Partial Knee Replacement

Introduction

If you have been told that arthritis is damaging your knee, but the damage is limited to one part of the joint, your surgeon may have discussed partial knee replacement with you. This guide is written for people who already have a diagnosis of knee arthritis and are now weighing their treatment options, planning surgery, or preparing for recovery.

Partial knee replacement is a more conservative form of joint replacement. Instead of resurfacing the entire knee, only the damaged compartment is replaced, and the healthy bone, cartilage, and ligaments are left in place. For people whose arthritis is confined to one area, this approach can relieve pain while keeping more of the knee’s natural feel and movement.

The pages that follow explain what partial knee replacement is, who is generally considered a candidate, the alternatives doctors discuss first, the surgical approaches used today, what to expect during surgery and recovery, the risks involved, and what life with a partial knee implant typically looks like over the long term.

What Is Partial Knee Replacement?

Partial knee replacement is a surgical procedure in which only the damaged section of the knee joint is resurfaced with an artificial implant. Its formal clinical name is unicompartmental knee arthroplasty, sometimes shortened to UKA. “Arthroplasty” simply means surgical reconstruction or replacement of a joint surface.

• The medial compartment — the inner side of the knee, between the inside of the thigh bone (femur) and shin bone (tibia). This is the most commonly affected area.
• The lateral compartment — the outer side of the knee.
• The patellofemoral compartment — the area where the kneecap (patella) glides against the thigh bone.

In some people with osteoarthritis, the cartilage wears down in just one of these compartments, while the rest of the knee remains healthy. In a partial knee replacement, the surgeon removes the damaged cartilage and a small amount of bone from that single compartment and resurfaces it with metal and plastic components. The healthy compartments, the cruciate ligaments (including the ACL), and the menisci in the unaffected areas are preserved.

This is the key difference from a total knee replacement, in which all three compartments are resurfaced and the cruciate ligaments are usually sacrificed. Because partial knee replacement removes less bone, keeps more of the natural ligaments, and disturbs less soft tissue, many people report that the knee feels closer to normal afterwards.

Why Is Partial Knee Replacement Performed?

Partial knee replacement is performed to relieve pain and improve function in a knee where arthritis or cartilage damage is limited to one compartment. The most common reason is medial compartment osteoarthritis — arthritis on the inner side of the knee — though lateral and patellofemoral partial replacements are also performed in selected cases.

Doctors typically consider partial knee replacement when:

• Pain is clearly localised to one side of the knee, not spread across the whole joint.
• Imaging confirms that cartilage loss is confined to a single compartment.
• Pain interferes with walking, climbing stairs, sleep, or daily activities.
• Non-surgical treatments have been tried over a reasonable period and no longer give adequate relief.

The aim of surgery is to remove the source of bone-on-bone pain, correct any mild deformity caused by cartilage loss on one side, and restore comfortable movement — while keeping the rest of the knee intact for as long as possible.

Who Is a Candidate?

Not everyone with knee arthritis is suitable for a partial knee replacement. The procedure works best in carefully selected patients, and your surgeon will look at several factors before recommending it.

Factors that generally favour partial knee replacement

• Arthritis confined to one compartment. Weight-bearing X-rays and, in many cases, an MRI scan are used to confirm that the other compartments are healthy.
• Intact ligaments, especially the ACL. A working anterior cruciate ligament is important for the stability of a partial knee replacement.
• Mild to moderate deformity. A knee with only mild bow-leg (varus) or knock-knee (valgus) alignment is more suitable than one with severe deformity.
• Good range of motion. Surgeons usually look for a knee that can still bend reasonably well and straighten almost fully before surgery.
• Localised pain. When pain is mainly on one side of the joint, results tend to be better than when pain is diffuse.

Factors that may make partial knee replacement less suitable

• Arthritis affecting more than one compartment, or widespread cartilage damage.
• Inflammatory arthritis, such as rheumatoid arthritis, which affects the whole joint.
• A torn or deficient ACL, depending on the technique and implant used.
• Severe knee deformity or significant stiffness.
• Substantial bone loss or previous fractures around the knee.

Age and weight are sometimes discussed as factors, but practice has changed in recent years. Surgeons now consider partial knee replacement in a broader range of patients than in the past, including some younger, active people and some heavier patients, provided the arthritis pattern is right. Whether partial knee replacement is appropriate in any individual case is ultimately a clinical decision based on examination, imaging, and a careful conversation with an orthopaedic surgeon.

Alternatives to Partial Knee Replacement

Surgery is rarely the first step. For most people with knee arthritis, doctors begin with non-surgical care and consider surgery only when these measures stop providing enough relief. Major orthopaedic societies, including the American Academy of Orthopaedic Surgeons, support a stepwise approach.

