Defective Footwear – An Unexpected And Often Overlooked
Cause of Lower Extremity Injuries

By Bruce Wilk, PT, OCS

William Gutierrez, PT, OCS, ATC

Medical workers routinely treat running injuries and are quite familiar with the etiology of their pathologies. They regularly assess running technique, musculoskeletal alignment  and shoe wear when evaluating an injured runner. However, as board certified physical therapists in a group private practice, we have noticed that further inspection of the running shoes has revealed an alarming finding.  Assessments of running shoes have revealed an increasing incidence of shoe manufacturing defects that correlate directly as causative factors in patients’ injuries. These findings demonstrate a need for clinicians to become aware of the possibility that the patient’s shoes may be an underlying cause of injury in conjunction with other more typically recognized biomechanical malalignment issues.

While most sports medicine specialists recognize the need for high quality athletic equipment (footwear included), it should be noted that defects in running shoes (i.e. crooked heel counters, loosely glued midsoles, underinflated shock absorbing pockets etc.) are not unusual. These defects have been overlooked by the general population and have the potential to cause an injury or aggravate an already existing injury.

As noted earlier, shoe design and wear patterns are routinely examined by clinicians to ensure that proper support is being provided for the athlete’s foot. A natural extension of this routine procedure is to also check the quality of the shoe’s construction for any possible defects which may relate to the patient’s musculoskeletal complaints.

This article will describe how running shoes with manufacturing defects or excessive mileage can contribute to or be potentially responsible for a variety of lower quarter musculoskeletal complaints. We will also describe how running shoe design can influence the prevention  and treatment of lower extremity overuse running injuries[1]. In order to prevent recurring injury or further injury, recommendations will be made regarding how to check existing shoes as well as new shoes, for defects prior to purchase.

Typical Runners’ Injuries

Running shoes are usually selected to provide support and counteract biomechanical deformities or deficiencies in the foot. Despite this, injuries such as shin splints, patellar tendonitis and iliotibial band friction syndrome commonly plague runners. The shoe itself may often be the cause of the runner’s problem. For instance, during the stance phase, a shoe that tilts medially due to uneven wear will have a tendency to cause the foot to pronate excessively. Conversely, if a shoe tilts laterally, it may prevent pronation and prolong supination. This may lead to stress fractures in the foot or leg as well as anterior knee pain.

In order to demonstrate how defective shoe construction can be a causative factor of running injuries, the patient’s running mechanics, lower extremity musculoskeletal alignment and shoe design and construction must be evaluated.

THE MECHANICS OF RUNNING

The gait cycle during running consists of a stance phase and a swing phase. The stance phase constitutes 60% of the gait cycle. Running is distinguished from walking by the flight phase – the period when both feet are off the ground. During running, the lower extremity absorbs 1.6 – 2.3 times the body weight as speed increases from an 8:56 minute mile to a 5:22 minute mile[2]. Cavanagh et al found that as running speed increases, peak forces of 2.5 to 3 times body weight are generated at heel strike[3] During a marathon, the body experiences over 25,000 heel strike impacts[4].This amounts to a tremendous amount of  load on the lower extremities. As a result most, if not all running injuries occur during the stance phase. [5]

The stance phase consists of heel strike, mid-stance and push off. At heel strike the foot initially contacts the ground in a supinated position. As the foot continues to make contact with the ground during mid-stance, it pronates to absorb shock; minimizing ground reaction forces. The flattening of the foot that occurs during pronation consists of subtalar joint eversion, forefoot abduction, and talocrural dorsiflexion[6]. This allows the foot to adapt to the ground’s contour and become a mobile adapter. During running each foot goes through these motions about 600 times per mile. When these motions are excessive, a torsional force is created which stretches the plantar fascia, resulting in inflammation and pain – the syndrome known as plantar fasciitis.

A TYPICAL RUNNER’S INJURY

Plantar fasciitis is characterized by inflammation or degeneration of the plantar fascia, particularly at the calcaneal attachment[7]. It has been mostly attributed to anatomical or biomechanical abnormalities such as excessive pronation of the subtalar joint beyond the normal range of approximately 9.4 degrees[8]. It has also been attributed  to training error – reasoning that is well supported by many related studies[9].

