Osteoarthritis of the Knee: What it is, Causes, Symptoms and Treatments

Knee osteoarthritis, knee osteoarthritis or gonarthrosis is the degeneration of articular cartilage with formation of new bone tissue (subchondral bone and osteophytes) affecting the entire joint: cartilage, bone, synovium and ligaments. 

It is a chronic disease that over time leads to pain with physical activity, decreased joint mobility, inability to walk and stand, and progressive deformity of the knee. In the most advanced cases, when the knee is severely damaged, patients are unable to perform daily activities without pain and osteoarthritis causes a significant worsening in quality of life.

Osteoarthritis is the most common arthropathy in the world, second only to cardiovascular diseases among chronic diseases. From a certain age (45-50 years), everyone has radiological manifestations of osteoarthritis in the knee or in other parts of the body. Some people, however, have no symptoms, while others experience a significant decrease in their quality of life. Before talking about osteoarthritis of the knee, it is important to know what components the joint has.

• Osteoarthritis of the knee is a problem that will eventually affect us all, although not all of us will suffer the symptoms.
• There are several treatments for osteoarthritis of the knee, with knee replacement surgery being used in the most severe cases.
• One of the main ways to reduce the symptoms of osteoarthritis of the knee is to have a balanced weight.

The knee is the largest joint in our body and one of the most complex. It consists of bone elements, menisci, ligaments, muscles, joint capsule, synovial membrane, bursae and retinaculum.

In our knee joint there are three bone elements: the distal epiphysis of the femur, i.e. the lower part of the femur, the patella, which is located in the anterior part of the knee, and the proximal epiphysis of the tibia, i.e. the upper part of the tibia. 

The femur and tibia form the tibiofemoral joint, and the femur with the patella or kneecap form the patellofemoral joint. All bone surfaces of the knee are covered by cartilage.

The menisci are located between the femur and the tibia and promote congruence between the articular surface. They are a wedge-shaped ring of fibrocartilage.

Two important ligaments are located inside the knee: the anterior cruciate ligament and the posterior cruciate ligament. On the outside of the knee are the internal lateral ligament and the external lateral ligament.

The muscles that act on the knee are the quadriceps and the hamstrings. The quadriceps is the main muscle, located on the anterior aspect of the thigh, it is made up of four bellies and performs knee extension. The hamstrings are located on the back of the thigh and are responsible for the knee flexion movement, i.e. bending the knee.

The joint capsule is a fibrous, strong and complex capsule. It is related to the synovial lining of the knee. It is cuff-shaped and surrounds the tibiofemoral joint and the patellofemoral joint.

The synovial membrane of our knee is the largest in the human body. It is a thin layer of tissue that lines the inner surface of the joint capsule. The synovial membrane is responsible for the production of synovial fluid. The word synovia is derived from the Greek "syn" (with) and the Latin "ovum" (egg), suggesting that this fluid resembles raw egg white. It is a plasma-like substance but has a high concentration of hyaluronic acid. 

It fills the joint cavity and acts as a lubricant, thus keeping friction between the bones during movement to a minimum. 

Apart from the lubricating function, it nourishes the cartilage, which is an avascular tissue and gets its nutrients by diffusion from the synovial fluid.

Bursae are structures that are located around the soft tissue and joint surfaces. They reduce joint friction and cushion movement.

The retinaculum are fibrous structures that connect the patella to the femur, meniscus and tibia.

Finally, there is the articular cartilage, which covers the bony part that forms the joint and whose wear and tear is the main symptom of osteoarthritis of the knee.

What is articular cartilage?

Articular cartilage is essential for the proper functioning of a joint. Its integrity is very important as it is the area of contact and friction. Articular cartilage covers and protects the bony elements of the knee: the femur, tibia and patella.

Articular cartilage has two basic components: chondrocytes, which are the cells specialised in the production and maintenance of the extracellular matrix, consisting of water (65-80%), collagens (10-30%) and proteoglycans (85-10%). The water present in cartilage allows it to deform in response to stress. Collagen gives cartilage a high tensile strength. Proteoglycans are responsible for the compressive strength of cartilage.

