Pelvic fractures are common injuries as a result of high-energy trauma. The incidence of these fractures is increasing [1]. Pelvic fracture often results in massive hemorrhage. The origin of the blood loss can be found in venous plexus lesion, arterial injury, and bleeding from fracture sites. Anatomic reduction and stabilization of pelvic fractures prevents blood loss by limiting bleeding from the fracture site and by reducing the pelvic volume. By reducing pelvic volume, bleeding can be stopped by mechanisms of tamponade, clotting or hemostasis [2]. External stabilization of the pelvis should reduce transfusion requirements and length of hospital stay, and has shown to improve survival in patients with unstable pelvic fractures [3]. In order to provide fast and easy reduction and stabilization, external pelvic compression is necessary. The biomechanical approach of pelvic compression has resulted in an introduction of a non-invasive compression method: the pelvic circumferential compression device (PCCD). A PCCD is a belt that is wrapped around the fractured pelvis and tightened with the closing mechanism. Currently, the three most commonly used PCCDs (Pelvic Binder^®, T-POD^® and SAM Sling^®) (Fig. 1A-C) are applied in pre-clinical and clinical situations for patients with pelvic fractures.

Fig. (1). The three most frequently used PCCDs tested in this study. 1A Pelvic Binder® Manufacturer: Pelvic Binder Inc., Dallas, TX, USA Size: One size fits all. “Cut-to-fit” 6-8” gap Closing mechanism: Velcro-backed fastener with shoelace mechanism Application instructions: Health care providers should be able to get at least two fingers between the patient and the binder after applying pressure 1B SAM-Sling® Manufacturer: SAM Medical Products, Newport, OR, USA Size: Sized to fit. Extra Small, Standard, and Extra Large. Small belt leaving more space for clinical diagnostics or entrance to the abdomen Closing mechanism: Fastener with an auto-stop buckle (33lbs) that limits circumferential compression at the time of PCCD application to the minimal required pulling force for pelvic reduction Application instructions: Buckle placed close to midline. Pulled tight with or without assistance with two hands in opposite directions 1C Trauma Pelvic Orthodic Device®(T-POD) Manufacturer: Bio Cybernetics Inter-national, La Verne, CA, USA Size: One size fits all. “Cut-to-fit” 6-8” gap. Closing mechanism: Simultaneous circumferential compression through Velcro-backed mechanical advantage pulley system with a pull-tab Application instructions: Health care providers should be able to insert two fingers between the patient and the T-POD

Pelvic circumferential compression is used in the pre-hospital phase and contributes to early non-invasive hemodynamical stabilization within the ‘Golden hour’[4, 5]. Advanced Trauma Life Support (ATLS) guidelines advise the use of a PCCD when an unstable pelvic fracture is suspected or diagnosed as a technique to stabilize the patient hemodynamically by reducing blood loss. The PCCDs provide circumferential compression to the bones within the pelvis. Compression forces will be most pronounced at the area of the pelvic bones that lie closely underneath the PCCD. In a clinical setting this denotes bony landmarks like the sacrum and the greater trochanters [6]. Also, the exact application location of the PCCD strongly affects the local pressure level and overall effects. Research into the transverse application level of a specific sling showed that the sling should be applied at the area of the greater trochanters and the symphysis pubis [7].

Data on the efficacy and safety of PCCDs is limited. The PCCDs currently available differ in design (material, shape and size) and closing mechanism, and may therefore have different functional characteristics, resulting in different mechanical and clinical effects. The applied pulling forces according to manufacturers application instructions differ substantially. A study on human cadaveric specimens showed the minimum strap tension required to achieve complete reduction of symphysis diastasis was 177 ± 44 N and 180 ± 50 N in the partially stable and unstable pelvis, respectively [7]. As opposed to the tension required to achieve complete reduction, there is no data available for the required tension to achieve hemostasis for initial resuscitation.

The forces that can be applied to the pelvic ring by the PCCDs are uncontrolled and unrestricted, except for the SAM-Sling^®, which has a fastener with an auto-stop buckle that limits circumferential compression when exceeding 150 N tensional force. The exerted pressure after applying a pulling force to the PCCD and the resulting effect on the underlying skin is unclear.

