Injectable Silicone: Can It Mitigate Plantar Pedal Pressure?

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A Closer Look At The Versatility Of Silicone

Silicone or polymerized siloxanes (polysiloxanes) are mixed inorganic-organic polymers. Silicones can be synthesized with a wide variety of properties and compositions. They also vary in consistency from liquid to gel and rubber to hard plastic.15

The physical properties of silicone make it an ideal biomaterial. It is chemically inert, non-carcinogenic, capable of sterilization, not physically modified by soft tissue, non-inflammatory, capable of resisting mechanical strains and produces no state of allergy or hypersensitivity.15,16

Silicone elastomers have also been incorporated into the design of implanted medical devices for decades. Medical devices that use silicone include pacemakers and heart valves, shunts, catheters, drains and tubing, penile and testicular implants, artificial urethra, breast implants, implants for paralyzed vocal cords, implants for cosmetic facial repair, intraocular lenses following cataract removal, birth control implants, and joint replacement implants for the hands and feet.

Fluid silicone is included in the group of implantable medical devices by the United States Food and Drug Administration (FDA) and the United Kingdom Medical Devices Agency. Silicone oil was used 45 years ago to lubricate needles and syringes. Coating the exterior of single use disposable needles with silicone reduces the pain of needle entry while lubricating the syringe interior facilitates plunger involvement.

Virtually every injection leaves a trace of silicone oil at the injected site. People with insulin dependent diabetes who require a lifetime of daily insulin injections accumulate silicone fluid in their bodies. However, the exact amounts are not clear. The fact that there is no known adverse reaction with silicone is indicative of excellent biocompatibility. A similarly safe application is the lubrication of surgical suture needles, which allows for easier passage through tissue.

The first silicone fluid injection for the treatment of complicated retina detachment was approved in the U.S. in 1994. Silicone also has a long history of use as facial soft tissue filler for the treatment of wrinkles and facial atrophy.15,16 Many consider liquid injectable silicone to be a unique soft tissue augmenting agent that one may effectively utilize for the correction of specific cutaneous and subcutaneous atrophies.17 Orentreich, et al., found liquid silicone to be a safe and effective method for treating HIV-associated facial lipoatrophy and it reportedly compares favorably with other methods of tissue agumentation.18

Zappi, et al., examined 35 skin biopsies by light microscopy. They obtained these biopsies from target areas where liquid silicone had been injected in 25 patients between one and 23 years prior for the correction of depressed scars on the face.16 In 100 percent of the cases, the authors found the continued presence, in significant amounts, of the silicone previously injected into the target areas, where it failed to elicit any significant adverse reaction.

Although some authors have noted complications, likely resulting from the presence of adulterants and impurities, physicians may employ modern purified silicone products approved by the FDA for injection into the human body with minimal complications as long as they follow strict protocol.14,15,17

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Author(s): 
By Stephanie C. Wu, DPM, MS

Ambulation exposes the foot to a collaboration of focal pressure and repetitive stress, and ground reaction forces generated in response to weightbearing activities are the commonly responsible stressors.1
The portion of the foot in contact with the ground varies during the stance phase of gait. Accordingly, the site of ground reaction force application varies, generally progressing from the heel at first contact to the hallux at toe-off.2
These forces contain vertical, anteroposterior and mediolateral components. However, the vertical force is much greater than the other two.3 Vertical forces can damage healthy tissue through compression and deformation. The mechanical stress generated by the anteroposterior and mediolateral components of ground reaction force are shear forces, which stretch and tear tissue.

The magnitude of ground reaction forces also varies over the course of the stance phase. Typically, the heel is in contact with the ground the first 64 percent of the contact phase while the forefoot is in contact the last 59 percent.1 The amplitude follows a bimodal pattern with force initially rising at heel strike, decreasing as the foot rolls forward and then ascending a second time during toe-off.
The midfoot therefore experiences significantly less pressure forces than the heel and forefoot due to variations in the site of application and the magnitude of ground reaction forces. Consequently, the heel and forefoot are subjected to greater pressure, making these two areas susceptible to increased wear and tear.
Anatomically, the body accommodates this by providing plantar fat pads in these locations to assist with shock absorption. However, progressive loss of fat pad occurs due to structural anomalies (such as plantarflexed metatarsals and limited joint mobility); pathologic conditions (such as collagen vascular disease and diabetes); and normal age-related changes during the course of a lifetime.
In situations in which the patient is sensate, the resulting skin on bone situation is extremely painful, especially with ambulation. This severely affects the patient’s activities of daily living and quality of life.
In situations with insensate patients, continued normal ambulation can wear a hole in their skin, akin to normal patients wearing holes in their socks. Fat pad atrophy, regardless of the cause, is often associated with substantial emotional, physical, productivity and financial losses.4-6

Understanding The Impact Of Fat Pad Atrophy And How Silicone Injection May Be Beneficial
It is well documented that plantar pressure is directly proportional to plantar tissue thickness.7,8 Historically, physicians have treated corns and calluses with a myriad of palliative measures and more recently by surgical intervention.
Fat pad atrophy is common among people with collagen vascular disease and diabetes, particularly in the forefoot.5,9 The loss of fatty tissue has been noted to be the fundamental mechanism associated with pressure related foot disorders.

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