What Is Knee Replacement Surgery?

During a total knee replacement (TKR), the bone and cartilage at the end of the thigh bone and shinbone are removed. An implant is then placed on the knee to create a new joint surface. This implant functions similarly to a normal knee.

Those who have disease limited to one area of their knee (for example, only the medial or inside compartment of their knee) may be candidates for partial knee replacement instead of TKR. However, most patients require the latter, which is focused on here.

Total knee replacement surgery takes one to two hours and is performed by an orthopedic surgeon in a hospital. Less often, it is performed in an outpatient surgical center.

Your surgical team will help you decide what type of anesthesia is best for you:

• General anesthesia
• Regional anesthesia (e.g., epidural, spinal, or femoral block)

Various Surgical Techniques

There are two main surgical techniques used in total knee replacement surgery: the traditional technique and the minimally invasive technique.

• The traditional technique involves making an 8 to 12 inch incision in the knee to expose the joint. Once this is done, damaged tissues are removed and the knee implant is placed.
• The minimally invasive technique involves making a smaller incision (3 to 5 inches) and using long, thin surgical instruments to remove the tissue and position the implant.

Over the years, the minimally invasive technique has evolved to include three main approaches: 

• The subvastus approach: This approach preserves the quadriceps tendon and most of the blood vessels supplying the knee.
• The midvastus approach: This approach preserves the quadriceps tendon and may be associated with less blood loss and a shorter operation time when compared with the subvastus approach.
• The quadriceps-sparing approach: This approach preserves both the quadriceps muscles and tendon.

Minimally invasive approaches are associated with less blood loss, reduced postoperative pain, and a shorter hospital stay. Additionally, because there is less tissue trauma during surgery, patients may be able to reach milestones - like walking with a cane- sooner than with traditional surgery.

Computer-Assisted Total Knee Replacement

Some surgeons utilize a sophisticated computer imaging system when performing total knee replacements. While this surgical approach involves a longer operation time and is more costly, it may allow for a more precise implant alignment. Talk with your surgeon if you are interested in this investigational technology.

Implant Types

A knee implant is usually made of metal (e.g., cobalt chrome or titanium) and plastic (polyethylene). Each prosthesis typically replaces up to three bone surfaces:

• The top surface of the tibia
• The lower end of the femur
• The back surface of the kneecap (patella)

There are a variety of knee joint implants out there. Your implant will be selected during a pre-operative visit with your surgeon. The specific implant used for your knee replacement will depend on various factors, such as:

• Age, weight, and activity level
• Surgeon's preference and prior experience with the implant
• Amount of arthritis-related bone loss that has occurred
• Integrity of the ligaments supporting the knee

Do not hesitate to ask your surgeon questions about why a particular implant is being recommended for you.

There are also different ways in which the implant is placed during the surgery. Traditionally, the implant is fixed into the bone with cement. Now, though, a novel cement-less technique may be used. This means that the implant is press-fit onto the bone, allowing the bone to grow and permanently bond to the implant without any adhesive.

There is still debate within the medical community about whether a cemented or cement-less fixation is better. Early research has found that in young patients, cement-less fixation may provide better outcomes in terms of pain relief and restoring knee function.

Contraindications

Absolute contraindications to undergoing knee replacement surgery include:

• An infected knee joint (current or within the last year)
• A current infection elsewhere in the body
• Knee extensor mechanism problems, such as a patella (kneecap) fracture or patella tendon tear
• Unstable medical condition

Relative contraindications include:

• Insufficient bone stock for prosthesis implantation
• A skin condition over the knee joint
• Morbid obesity
• Neuropathic arthropathy (called a Charcot knee)
• Severe peripheral vascular disease
• Certain psychiatric illnesses, especially a history of substance abuse
• Unrealistic expectations with regard to the potential surgical outcome

Potential Risks

Knee replacement surgery has become quite common. Fortunately, well over 90% of patients who undergo knee replacement surgery have good results, but there are still risks that must be considered.

