It is accepted practice that casts are applied so that we extend them to the boundaries created by the joint above and the joint below the injured area. In the case of the below elbow cast, applied for a distal radial fracture, this means that the cast extends from the metacarpal heads to the antecubital fossa.
In the years during which I have applied below elbow casts, I have become uncomfortable with casts which extend as far as the metacarpal heads. I also dislike the cast application technique which makes a cut in the cast tape at the thumb.
Then several folds of casting tape are taken through the 1st web space between the thumb and the index finger. Given that this is the accepted wisdom for applying a below elbow cast, I should state why I am unhappy with the current usual method of applying the casting tape for a below elbow injury.
A frequently seen problem with taking the cast edge as far as the metacarpal heads is that of preventing full flexion at the metacarpophalangeal (MCPJs) joints, especially where the volar aspect of the hand is enclosed by a cast which extends to the MCPJs.
It will be known that a failure to fully extend or flex the fingers at all of the joints, may potentially lead to contractures of the flexor tendons. The rehabilitation process is then delayed and we may leave the patient with a residual functional problem.
The casting technique that cuts the tape and winds it through the web space between the thumb and index finger is seen to rest on the 1st metacarpal. This limits the movement of the thumb and once again, it has implications for recovery and rehabilitation.
Where the 1st metacarpal is fixed, the pinch grip function of the patient is limited and it is highly probable that it is detrimental to the healing process... that is to say that the patient is having their movements limited unnecessarily.
I favour a method of cast application which keeps the cast below the metacarpal heads on the dorsal aspect of the forearm/wrist/hand and which comes to below the distal palmar crease (I much prefer to cast to the proximal palmar crease) on the volar aspect of the hand.
The thumb appears to play no part in stabilising distal radial fractures so I have found it beneficial to leave the thumb free to move. My patients appear not to experience any pain because I have given them the freedom to move their thumb and fingers. They also appear to heal within the usual expected healing times.
In conjunction with adequate cast moulding across the volar and dorsal surfaces of the forearm, to prevent the radius from crossing the ulna and preventing rotation inside the cast, it is even possible not to have any cast bar between the thumb and the index finger web space.
I have successfully used this method on all children and many elderly patients, where a solid bar of cast material can cause pressure on the web space where the thumb is not moved frequently enough. I finish the cast at a width of three fingers from the antecubital fossa.
Where a two finger width is used, patients who were quite fleshy on the forearm would complain that they could not bend the elbow to 90 degrees without feeling the cast edge impinging on the flexor surfaces of the elbow joint.
Lateral image showing thumb free to move. The cast has been padded at the edges with 2mm Hapla Fleecy Web
Dorsal image showing cast edge proximal to MCPJs. The cast shows that flexion at the MCPJs is not inhibited
Volar image demonstrating the cast boundary at the distal palmar crease. The cast ends at the distal palmar crease leaving room to flex the MCPJs