The Knee arthroplasty, Knee implant & Knee replacement are similar terms. This is a minimal invasive surgical procedure to replace either only damaged portion of knee or, total knee joint in order to remove the pain and movement disability.

The knee replacement may be required due to Osteoarthritis, Psoriatic arthritis (people having Psoriasis in which red patches with silvery scales are found on skin) or, Rheumatoid arthritis. However, in case of people, suffering with Osteoporosis, the knee replacement is not required because of absence of any pain, inflammation or, deformation.

Main reasons for Knee replacement:

1. Arthritis.

The knee pain is one of the major symptoms of a disease, called Arthritis which is occurred due to meniscus / ligament tears, roughness of articular cartilage, lack of a fluid, called synovial fluid, leading inflammation and stiffness of joints. The Synovial fluid works a natural lubricant in movement of joints. It is a is a viscous and non-Newtonian fluid, having white egg like consistency and stored in synovial joints. Its main function is to minimize the friction during movement of articular cartilage of synovial joints. The articular cartilage is a group of connective tissues and its main function is to provide a smooth and lubricated surface for transmission of shear loads with the least frictional force.

2. Rheumatoid arthritis:

It occurs when body’s immune system attacks and destroy the articular cartilage.

3. Deformities:

Sometimes, the patients with “bowed legs or, knock knees” also require surgery for the restoration of position of knee. This condition is called ‘genu varum’ or, ‘tibia vara’.

4. Knee injury:

The broken bone and/or, torn ligaments around knee may also need knee replacement.

5. Osteonecrosis:

It is a condition in which the blood supply, to bone, is stopped and then, the knee may be required to be implanted.

Types of Knee Surgery:

Any of the following four (4) types of knee surgery may be required, depending upon the condition of knee joint:

• Total knee replacement. This is most common surgery in which the surfaces of the thigh bone and shin bone that connects to the knee are replaced. The lower end of femur (femoral component), upper end of tibia (tibial component) and back surface of patella are main components which are replaced in total knee replacement/implant. The patients in whom, the patellectomy (removal of patella) has been done previously, may also go for knee replacement. However, the prosthesis, used, may be different in such cases.
• Unicompartmental (Partial) knee replacement. This type of knee replacement is normally performed through a cut, smaller than what needed for total knee replacement. If only one side is effected by arthritis, then, this surgery is However, this procedure is advisable only if the knee ligaments are strong. The knee is divided in 3 parts viz: inner (medial), outer (lateral) and the knee cap (patellofemoral). Many times, only inner side of knee is affected by arthritis. The half-knee replacement (partial replacement) may be suitable for these patients but, it is not suitable for everyone because, it needs strong & healthy ligaments within knee.

The probability is about 1 out of 10 persons who needs further surgery after 10 years. The partial knee replacement can be done at any age. Besides, this procedure is less stressful operation with less pain and less risk of bleeding for older patients. The success of this surgery depends more on the severity of arthritis than the age of patient.

• Patellofemoral (Knee cap) replacement. Here, only the under surface of knee cap (Patella) is replaced but, due to higher success rate of total knee replacement surgery, the same is recommended in such cases.

In this procedure, only under-surface of knee cap and Trochlea (a structure resembling like a pulley), affected by arthritis, are replaced. As the failure rate is higher in this procedure, hence, some times, total knee replacement is advised and on the other hand, others do feel like it is better to preserve the rest of knee till it is not impaired due to arthritis. The probability of success is as low as 1 out of 40 persons but, the success rate may be more in those patients whose arthritis does not worsen.

• Complex or, revision knee replacement. This procedure is repetitive and hence, very complicated also. It is, therefore, needed only in severe arthritis, where, 2-3 knee replacements have already been done earlier. The usual reasons for this procedure are:

1. Major bone loss due to arthritis or, fracture.
2. Major deformity of knee.
3. Weakness of knee ligaments.

The longer stem, allowing more securely fixed components in the damaged bone cavity, are found in complex knee replacements.

Materials and designs, used in knee implants: The alloys and compounds of mainly Titanium, Zirconium, Cobalt, Chromium and Polyethylene etc are used for knee implants. The Stainless Steel is not used in these procedures due to its limited capability to resist the corrosion for long time in the human body.

The weight, height and level of activity are main concerns to decide the design of implant. The materials, used, may be anti corrosive metal, ceramic, or plastic to allow smooth movement and suit with anatomy of patient. The life of new implant is about 20 years.

It is observed that the swelling may persist for 3 to 6 months after surgery. The ice packs are found to be very effective to reduce the swelling and inflammation in operated knee joint and its surrounding tissues.

Medicines: Morphine, Hydromorphone (Dilaudid)

• Hydrocodone, which is found in Norco and Vicodin.
• Oxycodone, which is found in Percocet.
• Meperidine (Demerol)

The medicines, given after knee replacement, minimizes pain, nausea, risk of post operative probable infections and prevents the blood clots. The success rates of knee joint replacements are more than 90 percent after 10 years.

Knee joint infection related complications occur in around 2% patients. The knee icing for 20 to 30 minutes during few weeks after surgery reduces pain & swelling. After 3 months, the patient may recover for main activities and after one year, may fully recover to gain maximal strength and endurance.

The sparing of quadriceps muscles reduces minimal invasive surgery after operation and tendon is cut through during a traditional TKR. The small incision which will move the soft tissue instead of cutting it.

The following complications need to be discussed with surgeon before TKR:

Blood clots. Blood clots in the deep veins in the leg, called Deep Vein Thrombosis (DVT) can cause pain and/or swelling.

Pulmonary embolism (blood clotting in Lungs).

Wound infection.
Nerve and other tissue damage.
Bone fracture.
Dislocation.
Bleeding and wound haematoma (swelling of clotted blood).
Pain.

Basic steps to be followed for Total Knee Replacement (TKR).

First of all, the infected bone is cleaned and prepared for procedure.

Then, damaged cartilage surfaces at the ends of the femur and tibia are removed along with a small amount of underlying bone. Then, metal implants are positioned at place. The Patella is resurfaced and a spacer is inserted.

The expected life of knee after TKR is around 20 years in 80-90% cases and the same is around 10 years in case of Partial Knee Replacement (PKR) and chances of repeat operation is 1 out of 10 persons.

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