Other (anatomical) causes of abnormal pronation include congenital pes planus, acquired deformities, and abnormalities secondary to neuromuscular disease[10]. Frequently, excessive pronation is associated with ankle joint equinus, most commonly caused by limited flexibility of the triceps surae, resulting in a shortened Achilles tendon[11]. The cavus foot, which actually has a tight plantar fascia, conversely has a tendency toward excessive supination.

Shoe defects are now proving to be an unexpected new cause for this common condition – and one that cannot be overlooked. Relating the effects of various types of shoes to plantar fasciitis, Gross[12] and others[13], have indicated that musculoskeletal pathologies caused by external factors (e.g., an overpronator wearing a shoe designed for shock absorption rather than motion control), can also be exacerbated by lower quarter malalignments or biomechanical imbalances. This conclusion is supported by clinical observations of changes in the patient’s symptoms with interventions such as training modifications, corrections in running form or style, use of foot orthoses, or replacement of shoes.

Stacoff et al[14], investigated relationships between peak impact, pronation, and forces at the subtalar joint and on muscles (under tension during pronation) at heel strike in the rearfoot during running. Stacoff’s study concluded that shoe design should concentrate more on controlling rearfoot movement and less on pure shock attenuation.

As  the push-off phase of running is approached, the foot supinates in order to become a rigid lever and propel the body forward. So in essence, the foot initially coils to absorb the body’s weight then recoils to propel the body onto the other foot[15].

Thus if the foot rolls in excessively, the subject is a pronator. Pronators tend to roll medially throughout the lower extremity during the stance phase. They also tend to have a more supple shock absorbing foot. The drawback to this type of foot is that more power will be necessary during push off. When looking at old shoes of a pronator they deform medially. The medial arch of the midsole is compressed and there is extensive wear at the lateral aspect of the heel and at the medial forefoot. The pronator may also have low arches. Therefore, while it is important for the foot to have good shock absorption athletes with pronated feet also need shoes which emphasize control of the rearfoot.

Research studies have shown that shoes constructed with soft materials in the soles and uppers, or shoes that are broken down on the medial aspect may allow a medial roll of the foot and ankle during stance[16]. Clarke et al[17] noted that shoes with a soft midsole and no heel flare allow the greatest amount of  pronation, while shoes with hard midsoles and a 30 degree flare allowed the least pronation.

Supination is on the opposite end of the spectrum from pronation. If the foot rolls out excessively, the subject is a supinator. Supinating feet do not absorb shock well and their shoes should provide adequate cushioning for the lateral edge of the foot. Tell-tale signs of shoe wear in a supinator include old shoes that tilt laterally, laterally compressed midsoles, and soles that are overly worn along the lateral edges. Supinators usually have high arches.

Thus, selecting a running shoe that will adequately support a runner’s lower extremity anatomy and biomechanics can be quite complex, as documented in various sources [18],[19].\

IF THE SHOE FITS…

The way people run varies considerably and a shoe that’s right for one person can cause another blisters, musculoskeletal strains or joint inflammation. Twenty years ago, the only criteria for buying sneakers was ensuring that the toes didn’t jam against the end of the toe box. Today however, shoe design has become quite sophisticated with a wide variety of choices available. It has become necessary for physical therapists to assess foot biomechanics and running style in order to provide the patient with helpful information in choosing the correct shoe.

CHECKING THE PATIENT’S FEET

It is important to determine if a patient is a pronator or a supinator. This can be done by drawing a line bisecting the Achilles tendon and the calcaneus. The alignment of these marks is evaluated with the patient in standing. If the calcaneal line tilts medially then the foot has a tendency to pronate. Conversely, if the calcaneal line tilts laterally then the foot has a tendency to supinate[20].

Another clinical technique use to determine foot posture is to palpate the talar dome. This is done with the patient standing. If the talus is more palpable medially then the foot is in a pronated position,  if the lateral aspect of the talus is more palpable the foot is in a supinated position.

