Orthopedics

Extensor Tendon Subluxation: Causes, Symptoms, and Treatment

By Alex 7 min read

The sensation of a tendon sliding off your knuckle is typically caused by extensor tendon subluxation, resulting from injury, repetitive stress, degenerative changes, or inflammatory conditions affecting the stabilizing sagittal bands.

Why does my tendon slide off my knuckle?

The sensation of a tendon "sliding off" your knuckle, particularly at the metacarpophalangeal (MCP) joint, is typically due to subluxation of the extensor tendon, often caused by injury or weakening of the stabilizing sagittal bands.

Understanding the Anatomy of the Knuckle

To comprehend why a tendon might "slide," it's crucial to first understand the intricate anatomy of your hand, specifically around the knuckle joints, known as the metacarpophalangeal (MCP) joints.

  • Bones: Each finger has three bones (phalanges) and connects to a metacarpal bone in the palm. The MCP joint is where the metacarpal meets the first phalanx.
  • Extensor Tendons: On the back of your hand, a complex network of extensor tendons runs from your forearm muscles down to your fingers. These tendons are responsible for straightening your fingers and wrist. Each finger typically has a primary extensor tendon (e.g., extensor digitorum communis).
  • Sagittal Bands: Crucially, these extensor tendons are held centrally over the top of the knuckle joint by specialized connective tissue structures called sagittal bands. These strong, fibrous bands form a sling around the tendon, anchoring it to the bone and joint capsule on either side. Think of them as tiny, yet vital, seatbelts for your tendons.
  • Joint Capsule and Ligaments: The MCP joint is enclosed by a joint capsule and reinforced by collateral ligaments on either side, which provide stability and prevent excessive side-to-side motion.

The sagittal bands are the primary structures preventing the extensor tendon from shifting off-center during finger movement.

The Phenomenon: Extensor Tendon Subluxation

The "sliding off" sensation you describe is medically termed extensor tendon subluxation or, in more severe cases, dislocation. This occurs when the extensor tendon slips out of its normal, centralized position over the top of the MCP joint, typically shifting to one side (ulnar or radial).

When the finger flexes, the tendon may snap back into place, often accompanied by an audible click or pop, and a palpable sensation of movement. This snapping is the tendon moving over the bony prominence of the knuckle as it returns to its central groove.

Why Does It Happen? Causes of Extensor Tendon Subluxation

Several factors can contribute to the weakening or tearing of the sagittal bands, leading to extensor tendon subluxation:

  • Acute Trauma or Direct Injury:
    • A direct blow to the knuckle, particularly when the finger is flexed.
    • A forceful hyperextension or hyperflexion injury of the finger.
    • A sudden, forceful gripping or twisting motion.
    • A "knuckle-popping" habit, if done aggressively or repeatedly, could theoretically contribute over time, though this is less common as a primary cause.
  • Repetitive Stress or Overuse:
    • Activities involving repetitive gripping, grasping, or forceful finger movements (e.g., certain sports like boxing, martial arts, or occupational tasks).
    • Chronic strain can gradually weaken the sagittal bands.
  • Degenerative Changes:
    • Wear and tear over time can cause the sagittal bands to thin or fray.
    • Age-related changes in connective tissue elasticity.
  • Inflammatory Conditions:
    • Rheumatoid Arthritis (RA): This autoimmune disease commonly affects the small joints of the hand, causing inflammation that can weaken and erode the sagittal bands and surrounding connective tissues. This is a common cause of chronic extensor tendon subluxation.
    • Other inflammatory arthropathies.
  • Anatomical Predisposition:
    • Some individuals may have naturally looser ligaments or shallower grooves for the tendons, making them more prone to subluxation.
    • Variations in the shape of the metacarpal head.

Common Symptoms and When to Be Concerned

If you experience extensor tendon subluxation, you might notice:

  • A Palpable or Audible "Click" or "Pop": As the tendon slips off and back on during finger movement (especially during flexion and extension).
  • Visible Tendon Movement: You may be able to see the tendon shift to one side of your knuckle.
  • Pain: Often localized to the back of the knuckle, especially during the snapping motion or with activity.
  • Swelling: Around the affected knuckle, particularly after acute injury or activity.
  • Weakness: In extending the affected finger.
  • Catching or Locking Sensation: The finger might feel like it's catching as the tendon moves.

It's important to seek medical attention if:

  • The subluxation is painful or persistent.
  • You notice swelling or bruising after an injury.
  • The condition interferes with your daily activities or athletic performance.
  • You suspect a tear or other significant injury.

Early diagnosis and intervention can prevent chronic problems and potentially more complex treatments.

