The influence of bandage characteristics and inter-individual application variations on underneath bandage pressures.

INTRODUCTION:: Cohesive bandages are applied to the legs of racehorses and horses with limb injuries for protection (prevention of abrasion) and support (reduction of movement at the fetlock joint). The support capacity of all commercially available bandages has been questioned. Consequently, the protection aspect of bandaging and the negative side effects, which can be caused by bandaging (eg pressure induced ischemia with subsequent necrosis), were emphasized. High pressures underneath bandages were shown to cause reduced blood flow. Pressures underneath certain types of bandages were shown to be higher than under others. It is unclear if these differences were due to differences in material characteristics between the bandage types or caused by differences in application by the trainers. The purpose of this study was to determine (a) if differences between different types of bandages are observed if these are applied similarly and (b) if earlier observed differences in pressures underneath bandages are reproducible when wrapped by different trainers. METHODS AND MATERIAL:: (a) A wrapping machine for the application of bandages to an artificial joint (simulating the human knee joint) was designed and built. The machine allows to wrap bandages with adjustable, constant tension under well defined wrapping angles in order to simulate a wrapping technique similar to the wrapping by trainers. The artificial joint is equipped with two pressure sensors (Parotec, Germany). After bandage application, the artificial joint was placed in a specially designed testing machine and cycled through 200 cycles from 0 degrees to 90 degrees of flexion at a frequency of 0.5 Hz. Pressure data were collected at a frequency of 20 Hz. The force required to unwind the bandage from its core was measured with a material testing machine. Five samples each of four different 4" wide cohesive bandages were tested: 'E': high modulus latex, 'V': low mod. latex, 'C': low mod. latex, 'F': medium mod. laminate non-latex. All bandages were applied at manufacturer suggested tensions (50% intercept length). (b) Fifth-three trainers from the Kentucky Horse Center (Lexington, KY) and the Payson Park Training Facility (Indiantown, FL) volunteered for the study. They applied their favoured brand and a type 'F' bandage to an artificial horse limb. Underneath bandage pressures were collected using a pressure mat (Mikro Emed, Novel GmbH, Germany) placed over the fetlock joint. RESULTS AND DISCUSSION:: (a) Maximum pressures during maximum flexion underneath the type 'E' bandage (5.7+/-0.4 N/cm(2)) were significantly higher than for all other bandages (no difference between other bandages, range 3.5+/-0.6 to 4.0+/-0.4 N/cm). The unwinding force for the type 'F' bandage was significantly lower (10.1+/-5.5N) than for all other bandages (range 22.7+/-11.3 to 42.3+/-15.1N). (b) Trainers applied the type 'E' bandage significantly tighter than the other bandages (18.7+/-3.7 N/cm(2) vs a range of 7.5+/-5.4 to 10.4+/-6.1 N/cm(2)); a tendency was observed that the type 'F' bandage was applied looser than the type 'V' bandage. The results of part (b) of this study are consistent with the earlier study. Based on the results of part (a) of this study it can be speculated that (I) The high pressures underneath the type 'E' bandage are clearly due to its material characteristics, and (II) The differences between the other bandages are not caused by material characteristics but probably by the differences in unwinding force. If the unwinding force is higher than the force required to extend the bandage to 50% intercept length, trainers will probably wrap tighter as suggested and desired.