This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn.

The use of plaster of Paris (POP) and fibreglass (FG) for the immobilisation of fractures of the arm and the leg.

Treatment.

Cost-effectiveness analysis.

The study population comprised patients aged at least 10 years with a fracture of the arm or leg, who had an expected immobilisation period of at least 4 weeks in a short cast of the arm or leg. The patients were required to have normal intact skin that was free of injury and other dermatological conditions in the area to be covered by the cast. Patients with fractures complicated by skin conditions that necessitated removal of the cast in less than 4 weeks for inspection were excluded, as were patients with allergies to casting materials. Also excluded were patients with other co-morbid conditions, such as osteomyelitis, severe dementia, or rheumatoid arthritis.

The setting was an army medical centre. The economic study was conducted in the USA.

The dates during which the resource use and effectiveness data were gathered were not reported. The price year was not given.

The effectiveness evidence was derived from a single study.

The costing was conducted prospectively on the same sample of patients as that used in the effectiveness study.

The use of power calculations was not reported. An initial sample of 183 patients was identified. Of these, 27 were excluded because they were immobilised for fewer than 4 weeks (16) or they failed to return to the clinic after the initial cast application (11). This left a sample of 156 patients. There were 79 patients in the FG group (43 short arm casts and 36 short leg casts) and 77 in the POP group (39 short arm casts and 38 short leg casts).

This was a prospective, randomised clinical trial that was conducted at a single centre, the Department of Orthopedic Surgery at the Madigan Army Medical Center in Tacoma. Randomisation was based on a computer-generated table. Qualified cast technicians (including both active duty personnel and civilian contracted technicians) selected the casting materials. The patients were followed until cast removal. Eleven patients did not return to the clinic after the initial cast application, but it was unclear whether these patients were considered as a loss to follow-up. The outcome assessment was not blinded.

It was unclear whether the analysis of the effectiveness was conducted on an intention to treat basis since some patients initially identified as eligible were not included in the effectiveness analysis. The outcome measures used in the analysis were:

the rate of cast breakdown, defined as cast damage requiring removal and replacement;

comfort assessment, using a questionnaire with a score ranging from 0 (objectionable) to 7 (tolerable); and

ADL assessment, using a questionnaire with a score ranging from 0 (no difficulty) to 7 ("unable to do").

The study groups were comparable at baseline in their age, weight and patient height.

In short arm casts, the rate of cast breakdown was 33% with POP and 21% with FG, (p=0.329).

In short leg casts, the rate of cast breakdown was 66% with POP and 17% with FG, (p=0.01).

For short leg casts, the overall comfort score was 3.9 with POP and 4.9 with FG, (p=0.01).

Among the five dimensions of comfort, statistically significant differences were observed for the weight of the cast (3.94 versus 5; p=0.01) and sweat under the cast (4.3 versus 5.3; p=0.04).

For short arm casts, the overall comfort score was 4.4 with POP and 5 with FG, (p=0.12). Statistically significant differences in the weight of the cast (4 versus 5.4; p<0.01) were observed.

In terms of ADL, FG patients with short leg casts rated them significantly better than POP patients for dressing (2.2 versus 1.8; p=0.04), work or home accomplishment (3 versus 2.3; p=0.04), and fewer limitations on daily activities (3.5 versus 2.9; p=0.01).

No statistically significant differences were observed for short arm casts.

The effectiveness study showed that, compared with POP, FG led to significant improvements in comfort and in some measures of ADL for short leg casts. No significant differences were observed for short arm casts.

The health outcomes were left disaggregated and no summary benefit measure was used in the economic analysis. In effect, a cost-consequences analysis was conducted.

Discounting was not relevant since the costs were incurred during a short time. The unit costs were presented separately from the quantities of resources for some items. A detailed breakdown of the cost items was provided. The health services included in the economic evaluation were materials and labour time for casting application and maintenance. Unscheduled visits were also considered. The time to harden was not included in the casting time. The cost/resource boundary of the study appears to have been that of the service provider, although it was not explicitly stated. The cost data were derived from the Information Management System, which averaged prices charged to different customers in the USA. Resource use was estimated from the sample of patients who were involved in the effectiveness study. The price year was not reported.

The costs were treated deterministically.

The indirect costs were not considered.

US dollars ($).

Sensitivity analyses were not conducted.

See the 'Effectiveness Results' section.

In short arm casts, the total costs per fracture were $12.90 with POP and $15.45 with FG.

In short leg casts, the total costs per fracture were $49.02 with POP and $47.85 with FG.

A synthesis of the costs and benefits was not relevant since a cost-consequences analysis was conducted.

Patient comfort and some aspects of activities of daily living (ADL) were better with fibreglass (FG) than with plaster of Paris (POP), especially for short leg casts. Other effectiveness results were comparable between the groups. Likewise, despite the higher initial acquisition costs of FG, the overall costs were similar since FG had a lower breakdown rate.

The authors discussed the reasons for their choice of the two interventions. POP represented a standard procedure for the immobilisation of a fracture and its clinical and economic characteristics were well known. On the other hand, FG was a newer synthetic cast that had some advantages over POP (stronger, lighter and more durable), although it was more expensive. Therefore, the choice of the comparators appears to have been appropriate. You should decide whether they are valid comparators in your own setting.

The effectiveness study was based on a clinical trial, which was appropriate for the study question. The method used to allocate the patients to the study groups was reported, as was the method used to select the sample. The study groups were comparable at baseline. Some patients did not return to the clinic for further evaluation and were excluded from the effectiveness analysis. Therefore, the analysis of the clinical study could have been conducted on the basis of treatment completers only, rather than on intention to treat. The evidence came from a single institution in a particular setting (army medical centre). Thus, it was unclear whether the study sample was representative of the patient population. Also, the demographics of the study patients were not reported and there was no evidence that the sample size was appropriate. The sample could, therefore, have been underpowered to detect statistically significant differences between the groups in some outcome measures. These issues could limit the internal validity of the analysis.

No summary benefit measure was used in the analysis because a cost-consequences analysis was conducted.

The authors did not explicitly state which perspective was adopted in the study, but it appears that the costs relevant to the service provider have been considered. Information on the unit costs and the quantities of resources used was presented separately only for some items. The cost calculations were reported in detail. This enhances the possibility of replicating the study in other settings. No statistical analyses of the costs were conducted. The authors stated that the costs used in the analysis reflected the average prices charged to different customers across the USA. The price year was not reported, making reflation exercises difficult. The source of the data was unclear, but it could have been the army medical centre where the study was conducted.

The authors did not compare their findings with those from other studies. They also did not address the issue of the generalisability of the study results to other settings. Sensitivity analyses were not conducted and the estimates were specific to the study setting, adversely affecting the external validity of the analysis. The study involved short arm or leg casts for at least 4 weeks and this was reflected in the authors' conclusions. The authors noted that POP could be the preferred options in certain clinical situations, while FG might be more desirable in military environments.

The study results suggested that the casting material should be chosen on the basis of clinical rather than financial reasons.

None stated.

Marshall PD, Dibble AK, Walters TH, et al. When should synthetic casting material be used in preference to plaster of Paris? A cost analysis and guidance for casting departments. Injury 1992;23:542-4.

Bowker P, Powell ES. A clinical evaluation of plaster of Paris and eight synthetic fracture splinting materials. Injury 1992;23:13-20.