A knee replacement operation is usually indicated in the following cases:

• severe knee pain or stiffness that limits daily activities, including walking, climbing stairs, and standing or sitting in a chair,
• in the case of a knee that has become flexed and no longer extends as a result of severe osteoarthritis,
• chronic inflammation and swelling of the knee that does not improve with rest, ice, hyaluronic acid or cortisone infiltrations,
• Inward (varus) or outward (valgus) knee deformity, in which other surgical interventions are not possible.

Most patients who have a knee replacement suffer from pain and flexibility problems caused by osteoarthritis (see below). Other conditions a knee replacement may be used to treat include gout and sports injuries, but this is not common.

Different knee implants are used in the procedure, categorized by the materials that interact during knee flexion:

• Metal on plastic: Common type, with a metal femoral component on a polyethylene plastic spacer. It’s cost-effective and has a well-established safety record.
• Ceramic on plastic: Uses a ceramic femoral component or a metal one with a ceramic coating on a plastic spacer. Suitable for those sensitive to nickel, but may lead to immune reactions.
• Ceramic on ceramic: Both femoral and tibial components are ceramic, minimizing body reactions. However, they can produce a squeaking noise and, in rare cases, may shatter, requiring surgery.
• Metal on metal: Both components are metal. Less common due to concerns about metal traces entering the bloodstream, causing inflammation and organ damage. Considered for young, active men seeking longer-lasting implants.

There are also other materials gaining prominence with the increasing demand for flexibility and agility in prosthetics. A new ceramic total knee replacement is starting to be available in some hospitals after clinical trials. Similarly, Polyetheretherketone (PEEK) and carbon-fiber-reinforced PEEK (CFR-PEEK) have been successfully used in the field of orthopedic implants.

Knee prostheses are also distinguished based on the condition of the cruciate ligaments. If the ligaments are in good condition, an attempt is made to preserve one or both cruciates resulting in a less invasive intervention.

Alternatively, there are interventions that involve the replacement of the cruciate ligaments. In this case the prosthesis is called posterior-stabilized, a mechanism that guarantees excellent recovery of functionality, especially with modern minimally invasive surgery protocols.

In cases with complex deformities or ligament damage, semi-constrained or constrained prostheses can be used. However, they guarantee the disappearance of pain and the patient can resume normal daily activities.

The knee replacement consists in removing the damaged parts of bone and cartilage, replacing them with artificial parts having the same shape. An incision is then created in the front of the knee and the damaged cartilage is removed. The damaged surfaces of the femur, tibia and patella are then prepared using a special instrument. The part that will be added includes a femoral part, a tibial part and sometimes a patellar part. They can be implanted in the bone regardless of the presence or absence of cement. Using a computer you can evaluate the correct positioning. The surgery can be performed under spinal anesthesia or general anesthesia.

An operation of this type lasts approximately 90 minutes and is performed during a hospital stay which lasts approximately 5-7 days. Post-operative pain is controlled through painkillers or by following other pain therapy techniques indicated by the professional.

The knee arthroplasty is usually carried out using robotics. The robotic system assists the surgeon during the implantation procedure and allows to drastically reduce knee prosthesis positioning errors, which are the cause of most failures and complications. The robotic technique in fact allows the surgeon to be certain of the exact positioning of the prosthesis during its application. The two most used knee robots are Mako and Navio systems.

The day after surgery, the patient will be helped by the physiotherapist. After just a few days you start going up and down the stairs, always with the help of a physiotherapist. After hospitalization in orthopedics, rehabilitation can be carried out in a Rehabilitation Department or through a physiotherapist in an outpatient clinic.

Resumption of driving is possible after just 2 months. Returning to work, however, depends greatly on the type of job. One that is more office-style or at least less physical, allows for a quicker return. Sports activities can be resumed gradually after approximately 3 months.

The results of this surgery are very encouraging: a complete disappearance of pain, a rapid recovery of mobility, normal daily activities and muscle strength. Normal movement without lameness is achieved within one month of surgery. The average lifespan is approximately 20-25 years. In any case, after 20 years, 90% of implanted prostheses are still stable and do not present any particular problems. With the progress of surgical techniques and materials used, the results can be continuously improved.

For this type of operation there are specific risks in addition to those typical of any surgical procedure:

• Stiffness in the joint in case post-operative rehabilitation was not performed correctly.
• Formation of a hematoma due to bleeding inside the joint.
• Infection, although now a rare event (risk less than 1%), becomes a serious complication. In addition to requiring the start of antibiotic therapy, there is the risk of having to change the entire prosthesis. When symptoms of an infection are recognized early, a simple surgical wash together with antibiotic therapy may be sufficient.
• Formation of small blood clots that can form and get stuck in the veins of the legs, requiring anticoagulant therapy for several weeks. Through correct heparin therapy for several weeks after surgery, this problem should no longer occur.

A complete list of complications should be provided to the patient prior to any procedure at the time of treatment discussion.