Knee Replacement: Complete Guide

What is Knee Replacement?

Knee replacement, also called knee arthroplasty, is surgery to replace a damaged knee joint with artificial components (an implant or prosthesis). The goal is to reduce pain and improve function when the knee is worn down or structurally damaged, most commonly from osteoarthritis.

In a healthy knee, smooth cartilage covers the ends of the femur (thigh bone), tibia (shin bone), and the underside of the patella (kneecap). That cartilage allows low-friction movement and distributes load. When cartilage breaks down, bone can rub on bone, the joint can swell, alignment can drift, and the knee may become stiff or unstable. Knee replacement removes the diseased joint surfaces and replaces them with metal and medical-grade plastic bearing surfaces designed to glide smoothly.

There are several types:

• Total knee replacement (TKR or TKA): The most common. Resurfaces the femur and tibia and may resurface the patella.
• Partial knee replacement (unicompartmental): Resurfaces only one compartment (medial, lateral, or patellofemoral) when disease is limited.
• Revision knee replacement: A re-do surgery for a failed, worn, loose, infected, or unstable implant.

> Important expectation: Knee replacement is primarily a pain-relief and function-restoration procedure, not a “new knee” that resets you to decades ago. Setting realistic goals is one of the biggest predictors of satisfaction.

If you want a step-by-step view of what happens in the operating room, see our related article: “What Really Happens in Knee Replacement Surgery.”

How Does Knee Replacement Work?

Knee replacement works through biomechanics, materials science, and controlled healing. The surgeon reshapes damaged joint surfaces so the implant can restore smooth motion, stable alignment, and predictable load transfer.

What gets replaced (and what does not)

In total knee replacement, the surgeon:

• Removes damaged cartilage and a thin layer of bone from the femur and tibia.
• Often removes the menisci (the joint’s cartilage “shock absorbers”) because the new bearing surface replaces that function.
• Typically removes the ACL (anterior cruciate ligament) in standard designs; the implant choice then provides stability through geometry and sometimes a post-cam mechanism.
• Preserves or balances other soft tissues (like the PCL depending on implant type) to maintain stability.

The knee is not simply “cleaned out.” It is resurfaced and rebalanced.

Implant components and materials

A typical total knee implant includes:

• Femoral component: Usually cobalt-chromium alloy or similar metal.
• Tibial baseplate: Metal platform.
• Polyethylene insert: Medical-grade plastic that acts as the new cartilage surface.
• Patellar button (optional): Polyethylene component on the underside of the kneecap.

Modern polyethylene is highly engineered to reduce wear. Wear particles can still occur over years, which is one reason alignment, weight, and activity choices matter.

Fixation: cemented vs. cementless

• Cemented fixation uses bone cement to secure components immediately. It remains the most common approach and has extensive long-term data.
• Cementless fixation relies on bone growing into a porous surface. It has expanded in use, especially in younger or higher bone-quality patients. Current evidence supports good outcomes when used appropriately, but patient selection and surgical precision are important.

Alignment and soft-tissue balancing

A knee replacement is not just about replacing surfaces; it is about putting the knee in a stable, functional position.

• Alignment influences how forces travel through the implant, similar to how tire alignment influences tread wear.
• Ligament balancing aims to prevent a knee that feels too tight, too loose, or unstable.

Surgeons may use conventional jigs, computer navigation, robotic assistance, or patient-specific guides. These tools can improve precision in certain steps, but they are not magic by themselves. Outcomes still depend on diagnosis, planning, soft-tissue management, rehab, and complication prevention.

Biology and recovery

After surgery, the body heals the incision and deeper tissues, swelling gradually decreases, and muscles re-learn coordinated movement. Pain relief comes from removing arthritic bone-on-bone contact and inflammatory tissue, but early recovery can still be uncomfortable because tissues were cut, stretched, and repaired.

Swelling control matters because swelling can inhibit quadriceps activation and limit motion. If you want a nuanced view of ice and rest, see our related piece: “RICE for Injuries: When Rest and Ice Help or Hurt.”

Benefits of Knee Replacement

Knee replacement is among the most studied and consistently effective orthopedic procedures when used for the right patient at the right time.

1) Meaningful pain reduction

The most reliable benefit is less arthritis pain with daily activities, especially walking, standing, and stairs. Many patients report major relief, though “zero pain” is not guaranteed. Residual aching, pressure sensations, or intermittent discomfort can persist, especially with weather changes, kneeling, or long days.

2) Improved function and walking tolerance

With pain reduced and stability improved, many people walk farther, stand longer, and return to activities like travel, shopping, and recreational exercise. Function gains are often largest in those who were most limited before surgery.

