Flexor Pollicis Manual Compression

Historical Overview

• The flexor pollicis longus (FPL) tendon may become ruptured spontaneously, through trauma, or as a consequence of several conditions.^1,2
• Evaluation of the continuity of the FPL tendon is clinically important in thumb disorders, but differentiating between FPL rupture and anterior interosseous nerve (AIN) palsy can be difficult, especially when trauma is not responsible.¹
• Various diagnostic tools have historically been used to investigate potential FPL tendon disturbance—such as ultrasound, MRI, neurophysiological studies, and alternative clinical examinations—but the accuracy of these tests is variable.^1,3
• Melton proposed the FPL manual compression test in 2005, which serves as a simple and reliable predictor of FPL tendon continuity.¹

Description

• The FPL manual compression test evaluates the continuity of the FPL tendon by applying pressure on its muscle belly and detecting for passive flexion in the thumb interphalangeal (IP) joint.¹

Pathophysiology

• The FPL originates from the anterior part of the radius to insert in the distal phalanx of the thumb, which allows for active flexion of the IP joint.⁴
• FPL tendon ruptures have been found to occur either spontaneously or from a variety of injuries and conditions, including rheumatoid arthritis, mucopolysaccharidosis, scaphoid fracture, nonunion, and exostosis, distal radius fracture, sesamoid osteophytes, and idiopathic causes.^1,2
  • FPL rupture is also a well-documented complication of internal fixation of the distal radius, with a reported prevalence after volar plating of the distal radius of 0.17-12%.⁵
• FPL lacerations represent ~8.7% of flexor tendon injuries and most commonly occur in zone I or zone II.⁴
• Closed flexor tendon ruptures of the hand are uncommon and usually occur at the flexor digitorum profundus (FDP) bony insertion, and less frequently at the FPL tendon.⁶

Instructions¹

1. Obtain an accurate and complete patient history that includes an injury description if applicable.
2. Have the patient place their forearm in supinated position and allow their wrist to fall into extension with the thumb in a neutral position.
3. While supporting the forearm with one hand, apply firm pressure with the thumb at a point ~10 cm proximal to the distal wrist crease and 1 cm to the radial side of the midline, on the FPL muscle belly.

Related Signs and Tests

• In one previously used clinical examination from Mody, the clinician forces the thumb carpometacarpal (CMC) and metacarpophalangeal (MP) joints into hyperextension.
  • If the FPL tendon is in continuity, the IP joint flexes spontaneously or resists passive extension when tested with the examiner's other hand. 
  • If the FPL tendon is ruptured, the IP joint remains extended.³
• Other diagnostic tools that may be used for FPL tendon injuries include:^1,5,6
  • Ultrasound
  • Nerve conduction studies
  • Doppler ultrasound
  • MRI
  • Neurophysiological studies
• Differential diagnosis for FPL tendon injuries:¹
  • AIN palsy
  • Trigger thumb