The 5 Most Common Finger Deformities Explained

Mallet Finger, Boutonnière, Swan Neck, Trigger Finger & Claw Finger

Finger injuries don’t all look the same—and finger deformities can be caused by very different conditions or types of trauma. While some happen suddenly after an injury, others develop gradually from overuse, inflammation, arthritis, or nerve involvement. Understanding the differences is key, because each deformity affects different structures and requires a different approach to treatment.

Below are the five most common finger deformities, how they occur, and what they typically look like.

1. Mallet Finger

Mallet finger occurs when the extensor tendon at the fingertip (DIP joint) is injured, most commonly from a direct blow or a jammed finger. This causes the fingertip to droop and prevents active straightening.

Common causes:

• Sports injuries (basketball, volleyball, baseball)

• Falls onto the hand

• Sudden force to the fingertip

Without proper treatment—often splinting—mallet finger can become a permanent deformity.

2. Boutonnière Deformity

A boutonnière deformity is characterized by flexion of the middle joint (PIP) and extension of the fingertip (DIP). This occurs due to damage to the central slip of the extensor tendon, which disrupts normal finger mechanics.

Common causes:

• Trauma to the finger

• Untreated tendon injuries

• Inflammatory conditions such as rheumatoid arthritis

Early recognition is important to prevent long-term stiffness and dysfunction.

3. Swan Neck Deformity

Swan neck deformity is essentially the opposite of boutonnière deformity. The middle joint hyperextends, while the fingertip bends into flexion.

Common causes:

• Ligament laxity

• Chronic inflammation or arthritis

• Imbalance between finger flexor and extensor tendons

This deformity can interfere with gripping and fine motor tasks if not addressed.

4. Trigger Finger

Trigger finger is not a fixed deformity, but rather a functional movement disorder. The finger may lock, catch, or snap when bending or straightening due to tendon irritation and thickening as it passes through the pulley system.

Common causes:

• Repetitive gripping

• Overuse

• Diabetes or inflammatory conditions

In more advanced cases, the finger may become stuck in a bent position.

5. Claw Finger

Claw finger causes the fingers—most commonly the ring and small finger—to curl at rest. This deformity is typically due to nerve injury, affecting the balance between intrinsic and extrinsic hand muscles.

Common causes:

• Ulnar nerve injury

• Cervical spine or peripheral nerve issues

• Long-standing nerve compression

Clawing can significantly impact hand strength and coordination.

Why Early Treatment Matters

While these deformities may appear similar, they involve different joints, tendons, ligaments, or nerves. Ignoring finger injuries or delayed treatment can lead to permanent stiffness, weakness, or loss of function.

If your finger won’t move normally after an injury, don’t ignore it—early treatment matters.

Understanding what you’re dealing with is the first step toward proper care and long-term hand health.