CHECKING THE WEAR PATTERN OF THE PATIENT’S SHOES

A running shoe, when placed on a flat level surface should not be biased medially or laterally. The main purpose of the shoe is to hold the foot stable. It should be constructed so its upper, midsole and outsole is firmly attached (Figure 1). The uppers, heel counter and the sole should be straight. The shoes should not rock from side to side and the shock absorbing pockets should resist collapsing under load. Defective or worn out shoes which don’t hold feet in a neutral position may accentuate a preexisting musculoskeletal imbalance (i.e. excessive pronation or supination). This may lead to unnecessary aches and pains and, if not treated, a more serious or permanent injury.

The importance of carefully inspecting running shoes for manufacturer’s defects  before purchase, and regular checks for uneven or excessive wear throughout the life of the shoe can not be overemphasized. The following guidelines will help the athlete avoid buying defective running shoes and may prevent unnecessary injuries.

The shoe should be glued together securely. Test this by holding the shoe and trying to pull the upper part of the shoe away from the midsole, and the midsole from the outsole (Figure 2). Any separation will weaken the shoe’s support.

The upper part of the shoe should be glued straight into the sole. Test this by putting the shoe on a level surface and inspect the back of the shoe (Figure 3A). The heel counter should appear even and should not lean to the right (Figure 3B) or left. A brand new shoe that leans medially or laterally could cause injury especially if there is a large asymmetry between each shoe of a pair.

The sole of the shoe should be level to the surface on which the shoe is resting. Test this by checking that the medial and lateral aspect of the heel is even when resting on  a flat, level surface (Figure 4A and B). Compare each shoe individually, then compare the right to the left shoe for symmetry. An asymmetry of two millimeters can tilt the shoe in or out significantly.

Test for asymmetry by applying a downward medial and a downward lateral force to both the right and the left shoe to see if the shoe rocks medially and/or laterally (Figure 5A and B).  Check for this asymmetry from side to side within each shoe. The shoes should remain even and not roll. If they roll when they are new, they will not stop the foot from rolling excessively when worn, and can cause injury.

Air pockets and gel pockets must be inflated evenly. Test this by pushing on the sides of the air pockets medial to lateral, and lateral to medial to check for symmetry of inflation (Figure 6). Push down into the air pockets both medially and laterally from the top of the pocket (Figure 7A and B). If the pockets are inflated unevenly, this may cause the shoe to collapse unevenly, and the foot to roll when it hits the ground.

THE LIFE OF THE SHOE…

A good running shoe lasts, on average, about 300 – 500 miles. The mileage could be less if the shoes get wet in a hot, humid environment or from running in the rain. The average runner who runs 30 miles per week with normal wear and tear can expect to have a shoe life of about 10 – 15 weeks. It is a good idea to put a date somewhere on the shoes to track how long they’ve been in use. Shoes should also be checked periodically for signs of premature wear since shoes that are no longer in alignment cannot keep the foot and leg in a neutral position.

With long distance runners, mileage increases dramatically while they are training for a competitive event. However, it is not unusual for shoe models to be discontinued and a favorite shoe may suddenly become unavailable. So, it makes sense to buy an extra pair before a long training program, and put 40 to 50 dry miles on them. This will break the shoes in and this pair can then be put away in the closet until the big race.

PRICE DOES NOT ALWAYS DETERMINE QUALITY…

The principal author, in conjunction with a feature story for a local television station, examined a variety of shoes (all different brands and styles) from several different sporting goods stores. The result was an alarming 30 – 50% defective rate. Surprisingly, more expensive shoes did not necessarily mean better built shoes. Even the most expensive designer brand running shoes were not exempt from a number of manufacturer’s defects.

SUMMARY…

The type of running shoe worn by an athlete can be a very important factor in the prevention and treatment of lower extremity overuse running injuries. Our experience indicates the importance of checking the construction of the patient’s running shoes as a possible cause of injury, particularly when other more common factors are eliminated by clinical evaluation and assessment.

