What are the symptoms of Flexor Pollicis Longus (FPL) tendon rupture?

From the Guidelines

Symptoms of a flexor pollicis longus (FPL) rupture primarily include the inability to bend the thumb at the interphalangeal (IP) joint, which is best diagnosed using MRI for evaluating tendon injuries and planning surgical interventions 1. The inability to flex the tip of the thumb interferes with pinch grip and precision movements, and patients may notice pain, swelling, and tenderness along the volar aspect of the thumb, especially at the site of rupture. Some key symptoms and signs include:

• Inability to bend the thumb at the IP joint
• Pain, swelling, and tenderness along the volar aspect of the thumb
• A palpable gap in the tendon if the rupture is complete
• Weakness in thumb movements, particularly during activities requiring thumb flexion
• A "pop" or snapping sensation at the time of injury
• The thumb may appear to be in an extended position at rest compared to the unaffected side These symptoms occur because the FPL is the only muscle that flexes the distal phalanx of the thumb, so when it ruptures, this specific movement becomes impossible. Prompt medical evaluation using MRI is essential for accurate diagnosis, as early surgical repair typically yields better functional outcomes than delayed treatment 1. Conservative management is rarely appropriate for complete ruptures in active individuals, and MRI is ideal for evaluating tendon injuries and helping with surgical planning, with a sensitivity of 92% and specificity of 100% for diagnosis of tendon injuries reported by Rubin et al 1.

From the Research

Symptoms of Flexor Pollicis Longus (FPL) Tendon Rupture

The symptoms of FPL tendon rupture include:

• Inability to flex the interphalangeal joint of the thumb 2, 3
• Loss of active flexion of the interphalangeal joint of the thumb 3
• Trigger thumb, which can be a preceding symptom of FPL tendon rupture 4
• Pain and decreased function in the thumb 5
• Decreased range of motion and strength in the thumb 5, 6

Diagnostic Considerations

Diagnosis of FPL tendon rupture can be made through:

• Clinical examination, including assessment of active flexion of the interphalangeal joint of the thumb 3
• Imaging modalities such as magnetic resonance imaging (MRI) or ultrasound 2, 4
• Histopathological examination of the debrided tissue from the ends of the ruptured tendon 2

Presentation and Natural History

FPL tendon rupture can present in various ways, including:

• Spontaneous rupture due to degenerative changes or tendolipomatosis 2
• Traumatic rupture due to injury or laceration 6
• Rupture secondary to rheumatoid arthritis 5
• Delayed-onset rupture after distal radius volar plate fixation 4