Subcutaneous depth in a traumatized lower extremity

Acute compartment syndrome is a rare but serious consequence of traumatic leg injury. Near-infrared spectroscopy (NIRS) is able to measure oxygenation to a depth of 2 cm to 3 cm below the skin, raising concerns over the ability of NIRS to accurately determine oxygenation of injured leg compartments in the presence of swelling and in the obese. The purpose of this study was to measure the thickness of the subcutaneous tissue overlying the posterior muscle compartment in subjects with tibia fractures to determine if it might compromise rSO₂ measurement in the muscle.

Data were analyzed on 50 patients with severe leg injuries. Distance from the skin to the fascia in the superficial posterior compartment of both legs was measured on each patient using a portable ultrasound device.

Subject age ranged from 18 years to 65 years (mean, 39 years), with 43 male and 7 female patients. The mean (SD) subcutaneous adipose tissue thickness (ATT) was 6.98 (3.17) mm for the injured leg and 7.06 (3.37) mm for the uninjured leg, and the mean body mass index for the group was 27.08 kg/m. No significant correlation was found between the ATT of the injured or uninjured legs and body mass index. Mean comparison testing revealed no difference in ATT between the injured and uninjured legs (null hypothesis: equal means, p > 0.05). Of the 50 subjects analyzed, no subject had a subcutaneous depth of more than 2 cm on the injured or uninjured leg.

These data suggest that, within this traumatically injured population, symptoms associated with leg injury (such as swelling and edema) do not significantly affect the distance from the skin to the fascia. It is also notable that subcutaneous depth beyond the 2-cm mark (validated in previous studies) is a rare occurrence in this population. These results further support the use of continuous NIRS monitoring for diagnosis of acute compartment syndrome.

Therapeutic study, level IV.