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DR. ARNO SMIT, M.D., F.R.C.S.(C)
ORTHOPAEDIC SURGERY Unit 44 - 1480 Foster Street
White Rock, B.C. V4B 3X7
Phone: (604) 538-0068
Fax: (604) 538-0703
You are scheduled for unicompartmental (partial) knee replacement, Oxford knee,
lateral compartment. This document summarizes the discussion that you and I had
about the benefits and risks associated with this procedure. Please read this
document carefully, then acknowledge your understanding and agreement by
initialling on the lines provided before the various points. This will help
ensure that you fully understand the implications of the decision to undergo
Please review the following points:
1/ Purpose of operation. The primary purpose of this procedure is relief of
pain. Secondary purpose of this procedure is to enhance walking ability.
Tertiary purpose is to restore anatomy as closely to normal as possible. The
prosthesis is designed for walking, even brisk walking. It is not designed to
allow running etc. It must be emphasized that most experience with this
prosthesis involves the medial side. The alternative of total knee replacement
has been discussed.
2/ Risks of operation. It is not difficult to see how this operation may be
beneficial to you. However, all of surgery carries inherent risks. Risks
pertinent to this operation include the following:
-Risk of anesthesia, general or spinal anesthetic. You will have the
opportunity to discuss this further with the anesthesiologist.
-Risk of infection. The infection risk is approximately 1:100. Superficial
infection can be managed by antibiotics, and/or washout of the wound and
surgical site. On occasion, the prosthesis will become infected. In this
scenario, removal of the prosthesis, temporary placement of an antibiotic
loaded spacer, and definitive placement of a new prosthesis after approximately
two or three months would be necessary. This would most likely involve a total
knee replacement, rather than another partial knee replacement. This is a very
grave complication, and is fortunately rather rare. Surgery to replace an
infected prosthesis would normally be carried out in a university hospital.
Extremely rarely, the infection cannot be controlled and a definitive
prosthesis cannot be placed. This may lead to a ‘flail knee’, knee fusion
(‘stiff leg’) or even amputation. Death from uncontrolled infection is
extremely rare, but possible. The risk of infection is increased in the
presence of smoking, diabetes, rheumatoid arthritis, and other conditions
affecting the immune system. Of note, late infection can occur when bacteria
circulate in the bloodstream, In situations such as invasive dental work,
urology/gynecology procedures, bowel procedures etc.. If possible, a discussion
with the treating practitioner regarding the need for protective antibiotics
should be carried out prior to performing these procedures.
-Injury to the neurovascular structures. Important nerves and blood vessels are
located around the surgical site. Great care is taken throughout the operation
to avoid damage to these structures. However, on occasion damage to nerves can
occur, possibly leading to numbness an/or weakness, possibly paralysis. This is
very rare. Damage to the blood vessels is very rare as well. However, such
injury could lead to rapid blood loss, and may lead to blood transfusion during
surgery. As well, vascular repair could be necessary, ordinarily performed by a
vascular surgeon on an emergent basis. This would require emergency transfer to
a hospital providing vascular surgery. Fortunately, major vascular injury is
-Deep venous thrombosis/pulmonary embolism and the need for anticoagulation.
This operation can lead to development of a blood clot in the deep veins of the
operated and/or non-operated leg. This impairs the circulation in the legs.
Furthermore, parts of this blood clot can be released into the bloodstream,
these can reach the heart and lungs and cause severe shortness of breath, even
sudden death. In order to minimize this risk, you will be asked to start
walking as soon as possible after the surgery. The risk of this complication
appears to be less than after a total knee replacement. Formal blood thinning
does not appear to be necessary, based on recommendations from the Oxford
group. It is my preference, however, that you take aspirin, 325 mg per day, for
six weeks, as a precaution. Under these circumstances, the risk of death from
pulmonary embolism appears to be well below one in thousand. If a blood clot
develops in the legs, this may lead to prolonged treatment with a blood
thinner. If heart/lungs become involved, intensive care treatment may be
required. These complications would ordinarily be treated by an internist.
-Possibility of a blood transfusion. This operation will lead to some blood
loss. Usually, this is between 20 and 200 ml. Most often, blood transfusion is
not necessary. No formal arrangements for blood transfusion will be made
preoperatively. However, it is possible that occasionally sufficient blood loss
would occur to warrant a blood transfusion.
-Possibility of bearing dislocation. This prosthesis has a mobile bearing. This
minimizes wear and tear, and is most likely responsible for the very good
long-term results that have been achieved with this prosthesis. It is possible
for this bearing to dislocate. This is quite rare medially, less than 1:100.
However, it is not quite as rare in the lateral compartment, approximately
10-15%, usually within the first year. Treatment for this would be replacement
of the bearing with a slightly thicker bearing, as an urgent operation. Current
designs of the lateral bearing hold the promise to diminish this risk. However,
this has not been conclusively proven.
3/ Expected postoperative course.
-Mobilization after surgery is important to prevent complications, and to
resume independent self-care as soon as possible. Usually, fully bearing is
allowed immediately postoperatively. Wearing a brace for six weeks may be
recommended, based on the inter-operative assessment of the stability of the
bearing. At the two-week assessment, a decision will be made regarding the need
for physiotherapy. Approximately 80% of patients will not require physiotherapy
after unicompartmental knee replacement. Final range of motion achieved after
lateral unicompartmental knee replacement is usually not as good as after
medial unicompartmental knee replacement, and in my assessment, seldom exceeds
100-110 degrees of flexion, usually just good enough for stationary bike
riding. This range of motion will not allow normal stairs walking.
-Hospital stay is dependent on achieving pain control through medication by
mouth, as well as achieving safe, independent, mobilization. After this
operation, the vast majority of patients will be able to go home the morning of
the day after surgery.
-Arrangements for staple removal and initial assessment are made for the
two-week mark, at which time the need for formal physiotherapy will be
assessed. As mentioned above, usually, no further physiotherapy is necessary.
-I explained that, initially, residual discomfort and swelling are common.
Numbness may be present, usually over the lateral aspect of the knee. These
issues usually settle in approximately six months, occasionally a year. Rarely,
these can persist.
- Further standard follow-up will be at 8 weeks, 6 months, and one year. After
this, yearly follow-up with X-rays is recommended, to allow early detection of
possible problems with the prosthesis.
If after reading this, you fully understand the issues and wish to proceed, your
signature on this document will confirm the previously obtained consent for
surgery and blood transfusion.
Arno Smit, M.D., F.R.C.S.C.