October 9, 2023

Knee Replacement Surgery: An In-Depth Look

A knee replacement aims to relieve pain and restore function in severely diseased knee joints, typically resulting from progressive arthritis or a severe knee injury.

The knee joint comprises three primary parts: the femur (thigh bone), tibia (shin bone), and patella (knee cap). In a knee replacement surgery, the ends of these bones are capped with artificial surfaces, mimicking the natural movements of the knee. These artificial components are known as prostheses.

There are different types of knee replacement surgeries, including total knee replacement, partial knee replacement, and revision knee replacement. In a total knee replacement, the entire knee joint is replaced with artificial components. Conversely, in a partial knee replacement, only a section of the knee joint is replaced. Revision knee replacement occurs when a previous knee replacement requires correction or replacement.

Knee replacement is a common orthopaedic procedure, and significantly improves the quality of life for individuals who have been living with chronic knee pain and mobility issues. By addressing the damaged or diseased parts of the knee, knee replacement surgery offers a viable solution for regaining mobility and returning to a more active and comfortable lifestyle.

Understanding the Knee Joint

Anatomy of the Knee

The knee is a complex hinge joint situated between the femur (thigh bone) and the tibia (shin bone), with the patella (knee cap) gliding over the front of the joint. This joint is the largest in the human body and is pivotal for various forms of movement. The key structures of the knee joint include:

Bones

  • Femur: The thigh bone or femur comprises the top portion of the knee.
  • Tibia: The shin bone or tibia makes up the bottom portion.
  • Patella: The knee cap, or patella, is a small bone that protects the front of the knee joint.

Cartilage

  • Meniscus: Two crescent-shaped discs of cartilage between the femur and tibia act as shock absorbers and help distribute weight across the knee.
  • Articular Cartilage: This smooth, slippery substance covers the ends of the bones in the knee joint, facilitating smooth movement and cushioning the bones.

Ligaments:

  • Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL), and Lateral Collateral Ligament (LCL) are crucial for joint stability, each connecting the bones and bracing the joint against unusual movement.

Tendons:

  • Quadriceps Tendon: This tendon connects the quadriceps muscles to the patella.
  • Patellar Tendon: Extending from the patella to the tibia, this tendon facilitates straightening of the knee.

Muscles:

  • Quadriceps Muscles: These are powerful extensors of the knee joint.
  • Hamstring Muscles: Located at the back of the thigh, these muscles help in bending the knee.

Bursae:

  • These small sacs of fluid cushion the outside of the knee joint and reduce friction between the bones, muscles, and tendons.

Function of the Knee

The primary function of the knee joint is to facilitate movement, particularly straightening and bending, which are crucial for basic activities such as walking, running, sitting, and standing. Additionally, the knee joint plays a vital role in supporting the body’s weight in both static (standing) and dynamic (walking or running) postures.

Furthermore, the knee’s ability to slightly rotate and glide allows for more complex movements, enhancing the body’s overall agility and balance. The joint’s robust structure and complex interplay of bones, cartilage, ligaments, tendons, and muscles enable the knee to withstand substantial amounts of stress, making it a critical component in the biomechanics of the lower body.

When Do You Need A Knee Replacement

The decision to proceed with knee replacement surgery often arises from the desire to alleviate chronic knee pain and restore function, which is compromised due to various underlying conditions. These conditions lead to the deterioration or damage of the knee joint, making daily activities increasingly difficult. Below are some common indications for knee replacement.

Osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease and a leading cause of knee replacement surgery. It primarily affects the articular cartilage cushioning the bones of the knee joint, leading to its gradual wear. Over time, the cartilage becomes thin and rough, and the protective space between the bones decreases. This degeneration causes bone-on-bone contact, resulting in pain, swelling, stiffness, and a loss of mobility. When conservative treatments such as medication, physical therapy, or injections fail to provide relief, and the symptoms severely impact the quality of life, knee replacement surgery may be considered to restore joint function and alleviate pain.

Rheumatoid Arthritis

Unlike osteoarthritis which is a wear-and-tear condition, Rheumatoid Arthritis (RA) is an autoimmune disease where the body’s immune system mistakenly attacks its own tissues, including the joints. In the knee joint, RA causes the synovial membrane that encloses the joint to become inflamed, leading to pain and swelling. Over time, the chronic inflammation can erode the cartilage and bone within the joint, leading to deformities and loss of function. Knee replacement surgery may be recommended for individuals with severe rheumatoid arthritis when other treatments do not provide adequate relief.

Post-traumatic Arthritis

Post-traumatic arthritis develops following a serious knee injury, such as a bone fracture or ligament tear. These injuries can damage the cartilage and other joint structures, leading to irregularities in the joint surface. Over time, these abnormalities can cause excessive wear and tear on the joint, similar to the effects seen in osteoarthritis. When significant joint damage occurs, and conservative treatments are ineffective, knee replacement surgery may be a viable option to relieve pain and restore normal knee function.

Before A Knee Replacement Surgery (Preoperative Assessment)

Prior to knee replacement surgery, a thorough preoperative assessment is conducted to determine the patient’s overall health status and the extent of knee joint damage. It consists of medical evaluation, physical examination, and imaging studies.

