Arthroscopic examination and surgery of the knee have become mainstays in the diagnosis and treatment of many different knee problems. But depending on the particular problem, entry of the scope may vary. Many studies have been done to determine the precise approach to use (from the front, side, back or some combination). More posterior arthroscopic procedures are being done now as the surgical techniques and tools have improved over time.
For example, repair and reconstruction of the posterior cruciate ligament can be done using a posterior arthroscopic portal. Likewise, removing loose fragments of cartilage, repairs of avulsion fractures of ligaments, synovectomies, and repairing tears of the posterior horn of the menisci can be done with this posterior technique.
However, every knee is slightly different in shape and the position of vital structures (e.g., blood vessels and nerves may vary from person to person). Depending on the position of the knee and the portal (opening) used, the surgeon can be challenged by the smallest anatomic difference.
And living tissue is dynamic, not static. In other words, these important structures can move during the procedure. That factor alone can increase the risk of damage or injury caused by the arthroscopic technique. So choosing the safest method of entry for the needle used during the arthroscopic procedure is important.
Only a thin layer of fat separates the popliteal artery along the back of the knee from the thin posterior capsule. This can add to the risk of damage during posterior arthroscopic approaches to the knee. Sometimes the surgeon must change the knee position during the procedure. Saline fluid flows through the joint during the procedure and can also push soft tissue structures away from their normal positions.
Entering from the back of the knee, the scope can be placed in a posterolateral, posteromedial, or transseptal position. Posterolateral refers to the back and outside location of the knee. Posteromedial scope placement comes in from the back and inside edge (closest to the other knee).
Transseptal arthroscopic placement describes the passing of the scope from the posteromedial portal through the posterior septum of the knee. The posterior septum is an anatomical structure in the back of the knee. It divides the posterior compartment of the knee into two parts: lateral and medial. It is in the posterior compartment where some of the blood vessels and nerves are located.
There is some evidence that the risk of injury to the popliteal artery and peroneal nerve might be less when the knee is bent more than 90 degrees. Likewise, the risk of damage could be greater the straighter the knee during the arthroscopic procedure.
Studies have shown that the use of MRIs before surgery can aid in preventing injuries during posterior knee arthroscopic procedures. It sounds like your surgeon has taken all of the important factors into consideration when planning your procedure and is proceeding with the appropriate cautionary preliminary steps such as an MRI.