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Definition and What causes knee pain?

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Definition

The knee is a joint that has three compartments. The thighbone (femur) meets the large shinbone (tibia) forming the main knee joint. This joint has an inner (medial) and an outer (lateral) compartment. The kneecap (patella) joins the femur to form a third compartment, called the patellofemoral joint.

The knee joint is surrounded by a joint capsule with ligaments strapping the inside and outside of the joint (collateral ligaments) as well as crossing within the joint (cruciate ligaments). These ligaments provide stability and strength to the knee joint.

The meniscus is a thickened cartilage pad between the two joints formed by the femur and tibia. The meniscus acts as a smooth surface for motion and absorbs the load of the body above the knee when standing. The knee joint is surrounded by fluid-filled sacs called bursae, which serve as gliding surfaces that reduce friction of the tendons. Below the kneecap, there is a large tendon (patellar tendon) which attaches to the front of the tibia bone.

There are large blood vessels passing through the area behind the knee (referred to as the popliteal space). The large muscles of the thigh move the knee. In the front of the thigh, the quadriceps muscles extend the knee joint. In the back of the thigh, the hamstring muscles flex the knee. The knee also rotates slightly under guidance of specific muscles of the thigh.

What causes knee pain?

Injury can affect any of the ligaments, bursae, or tendons surrounding the knee joint. Injury can also affect the ligaments, cartilage, menisci (plural for meniscus), and bones forming the joint. The complexity of the design of the knee joint and the fact that it is an active weight-bearing joint are factors in making the knee one of the most commonly injured joints.

Other causes of knee pain could be due to diseases or conditions that involve the knee joint, the soft tissues and bones surrounding the knee, or the nerves that supply sensation to the knee area. In fact, most of the time, the knee joint is affected by rheumatic diseases and immune diseases that affect various tissues of the body.

Knee Arthritis

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Arthritis is disease of a joint that may invlove pain, stiffness, swelling and/ or inflammation within the joint. The causes of knee joint arthritis range from degenerative types of arthritis such as osteoarthritis, to inflammatory types of arthritis such as rheumatoid arthritis or gout. Treatment for the condition depends on the specific type of arthritis encountered.

Osteoarthitis
This is most often due to wear-and-tear of the knee joint, and is age and activity related. It can also be due to previous injuries of the knee as well as pre-existing malformations. Osteoarthritis most often affects individuals over the age of 50, but with increasing active lifestyles, even younger people can be affected. In the early stages, the condition can be treated by activity modification, medications and other non-surgical means. However in more severe cases, surgery may offer the best chance of long-lasting results, and this may range from simple procedures such as arthroscopy, to more complex operations such as realignment surgeries and knee replacement.

Rheumatoid and other inflammatory arthritis
This group of diseases include rheumatoid, sero-negative arthritis, systemic lupus erthematosus (SLE), ankylosing spondylitis (AS), psoriatic arthritis and other rare forms of arthritis. They are often autoimmune in nature, and the disease process can often be suppressed by medications, but not usually cured. If joints become irreversibly damaged by the disease, joint replacement is often a good option that can yield excellent results.
Gout and other crystal diseases
These conditions are caused by the presence of various types of crystals within joints. Uric acid crystals give rise to gout, while calcium pyrophosphate crystals cause pseudogout. The crystals are responsible for pain, swelling and inflammation of joints, including the knee, ankle and foot joints. Medications can often control the acute attacks, and dietary measures may help. In severely affected knee joints, total knee replacement can often give long-lasting relief.

Ligament injury

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Trauma can cause injury to the ligaments on the inner portion of the knee (medial collateral ligament), the outer portion of the knee (lateral collateral ligament), or within the knee (cruciate ligaments). One will experience immediate pain for such injuries which are sometimes difficult to localise.

Usually, a collateral ligament injury is felt on the inner or outer portions of the knee. A collateral ligament injury is often associated with local tenderness over the area of the ligament involved.

A cruciate ligament injury is felt deep within the knee. It is sometimes noticed with a "popping" sensation with the initial trauma. The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments of the knee, especially in sports such as basketball and football. The ACL stabilises the knee for cutting, twisting and jumping and pivoting activity. The anterior cruciate ligament is in the center of the knee joint. When you tear an ACL, you will often feel or hear a pop, feel the knee shift out of place and develop significant swelling in just a few hours.

