Measurement of Pressure in Compressive Magnet Therapy for Auricular Keloids

Keloid scars are benign overgrowths of collagen deposits that can arise from various types of injury. Although they can develop anywhere on the body, keloids are a particularly common complication of ear piercings, with incidence estimated to be as high as 2.5%.1 Excision of keloids without adjuvant therapy results in recurrence rates between 45% and 100%.2 One method of adjuvant therapy is compressive magnet therapy which, when performed after surgical excision, has been shown to drop recurrence rates significantly.1,3 Although these studies provide some information on the magnets studied, such as diameter, thickness, gauss rating, or pressure measured with a digital manometer, reporting of such data is inconsistent, and replication of use is complicated by other factors such as size, location, and thickness of the scars. Based on critical responses to these studies, there is a clear need for a more systematic approach to magnet therapy. In addition, for magnets of such small diameter and distance, theoretical calculations of force are inaccurate. This is particularly important when considering that sufficient external pressure exerted against skin can impair the underlying circulation and lead to ischemia, cell death, and necrosis.4 The compressive pressures of 6 magnets of different surface areas and thicknesses with estimated pressures of about 40 mm Hg were quantified using an Instron 5542 (Instron, Norwood, Mass.). The testing was performed using displacement control at a rate of 1 mm/min. Silicone sheets of various thicknesses were placed in between the magnets to simulate the presence of auricular tissue. We compared our data with the Gilbert Model approximation of force between 2 cylindrical magnets. We measured the magnetic force (N) as a function of the separation between magnets for a sample size of 6 magnets (Table 1). Figure 1 shows magnetic compression pressure for a grade N42 magnet pair (diameter, 0.5 in; thickness, 0.03125 in). Color curves represent empirically measured pressure between 2 magnets over increasing simulated tissue thickness. In order of increasing thickness: 0 mm (red), 0.725 mm (yellow), 1.3165 mm (lime green), 1.866 mm (green), 2.408 mm (sky blue), 2.975 mm (blue), 3.56 mm (purple), and 4.244 mm (magenta). The black curve represents calculated pressure using the Gilbert Model approximation of force between 2 cylindrical magnets. This calculation approaches infinity at small distances. Major discrepancies were found between the calculated and measured values of magnet pressures. We also found that the presence of silicone sheets representing auricular tissue did not affect the magnet pressures at any given distance. In conclusion, although compressive magnet therapy is a promising adjuvant treatment for auricular keloids, major discrepancies between the calculated and actual values of magnet pressures elucidate the need for a quantified approach to keloid magnet therapy. The measurement of compression forces is the first step in standardizing this approach for future studies and the development of treatment algorithms for keloids incorporating compressive magnet therapy.Table 1.: Magnet grade, surface field, diameter, and thickness specifications for all 6 magnet pairs, as well as comparisons of theoretical and observed pressures (mm Hg) over increasing simulated tissue thicknessFig. 1.: Magnetic compressive pressures for a grade N42 magnet pair (diameter, 0.5 in; thickness, 0.03125 in). Color curves represent empirically measured pressure between 2 magnets over increasing simulated tissue thickness. In order of increasing thickness: 0 mm (red), 0.725 mm (yellow), 1.3165 mm (lime green), 1.866 mm (green), 2.408 mm (sky blue), 2.975 mm (blue), 3.56 mm (purple), and 4.244 mm (magenta). The black curve represents calculated pressure using the Gilbert Model approximation of force between 2 cylindrical magnets. This calculation approaches infinity at small distances.

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