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For a considerable amount of
time after surgery, you will be placed on restrictions regarding your
movements. Some of these will occur naturally because of the pain and
trauma of surgery. Others
will be things about which you must constantly remind yourself,
especially as the pain subsides and your flexibility increases.
One is crossing your legs (i.e. not allowing your operative leg
to cross the centerline of your body) and the other is the 90-degree rule.
The 90-degree rule means that
you must not bend your knee up any closer to your chest than 90-degrees,
and this restriction applies to standing as well as sitting (i.e. no
bending over to pick up things on the floor, no reaching down to tie
your shoes, no sitting on low stools, etc.).
This is meant to help you avoid dislocation after surgery.
After a time, your doctor may remove the 90-degree restriction,
but you should always be aware of dislocation risks whenever you bring
your knee toward your chest.
While vacationing on a cruise
ship, I had the opportunity to talk for an extended time with a physical
therapist who was also vacationing.
I told her that I had read horror stories of people who had
dislocated their hips after breaking the 90-degree rule or by twisting
their bodies. I wanted to
know whether it was okay to twist toward or away from the prosthetic
hip. She told me that,
taken individually, the movements (i.e. breaking 90 degrees and
twisting) were not intrinsically bad in themselves; but when they were made in
combination, the results could be unfortunate.
As far as the twist direction was concerned, it all depended on
the surgical approach used in performing the hip replacement—i.e.,
anterior (front), posterior (rear), lateral (side).
I told her that my scar was up
the side curving slightly over the back of the buttocks that indicated a
lateral or posterior/lateral approach. She said
what I needed to avoid were the movements the surgeon had used in
dislocating my hip for surgery. His
method for dislocating my hip established a weakness in my body that
could lead to dislocation if the movements were performed again in the
proper combination. In my
case, the weakness was probably even more extreme because he dislocated
my hip twice due to my two hip surgeries.
(Recipients of revision surgery are more prone to dislocation
than individuals who have had only one hip replacement.)
For a lateral or posterior/lateral approach, the
surgeon brings the knee up toward the chest and rotates the knee toward
the center of the body. He
then rotates the knee past the center line toward the opposite side of the body—the same
motion as twisting the body toward the hip—and applies pressure that
“levers” the hip out of joint. (This may also explain the groin discomfort after surgery due
to the pinching of the skin, muscles, and tendons near the hip capsule that occurs when the hip is levered out of joint.
It might also explain how the artery in that area can become
disturbed leading to avascular
necrosis (AVN) in anyone who suffers a hip
dislocation or has the hip dislocated for hip resurfacing surgery.)
I suffered a sever sprained ankle as a child, and as an adult I’m still plagued with a weakness in that ankle that has allowed it to become sprained numerous times throughout my life; therefore, I understand how a propensity toward dislocation can occur after having had the hip dislocated once—or twice. Even though I have a large femoral head on my total hip replacement stem, I’m still conscious of not repeating the series of motions that were used to dislocate my hip for surgery—raised knee, inward rotation of the leg, and twisting the truck of the body toward the prosthetic hip.
It is therefore a good idea to learn what surgical approach was used for your hip replacement—anterior, posterior, lateral—and then to learn exactly what movements were used to dislocate your hip based on that approach. Afterward, you should strive to be conscious of those movements and endeavor not to perform them in that particular order.
Another thing that is beneficial is to examine a human skeleton model that many physicians have in their offices. It is one thing to be told how the femur can impinge on the acetabulum and cause a dislocation, but it is really hard to visualize the movements that lead to it. However, the simple act of moving around the femur of a skeleton brings everything into clear focus, and instantly you understand how easy it is for the femur to slip out backwards when the knee is brought to the chest and internally rotated. This type of "hands-on" experience could greatly increase patient education about hip restrictions and prevent a lot of dislocations.