A Radiographic Study Of Scaphoid Movement In A Conventional Short Arm Cast

摘要

It has been long debated whether inclusion of the thumb in a cast is necessary for scaphoid immobilization. This study aims to evaluate scaphoid movement in a conventional short arm cast with the thumb held in different positions using four standard radiographs. Four subjects (group A - control) were placed in short arm casts and radiographs taken with the thumb in a neutral position. Ten subjects (group B) were placed in short arm casts and radiographs taken with the thumb in abduction, adduction, flexion, and extension. The maximum amount of movement of the scaphoid between each thumb position was recorded for both groups. The mean maximum movement was compared using a student t-test. A mean maximum scaphoid movement of 1.06mm (sd 0.826) in group A and 2.35mm (sd 0.53) in group B. This was statistically significant with a p-value <0.002 using a student t-test. There have been numerous studies comparing short arm casts and short arm thumb spica casts. To date, there is no evidence supporting the inclusion of the thumb metacarpophalangeal joint in scaphoid fractures and subsequent non-union. Within its limits, this paper has shown that with exclusion of the thumb, there is significant scaphoid movement. Introduction There have been numerous studies conducted on scaphoid fractures. There is debate on the best method treatment including long arm thumb spicas, short arm thumb spicas, conventional short arm casts or bandaging. There is no consensus on materials used for immobilisation, the position of the wrist in cast, duration in cast, or degree of displacement in the decision to proceed with surgery.There is postulation that micromotion of the scaphoid occurs with thumb movement and therefore, the thumb must be immobilised to minimise the risk of scaphoid non-union. But the carpus is a structure of intercalating, interlocking bones. Movement of a single carpal bone should be accompanied by movement of the entire carpus. By immobilising the carpus in a short arm cast, we seek to prevent scaphoid movement. Morbidity from stiffness of the first carpometacarpal joint can be prevented and freedom of thumb movement allows for overall greater hand function.To date, there is no study on scaphoid movement in a conventional short arm cast with different thumb positions. Methods After obtaining ethics committee approval and informed consent, 14 healthy individual subjects aged between 18 and 34 were enrolled into the study. Four subjects were allocated to the control group (Group A) and 10 to the experimental group (Group B).All subjects had moulded conventional short arm fibreglass casts with the wrist in neutral.Four radiographs were obtained from subjects in group B with the thumb in maximal abduction, extension, flexion and neutral. Four radiographs were taken in an identical manner from subjects in group A with the thumb in resting position and without movement between the radiographs.The radiographs were performed by a senior radiographer onto a standard x-ray plate. The pronated forearm was resting on a foam bed with the same distance from the x-ray plate for all subjects.An outline of the carpal bones and wrist were obtained from all radiographs using a sharp lead pencil and tracing paper. The tracings of the distal ends of the radius and ulna for each individual were identical between radiographs. This was used as a reference point for comparisons.The maximum distance between the tracings of the scaphoid in the four radiographs of each individual was recorded. All measurements were done using a precision ruler to the nearest 0.25mm. This was thought to be the maximum quantative measure of Scaphoid movement. The mean figure for each group was calculated and the means analysed for statistical difference using the standard student t-test. Results Maximal scaphoid movement in Group A and B are shown in table 1. The average movement is 1.06 ± 0.826 (95% CI 0.5773 – 1.548) for Group A and 2.35 ± 0.530 (95% CI 2.043 – 2.657) for Group B