How to Apply a Posterior Slab in Colles Fracture
Apply a posterior splint extending from the upper arm to just proximal to the metacarpal heads with the wrist in slight palmar flexion (not marked flexion) and the elbow at 90 degrees, using a near-encircling technique with proper three-point molding to maintain reduction. 1
Positioning and Preparation
Position the forearm with the elbow flexed to 90 degrees and the wrist in slight palmar flexion rather than marked palmar flexion—this represents a significant change from older practice and improves outcomes. 1
The forearm should be in neutral rotation (thumb pointing upward) to optimize reduction maintenance. 1
Splint Construction Technique
Use plaster slabs that extend from the upper arm (just below the elbow crease posteriorly) down to just proximal to the metacarpal heads, creating a near-encircling slab rather than a fully circumferential cast. 1
Apply 8-10 layers of plaster to create a strong slab capable of safely maintaining reduction—inadequate thickness is a common pitfall that leads to loss of reduction. 1
The slab should cover approximately 2/3 to 3/4 of the circumference of the forearm, leaving a gap anteriorly to allow for swelling. 1
Critical Molding Technique
Apply three-point molding immediately after slab application while the plaster is still malleable:
- Apply pressure dorsally over the distal fracture fragment
- Apply counter-pressure volarly at the fracture site
- Apply pressure dorsally at the proximal forearm 1
Maintain this molding pressure continuously for 5-7 minutes until the plaster has fully set—premature release of molding pressure is a major cause of reduction loss. 1
Avoid creating pressure points over bony prominences, particularly the ulnar styloid and radial styloid. 1
Post-Application Management
Split the slab fully if there is any concern for swelling to prevent compartment syndrome, though the near-encircling design inherently allows for expansion. 1
This slab can be converted to a definitive encircling cast at follow-up (typically 7-10 days) once swelling has subsided, making it both time and cost-effective. 1
Obtain radiographs immediately after application to confirm maintained reduction, then repeat at 1 week to detect any early loss of position. 2
Common Pitfalls to Avoid
Never use marked palmar flexion—slight palmar flexion is sufficient and reduces complications while maintaining reduction. 1
Inadequate slab thickness (fewer than 8 layers) will fail to maintain reduction in unstable fractures. 1
Insufficient molding or releasing molding pressure too early leads to predictable loss of reduction. 1
Extending the slab too far distally (beyond the metacarpal heads) restricts finger motion and increases stiffness risk without improving fracture stability. 1
When Posterior Slab is Insufficient
For severely displaced or comminuted Colles fractures, particularly in younger patients, posterior slab immobilization alone may be inadequate—these fractures often require percutaneous pinning or external fixation to maintain reduction. 3, 4, 5, 6
If initial reduction cannot be maintained with closed methods, consider operative intervention with locking plates, Kirschner wires, or external fixation rather than accepting malunion. 2