Osteoarthritis of the knee

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What is knee degeneration?

The degenerative process begins within the articular cartilage, the role of which is to absorb shocks and to provide as little resistance as possible during knee movements. The surface of the cartilage in a healthy joint should be smooth and intact.

Articular cartilage is built by cartilage cells (chondrocytes) suspended in the extracellular space (matrix). The matrix constitutes 95% of the cartilage volume and consists of collagen, proteoglycans and non-collagen proteins. Articular cartilage is devoid of blood vessels - it is nourished mainly by the diffusion of nutrients from the synovial fluid into the cartilage matrix.

Prolonged standing or local overload of the articular surface causes constant compression of the cartilage and prevents the penetration of nutrients into its interior. Moreover, the deterioration of the synovial fluid composition (e.g. in conditions of synovial inflammation) negatively affects the nutritional status of the cartilage. Nutritional disorders of cartilage in combination with its excessive overload lead to the process of its softening (chondromalacia). There are unfavorable changes in the cartilage structure consisting in a decrease in proteoglycans and a decrease in the strength of collagen fibers. Cartilage gradually loses its elasticity and resistance to abrasion. In response to microtrauma, chondrocytes multiply, but the process does not keep up with the destruction processes. Some chondrocytes die, creating cavities that are a potential site of cartilage defect. Microcracks occur, the cartilage collapses and becomes thinner, losing its role as a shock absorber. Loads begin to be transferred through the subcartilage layer of the bone, which leads to an over-densification of the bone tissue (sclerotization). Osteophytes (osteophytes) form on the edges of the articular surfaces and irritate the surrounding soft tissues.

Exposing the subcartilage layer (when the bone starts rubbing against the bone) irritates the nerve endings and aggravates knee pain. Synovial fluid penetrates into exposed bone, forming bone cavities (geodes). As a result of the damage, secondary inflammation develops - the migration of fibroblasts and the ingrowth of blood vessels from the subcartilage layer of the bone into the joint cavity. The release of pro-inflammatory cytokines leads to the formation of granulation tissue, followed by the process of tissue scarring. The inflammation spreads to the capsulo-ligamentous apparatus, leading to its contraction and limitation of mobility in the joint.

The degree of advancement of degenerative changes can be clearly defined using the Outerbridge scale:

• 0 - proper condition of cartilage,
  1 - softening and splitting of cartilage,
  2 - the presence of incomplete cartilage defects,
  3 - damage reaching the bone subcartilage layer, but not exposing it,
  4 - bone-to-bone contact.

Cartilage destruction may predominate in one of the compartments of the knee joint, hence gonarthrosis is distinguished:

• the medial compartment of the knee - the articular surface of the medial condyle of the femur and the medial articular surface of the tibia,
• the lateral compartment of the knee - the articular surface of the lateral femoral condyle and the lateral articular surface of the tibia,
• anterior knee compartment (patellar femoral joint) - the articular surface of the patella and the patellar articular surface of the femoral condyle.

Symptoms of osteoarthritis of the knee

1. Knee pain
   In the initial stages of osteoarthritis, pain in the knee joint occurs only during walking, running or squatting, and they are associated with increased joint overload. In the advanced stages of gonarthrosis, knee pain is also present during unloaded knee movements. In extreme cases, the pain occurs at rest, which forces the sick person to take painkillers.
2. Increased heat and swelling in the knee
   The swelling and edema in the knee result from the inflammation of the knee, which worsens when the joint is overloaded.
3. Restriction of mobility
4. Under proper conditions, the knee joint has mobility that allows for full extension and flexion that allows the heel to touch the buttock. Gonarthrosis leads to a gradual limitation of the range of mobility caused by the conflict of scarred soft tissues as well as degenerative and productive changes in bone tissue (osteophytosis).
5. You can feel friction or hear a click when you move your knee
6. Thickening the outline of the knee joint
7. Weakness of the quadriceps muscle of the thigh
   Pain in the knee causes the forced relief of the affected limb and restriction of activity, which is associated with the gradual weakening of muscle strength, especially the quadriceps muscle.

The causes of degeneration of the knee joint

Genetic factors

The tendency to develop a degenerative disease more quickly may be inherited. Many genes that code the composition of the connective tissue that builds the joint cartilage are important for the progression of knee degeneration. Therefore, some people have a type of cartilage with reduced mechanical strength.

Age, gender, race

The risk of degenerative symptoms increases with age, is higher in women (especially in the menopause) and in people of European descent (compared to the indigenous people of other continents).

Acute knee cartilage injuries

In the case of articular fractures, it is necessary to very carefully reconstruct the articular surfaces by adjusting the fragments and their stable fixation (ORIF, open reduction and internal fixation). If the procedure is unsuccessful, the articular surfaces will be mismatched, which will cause local pressure increase and aggravation of cartilage damage. Knee contusions (sprains, bruises) can also lead to acute cartilage or chondro-bone injuries. Treatment of local articular cartilage defects is of great importance for the secondary prevention of post-traumatic osteoarthritis of the knee.

Knee instability

Knee instability results from insufficiency of the anterior cruciate ligament (ACL) and / or posterior cruciate ligament (PCL), leading to dysfunction of the joint biomechanics and excessive abrasion of the articular cartilage.

Knee meniscus injuries

A rupture of the meniscus, its partial excision or removal of the entire meniscus causes a disturbance of the mutual alignment of the articular surfaces, leading to acceleration of degenerative changes of the knee.

Chronic knee overload

- Occupation - workers performing work related to frequent kneeling, crouching and carrying heavy objects, people who spend the whole day "on their feet",
- Professional sports - running on hard ground, lifting weights,
- Overweight and obesity.

