Flexor Pollicis Longus Trigger Points

Introduction

The flexor pollicis longus (FPL) is a key forearm muscle responsible for thumb flexion and grip strength. When trigger points develop in this muscle, they can cause pain in the thumb, palm, and wrist, often mimicking carpal tunnel syndrome, arthritis, or De Quervain’s tenosynovitis.

Name and Area

  • Name: Flexor Pollicis Longus (FPL)

  • Area: Located on the anterior forearm, running from the radius to the base of the thumb (distal phalanx).

Indications

Flexor pollicis longus trigger points may contribute to:

  • Pain in the Thumb and Palm (Mistaken for Carpal Tunnel Syndrome or Arthritis)

  • Pain That Radiates to the Wrist and Forearm (Can Mimic Tendinitis or Nerve Compression)

  • Weakness in Thumb Flexion (Difficulty Gripping, Pinching, or Holding Small Objects)

  • Pain When Writing, Typing, or Using a Smartphone

  • Thumb Fatigue or Cramping with Repetitive Use (E.g., Texting, Playing an Instrument, Sewing, Knitting)

  • Pain That Worsens with Gripping, Lifting, or Fine Motor Tasks

Pain from this muscle is often mistaken for carpal tunnel syndrome, arthritis, or tendinitis.

Muscle Action

  • Flexes the Thumb (Pollex): Bends the thumb at the distal interphalangeal (DIP) joint.

  • Assists in Wrist Flexion: Helps stabilize the wrist while gripping objects.

The FPL is essential for precision gripping, fine motor tasks, and thumb function.

Signs and Symptoms

Individuals with flexor pollicis longus trigger points often report:

  • Pain in the Thumb, Palm, and Inner Wrist

  • Difficulty Flexing the Thumb (Pain When Pinching, Holding a Pen, or Using a Phone)

  • Weakness in Thumb Grip (Difficulty Turning Keys, Holding a Cup, or Typing on a Keyboard)

  • Pain That Worsens with Repetitive Hand and Thumb Movements (Writing, Texting, Gaming, Playing an Instrument)

  • Burning or Aching Sensation in the Palm (Mistaken for Carpal Tunnel or Tendinitis)

Pain worsens with prolonged gripping, pinching, or repetitive thumb use.

Perpetuating Factors

Common causes of flexor pollicis longus trigger points include:

  • Repetitive Thumb Flexion Movements (Texting, Typing, Gaming, Playing Instruments, Writing, Knitting)

  • Frequent Use of a Computer Mouse or Touchscreen Devices (Sustained Thumb Flexion Without Support)

  • Prolonged Hand Grip or Holding Objects for Extended Periods (Driving, Holding a Phone, Cooking, Holding a Steering Wheel)

  • Overuse in Racquet Sports (Tennis, Badminton, Squash, or Rock Climbing)

  • Poor Ergonomics (Awkward Wrist Position While Using a Keyboard, Phone, or Mouse)

Trigger Point Referral Pattern

Trigger points in the flexor pollicis longus refer pain to:

  • The palm and thumb (Mistaken for Carpal Tunnel Syndrome or Arthritis)

  • The inner wrist and forearm (Can Resemble Tendinitis or Nerve Compression)

  • The base of the thumb (Mistaken for De Quervain’s Tenosynovitis or Joint Pain)

Pain from this muscle is often confused with thumb arthritis, carpal tunnel syndrome, or overuse injuries.

Differential Diagnosis

Flexor pollicis longus trigger points may be mistaken for:

  • Carpal Tunnel Syndrome (Pain, Numbness, and Tingling in the Thumb and Fingers, Particularly at Night)

  • De Quervain’s Tenosynovitis (Pain at the Base of the Thumb, Worsens with Gripping or Lifting Movements)

  • Thumb Osteoarthritis (Joint Pain and Stiffness, Especially in the Morning)

  • Wrist Flexor Tendinitis (Pain and Stiffness in the Wrist and Forearm After Repetitive Use)

  • Median Nerve Compression (Pain, Weakness, or Numbness in the Thumb, Wrist, and Forearm)

A thorough hand, wrist, and forearm examination is necessary to rule out these conditions.

Associated Trigger Points

Flexor pollicis longus trigger points often co-exist with:

  • Flexor Digitorum Profundus (Pain in the Palm and Fingers, Weak Grip Strength)

  • Flexor Carpi Radialis (Pain on the Inner Wrist and Hand, Affects Grip Strength)

  • Pronator Teres (Pain in the Forearm and Wrist, Weakness in Forearm Rotation)

  • Extensor Pollicis Longus and Brevis (Pain in the Thumb and Wrist, Weakness in Thumb Extension)

Anatomy and Innervation

Muscle Origin Insertion Innervation
Flexor Pollicis Longus Anterior surface of the radius, interosseous membrane Base of the distal phalanx of the thumb Median nerve (anterior interosseous branch, C8–T1)

The FPL is innervated by the median nerve, which also controls thumb flexion and precision grip.

Patient Examination

A comprehensive examination should include:

  • Palpation: Identify tender nodules along the forearm, near the wrist and base of the thumb.

  • Resisted Thumb Flexion Testing: Assess pain and weakness when curling the thumb against resistance.

  • Grip Strength Testing: Determine if pain affects endurance when holding objects for long periods.

  • Median Nerve Compression Testing: Rule out nerve-related causes of wrist and hand pain.

Corrective Actions

Dry Needling

  • Dry needling can release trigger points in the flexor pollicis longus, reducing muscle tightness and improving thumb mobility.

Manual Therapy

  • Trigger Point Release: Apply direct pressure to tight spots in the forearm and base of the thumb.

  • Massage Therapy: Helps improve circulation and reduce thumb and wrist tension.

Stretching

  • Thumb Flexor Stretch: Extend the thumb outward while keeping the wrist straight.

  • Wrist and Forearm Stretch: Rotate the wrist gently to release tension in the thumb flexors.

Strengthening Exercises

  • Thumb Gripping Exercises: Strengthens the flexor pollicis longus and hand stabilizers.

  • Resistance Band Thumb Flexion: Improves thumb control and grip strength.

  • Pinch Strength Drills: Enhances precision grip and endurance.

Postural and Ergonomic Adjustments

  • Modify Keyboard and Mouse Positioning (Reduce Thumb and Wrist Strain)

  • Use an Ergonomic Mouse or Wrist Support (Prevents Overuse Injuries)

  • Take Frequent Breaks During Repetitive Tasks (Allows Hand and Forearm Muscles to Recover)

Conclusion

The flexor pollicis longus plays a crucial role in thumb flexion and grip strength, but trigger points in this muscle can cause significant thumb, palm, and wrist pain. By incorporating dry needling, manual therapy, stretching, and strengthening exercises, individuals can reduce pain, improve mobility, and prevent future dysfunction.

➡️ Learn more about Trigger Points

Sources:

  • Travell, J. G., & Simons, D. G. (1983). Myofascial Pain and Dysfunction: The Trigger Point Manual (2nd ed.). Williams & Wilkins.

  • Simons, D., & Travell, J. (1999). The Trigger Point Manual, Volume 2: The Lower Extremities. Williams & Wilkins.