Minimally Invasive Knee Replacement Preparation

Being educated about what to expect is important after minimally invasive knee replacement surgery. Patients should have realistic goals for their recovery. Keep in mind that each person recovers differently. In fact, people who undergo knee replacements of both knees at once often experience somewhat different recoveries on each side.

The term minimally invasive is somewhat misleading and overused. It is still a surgery, and any surgery is invasive. The human response to injury includes discomfort, altered emotions, and a recovery period until healing occurs. Minimally invasive surgery can reduce, but not eliminate, these normal responses to the trauma of surgery. Minimally invasive surgery also does not mean risk-free surgery. Knee replacement surgery, regardless of technique, is associated with risk of infection, nerve injury, deep blood clots, premature implant loosening and failure, unexpected knee stiffness, continued pain, unpredictable medical complications, and even death. While these complications are uncommon, people undergoing knee replacement surgery need to be aware of them before undergoing any type of reconstructive procedure.

Usually, minimally invasive surgery simply means performing a big operation through a small incision. In other words, the deep muscle injury is often unchanged, but the scar is smaller. Surgeons who perform at least 100 knee replacement procedures per year are most able to progressively begin shortening the incision, while keeping the procedure the same. Many orthopedic implant companies have developed special instruments and training for surgeons. Learning more about the procedure by reviewing the patient educational materials provided on an orthopedic company's Web site, such as Zimmer, Inc., can be helpful. The Web site can help identify surgeons in the area who use a particular company's implants and are therefore qualified to perform the procedures safely.

Considerable difference exists between most knee replacement procedures that are performed by making a shorter incision and the so-called quadriceps-sparing knee replacement procedure.

Minimally Invasive Knee Replacement

The quadriceps muscle is actually a group of four well-developed muscles in front of the thigh that connect to the kneecap through a common tendon called the quadriceps tendon. This group of muscles controls movement of the knee and is critical for normal walking and standing. Traditional knee replacement surgery involves cutting into the quadriceps tendon to turn the kneecap over and push it out of the way in order to expose the arthritic joint that is to be replaced.

In minimally invasive surgery, a surgeon uses the same surgical technique as described above, except the cut in the quadriceps tendon is smaller. Instead of being turned over, the kneecap is pushed to the side. Special instruments allow the entire surgery to be performed through a smaller skin incision. The smaller cut to the quadriceps tendon considerably eases recovery. A patient who has had this type of surgery may be able to leave the hospital on the day of surgery or just a day or two later.

Well-trained surgeons using special instruments can shorten the incision of a standard knee replacement from 8-12 inches to about 4 inches. Incision size is ultimately dependent on each person's anatomy and body fat. Severe arthritis with deformity and heavier people require longer incisions to allow the replacement to be done safely. In most cases, a 4-inch scar is sufficient for the surgeon to enter the knee joint and to perform the procedure properly.

Quadriceps-Sparing Knee Replacement

To truly spare the quadriceps tendon from any cutting, a different variation of minimally invasive surgery, called quadriceps-sparing knee replacement, can be used. This surgical approach is not new. Another name for it is the subvastus approach. "Subvastus approach" means going under the vastus muscle, which is part of the quadriceps muscle group. In essence, the surgeon makes a small (3- to 4-inch) skin opening. Next, the surgeon opens a fibrous layer of tissue called the retinaculum and enters the knee joint. Finally, to expose the knee joint enough to insert the artificial parts, the surgeon takes the cut in the retinaculum further up into the thigh. This is done without cutting or injuring the quadriceps tendon. The quadriceps muscle is instead lifted up out of the way, so special instruments can be positioned for the operation.

The incision for the quadriceps-sparing knee replacement is only as large as is necessary to place the artificial parts in the body. The cut into the skin is shorter, and the underlying cut to reach the bone through the deep tissues is also shorter than for standard knee replacement surgeries, so the quadriceps is not cut. Special instruments are used to access and prepare the bone through such a small incision. Implants designed for this type of procedure and occasionally x-ray guidance are also used for this surgery. This surgery is best performed by capable surgeons with training in this procedure.

This type of surgery cannot be performed on all people. Surgeons carefully select people for whom this procedure is possible. Yet 90-95% of people who are candidates for total knee replacement are suitable for this procedure.

Results after quadriceps-sparing knee replacement are dramatically better than results after knee replacements performed through a 4-inch incision using the standard technique. Benefits include an early return to walking, greatly reduced pain, and a remarkably different overall recovery. Scarring and soft tissue trauma underneath the skin are minimal.

Pain control measures can also speed up recovery. A painkiller may be given before the surgery, and a nerve block may be given in the thigh to numb the leg. Pain pumps that infuse painkillers into the incision may also be used. Early exercise is also encouraged to speed up recovery.

Today, most knee replacements done in the United States use parts that attach to the bone with special cement. A newer material called tantalum, a very porous material similar to bone, may also be used. When this metal is placed against bone, it allows bone to fuse into it.

By a few weeks after surgery, the bone is attached to the metal parts. The bone is stable and the implant is durable. By not using cement, the surgeon can also avoid using a tourniquet. A tourniquet is used by most surgeons in the United States to drain blood from the leg and to shut off the blood supply to the leg during surgery. However, restricting this blood flow is known to result in damage to the leg and thigh muscles and to prolong recovery. Avoiding use of a tourniquet allows faster recovery.

Using modern implants without bone cement and avoiding tourniquets allow for a faster recovery and better pain relief, particularly when combined with appropriate painkillers and the quadriceps-sparing surgical approach.

Lateral Approach Knee Replacement

Another method of performing knee replacement surgery, although rarely used, involves entering the knee joint from the outside. The incision is made on the lateral side (outside) of the knee joint, and the kneecap and the muscles supporting it are disturbed even less than during a routine knee replacement procedure. This surgical approach, called the lateral approach, is another type of minimally invasive knee replacement surgery. The lateral approach allows muscle damage to be avoided, and the kneecap mechanics are improved. Because this method of knee replacement is unusual, surgeons rarely use it. However, it has distinct advantages over traditional knee replacement surgery. Pain is decreased and people are able to return to walking faster.