Diagnosis and Treatment Options

A healthcare professional, typically an orthopedic specialist or hand surgeon, will diagnose extensor tendon subluxation through:

  • Clinical Examination: Assessing your symptoms, palpating the tendon, and observing its movement during finger flexion and extension. They may apply pressure to the tendon to try and elicit the subluxation.
  • Imaging Studies:
    • X-rays: Primarily to rule out fractures or underlying bone abnormalities.
    • Ultrasound: This is often the most effective imaging modality as it can dynamically visualize the tendon moving in real-time and assess the integrity of the sagittal bands.
    • MRI: May be used in complex cases to evaluate soft tissue damage more comprehensively, though less common for this specific diagnosis.

Treatment approaches vary based on the severity and cause:

  • Conservative Management (Non-Surgical):
    • Rest and Activity Modification: Avoiding activities that aggravate the condition.
    • Splinting: A custom-made splint (e.g., an MCP extension block splint) may be used to hold the finger in a slightly extended position, keeping the tendon centered and allowing the sagittal bands to heal. This is often worn for several weeks.
    • Anti-inflammatory Medications: NSAIDs (non-steroidal anti-inflammatory drugs) to reduce pain and swelling.
    • Physical Therapy/Occupational Therapy: Exercises to improve range of motion, strength, and tendon gliding once the initial healing phase is complete.
  • Surgical Intervention:
    • Surgery is considered if conservative treatments fail, if there's a complete tear of the sagittal band, or in cases of chronic, painful subluxation.
    • Surgical procedures aim to repair or reconstruct the damaged sagittal band, often by tightening the existing tissue or using a graft from another tendon.

Prevention and Management Strategies

While not all cases are preventable, especially those due to acute trauma or inflammatory conditions, certain strategies can help manage and reduce the risk:

  • Proper Technique in Sports/Activities: Ensure correct form in activities that involve repetitive hand movements to minimize stress on finger joints and tendons.
  • Warm-up and Cool-down: Prepare your hands and fingers for activity and aid recovery.
  • Strength and Flexibility: Maintain overall hand and forearm strength and flexibility to support joint health.
  • Listen to Your Body: Avoid pushing through pain, especially if you feel a "click" or "pop" in your knuckle.
  • Ergonomics: Adjust your workstation or tools to reduce strain on your hands and fingers.
  • Address Underlying Conditions: If you have an inflammatory condition like rheumatoid arthritis, diligent management with your rheumatologist is crucial to protect your joints and tendons.

Understanding the role of the sagittal bands and the mechanics of extensor tendon subluxation is key to addressing this common, yet often perplexing, sensation. If you experience persistent issues, consulting a hand specialist is the best course of action for an accurate diagnosis and appropriate treatment plan.

Key Takeaways

  • The sensation of a tendon sliding off your knuckle is medically termed extensor tendon subluxation, where the tendon slips from its central position over the metacarpophalangeal (MCP) joint.
  • This phenomenon occurs due to weakening or tearing of the sagittal bands, which are crucial connective tissues that normally hold the extensor tendons centrally over the knuckle.
  • Causes include acute trauma or direct injury, repetitive stress or overuse, degenerative changes, and inflammatory conditions such as rheumatoid arthritis.
  • Common symptoms include a palpable or audible "click" or "pop," visible tendon movement, pain, swelling, and sometimes weakness or a catching sensation.
  • Diagnosis involves clinical examination and imaging (especially ultrasound), with treatment ranging from conservative management (rest, splinting, NSAIDs) to surgical repair for persistent or severe cases.

Frequently Asked Questions

What does it mean when a tendon slides off your knuckle?

The sensation of a tendon sliding off your knuckle, known as extensor tendon subluxation, occurs when the extensor tendon slips out of its normal position over the MCP joint, often due to weakening or tearing of the stabilizing sagittal bands.

What causes the extensor tendon to slide off the knuckle?

Extensor tendon subluxation can be caused by acute trauma (like a direct blow or forceful injury), repetitive stress or overuse, degenerative changes, or inflammatory conditions such as rheumatoid arthritis.

What are the symptoms of a sliding tendon in the knuckle?

Common symptoms include a palpable or audible "click" or "pop" during finger movement, visible tendon shifting, localized pain, swelling, weakness in extending the affected finger, and a catching sensation.

When should I see a doctor for a tendon sliding off my knuckle?

You should seek medical attention if the subluxation is painful or persistent, if you notice swelling or bruising after an injury, if it interferes with daily activities, or if you suspect a significant tear or injury.

How is a sliding tendon in the knuckle diagnosed and treated?

Diagnosis is typically made through a clinical examination and imaging, especially ultrasound, which can dynamically visualize the tendon. Treatment ranges from conservative methods like rest, splinting, and anti-inflammatory medications to physical therapy, or surgical intervention for severe cases.