Soft Feet, Strong Legs

Want an easy way to help treat lower extremity injuries in your athletes? Orthotics are the answer, although it’s not clear whether they control mechanics or alter neuromuscular activation patterns.

By Dr. Jay Hertel & Dr. Lauren Olmsted

Jay Hertel, PhD, ATC, is an Assistant Professor with the Graduate Athletic Training/Sports Medicine program in the Curry School of Education at the University of Virginia. Lauren Olmsted, PhD, ATC, is the Clinical Coordinator and Interim Athletic Training Education Program Director in the Department of Kinesiology at Penn State University.

Training & Conditioning, 14.5, July/August 2004, http://www.momentummedia.com/articles/tc/tc1405/feetlegs.htm

Whether they like the Nike swoosh, the Adidas stripes or another brand of footwear, most athletes are pretty particular about their athletic shoes. They want them to fit well, be comfortable, and look hip. But what may actually be more important than the shoe they choose is what they are—or are not—putting in the bottom of it.

We are referring to foot orthotics, which should be an important part of any athletic trainer’s treatment toolbox for lower extremity injuries. Orthotics frequently include posts, or wedges, on their bottom side that aim to alter the biomechanics of the lower extremity by controlling faulty motion. Another common use of orthotics is to increase shock absorption by the musculoskeletal system during weight bearing. More recently, the role of orthotics in altering neuromuscular control of the lower extremity has also gained interest.

The purpose of this article is to highlight the contemporary clinical uses of foot orthotics in sports medicine. We will also review the mechanisms by which these devices may influence the musculoskeletal system.

Different Types
Foot orthotics are available in two types: off-the-shelf and custom-made. Off-the-shelf orthotics, such as full-length shoe inserts, arch supports, and heel lifts, are sold by shoe size and are not designed to treat specific individuals or pathologies. These devices are frequently sold at pharmacies, athletic shoe stores, and sports medicine clinics. Various types of posts are available in some brands.

The more expensive custom-made orthotics are constructed based on an impression of an individual’s feet. The impressions have traditionally been made from plaster or foam casts of the patient’s feet, although more recently digital scanning techniques have also become available. The custom-made orthotic can be made from a wide variety of materials, and specific posts prescribed by the clinician may be added to the outside of the orthotic or may be built directly into it.

For both custom and off-the-shelf models, there are three primary stiffness classifications: flexible, semi-rigid, and rigid. The more flexible an orthotic, the less motion can be controlled. Flexible orthotics are prescribed when only a small amount of motion control is needed but considerable shock absorption is desired. Conversely, rigid orthotics are typically used in extreme biomechanical cases when a great deal of motion control is needed and shock absorption is not of primary concern. Semi-rigid orthotics are the most common orthotics and provide a balance of motion control and shock absorption.

How Do Orthotics Work?
Traditionally, foot orthotics have been thought to work by controlling the range and velocity of motion of the foot and proximal segments of the lower extremity. And research has consistently shown that medially posted orthotics decrease the amount of foot pronation and internal tibial rotation, as hypothesized. Additionally, these orthotics significantly decrease knee abduction and adduction movements, demonstrating that orthotics can alter the mechanics of the proximal lower extremity joints.

However, there are still some question marks in the literature on orthotics and biomechanics. For one thing, there is research showing lack of significant motion restriction and large variations in individual responses to orthotic intervention. In addition, there has been very little research examining the differential effects of off-the-shelf and custom-made foot orthotics on motion control.

Much of the current research on orthotics examines the role that foot orthotics have on the neuromuscular system. At least three studies have found that orthotics enhance the cutaneous sensation on the plantar aspect of the foot thus changing the afferent input from the somatosensory system. This change in sensory input is thought to positively alter the neuromuscular activation patterns of the lower extremity. In a recent study at Penn State, off-the-shelf orthotics, regardless of rearfoot posts, led to increased electromyographic activity of the vastus medialis and gluteus medius muscles, suggesting that the sensory, not the mechanical, effects of the orthotics led to positive changes in lower extremity neuromuscular activity.

Similarly, both off-the-shelf and custom orthotics have been shown to improve postural control, a measure of neuromuscular function. Also emphasizing the importance of the sensory effect of orthotics is the finding that orthotic comfort is significantly related to the kinematics, kinetics, and neuromuscular activation patterns during gait.

Benno Nigg, PhD, Director of the Human Performance Laboratory at the University of Calgary, proposes a new paradigm to explain the effect of orthotics on motion control. He states that forces acting on the foot during the stance phase of gait provide an input signal producing a muscle reaction. The orthotic is thus a tool that may be manipulated to influence the cutaneous receptors on the plantar aspect of the foot as well as the articular and musculotendinous receptors of the lower extremity.

Sensory changes can alter motor patterns in either a positive or negative manner. If the adaptation process causes a preferred joint movement path for a given movement task, muscle activity will decrease. If an intervention counteracts the preferred movement path, muscle activity must be increased. An optimal orthotic will reduce muscle activity and optimize lower extremity function. Further research, however, is needed to validate this intriguing hypothesis.

Clinical Uses
While the research continues on both the biomechanical and neuromuscular aspects of orthotics, athletic trainers can be confident of the devices’ effectiveness in several areas. Foot orthotics have been shown to be efficacious in the treatment of a variety of lower extremity conditions including medial tibial stress syndrome, stress fractures, patellofemoral pain, and lateral ankle sprains.