Adverse effects are related to high pressures on the skin and long-term use of the PCCD. The compression devices may cause pressure induced skin breakdown and accompanying co-morbidity in case of prolonged use in the period before invasive pelvic fixation. Tissue damage may occur if a continuous pressure exceeding 9.3 kPa (9300 N/m², corresponding with 69.8 mmHg) is sustained for more than two or three hours [8]. It is recommended that the pressure at the interface is kept below 4.66 kPa, i.e. below capillary blood pressure, allowing circulation to the skin to be maintained [6, 8].

The aim of this study was to gain insight into the pressure build-up at the interface, by measuring the PCCD-induced pressure when applying pulling forces to three different PCCDs (Pelvic Binder^®, SAM-Sling^® and T-POD^®) in a simplified artificial model.

The non-invasive pressure cuffs behaved elastically. Upon fastening and releasing the PCCDs, the cuffs always returned to their original state and calibrated pressure. A stepwise increase in tension resulted in a stepwise increase in exerted pressure (Fig. 3). The mean exerted pressure series on day one and day two are illustrated (Fig. 4). All twelve bar graphs show a linear trend for the exerted mean pressure on day one and two. The exerted pressure varies substantially, both between the different locations as well as between the different PCCDs. In order to calculate the average maximum pressure when strictly following the application instructions of the manufacturers, data of the six replicates were combined. The average maximum exerted pressure on the right location is 23.3 kPa for the Pelvic Binder^®, 18.9 kPa for the SAM-Sling^® and 19.9 kPa for the T-POD^®. Likewise, the average maximum pressure is 21.3 kPa, 27.5 kPa and 19.2 kPa at the left location, 18 kPa, 11.5 kPa and 15.3 kPa at the posterior location and 2.7 kPa, 18.4 kPa, and 51.2 kPa at the anterior location, respectively.

Fig. (4). Exerted pressure by three different PCCDs at the right, left, posterior and anterior locations. For each PCCD triplicate measurements were performed on two consecutive days. The mean exerted pressure series on day one (black bars) and day two (white bars) are illustrated. For each PCCD the error values: mean pressure and the Standard Error of the Mean (SEM) are represented. The y-axis scale shows the mean exerted pressure (kPa) from 0 to 60 kPa. The x-axis shows the mean pulling force (N) with a categorical 20 N interval and ends with 150 N. This categorical deviance at 150 N is due to the SAM-Slings auto-stop buckle. Measurements were performed according to manufacturer application instructions.

An exerted pressure of 10 kPa is achieved with the Pelvic Binder^® and the T-POD^® when a pulling force of 20 N is applied. For the SAM-Sling^®, on the other hand, a pulling force up to 40 N must be applied before the exerted pressure reaches 10 kPa.

An apparent observation is that measurements using the SAM-Sling^® structurally produced higher mean pressures on the left location as compared to the right location. The measured exerted pressure on day one was markedly higher than the exerted pressure on day two.

With all three different PCCDs the exerted pressure on the posterior location was generally lower than the pressure measured at the right and left location. At the anterior location, the pressure exerted by the different PCCDs varied. Pressures with the Pelvic Binder^® did not exceed 4 kPa, whereas with the T-POD^® the pressure reached values that exceeded 52 kPa (Fig. 4).

The measurements in this study provided insight into the pressure build-up by the three different PCCDs at the interface at four locations when using a novel simplified, artificial model of the human pelvis. Since the shape of the model does not reflect the anatomy of the human pelvis, extrapolation of the data to the human situation should be done with great caution.

Knowing the pulling force at which the pressure exerted by PCCDs exceeds the tissue damaging level (9.3 kPa) is relevant from a clinical point of view, as that will indicate the risk of developing soft tissue damage upon prolonged use.

