In the initial stage, arthritis in knee can improve with weight loss and targeted rehabilitation for muscle strengthening and stretching. Cartilage supplements, pain management with ice and anti-inflammatories, and joint injections of medications can also be used.
As the disease progresses, it becomes impossible to engage in sports, and daily life activities such as walking or climbing stairs are limited. Additionally, pain may be present even at rest or during the night. Unfortunately, in advanced stages, conservative treatments are not effective, and prosthetic surgery is necessary to resolve symptoms, remove or significantly alleviate pain, and restore movement to the joint.
Surgery is advisable when a severe osteoarthritis is evident in X-rays with bone-on-bone contact and in the presence of any of the following symptoms:
- Pain resistant to pain-relieving therapies
- 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 physiotherapy and conservative treatments.
There are various types of knee prostheses:
- Total covering prosthesis
- Partial or uni-compartmental prosthesis
- Revision prosthesis
- The surgical procedure removes damaged cartilage and bone, which is replaced with the prosthetic implant. Prostheses are composed of various materials, including titanium, polyethylene, chrome, cobalt, and cement is often used to securely attach them to the bone.
The choice of implant type varies from person to person, depending on the type of osteoarthritis, the patient’s age, activity level, and bone quality.
Usually, during the procedure, a small amount of bone is removed from the tibia, femur, and patella, eliminating damaged structures and creating high-quality bony surfaces for the prosthetic implant. Most ligaments and tendons are left in place, allowing natural knee movement.
Total Knee Prosthesis
The prosthesis consists of 4 components:
- The femoral shield is typically made of metal, such as titanium, coated with alloys that reduce friction and wear during movement. One of the most common is chrome-cobalt. Once positioned, it wraps around the joint part of the femur.
- The tibial component is made of titanium and usually has a small stem that enters a few centimeters into the tibia bone for increased stability.
- An insert in polyethylene, a highly resistant plastic material that generates minimal friction during prosthesis movement, is placed on the tibial component.
- The patellar component is a polyethylene button applied to the patella when this bone is damaged by osteoarthritis or in cases of rheumatologic joint diseases.
Each knee prosthesis procedure is tailored to the patient’s needs, and there can be significant variations from case to case. The general steps of the procedure include:
- Administering anesthesia and, in agreement with the patient, sedation to ensure comfort during the procedure.
- Performing a surgical incision in front of the knee to access the joint.
- Removing damaged cartilage and bone to prepare the bone ends for implanting prosthetic components.
- Ensuring that the prosthetic components are correctly positioned on the bone.
- Testing the new joint.
- Closing the incision.
Uni-compartmental or Partial Prosthesis
In some patients, osteoarthritis develops in only one area of the knee (inner compartment, outer compartment, joint between the femur and patella). In these cases, partial prosthesis may be the best solution. Instead of replacing the entire knee, patients with partial damage can undergo a partial prosthesis procedure, which involves less surgical stress, less blood loss, less pain, and faster functional recovery. Additionally, the healthy joint portion is preserved. There are partial prostheses for the inner compartment, the outer compartment, and the patella. Uni-compartmental prostheses have smaller femoral and tibial components but are composed of the same materials; the surgical technique is similar but involves a smaller incision.
Some patients develop selective patellar osteoarthritis and experience symptoms primarily during flexion movements, such as rising from a chair or climbing stairs. A small-sized prosthesis has been developed to address this condition and is called a femoro-patellar prosthesis.
Materials in Knee Prostheses
In recent years, prosthesis designs and the number of available sizes have greatly increased, allowing for true customization of knee prostheses. The most commonly used metal is titanium, coated with a chrome-cobalt alloy that has shown excellent durability over time. Chrome-cobalt contains nickel, to which some patients may be allergic. It is not yet clear whether skin allergies to nickel can lead to joint complications; however, prostheses without nickel are available for allergic patients. The latest generation of polyethylene, called cross-linked, is highly resistant to wear. Typically, knee prostheses are fixed to the bone with cement. Cement ensures immediate and solid anchoring and has a very long lifespan. In certain patients, such as young patients with good bone quality, non-cemented prostheses can be used, composed of a material that integrates with the bone.