Knee replacements are carried out through one of several different surgical approaches. In practice, however, there is not as much difference between knee surgical approaches as there is between hip surgery approaches. There are advantages and disadvantages to each approach, and there is some controversy among knee surgeons as to which is the best. All surgeons have a favored surgical approach, and while there are often heated and spirited debates at academic conferences and meetings, it is a testament to the success of the procedure that all of them generally produce good results.
Recently there has been much interest in minimally invasive surgery for knee replacement, as there has been with hip replacement surgery. There is no widespread agreement as to exactly what constitutes "minimally invasive," but most surgeons would agree that the general principal is to have less soft tissue disruption and dissection. As with the hip, this often may translate into a smaller skin incision, but it is what goes on under the skin that is far more important for speed of recovery. The single most important difference for minimally invasive knee surgery appears to be decreasing the amount of muscle and tendon that is disrupted.
Anterior Surgical Approach
Most of the surgical approaches for the knee have a similar skin incision, going vertically over the front of the knee. The reason for this is primarily that most of the important blood vessels and nerves are in the back of the knee and are avoided. It is also important to have an extensile approach, meaning that the incision can be extended upwards or downwards as needed.
The traditional anterior surgical approach goes straight down the middle of the knee. The tight capsule around the knee, called the retinaculum, is usually opened along the inner (or medial) side of the patella (knee cap). This is often called a "medial peripatellar arthrotomy," meaning an opening into the knee joint is made just along the inside of the patella. The patella is then moved out of the way to expose the knee joint. Traditionally, this involved everting (flipping) the knee cap, but recent studies have shown that patients rehabilitate faster if the surgeon takes care to simply slide the knee cap to the side. It does not offer as much visualization, but we find in our practice it is worth doing it this way in order to promote a faster recovery, and most surgeons who perform many knee replacements a year have a good understanding of the anatomy that facilitates such less invasive techniques.
On the surface, this incision also typically goes vertically down the front and center of the knee, and from the outside skin incision it is difficult to tell a difference between the various approaches described here. However, the subvastus approach, first described in 1929, employs a slightly different approach once under the skin layer. Instead of making an incision along the patella, this approach lifts the vastus muscle up and over the knee. It requires starting far along the inner aspect (medial side) of the knee and elevating the entire front muscle mass up and over to expose the joint. Advantages include less muscle disruption and possibly better patella tracking by leaving the extensor mechanism intact. However, disadvantages include less visualization and access to the joint, and because of the nature of the approach it is not well-suited for patients who are not thin. Access to the joint can be problematic if the patient is at all obese, has a tight knee or contractures, has significant bowing or deformity, or has had any previous surgery. For these reasons, it is not used as commonly as the anterior/medial peripatellar approach described above.
The midvastus approach is very similar to the anterior approach described above, except that in the muscle layer (the skin incision again is the same) the incision turns away from the center of the knee and avoids cutting into the quadriceps tendon. This approach gained popularity in the 1990's because it offers some of the advantages of both the anterior and subvastus approaches, with good visualization and access but better preservation of the extensor mechanism. Advocates of this approach believe that avoiding cutting into the quadriceps tendon leads to a rapid restoration of post-operative extensor mechanism function and knee range of motion. This is the technique most often used in our own practice, and we are advocates of its use in evolving minimally invasive techniques.
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