Biomechanics Notes
07-23-98
ANKLE
The ankle is the most commonly injured joint in the body. Most
of these injuries are Type I sprains and people deal with these with
rest. In our practices, we’ll se lots of Type II and Type III sprains.
These don’t get better on their own.
X-Rays:
 The joint is parallel to the ground, so you have to shoot the
beam parallel to the ground. (Don’t need to include the toes)
 Oblique view – to see the space in between the tibia and fibula
Function of the Ankle:
It is a hinge joint that moves basically just forward and
backward.
There is only 10 – 15 degrees of flexion & extension of this
joint when walking.
If the pace of walking is slower, the ROM is greater in this
joint. Similarly, if the walking
pace is quicker, the ROM is less. (See Figure 8-3 B, pg.
155)
Closed Pack Position:
Definition: the joint in a position of maximum congruence (most
locked).
The closed pack position of the ankle is in dorsiflexion.
It is easier to fracture the bones in a closed pack position.
(If there is injury in an open pack
position as in plantar flexing and rolling the ankle, there
is more soft tissue injury.)
Stability of the Ankle Joint:
The ankle is a very stable joint. There are lots of strong
ligaments that keep it stable. This is good, it is hard to make this
joint unstable. But, if it does become unstable, you could get a shift
due to one weak ligament and this could really mess up the wear pattern
at the tibio talar joint. (See Figure 8-9, Page 159) After injury,
the wear on the talus becomes excessive at the points where the
cartilage is not the thickest resulting in a bad wear pattern.
Furthermore, the surface area of contact between the two bones
decreases which increases the stress at the joint.
Factoid: A person is more likely to get osteoarthritis of the ankle
if he has had a previous ankle fracture.
Force on the Ankle:
There is the greatest force on the ankle joint is just before
toe-off in the walking cycle. There’s not much force at heal strike.
Here, the force is 4.5 times the body weight. (See Figure 8-8, page
159) Also, the pace of the walking doesn’t have much effect upon the
force on the ankles.
Ankle movement:
 The talus should pronate at heel strike.
 If othotics are in place to decrease ankle pronation, the
talus can’t pronate and the force is shifted up into the ankle
joint which increases the stress on the knee and creates knee
problems.
 Talar pronation is VITAL is absorbing shock.
 We don’t know the biomechanics of the “ideal foot” so be
careful when adding orthotics. You should really know what
you’re doing.
FEET
Proprioception:
The most sensitive place on the entire body for proprioception
is the bottom of the foot. You need loose joints here!
Anatomy of the Foot: like a bag of bones
Function of the Foot:
1. To provide support when standing, it grips the ground. It
gives us a wide, flat and mobile stance.
2. To provide a hard lever between the heel and the toes. You
need fixed joints here.
Palpate feet when the pt. Is standing (the foot is being used) and
when the foot is at rest.
In standing, the foot pronates and the foot locks up. It gets screwed
into a hard lever. (this is one of those sentences that sound obscene
but really isn’t) The longer the lever, the more power.
When the knee is extended, the tibia externally rotates to lock foot
joints up. If the tibia doesn’t rotate enough, as in osteoarthritis,
the feet don’t lock and the muscles have to tighten to take up the
slack causing sore feet and legs.
Base of the Second Metatarsal:
Unlike other metatarsals, the second metatarsal is depressed
between the cuneiforms.
It is the highest stressed bone of the foot and the most common
sight of stress fracture in
the body.
It helps to lock the bone of the foot in place.
This bone isn’t supposed to move much.
Lisfranc’s Joint:
Figure 9-9, Page 168.
Named for Napoleon’s surgoen (they did a lot of amputations at
this joint because soldiers
were always in soggy boots and their feet were in bad shape.
This joint is located between the metatarsals and the
cuneiforms.
Metatarsal Break:
Figure 9-11, Page 169. From the book, it is “a generalization
of the instant centers of rotation of all five metatarsophalangeal
joints”. Roughly, it is anatomically the joints between the proximal
phalanges and metatarsals. In buying shoes, try to get shoes that
have approximately the same matatarsal break as your feet. This will
prevent lots of discomfort.
Plantar Fascia:
Reference figure 9-23, page 174.
Palntar Fascitis: 95% of us will have plantar fascitis. It commonly
occurs in people between 35 and
50 years of age.
Symptoms: wake up one morning and it hurts to put pressure on
your foot. At this point,
you’ve torn something on that first stretch. But by the time
you’ve stretched it out, it’s
not painful anymore. But eventually, it takes longer and longer
for it to go away and then it aches all day. Usually, this happens
to one foot at a time. People use painkillers and surgery.
Causes: while asleep, your plantar fascia relaxes and can become
fibrotic. When you stretch
it, it tears.
Prevention: wear bed boots (rubber booties) to keep your toes
from curling. This prevents
the fascia from shortening up.
Construction workers can get this from wearing steel-toes shoes
– there’s no break in these
shoes. This keeps the foot from flexing. Combat boots do a
similar thing.
Hallux Valgus:
Reference figure 9-33, page 179.
The hallux deviates laterally and the first metatarsal deviates
medially. When the hallux
deviates laterally, it also rotates and the muscles surrounding
it pull it even more laterally.
This forms a “bunion” along the
medial aspect of the foot.
This condition is 99% preventable, 1% is hereditary. 98% of the
people who have this are
women between the ages of 48 and 60 years old. This is often
due to wearing pointed, high
heals (cowboy boots can have the same effect).
3 to 10 billion dollars are spent on this treatment of this
condition alone each year. (Less
than 10 billion dollars is spent on chiropractic care each
year.) For podiatrists, this is
95% of their business. This is one of the most common, most
painful, and most expensive diseases in the US.
So, comfortable shoes are the best!!
High Heels: legs are more tired at the end of the day since you have
to use more muscles to walk .
Achilles tendonitis: shortening of the Achilles’ tendon when
wearing high heels all week. Then,
when the person exercises on the weekend and wears shoes with
no high heel, there is a
tendency to snap the tendon.
Running Shoes: cheaper shoes are better because the feet do more of
the shock absorption. If the
shoes do more of the shock absorption, more force is transferred
to the ankle, knee, etc.
Best foot exercise: go barefooted! Sandals are often better than
most shoes.
Factoid: more money is spent on feet than on chiropractic.
If you treat feet, make sure that you know what you’re doing.