3) Better alignment and stability

Arthritis can push the knee into bow-legged (varus) or knock-kneed (valgus) alignment, stressing ligaments and worsening wear. Knee replacement can restore a more functional alignment and improve the feeling of stability.

4) Improved sleep and quality of life

Chronic knee pain often disrupts sleep and limits social life. Quality-of-life improvements are a major reason knee replacement is considered a high-value procedure.

5) Long-lasting results for many patients

Modern implants commonly last well over a decade, and many last 15 to 20 years or longer depending on age, activity, alignment, body weight, and implant factors. Younger, more active patients generally face a higher lifetime chance of needing revision.

> Practical expectation-setting: A successful knee replacement often means “usable motion and reliable pain relief,” not necessarily the ability to run, kneel comfortably, or feel a completely normal knee.

For a reality-based framework, see our related article: “5 Real Goals of Knee Replacement, Explained Clearly.”

Potential Risks and Side Effects

Every surgery has tradeoffs. Knee replacement is common, but it is not minor. Understanding risks helps you plan prevention and recognize warning signs early.

Common short-term side effects

• Pain and swelling for weeks, often peaking in the first 1 to 2 weeks.
• Bruising and warmth around the knee.
• Sleep disruption early in recovery.
• Temporary stiffness if motion is not gradually restored.

These are expected to some degree and usually improve with time, activity progression, and rehab.

Major medical and surgical risks

• Infection: A serious complication that may require antibiotics, washout surgery, or revision. Prevention includes perioperative antibiotics, sterile technique, and optimizing risk factors.
• Blood clots (DVT/PE): Risk is highest in the first weeks. Prevention may include early walking, compression, and blood-thinning medication tailored to your risk.
• Bleeding or wound problems: More likely with certain medications, diabetes, smoking, or poor nutrition.
• Nerve or blood vessel injury: Rare but potentially serious.
• Stiffness (arthrofibrosis): Can limit motion and function; early, consistent rehab and swelling control reduce risk.
• Persistent pain: A minority of patients have ongoing pain despite a technically successful implant. Causes can include nerve sensitivity, referred pain from hip or spine, instability, malalignment, infection, or patellofemoral issues.
• Implant loosening, wear, or instability: Can develop over years and may require revision.

Who needs extra caution (risk factors)

Risk is individualized. Factors associated with higher complication risk include:

• Poorly controlled diabetes
• Smoking or nicotine use
• Severe obesity (especially with additional metabolic risk)
• Immune suppression or inflammatory arthritis medications (timing may need adjustment)
• Prior knee infection, skin ulcers, or recurrent skin infections
• Significant vascular disease
• Poor bone quality or prior complex knee surgeries

This does not automatically rule out surgery, but it changes the preparation plan.

> Call your surgical team urgently for fever, increasing redness or drainage, calf swelling, sudden shortness of breath, chest pain, or rapidly worsening pain.

Practical Guide: Preparing for Surgery and Recovering Well

Outcomes depend heavily on preparation, early choices, and consistent rehab. This section focuses on actionable best practices.

Pre-surgery: how to set yourself up for success

#### 1) Confirm the diagnosis and the pain source

Not all knee pain is knee arthritis. Hip arthritis, lumbar spine issues, or nerve pain can mimic knee symptoms. Before surgery, ask:

• What imaging findings match my symptoms?
• Is my pain mostly from arthritis, or could there be another driver?
• Have we tried an adequate course of non-surgical care?

#### 2) Optimize modifiable risks

Common high-impact steps:

• Stop nicotine (including vaping) well before surgery. Nicotine increases wound and infection risk.
• Improve blood sugar control if you have diabetes.
• Address anemia and nutrition if present.
• Strengthen the leg with prehab: quadriceps, glutes, calf strength; practice sit-to-stand and step-ups within pain limits.

Weight loss can reduce joint load and may lower risk, but it is not a guaranteed outcome after surgery and should not be framed as the primary “benefit” of knee replacement.

#### 3) Plan your home setup

• Clear trip hazards, prepare a stable chair with arms, consider a raised toilet seat.
• Arrange help for meals, pets, and transportation for at least 1 to 2 weeks.
• Put frequently used items at waist height.

The hospital and first 2 weeks

#### Pain control: multimodal is the modern standard

Most programs use a combination of:

• Acetaminophen (if safe for you)
• Anti-inflammatory medication when appropriate
• Regional anesthesia blocks
• Limited opioids for breakthrough pain

The goal is not “no pain.” The goal is pain low enough to walk, sleep, and do rehab.

#### Swelling management: use cold strategically

Ice and compression can help reduce pain and swelling early, which can improve movement and reduce opioid needs. Avoid extreme icing durations that leave skin numb for long periods. Short, repeated sessions are typically used.

