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.
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.
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
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