What are the clinical findings, X-ray and MRI findings, and treatment options for Extensor Pollicis Longus (EPL) versus Abductor Pollicis Longus (APL) tendon injuries of the thumb?

EPL vs APL Tendon Injuries: Clinical Findings, Imaging, and Treatment

Clinical Findings

EPL injuries present with inability to extend the thumb interphalangeal joint and loss of thumb retropulsion, while APL injuries result in impaired thumb abduction and difficulty grasping larger objects.

Extensor Pollicis Longus (EPL) Injury

• Loss of active extension at the thumb interphalangeal (IP) joint is the hallmark finding 1
• Loss of active extension at the metacarpophalangeal (MCP) joint when the extensor hood is also ruptured 1
• Prodromal radial-sided wrist pain often precedes spontaneous ruptures 2
• Ulnar displacement of the EPL tendon may occur with concomitant extensor hood ruptures at the MCP joint, which is frequently misdiagnosed as ulnar collateral ligament rupture 1

Abductor Pollicis Longus (APL) Injury

• Impaired thumb abduction and radial deviation 3
• Difficulty grasping larger objects due to loss of the APL's critical role in thumb positioning 3
• APL injuries are almost exclusively seen in open trauma rather than closed or spontaneous ruptures 1

Imaging Findings

X-ray

• Standard radiographs are typically normal in isolated tendon injuries but should be obtained to rule out fractures or other bony abnormalities 4
• X-rays may reveal bone abnormalities at the site of EPL rupture, particularly in spontaneous cases 2

MRI

• MRI is the ideal imaging modality for evaluating tendon injuries and surgical planning, with sensitivity ranging from 28% to 85% for extensor tendon injuries 4
• MRI without IV contrast is preferred for detecting both tendon rupture and associated soft tissue abnormalities 4
• MRI confirms the diagnosis and identifies predisposing abnormalities such as bone irregularities or synovitis that may contribute to spontaneous rupture 2
• Clinical examination remains the most effective diagnostic measure, with MRI serving as confirmatory 2

Treatment

EPL Tendon Injuries

Extensor indicis proprius (EIP) to EPL tendon transfer using the Pulvertaft weave technique is the preferred reconstruction method for EPL ruptures.

Acute Open Injuries

• Require primary tendon reconstruction by direct suture 1
• Immobilization requirements depend on the zone of injury 1:
  • Distal injuries (zones T1-T3): Static splinting 1
  • Proximal injuries (zone T4 and above): Dynamic aftercare protocol 1

Chronic or Spontaneous Ruptures

• Tendon defects preclude primary repair and require tendon transfer or autograft 1
• EIP to EPL transfer is the most practiced reconstruction technique 5
• Intraoperative tension testing should be performed with the IP joint in extension, hand flat, forearm pronated, and wrist in neutral position 5
• When EIP is unavailable, alternative transfers include extensor pollicis brevis (EPB) if it extends the IP joint 6, or other donor tendons 5
• Tendon autograft is reserved for cases with isolated defects and minimal tendon attrition 5
• Follow-up averages 28 months with generally favorable outcomes 5

Extensor Hood Ruptures

• Require refixation of the ruptured structures to prevent ulnar displacement of extensor tendons 1
• Must be distinguished from ulnar collateral ligament injuries 1

APL Tendon Injuries

Tendon transfer is the definitive treatment for chronic APL injuries, as the muscle loses contractility rapidly due to its small gliding amplitude.

Acute Injuries (Within 6-8 Weeks)

• Tendon graft interposition is the best method if performed early 3
• The APL muscle loses contractility quickly due to its small 28mm gliding amplitude 3

Chronic Injuries (Beyond 6-8 Weeks)

• Extensor indicis to APL transfer is the optimal reconstruction method 3
• The EIP is a functional synergist with the APL and under voluntary brain control 3
• The EIP has a 55mm gliding amplitude compared to APL's 28mm, but when placed under moderate tension, amplitudes become identical 3
• Loss of EIP does not disturb index finger function 3
• Alternative transfers (palmaris longus, flexor carpi radialis, radial half of extensor carpi radialis longus) do not fulfill optimal tendon transposition requirements 3

Critical Pitfalls

• Do not misdiagnose extensor hood ruptures with ulnar EPL displacement as ulnar collateral ligament injuries 1
• Consider anatomical variations of EPB distal to the MCP joint during surgical planning 1
• Reserve MRI for surgical planning and confirmation rather than routine screening, as clinical examination is most effective 4, 2
• Recognize that spontaneous EPL ruptures can occur without identifiable risk factors, trauma, or rheumatological disease 2