I would like to thank Dr. Kumar for his interest in our study and for raising several important questions. The first issue raised is the explanation for the higher failure rate in the long-arm cast group. As stated in the paper, this result was unexpected. Dr. Kumar suggests that this may be related to the fact that a larger number of the fractures treated in long-arm casts involved both the radius and ulna. As seen in figure 3, there was no significant difference in the distribution of fracture types when they were looked at individually. However, it does appear that when grouped by radius only vs. both bones, there is an uneven distribution (26 short arm and 38 long arm). When all fractures involving both bones are considered, these accounted for 26/53 (49.2%) of the short arm casts, and 38/60 (63.3%) of the long arm casts. Out of those 26 both bone fractures treated in short arm casts, only one failed (3.8%). Out of the 38 treated in long arm casts, there were 7 failures (18.4%). If the uneven distribution were the only explanation for the greater number of failures seen in the long-arm group, the total number of failures would be larger, but the rate of failure should be similar between the cast groups. Examining all of the failures, 8/11 (72.3%) involved fractures of both bones, whereas 6/11 (54.5%) were complete fractures. It does appear that instability may be more closely related to the involvement of both bones than to the amount of initial displacement.

The study by Bohm, et al, (1) published in the same issue, found that fractures involving the radius and ulna had a higher risk of losing reduction. As far as lumping together ‘stable’ and ‘unstable’ fractures, the numbers available in each specific subgroup in our study, unfortunately, were not large enough to conduct a meaningful statistical analysis without grouping them together.

The theoretical need to immobilize the elbow to prevent forearm rotation has certainly been a major historical argument for the need to use long-arm casts to treat these fractures. This notion along with a basic fracture principal that the joint proximal and distal to the fracture must be immobilized is a major reason this prospective randomized trial was undertaken. Both of these ideas are logical, but have not been supported by any clinical trials.

The question of the source of error in determining cast index raises a valid point. The distance from the x-ray tube to the x-ray plate was not measured in the study. However, if there were a systematic bias, one would expect to see a statistical difference in the average cast index between the short and long-arm casts, which was not seen. The only significant difference in the cast indices was seen in the cases that lost reduction. There should not have been any reason that long-arm cases that lost reduction were positioned any differently than those than maintained it.

In response to the final question raised, the results of our study suggest that it is as safe to treat a fracture of the distal third of the radius, ulna or both bones with a short-arm cast as it is with a long-arm cast. Fractures of the distal radial shaft were not specifically examined as a separate subgroup, but were included in both the long and short arm groups.

Even with the weaknesses of our study, taken with the results of the similar prospective randomized controlled trial by Bohm, et al,(1) we believe there is now strong clinical evidence that fractures of the distal third of the forearm in children can be safely and effectively treated with well -molded short-arm plaster casts.

References:

1. Bohm ER, Bubbar V, Hing KY, Dzus A. Above and Below-the-Elbow Plaster Casts for Distal Forearm Fractures in Children. Journal of Bone and Joint Surgery. 2006;88:1-8.

To The Editor:

I read with interest the paper, ‘Comparison of Short and Long Arm Plaster Casts for Displaced Fractures in the Distal Third of the Forearm in Children.’ by GR Webb, et al (1). I congratulate the authors on performing a prospective randomised trial, but I would ask them to respond to a number of remaining and important questions.

One of the results of this paper is that long arm casts have a higher failure rate than short arm casts. A possible reason described by the authors is that they ‘are technically more difficult to apply, which results in poorer molding around the forearm’. However, the authors’ method of applying a long arm cast was to apply a moulded short arm cast first and then convert it into a long arm cast. An extension of a short arm cast to a long arm cast should not be technically more difficult than applying a short arm cast alone. A more likely explanation for the disproportionate failure of long arm casts could be that more long arm casts were used to treat the ‘unstable’ variety of distal radius shaft fractures. From Fig 3, when both the radius and the ulna were fractured (combining partially and completely displaced fractures as a group,) only 11 short arm casts were used compared to 20 long arm casts. Thus, the numbers were not evenly distributed between the two cast groups.

Many would agree that managing a partially dorsally displaced Salter Harris type II distal radius fracture with closed reduction and a short arm cast is an appropriate procedure as it is a ‘stable’ fracture after reduction. However, a fracture of the distal diaphysis of the radius is not as stable as the physeal injury post reduction. Lumping together ‘stable’ and ‘unstable’ fractures does not allow us to judge whether short arm casts are appropriate for the ‘unstable’ variety of distal forearm fractures.

Unstable distal shaft of radius fractures with volar angulation (which very often include a variety of distal ulna fractures) can be immobilised with the wrist held in pronation or supination or neutral rotation.(2) No matter which rotational position is chosen, a short arm cast cannot successfully prevent supination in a wrist that is held in pronation and vice versa. Hence, theoretically, there is a higher risk of loss of reduction in these distal radius shaft fractures.

The authors, while discussing causes of error in the cast index, did not mention the distance from the X-ray tube to the X-ray plate which may not necessarily be the same when the antero posterior and lateral views are taken. This could bias against the long arm cast group as they are the ones that have more difficulty in changing position of the forearm for the two radiographs.

A long arm cast does limit a patient’s daily activities and does prolong recuperation time but that alone should not decide how a distal shaft of radius fracture should be managed.

The authors have not addressed the question that I would have liked them to answer: ‘Is it safer to manage a distal radius shaft (from metaphysis to distal third of the shaft) fracture in a short arm cast?’

References:

1. Webb GR, Galpin RD, Armstrong DG. Comparison of Short and Long Arm Plaster Casts for Displaced Fractures in the Distal Third of the Forearm in Children. Journal of Bone and Joint Surgery (American). 2006;88:9-17.

2. O’Brien ET. Fractures of the hand and wrist region. In Rockwood Jr, CA, Wilkins KE, King RE, editors Fractures in children. Vol.3 Rockwood and Green, 3rd ed. Philadelphia: JB Lippincott; 1991. p384 -386.