Conditions requiring hip replacement surgery: osteoarthritis, osteonecrosis, rheumatoid arthritis and post-traumatic arthritis.
The knee is the largest joint in the human body. It is formed by the femur, tibia and patella, functioning like a hinge to allow leg flexion and extension. Muscles and ligaments hold the joint surfaces together, providing stability and enabling movement. The joint surfaces of the three bones are covered by cartilage, which cushions the contact between the joint surfaces and significantly reduces friction during movement. The knee is composed of three compartments: the medial compartment, the lateral compartment and the patellofemoral joint.
Some diseases lead to irreversible destruction of the joint surfaces and only a prosthesis can definitively resolve the symptoms.
Read also: Conditions that can be treated with total knee replacement
TREATMENT
In the initial stage osteoarthritis can improve with weight loss and rehabilitation aimed at muscle strengthening and stretching. It is possible to use cartilage supplements, manage pain with ice and anti-inflammatory drugs and perform joint injections. As the disease progresses, it becomes impossible to engage in sports and even daily activities like walking or climbing stairs are limited. Additionally, pain may be present even at rest or during the night. In advanced stages, unfortunately, conservative treatments are ineffective and prosthetic surgery is necessary to resolve the symptoms, significantly alleviate or eliminate pain and restore joint movement.
Personally I recommend surgery for patients who show severe osteoarthritis with bone-on-bone contact on X-rays and any of the following symptoms:
- Pain resistant to painkillers
- Constant pain even at rest
- Difficulty standing for long periods
- Inability to perform daily activities such as walking or climbing stairs
- Pain while walking
- No benefit or limited benefit from physical therapy and conservative treatments.
KNEE PROSTHESIS
There are different types of knee prostheses: total knee replacement, partial or unicompartmental knee replacement and revision prostheses. The surgical procedure removes the damaged cartilage and bone, which are replaced with the prosthetic implant. Prostheses are made from various materials: titanium, polyethylene, chromium, cobalt and often cement used to secure them firmly to the bone. The choice of implant type varies from person to person and depends on the type of osteoarthritis, the patient’s age and activity level and the bone quality. During surgery a small amount of bone is usually removed from the tibia, femur and patella to eliminate the damaged structures and create good quality bone surfaces on which to place the prosthetic implant. Most ligaments and tendons are left in place, allowing for natural knee movement.
TOTAL KNEE REPLACEMENT
In total knee replacement the diseased bone and cartilage are removed and replaced with prosthetic components, usually made of metal and polyethylene. This combination of materials has shown excellent results with minimal wear over time despite use.
The prosthesis consists of four components:
- the femoral shield, made of metal, usually titanium, coated with alloys that reduce friction and wear during movement (one of the most common is cobalt-chrome). Once positioned, it encases the femoral joint surface;
- the tibial component, made of titanium, typically has a small stem that penetrates a few centimeters into the tibial bone to increase stability;
- an insert, placed on the tibial component, made of polyethylene, a high-strength plastic material that develops minimal friction during prosthetic movement;
- a polyethylene button that replaces the patellar component, applied to the patella when this bone is also damaged by osteoarthritis or in cases where the joint is affected by a rheumatologic disease.
SURGICAL PROCEDURE STEPS
Every knee replacement procedure is personalized based on the patient’s needs and there can be significant variations from case to case. The general steps of the procedure include:
- administration of anesthesia and, in agreement with the patient, sedation to ensure comfort during surgery;
- surgical incision in front of the knee to access the joint;
- removal of damaged cartilage and bone to prepare the bone ends for the prosthetic components;
- ensuring the prosthetic components are correctly positioned;
- testing the new joint;
- closing the incision.
UNICOMPARTMENTAL OR PARTIAL KNEE REPLACEMENT
Osteoarthritis develops in only one area of the knee (medial compartment, lateral compartment or patellofemoral joint) in some patients. In these cases a partial knee replacement may be the best solution. Instead of replacing the entire knee, patients with partial damage can undergo partial knee replacement, which involves less surgical stress, less blood loss, less pain and quicker functional recovery. Additionally, the healthy part of the joint is preserved. Partial prostheses are available for the medial, lateral and patellar compartments. Unicompartmental prostheses have smaller femoral and tibial components, but are made of the same materials. The surgical technique is similar, but involves a smaller incision.
PATELLOFEMORAL PROSTHESIS
Some patients develop selective osteoarthritis of the patella and mainly experience symptoms during movements with a bent knee, such as rising from a chair or climbing stairs. A small prosthesis has been developed to address this condition and is called a patellofemoral prosthesis.
MATERIALS IN KNEE PROSTHESIS
In recent years prosthesis designs and the number of available sizes have significantly increased, allowing for true customization of knee prostheses. The most commonly used metal is titanium, coated with a cobalt-chrome alloy that has shown excellent durability over time. Cobalt-chrome contains nickel, to which some patients may be allergic. It is still unclear if skin allergies to nickel can cause joint complications, but nickel-free prostheses are available for allergic patients. The latest generation of polyethylene, called cross-linked, is highly wear-resistant.
The knee prosthesis is typically cemented to the bone, providing immediate and solid anchorage with long-lasting durability. In certain patients, such as young individuals with good bone quality, non-cemented prostheses made of material that integrates with the bone can be used.
