Fused Finger: Movement, Causes, Functional Impact, and Adaptations

Can you move a fused finger?

A truly fused finger, whether surgically (arthrodesis) or pathologically (ankylosis), cannot move at the specific joint that has undergone fusion. While the fused joint itself becomes rigid, the body often develops compensatory movements at adjacent joints or through the wrist and entire upper limb to maintain function.

Understanding Finger Fusion (Arthrodesis vs. Ankylosis)

To understand movement in a fused finger, it's crucial to differentiate between the two primary forms of fusion:

• Arthrodesis (Surgical Fusion): This is an intentional surgical procedure where the bones forming a joint are permanently joined together, eliminating all motion at that specific joint. The goal is typically to alleviate severe pain, correct instability, or fix a significant deformity that cannot be addressed by other means. Common reasons for finger arthrodesis include severe osteoarthritis, rheumatoid arthritis, or complex trauma. The joint surfaces are prepared, and often internal fixation (like screws or plates) is used to hold the bones together until they heal into a single, solid bone.
• Ankylosis (Pathological Fusion): This refers to the unintentional stiffening and immobility of a joint due due to disease, injury, or abnormal bone growth. Conditions like severe inflammatory arthritis (e.g., advanced rheumatoid arthritis), long-term infection, or severe, untreated trauma can lead to ankylosis. In this scenario, the joint space diminishes, and the bones may fuse naturally, resulting in a loss of movement.

In both cases, the fundamental outcome for the specific fused joint is the same: the absence of movement.

The Biomechanics of a Fused Joint

A healthy synovial joint, like those in the fingers, relies on articular cartilage, synovial fluid, and a joint capsule to allow smooth, pain-free movement. When a joint is fused, these components are replaced by a solid bony bridge.

• Loss of Articular Cartilage: The smooth, gliding surfaces are removed or degraded.
• Elimination of Joint Space: The gap between the bones is obliterated as they unite.
• Bone-to-Bone Union: The two bones that previously articulated become one continuous bone.

This bony union means that the muscles and tendons that once crossed and acted upon that specific joint can no longer produce motion there. Any attempt to "move" the fused joint will be met with rigidity, and forcing it can cause pain or damage to adjacent structures.

Why Fusion Occurs

Finger fusion is typically performed or occurs due to:

• Severe Pain: When conservative treatments or joint replacement surgery are not viable options for chronic, debilitating pain.
• Instability: To stabilize a joint that is chronically dislocating or subluxing, often due to ligamentous injury or degenerative disease.
• Deformity: To correct severe deformities that impair function or are cosmetically distressing.
• Non-Union of Fractures: In cases where a finger fracture fails to heal properly, leading to a "floppy" or unstable joint.
• Infection: To eradicate infection in a joint by removing the diseased tissue and fusing the bones.

Functional Implications of a Fused Finger

The impact of a fused finger on overall hand function depends significantly on which joint is fused and the position in which it is fused:

• Distal Interphalangeal (DIP) Joint: Fusion of the outermost joint of the finger often has the least impact on overall hand function. It can improve stability for pinching and grasping small objects.
• Proximal Interphalangeal (PIP) Joint: Fusion of the middle finger joint can significantly affect grip strength and dexterity, particularly for activities requiring a hook grip (e.g., carrying a bag) or precise manipulation. The ideal fusion position for the PIP joint is often a slight degree of flexion, allowing for better object grasp.
• Metacarpophalangeal (MCP) Joint: Fusion of the joint connecting the finger to the palm has the most profound impact on hand function. This joint is crucial for full flexion and extension of the finger, affecting the ability to make a fist or fully extend the digits.

Despite the loss of movement at the fused joint, the primary goal of fusion is often to provide a stable, pain-free platform for the rest of the hand to function more effectively.

Compensatory Movements and Adaptations

While the fused joint itself cannot move, the human body is remarkably adaptable. Individuals with a fused finger often develop compensatory strategies to perform daily tasks:

• Increased Movement at Adjacent Joints: The joints immediately proximal and/or distal to the fused joint may develop an increased range of motion to compensate. For example, if a PIP joint is fused, the MCP and DIP joints of that finger may become more mobile.
• Wrist and Forearm Adjustments: The wrist can adopt different positions (flexion, extension, ulnar/radial deviation) to orient the hand and fused finger optimally for tasks.
• Enhanced Use of Other Digits: Non-fused fingers and the thumb may become more dominant in performing fine motor tasks and grasping.
• Whole Upper Limb Compensation: In some cases, larger movements at the elbow or shoulder may be used to position the hand effectively, compensating for reduced finger dexterity.

These are not movements at the fused joint but rather clever adaptations of the entire kinetic chain to work around the fixed segment.

Life with a Fused Finger: Rehabilitation and Management

For individuals with a surgically fused finger (arthrodesis), the initial phase involves immobilization to allow the bones to heal. Post-immobilization, rehabilitation focuses on:

• Maintaining Range of Motion: Ensuring that adjacent, non-fused joints remain mobile and do not stiffen.
• Strengthening: Building strength in the intrinsic and extrinsic hand muscles, as well as the forearm and wrist, to maximize overall hand function.
• Compensatory Strategies: Training the individual to effectively use their remaining hand and upper limb mobility for daily activities.
• Pain Management: Addressing any residual discomfort or pain that may arise from altered biomechanics or adjacent joint stress.

For those with pathological ankylosis, management involves adapting to the existing limitations through similar strategies, often with the help of occupational therapists who can provide assistive devices or teach modified techniques for tasks.

When to Seek Professional Advice

If you have a fused finger and experience any of the following, it is advisable to consult a hand specialist, orthopedic surgeon, or physical/occupational therapist:

• New or Increased Pain: Especially if it occurs in the fused digit or adjacent joints.
• Swelling, Redness, or Warmth: Could indicate infection or inflammation.
• Decreased Function: A noticeable decline in your ability to perform tasks despite previous adaptations.
• Concerns about Compensation: If you feel your compensatory movements are leading to pain or overuse in other areas.
• Questions about Assistive Devices: Seeking advice on tools or modifications to improve daily living.

While a fused finger cannot move at the point of fusion, understanding its biomechanics and the body's adaptive capacity allows for effective management and optimized function.