Effects of Upper Extremity Elevation on Intra-Cast Pressure and Digital Perfusion in a Fiberglass Short-Arm Cast...

The goal of this study was to determine the relationship of digital artery pressure to arm position and forearm skin surface pressure using a short-arm cast experimental setup, to ascertain the safest position for the injured casted upper extremity. A total of 27 volunteers were placed in bilateral short-arm fiber-glass casts with an empty 50-mL bladder bag under the cast and attached to a pressure transducer. Digital systolic pressure (P_dig), and skin surface pressure under the cast (P_skin) were assessed in 4 positions. Measurements were taken with and without 50 mL air in the bladder bag. A total of 54 forearms were evaluated. Both arm position and P_skin had a significant effect on P_dig (P<.001 for both), with increasing elevation leading to a decrease in P_dig (r=-0.50). The effect size of position on P_dig was large, whereas that of Pskin was small (partial eta-squared=0.371 and 0.028, respectively). Linear regression analysis of P_skin and P_dig with air in the neutral position yielded a moderate negative relationship with body mass index (r=-0.64, P<.001 for P_skin; r=0.49, P<.001 for P_dig) and wrist circumference (r=-0.66, P<.001 for P_skin; r=0.52, P<.001 for P_dig), without significant association with forearm length. For volunteers with short-arm fiberglass casts, increasing arm elevation had a large effect size on digital arterial pressure, whereas 50 mL simulated swelling had only a small effect size. Decreasing body mass index and forearm circumference correlated with increased skin surface pressure and decreased digital arterial pressure. These findings show that aggressive elevation of the injured limb may not be as desirable as previously believed. [Orthopedics. 2021;44(4):e487-e492.].