Page 61 - JSOM Winter 2018

FIGURE 3 Diagrams of the band-only, the bone, and the boneless Results
groups.
Boneless Group Versus Bone Group:
(A) Study Group Versus Positive Control Group
For bone absence compared with its presence, the mean vol-
umes of the compressed soft tissues were 306mL and 303mL,
respectively. In other words, when bone was present, the soft
tissues were squeezed more to yield a smaller size by 3 mL, or 1%
(rounded from 0.87%, [{305.7mL−303.03mL}/305.7mL]).
The bone (41mL volume) statically pressed outward with
an equal amount of force in the opposite direction against
(B)
the overlying soft tissues, which were compressing inward.
Without bone, the soft tissues caved into the void remaining
after bone removal. The degree of collapse was incomplete,
because the inner surface of the soft tissues came to rest sus-
pended over a residual void of 16mL (Figures 2E, 2F, and 3).
Without bone, a mean 25mL (41mL−16mL) of soft tissues
had collapsed into the void. The volume of the limb under
the tourniquet for the boneless group and the bone group was
344mL and 322mL, respectively. The collapse volume, 25mL,
was 3mL more than the difference between the two groups
Diagram is of Figure 2B, 2D, and 2F, but additional dashed arrows are (22mL).
overlaid to ease comparison of changes.
We also compared girths of the limb under the tourniquet
the other on the minor axis. Measurement points were on the because caregivers might see specific traits of the limb change
cylinder surface adjacent to the tourniquet marks (Figure 2C). by compression. Mean differences between the bone group
Similarly, points for the bone or its void were made at the and boneless group for major and minor axes measured on
inner surface of the soft tissues. For the bone, this was at the both sides of the tourniquet were statistically significant (p <
edge of the soft tissues, and for the void it was in line with the .03, all eight pairs (two axes [major, minor], two sides [left,
estimated edge of the overlying tourniquet (Figure 2E). right], two surfaces [limb, bone or void]), and mean axis dif-
ferences between bone group and boneless group were 2mm
Looking lengthwise down the tourniquet band wrapped (major axis) and 4mm (minor axis; Table 1). The overall av-
around the limb with its tip away from the viewer and its erage among these differences was 3mm. Although the ma-
buckle toward the viewer, right and left edges of the tourniquet jor axes of the boneless group were a mean of 103mm, that
were named. A measurement at the left edge is shown (Figure 3mm difference indicated the relative difference to be 3%
2C). Paired left and right measurements were averaged. (3mm/103mm). Simple visual assessment revealed that the
appearance of the girth at the limb surface was not reliably
The tourniquet was applied with the aid of marks so that ten- discerned between different groups because such differences
sioning was systematic by distance. First, the band was routed were too small (Table 2).
through the buckle and centered on the segment. The user got
a firsthand feel pulling the band until its mark aligned with the Bone Group Versus Band-only Group:
edge of the buckle, and then the band was adhered to itself. Positive Control Versus Negative Control
This baseline was common to all groups. Next, we compared compression with bone with no compres-
sion with bone (i.e., the bone group with the band-only group,
Data gathering was by group. First was the band-only group. respectively). When just looking at the soft tissues, the mean
The order of testing between the bone group and boneless volume changed 63mL as compression squeezed 366mL into
group was randomized for both investigators. The scientist 303mL, making a compression effect of 17%, or approxi-
measured first, the fellow followed. The start position of the mately one-sixth ([366.23mL−303.03mL]/366.23mL; Figure
unclipped rod was at rest and perpendicular to the band (Fig- 2C, 2D). When bone was present in the model but not in-
ure 2A). The compression was made by turning the rod three cluded within the sampled material, the squeeze was 17%. Of
times (540° total arc), and the rod was secured into a clip. note, all the change of volume was in the soft tissues because
compression did not change the bone volume. Our studies re-
The investigators each made tests with paired left and right vealed that the soft tissues were the location where compres-
measurements of major and minor axes of both the bone and sion regulated bleeding, whereas bone was essential to provide
limb or boneless limb under the tourniquet. Notably, when a base of support for the overlying soft tissues, thus optimizing
the limb compression was released, it took just a few min- the compression effect.
utes to return to baseline size and shape, as confirmed by
measurements. Furthermore, we consistently observed that the mechanical
actions taken and the outcomes of compression rendered
Altogether, this study comprised 36 tests (two investigators, temporality and scalability as typically observed in a cause-
three groups, six tests per group), and data analyses were con- and-effect relationship. Notably, collapse began at tension-
ducted using Excel 2003 (Microsoft; www.microsoft.com). ing, progressed stepwise during each turn of the rod, paused
Mean differences were compared with two-tailed Student t only when turning paused, and ended when the rod was
tests. secured.

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