Focused rigidity casting: a prospective randomised study

A.P. COHEN and D.L. SHAW
Department of Orthopaedic Surgery, Bradford Royal Infirmary, Duckworth Lane, Bradford, UK

Introduction Methods and materials Results

Discussion Conclusion Acknowledgement References

Focused rigidity casting was compared with standard casting in a randomised prospective study. Two hundred consecutive patients attending a fracture clinic were assigned to have either a standard cast consisting of synthetic or plaster of paris, or a focused rigidity cast of synthetic material. Patients were assessed using a specially developed scoring system termed the Bradford Plaster Index. In patients with fractures of the base of fifth metatarsal, focused rigidity casting proved superior to traditional techniques for ability score (p=0.0001), satisfaction score (p=0.0023), overall impairment of function (p=0.019), limitation of movement following cast removal (p=0.024) and in limitation of muscle strength following cast removal (p=0.001). In fractures of the distal radius, focused rigidity casting was superior for ability score (p=0.0002) and satisfaction score (p=0.00009). Patients with scaphoid fractures were better for satisfaction score (p=0.0483). Compared with the standard technique, focused rigidity casting has been shown to be superior to traditional methods with regard to satisfaction and functional scores without any detriment to clinical results.

Keywords: casting, fracture, function, synthetic, scoring system

J.R.Coll.Surg.Edinb., 46, October 2001, 265-270

INTRODUCTION

Standard fracture treatment regimens involve immobilisation of the affected limb in a rigid, cylindrical cast until sufficient bony union allows mobilisation. Plaster of paris remains the most widely used material for this purpose, particularly because of its cost. Synthetic materials were introduced in the 1970’s, and the mechanical properties of these materials have been validated by previous authors. ^1-4

The suitability of synthetic materials in clinical practice has also been shown, as has the cost effectiveness of these materials. ^5-11 Despite this advancement in technology, however, the technique of applying casting materials has remained relatively unchanged. Focused rigidity casting was described by Wierzimok et al (1996). ¹² This technique involves the use of elasticated synthetic tape in a more structured manner, applying most of the material (up to five layers) around the fracture site to confer relative rigidity, whilst sparing material proximally and distally, with a minimum of one layer at the ends of the cast to produce a more flexible construct. Reinforcement of the construct, for example in the case of below knee casts, can be achieved using additional slabs of material. The resulting casts, therefore, are expansible to allow for swelling, and are also semi-flexible to allow excursion of soft tissues around the fracture site and to allow removal of the cast without altering its integrity. This may allow relatively more movement of muscle groups acting around the fracture site, thereby, minimising muscle atrophy. The cast, in addition, is not completed cylindrically, allowing adjustment to accommodate swelling, thus sparing the need for change of cast, with the potential problems of loss of position of the fracture. In addition, when clinical judgement allows, the patient can remove the cast for bathing and other activities of daily living, thereby exercising the injured part (Figure 1). Casts constructed using this technique require an average of 55.5% of the synthetic material, when compared with the standard technique, measured by weight of the cast.

METHODS AND MATERIALS

Following informed consent, 200 patients with arm and leg injuries requiring cast support were randomised to receive either a complete plaster of paris or synthetic (standard) cast, or a focused rigidity cast (FRC). All these injuries were minimally displaced, and suitable for conservative treatment from the outset. None required manipulation either initially or during the treatment period. Fractures displaying an ‘ unstable’ configuration were excluded, as were patients under 16 years or those with psychiatric morbidity rendering their participation in this study unsafe. The synthetic material used was ‘Deltacast Conformable’ (DePuy Johnson and Johnson). A literature search revealed no suitable cast function scoring system. Accordingly, we developed a scoring system based on questionnaires validated by previous authors. ^13,14 The resulting Bradford Plaster Index involves assessment of ten activities of daily living, scoring for ability and satisfaction. A visual analogue scale for ability in the cast compared with the pre-fracture state was also included, and separate gradings for comfort and overall ability were recorded on a four-point scale. Data was collected on cast application, at each followup visit, and at cast removal (Figure 2).

Following completion of treatment and removal of the cast, the patients were assessed for limitation of movement and reduction of muscle strength by comparing these modalities with the contralateral limb. This assessment was performed by a member of the medical staff who was not informed of the type of cast used for the individual patient. Limitation of movement was assessed by measuring the range of motion of both sides and categorising the patients depending on whether they displayed no limitation of movement, slight reduction (up to 25%), moderate reduction (up to 50%), or severe reduction of movement (greater than 50%). In the assessment of power, clinical assessment enabled the categorisation of patients into one of four groups depending on loss of power, compared with the contralateral side. The categories were equal power, slight reduction (up to 25% deficit), moderate reduction (up to 50% deficit) and severe reduction (greater than 50% deficit). A final subjective grading was obtained of overall satisfaction with treatment; a four-point scale was used with a maximum score of 4 indicating the least favourable outcome (Figure 3).

All patients in both groups had their casts definitively removed as indicated in our departments’ protocols for each type of fracture. The Mann-Whitney U test was used to analyse the scores for ability and satisfaction. The Monte Carlo one tailed exact test was used to analyse the patients’ scores for overall function, comfort in cast, limitation of movement following removal of cast, comparison of muscle strength and overall satisfaction with treatment. The two sample t-test was used to analyse impairment of function on the visual analogue scale.

