Swollen Knee – Causes and Treatment

Introduction to Swollen Knees

A swollen knee joint (Picture 1) is a common symptom arising either from knee or other disorders. Knee swelling can originate from almost any structure forming the joint, like ligaments, synovial membrane, bursae, etc., or from fluid accumulating within the knee, such as blood or pus. A swollen knee, for example from knee effusion, is not always painful. Though all knee swellings do not require urgent treatment, there are a few conditions, like septic arthritis, in which lack of prompt treatment can cause lifelong disability. Hence, it is always better to consult a physician or orthopedist, to find the exact cause of knee swelling.

Swollen Knee

Picture 1: Swollen left knee
(source: Wikimedia)

Anatomy and Function of the Knee

The knee joint is the largest joint in the human body; it has a complex arrangement of ligaments, which provide a uni-planar stable movement. The locking mechanism of the knee joint helps us stand for prolonged periods without putting strain on the leg muscles. In order to understand how locking works, try standing upright with the knee joint half bent, and then stand with the knee joint completely straight. The difference you feel in both instances, is because of the rotation of the bones forming the knee joint over each other at the end part of knee unfolding (extension). This rotation locks the knee in the position of extension (straight knee), and no muscles have to be continuously contracting to keep it straight.

Knee Back View

Picture 2: Knee joint: back view
(source: Wikimedia)

The complex movements of the knee joint are only possible because of the ample cartilage that allows smooth movement and ligamentous structures that provide strength. The knee joint is extremely important for walking; any minor defect in the functioning of the knee joint makes a person unable to walk properly (limping gait) or even stand upright.

How Swelling of the Knee Occurs ?

The knee joint not only bears the weight of the entire body but also changes the direction of the weight-bearing forces, so that only a part of it is transferred to the ankle joint. However, this shunting of forces becomes a cause of its early wear and tear, especially in the obese individuals.

Athletes often injure their knees. Twisting injuries are a major culprit in damaging the ligaments of the knee and frequently lead to an unstable knee.

Apart from traumatic causes, there are numerous other causes, like knee infections or rheumatoid arthritis, which make the cartilage soft and vulnerable to tear (and thus causing swelling) even in young people. The protective immune system gives rise to a host of inflammatory reactions to the frictional irritation of the bones and soft tissues, leading to the knee swelling. However, after prolonged episodes of pain and stiffness, the joints may become permanently fused (ankylosed), either because of fibrosis and shortening of the muscles, or fusion of the bones forming the joint.

Causes of Knee Swelling

Conditions causing knee swelling can be divided into the ones that originate in the knee joint (primary) and the ones that originate from other parts of the body (secondary). Knee swelling can occur all of a sudden (acute) or slowly over a period of months (chronic) (see table).

PrimarySecondary
OsteoarthritisRheumatoid arthritis
Ligament injury (ACL, PCL, or Meniscus)Rheumatic arthritis
Knee dislocationAnkylosing spondylitis
Septic arthritisTuberculosis
Bone tumorsReiters disease
HemarthrosisPsoriatic arthritis
Knee effusion (water on the knee)Enteropathic arthritis
Knee bursitis (prepatellar, infrapatellar)Gout
Fractures (Patella, Tibia, or Femur)Pseudogout

Investigations

  • Presence of a swollen knee can be simply confirmed by comparing the size of the both knees (Picture 1), as long as the problem is in a single knee.
  • X-ray films are used to rule out bony injuries, acute or chronic, and are an important first line investigation.
  • Ultrasound of the knee is important to rule out water on the knee, like hemarthrosis (bleeding into the joint) or effusion.
  • MRI is the investigation of choice to confirm soft tissue injuries, like muscle tears, ligament injuries, etc., but is not used frequently because of its high cost.

Treatment

Traumatic conditions, like fractures, ligament injuries, etc., are better treated in hospitals rather than by a family physician, as they have specially trained personnel, who can handle emergencies better, and facilities, like ventilators, blood banks, X-ray centers, etc., which are important in primary care. Care must be taken as to not worsen the damage caused by the original trauma by keeping the knee straight during ambulation (Picture 3), which locks the knee in a stable configuration and keeps the muscles relaxed.

Sports Injury to Right knee

Picture 3: Sport injury of the right knee
(source: Wikimedia)

Fractures may benefit from some form of splinting that supports the knee in the straight position. However, this is not always necessary, as frequently keeping the knee straight at all times can suffice without any rigid immobilisation, like a plaster, which is uncomfortable. Following the post-treatment advice is of utmost importance, as even a small mistake, like early weight-bearing, can cause re-fracture and make the prognosis worse. Ligament injuries, once diagnosed, can be effectively managed with cold compresses for the first couple of days followed by rest for a week. Any form of massage has to be avoided to the injured part, as it is known to increase the soft tissue damage.

Chronic arthritic conditions, like rheumatoid arthritis, psoriatic arthritis or gout (Picture 4), require prolonged treatment with anti-inflammatory medications and physiotherapy.

Gout Tophi

Picture 4: Gouty arthritis left knee
(source: Wikimedia)

These medications have a lot of harmful side-effects. An understanding of the possible side effects and prompt medical aid can do a great deal in preventing any major damage to your body. Complete body exercises, like swimming or yoga, form the mainstay in the treatment of conditions, like ankylosing spondylitis.

Certain infectious conditions, like septic arthritis or knee effusion, cause degeneration of the cartilage in as early as six hours, so they need to be treated promptly. Any delay in treatment can cause complete destruction of the cartilage, causing early arthritis and permanent deformity of the knee joint. Draining of the excessive joint fluid (blood, pus, or effusion), using a needle (arthrocentesis), or with a surgical incision (arthrotomy), is the primary treatment followed by intravenous antibiotics.

Prevention

General preventive measures, like wearing protective gear (Picture 5) during sports activities, active lifestyle, and weight reduction (if necessary) can prevent a lot of disorders with swollen knee.

Polo kneepad

Picture 5: Protective knee pads
(source: Wikimedia)

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About Dr Gauresh (69 Articles)
An orthopedic surgeon trained in JJ Group of Hospitals and Grant Medical College. I have worked in this field for the past 3 years and have significant clinical experience to guide students and patients on any topic in orthopedics.