Injectable Silicone: Can It Mitigate Plantar Pedal Pressure?

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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