(For nuance on when rest and ice help vs. hinder, see: “RICE for Injuries: When Rest and Ice Help or Hurt.”)

#### Movement begins early

Most patients are encouraged to stand and walk the same day or next day. Early walking:

• reduces clot risk
• improves confidence
• helps restore normal movement patterns

Weeks 2 to 12: building motion, strength, and endurance

#### Range of motion goals (general)

Exact targets vary, but many rehab plans aim for:

• Gradual improvement in bending and straightening over the first 6 to 12 weeks
• Full extension (straightening) is often emphasized early because it affects gait and function

A key concept: your pre-surgery flexibility influences post-surgery bend. If the knee was very stiff beforehand, it may take longer and may not reach deep bending.

#### Strength and function

The quadriceps often “shut down” after surgery due to swelling and pain inhibition. Consistent strengthening and gait practice are essential. Common milestones include:

• walking without a walker or cane (timing varies)
• comfortable stairs with a rail
• longer outdoor walks

#### Physical therapy: what matters most

Whether rehab is clinic-based, home-based, or hybrid, priorities are similar:

• restoring extension and functional flexion
• rebuilding quadriceps and hip strength
• normalizing walking mechanics
• gradually increasing load tolerance

Return to work, driving, and sports

• Driving: commonly when you are off sedating pain meds and can brake confidently. Right knee surgery often takes longer than left.
• Work: desk work may return sooner than jobs requiring prolonged standing, kneeling, or lifting.
• Sports: walking, cycling, swimming, and golf are common. High-impact running and jumping are often discouraged to reduce wear and loosening risk, but recommendations vary by surgeon and patient goals.

Long-term implant care: how to protect your outcome

• Maintain leg strength and general fitness.
• Manage body weight as feasible.
• Treat new pain early rather than “pushing through” for months.
• Keep routine follow-ups if recommended, especially if symptoms change.

What the Research Says

Knee replacement has a large evidence base including randomized trials (for perioperative strategies), registry studies (for implant survival and revision risk), and long-term cohort data (for patient-reported outcomes).

Effectiveness: pain and function

Across large studies and registries, most patients experience substantial improvements in pain and function after total knee replacement. Patient-reported outcome measures typically show major gains by 3 months, with continued improvement up to 12 months. Some patients continue to improve beyond a year as strength and confidence build.

A consistent finding across research is that expectations, mental health, and preoperative function influence satisfaction. People with severe pain and disability often improve greatly, but those expecting a “perfect” knee or those with widespread pain conditions may report less satisfaction even if the implant is mechanically sound.

Implant longevity and revision risk

National joint registries in several countries track revision rates and implant survival. In general:

• Many modern implants show strong durability beyond 10 years.
• Revision risk is higher in younger patients due to longer lifetime exposure and higher activity.
• The most common reasons for revision include infection, loosening, instability, stiffness, and patellofemoral problems.

Surgical technique and technology

Research on robotic assistance, navigation, and alignment philosophies shows:

• These tools can improve precision of bone cuts and component positioning.
• Clear, universal superiority in patient outcomes is not guaranteed, because pain and function are influenced by many non-technical factors.
• Surgeon experience, soft-tissue balancing, and complication prevention remain central.

Rehab and pain strategies

Evidence supports:

• Early mobilization to reduce complications and improve function.
• Multimodal analgesia to reduce opioid exposure while maintaining adequate pain control.
• Structured rehab focusing on strength, gait, and functional tasks.

What is still debated includes the best “dose” of supervised physical therapy versus well-designed home programs, and which subsets of patients benefit most from more intensive supervision.

What we know vs. what we do not

We know:

• Knee replacement reliably reduces arthritis pain for most appropriately selected patients.
• Complication prevention improves with risk-factor optimization and standardized perioperative protocols.

We do not fully know:

• The best universal alignment target for every patient anatomy and activity profile.
• Exactly who will develop persistent pain despite a well-functioning implant, though risk factors are increasingly recognized.

Who Should Consider Knee Replacement?

Knee replacement is usually considered when symptoms and imaging show advanced joint damage and quality of life is meaningfully affected.

Common candidates

You may be a good candidate if you have:

• Advanced osteoarthritis with significant pain, stiffness, and functional limitation
• Rheumatoid arthritis or inflammatory arthritis with joint destruction (with coordinated medication management)
• Post-traumatic arthritis after fractures or ligament injuries
• Severe deformity (bow-legged or knock-kneed) with worsening function

Practical “readiness” signs

• Pain limits daily activities (walking, stairs, sleep) despite appropriate non-surgical care.
• You have tried a reasonable course of conservative treatment such as strengthening, activity modification, weight management when feasible, anti-inflammatory strategies when safe, injections where appropriate, and assistive devices.
• The knee feels unstable or increasingly deformed.
• You are willing and able to participate in rehab.

