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Reverse Shoulder A Final Option For Restoring Function
03 Aug 2007
As edited by Joint-Pain-Forum.com
Athough most artificial joints resemble the shape and structure
of the joint they're designed to replace, one new prosthesis the
reverse shoulder takes a different approach, reversing the position of
the normal ball-and-socket design. The purpose of this anatomical
flip-flop is to give you a shoulder that is stable enough to let you
raise your arm, even if your rotator cuff is torn beyond repair,
according to Cleveland Clinic's Arthritis Advisor.
"When we replace a shoulder joint, it's normally with a traditional,
anatomically shaped design," says Joseph P. Iannotti, M.D., Ph.D.,
chairman of the department of orthopaedic surgery at Cleveland Clinic.
"But this design only makes sense if the tears in your rotator cuff are
repairable."
A working rotator cuff is the key to normal shoulder function since
it's this group of four tendons encircling the shoulder that keeps the
joint stable, holding the head of the humerous firmly against the curve
of the scapula (glenoid cavity). Only when this head is stable can it
act as an effective fulcrum, allowing the pull of your rotator cuff and
deltoid muscles to raise your arm.
Loss of function
"As you age, it's not uncommon to
develop a large tear in your rotator cuff," says Dr. Iannotti. "We
often see tears in people in their 60s and 70s that may have been there
for months or even years."
At some point, when a tear develops, the rotator cuff is unable to hold
the humeral head within the socket, allowing it to slip out of place,
hindering shoulder function. "Such tears can lead to pseudo or
functional paralysis," says Dr. Iannotti. "Though your nerves are fully
functional, you can no longer raise your arm to shoulder level."
If the tear is repairable, the shoulder muscles not too atrophied, and
the shoulder has severe arthritis, your surgeon will likely recommend a
traditional shoulder prosthesis whose design mimics the natural
position of the humeral head (ball) and scapular depression (socket).
This anatomic design is an effective solution as long as your repaired
rotator cuff can provide adequate stability to the new joint.
"Some 20 to 30 percent of patients with significant rotator cuff tears
and arthritis still have enough residual function to raise their arms
to shoulder level before surgery, and are still good candidates for an
anatomic prosthesis," says Dr. Iannotti.
Reverse-shoulder prerequisites However, if your tears are irreparable,
the pain from arthritis is significant and, most importantly, you are
unable to lift your arm to 90 degrees, then you may be a candidate for
a reverse-shoulder procedure. Though the reverse shoulder prosthesis
(made by DePuy, Tornier, Encore, and Zimmer) has been used clinically
in Europe for more than two decades, it only received approval from the
U.S. Food and Drug Administration in November 2004.
"Though I mostly recommend reverse shoulders for those over age 70, it
can also make sense for younger patients who have a previous shoulder
implant that has failed," says Dr. Iannotti, who has performed more
than 120 of the procedures.
Candidates for a reverse shoulder must meet two other criteria good
deltoid muscle function and a healthy glenoid bone. The importance of
these is best explained by looking at the design of the reverse
shoulder prosthesis.
Stable by design
As the name implies, the reverse
shoulder flip-flops the normal position of the shoulder's ball and
socket, putting a metal (titanium) stem topped with a plastic cup where
the head of your humerus was and, on the other side, putting a metal
plate and partial sphere (glenosphere) where the depression (glenoid
cavity) on your scapula was. According to design engineers, this
reversal changes the center of rotation within the joint, making the
new head of the prosthesis inherently stable, regardless of the health
of your rotator cuff.
With this design, good glenoid bone quality is a must because the bone
must hold the screws which anchor the plate that holds the metal
glenosphere. A functioning deltoid muscle is important since the new
prosthesis depends upon this muscle for its arm-lifting power.
"As long as you have about 75 percent deltoid function, you'll be eligible for a reverse shoulder," says Dr. Iannotti.
Measured expectations
The range of motion you regain
with a reverse shoulder will depend, in part, on how much function
remains in your rotator cuff. "At a minimum, even with a little or no
cuff function, you should be able to raise your arm to shoulder level,"
says Dr. Iannotti. "And those who retain at least partial function,
especially in the posterior rotator cuff tendons, will often obtain 120
to 140 degrees of shoulder elevation."
Of course, getting to that point means a serious commitment to
rehabilitation. The rehab program with a reverse shoulder is similar to
that with an anatomic shoulder design, but it often can begin a bit
sooner, since the shoulder's more innately stable design is less
dependent on the health and healing of surrounding tissues.
Imperfect solution
Though a reverse shoulder can be a
big help to certain people, it's far from an ideal solution. "The
nature of the design puts a higher than normal load on the screws that
are anchored into the glenoid process and, with repeated stress, can
become loose and cause premature failure," explains Dr. Iannotti, who
still views the reverse shoulder as a last-resort salvage solution in
very selected patients.
"The reverse shoulder remains a complex procedure, for which there is
not enough data to know long-term greater than 10-year results," says
Dr. Iannotti. "What we do know is that, for a select group, it may be
the best hope for more normal shoulder function."
Are You a Candidate?
If you experience or have one or more of the following, you may be eligible for a reverse shoulder procedure:
-- Severe shoulder arthritis with ongoing pain
-- Inability to raise extended arm to shoulder height
-- Irreperable large or massive rotator cuff tears
-- Healthy bone stock in scapula clavicle (glenoid cavity)
-- Functioning deltoid muscle
-- At least 65 years old, but younger if you've experienced failure of a previous shoulder replacement
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