Casting Position for Distal Radius Fractures Changes Radiocarpal Joint Forces: A Cadaveric Study.

Purpose: Nonsurgical distal radius fracture treatment requires immobilization and classical teaching suggests varying cast positions. We investigated the effect of cast position on the force and pressure experienced by the articular cartilage in the scaphoid and lunate fossae.

Methods: Ten fresh-frozen cadaveric specimens were used. A standardized extra-articular distal radius fracture was made. Force sensors were affixed to the articular cartilage of the scaphoid and lunate fossae. Baseline data were obtained. Specimens were then placed into a short arm cast with the wrist either neutrally aligned or flexed and ulnarly deviated (FUD). Specimens had a standard load applied, and a force profile was obtained. The cast was removed and the other cast type was placed and measurements were repeated. Overall force and pressure values were compared between baseline data and the 2 cast types. Additionally, differences in volar and dorsal scaphoid and lunate fossa forces and pressures were compared pairwise within the 2 cast types. The relative force and pressure values across cast types were also compared.

Results: Both cast types significantly reduced the median force and pressure experienced by the radiocarpal joint compared with no cast. In the FUD cast, the volar and dorsal lunate fossa experienced significantly greater force, and the dorsal lunate fossa experienced significantly greater pressure compared with the dorsal scaphoid fossa. There were no differences for any fossae in the neutral cast. When comparing between casts, the volar lunate fossa experienced a significantly greater relative force in the FUD cast compared with the neutral cast.

Conclusions: Casting a distal radius fracture decreases the forces and pressures in the radiocarpal joint. Placing the wrist in a FUD position results in greater forces and pressures on the lunate fossa compared with the scaphoid fossa.

Clinical Relevance: When immobilization is needed, we advocate for the placement of patients in a relatively neutral short-arm cast with minimal FUD to avoid this increased pressure.