Principles of MIS in total knee arthroplasty

In the past few years a growing interest has arisen on minimal invasive surgical (MIS™) techniques. In orthopedic surgery, in particular, minimally invasive total knee arthroplasty (TKA) has gained special attention. Minimally invasive techniques in joint arthroplasty had, however, a premature birth. In other terms, surgeons have been implanting prosthetic components, already in use and designed without any constraints deriving from the surgical exposure, through reduced skin and soft tissue incisions. Those are either analogous to the traditional ones but smaller or newer and obtained using more innovative approaches and «ad hoc» instruments. MIS is, therefore, still evolutionary and this is giving rise to several innovative trends in arthroplasty. Defining MIS only based on the incision size is inappropriate: smaller scars should not be the final goal, but only the consequence of a procedure that aims at an increased preservation of the existing and still functional tissues. In total knee arthroplasty, minimally invasive surgery basically means preserving the extensor mechanism. The surgical exposure of the knee joint for bone resection and prosthetic components implantation needs to be performed with the least possible damage to: . The vastus medialis and quadriceps tendon. Von Langebeck's approach, conventionally the most used, involves an incision between tendon and VMO that, after scaring, hinders active contraction and active and passive flexion-extension for a long time. Allowing a patient to undergo a faster rehabilitation and functional recovering is considered one of the most important pillars in MIS TKA; . The patella and patellar tendon and their blood perfusion. Eversion of the patella stretches the patellar tendon, altering blood perfusion. This induces tendon shortening which can result in a patella baja that is not correlated to unintentional alterations of the joint line. Three key topics need to be addressed as an overview to MIS TKA: . The diverse surgical approaches and the instruments enabling them; . New prosthetic components designed «ad hoc» for MIS (a field that offers unlimited development opportunities); . The possibility to combine MIS and computer assisted navigation, as a method to control implant alignment and ligament balancing when the surgical approach does not allow a complete and continuous visualization of the joint.