The finding that pressures returned to baseline upon release of the PCCDs implies that hysteresis (a property of systems that do not return completely to their original state, depending on its immediate history) has not affected these measurements. This is perceptible in Fig. (3). The linear trend between mean exerted pressure and mean force was expected. The finding that mean pressures of both days were most alike for the T-POD^® might imply that reproducibility of the measurements was best when using the T-POD^®. Measurements with the SAM-Sling^® were subjected to the highest “between-day” variations. Measurements with the SAM-Sling^® showed the lowest pressure build-up at the right and posterior locations and measurements with the T-POD^® showed the lowest pressure build-up at the left location.

The most important differences between the binders are the closing mechanisms or fasteners and the size of the slings (Fig. 1A-C). The Pelvic Binder^® has a shoelace mechanism which is liable to friction, causes a wedge shaped tightened binder, and results in increased pulling force. The SAM-Sling^® has an auto-stop buckle (limited at 150 N) and needs to be pulled together with two hands in opposite direction. The sling is relatively small as opposed to the other two PCCDs. It has the advantage of leaving more space for clinical diagnostics or entrance to the abdomen and the disadvantage of early misplacement at the level of the trochanters. The T-POD^® has a mechanical advantage pulley system and only a small amount of pulling force is needed to accomplish simultaneous circumferential compression.

A quantification of the exerted pressure in the model showed that, when a standardized pulling force was put upon the PCCDs using the gauge, the pressure varied at the different locations underneath the PCCDs. There was a markedly difference between the different types of PCCD. Some of this variation is caused by the differences in the designs and the closing mechanisms of the PCCDs. Right location and left location mean pressure differences can be explained for the SAM-Sling^® and the T-POD^® as follows. The Velcro-belt of the SAM-Sling^® is pulled tight through the auto-stop buckle with two hands in opposite directions, but most of the force is provided towards the right-hand side (left location), while facing the model. The pulling force first encounters the left location, thereby exerting a higher pressure on the left location than on the opposite right location. In contrast, the design of the T-POD^® accounts for slightly higher mean pressures on the right location because this device is pulled tight in the opposite direction; towards the right-hand side in a straight line, while facing the model. The T-POD^® is pulled tight against the substratum, the right location.

Because the measurements have been performed with the model in an upright position, the exerted pressure at the posterior location is due to the pressure delivered by the binder, and not by the gravitation. The exerted pressure on the posterior location in the current model is generally lower than the pressure measured at the right and left locations. A reason for this is that the posterior reference point is the farthest point from the fastener. The pulling force is not completely proportional passed on both right and left locations because of opposing friction forces. In clinical practice, the pressure at the posterior location will probably be higher, as patients will be in a supine position. In such situations, the resulting pressure at the posterior location (i.e. posterior pelvic region and the sacrum) will be a combination of the bodyweight of the patient and the pressure exerted by the binder. As a consequence, it is to be expected that in clinical situations the posterior pressure will be the highest of all four pelvic locations.

The mean pressure at the anterior location was difficult to assess and not reproducible for day one and two, although repeatability of multiple measurements on the same day showed only marginal differences in reproducibility. Major differences in closing mechanisms (i.e., shoelace versus auto-stop buckle versus pulley system) may be an explanation for these differences in exerted pressure. The exerted pressure with the T-POD^® at the anterior location is very high as the fastener strings were cutting in the pressure cuff. In general, the data for the T-POD^® show that the anterior location could form a risk-bearing area for the development of vascular insufficiency to skin tissue, especially in adipose persons (enlarged circumference with protrusive tissue). Placing a cover beneath the closing mechanism to protect the substratum might be a recommendable improvement.

The circumferential compression by the different PCCDs showed high pressures measured at the four locations using a simplified artificial model. Difference in design and functional characteristics of the PCCDs resulted in different pressure build-up at the four locations. When following the manufacturer’s instructions, the exerted pressure of all three PCCDs tested exceeded the tissue damaging level (9.3 kPa) in case of prolonged use. If these results were to be carefully extrapolated to a clinical setting, all three binders would cause a risk for skin problems, with regard to the exerted pressure.

Clinical research is necessary in order to measure the exerted pressure and resulting reduction characteristics of the different PCCDs in vivo. This may contribute to optimizing the application protocol of the current PCCDs for patients with pelvic fractures, and could also aid in the development of effective and safe PCCDs.