Articular cartilage is an avascular, aneural and alymphatic tissue, i.e. it does not contain blood vessels, neurons and lymphatic vessels. Four layers can be distinguished in the articular cartilage.

• The upper or gliding layer is located on the articular surface. It has the smallest thickness of the four layers. It has little metabolic activity. It is rich in collagen and poor in proteoglycans. It supports shear forces. The chondrocytes in this layer are flattened and parallel to the surface.
• The intermediate or transmission layer is thicker than the first layer. It has high metabolic activity. It contains less collagen and more proteoglycans. It supports compressive forces. The chondrocytes in this layer are more rounded.
• The deep or radial layer is about twice as thick as the second layer. It is rich in both collagen and proteoglycans and supports compressive forces. Rounded cells form columns in this layer.
• The calcified layer is the area adjacent to the subchondral bone. It supports shear forces.

As cartilage is an avascular tissue, i.e. it has no blood vessels of its own, it is mainly nourished by synovial fluid, a process in which the joint lubrication mechanism is heavily involved, although the deepest layer (about 1/3 thick) can be nourished by the epiphyseal vasculature, i.e. the blood vessels of the bone.

Osteoarthritis of the knee is the loss of articular cartilage with overgrowth and remodelling of the underlying bone. It is a disorder that affects all components of the joint: cartilage, bone, synovial membrane and joint capsule, although cartilage is the most affected tissue. It is a combination of clinical symptoms, radiological and laboratory signs. 

It is a chronic, degenerative, non-inflammatory disease. The disintegration of the cartilage causes the bones to rub against each other, which over time leads to stiffness, pain, inflammation and decreased mobility. Once the degenerative process in the knee begins, it is difficult to stop.

The causes of gonarthrosis (osteoarthritis of the knee) are different and often occur together in the same person.

Two types of knee osteoarthritis can be distinguished:

Primary knee osteoarthritis or idiopathic gonarthrosis

In this case, no specific cause of the disease is found, however, certain risk factors are associated:

• Age
• Obesity
• The practice of impact sports for years
• Strength work
• Positive family history
• Menopause

Secondary knee osteoarthritis

In this case, osteoarthritis of the knee is a direct consequence of a previous illness or injury:

Post-traumatic knee osteoarthritis

• Fracture of the patella, condyles, tibial plates, meniscal tears, meniscectomy, chronic ligament instability.
• Congenital diseases: epiphyseal dysplasias, spondyloapophyseal dysplasias, osteochondrodystrophies.

Post-infectious knee osteoarthritis

• Diseases due to deposition of substances in the knee: calcium pyrophosphate, apatite and endocrine diseases: diabetes, hypoparathyroidism, acromegaly, haemochromatosis, ochronosis.
• Joint diseases: gout, rheumatoid arthritis, Paget's disease, haemophilia.
• Bone diseases: osteochondritis, osteopetrosis, Charcot disease, osteonecrosis.
• Neurological diseases: leprosy, Kashin-Beck disease.
• Mechanical and local factors: varus, valgus, dyssymmetries, hypermobility, scoliosis, obesity.

All of the above factors and diseases increase the risk of osteoarthritis. Not to mention all, the people most prone to suffer from osteoarthritis of the knee are:

• People who are overweight are more likely to suffer from osteoarthritis of the knee. Experts estimate that being 20% overweight increases the risk of osteoarthritis of the knee tenfold. For a knee it is not the same to support 65 kilos as 90kg. On the other hand, in the blood of obese people there are certain hormones in high concentrations that accelerate the wear and tear of the cartilage and cause inflammation. Fat located in the abdominal area produces leptin, neuroleptin and resistin which influence cartilage homeostasis.
• Athletes are also more prone to this disease: Knee and hip osteoarthritis are more common in football, rugby, basketball, tennis and volleyball players. To prevent the disease in this group of people it is important to know the correct exercise technique, to train with the right shoes, to warm up beforehand and to stretch. In athletes, it is not only continuous overloading that increases the risk of osteoarthritis, but also injuries and surgery following sports injuries.
• The incidence of osteoarthritis of the knee is higher in heavy loaders, construction workers, bricklayers. Continuous microtrauma in these people increases the likelihood of joint wear and tear and the development of osteoarthritis.
• Menopausal women are more likely to suffer from osteoarthritis of the knee due to the loss of oestrogen, as this hormone is able to protect the cartilage.
• Over time, the risk of gonarthrosis (osteoarthritis of the knee) or osteoarthritis of any joint increases. In older people, the flexibility and elasticity of the tissues decreases and stiff tissue is more prone to microfractures.
• After surgery or trauma to the knee, the risk of osteoarthritis of the knee always increases.

