Knee Prosthesis: Indications, Surgery and Rehabilitation

Frequently Asked Questions

What is a knee prosthesis?

A knee prosthesis is an artificial implant designed to replace the damaged components of the knee joint. This surgical intervention aims to alleviate pain, restore function, and improve mobility in individuals with severe knee joint degeneration.

For a complete overview, see the comprehensive guide to knee pain.

What are the primary indications for considering a knee replacement?

Knee replacement surgery is typically considered for individuals experiencing severe knee pain and functional limitations that have not responded to conservative treatments. The most common underlying condition necessitating this procedure is osteoarthritis, characterized by significant cartilage wear and joint damage.

What are the main types of knee prostheses available?

The primary types of knee prostheses are Total Knee Replacement (TKR) and Partial Knee Replacement (PKR). TKR involves replacing all three compartments of the knee joint, while PKR targets only the most damaged compartment, preserving healthier tissues.

What is the role of rehabilitation following knee prosthesis surgery?

Rehabilitation is a crucial component of recovery after knee prosthesis surgery, focusing on restoring strength, flexibility, and range of motion. A structured program, often guided by a physical therapist, helps optimize functional outcomes and facilitates a safe return to daily activities.

For a broader overview of related conditions, see our knee pain guide.

Sources and Scientific References

1. Šťastný E et al. (2016). [Rehabilitation after total knee and hip arthroplasty]. Cas Lek Cesk. 155:427-432. PubMed
2. Lespasio MJ et al. (2017). Knee Osteoarthritis: A Primer. Perm J. 21:16-183. DOI | PubMed
3. Aftab S et al. (2025). Early Physiotherapy for Post-Total Knee Arthroplasty Recovery: A Systematic Review of Randomized Controlled Trials on Quality of Life, Pain, and Range of Motion Outcomes. Musculoskeletal Care. 23:e70158. DOI | PubMed
4. Wainwright TW et al. (2020). Consensus statement for perioperative care in total hip replacement and total knee replacement surgery: Enhanced Recovery After Surgery (ERAS(®)) Society recommendations. Acta Orthop. 91:3-19. DOI | PubMed
5. Alonso-Rodríguez AM et al. (2021). [Efficacy of hydrotherapy versus gym treatment in primary total knee prosthesis due to osteoarthritis: a randomized controlled trial]. An Sist Sanit Navar. 44:225-241. DOI | PubMed

A Complete Guide from Diagnosis to Rehabilitation

Knee replacement surgery: Knee arthroplasty is a surgical procedure aimed at replacing the damaged knee joint with an artificial prosthesis. This procedure becomes necessary when pain and disability caused by degenerative or inflammatory knee diseases significantly compromise the patient’s quality of life and do not respond to conservative treatments.

The main causes that lead to the need for knee arthroplasty are:

1. Osteoarthritis (arthrosis):

• The most common cause: Gradual wear of the articular cartilage, which acts as a natural shock absorber, leads to joint degeneration.
• Typical symptoms: Pain, stiffness, swelling and reduced movement.
• Risk factors: Advanced age, overweight, previous trauma, genetic factors.

Comparison between a Healthy Knee and one Affected by Osteoarthritis

What the images show:

• Left image: A healthy knee with intact cartilage and wide joint space.
• Right image: A knee with osteoarthritis, with damaged cartilage, reduced joint space and presence of osteophytes

Healthy Knee:

• Cartilage: Smooth, elastic and thick, allows fluid and frictionless movement between bones.
• Joint space: Wide, allowing complete joint movement.
• Bones: Smooth and rounded surfaces, covered by cartilage.
• Menisci: Cartilage discs that act as shock absorbers and joint stabilizers.
• Ligaments: Resistant connective tissue that stabilizes the joint.

Knee with Osteoarthritis:

• Cartilage: Worn, thinned and rough, causing friction and pain during movement.
• Joint space: Reduced, limiting range of motion.
• Bones: Development of osteophytes (bone spurs) at bone margins, which can further limit movement.
• Menisci: Damaged or degenerated, losing their shock-absorbing function.
• Inflammation: Presence of swelling and redness due to inflammation.

Why are these differences important?

Healthy cartilage allows the knee bones to glide over each other without friction, ensuring fluid and painless movement. In osteoarthritis, cartilage loss causes increased friction between bones, resulting in pain, stiffness and limited movement.

Symptoms of osteoarthritis:

• Knee pain, often worsened by physical activity and relieved by rest.
• Morning stiffness.
• Swelling and warmth in the knee.
• Limitation of movement.
• Sensation of grinding or rubbing during movement.

It is important to emphasize that osteoarthritis is a progressive degenerative disease, meaning it worsens over time.

What to do in case of suspected osteoarthritis?

• Consult a doctor: the doctor can make an accurate diagnosis through a specialist visit and radiological examinations (X-rays, magnetic resonance imaging).
• Conservative treatments: Physiotherapy, anti-inflammatory drugs, injections.
• Surgery: In case of failure of conservative treatments, knee arthroplasty may be considered.

