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The Effects of Upper Extremity Elevation on Intra-Cast Pressure and Digital Perfusion in a Fiberglass Short Arm Cast Model
Asif Ilyas, MD, Orthopaedics, Rothman Institute at Thomas Jefferson University, Philadelphia, PA and Brianna Fram, MD, Thomas Jefferson University, Philadelphia, PA

Conventional wisdom is that elevation of an injured extremity decreases edema and pain, but there is also conflicting evidence that limb elevation can also lead to decreased tissue perfusion. We sought 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.

Twenty-seven volunteers were placed in bilateral short-arm fiberglass casts with an empty 50cc bladder bag under the cast, which was attached to a pressure transducer. Digital systolic pressure (“Pdig”), and skin surface pressure under the cast (“Pskin”) were assessed in four positions: with participants supine with their arm at their side (“neutral”), supine with their arm at 45⁰ (“45”), sitting upright with their arm on their lap (“lap”), and sitting upright with their arm at 90⁰ vertically (“90”). Measurements were taken without (“baseline”) and with (“air”) 50cc of air in the bladder bags. Baseline demographic and biometric data was collected.

Fifty-four forearms were evaluated. Arm position and Pskin both had a significant effect on Pdig (p<0.001 for both), with increasing elevation leading to a decrease in Pdig (R=-0.50). 2-way ANOVA showed the effect size of position on Pdig was large, while that of Pskin was small (partial Eta squared=0.371 and =0.028, respectively). Linear regression analysis of Pskin and Pdig with “air” in neutral position yielded moderate negative relationship with BMI (R=-0.64, p<0.001 for Pskin, R=0.49, p<0.001 for Pdig) and forearm circumference (R=-0.66, p<0.001 for Pskin, R=0.52, p<0.001 for Pdig) without significant association with forearm length.

Using an experimental setup for simulating edema under a short arm fiberglass cast, we found that increasing upper extremity elevation negatively effects digital arterial pressure distal to the cast. While increasing skin surface pressure under the cast rom simulated edema also had a significant negative effect on digital artery pressure, this effect size was small compared to a larger effect size for limb elevation. We caution orthopedic providers against recommending excessive elevation of the casted injured extremity due to its potentially negative effect on distal perfusion.

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