Finger joint capsules !

The finger joint capsules are the sleeves that seal the knuckles and finger joints; they swell in arthritis.

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What it is

Small bags of tissue around the knuckles and finger joints.

What it does

Seal the joints; they swell in arthritis.

Key facts

Attaches: Around each MCP and IP joint, from head to base of the next bone
Function: Thickened at the sides by the collateral ligaments and in front by the volar plates

Relations

In front: Volar plate; in front of it the flexor tendons in their fibrous sheath, with the A1 pulley over the MCP and the A3 pulley over the PIP
Behind: Extensor mechanism: the sagittal bands over the MCP, the central slip on the base of the middle phalanx over the PIP, the terminal tendon over the DIP
Lateral: On both sides, proper and accessory collateral ligaments; the lateral bands and the digital nerves and arteries run alongside

How to find it

In a fist the knuckle is the metacarpal head, so the MCP joint line lies just distal to it; the palmar crease at the base of the finger is well distal to the joint. Synovitis fills the valleys between the knuckles; an IP effusion gives a spindle-shaped finger.

Examination

MCP squeeze test: pain on squeezing across the knuckles suggests MCP synovitis, as in early inflammatory arthritis
Collateral stress testing (MCP flexed, IP joints straight): more opening than on the other hand means a collateral ligament tear

On imaging

Ultrasound with Doppler finds synovitis and effusion in the MCP and PIP capsules before X-ray changes. X-ray shows rheumatoid erosions first at the bare areas, where the capsule attaches to bone not covered by cartilage.

Clinical notes

Fight bite: a tooth wound over a clenched MCP often enters the capsule; with the fingers straight, the skin wound slides away from the joint wound, and septic arthritis can follow
In rheumatoid arthritis, boutonnière and swan-neck deformities start with synovitis stretching the PIP capsule and its supports
A jammed finger with a volar plate injury at the PIP can leave a fixed flexion contracture (pseudo-boutonnière)

Test yourself

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

In what position is the hand splinted to protect the finger joint capsules, and why?

MCPs flexed and IPs straight (safe position), because the MCP collaterals are tight in flexion and would otherwise shorten.

Which finger joint stiffens more than any other after injury?

The PIP joint: its volar plate and accessory collaterals contract after even minor sprains, leaving a flexion contracture.

Which finger joint capsules does rheumatoid arthritis swell, and which does osteoarthritis favour?

Rheumatoid arthritis swells the MCP and PIP capsules and spares the DIPs; osteoarthritis favours the DIPs (Heberden) and PIPs (Bouchard).

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

Its names

Official Latin (TA2): capsulae articulares articulationum metacarpophalangearum et interphalangearum manus TA2 1536
Official Spanish (DeCS): Cápsulas articulares metacarpofalángicas e interfalángicas de la mano
English (TA2): Finger joint capsules

Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Metacarpophalangeal Joints.

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Representative model, for educational purposes only.

Finger joint capsules highlighted on the Durgical 3D model