it. ## Which pulley is released in trigger finger surgery, and which must be preserved? Only the A1 pulley is divided; keeping A2 intact prevents bowstringing. ## Which nerve is at risk in thumb A1 pulley release? The radial digital nerve, which crosses obliquely in front of the pulley close to the skin. ## Where is the proximal edge of the A1 pulley of the ring and little fingers? Near the distal palmar crease (the proximal palmar crease for the index; the MCP flexion crease for the thumb). ## Why is the A1 pulley usually preserved in rheumatoid arthritis? Releasing it can worsen ulnar drift; tendon synovectomy is preferred. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/a1-pulleys-of-the-flexor-tendon-sheaths/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** pars anularis vaginae fibrosae digiti manus TA2 2585 **Official Spanish (DeCS)** Porción anular I de la vaina fibrosa de los dedos de la mano **English (TA2)** A1 pulleys of the flexor tendon sheaths **Also called** A1 pulley · annular pulley · Annular part of the fibrous digital sheath (A1) ## Related - [FDS tendons](https://durgical.com/en/anatomy/flexor-digitorum-superficialis-tendons/) - [FDP tendons](https://durgical.com/en/anatomy/flexor-digitorum-profundus-tendons/) - [Finger pulleys](https://durgical.com/en/anatomy/flexor-tendon-sheaths-and-pulleys/) - [Volar plates (knuckles)](https://durgical.com/en/anatomy/volar-plates-of-the-mcp-joints/) - [1st metacarpal](https://durgical.com/en/anatomy/1st-metacarpal/) - [2nd metacarpal](https://durgical.com/en/anatomy/2nd-metacarpal/) - [3rd metacarpal](https://durgical.com/en/anatomy/3rd-metacarpal/) - [4th metacarpal](https://durgical.com/en/anatomy/4th-metacarpal/) Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Metacarpophalangeal Joints](https://www.ncbi.nlm.nih.gov/books/NBK538428/); [Anatomy, Shoulder and Upper Limb, Hand Metacarpal Phalangeal Joint](https://www.ncbi.nlm.nih.gov/books/NBK538343/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/a1-pulleys-of-the-flexor-tendon-sheaths/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/a1-pulleys-of-the-flexor-tendon-sheaths/