Keeping casts dry: A comparison of commercially available cast protectors using a mechanized short arm cast model

Background: Upper extremity fractures requiring cast immobilization are exceedingly common, especially in the pediatric population. Studies have shown improved outcomes when patients can participate in water-based activities while casted. However, waterproof cast material is not feasible in all clinical settings and wet cast complications remain a source of morbidity and expense. External cast protectors play an important role in preventing wet casts, but the efficacy of various commercially available brands during relevant water-based activity remains unknown. Purposes: To determine if there are differences in the rate and extent of moisture exposure for four commercially available cast protectors using a mechanized cast arm model and human volunteers. Methods: A mechanized arm model was developed with four implanted humidity sensors. Cast protectors were applied over the arm, the model was submerged in water, and moved back and forth, simulating cast-wearers’ motion. Data regarding humidity was recorded for successive 10-minute trials. Trials were analyzed using a mixed effects linear model to determine change in humidity over time. The top and bottom performing cast protectors were then applied to four adult volunteers prior to thirty minutes of swimming. Questionnaires regarding comfort and a qualitative assessment of cast wetness using a chemical color indicator were completed. Results: 372 instances of sensor data from 96 10-minute trials was collected. The CVS, SealTight and Walgreens brands showed significant increases in humidity beginning at 10, 20 and 20 minutes, respectively. DryPro showed no significant increase in moisture level up to 50 minutes. In successive trials up to 120 minutes, DryPro showed only a 2% increase in moisture. In human subjects testing, 3/4 casts underneath CVS protectors had some degree of wetness-related color change that would require cast change as compared to 0/4 casts underneath DryPro protectors. Conclusions: Significant differences exist between commercially available cast protectors. Vacuum-sealed protectors performed best in both mechanical and human subject portions of this study and allowed minimal change in humidity for extended periods of sequential water immersion. Their cost is notably less than management of a wet cast. Lower-performing products may expose cast-wearers to an increased risk of wet cast complications.