Why is above elbow immobilization sometimes recommended for a Smith fracture?

Above Elbow Immobilization for Smith Fractures

Above elbow immobilization is recommended for Smith fractures to counteract the volar displacement of the distal fragment by neutralizing the deforming force of the brachioradialis muscle, which is the only muscle attached to the distal fracture fragment.

Rationale for Above Elbow Immobilization

The decision to immobilize above the elbow for Smith fractures (reverse Colles' fractures) is based on biomechanical principles:

• The brachioradialis muscle exerts a strong deforming force on the distal fracture fragment when the elbow is allowed to flex freely 1
• Electromyographic studies support that immobilizing the elbow in flexion and the forearm in supination helps minimize this deforming force 1
• The American Academy of Orthopaedic Surgeons recommends immobilizing fractures with a cast in a position of wrist flexion and forearm supination to counteract volar displacement 2

Optimal Immobilization Technique

For Smith fractures, the recommended immobilization approach includes:

• Initial immobilization in an above-elbow cast with:
  • Elbow in flexion
  • Forearm in supination
  • Wrist in moderate ulnar and volar flexion 1

This position helps maintain the reduction by:

1. Neutralizing the pull of the brachioradialis muscle
2. Reducing the risk of secondary displacement
3. Minimizing fragment collapse during healing

Evidence on Effectiveness

Research findings on above vs. below elbow immobilization show mixed results:

• A 2019 study found no statistically significant difference between above-elbow and below-elbow casts in maintaining reduction of manipulated distal radius fractures, with only minimal differences in radial height (0.8 mm), inclination (0.4°), and volar tilt (0.9°) 3

• However, the classic study by Sarmiento (1975) demonstrated that above-elbow immobilization with the forearm in supination helped minimize fragment collapse in Colles' fractures 1

Duration of Immobilization

Recent evidence suggests shorter immobilization periods may be beneficial:

• A 2023 randomized controlled trial found that four weeks of immobilization produced similar outcomes to six weeks for displaced distal radial fractures following closed reduction 4
• The mean PRWE score after one year was 6.9 in the four-week group compared to 11.6 in the six-week group, though this difference was not clinically significant 4

Potential Complications and Considerations

Immobilization, particularly above-elbow casting, can lead to several complications:

• Joint stiffness (most common complication) 2
• Significant impairments immediately after cast removal:
  • 40% deficit in pronation and supination
  • 50% reduction in wrist motion
  • 24% reduction in grip strength 5

Rehabilitation After Immobilization

To address post-immobilization impairments:

• Begin progressive range of motion exercises after the immobilization period (typically 3-4 weeks) 2
• Implement directed home exercise programs including active finger motion exercises 2
• Consider referral to hand therapy for evaluation and treatment to prevent long-term disability 5

Key Clinical Pearls

• The position of immobilization is critical - avoid the classic position of elbow flexion with forearm pronation for Smith fractures, as this increases the risk of displacement 1
• Consider transitioning to a functional brace after initial immobilization that permits elbow motion while preventing forearm rotation 1
• Balance the need for adequate immobilization against the risk of stiffness and functional limitation
• Patients should be warned about the temporary functional limitations they will experience after cast removal 5