Why does osteoarthritis of the knee occur?

During the degenerative process in osteoarthritis of the knee, the cartilage loses consistency and elasticity. First, the surface area swells and becomes softer. Cracks and erosions appear on this soft surface.

Over time, the thickness of the cartilage decreases due to surface erosion, and in some cases it disappears completely. The cartilage no longer protects the bones and they are exposed and rub against each other. The exposed bone becomes denser, cysts appear within its structure. New bone forms around the edges of the joint, called osteophytes. Free bodies may appear inside the joint, which may be cartilaginous elements, osteocartilaginous elements or broken osteophytes.

These bodies move freely in the knee, causing further damage through friction and irritation of the joint surface. The synovial membrane becomes inflamed, thickens and produces more but less viscous synovial fluid that does not lubricate the joint surfaces well. Fibrosis extends to the joint capsule which thickens, loses its elasticity and limits knee movement. Excess synovial fluid causes the knee to swell. This swelling together with the formation of osteophytes causes joint deformity.

The first changes occur without the patient noticing any symptoms, as the cartilage has no pain-producing capacity, it is aneuronal, i.e. it has no neurons or pain receptors. At this stage the cartilage can still recover and the disease is potentially reversible. When the cartilage disappears completely, the disease is very severe and the process is irreversible.

Macroscopically, i.e. by looking at the articular surface of the knee during arthroscopy or open surgery, the severity of the disease can be:

• Stage I: no signs of disease, the cartilage is healthy.
• Stage II: fibrillation is observed on the articular surface, marking the beginning of cartilage wear.
• Phase III: fissures appear, i.e. small cracks in the cartilage, which are deeper wear and tear.
• Stage IV: ulceration of the articular cartilage causes subchondral bone (the bone tissue just below the cartilage in a joint) to appear on the articular surface, rubbing against each other.

Osteoarthritis of the knee can be classified according to radiological signs. These signs are:

• Decreased joint interlinearity, i.e. decreased space between the two joint surfaces.
• Osteophytes in the marginal areas of the joint, which are the result of reactive proliferation of the subchondral bone to the cartilage destruction.
• Sclerosis of the subchondral bone, subchondral cysts resulting from intra-articular hyperpressure.

Archibeck has classified osteoarthritis into 5 stages based on the results of loaded anteroposterior radiographs of the knee:

• Stage I. Inter-joint line decreased in height by 50% in the affected compartment (usually internal); normal in the opposite compartment.
• Stage II. Complete disappearance of the interlining on the affected side, unstable knee; opposite compartment undamaged.
• Stage III. Bone wear less than 5 mm; knee more unstable and injury to opposite femoral condyle by tibial spine action begins.
• Stage IV. Greater bone wear, between 5 mm and 1 cm; significant involvement of the contralateral compartment.
• Stage V. Bone wear greater than 1 cm; lateral tibial subluxation and global femorotibial injury, usually extending to the patellofemoral joint.

All this must be diagnosed by a specialist, who knows best how to detect osteoarthritis of the knee.

If we were to x-ray several people over 50 years of age, most of them would show radiological signs of osteoarthritis. However, not all of them show symptoms. Patients who have symptoms usually have pain, crunching, stiffness, swelling, oedema and joint deformity. 