Non-surgical management

• Activity modification. Adjusting how you move — for example, reducing high-impact activities — can ease load on the affected compartment.
• Weight management. Even modest weight loss can meaningfully reduce knee pain, because the knee bears several times body weight during walking and stair use.
• Physiotherapy and exercise. Targeted strengthening of the quadriceps, hamstrings, and hip muscles, along with low-impact aerobic exercise (cycling, swimming, walking), is a cornerstone of conservative care.
• Pain-relieving medication. Paracetamol and non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used, under medical supervision, especially when there are concerns about stomach, kidney, or cardiovascular side effects.
• Knee braces and offloader braces. Specialised braces can shift load away from the damaged compartment in some patients with single-compartment arthritis.
• Joint injections. Corticosteroid injections can help with flare-ups. Hyaluronic acid and platelet-rich plasma (PRP) injections are offered in some settings, though the strength of evidence varies and guidelines treat them with caution.

Other surgical alternatives

If conservative care no longer controls symptoms, partial knee replacement is one of several surgical options doctors may discuss:

• High tibial osteotomy (HTO). This is a bone-realignment procedure where the shin bone is cut and reshaped to shift load off the worn compartment onto a healthier part of the knee. It is sometimes considered in younger, more active patients with isolated medial compartment arthritis and good range of motion.
• Total knee replacement. When arthritis affects more than one compartment, when ligaments are damaged, or when deformity is significant, total knee replacement is the more usual option. Many people who eventually need replacement surgery are candidates for total rather than partial knee replacement.
• Arthroscopic surgery. Keyhole “clean-up” procedures (such as washout or debridement) are no longer routinely recommended for osteoarthritis by major guidelines, although arthroscopy may still be used for specific mechanical problems such as a clearly torn meniscus.

The choice between these options depends on the pattern of arthritis, your age and activity level, deformity, ligament status, and personal preferences. It is a conversation worth having more than once with your orthopaedic surgeon.

Surgical Approaches

Partial knee replacement is most commonly performed through a small open incision over the affected side of the knee. Within that broad approach, surgeons may use conventional instruments or computer- and robotic-assisted technology. Each has the same goal: to position the implant precisely so the knee feels stable and balanced.

Minimally invasive (small-incision) partial knee replacement

This is the standard approach for most partial knee replacements today. The incision is typically smaller than that used for a total knee replacement, and the surgeon works through the side of the knee without dislocating the kneecap. Because less soft tissue is disturbed:

• Blood loss is generally lower than with total knee replacement.
• Early pain after surgery is often reduced.
• Patients usually begin walking and bending the knee sooner.

The term “minimally invasive” here refers to the soft-tissue handling and incision length; it is still an open procedure, not keyhole surgery.

Computer-navigated partial knee replacement

Computer navigation uses sensors and a tracking system to give the surgeon real-time feedback on alignment and implant position during the operation. The aim is to improve accuracy compared with traditional jigs and instruments.

Robotic-assisted partial knee replacement

Robotic-assisted systems combine pre-operative planning (often based on a CT scan) with intra-operative guidance. The surgeon plans implant size and position on a digital model of your knee, then uses a robotic arm during surgery that helps deliver precise bone cuts within the planned boundaries. Studies suggest that robotic assistance can improve the accuracy of implant alignment in partial knee replacement, although long-term data comparing outcomes with conventional techniques continue to develop.

The surgeon, not the robot, performs the operation. Robotic systems are tools that assist with planning and precision. Which approach is used depends on the surgeon’s training, the hospital’s equipment, and what is judged most appropriate for your knee.

Preparing for Partial Knee Replacement

Good preparation can make recovery smoother. Once you and your surgeon have decided on surgery, the lead-up usually includes medical assessment, planning, and practical preparation at home.

Pre-operative assessment

• Medical review. Your overall health is assessed, including heart, lung, and kidney function. Blood tests, an ECG, and sometimes a chest X-ray are typical.
• Medication review. You will be advised which medicines to stop and which to continue. Blood thinners, certain diabetes medications, and some anti-inflammatory drugs often need to be adjusted before surgery.
• Dental and skin checks. Active dental infections or skin problems near the knee are usually treated first, to reduce the risk of bacteria reaching the new implant.
• Imaging. Updated X-rays, and sometimes a CT or MRI scan, are used for planning, especially if a robotic-assisted technique is planned.

Lifestyle preparation

• Stop smoking. Smoking slows wound healing and increases infection risk. Even short periods of stopping before surgery help.
• Limit alcohol. Excess alcohol affects healing and anaesthesia.
• Pre-habilitation. Strengthening the muscles around the knee and improving general fitness before surgery (sometimes called “prehab”) often supports a faster recovery.
• Healthy weight. Where possible, working towards a healthier weight reduces load on the new joint.

