Minimally invasive total knee arthroplasty: the importance of instrumentation

MIS TKA is in the early stages of development. There are many opponents who believe that the technique is nothing more than a cosmetic modification of the standard TKA that leads to more complications and less patient satisfaction. It is important to respect these comments and to thoroughly address them. MIS surgery should not be based on the length of the incision or the cosmetic result. The term "minimally invasive" should refer to the extent of disruption of the anatomic structures about the involved joint. In the knee, the MIS approach should not violate the extensor mechanism and should not violate the suprapatellar pouch. MIS should be a capsular approach, and as such it should produce less discomfort and a faster recovery. Modifications of the MIS technique that extend the arthrotomy into the extensor mechanism, violate the suprapatellar pouch, and evert the patella while using a limited incision are not truly minimally invasive. The MIS procedure should allow the patient to recover faster while keeping the incidence of complications at the same or lower levels as the open procedure. There will certainly be a learning curve for this operation and a smaller incision with standard TKA techniques maybe the interim step for the surgeon attempting to master the new approach. MIS TKA must be performed with accurate instruments that are coordinated with the procedure. It is not possible to perform the operation with the traditional instruments that have been made for the open operations. The older instruments do not fit into the knee joint and do not allow visualization of the joint at the same time that the cuts and balancing are performed. The visual appearance is totally different and new. The surgeon must learn a completely new image of the knee joint while continuing to apply the basic principles that have been well established. The instruments are a critical part of this new technology and are central to its success. There is no room for guessing or "eye balling" the bone cuts or the alignment and balancing. Instruments and computer-assisted technology will help advance MIS surgery in the next few years. The results of MIS TKA must be thoroughly studied and compared with the existing literature. The author has tried to advance this development ina logical fashion. The initial step was to design instruments that would allow implantation of the presently accepted knee prostheses. This step has now been completed; however, the operation is not simple and is time consuming. The next step therefore is to change the prostheses to facilitate the surgery. The femoral and tibial components are presently too large for the working incision. They are now being modified so that they can be implanted in two or more pieces. This will permit less soft tissue dissection and work better with the smaller incision. The final step will incorporate computer navigational systems. All of the present instruments are designed with attachments for the appropriate arrays to interact with these systems. Ideally, the computer image will allow precise visualization of the knee, particularly the lateral side. All new surgical approaches and devices must be introduced with the expectation to improve the surgical results. There is no doubt that the final goal of this work should be technical improvement without early clinical failures or complications.