These symptoms appear gradually and the progression is slow:

• The most common symptom of gonarthrosis (osteoarthritis of the knee) is pain. The pain is caused by degeneration of the cartilage and the bare bones rubbing against each other. Initially the pain occurs after prolonged standing or walking. Usually in this phase the pain is more intense in the morning, during the first few minutes when the patient starts to move his or her knee after the night's inactivity. Activities such as walking up and down stairs, walking on uneven ground or getting up from a chair cause more intense pain, although of shorter duration. As the disease progresses, it hurts earlier and earlier to start walking or standing. In the very advanced stage of the disease, continuous and severe pain prevents the patient from carrying out daily activities.

• The next most common symptom is joint stiffness. After sitting for a while or in the morning, the patient feels stiffness and pain when trying to get up. It is as if the knees are stiff and need to warm up in order to regain their natural movement. The patient has difficulty flexing and extending the leg. After a short time, the initial stiffness and pain disappears, but after a variable period of walking, the pain reappears. If the person with osteoarthritis of the knee stands up, the pain gradually subsides.

• Sometimes the knee becomes swollen and hot. These are episodes of inflammation that are occasionally observed in osteoarthritis of the knee. The synovial membrane produces too much synovial fluid, which is why the knee appears swollen. In osteoarthritis of the knee, it is the joint that swells, while the leg, ankle and foot remain normal. In contrast, in people who retain fluid, it is the whole leg, from the knee down, that swells. Over time, the knee deforms due to the reaction of the joint bone to the osteoarthritis, forming bony protrusions on the edges of the joint called osteophytes.
• Because of the irregularity of the joint surface, patients may notice crepitus and joint noises when moving the knee.
• In very advanced cases the patient has atrophy and muscle weakness around the knee and palpation can be very painful.

What is the difference between arthritis, osteoarthritis and osteoporosis?

Arthritis is an inflammatory disease of the synovial membranes that secondarily damages bone and cartilage. It is an autoimmune disease that attacks the synovial membrane and its main symptom is joint inflammation. Patients are young people between 20-40 years old and apart from the joint symptoms, extra-articular symptoms occur. Stiffness is important and pain worsens with rest.

Osteoarthritis, also called osteoarthritis, is the wearing away of joint cartilage resulting in pain, stiffness and loss of normal movement. Patients are older than 40 years. There are no extra-articular symptoms. Stiffness is less long-lasting and pain worsens with mobility.

Osteoporosis or porous bone is a disease of bone tissue that causes loss of bone density and mass.

Osteoarthritis of the knee cannot be diagnosed exclusively by looking at an X-ray, because from a certain age everyone has signs of osteoarthritis on X-rays. Without a medical interview, i.e. a proper medical history and physical examination, it is not possible to diagnose osteoarthritis of the knee. Sometimes a joint fluid analysis is performed to confirm the diagnosis and to rule out other pathologies.

During the anamnesis the patient tells us the characteristic symptoms of osteoarthritis of the knee such as pain, joint stiffness, functional disability, absence of fever and absence of extra-articular manifestations. The pain appears at the onset of movement, then improves and reappears with intense or prolonged exercise. 

Over time, as the disease progresses, the pain appears earlier and earlier. In a very advanced stage, any small movement causes pain. This pain subsides or improves with rest. Joint stiffness appears after a prolonged period of immobility and improves rapidly with movement. Both pain and stiffness decrease the patient's quality of life and limit the performance of daily living tasks. 

Physical examination consists of inspection, palpation of the knee and assessment of its mobility. During inspection of the knee, deformity and malalignment, muscle hypertrophy around the knee and swelling may be observed. Palpation can be used to assess pain, crepitus or crunching and to rule out other pathologies. 

During the passive mobility examination, pain appears in the last degrees of flexion and extension, and joint instability is noted due to muscle atrophy. Intra-articular free bodies can cause joint locking.

X-rays show:

• Osteophyte formation
• Decreased joint space
• Sclerosis of the subchondral bone
• Bone cyst formation
• Alteration in bone contouring
• Periarticular calcifications
• Soft tissue oedema

Examination of synovial fluid may reveal cartilage fragments, calcium pyrophosphate crystals, hydroxyapatite or other calcium and phosphate salts. A small to moderate effusion is common but large effusions are rare in gonarthrosis.