Figure 1 (a): Distal radial cast                 Figure 1 (b): Fifth metatarsal cast

RESULTS

Four main injury types were identified and grouped according to the type of cast applied. Patients with injuries other than these types were excluded from analysis because of small numbers. Complete casts using plaster of paris comprised only 22 of the total and were excluded leaving 115 patients. The groups and numbers included are shown in Table 1.1 Comparison of ability scores between those patients treated in FRC, and standard casts shows that in all groups, other than the ankle fracture group, the patients reported an increase in ability when treated with the FRC casts, statistically significant for the patients with distal radius (p=0.0002) and fifth metatarsal fractures (p=0.0001) (Figure 4). In the case of ankle fractures, the difference demonstrated in favour of standard casting was not statistically significant (p=0.644).

A similar comparison of satisfaction scores between the patients again showed that, other than the ankle fracture group, all groups reported greater satisfaction in FRCs, statistically significant for distal radial fractures (p=0.00009), scaphoid fractures (p=0.0483) and fifth metatarsal fractures (p=0.0023) (Figure 5). Although ankle fracture scores for satisfaction showed a slight difference in favour of standard casting, this was not statistically significant (p=0.535).

Comparison of the patients’ overall assessment of function indicated a statistically significant difference in favour of fifth metatarsal base fractures treated in FRCs (p=0.019) (Figure 6).

Figure 2: The Bradford Plaster Index

Figure 3: The completion of treatment assessment form

Responses on the visual analogue scale for each group and analysis of comfort in the casts indicated no significant differences between the groups. Following removal of the cast, those patients treated in FRCs, for fractures of the base of the fifth metatarsal, showed a statistically significant reduction in limitation of movement (p=0.024) (Figure 7).

Loss of muscle strength compared with the contralateral side following cast removal was also significantly better (p=0.001) following treatment in FRCs, when compared with patients treated with standard casts for fractures of the base of fifth metatarsal (Figure 8).

Overall satisfaction with treatment showed no significant difference between the two groups for each fracture type. All casts were removed according to the protocols for treating these injuries in our department. There were no cases of clinically delayed union in any of the treatment groups. In two patients with scaphoid fractures, one patient with a fracture of the base of the fifth metatarsal and one patient with a fractured lateral malleolus treated by FRCs, and in one patient with a fracture of the base of the fifth metatarsal treated by standard casting, there was radiological evidence of incomplete union at the time of cast removal. None of these patients have gone on to develop delayed or non-union. Adjustment of the FRCs, where required, consisted only of tightening by trimming a strip of material along the length of the cast. No casts required loosening. Instead of adjustment, three FRCs needed to be replaced because of damage sustained during use. In addition, we refitted nine FRCs because of rubbing. Twenty-five standard casts were replaced because of rubbing, or the need for clinical examination of the limb.

   Figure 4: Change in ability scores following casting           

   Figure 5: Change in satisfaction scores following casting

DISCUSSION

Focused rigidity casting was compared in our study with standard casting using synthetic casting materials in both groups. Our results indicate that focused rigidity casting is better than standard casting for patient satisfaction in performing ten activities of daily living in the case of fractures of the base of the fifth metatarsal, fractures of the distal radius and scaphoid fractures. Ability to perform these tasks is also better with fractures of the base of the fifth metatarsal and distal radius. In addition, fractures of the base of the fifth metatarsal treated by FRCs are better for overall function, reduction of limitation of movement and preservation of muscle strength following cast removal. No statistically significant differences were found in favour of standard casts.

The technique of focused rigidity casting can be recommended in the treatment of fractures of the fifth metatarsal and distal radius in preference to standard casts. Focused rigidity casting provides greater ability in the cast and patient satisfaction during treatment without loss of clinical effectiveness. It also seems probable that fractures of the scaphoid should be treated by this technique.

Casts constructed by this technique are less expensive than standard casts, and there is also a reduced requirement for changing the cast, with a single cast suitable for the entire treatment programme in most cases. This represents a cost saving using this method, compared with standard techniques. This study has demonstrated that this has been achieved without loss of effectiveness of the treatment.

CONCLUSION

Despite developments in casting materials, the use of new and innovative casting techniques has not been widely reported or subject to rigorous scientific investigation. Rather it has remained the domain of the ‘artisan’ cast technician. This study has addressed this issue. Further clinical studies and studies of the mechanical properties of various casting methods are being undertaken.

Figure 6: Functional ability in the casts

Figure 7: Limitation of movement following cast removal

   Figure 8: Muscle strength following cast removal

ACKNOWLEDGEMENT

We would like to thank Sister Anne Petty and the staff of the Plaster Room at Bradford Royal Infirmary for their contribution to this study, both in application of casts and collection of data. We should also like to thank Georgina Havers, Clinical Research Assistant, Johnson and Johnson, for her assistance with the statistical analysis of the results we have presented, and the Departments of Medical Illustration at York District Hospital and Bradford Royal Infirmary for the preparation of the photographs and tables we have presented.

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Copyright date: 7th July 2001

Correspondence: A.P. Cohen, Department of Orthopaedic Surgery, Bradford Royal Infirmary, Duckworth Lane, Bradford BD9 6RJ, UK
E-mail: andrewcohen_uk@yahoo.co.uk