Lower Leg Pain: Perhaps the most common use of foot orthotics is to control hyperpronation, which has been linked to increased incidence of injuries, including medial tibial stress syndrome (shin splints). Excessive foot pronation is often caused by structural malalignments of the foot such as forefoot varus, pes planus, or rearfoot valgus. Thus, orthotics designed to limit excessive hyperpronation aim to do one of three things: control forefoot motion, increase arch support, or control rearfoot motion.

Control of forefoot motion in an individual with forefoot varus is typically accomplished by adding a medial post to the orthotic at the level of the metatarsal heads. This is done in an effort to provide a mechanical block to excessive forefoot pronation.

Athletes with pes planus need increased support of the medial longitudinal arch to limit hyperpronation. This may be done with a variety of materials including foam, felt, rubber, or plastic.

Medial posts of the rearfoot will help to limit hyperpronation in patients with rearfoot valgus. Limiting the range and velocity of pronation through increased medial support is thought to reduce strain of the posterior tibialis and soleus muscle origins on the posteromedial aspect of the tibia.

The clinical efficacy of foot orthotics in the treatment of lower leg pain related to hyperpronation has been long-established, but some practitioners are also recommending the prophylactic use of custom orthotics. A study among military recruits showed that using orthotics on healthy subjects proved to be beneficial in the prevention of lower extremity stress fractures.

Another use for orthotics in the treatment of lower leg pain involves athletes who have suffered stress fractures but have limited foot pronation. Athletes with rigid pes cavus, or high, arched feet do not dissipate as much shock through their arches as do athletes with more flat and less rigid arches. This places them at increased risk of lower leg stress fractures as the tibia and fibula must then absorb more shock during the stance phase of gait. These athletes often benefit from using flexible orthotics made of very compliant materials that absorb shock.

Patellofemoral Pain: Using orthotics also works well to help treat chronic patellofemoral pain. Like with treating lower leg pain, the clinical rationale is that the orthotic will limit hyperpronation. By limiting foot pronation, internal rotation of the long bones of the leg is also reduced.

Historically, patellofemoral pain has been linked to abnormal lateral tracking of the patella in the distal femoral groove. But a more contemporary theory suggests that too much internal rotation of the femur is actually the culprit. This leads to a femur that is rotated too far medially and a patella that then rubs against a more prominent lateral femoral condyle.

One study, conducted by Janice Eng, PhD, and Michael Pierrynowski, PhD, and published in Physical Therapy in 1993, focused on female adolescents suffering from PFPS with greater than six degrees of rearfoot valgus or forefoot varus. All the girls were subject to a supervised rehabilitation program that emphasized strengthening and flexibility exercises for the quadriceps and hamstring muscles. Half the subjects were also treated with soft orthotics with appropriate medial forefoot and rearfoot posts to help limit hyperpronation.

Both groups demonstrated improvement in symptoms over eight weeks, but the group treated with the orthotics had significantly greater reduction in symptoms than the control group. The authors speculate that the benefits of using orthotics in the treatment of PFPS are derived from altering the biomechanics associated with hyperpronation at the tibiofemoral and patellofemoral joints.

Lateral Ankle Sprains: Use of foot orthotics in the treatment of lateral ankle sprains is less commonly advocated than with lower leg and knee pain, but it is an area that is gaining interest. Some recommend laterally posted rearfoot orthotics, while others suggest using neutral orthotics with no posts.

Laterally posted orthotics are hypothesized to work via a mechanism opposite that of medially posted orthotics. Since the mechanism of injury for lateral ankle sprains is hypersupination (comprised of excessive plantar flexion, inversion, and internal rotation), an orthotic that limits hypersupination would prevent the rearfoot from returning to the position in which the lateral ligaments were injured. Laterally posted orthotics limit hypersupination rather than hyperpronation.

The use of a neutral orthotic in the treatment of lateral ankle sprains is advocated for maintaining the subtalar joint in the midrange of its range of motion, which keeps the ankle away from the extremes of both hyperpronation and hypersupination. This is thought to reduce the strain on the healing ligaments that support the subtalar joint including the calcaneofibular, cervical, and interosseous ligaments.

When might you use the two different types? Although this is only our anecdotal experience, we’ve found that athletes with pes planus will respond better to neutral orthotics, whereas those with normal foot structure or pes cavus respond better to lateral posts.

Another idea is to use rearfoot orthotics as an intervention to improve postural control in ankle injured subjects. Rearfoot orthotics are hypothesized to stabilize the subtalar joint and thus provide a more stable base of support. One study found that patients suffering from acute lateral ankle sprains who wore orthotics had better balance and less pain while jogging than those who did not wear orthotics. Another found that athletes recovering from acute ankle sprains demonstrated less postural sway during single leg stance when they were prescribed foot orthotics versus a group not prescribed orthotics. Overall, there is not enough empirical evidence yet to support or refute the efficacy of foot orthotics in the treatment of lateral ankle sprains, but these studies show promise.

How to Choose
There is still much mystery around the exact workings of orthotics. The mechanism by which orthotics work is most likely a combination of biomechanics and neuromuscular effects, but the specific contribution of each component is unknown. In addition, there are no hard and fast rules about when to use off-the-shelf orthotics and when to have them custom-made.

Our recommendations: Consider using orthotics when rehabbing athletes with lower extremity injuries and also consider using them as a prophylactic measure if the athlete has suffered a previous injury that was likely caused by hyperpronation, or in the case of stress fracture, too little pronation. If cost is a factor, starting with an off-the-shelf models is justified before getting a prescription for a custom-made orthotic.
In all cases, however, athletic trainers should work with their team physician to carefully assess and treat athletes. Orthotics can be very effective for a rehabbing athlete, as long as they are used correctly.

For a copy of references for this article, please go to
www.AthleticSearch.com/footrefs