Osteoarthritis is directly related to age, so it is not possible to prevent the disease, but it is possible to delay its onset to a large extent. Rehabilitation activities can also be carried out to preserve the functionality of the joint and relieve the patient's pain. We do not know much about the natural progression of osteoarthritis, but in general it evolves slowly in a non-linear fashion. Sometimes patients experience improvements.

 In most people, radiological signs do not correlate with the patient's symptoms and joint function.

One of the factors of poor prognosis is obesity, which is why weight loss or the maintenance of an ideal weight is of fundamental importance among the preventive measures. Our knees support a higher than optimal weight over a prolonged period of time when we are overweight. This higher load leads to progressive joint degeneration. In case of a family history of osteoarthritis of the knee, weight control is even more important.

The muscles around the knees support, protect the joint and give consistency and strength to the area. Daily physical exercise strengthens the musculature not only around the knees but all the muscles in our body in general. A stable, strong musculature protects the knees and prevents overloading of the knees. 

Daily physical exercise also helps to lose weight and provides important cardiovascular and pulmonary benefits. Exercises for a joint affected by osteoarthritis should be very gentle, but prolonged and low-impact. Pain should always be avoided. 

The most recommended exercises are:

• Swimming
• Aerobic exercise
• Walking on regular terrain
• Cycling
• Hydrotherapy
• Pilates

Exercises or physical activities not recommended are:

• Squatting
• Kneeling
• Walking up and down stairs
• Walking on uneven ground
• Heavy walking
• Sitting on low sofas
• Standing for prolonged periods of time
• Putting pads under the knee because this action increases joint limitation.

Other elements that can help are:

• Appropriate footwear with rubber soles helps to absorb some of the energy of the impact against the ground. It is recommended that shoes have a heel height of 2-3 centimetres. In addition to suitable footwear, the use of insoles made of soft materials can reduce pain and allow the patient to improve his or her walking ability.
• The use of crutches and canes reduces strain, reduces pain and cartilage degeneration.
• Proper nutrition plays an important role in preventing osteoarthritis or slowing down the progression of the disease. A balanced diet helps to maintain a healthy weight. Foods rich in vitamins A, C, E and D and omega-3 fatty acids are beneficial for joint health.
• In order to slow down the progression of osteoarthritis, it is recommended to take food supplements based on collagen, hyaluronic acid, glucosamine, chondroitin and methyl sulphonyl methane.
• The psychological preparation of the patient is very important so that he/she understands that he/she will lead an active life, albeit with certain limitations.

Conservative treatment includes all the preventive measures mentioned above. The objectives of conservative treatment are as follows:

• Slow down the degenerative process of the knee joint.
• Reduce the patient's pain
• Maintain or improve joint mobility
• Improve joint stability
• Improve or maintain functional independence
• Prevent deformities and contractures

Pain relief is one of the most important goals, considering that osteoarthritis causes chronic pain that the patient has to deal with every day and this chronic pain significantly worsens the patient's quality of life. Without the use of medication, pain relief can be achieved in the following ways:

• Rest: during painful flare-ups, rest is recommended but for as short a time as possible to avoid stiffness, muscle atrophy and contractures.
• Postural treatment is especially important when osteoarthritis is generalised and also affects the spine.
• Throughout the course of the disease, weight control is very important to reduce the load on the knees. With the help of a nutritionist and a personalised diet, it is possible to achieve the objectives and maintain a healthy weight.
• Mobilisation is important to avoid stiffness and contractures and to improve joint mobility.
• The most commonly used physiotherapeutic treatments for patients with osteoarthritis of the knee are: massage, ultrasound, hydrotherapy, magnetotherapy, electrotherapy, lasertherapy and cryotherapy.
• Electro-stimulation of the musculature around the knee helps to strengthen these muscles when the patient is unable to do much physical exercise due to pain.
• Heat and cold: Heat is most beneficial in osteoarthritis. A hot water bottle placed over the painful joint relieves the pain and relaxes the muscles. Cold, after a flare-up, i.e. an inflammatory flare-up and after exercise, is useful, as it helps to reduce the inflammation.

Conservative treatment includes all medications that reduce pain and slow down the progression of the disease. Intra-articular injections are also part of conservative treatment.

