Health Care Professionals

AFOs and Interfaces: The Important Role of Socks

By Harry “J.R.” Brandt Jr, CO, LO, BOCO

Harry “J.R.” Brandt Jr, CO, LO, BOCO, is director of Orthotics at Collier Rehabilitation Systems/Orthotics and Prosthetics in Pleasant Hill, CA, and of Northern California Medical in Sacramento and a member of the Institute for Preventive Foot Health’s Scientific Advisory Board.

NOTE: This article was originally published in the September, 2014 edition of Lower Extremity Review.  Click to see the original article.


Ankle foot orthoses (AFOs) are the most commonly prescribed lower limb orthoses.1  The biomechanical design, materials, and components of these devices vary according to the specific function they are intended to serve, and they can be either prefabricated (off-the-shelf) or custom made from metal, high-temperature thermoplastics, or composite materials. AFOs can be static or dynamic and flexible, rigid, or articulated with a hinge that allows controlled ankle flexion.

AFOs serve four primary purposes: 2

  1. To assist or restore diminished or lost dorsiflexion, plantar flexion, inversion, or eversion in the foot;
  2. To prevent or correct deformities in the lower limb;
  3. To reduce or redirect weight bearing in an injured lower limb; and
  4. To assist and reduce the energy cost of ambulation in patients with neuromuscular issues such as spastic diplegia in patients with cerebral palsy, weakness in survivors of poliomyelitis, or spastic hemiplegia in chronic stroke patients.

A proper AFO prescription considers the biomechanical influence of the orthosis at the foot, ankle, and knee in all planes of movement.1 I believe selecting the most appropriate AFO for a patient requires proper evaluation, design, measurement, and fitting during the production of the orthosis, as well as ongoing adjustments as the patient progresses or if other changes in gait, capability, or both occur after delivery of the orthosis. This attention to biomechanical influences should include an understanding of the multiple interfaces that exist between an AFO and the patient’s lower leg, ankle, and foot.


Importance of the interface

In my experience, the design, construction, and functionality of an AFO can lead to stress on the skin and soft tissues of the lower extremity. In clinical practice, I have observed that protecting the soft tissues is often an overlooked or underestimated aspect of AFO performance: Skin interfaces are addressed primarily with foam or gel padding built into the AFO or added after manufacture, and patients often wear thin socks that offer little protection to the lower leg. While soft tissue protection has long been a major consideration in the field of prosthetics, I am not aware of any specific orthotic standard or protocol for the provision of an interface—ie, sock—between the lower extremity anatomy of the patient and the AFO. Yet, I believe that a robust interface between the skin and soft tissue and an AFO can help minimize soreness, discomfort, and damage to the skin and soft tissue as well as some of the adjustment issues that we as practitioners must address.

[Foam and gel cushioning built into an AFO do not always fully protect against stresses to the skin, especially in the foot region, where there is little space for cushioning.]

Foam and gel cushioning built into an AFO do not always fully protect against stresses to the skin, especially in the foot region, where there is little space for cushioning.

Some skin interface locations can be identified in the design and manufacture process, but not all. Issues with fitting and adjustment often are addressed after the fact, and may create unanticipated soft tissue “hot spots” at the interfaces of the AFO and the lower limb. Damage to the skin of the feet and lower legs can cause pain and discomfort for the patient, which in turn can negatively affect patient compliance with device wear.

Some clinicians may not discuss the patient’s lifestyle and physical activities prior to the fitting, design, and manufacture of the AFO; therefore, the clinician may not be aware of all of the soft tissue protection requirements for a specific patient. I contend that it is desirable, even critical, to have these conversations in the initial phases of AFO fitting and design, and to establish the performance requirements for a sock that integrates with the AFO and the footwear the patient will use.

Stresses on the skin and soft tissues of the lower leg and feet are dependent to some extent on the condition for which the AFO is prescribed and on the primary function of the orthosis. With plastic AFOs, researchers have calculated that stress is concentrated in the heel and the neck (the area on the rear of the orthosis interfacing with the Achilles tendon just below the gastroc-soleus complex) regions of the orthosis.3 In a simulation of a solid molded polypropylene AFO in a patient with drop foot, Chu and Reddy calculated that the maximum compressive stress during stance phase occurred under the heel at ground contact and moved from the center to the lateral part of the heel, with a subsequent shift of stress concentration to the neck of the AFO just prior to toe-off. 3 Although the study was done in 1995, and AFO design and materials have changed, the materials that come in contact with the skin remain hard. Polypropylene, copolypropylene, polyethylene, and other plastics are still used, and though newer carbon fibers are used, they too are hard and require an interface to help protect the skin. Therefore, it is likely that high levels of stress on the limb occur at the interfaces in the same areas of the orthosis.

As noted earlier, skin interfaces are typically addressed with foam and gel cushioning built into the AFO, but in my experience these materials are not always sufficient to provide full protection against stresses to the skin, especially in the foot region, where there is little space for such cushioning. Therefore, I suggest that patients wear a padded sock to help cushion and protect the interfaces between the AFO and the lower leg, and the foot in particular.

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