Background: Acute compartment syndrome has been an underreported
complication during spine surgery with the patient positioned on the so-called
90/90 kneeling frame (with 90° of both hip and knee flexion), presumably
because of elevated intramuscular pressures in the dependent leg compartments.
The purpose of the present study was to characterize and quantify certain
parameters that affect the risk for acute compartment syndrome experimentally
and to make objective comparisons with other spine surgery positions.
Methods: Eight healthy volunteers were positioned in three spine
surgery positions: the 90/90 kneeling position, the so-called 45/45 suspended
position (with the hips and knees both flexed to 45° with the legs
suspended on a sling), and the prone position. Intramuscular pressures were
measured in all four left leg compartments with slit catheters. Local blood
pressure and applied load beneath the leg were also measured.
Results: The 90/90 kneeling position was associated with
significantly increased intramuscular pressure in the anterior compartment
(30.8 ± 5.7 mm Hg) in comparison with the prone position (13.5 ±
1.7 mm Hg) and the 45/45 suspended position (13.8 ± 1.7 mm Hg). In the
90/90 kneeling position, these values correlated with subject weight (r =
0.72, p = 0.045) and the applied body weight load measured beneath the leg (r
= 0.74, p = 0.037). The mean differences between intramuscular pressure and
ankle blood pressure were more pronounced as the position of the ankle dropped
below the level of the heart in the 45/45 suspended and the 90/90 kneeling
Conclusions: The 90/90 kneeling position results in elevated
intramuscular pressure in the anterior compartment of the leg. This elevated
pressure correlates also with subject weight. The 90/90 kneeling position may
predispose patients to the development of an acute compartment syndrome during
prolonged spine surgery, with heavier patients being at increased risk. In
certain instances, the surgeon may consider using the 45/45 suspended position
to minimize this risk.