Partial Knee Replacement: Procedure Steps, Recovery, and Benefits

How do you do a partial knee replacement?

A partial knee replacement, also known as unicompartmental knee arthroplasty (UKA), is a surgical procedure that involves replacing only the damaged compartment of the knee joint, typically due to osteoarthritis, while preserving the healthy cartilage, bone, and ligaments in the other compartments.

Understanding the Knee Joint and Arthritis

The knee is a complex hinge joint formed by the articulation of three bones: the femur (thigh bone), tibia (shin bone), and patella (kneecap). It is divided into three main compartments:

• Medial Compartment: The inner side of the knee, between the femur and tibia.
• Lateral Compartment: The outer side of the knee, between the femur and tibia.
• Patellofemoral Compartment: The front of the knee, between the patella and the femur.

Osteoarthritis, a degenerative joint disease, causes the protective cartilage that cushions the ends of bones to wear down. When this wear is confined to just one of these compartments, typically the medial compartment, a partial knee replacement may be an appropriate treatment option.

What is a Partial Knee Replacement (Unicompartmental Arthroplasty)?

Unlike a total knee replacement (TKR) which resurfaces all three compartments of the knee, a partial knee replacement is a less invasive procedure that specifically targets and replaces only the diseased portion of the joint. The goal is to relieve pain, restore function, and preserve as much of the natural knee anatomy as possible, including healthy cartilage, bone, and all knee ligaments (anterior cruciate ligament - ACL, posterior cruciate ligament - PCL, medial collateral ligament - MCL, lateral collateral ligament - LCL). This preservation is key to maintaining more natural knee motion and proprioception.

Candidate Selection for Partial Knee Replacement

Not everyone with knee osteoarthritis is a candidate for a partial knee replacement. Ideal candidates typically exhibit the following characteristics:

• Localized Arthritis: Damage confined primarily to one compartment of the knee, usually the medial compartment.
• Intact Ligaments: Healthy and functional ACL, PCL, and collateral ligaments, which are crucial for knee stability and are preserved during the procedure.
• Good Range of Motion: Generally, a relatively good range of motion pre-operatively, without significant stiffness.
• Lower Activity Levels: While not a strict rule, it is often considered for individuals who may not put extreme stress on the knee.
• Failed Conservative Treatments: Pain and functional limitations that have not responded to non-surgical interventions like medication, physical therapy, injections, or activity modification.

The Surgical Procedure: A Step-by-Step Overview

A partial knee replacement is typically performed by an orthopedic surgeon. While specific techniques may vary, the general steps involved are as follows:

• Pre-Operative Preparation:

  • The patient undergoes a thorough medical evaluation, including imaging (X-rays, MRI) to confirm the extent and location of arthritis.
  • The surgeon reviews the patient's medical history and current medications.
  • Anesthesia options are discussed.

• Anesthesia:

  • The procedure is usually performed under general anesthesia, regional anesthesia (spinal or epidural), or a combination of both.
  • A nerve block may also be administered to help manage post-operative pain.

• Incision and Exposure:

  • A smaller incision (typically 3-5 inches) is made on the front or side of the knee, over the affected compartment. This is generally smaller than the incision for a total knee replacement.
  • The soft tissues are carefully retracted to expose the damaged bone and cartilage of the specific compartment (e.g., medial condyle of the femur and tibia).

• Resection of Damaged Bone:

  • Using specialized instruments, the surgeon precisely removes only the damaged cartilage and a minimal amount of underlying bone from the surfaces of the femur and tibia within the affected compartment.
  • Care is taken to preserve healthy bone, cartilage, and all intact ligaments.

• Implant Placement:

  • Femoral Component: A metal cap (femoral component) is precisely fitted and secured to the end of the femur to replace the worn surface.
  • Tibial Component: A metal tray (tibial component) is secured to the top of the tibia. A plastic (polyethylene) insert is then placed between the femoral and tibial components, acting as a new smooth gliding surface, mimicking the natural cartilage.
  • The implants are typically secured using bone cement, though some designs may allow for cementless fixation.

• Closure:

  • The surgeon checks the knee's stability and range of motion.
  • The incision is closed in layers using sutures or staples. A drain may be inserted temporarily to remove excess fluid.
  • A sterile dressing is applied.

Post-Operative Recovery and Rehabilitation

Recovery from a partial knee replacement is generally faster and less painful than a total knee replacement due to the less invasive nature of the surgery and the preservation of more natural tissues.

• Immediate Post-Op: Patients typically begin walking with assistance (crutches or walker) within hours or the day after surgery.
• Physical Therapy: A structured physical therapy program is crucial for regaining strength, flexibility, and range of motion. This will focus on:
  • Early mobilization and weight-bearing as tolerated.
  • Range of motion exercises (flexion and extension).
  • Strengthening exercises for the quadriceps, hamstrings, and glutes.
  • Balance and proprioception training.
  • Gait training to restore a natural walking pattern.
• Return to Activities: Most patients can resume light daily activities within a few weeks and return to more moderate activities (e.g., walking, cycling, swimming) within 2-3 months. High-impact activities are generally discouraged.

Benefits of Partial Knee Replacement

• Less Invasive: Smaller incision, less blood loss, and less trauma to surrounding tissues compared to TKR.
• Faster Recovery: Shorter hospital stay and quicker return to normal activities.
• More Natural Feel: Preservation of healthy bone, cartilage, and ligaments often results in a knee that feels more "normal" with a better range of motion and proprioception.
• Reduced Pain: Effective relief of pain caused by localized arthritis.
• Future Option: If necessary, a partial knee replacement can be converted to a total knee replacement later in life.

Potential Risks and Considerations

While generally safe, like any surgical procedure, partial knee replacement carries potential risks, including:

• Infection
• Blood clots
• Nerve or blood vessel damage
• Loosening or wear of the implant over time
• Continued pain or stiffness
• Progression of arthritis in the other compartments (though this is not always a reason for revision)

When to Consult a Specialist

If you are experiencing persistent knee pain, stiffness, or functional limitations, especially if conservative treatments have not provided relief, it is essential to consult with an orthopedic surgeon. They can accurately diagnose the cause of your knee pain and determine if a partial knee replacement or another treatment option is appropriate for your specific condition.