A ligament injury to the knee is usually painful at rest and may be swollen and warm. The pain usually worsens if one bends, puts weight on the knee or walks. The severity of the injury can vary from mild (minor stretching or tearing of the ligament fibres, such as a low grade sprain) to severe (complete tear of the ligament fibers). Patients can have more than one area injured in a single traumatic event.

Ligament injuries are initially treated with ice packs and immobilisation, with rest and elevation. We generally recommend that patients avoid bearing weight on the injured joint, and use crutches for walking, if necessary. Some patients are placed in splints or braces to immobilise the joint to reduce the pain and promote healing. Arthroscopic or open surgery may be necessary to repair severe injuries.

Surgical repair of ligaments can involve suturing alone, grafting, and synthetic graft repair. These procedures can be done by either open knee surgery or arthroscopic surgery. The type of surgery depends on the level of damage to the ligaments and the activity expectations of the patient. Many repairs can now be done arthroscopically. However, certain severe injuries will require an open surgical repair. Reconstruction procedures for cruciate ligaments are increasingly successful with current surgical techniques.

Watch this video to learn more about anterior cruciate ligament (ACL) reconstruction surgery:

Watch this 3D animation video to learn about what happens during an anterior cruciate ligament (ACL) reconstruction surgery:

Watch the following three videos to learn about the rehabilitation exercises to do after an anterior cruciate ligament (ACL) reconstruction surgery:

Meniscus tears

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Menisci can be torn by shearing forces of rotation that are applied to the knee during sharp, rapid motions. This is especially common in sports activities that require reaction body movements. There is a higher incidence with aging and degeneration of the underlying cartilage. More than one tear can be present in an individual meniscus. The patient with a meniscal tear may have a rapid onset of a popping sensation with a certain activity or movement of the knee.

You may experience pain on the inner or outer side of the knee during activities. Some patients also experience ‘locking’ which is a sensation of a ‘jammed’ knee that is unable to fully straighten.

Occasionally, it is associated with swelling and warmth in the knee. It is often associated with locking or an unstable sensation in the knee joint. The doctor can perform certain maneuvers while examining the knee which might provide further clues to the presence of a meniscal tear.

Routine X-rays, while they do not reveal a meniscal tear, can be used to exclude other problems of the knee joint.

The meniscal tear can be diagnosed in one of three ways:

Arthroscopy - A surgical technique where a small diameter video camera is inserted through tiny incisions on the sides of the knee to examine and repair internal knee joint problems. Tiny instruments can be used during arthroscopy to repair the torn meniscus.

Arthrography - A radiology technique where a contrast liquid is directly injected into the knee joint and internal structures of the knee joint so that they become visible on X-ray film. It is not used commonly used nowadays as MRI is getting more popular.

MRI scan - A radiology technique where magnetic fields and a computer combine to produce two- or three-dimensional images of the internal structures of the body. It does not use X-rays and can give accurate information about the internal structures of the knee when considering a surgical intervention. Meniscal tears are often visible using an MRI scanner.

Once diagnosed, meniscal tears are generally repaired arthroscopically.

Watch this video to learn more about meniscus tear:

Watch this video to learn about post-meniscus tear surgery care advice:

Tendinitis

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Tendinitis of the knee occurs in the front of the knee, below the kneecap at the patellar tendon (patellar tendinitis), or in the back of the knee at the popliteal tendon (popliteal tendinitis).

Tendinitis is an inflammation of the tendon, which is often produced by a strain event, such as jumping. Patellar tendinitis, therefore, also has the name "jumper's knee."

When one has Tendinitis, there is usually localised pain and tenderness at the tendon. It is treated with a combination of ice packs, immobilisation with a knee brace as needed, rest, and anti-inflammatory medications.

Exercise programmes can help the tissues in and around the affected tendon. Steroid injections, which can be given for tendinitis elsewhere, are generally avoided in patellar tendinitis as there are reports of risk of tendon rupture as a result of corticosteroids in this area. Surgery may be required for severe cases of tendonitis.