Besides general surgical risks like blood clots, pneumonia, and bleeding, other potential complications that may occur after a knee replacement surgery include:

• Surgical site infection
• Wound dehiscence
• Continued stiffness
• Peripheral nerve injury
• Knee fracture

Purpose of Knee Replacement Surgery

The joint inflammation that characterizes arthritis can lead to cartilage loss and exposed bone over time. With the normal, smooth joint surface compromised, pain and disability can occur.

The purpose of knee replacement surgery is to restore knee function, alleviate symptoms like knee pain and stiffness, and improve mobility and overall quality of life.

Knee replacement surgery is indicated for patients who:

• Have failed to get better after six months of nonsurgical therapies (e.g., weight loss, aerobic exercise, taking a nonsteroidal anti-inflammatory drug, and undergoing corticosteroid knee joint injections).
• Have evidence of end-stage knee arthritis on X-rays
• Have severe knee pain, especially at night
• Have decreased mobility and difficulty performing activities of daily living (e.g., bathing and dressing)

While the vast majority of knee replacement surgeries are performed in older individuals with osteoarthritis, surgery may also be performed in people with one or more damaged knee joints from post-traumatic arthritis, or in people with inflammatory arthritis like rheumatoid arthritis or psoriatic arthritis.

Rarely, children with juvenile idiopathic arthritis may undergo knee replacement surgery.

How to Prepare

After scheduling your knee replacement surgery, you will be provided with instructions on how to prepare for the operation.

In addition to standard directions all surgical patients are given - like stopping certain medications for a period of time, stopping smoking for at least two weeks prior to surgery, and avoiding food after midnight on the eve of your surgery - your healthcare provider may suggest:

• Meeting with your primary care physician to optimize underlying health conditions (e.g., diabetes) and undergo preoperative studies, like an electrocardiogram (ECG) and blood tests
• Attending a preoperative education class
• Packing rubber-soled, flat shoes to leave the hospital in
• Renting/purchasing a walker, which a loved one should bring to the hospital before you are discharged
• Lining up help at home for a week or two after being discharged from the hospital

You will also want to prepare your home for recovery after surgery. Start by removing fall hazards like throw rugs and loose electrical cords. Since stairs can be challenging to manage after surgery, setting up a temporary bedroom on your first floor is also a reasonable idea.

Day of Surgery : What to Expect

On the day of surgery, you will first go to a pre-operative room where you will change into a hospital gown. A nurse will then record your vital signs and place a peripheral IV in your hand or arm.

After briefly meeting with members of the surgical and anesthesia teams, you will be taken into the operating room.

If undergoing general anesthesia, you will be given medications to put you to sleep and an endotracheal tube connected to a breathing machine (ventilator) will be placed. If you are undergoing regional anesthesia, you will be given a sedative to relax you while the anesthesiologist performs a nerve block (usually in your lower back).

Knee replacement surgery will then typically proceed with the following steps:

1. The surgeon will first clean the area around the knee with an antiseptic solution.
2. The surgeon will make an incision on your knee (larger if using the traditional technique, smaller if opting for a minimally invasive one).
3. The damaged parts of your knee joint will be removed. If the minimally invasive technique is used, the surgeon will use special surgical instruments to minimize tissue disturbance.
4. Next, the surgeon will attach a prosthesis to the bone, most commonly with cement.
5. Once the prosthesis is placed, the incision site will be closed with staples or stitches. A drain may be placed at the surgical site, which will be removed later.
6. A sterile bandage will then be placed over the knee wound.

Recovery

You can expect to stay in the hospital for approximately one to four days after your operation. While many patients experience significant pain relief and a rapid improvement in knee functioning within weeks of the surgery, full recovery can take anywhere from six months to a year.

As you recover in the hospital, you can expect the following:

• You will begin knee exercises and work with a physical therapist.
• You may use a continuous passive motion (CPM) machine for your knee (based on surgeon preference).
• You will take a blood thinner (an anticoagulant) to prevent blood clots.

Once discharged home, it's important to follow your surgeon's post-operative instructions, which may include: 

• Wearing a compression sock
• Elevating/icing your knee to reduce swelling
• Taking medication as directed
• Resuming your normal diet and maintaining a normal weight
• Keeping your wound clean and dry and changing the knee bandage as instructed.
• Resuming normal activities within three to six weeks after surgery.