Pharmacological treatment includes:

• Oral medications to relieve the patient's pain.
• Local medications such as pain relieving creams, gels and patches
• Oral medications to slow the progression of the process
• Intra-articular infiltrations

In osteoarthritis of the knee there is often an overuse of drugs as the disease causes severe and continuous pain that prevents the patient from carrying out daily activities. Generally, 3 main groups of analgesics are used: paracetamol, non-steroidal anti-inflammatory drugs and opioid analgesics.

Paracetamol is the first analgesic prescribed by the physician for mild to moderate pain. The daily dose can be increased up to 4 grams.

If paracetamol is not sufficient, the second step is the administration of non-steroidal anti-inflammatory drugs that relieve moderate pain and stiffness. Prolonged use of these drugs is not recommended because of their side effects. In patients with a history of peptic ulcer disease, these drugs should be administered together with stomach protectants. 

Prolonged use of some analgesics in this group has been reported to accelerate joint damage. The use of opioid analgesics is reserved for periods of exacerbation of chronic pain and for short periods of time.

Local medicines such as gels, creams and patches contain non-steroidal anti-inflammatory drugs, capsaicin, and certain medicinal plants. Some products have a cold or heat effect. Their benefit over oral analgesics is that they are less likely to have serious side effects.

Intra-articular infiltrations are of 3 main types: corticosteroids, hyaluronic acid and growth factors.

Intra-articular corticosteroids are only indicated in cases of acute synovitis with or without crystal-induced effusion. 

Hyaluronic acid administered as intra-articular injections functions as a lubricant and shock absorber, preventing painful friction between irregular and bare surfaces. Growth factors are proteins that promote tissue development. Theoretically growth factors by their action could help in the regeneration of cartilage. 

However, since this type of treatment is quite new and there is still not enough experience with it, it has not yet been demonstrated that they have any effect on the evolution of osteoarthritis. Growth factors have a very powerful anti-inflammatory effect that can improve the symptoms caused by osteoarthritis, helping patients to normalise their lives and improve their quality of life, which in some cases can prolong the life of the joints, thus delaying their replacement by prostheses.

When osteoarthritis is very advanced, the pain is very intense and continuous and prevents the patient from performing daily activities and the deformity is severe, it is time to consider surgical intervention.

There are different types of surgical interventions. The choice among the wide variety of therapeutic measures depends on several factors such as the patient's age, the severity of the disease, the location of the disease. Surgical interventions include joint lavage by arthroscopy, osteotomies, partial and total arthroplasty and cartilage grafting.

One of the simplest procedures is joint lavage or joint lavage and debridement. Through this surgery, fragments of articular cartilage, menisci, synovial membrane and degradative enzymes can be removed in order to avoid joint irritation.

In young patients in whom osteoarthritis only affects one part of the joint, usually the inner part, a tibial osteotomy can be performed, which consists of making a cut in the upper part of the tibia to modify its load angle so that it is redistributed in a way that is less harmful to the knee.

In patients under 45-50 years of age with lesions less than 4 centimetres in diameter and with knees without deformity or instability, mosaicplasty is possible. 

Mosaicplasty is a surgical technique that consists of placing articular cartilage in an area where it is damaged, from another area where it is healthy. It is a kind of cartilage grafting, just as surgeons graft skin from a so-called donor area. It is also called osteochondral autograft.

In more advanced cases, when the knee is severely damaged and this prevents the patient from performing simple daily activities and painkillers and other therapeutic measures no longer help, the solution will be a total knee replacement, which will relieve the pain, correct the knee deformity and help the patient to perform daily activities without discomfort. 

This type of surgery takes about an hour to an hour and a half and involves removing the damaged cartilage and bones and then fitting a new joint surface made of plastic and metal.

How is knee replacement surgery performed?