Medical Evaluation

The medical evaluation is an extensive review of the patient’s medical history and current health status. This includes:

  • Chronic Conditions: Assessment of chronic diseases such as diabetes, hypertension, heart disease, or any other conditions that could affect the surgery or recovery.
  • Medications: Review of all current medications, including prescription drugs, over-the-counter medications, and dietary supplements.
  • Allergies: Documentation of any known allergies, especially to medications or materials like latex.
  • Previous Surgeries: Information on previous surgeries, especially any prior surgery on the affected knee.
  • Infections: Checking for any current or recent infections, as infections can significantly impact the surgery and recovery.

Physical Examination

The physical examination focuses on the affected knee, although the other knee and nearby joints may also be examined. The examination assesses:

  • Range of Motion: Measurement of the knee’s range of motion and any limitations.
  • Strength: Assessment of muscle strength around the knee.
  • Stability: Evaluation of knee stability.
  • Pain: Determination of pain levels and the specific areas within the knee that are painful.
  • Alignment: Analysis of the alignment of the knee and leg.

Imaging Studies

Imaging studies provide a visual representation of the knee joint, offering invaluable insights into the extent of joint damage and anatomical abnormalities. They form an integral part of the preoperative assessment, aiding in surgical planning. These include:

  • X-rays: Showing bone alignment, joint space, and the presence of bone spurs or other abnormalities.
  • Magnetic Resonance Imaging (MRI): Providing detailed images of soft tissues, including ligaments, tendons, and cartilage.
  • Computer Tomography (CT) Scan: Offering cross-sectional images of the knee to assess bone quality and density.
  • Bone Scan: Identifying areas of bone inflammation or abnormal bone metabolism.

The data gathered from these imaging studies are pivotal in formulating a tailored surgical plan that addresses the unique needs and anatomy of each patient.

Risks and Complications

Like any surgical procedure, knee replacement carries certain risks and potential complications. Although it is a highly successful operation, being informed about the possible challenges that may arise, is crucial for making well-informed decisions and for understanding what to expect during the recovery period.

Infection

Infection is a serious complication that can occur after knee replacement surgery. It may manifest in the wound or deep within the joint itself. The symptoms of infection include fever, chills, swelling, redness, and discharge from the surgical site. Infections can occur shortly after surgery or even years later. While superficial infections can often be treated with antibiotics, deep joint infections may require additional surgery to clean the joint or even replace the prosthesis.

Blood Clots

The formation of blood clots in the deep veins of the leg (deep vein thrombosis, DVT) is a common complication post-surgery. These clots can break loose and travel to the lungs (pulmonary embolism, PE), which is a serious condition that requires immediate medical attention. Symptoms of DVT include swelling, pain, and redness in the calf, while PE symptoms include shortness of breath and chest pain. Preventative measures, such as blood-thinning medication and compression stockings, are often employed to reduce the risk of blood clots.

Other Potential Complications

  1. Implant Loosening or Failure: Over time, the prosthetic components may loosen or wear out, potentially requiring a revision surgery to replace the failed components.
  2. Stiffness: In some cases, the knee may become stiff and lack the desired range of motion, often requiring physical therapy to improve flexibility.
  3. Nerve Damage: Although rare, nerves around the knee joint may be damaged during surgery, leading to numbness, weakness, or tingling in the affected leg.
  4. Bone Fracture: Bones may be fractured during surgery, which may require additional interventions to repair.
  5. Bleeding: As with any surgery, there is a risk of bleeding, which may require a transfusion in severe cases.
  6. Anesthetic Risks: The risks associated with anesthesia include allergic reactions and breathing difficulties, among others.

Each of these complications may affect recovery and the overall success of the knee replacement surgery. Therefore, discussing these risks with the orthopaedic surgeon and understanding the preventive measures and management strategies is crucial for ensuring optimal surgical outcomes.

Outcomes and Prognosis

The outcomes and prognosis following knee replacement surgery are generally favorable, with many patients experiencing significant pain relief and improved mobility. Understanding the success rates and the longevity of knee implants can provide a clearer picture of what to expect post-surgery, aiding in setting realistic expectations and long-term planning.

Success Rates

Knee replacement surgery boasts high success rates, with substantial improvement in knee pain and function. Most patients are able to return to their daily activities with less pain and greater ease of movement. The success of the surgery is often gauged by the reduction in pain, increased mobility, improved quality of life, and patient satisfaction. Studies indicate that over 90% of individuals who undergo knee replacement experience substantial pain relief and are satisfied with the outcome of their surgery. Moreover, the success rates in terms of implant survival are also high, with many knee replacements functioning well for two decades or more.

Longevity of Knee Implants

The longevity of knee implants is influenced by several factors including the material quality of the implant, the surgical technique, the patient’s activity level, weight, and overall health. On average, modern knee implants are expected to function well for 15 to 20 years or longer. With advancements in prosthetic materials and design, the longevity of knee implants is continually improving. Over time, wear and tear can occur, and in some cases, revision surgery may be required to replace worn or loosened components. Following a healthy lifestyle and adhering to the post-operative guidelines can play a pivotal role in extending the lifespan of the knee implant and ensuring a favourable long-term outcome.