When to consider delaying or reconsidering

Knee replacement may not be the best next step if:

• Pain source is unclear or likely referred from hip/spine.
• Arthritis is mild on imaging and symptoms are better explained by tendinopathy, meniscus irritation, or overload.
• Major modifiable risks are not optimized (for example, active smoking, uncontrolled diabetes).
• You have unmanaged depression, anxiety, or widespread pain sensitization that could reduce satisfaction unless addressed.

Alternatives, Common Mistakes, and Decision-Making

Many people benefit from delaying surgery until it is truly needed, not out of fear, but to ensure the timing matches the expected benefit.

Non-surgical alternatives (and when they make sense)

• Targeted exercise therapy: Strengthening the quadriceps and hips, improving balance, and gradually increasing walking tolerance. Often the highest-value first-line treatment.
• Weight management: Can reduce symptoms and may reduce surgical risk.
• Medications: Acetaminophen or anti-inflammatories when appropriate; topical anti-inflammatories for some patients.
• Injections: Corticosteroid injections can provide temporary relief for some; hyaluronic acid has mixed evidence; biologic injections remain controversial and are not a substitute for end-stage arthritis.
• Bracing and assistive devices: Unloader braces for unicompartmental arthritis; cane use can reduce knee load.

If arthritis is isolated to one compartment, partial knee replacement or osteotomy (bone realignment) may be options in select patients.

Common mistakes to avoid

#### 1) Expecting a “perfect” knee

A knee replacement is a mechanical solution to an arthritic joint, not a restoration of youthful tissue. Satisfaction improves when goals are framed around pain relief, functional walking, and quality of life.

#### 2) Skipping prehab and risk optimization

Strength, mobility, and health factors before surgery influence early recovery and complication risk.

#### 3) Overdoing activity too soon

Pushing hard in the first weeks can increase swelling and pain, which can slow progress. Rehab should be progressive, not punishing.

#### 4) Ignoring persistent or new symptoms

New redness, drainage, fevers, calf swelling, or sudden loss of function should be evaluated promptly.

Questions to ask your surgeon

• Is total or partial knee replacement more appropriate for my pattern of arthritis?
• What are my top 3 personal risk factors, and how can we reduce them?
• What implant design and fixation method are you recommending, and why?
• What range of motion and function should I realistically expect?
• What does my rehab plan look like for the first 6 weeks?

Frequently Asked Questions

How long does a knee replacement last?

Many last 15 to 20 years or longer, but durability varies by age, activity level, weight, alignment, and complications. Younger patients generally have a higher lifetime chance of revision.

How painful is recovery?

The first 1 to 2 weeks are often the most uncomfortable. Pain typically improves steadily over the first 6 to 12 weeks, with continued gains in strength and comfort for up to a year.

Will I be able to kneel after knee replacement?

Some people can kneel, but many find it uncomfortable due to sensitivity, stiffness, or pressure on the front of the knee. Technique training and gradual exposure can help, but it is not guaranteed.

Do I need physical therapy?

Most patients benefit from structured rehab, whether supervised or home-based. The essentials are restoring extension, building quadriceps strength, normalizing gait, and gradually increasing function.

What are signs something is wrong after surgery?

Concerning signs include fever, increasing redness or drainage from the incision, worsening calf swelling, sudden shortness of breath, chest pain, or rapidly worsening pain and stiffness. Contact your surgical team urgently if these occur.

Is robotic knee replacement better?

Robotics can improve precision in certain steps and may help in complex anatomy, but outcomes still depend on correct indications, soft-tissue balancing, rehab, and complication prevention. It is a tool, not a guarantee.

Key Takeaways

• Knee replacement replaces damaged joint surfaces with metal and plastic components to reduce arthritis pain and improve function.
• The most reliable benefit is pain relief and better daily mobility, not a return to a “perfect” or youthful knee.
• Risks include infection, blood clots, stiffness, persistent pain, and long-term loosening or wear; optimizing health factors lowers risk.
• Recovery is an active process: swelling control, early walking, and progressive strengthening drive results.
• Pre-surgery flexibility and strength influence post-surgery motion and function.
• Alternatives like exercise therapy, bracing, medications, and injections can help earlier-stage disease and may delay surgery.

Related reading on our site:

• 5 Real Goals of Knee Replacement, Explained Clearly
• RICE for Injuries: When Rest and Ice Help or Hurt
• What Really Happens in Knee Replacement Surgery