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.
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].