Limb axis disorders

• Varus knee joints - leads to faster abrasion of the cartilage of the medial part of the knee,
• Valgus knee joints - leads to faster wear of the cartilage of the lateral part of the knee.

Inflammatory diseases

 Inflammatory diseases (e.g. rheumatoid arthritis) cause joint synovitis, which deteriorate the quality of the synovial fluid and, secondly, lead to disorders of the nutritional cartilage.

Metabolic diseases

Crystallopathies leading to joint inflammation:

•  Chondrocalcinosis - deposition of calcium crystals in articular cartilage,

• Gout - deposition of uric acid crystals in the synovial fluid.

Haemophilia

Haemophilia is associated with a disorder of blood clotting, which causes haemorrhages into the joint cavity. The consequence is recurrent inflammation of the knee joint.

Knee degeneration diagnosis

The orthopedic doctor conducts a detailed interview, which concerns:

- the location and nature of your knee pain
- types of activities that aggravate pain,
- the presence of accompanying diseases (especially inflammatory diseases),
- past injuries and operations within the lower limbs,
- profession and the patient's level of activity.

Then the orthopedist conducts a clinical examination, which should include:

- Examination of the range of mobility of the knee, assessment of muscle strength, palpation,
- Tests assessing the efficiency of the ligaments, the condition of the menisci and other knee structures,
- Assessment of the linearity of the lower limb, including the assessment of the hip joint and foot positioning - it is worth remembering that the biomechanics of the knee depends on the work of the hip and foot,
- Initial diagnosis of possible biomechanical disorders while walking or running.

Picture diagnosis

1. X-rays  
   

   The Kellgren and Lawrence scale according to Kellgren and Lawrence is used to assess radiological changes in the course of osteoarthritis:

   • 0 - no pathological changes,
   • 1 - the beginning of osteophytosis, i.e. the formation of bone spurs on the edges of the articular surfaces,
   • 2 - moderate narrowing of the articular space indicating a loss of thickness of the articular cartilage; sclerotization of the subcartilage layer of the bone indicative of bone overload, moderate osteophytosis,
   • 3 - loss of more than 50% of the thickness of the cartilage (joint space narrowing), marked sclerotization of the subcartilage layer of the bone, significant osteophytosis,
   • 4 - no joint space, bone-to-bone contact, presence of subchondral bone cysts, possible joint subluxation.
2. Knee ultrasound examination
   Usg kolana The knee ultrasound allows the evaluation of soft tissues (ligaments, tendons, bursae), bone contours and partially the menisci and cruciate ligaments of the knee.
3. Magnetic resonance imaging of the knee (MRI)
   Magnetic resonance imaging is the only non-invasive diagnostic method that allows the assessment of damage to the articular cartilage of the knee. MRI scans show degenerative changes affecting both soft and bone tissues. The structures of the knee joint (including the meniscus and cruciate ligaments) are shown in the most detailed way in the form of sections made in any plane.

It should be noted that the presence of degenerative changes in imaging studies does not always correlate with pain or reduced joint function reported by the patient. However, imaging diagnostics is a valuable help in assessing the extent of joint damage, which undoubtedly facilitates the selection of the appropriate treatment method - i.e. it allows avoiding the use of procedures that would be ineffective at a given stage of knee degeneration.

Treatment of osteoarthritis of the knee (gonarthrosis)

Conservative treatment of gonarthrosis includes:

1. Limiting the factor associated with excessive joint overload: 
   
   • limiting the standing position, avoiding carrying heavy objects, weight reduction,
   • modification of sports activity, e.g. switching from running to cycling or swimming,
   • the use of knee relief orthoses or shoe inserts that correct the wrong foot position,
2. Physiotherapy:
   
   • exercises for degeneration of the knee joint, strengthening the muscles stabilizing the knee joint,
   • treatments in the field of physical therapy,
3. Medications for degeneration of the knee joint:
   
   • hyaluronic acid injections to improve the quality of synovial fluid,
   • plasma injections with concentrated platelets (PRP, Orthokine therapy - methods that inhibit inflammation and support the natural repair processes of joint structures,
   • painkillers and anti-inflammatory drugs by mouth or by injection (joint blockage).

More information on how to conservatively treat arthrosis can be found in the article Conservative treatment of cartilage defects.

Surgical treatment is undertaken in the event of failure of conservative treatment or in the case of diagnosis of joint damage, which should be treated surgically. The main surgical procedures performed in osteoarthritis of the knee are:

1. Knee arthroscopy  
   
   • "Debridement", i.e. arthroscopic cleaning of the joint from an enlarged synovial membrane, post-inflammatory adhesions, degenerative changes (osteophytes),
   • simultaneous repair of meniscus damage possible,
   • simultaneous treatment of knee instability possible - reconstruction of the anterior cruciate ligament ACL / link / or posterior cruciate ligament PCL / link /
   • treatment of early degenerative changes,
2. Surgical treatment of traumatic cartilage injuries
3. Popliteal osteotomy (HTO, high tibial osteotomy) 
   
   • a procedure involving the correction of the limb axis in order to relieve the cartilage of one of the compartments of the knee joint,
   • allows you to keep your own joint and slow down the degeneration process,
   • the procedure is performed on young, active people,
   • most often it is the correction of the varus setting of the tibia in order to relieve the medial compartment of the knee joint,
4. Knee prosthesis implantation   
   
   • a procedure consisting in replacing the damaged joint with an artificial implant,
   • treatment of advanced degenerative changes of the knee.
   • the procedure is performed mainly in the elderly.

Source:

Michael, Joern W.-P., Klaus U Schlüter-Brust, and Peer Eysel. “The Epidemiology, Etiology, Diagnosis, and Treatment of Osteoarthritis of the Knee.” Deutsches Arzteblatt International 107.9 (2010): 152–162.

The most common questions about osteoarthritis of the knee: