Footwear and Orthotics
Jay Dicharry
Eric M. Magrum
FOOTWEAR
The goal of this chapter is to educate clinicians on current footwear design, to enable them to select beneficial aspects of footwear as part of a patient’s comprehensive rehabilitation plan. Most of what is known and prescribed with regard to footwear recommendations is based on “running lore” and the rapidly changing footwear model revisions driven by industry. There has been very little independent research done to prove or disprove footwear claims, and the lack of prospective footwear studies limits our knowledge base. At the time of this writing, there is a revolution in footwear design by most manufacturers due to elevated interest in this field as well as the recent focus on barefoot and minimal shoe design. Clinicians will have better results recommending types of shoes based on construction and features over specific model designations.
The basis of overuse injury risk lies within the balance of intrinsic and extrinsic factors. Running shoes are a modifiable extrinsic factor. To assess proper footwear selection, the athlete’s intrinsic factors (alignment, stability, flexibility, and imbalances) must be assessed to determine the best functional outcome (60).
Despite the lack of conclusive data on how to best match the runner to shoe type, shoe design clearly has an effect. Running mechanics can be influenced by shoe midsole stiffness/geometry as demonstrated in studies where subjects ran in shoes with varied specific stiffness/geometry (30,51,57,58,72,77).
Incorrect footwear choices can exacerbate or cause lower extremity dysfunction, while ideal footwear can help in prevention or even speed healing due to decreased tissue stress on impaired structures (4,33,57,70,81,89).
The goal of any shoe/foot interface is to allow shock attenuation and functional stability about the foot’s three-dimensional motions of pronation and supination throughout the stance phase of gait and provide a proper support for the propulsion phase of the gait cycle (4).
Shoe Construction and Anatomy
Upper—Usually made of highly breathable fabric to minimize heat buildup. May be reinforced by Gore-Tex or similar fabric for water resistance. Typically includes a heel counter — plastic molding wraps around the heel that are thought to control pronation at the rear foot. Achilles tab cutouts in the rear can be used to decrease friction on the Achilles complex.
Lacing — Various lacing techniques are available to minimize pressure or increase stability and tension on the foot.
Midsole — Functional part of the shoe. The midsole is usually made up of a mixture of ethyl vinyl acetate (EVA) and polyurethane. EVA has the advantage of being light in weight and available in multiple densities so that the manufacturer can manipulate the amount of support for a given shoe type. Polyurethane is heavier but longer lasting. Most shoes use a combination of the two to achieve the desired balance between weight and cushioning. Most shoe companies have developed a trademark insert such as Air, Gel, Grid, Hydro Flow, Torsion, Roller Bar, Wave, or Adeprene. Their goal is to provide cushioning, dissipate stress, and increase durability, while keeping weight low. Increased density materials are commonly used on the medial aspect of the stability and motion control midsoles in an attempt to control pronation.
Lastings — The lasting sits on top of the midsole and is glued or stitched depending on the stability requirements. The following are types of lastings: board — increases torsional rigidity; slip or California — favors cushion and flexibility; combination — board last rear, slip last in the forefoot.
Insole or sock liner — Thin layer of cushion material, mostly to smooth the surface of the foot. The insole does not provide any functional stability to the shoe and usually breaks down in its cushioning properties with 1 week. This is removed if the individual uses orthotics or over-the-counter inserts.
Outsole — Most current shoe models are a mixture of carbon rubber for firm support and durability and blown rubber, which is softer and provides increased cushioning. Flex grooves in the outsole influence how the midsole deforms during loading (more flex grooves yield a more compressible midsole).
Last or shape — This is different from the lasting and is not a separate component of the shoe, but the design shape on which the shoe is built. A straight last will provide more contact for a flatter foot and may increase torsional rigidity of the shoe, whereas a curved last will better fit the shape of a higher arched foot while decreasing torsional rigidity. A semi-curved last is a popular shape for the top-selling stability category of shoes and has elements of both.
Geometry — The angle of the posterolateral aspect of the shoe (heel bevel angle) is typically beveled (reduced) or even increased to vary the lever arm of the shoe. The toe spring refers to the flex placement of the forefoot.
Common Descriptors of the Five Shoe Types (25)
Motion control: Board lasting, dense midsole, straight last, rear and forefoot postings, for overpronators and heavy runners
Stability: Combination last, semi-curved shape, dense midsole, usually only rearfoot posting, usually forefoot cushion, for mild pronators and light runners
Cushion: Slip lasting, soft midsole, curved shape last, cushion in the heel and forefoot, mostly for supinators
Trail: Usually a stability shoe for increased support on uneven surface; carbon rubber for additional durability
Racing flats: Light thin midsole with little to no posting
Shoe Selection
Shoe selection for an individual athlete is an art, because the literature is limited in its ability to assist providers. In light of the lack of evidence-based information to assign shoe type to a runner, clinicians have traditionally used foot type to guide shoe prescriptions. Although the efficacy of this approach in either reducing or mitigating injury has not been demonstrated, this technique remains one of the most commonly used strategies in the United States.
Traditional beliefs about shoe selection use three different shoe categories (cushioned, stability, and motion control) for each respective foot type (cavus, neutral, and planus foot type). This hierarchy is widespread among shoe manufacturers, media, stores, and clinicians.
This type of shoe prescription can be done using objective tests such as navicular drop or arch index, or more subjectively using the wet foot test, during which the athlete, with a wet foot, steps across an absorbent surface to observe the high or low arch alignment of the foot.
Foot structure plays a significant role in the quantity of force transmitted to bone and soft tissues (4). The rigid arch of a cavus foot, while stable, passes on a significant amount of stress up the kinetic chain (4). Thus, traditionally, cavus foot types are shod with a curved shaped last with slip lasting, a soft midsole, and no medial posting (25,73) with a goal to increase shock absorption. Conversely, the flexible or planus foot dissipates considerable vertical force loads inside the foot structure and is commonly thought to benefit from additional stability control from the shoe (4). Planus feet are traditionally shod with a straight last, board lasting, firm heel counter, multidensity midsole, and medial heel posting (25,73).
In this traditional approach, the athlete’s foot type should guide your recommendation toward the ideal last configuration with the goal of increasing shock absorption of the cavus (high) hypomobile arch, increasing stability of the planus (low) arch, or promoting the mechanics of the neutral foot.
Despite their wide use, these current conventions for assigning stability categories are likely simplistic and are not successful in preventing pain and injury in runners (74,87).
A critical look at the literature reveals that the clinical efficacy of typical running shoe construction (elevated heel height with pronation control systems) is not as commonly accepted. Their effect on running injury rates, enjoyment, performance, osteoarthritis risk, physical activity levels, and overall athlete health and well-being remain unknown, and they may in fact have potential to cause harm. The prescription of shoe categories to runners is not evidence based (67).
Peak pronation in the running gait cycle occurs after heel off (20). Thus, at the time of maximum foot deformation, pronation control systems used in typical running shoe designs are not in contact with the ground to limit foot pronation.
In light of the lack of evidence-based information to assign shoe type to a runner, the clinician is encouraged to combine clinical evaluation of a runner’s structural alignment, flexibility, and intrinsic muscular stability with dynamic walking and running assessments to identify the runner’s unique needs regarding footwear. Once the runner’s individual needs have been identified, the clinician can recommend footwear that contains specific design aspects for that runner’s needs.
The experience of the runner with their current footwear is valuable. If they have had success with a given shoe, continue its use, or suggest other brands/models within a specific category to improve comfort. Different models feature subtle differences in construction/shape that may fit the individual’s foot contour better. A subjective impression of improved comfort yields improved function with the individual’s foot.
What to Look for When Buying Shoes
Athlete structural alignment, flexibility, and muscle control
Weight: Typical running shoes are made for a 160-lb male and a 125-lb female. Runner weight significantly above or under this range may impact selection or longevity.
Lightweight shoes: It is speculated that there is energy savings from lighter shoes.
Previous pathology and wear patterns
Try on shoes in early evening due to the foot swelling during the day.
One-half inch between longest toe and the shoe
Check to ensure that the flex point of the toe spring is underneath the metatarsal heads.
Adequate width (most shoes are a size D). A wide toe box allows the forefoot to spread out during contact. Narrow shoes limit this normal motion of the foot and may alter foot shape.
If using orthotics for stability purposes, use board or California lasting to provide a stable base for the orthotic.
Arch cookies should not be used to make up for poor fit because the arch is not a weight-bearing part of the foot. It should be allowed to move as needed.
Barefoot Running and Minimal Footwear Design
Recent work has highlighted the differences between barefoot running and shoes. Barefoot running typically results in a more plantarflexed ankle at contact and reduction/elimination of the impact peak component of the ground reaction force (GRF) and a decreased loading rate (39,46,80).
Barefoot running results in a shorter stride length and increased cadence compared to shod running (39,80). These temporal spatial changes in stride length act to lower joint torques across the board, but they do not alone explain the significant decrease in hip rotation, knee varus, and sagittal plane knee torques (39).
The previously discussed studies do not clearly state that barefoot is “better” than shod running, but that shoes allow the runner to adopt a gait style that is different from barefoot and potentially shift stresses to the body in the wrong direction (19).
There is an emerging category of “natural running” shoes that feature minimal heel-toe drops (typically ˜0-4 mm) to achieve a contact style more similar to barefoot running (forefoot/midfoot) than the heel contact style observed in traditional elevated heel shoes (18,80).
New “natural running” shoes feature firmer midsoles to improve proprioceptive feedback to maximize the elastic recoil of the body’s connective tissues.
Traditional running shoes are built with a 2:1 ratio, where the rearfoot is twice as high as the forefoot. This impacts contact style and muscle activation. Heel elevation during stance places the ankle joint in a position where proprioception is inherently poor (76). Further, this translates loading toward the forefoot, which creates a quadriceps-dominant firing pattern above the gluteus maximus, which results in postural changes in the runner (75).
Supporters of existing footwear design argue that reducing the heel heights of existing shoes would spark a number of lower leg (specifically Achilles) injuries. However, several studies have shown no decrease in stress to the Achilles with elevated heel shoes, with one study finding an increase in injuries with elevated heels (21,37,66).
Special Considerations
Midsole characteristics are the primary determinant of the rate of loading imposed during initial ground contact (50). Midsole stiffness has a marked effect on proprioception, illustrating that peripheral sensory information is a variable in performance (42).
Too much cushioning causes the runner to land with increased limb stiffness and can lead to instability due to less proprioceptive feedback for stability (4,8).
Shoes with a softer durometer midsole allowed significantly increased pronation and total rearfoot movement when compared to medium or hard midsoles (12).
Functional stability of the foot requires effective muscle contraction, coordination, and firing patterns. Fatigued muscle firing patterns cause increased peak strain on the lower extremity, thus leading to injury. Patellofemoral pain syndrome, osteoarthritis, iliotibial band syndrome, and tibial stress syndrome have been linked to abnormal muscle firing patterns (1,4,35,38,78).
Proper footwear has been shown to increase internal stability and decrease onset time to achieve stabilization in the low back via postural changes (61).
Race flats and spikes: GRFs have been found to increase in race flats and spikes as compared to traditional running shoes. Thus, runners should adopt a gradual transition into race footwear prior to competition season to allow the body to acclimate to the increased stress (47).
Durability: Expect 300-500 miles or 3-6 months out of a pair of shoes prior to midsole break down. Midsoles lose 40% of their cushioning ability after 400-500 miles (65). Look to purchase new shoes when the midsole shows signs of compression, the outer sole shows signs of wear, or injury rate increases.
Shoe wear adaptations: Running in worn shoes caused increased stance time and kinematic adaptations but did not change force variables, suggesting that as shoe cushioning decreases, runners modify their patterns to maintain constant external loads (41).
Footwear cost: Low- and medium-cost running shoes in three brands tested provided the same (if not better) cushioning of plantar pressure as high-cost running shoes (13).
Despite claims, no manufacturer has successfully achieved energy return to the runner. Shoemakers have made functional gains in minimizing energy lost through lightweight alterations in materials (82).Related posts:
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