Stiffness vs. Instability

• During surgery, we can remove more bone, release more soft tissue, and/or use thinner implants to give the knee replacement more motion, but this increases the risk of instability.

• We can remove less bone, release less soft tissue, and/or use thicker implants to give the knee replacement more stability, but this increases the risk of stiffness.

• Patients with considerable pre-operative stiffness often become stiff after surgery.

• The immediate post-operative swelling will make most knees stiff for the first few months after surgery.

• Goal to achieve an ideal balance between stability and range of motion when the patient is fully recovered

• Therefore, most knee replacements will initially be stiff for a few months and achieve an ideal balance between stability and range of motion around 3-6 months.

Infection

• The risk of a post-operative infection is about 0.25% for healthy patients.

• The risk of a post-operative infection is about ~3-4% for smokers.

• The risk of a post-operative infection is about 2-3% for poorly controlled diabetics.

• The risk of a post-operative infection in obese patients range from about 1% with a BMI of 45 to 2-3% with a BMI of 55.

Blood Clots

• Patients without a history of blood clots are usually asked to take aspirin for 4 weeks.

• Low risk patients have a ~0.5% risk of a blood clot while on aspirin.

• Low risk patients have a ~2-3% risk of a blood clot if they do not take their aspirin.

• Patients with a history of blood clots are asked to take a strong blood thinner (Xarelto, Eliquis, etc.) for 4 weeks or longer.

• High risk patients have a ~2-3% risk of a blood clot while on a strong blood thinner.

• High risk patients can have a very high risk of a blood clot if they do not take their strong blood thinner. (not advisable)

• A blood clot is associated with calf pain, swelling and pain with ankle flexion.

• Early motion, ambulation and ankle pumps can help prevent blood clots.

• Ultrasound can be used to diagnose a blood clot.

• A blood clot can break off and move to your lungs (Pulmonary Embolus).

• Pulmonary Embolus can cause chest pain and difficulty breathing. In rare cases, pulmonary emboli can be fatal.

Alignment issues

• Most patients start out with some mal alignment (abnormal bow) to the knee before surgery.

• Varus deformity describes being bow legged (knees go out, feet go in)

• Valgus deformity describes being knock kneed (knee go in, feet go out)

• We will attempt to straighten your knee during surgery.

• Most knee replacements end up within 3 degrees of normal alignment.

Medical complication

• The stress of having any surgery can sometimes trigger medical issues.

• Heart arrythmias, stroke, GI bleeds, post op ileus and even death have rarely happened after some knee replacements

Fracture

• Fractures are exceedingly rare but occur to the femur, tibia, or patella both during surgery and after a fall after surgery.

• Patella fractures can sometimes occur years later if a patient falls directly on their knee.

Ligament Injury

• Ligaments injuries are exceedingly rare but occur to the medial collateral ligament (MCL), lateral collateral ligament (LCL), posterior cruciate ligament (PCL), patella tendon, and/or quadricep tendon both during surgery and after a fall after surgery.

Neurovascular Injury

• Nerve and vascular injuries are exceedingly rare but can occur to the popliteal artery and/or peroneal nerve.

Implant Loosening

• Knee implants are typically attached to the bone with cement.

• Sometimes, the bone cement or implant can loosen from the bone.

• If implant loosening occurs (micro motion), patients may have “startup” pain.

• Patients with startup pain may have temporary pain with weight bearing after prolonged sitting.

Implants Wearing Out

• Modern knee replacements can last 5-6 decades, but there are no assurances that they will last that long.

• Most knee replacement prior to 2000 had standard polyethylene that would typically wear out after 1-2 decades, cause osteolysis, lead to bone resorption around the implant.

• All modern polyethylene since 2005 has been highly cross linked and does not seem to cause osteolysis

Chronic Pain

• Knee replacements are very successful at relieving knee pain, but few patients can have persistent pain after their knee replacement.

• Any patient with persistent knee pain more than 12 months after their surgery should have a complete work up including x-rays, infection work-up (labs), metal suppressed MRI of the knee, and/or nuclear bone scan.

Functional Problems

• Knee replacements are successful at returning function, but a few patients can have long term functional difficulty including limping, stiffness, difficulty with stairs, and/or weakness.

• Any patient with functional problems more than 12 months after their surgery should consider a complete work up including x-rays, infection work-up (labs), metal suppressed MRI of the knee, and/or nuclear bone scan.

Late Instability

• Knee replacements can become unstable years after surgery through falls and other trauma to the ligaments.

• The patella can dislocate by sliding off the side of the knee.

• Constrained implants are sometimes necessary to correct the instability.

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The risk percentages discussed above are estimates for primary knee replacements. The risks for revision knee surgeries are often double those of primary knee replacements.