Predicting initial treatment failure of fiberglass casts in pediatric distal radius fractures: utility of the second metacarpal-radius angle

PURPOSE Recent literature comparing the effectiveness of above-elbow and below-elbow plaster casts appears to suggest that either cast type offers adequate immobilization for distal radius and ulna fractures. The idea that an appropriate mold placed on the cast is the most significant determinant of successful immobilization and, thereby, patient outcome has also been elucidated. The purpose of this study was to compare the effectiveness of above-elbow versus below-elbow fiberglass casts in maintaining distal radius/ulna fracture reduction and to identify factors associated with treatment failures. METHODS We reviewed the radiographs and clinical data of 253 children with distal third forearm fractures requiring reduction under conscious sedation or a hematoma block. Outcome measures included rates of re-manipulation, loss of reduction, and cast complications. RESULTS One hundred and nineteen children were treated with below-elbow fiberglass casts and 134 were treated with above-elbow fiberglass casts based on a clinical pathway created before the study period. There were no differences between the two groups in age, weight, fracture pattern, percentage of both-bone fractures, and initial fracture angulation. Of the 253 fractures in the study, 38 (15%) were considered to have less than ideal outcomes. There were no differences between the 'ideal' and 'non-ideal' groups in age, fracture pattern, presence of ulna fracture, cast index, or cast type. All immediate post-reduction measures (anterior-posterior [AP] and lateral displacement/angulation) were significantly correlated with treatment outcome, except angulation on AP films. The magnitude of reduction as measured by a newly described variable, the angle between the second metacarpal and long axis of the radius in the AP projection, was significantly correlated with treatment failure (r = -0.139, P = 0.027). Binary logistic regression was performed and demonstrated that the success of the reduction, as determined by the AP radiograph second metacarpal-radius angle, was a significant predictor of treatment success (odds ratio 1.6, P < 0.001). Also, the change in lateral view angulation post-reduction was a significant predictor of treatment failure based on regression (odds ratio 1.2, P = 0.004). The above-elbow cast group had a slightly greater cast index (0.80) compared to the below-elbow cast group (0.77) (P = 0.003). Whereas below-elbow fiberglass casts appear to be equally effective in immobilizing pediatric distal third forearm fractures as above-elbow fiberglass casts, it seems that they have an increased risk for poor molding, particularly with regards to ulnar deviation. We did not find an association between the treatment 'failure' and cast index, likely because the number of poor molds (cast index >0.8) was nearly equal in each group (above-elbow with 61 and below-elbow with 45). However, the mold seen on the AP radiograph as determined by the second metacarpal-radius angle was a reproducible radiographic predictor of treatment success. If molded with ulnar deviation (second metacarpal-radius angle >0 degrees ), the outcome was considered to be ideal in 86.7% of cases compared to only 74.4% when it was <0 degrees . CONCLUSION We agree with prior studies suggesting the equal efficacy of below-elbow versus above-elbow casts in distal radius and ulna fracture treatment using either plaster or fiberglass, but wish to emphasize the importance of not only the cast index, but also the ulnar deviation mold (for most dorsally displaced fractures), as measured by the second metacarpal-radius angle.