Rheumatoid arthritis:

• Autoimmune disease: The immune system mistakenly attacks the joint’s synovial membranes, causing chronic inflammation and damage to cartilage and bones.
• Symptoms: Pain, swelling, morning stiffness, joint deformities.
• Characteristics: May affect other joints besides the knee.

Post-traumatic arthritis:

• Consequence of injuries: Fractures, ligament or meniscal tears can accelerate the joint’s degenerative process.
• Symptoms: Chronic pain, joint instability, limited movement.
• Types of injuries: Anterior cruciate ligament injuries, medial meniscus injuries, tibial plateau fractures.

Avascular necrosis:

• Bone tissue death: Reduced blood flow within the bone causes bone cell death and subsequent joint degeneration.
• Causes: Trauma, prolonged use of corticosteroids, alcoholism.
• Symptoms: Deep pain, limited movement.

Other less common causes:

• Gouty arthritis: Urate crystal deposits in the joint.
• Septic arthritis: Joint infection.
• Bone tumors: Less frequent, but can cause pain and joint destruction.

Factors that may influence the decision to proceed with arthroplasty:

• Symptom severity: Pain, stiffness, functional limitation.
• Patient age: Generally indicated for patients over 55 years of age.
• General health conditions: Presence of other pathologies.
• Patient expectations: Desire to resume daily activities and improve quality of life.

The diagnosis of the need for knee arthroplasty is based on careful clinical evaluation and a series of diagnostic examinations. The specialist doctor, usually an orthopedist, will follow a diagnostic pathway that includes:

Detailed medical history:

• Symptoms: The doctor will ask the patient to describe symptoms in detail, such as pain (intensity, location, triggering factors), stiffness, swelling, limited movement and impact on daily life.
• Clinical history: Any previous trauma, inflammatory diseases, knee surgery and previous treatments will be evaluated.
• Risk factors: Factors such as age, weight, lifestyle and presence of other pathologies will be assessed.

Physical examination:

• Inspection: The doctor will observe the knee looking for signs of swelling, redness, deformity or signs of instability.
• Palpation: Different knee structures (bones, tendons, ligaments) will be palpated to identify any tender points or areas of inflammation.
• Movement assessment: The doctor will evaluate knee range of motion, muscle strength and joint stability.

Diagnostic tests:

• X-rays: The most common examination, allowing visualization of knee bones, joint space and presence of osteophytes (bone spurs).
• Magnetic Resonance Imaging (MRI): Provides more detailed images of knee soft tissues, such as cartilage, menisci and ligaments, allowing assessment of damage extent.
• Computed Tomography (CT): May be used to evaluate bone structure more precisely.
• Synovial fluid analysis: In some cases, it may be necessary to extract a small amount of synovial fluid from the joint for analysis to exclude infections or other pathologies.

Diagnostic criteria:

The decision to proceed with knee arthroplasty is based on several factors:

• Pain intensity and duration: Chronic and disabling pain that significantly limits daily activities is an important indicator.
• Movement limitation: Significant reduction in knee range of motion can compromise quality of life.
• Conservative treatment failure: When conservative treatments (medications, physiotherapy, injections) do not lead to significant symptom improvement.
• Advanced joint damage: Evidenced by radiological examinations and magnetic resonance imaging.
• Age and general health conditions: Advanced age and presence of other pathologies may influence the decision.

It is important to emphasize that diagnosing the need for knee arthroplasty is a complex process requiring accurate evaluation by a specialist.

Types of Knee Prostheses

The choice of knee prosthesis type depends on several factors, including patient age, severity of joint damage and activities desired after surgery. There are mainly two types of prostheses:

Total Knee Replacement (TKR)

Total prosthesis completely replaces the articular surfaces of the femur, tibia and often the patella as well. It is indicated in cases of advanced arthrosis involving the entire joint.

Advantages:

• Wide mobility: Allows a wide range of motion.
• Durability: Has long durability, often exceeding 15 years.

Disadvantages:

• More invasive surgery: Requires a longer incision and greater bone tissue removal.
• Longer recovery: Recovery period may be slightly longer compared to partial prostheses.

Partial Knee Replacement (PKR)

Partial prosthesis replaces only the damaged part of the joint, preserving healthy parts. It is indicated in cases of arthrosis involving only part of the knee and when ligaments are still in good condition.

Advantages:

• Less invasive surgery: Smaller incision and less bone tissue removal.
• Faster recovery: Recovery period is generally shorter.
• Bone tissue preservation: A greater amount of healthy bone is preserved.

Disadvantages:

• More restricted indications: Not suitable for all patients, as it requires specific joint conditions.
• Potentially shorter durability: Prosthesis duration may be slightly less than total prosthesis.

Types of partial prostheses:

• Unicondylar: Replace only one of the two articular surfaces of the femur.
• Bicondylar: Replace both articular surfaces of the femur.