Preparing your home

• Arrange a clear, uncluttered walking path through main living areas.
• Set up a comfortable chair with arms and a firm seat, and a bed at a comfortable height.
• Place daily-use items within easy reach.
• Consider a raised toilet seat and grab bars in the bathroom.
• Plan for help with shopping, cooking, and transport in the first one to two weeks.

What Happens During the Surgery

1. Anaesthesia and positioning. You are positioned on your back, and the leg is cleaned and draped.
2. Incision. A small incision is made over the front and inner (or outer) side of the knee, depending on the compartment being replaced.
3. Joint inspection. The surgeon examines all three compartments and the cruciate ligaments to confirm that partial knee replacement is still the right choice. If unexpected damage is found in other compartments, the plan may be changed to total knee replacement — a possibility that is usually discussed with you in advance.
4. Bone preparation. The damaged cartilage and a thin layer of bone are removed from the affected compartment, using precise cutting guides or robotic assistance.
5. Trial components. Trial implants are placed and the knee is moved through its range of motion to check stability and alignment.
6. Final implants. The metal component is fixed to the bone, often with bone cement, and a smooth plastic insert is placed between the metal surfaces to act as the new joint surface.
7. Closure. The wound is closed in layers, usually with absorbable sutures and skin clips or glue, and a dressing is applied.

Surgery commonly takes around 60–90 minutes, although individual times vary. Most patients move from the operating room to a recovery area, then to the ward once the anaesthesia wears off enough.

Recovery and Healing

In hospital

Many patients stand and take their first steps within a few hours of surgery, with the support of a physiotherapist and a walking frame or crutches. The hospital stay is commonly one to three days, although some centres now offer same-day or next-day discharge in selected patients. Before going home, you should be able to:

• Walk safely with a walking aid.
• Get in and out of bed and a chair.
• Manage stairs if needed at home.
• Understand your pain medicines and blood-clot prevention plan.

The first two weeks

• Walking short distances with a frame or crutches, gradually increasing as comfort allows.
• Simple exercises to maintain knee bending and strengthen the thigh muscles.
• Ice, elevation, and prescribed pain medicine to manage swelling and discomfort.
• Wound care, with stitches or clips usually removed around 10–14 days.
• Blood-clot prevention, often with medication and exercises.

Weeks two to six

• Most patients move from crutches to a stick, then to walking unaided, over these weeks.
• Physiotherapy focuses on strength, balance, and range of motion.
• Many people return to light office work and start driving when they can control the car safely and are off strong pain medicines — commonly around three to four weeks, but only when their surgeon agrees.

Six weeks to three months

• Walking distances and stair confidence usually improve substantially.
• Low-impact activities such as cycling, swimming, and gentle gym work are gradually reintroduced under guidance.
• Sleep, stiffness, and swelling continue to improve, often noticeably from week to week.

Three to twelve months

Most of the recovery is complete by three to six months, but small improvements in strength, endurance, and comfort can continue up to a year. Many people report that the knee feels increasingly “forgotten” over this period.

Recovery speed varies. Age, fitness, the strength of the leg before surgery, and other medical conditions all play a role. Following the physiotherapy plan is one of the strongest predictors of a good outcome.

Risks and Complications

Partial knee replacement is generally considered a safe procedure in suitable candidates, but like any surgery, it carries risks. Discussing these honestly with your surgeon is part of informed consent.

General surgical risks

• Infection. Superficial wound infections can usually be treated with antibiotics. Deeper infection involving the implant is uncommon but serious and may require further surgery.
• Blood clots. Deep vein thrombosis (DVT) and pulmonary embolism (PE) are recognised risks after lower-limb surgery. Preventive medication, early movement, and exercises reduce this risk.
• Bleeding and haematoma. Some bruising and swelling are normal; significant bleeding is uncommon.
• Anaesthetic complications. These are generally rare in people who have been medically optimised before surgery.

Risks specific to partial knee replacement

• Persistent pain. A small number of patients continue to have pain after surgery, sometimes from the operated compartment and sometimes from elsewhere in the knee.
• Implant loosening or wear. Over many years, the bond between implant and bone can loosen, or the plastic insert can wear, sometimes requiring revision surgery.
• Progression of arthritis in other compartments. Because the rest of the knee is preserved, arthritis can develop later in the compartments that were not replaced. If this becomes severe, the partial knee replacement may be converted to a total knee replacement.
• Fracture or alignment problems. Rarely, small fractures around the implant or alignment issues may occur and need treatment.
• Stiffness. Some patients struggle to regain full bending; this is usually addressed with physiotherapy.