A rupture of the tendon below or above the kneecap may occur. When this happens, there may be bleeding within the knee joint and extreme pain with any knee movement. Surgical repair of the ruptured tendon is often necessary.

Fractures

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With severe knee trauma, such as motor vehicle accidents and impact traumas, bone breakage (fracture) of any of the three bones of the knee can occur. Bone fractures within the knee joint can be serious and can require surgical repair as well as immobilisation with casting or other supports.

Baker cyst

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The swelling of the knee joint from arthritis can lead to a localised collection of fluid accumulating in a cyst behind the knee known as a Baker cyst. This is a common cause of pain at the back of the knee.

Infection

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Infections of the bone or joint can rarely be a serious cause of knee pain. Symptoms of infection include fever, extreme heat, warmth of the joint, chills of the body.

Plica Syndrome

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This is due to the presence of an extra synovial fold or membrane (plica) inside the knee joint, usually on the medical side or inner aspect of the knee. When the plica causes friction or pressure on the joint surface, tenderness and pain on movement can result. This condition can effectively be treated by arthroscopy (keyhole surgery).

Chondromalacia

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This refers to the softening of the cartilage under the kneecap (patella). It is a common cause of deep knee pain and stiffness in younger women and can be associated with pain and stiffness after prolonged sitting and climbing stairs or hills. Treatment with anti-inflammatory medications, ice packs and rest can provide short-term relief of the condition. The long term cure is to strengthen the quadriceps muscles of the front of the thigh through exercises.

Bursitis

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Bursitis of the knee commonly occurs on the inside of the knee (anserine bursitis) and the front of the kneecap (patellar bursitis, or "housemaid's knee"). Bursitis is generally treated with ice packs, immobilisation, and anti-inflammatory medications such as ibuprofen (Brufen) or aspirin and may require local injections of corticosteroids (cortisone medication) as well as exercise therapy to develop the musculature of the front of the thigh.

Treatment Options & Doctors

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Treatment Options

The surgical treatment options vary according to the different conditions. Common knee surgeries include:

Diagnostic and therapeutic arthroscopies

This is usually done as a day surgery procedure through a small telescope that is inserted into the knee. Patients with meniscal and cruciate ligament injuries usually go through arthroscopy. Patients can either go home on the same day or a day later. In younger patients with isolated cartilage injuries/ defects, two-stage articular cartilage transplantation is offered.

Open surgeries

This includes proximal and distal realignment procedures for isolated patellofemoral problems and involves doing a lateral retinacular release of the patella and tibial tubercle elevation and medialisation to improve the patellar tracking.

High tibial osteotomies (cutting bone) are commonly done procedures which involve either a medial opening wedge or lateral closing wedge osteotomy of the proximal tibia to redirect the weight bearing forces from the medial compartment of the knee to the lateral side and reduce the intraosseous pressure thereby relieving patients of their pain and varus deformities. These surgeries can be performed bilaterally in one sitting or in a staged manner.

Total knee replacement

This is done commonly nowadays for severe tricompartmental arthritis. This surgery involves the resurfacing of the damaged articular lining of the knee mainly the distal femur and proximal tibia with metal prosthesis and inserting a tibial articular liner/ insert made of high density polyethylene. The patellar articular surface may also be replaced but to a lesser extent depending on the findings of the surgeon during the surgery, with a patellar button which is also made from the similar material as the tibial insert.

The prosthesis is usually fixed with bone cement. If only one compartment is involved, unicompartmental knee replacements are offered. The risks of this elective surgery is weighed against the benefits of this procedure as it improves the quality of life of most patients and gives them significant relief from pain.

The commonly cited risks are of that related to anaesthesia, bleeding, infection, deep venous thrombosis in the veins of the lower limbs, fracture, loosening of the prosthesis- aseptic or septic.

Patients are usually assessed preoperatively by the anesthetists and if fit can usually come in on the day of surgery. Post operatively there would usually be a drain placed in the knee which would be removed on post operative day 1 or 2 followed by making the patient sit up in bed, out of bed, and allowed to walk bearing full weight on the operated limb with the help of a walking frame. Usually patients would go home by the 4th or 5th postoperative days.

Doctors

Dr Chua Wei Liang
Prof K Satku
A/Prof Wilson Wang
Dr Ng Yau Hong

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2023/04/20