Factors influencing choice:

• Patient age: Younger patients may be candidates for partial prostheses.
• Damage extent: Partial prosthesis is indicated when damage is limited to one part of the knee.
• Ligament quality: Presence of stable ligaments is essential for partial prosthesis.
• Activity level: For very active patients, total prosthesis may offer greater stability.

The choice of prosthesis type should be made together with the specialist doctor, carefully evaluating the individual characteristics of each patient.

Knee Prosthesis Surgery

Knee replacement surgery, or arthroplasty, is an established and safe procedure. It is performed under spinal or general anesthesia and involves replacing damaged articular surfaces with metallic and polymeric prosthetic components.

Surgical phases:

1. Incision: An incision is made on the front of the knee, of variable length depending on the type of prosthesis and surgical techniques used.
2. Joint exposure: The surgeon exposes the knee joint, removing damaged cartilage and underlying bones to create support surfaces for the prosthesis.
3. Prosthesis positioning: Prosthetic components (femoral, tibial and sometimes patellar) are positioned and fixed to the bone with the aid of bone cement or through a press-fit technique.
4. Incision closure: The incision is closed with sutures and a compression bandage is applied.

Surgical techniques:

There are various surgical techniques for prosthesis implantation, including:

• Traditional technique: Longer incision and greater tissue exposure.
• Minimally invasive technique: Smaller incision and less trauma to surrounding tissues.
• Computer-assisted navigation: Use of navigation systems for greater precision in prosthesis positioning.

Surgery duration:

Surgery duration varies depending on case complexity and surgical technique used, but generally lasts about 1-2 hours.

Anesthesia:

Surgery can be performed under spinal anesthesia (only the lower part of the body is anesthetized) or general anesthesia (the patient is completely asleep). Anesthesia choice depends on patient preferences and doctor indications.

Complications:

Like any surgical procedure, knee arthroplasty may present some complications, although they are rare. The most common complications include:

• Infections:
• Deep vein thrombosis:
• Prosthesis dislocation:
• Prosthesis loosening:
• Persistent pain:

Rehabilitation after knee prosthesis surgery

Post-operative rehabilitation is fundamental for complete and functional recovery after knee prosthesis surgery. The rehabilitation pathway is personalized based on individual patient characteristics and doctor and physical therapist indications.

Rehabilitation objectives:

• Pain and swelling reduction.
• Joint mobility recovery.
• Knee and thigh muscle strengthening.
• Walking and balance improvement.
• Return to daily and sports activities.

Rehabilitation phases:

1. Initial phase (first weeks):
   • Pain control: Use of ice, analgesic drugs and pain management techniques.
   • Isometric exercises: Muscle contraction without joint movement to maintain muscle tone.
   • Ambulation with aids: Use of canes or crutches to support weight and protect the joint.
   • Passive mobilization: The physical therapist gently moves your knee to maintain range of motion.
   • Heel sliding exercises: Lying in bed, slide heel toward buttocks to increase knee flexion.
   • Foot sliding exercises: Lying in bed, slide foot toward wall to increase knee extension.
2. Intermediate phase:
   • Increased active mobility: Patient begins to move the knee independently.
   • Muscle strengthening: Specific exercises to strengthen quadriceps, hamstring and gluteal muscles.
   • Proprioception: Exercises to improve balance and coordination sense.
   • Knee flexions: Sitting on a chair, bring heel toward buttocks.
   • Knee extensions: Standing, leaning on a table, lift leg behind you.
   • Static lunges: Standing, take a step forward and bend leg to form a 90-degree angle.
   • Wall squats: Back against wall, slide down as if sitting on a chair.
3. Advanced phase:
   • Functional strengthening: More complex exercises that simulate daily and sports activities.
   • Aerobic activities: Walking, swimming, cycling (initially stationary).
   • Return to sports activities: Gradual resumption of sports activities, with medical approval.
   • Walking on uneven terrain: To improve balance and coordination.
   • Stair climbing and descending: Start with one hand on handrail and gradually decrease support.
   • Exercise bike: Start with stationary bike then move to traditional one.
   • Swimming: Excellent for muscle strengthening and joint mobility improvement.

Recovery times:

Recovery times are individual and depend on various factors, such as age, pre-existing health conditions, type of implanted prosthesis and adherence to rehabilitation. Generally, it is estimated that:

• First 6 weeks: Mobility recovery and pain reduction.
• 3-6 months: Return to daily activities.
• 6-12 months: Complete recovery and return to sports activities.

Importance of rehabilitation:

Adequate rehabilitation is fundamental to obtain the best results after knee prosthesis surgery. Good rehabilitation allows:

• Pain and swelling reduction.
• Recovery of good mobility and muscle strength.
• Quality of life improvement.
• Prosthesis durability extension.

Remember: This is only an example of exercises. Your physical therapist will provide a personalized program and guide you throughout the entire rehabilitation pathway.