Unicompartmental Knee Replacement: A Minimally Invasive Option for Joint Pain Relief

What is Unicompartmental (Partial) Knee Replacement?

Knee replacement surgery involves resurfacing damaged bone and cartilage caused by osteoarthritis with metal and plastic components. In unicompartmental knee replacement, also known as partial knee replacement, only the affected portion of the knee is treated. This makes it a less invasive alternative to total knee replacement for patients whose osteoarthritis is confined to a single compartment of the knee.

Since partial knee replacement requires a smaller incision, patients typically experience a shorter hospital stay—or no hospitalization at all—and can return to normal activities much sooner compared to those undergoing total knee replacement.

There are multiple treatment options for knee osteoarthritis, and your doctor will help determine the approach that best alleviates your specific symptoms and meets your individual needs.

Description of Unicompartmental Knee Replacement

In knee osteoarthritis, the protective cartilage that cushions the bones of the knee gradually wears away. This degeneration can affect the entire knee joint or be confined to a single compartment.

The knee is divided into three main compartments:

Medial Compartment: The inner portion of the knee.
Lateral Compartment: The outer portion of the knee.
Patellofemoral Compartment: The front portion of the knee, between the kneecap and the thighbone.

When advanced osteoarthritis is restricted to one compartment, it can be treated with a unicompartmental knee replacement. This procedure replaces the damaged compartment with metal and plastic components while preserving the healthy cartilage, bone, and all supporting ligaments, allowing for a more natural knee function.

(Left) Illustration of a normal knee joint: The medial, lateral, and patellofemoral compartments are shown with red arrows. (Right) An X-ray of a normal knee joint showing healthy space between the bones.

(Left) Illustration of osteoarthritis that is limited to the medial compartment. (Right) This X-ray shows severe osteoarthritis with bone-on-bone degeneration in the medial compartment (arrow).

Advantages and Disadvantages of Partial Knee Replacement

Unicompartmental knee replacement has shown positive outcomes for most patients who are appropriate candidates, offering significant benefits over total knee replacement.

Advantages

Quicker Recovery: Patients often heal and resume activities faster.
Less Pain: Post-surgical discomfort is typically reduced.
Minimal Blood Loss: The procedure is less invasive, leading to less blood loss.
Lower Risk of Infection and Blood Clots: Smaller incisions and less surgical trauma decrease complication risks.
More Natural Knee Function: Since the healthy bone, cartilage, and ligaments are preserved, many patients report that partial knee replacement feels more natural and allows for better bending compared to total knee replacement.

Disadvantages

The main drawback of partial knee replacement is the potential need for additional surgery. If arthritis develops in the unaffected parts of the knee, a total knee replacement may eventually be required. Studies indicate that the likelihood of needing future surgery is slightly higher with partial knee replacement compared to total knee replacement.

Despite this risk, partial knee replacement remains an excellent option for patients with arthritis confined to a single compartment, offering significant benefits in recovery and knee function.

An advantage of partial knee replacement over total knee replacement is that healthy parts of the knee are preserved, which helps to maintain more natural function of the knee.

Candidates for Unicompartmental Knee Replacement

If osteoarthritis has progressed to the point where nonsurgical treatments are no longer effective, your doctor may recommend knee replacement surgery. To qualify for unicompartmental (partial) knee replacement, the arthritis must be confined to a single compartment of the knee.

Who May Not Be Eligible

You may not be a candidate for this procedure if you have:

Inflammatory arthritis (e.g., rheumatoid arthritis).
Significant knee stiffness, which could limit motion.
Ligament damage, as it affects knee stability.

Outcomes with Proper Selection

When patients are carefully selected, modern unicompartmental knee replacements have shown excellent medium- and long-term results, benefiting both younger and older individuals with localized knee arthritis. This procedure offers an effective solution for many patients seeking pain relief and improved mobility.

Orthopaedic Evaluation for Partial Knee Replacement

A detailed evaluation by an orthopedic surgeon is essential to determine if you are a suitable candidate for unicompartmental (partial) knee replacement. This process involves assessing your medical history, conducting a physical examination, and performing imaging tests.

Medical History

Your doctor will ask about your overall health, the nature of your knee pain, and how it affects your daily activities.

Location of Pain: Pain localized to either the inside (medial) or outside (lateral) portion of the knee may make you a candidate for partial knee replacement. However, if your pain is widespread throughout the knee or concentrated in the front of the knee (beneath the kneecap), total knee replacement may be a better option.

Physical Examination

Your doctor will examine your knee to identify the precise source of your pain and assess its condition.

Range of Motion: They will check how easily you can move your knee.
Ligament Quality: If your ligaments are weak or torn, or if your knee is excessively stiff, partial knee replacement may not be suitable, though total knee replacement might still be an option.

Imaging Tests

X-rays: These provide a clear view of the damage and deformity in your knee and help identify the pattern of arthritis.
MRI Scans: Your doctor may use MRI imaging for a more detailed assessment of the cartilage.

Your Surgery

Before Surgery

Anesthesia Options: During your preoperative visit and on the day of surgery, a doctor from the anesthesia team will discuss options, including:
- General Anesthesia: You are put to sleep.
- Spinal Anesthesia: You are awake, but your body is numb from the waist down.
- Peripheral Nerve Block: A targeted numbing injection that blocks pain from specific nerves. This can be combined with general or spinal anesthesia.
Surgical Site Verification: Your surgeon will confirm the surgical site by marking your knee before the procedure.

Surgical Procedure

Duration: The surgery typically lasts 1 to 2 hours.
Inspection of the Joint: Your surgeon will make an incision at the front of your knee and inspect all three compartments to confirm that cartilage damage is limited to one compartment and that the ligaments are intact.
Contingency Plan: If your knee is deemed unsuitable for partial knee replacement during surgery, a total knee replacement may be performed instead. This alternative approach will be discussed with you beforehand to ensure your agreement.

This thorough evaluation and surgical planning ensure that you receive the most effective treatment tailored to your knee’s specific condition.

Recovery After Partial Knee Replacement

Hospital Discharge

Patients undergoing partial knee replacement typically experience less postoperative pain and swelling compared to total knee replacement. Rehabilitation is also generally easier. Most patients return home the same day or shortly after surgery, though in rare cases, a stay at a skilled nursing or rehabilitation facility may be necessary.

Pain Management

Post-surgery, some pain is expected, but your care team will work to ensure you remain comfortable.

Medications: Options for pain relief include:
- Opioids: Effective for managing pain but should only be used as directed due to their addictive potential. Discontinue use as soon as your pain improves.
- Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and local anesthetics: These provide additional pain control and reduce inflammation.

Effective pain management supports a smoother recovery and faster healing.

Weight-Bearing

You will begin putting weight on your knee immediately after surgery. Initially, you may require support from a walker, cane, or crutches for a few days or weeks until you feel comfortable walking independently.

Rehabilitation Exercises

A physical therapist will provide exercises to:

Maintain and improve range of motion in your knee.
Restore strength to the surrounding muscles.

Performing these exercises regularly is crucial for achieving the best recovery outcomes.

Follow-Up Visits

You will have regular follow-up appointments with your orthopedic surgeon to monitor your progress and ensure proper healing.

Timeline for Recovery

Most patients can return to their normal daily activities within 6 weeks after surgery, with continued improvement in knee function and mobility over time.