The following are some common causes of a stiff knee.
Injury to menisci
The menisci are two “C” shaped pieces of cartilage that sit inside the knee joint. Their role is to act as a cushion, or shock absorber, between the bones that make up the joint.
A person can injure or damage a meniscus by suddenly moving or twisting the knee. This is most likely to occur during sports or other types of physical activity.
The menisci are also prone to degeneration with age. Specifically, as the menisci degrade, they become more prone to tearing.
A person will likely hear or feel a “pop” when a meniscus tears. According to the American Academy of Orthopaedic Surgeons, the knee will then start to feel stiff. In many cases, people can still walk on the knee, though they may also experience symptoms such as:
- locking knee
- loss of full range of motion
- a feeling that the knee is giving out
Injury to ligaments
Ligaments are bands of fiber that connect bone to bone. Ligaments that run through the knee connect the thigh bone, or femur, to the lower leg bone, or tibia.
A person may sprain, tear, or rupture their knee ligaments. If this occurs, a person may experience:
- pain in the knee joint
- instability of the knee
- swelling in the knee
Arthrofibrosis, or stiff knee syndrome, occurs when an excessive amount of scar tissue forms around the knee joint.
It is not uncommon for people to experience arthrofibrosis following knee surgeries such as knee replacement or anterior cruciate ligament surgery. In fact, according to the Saint Alphonsus Rehabilitation Services, around 6% of people who have knee replacements experience arthrofibrosis.
Some additional symptoms of arthrofibrosis include:
- knee pain that worsens
- swelling and warmth around the knee
- walking with a bent knee
There are three common types of arthritis that can contribute to knee pain and stiffness. The following sections outline these in more detail.
Rheumatoid arthritis is the result of an autoimmune condition that causes the body to attack its own tissues. Rheumatoid arthritis typically affects both knees.
People with rheumatoid arthritis sometimes experience swelling of the synovial membrane, which is a thin membrane that covers the inner lining of the knee joint. Swelling of the synovial membrane causes knee stiffness and pain.
Osteoarthritis occurs as a result of wear and tear of the cartilage between bones. As the cartilage within the knee degrades, it causes the bones within the knee to rub against each other. The rubbing bones can cause bony growths called spurs. These can cause joint stiffness and pain.
According to one 2013 study, knee osteoarthritis is more common among people aged 55–64 years.
Injuries such as meniscal and ligament tears can increase the likelihood of further injury to the knee joint. Over time, this can lead to post-traumatic arthritis (PTA). PTA occurs years after a person sustains an injury to their knee.
People with PTA may experience the following symptoms:
- swelling in the knee joint, which may make it difficult to move the knee
- knee pain
- a feeling of weakness in the knee
- worsening of symptoms following physical activity
- worsening of symptoms during wet weather
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