Minimally invasive knee replacement surgery refers to modifications of conventional knee replacement surgery designed to reduce tissue trauma and improve recovery time. Knee replacement surgery is one of the most successful procedures in modern orthopedics. The procedure involves resurfacing the knee joint with biomaterials that substitute for the worn-out bone and cartilage.  Many conditions can lead to the need for knee replacement surgery. The most common causes are:  

• Osteoarthritis
• Rheumatoid arthritis
• Injury
• Avascular necrosis
• Knee deformity
• Gout

Although modern techniques have allowed conventional knee replacements to last well and improve function, many patients still experience considerable pain and lengthy recovery following surgery. Uncomfortable physical therapy is a particular concern for patients looking to make a quick return to work and activity.  While adults of any age can be considered for knee replacement, most are performed on patients between the ages of 55 and 80. The best results tend to be seen in healthy active patients with few medical problems.

Surgeons are constantly modifying their technique to improve the results of knee replacement surgery. “Minimally invasive” refers to those techniques that minimize the trauma to the soft tissues and bone around the knee.  Traditionally this meant simply making a smaller skin incision but more recently implant companies have developed specialized instruments that cause less trauma beneath the skin as well. Perhaps the most radical form of “minimally invasive” knee replacement involves modern robotic-assisted procedures where the soft tissues are protected during the cutting of bone by a robotic controlled saw blade.  These modifications to conventional knee replacement surgery are allowing greater numbers of patients to return home within hours of their surgery.

What Does Conventional or “Traditional“ Knee Replacement Surgery Typically Involve?

• Large incisions
• Significant postoperative pain
• Several day stay in a hospital
• Postoperative rehabilitation
• Extensive physical therapy

Patient satisfaction after traditional knee replacement has been described as ranging from 75% to 92%. This means that up to 25% of patients are dissatisfied with their results following surgery.  There are many reasons why patients are dissatisfied after knee replacement surgery but the most common are pain, stiffness, and deformity. The demand for knee replacement is increasing and the average age of patients receiving knee replacement is decreasing.  As people live longer and stay active later in life they put a greater demand on their joints. Modern medicine has responded with technological advances designed to improve the function and longevity of knee replacements.

Another major reason for dissatisfaction after knee replacement is the development of complications associated with the surgery.  Although knee replacement is one of the safest orthopedic procedures performed serious complications can still occur. These can range from skin reactions caused by medications to infection and blood clots.  A person’s overall health should be optimized prior to undergoing surgery to lessen the possibility of complications. Many times a patient’s primary care physician or specialist is consulted to help with this process.  Major advances have been made to our surgical protocols that decrease the risk of complications.

Benefits Of Minimally Invasive Surgery

One example is outpatient joint replacement.  Healthy patients undergoing “minimally” invasive surgery are usually candidates for returning home the same day as surgery.  This promotes rapid recovery with early walking and decreases the chances of hospital-acquired infection. Many other advances will be discussed in upcoming articles.

The overall concept of knee replacement surgery is the same for minimally invasive and traditional knee replacement. Biomaterials are used to resurface the worn-out cartilage on the ends of the knee joint.  The most commonly used materials are cobalt chrome, titanium, and polyethylene plastic. The design of the implants is fairly standardized with slight differences between manufacturers. The same implants can be used for either minimally invasive or traditional knee replacement.  It may be best to think of “minimally invasive” and “traditional” knee replacement as different techniques used to perform the same procedure.

What Should I Expect During Minimally Invasive Knee Surgery?

Knee replacement surgery begins with an incision over the front of the knee. A second lengthwise incision is made beneath the skin going around the kneecap. This allows the surgeon access to the knee joint. In traditional knee replacement surgery, blocks of metal are aligned and fixed to the bone to guide the surgeon as he removes the ends of the bones with a special saw.  Metal implants are then fixed to the ends of the bones with a piece of plastic fixed in between. A plastic button is also sometimes fixed to the underside of the kneecap to complete the joint replacement. The soft tissue incisions are then repaired with suture material and a soft tissue dressing is applied. Patients are encouraged to start walking as soon as possible after surgery.  A physical therapist often helps the patient get out of bed and walk during their stay in the hospital.   

The major difference between minimally invasive and traditional knee replacement is in the handling of the soft tissues. The same implants still need to be attached to the ends of the bones in the joint but how the soft tissues are handled appears to make a big difference in patient recovery.  Smaller incisions and less soft tissue dissection results in less soft tissue damage which can lead to less inflammation which in turn can lead to less pain and stiffness. However, as with most things there is a trade-off. Sparing soft tissue can lead to better results but it makes the procedure significantly more technically demanding for the surgeon.  A surgeon is typically only as good as what he can see. Making smaller incisions decreases the surgeons ability to see and visualize the joint and increases the potential to make mistakes with implant positioning. Where the implants are fixed on the ends of the bones is probably even more critical to optimal results than minimizing soft tissue damage.

Decreased visualization and the technically demanding nature of minimally invasive surgery are the two biggest disadvantages. The next generation of knee replacement surgery utilizing robotic-assistance promises to minimize or eliminate these drawbacks.  This next generation of minimally invasive knee replacement utilizes software that allows the surgeon to visualize a patient’s joint without physically “seeing” it and helps the surgeon determine the optimal position for the implants. After this is done a robotically controlled sawblade protects the soft tissue surrounding the bones of the knee during cutting.  The precise cutting with the robotic arm ensures accurate placement of the implants. These advances improve results with many patients experiencing less pain and better range of motion following surgery than with traditional knee replacement.