Knee replacement is indicated for patients with severe impairments. Most of them are over 55 years of age and:

• Have severe pain on a daily basis
• Severe pain not only limits them for work but also for daily activities such as dressing, putting on shoes, going up and down stairs.
• The pain does not improve with other therapeutic measures such as analgesics, rest and use of crutches.
• Patients have significant stiffness in the knee.
• They have instability in the joint with continuous failures.
• The knee is grossly deformed
• There is significant wear and tear on the X-ray

There are different types of knee prostheses:

• Tri-compartmental prostheses are the most common. This type of prosthesis is also called a total knee prosthesis, as it replaces the entire joint. Within this type of prosthesis there are several models: some are fixed with cement and others without cement. Some models allow both cruciate ligaments to be retained, others only one or none at all. Depending on the mobility of the plateau, there are fixed or mobile models.
• The patello-femoral prosthesis is used exceptionally in the case of osteoarthritis of the joint between the patella and the femur.
• Partial or uni-compartmental prostheses replace only the worn part of the knee: the internal or external femoro-tibial compartment or the joint between the patella and the femur.

Preparation for knee replacement surgery begins weeks before the surgery.

• It is advisable to strengthen the muscles of the whole body, especially the muscles of the arms and trunk, because after the operation the patient will have to use crutches. The best way to strengthen the muscles around the knee is swimming.
• If you are overweight, ask for help from a nutritionist or your family doctor to lose the extra kilos. An overweight patient increases the pressure on the new knee, decreasing the lifespan of the prosthesis.
• Stop smoking before surgery, as smoking damages the circulatory system, causes lung complications and delays healing.
• Stop taking anti-inflammatory painkillers one week before admission. In the case of severe pain you can take paracetamol or Nolotil.
• Consult your doctor about your usual medications, especially if you are taking anticoagulants or antiplatelet drugs.
• If you have dental problems, consult your dentist, as teeth can be a source of infection.
• Prepare your home and ask for help from a relative for the first few days after the operation.
• Before the surgery, you will undergo preoperative tests.

On the day of admission:

• You will usually be admitted to hospital the day before or a few hours before the surgery. You should bring all your medical documents relating to the intervention and some crutches with you. The nurses will give you all the information you need about your surgery and your stay in hospital.
• Do not eat or drink for 6 hours before the surgery.
• You will shower and prepare the skin area where the incision will be made by removing the hair and painting it with antiseptic.
• Dentures, jewellery and nail polish must be removed.
• You will be given an injection in your tummy to prevent the formation of clots, which will continue to be administered over the next 4-6 weeks until you are fully mobilised.

On the day of the intervention:

• Take a shower.
• You will dress in a hospital gown before going to the operating theatre.
• An IV will be placed in a vein in your arm to administer fluids and medicines before, during and after surgery.
• In the operating theatre you will be given anaesthesia. If your doctor chooses general anaesthesia, you will be asleep during the entire surgery and will not feel anything. When the anaesthesia is regional (epidural or spinal) you will be given medicine inside your back. You will not feel anything below your waist. Sometimes regional anaesthesia is supplemented with sedation and in this case you will be asleep during the entire procedure.
• First the surgeon will disinfect the area with an antibacterial liquid to prevent infection.
• Once the patient is under anaesthesia, a catheter will be placed to empty the bladder.
• The doctor will make an incision over the knee to open it.
• After the patella is set aside, the surgeon will cut off the worn ends of the tibia and femur with a surgical saw. Once this is done, the bones are prepared with bone cement if necessary, and the tibial and femoral components of the knee prosthesis are placed. Attached to the tibial component is the insert, the piece of high-density polyethylene that will act as a meniscus to prevent the components from rubbing together.
• In the event that the kneecap has also been affected by osteoarthritis, the inside of the kneecap will be filed down, eliminating the worn area and in its place a metal part will be placed in contact with it and on the other side a polyethylene piece will be placed that will be in contact with the femoral component and will allow it to slide correctly during movement.
• The surgeon will repair the muscles and tendons around the new joint and close the surgical incision.
• Finally, the surgical incision will be sutured and a bandage will be placed around the knee.
• You will be taken to the recovery room where you will stay until your vital signs are stable.

Knee replacement surgery is a major surgery that requires a hospital stay of 4 to 5 days. Total recovery is between 4 and 6 months. The duration of current knee prostheses is between 20 and 25 years, although this will depend on each patient, the type of knee prosthesis used and some important instructions such as maintaining an adequate weight.