Studies show that overall complication rates after partial knee replacement are generally low, particularly when the surgery is performed by experienced surgeons on well-selected patients. Surgeon and centre experience with partial knee replacement is one of the factors associated with better outcomes.

Life After Partial Knee Replacement

Most people who have a partial knee replacement do so because their knee was limiting their daily life. The aim of surgery is to give them back the activities that matter.

Pain and function

Many patients experience a significant reduction in pain compared with before surgery, often noticeable within the first few weeks and continuing to improve for months. A common comment is that the operated knee feels “more natural” than expected, especially when compared with descriptions from people who have had total knee replacement. This is thought to be related to the preservation of the ligaments and the unaffected compartments.

Returning to activity

Once recovery is well established, most people can return to:

• Walking, including longer distances and gentle hikes.
• Swimming and water aerobics.
• Cycling, both stationary and outdoor.
• Golf, bowls, and similar low-impact sports.
• Yoga and Pilates, with modifications to avoid extreme positions.
• Light gardening and household activities.

High-impact activities such as running, jumping sports, and contact sports place greater stress on the implant. Whether these are advisable depends on the individual, and is a conversation worth having with your surgeon.

Implant longevity

Modern partial knee implants are designed to last many years. National joint replacement data and long-term studies show that a large majority of partial knee replacements continue to function well for ten to fifteen years or more, with many lasting longer. Implant survival depends on factors including patient weight, activity, alignment, surgical technique, and implant design.

If a partial knee replacement does fail or arthritis progresses elsewhere in the knee, revision to a total knee replacement is generally possible.

Protecting your new knee

Doctors commonly advise patients to:

• Maintain a healthy weight.
• Stay active with low-impact exercise to keep muscles strong.
• Avoid sudden, repetitive high-impact activity.
• Take infections elsewhere in the body (dental, urinary, skin) seriously, and tell your dentist or doctor about your knee implant when relevant.
• Attend follow-up appointments, even when the knee feels well, so the implant can be checked over time.

Frequently Asked Questions

How is partial knee replacement different from total knee replacement?

In partial knee replacement, only one of the three compartments is resurfaced, and the cruciate ligaments and other healthy structures are preserved. In total knee replacement, all three compartments are resurfaced and the ligaments at the centre of the knee are usually removed. Both can relieve arthritis pain, but they suit different patterns of disease.

Is partial knee replacement always better than total knee replacement?

No. It is better suited to people whose arthritis is confined to a single compartment with stable ligaments. When arthritis affects more than one compartment, total knee replacement is usually the more reliable option. The choice is a clinical decision based on examination and imaging.

How long will my partial knee implant last?

Long-term studies and national joint replacement data suggest that most partial knee replacements continue to function well for ten to fifteen years, and many last longer. Individual lifespan depends on weight, activity, surgical technique, and implant factors. Your surgeon can give a more personalised estimate.

When can I drive again?

Most people start driving when they are off strong pain medicines, can move the leg confidently, and feel able to perform an emergency stop — commonly around three to four weeks after surgery on the right knee, and sometimes sooner for the left knee in cars with automatic transmission. Your surgeon’s clearance is essential before you start.

Will I need physiotherapy?

Yes. Structured physiotherapy is an important part of recovery. It helps restore strength, range of motion, and balance, and it influences long-term function. Most patients follow a physiotherapy plan for several weeks to a few months after surgery.

What if arthritis develops in another part of my knee later?

If arthritis progresses in a compartment that was not replaced, your surgeon may suggest non-surgical management again, additional treatments, or, in some cases, revision to a total knee replacement. Knowing this possibility exists is one reason regular follow-up matters.

Can both knees be done at the same time?

Some centres offer same-day surgery on both knees in carefully selected patients, while others prefer to stage the operations weeks or months apart. The decision depends on your overall health, fitness, and the surgeon’s assessment.

Will the knee feel normal?

Many people report that a partial knee replacement feels closer to a natural knee than a total knee replacement, partly because the ligaments and unaffected compartments are preserved. However, some people are always aware of the implant, especially during certain activities. Full sensation and feel may continue to improve over the first year.

Conclusion

Partial knee replacement is a focused, bone-preserving option for people whose knee arthritis is limited to one compartment. For carefully selected patients, it offers meaningful pain relief, a generally faster recovery than total knee replacement, and a knee that often feels closer to natural.

It is not the right choice for every knee. The decision depends on the pattern of arthritis, the condition of the ligaments, alignment, overall health, and personal goals. A thorough assessment by an orthopaedic surgeon, with up-to-date imaging and a clear discussion of alternatives, is the foundation for making that decision well.

Whether your next step is continuing conservative care, exploring an osteotomy, considering partial knee replacement, or planning a total knee replacement, understanding what each option involves — and what it asks of you during recovery — helps you take part in the decision with confidence.