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# FCU tendon

The flexor carpi ulnaris tendon runs on the little-finger side of the front of the wrist; it bends the wrist and tilts it toward the little finger.

Official name: Flexor carpi ulnaris tendon

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## What it is

The tendon on the little-finger side of the front of the wrist, ending at the pisiform.

## What it does

Bends the wrist and tilts it toward the little finger.

## Key points

- The ulnar nerve enters the forearm between its two heads and runs under the muscle to the wrist, so the tendon is the guide to the nerve and artery
- Its branch from the ulnar nerve arises near the elbow: FCU weakness places an ulnar nerve lesion at or above the elbow
- Calcific tendinitis near the pisiform is a classic cause of sudden pain on the ulnar side of the wrist

## Key facts

**Attaches**
To the pisiform, a sesamoid in it, then by the [pisohamate and pisometacarpal ligaments](https://durgical.com/en/anatomy/pisohamate-and-pisometacarpal-ligaments/) to the hook of the hamate and the base of the [5th metacarpal](https://durgical.com/en/anatomy/5th-metacarpal/)

**Function**
Wrist flexion and ulnar deviation; the ulnar artery and nerve run just radial to it into Guyon's canal

**Tight in**
Wrist extension with radial deviation

## Relations

**Course**
The tendon forms on the front of the forearm along its ulnar border and runs straight down to the [pisiform](https://durgical.com/en/anatomy/pisiform/), continuing beyond it as ligaments to the [hamate](https://durgical.com/en/anatomy/hamate/) and fifth metacarpal

**Lateral**
[Ulnar artery](https://durgical.com/en/anatomy/ulnar-artery/) and [ulnar nerve](https://durgical.com/en/anatomy/ulnar-nerve/), beneath its radial edge, then the [FDS tendons](https://durgical.com/en/anatomy/flexor-digitorum-superficialis-tendons/)

**Deep**
[Flexor digitorum profundus](https://durgical.com/en/anatomy/flexor-digitorum-profundus/) and, near the wrist, the [pronator quadratus](https://durgical.com/en/anatomy/pronator-quadratus/) and the [ulna](https://durgical.com/en/anatomy/ulna/)

**Behind**
The subcutaneous border of the ulna, beyond which lies the ECU

## How to find it

With the wrist flexed and tilted toward the little finger against resistance, the tendon stands out on the ulnar side of the front of the wrist and ends on the pisiform; the ulnar pulse is felt just radial to it.

## Examination

- Resisted wrist flexion with ulnar deviation: pain near the pisiform suggests FCU tendinitis; weakness suggests an ulnar nerve lesion at or above the elbow

## On imaging

X-rays, including an oblique view in supination, show calcification near the pisiform; ultrasound shows tendinosis and fluid around the tendon.

## Clinical notes

- Ulnar nerve lesions at the wrist spare the FCU, which is supplied near the elbow
- FCU to [extensor digitorum](https://durgical.com/en/anatomy/extensor-digitorum/) transfer is a classic way to restore finger extension in [radial nerve](https://durgical.com/en/anatomy/radial-nerve/) palsy
- Surgical exposure of the ulnar nerve and artery at the wrist and in Guyon's canal starts along its radial border

## Development

The pisiform forms as a sesamoid inside this tendon and is the last carpal bone to ossify, late in childhood; before that the tendon ends on cartilage that does not show on X-rays.

## Test yourself

Think of the answer, then tap the question to see it.

## Where does the FCU tendon insert?

On the pisiform, a sesamoid in it, then via the pisohamate and pisometacarpal ligaments to the hook of the hamate and 5th metacarpal base.

## What does FCU weakness tell you about the level of an ulnar nerve lesion?

It places the lesion at or above the elbow, since the FCU branch arises near the elbow; wrist lesions spare the FCU.

## Which structures run just radial to the FCU tendon at the wrist?

The ulnar artery and ulnar nerve, on their way into Guyon's canal.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
tendo musculi flexoris ulnaris carpi TA2 2483

**Official Spanish (DeCS)**
Tendón del músculo flexor ulnar del carpo

**English (TA2)**
Flexor carpi ulnaris tendon

## Related

- [Hamate](https://durgical.com/en/anatomy/hamate/)
- [5th metacarpal](https://durgical.com/en/anatomy/5th-metacarpal/)
- [Pisiform](https://durgical.com/en/anatomy/pisiform/)
- [Triquetrum](https://durgical.com/en/anatomy/triquetrum/)
- [Ulna](https://durgical.com/en/anatomy/ulna/)
- [Flexor carpi ulnaris](https://durgical.com/en/anatomy/flexor-carpi-ulnaris/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Forearm Flexor Carpi Ulnaris Muscle](https://www.ncbi.nlm.nih.gov/books/NBK526051/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/flexor-carpi-ulnaris-tendon/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/flexor-carpi-ulnaris-tendon/