Additionally, when defective or excessively worn shoes are found to be the cause of any injury, it is vital that the clinician educate the patient as to the nature of the problem. Knowing the difference between poor and good athletic shoe construction and carefully checking running shoes for manufacturer’s defects prior to purchase will prevent unnecessary injury to the patient who runs frequently for exercise or competition.

#  #  #  #  #

AMAA member, Bruce Wilk, is a board certified orthopedic physical therapist and director of Orthopedic Rehabilitation Specialists. William Gutierrez is a board certified orthopedic physical therapist and certified athletic trainer at Orthopedic Rehabilitation Specialists. Orthopedic Rehabilitation Specialists is located at 8720 North Kendall Drive, Suite 206 Miami Florida 33176, and can be reached by calling (305) 595-9425 or at ORS@icanect.net .



References:

[1] Arnheim DD: Modern principles of athletic training, St. Louis, MO: Times Mirror/Mosby College Publishing, 1989.

[2] Hall SJ, Messier SP: Biomechanics of fitness exercises. In: Durstine JL (ed), King AC (ed), Painter PL (ed), Roitman JL (ed), Zwiren LD (ed), ASCM’s Resource Manual for Guidelines for Exercise Testing & Prescription (2nd ed), pp. 38-47. Indianapolis, IN: ACSM, Lea & Febiger, 1993.

[3] Cavanagh PR, Lafortune MA: Ground reaction forces in distance running. J Biomech 13:397-406, 1980.

[4] Heil B: Lower limb biomechanics related to running injuries. Physiother 78(6):400-406, 1992.

[5] Pink MM, Jobe FW: The foot/shoe interface. In: Guten, GN (ed), Running Injuries, pp. 20-29. Philadelphia, PA: W.B. Saunders Company, 1997.

[6] Engsberg JR, Andrews JG: Kinematic analysis of the talocalcaneal/talocrural joint during running support. Med Sci Sports Exerc 19(3):275-284, 1987.

[7] Roy S: How I manage plantar fasciitis. Phys Sportsmed 11(10):127-131, 1983.

[8] Hall SJ, Messier SP: Biomechanics of fitness exercises. In: Durstine JL (ed), King AC (ed), Painter PL (ed), Roitman JL (ed), Zwiren LD (ed), ASCM’s Resource Manual for Guidelines for Exercise Testing and Prescription (2nd ed), pp. 38-47. Indianapolis, IN: ACSM, Lea & Febiger, 1993.

[9] Eggold JF: Orthotics in the prevention of runners’ overuse injuries. Phys Sportsmed 9(3):125-131, 1981.

[10] Frey C: Helping the athletic woman find a shoe that fits. J Muskuloskel Med 15(3):35-45, 1998.

[11] Hunt GC (ed): Physical therapy of the foot and ankle. New York, NY: Churchill Livingstone Inc., 1988.

[12] Gross MT: Lower quarter screening for skeletal malalignment-suggestions for orthotics and shoewear. J Orthop Sports Phys Ther 21(6):389-405, 1995.

[13]James SL, Bates BT, Osternig LR: Injuries to runners. Am J Sports Med 6(2):40-50, 1978.

[14] Stacoff A, Denoth J, Kaelin X, Stuessi E: Running injuries and shoe construction: some possible relationships. Int J Sport Biomech 4:342-357, 1988.

[15] Novacheck TF: The biomechanics of running and sprinting. In: Guten, GN (ed), Running Injuries, pp. 4-19, Philadelphia, PA: W.B. Saunders Company, 1997.

[16] Heil B: Running shoe design and selection related to lower limb biomechanics. Physiother 78(6):406-412, 1992.

[17] Clarke TE, Frederick EC, Hamill CL: The effects of shoe design parameters on rearfoot control in running. Med Sci Sports Exerc 15(5):376-381, 1983.

[18] Martin DR: How to steer patients toward the right sport shoe. Phys Sportsmed 25(9):138-144, 1997.

[19] McPoil TG: Footwear. Phys Ther 68(12):1857-1865, 1988.

[20] Fromherz WA: Examination. In: Hunt GC, M.A., P.T. (ed), Physical therapy of the foot and ankle, pp. 75-79. New York, NY: Churchill Livingstone, 1988.