Central Slip Extensor Tendon Injury

• Central Slip Extensor Tendon Injury

Pathophysiology

• General
  • Typically occurs as a result of forced passive PIP flexion against active extension
  • Subsequent disruption of the central slip of the extensor tendon.
• Closed injury: hyperflexion, direct blunt trauma
• Open injury: penetrating trauma
• Extensor Tendon
  • Trifurcates into 1 central slip and 2 lateral bands
  • Central slip attaches to the dorsal side of the middle phalanx
  • Lateral bands attach to the sides of the distal phalanx

Causes

• Fractures
  • Phalanx Fractures (Hand)
  • Metacarpal Fractures
    • Boxer’s Fracture
    • Rolando Fracture
    • Bennett Fracture
• Dislocations
  • Metacarpophalangeal Joint Dislocation
  • Proximal Interphalangeal Joint Dislocation
  • Distal Interphalangeal Joint Dislocation
  • Carpometacarpal Joint Dislocation
• Tendinopathies
  • Extensor Tendon Injuries (Hand)
  • Central Slip Extensor Tendon Injury
  • Flexor Tendon Injuries (Hand)
  • Boutonniere Deformity
  • Swan Neck Deformity
  • Jersey Finger
  • Mallet Finger
  • Trigger Finger
  • De Quervains Tenosynovitis
• Ligament Injuries
  • Gamekeepers Thumb (UCL)
  • Radial Collateral Ligament of the Thumb Injury (RCL)
  • Volar Plate Avulsion Injury
• Neuropathies
  • Wartenbergs Syndrome
  • Carpal Tunnel Syndrome
  • Guyon Canal Syndrome
• Arthropathies
  • Carpometacarpal Arthritis
  • Finger Arthritis
  • Rheumatoid Arthritis
• Nail Bed Injuries
  • Nail Bed Lacerations
  • Nail Bed Avulsions
  • Subungual Hematoma
  • Paronychia
  • Felon
• Pediatric Considerations
  • Proximal Phalanx Avulsion Fracture (Thumb)
  • Middle and Distal Phalanx Avulsion Fracture
• Other
  • Dupuytrens Contracture

Diagnosis

• History
  • Typically describe some form of trauma
  • Reports pain, swelling, ecchymosis
• General: Physical Examination Hand
  • Inability to extend at PIPJ of affected joint

Radiographs

• Standard Radiographs Hand
  • Typically normal
  • May show avulsion fracture

MRI

• Can consider if the diagnosis is uncertain or to further clarify the injury

US

• It May be used to help confirm tendon injury

Special Tests

Special tests that help in identifying injury to the extensor mechanism include:

1. Elson Test – Fixing PIP Joint at 90° and asking the patient to extend the DIP joint. A lax DIP joint, despite the patient’s effort to extend, is a negative or normal finding (if the central slip is intact, the loose lateral bands/slips when the PIP is flexed prevent DIP extension). A positive finding is a rigid DIP joint because of increased unopposed pull through the lateral bands/slips.
2. Modified Elson Test – The injured digit and its normal counterpart are placed in full proximal interphalangeal flexion, with the dorsum of each middle phalanx firmly against each other. If the injured digit has visibly better distal interphalangeal extension than the uninjured digit, a central slip injury is likely.
3. Boyes Test – Extend PIP and ask to flex DIP; positive is unable to flex DIP actively

Boyes test may become positive only in the late stages.

Management

Nonoperative

• Indications
  • Most cases
• Immobilization
  • PIP Extension Splinting, DIP in partial flexion
  • Dynamic splinting vs progressive static splinting (serial splinting)
• Typically for 6 weeks

Operative

• Indications
  • Open injury
  • Some avulsion fractures
• Technique^[2]
  • Acute central slip repair
  • Open reduction and internal fixation (ORIF)
  • Tendon reconstruction
  • Arthrodesis

Post-Surgical Rehabilitation of Central Slip Repairs

Geoghegan et al (2018) recently conducted a systematic review on treatments of central slip extensor tendon injuries. Different rehabilitation regimes are reported in the literature and these can be broadly classified into

• PIP joint immobilisation, followed by an isolated PIP flexion-extension exercise
• Controlled early active short arc motion
• PIP joint immobilisation followed by mobilisation with a dynamic spring coil finger splint

Evans et al (1994) reported significantly better functional results in a cohort of early short arc motion compared to a cohort of prolonged immobilisation.

Early Short Arc Motion Regime

The basis for the early short arc motion regime is that sufficient tendon excursion is necessary to prevent adhesions. An arc of 30° of flexion at the PIP joint will achieve the desired amount of (3 -5 mm) of tendon excursion. With this protocol patients need to be seen on a weekly basis to monitor progress and monitor for an extensor lag. It is also necessary to remould the exercise splint.

Splinting

Patients who have had a surgical repair of a central slip tendon injury will require different splints

• Full finger volar extension splint – worn at all times, except for during exercises
• Exercise splints:
  • Volar slab from distal metacarpophalangeal (MCP) joint to the end of the finger – allowing 30° PIP joint flexion and 20° DIP flexion
  • Short volar splint with PIP in neutral, but allowing DIP to flex over the top of the splint

Rehabilitation Exercises

These exercises are done in the different exercise splints usually made out of thermoplastic. The splints are also remoulded as the flexion angles increase.

• Week 1: 30° PIP and 20° DIP flexion
• Week 2: 40° PIP and DIP flexion (if no extensor lag present)
• Week 3: 50° PIP and DIP flexion
• Week 4: 70° – 80° PIP and DIP flexion
• Week 5: full composite flexion
• Week 6 -8: light functional use allowed
• Week 8: Strengthening with Theraputty
• Perform exercises 3 times a day and 10 repetitions of each exercise
• Scar management is crucial for post-surgical zone III tendon repairs to prevent adhesions.