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What is Causing the Pain on the Side of My Knee?

By Last updated on February 1st, 2021February 1st, 2021No Comments

Knee pain is increasingly becoming a very common ailment in today’s fast-paced and demanding living conditions. The knees support our entire body weight, and due to their complex structure and mechanism of working, they are prone to a number of ailments and injuries.

Pain or swelling in the knees can cause great discomfort, and can totally disrupt one’s day-to-day activities. Side knee pain can result from a variety of reasons, depending upon the individual’s age, lifestyle, and activity factors.

Anatomy of the Knee

The knee is the meeting point of the femur (thigh bone) in the upper leg and the tibia (shinbone) in the lower leg. The fibula (calf bone), the other bone in the lower leg, is connected to the joint but is not directly affected by the hinge joint action. Another bone, the patella (kneecap), is at the center of the knee.

Two concave pads of cartilage (strong, flexible tissue) called menisci minimize the friction created at the meeting of the ends of the tibia and femur.

The knee has two menisci:

  • Medial – on the inner side of the knee, this is the largest of the two.
  • Lateral – on the outer side of the knee.

There are also several key ligaments, a type of fibrous connective tissue, that connect these bones. The four key ligaments of the knee are:

  • Anterior Cruciate Ligament (ACL) – At the front of the knee, this ligament prevents the femur from sliding backward on the tibia, and the tibia from sliding forward on the femur.
  • Medial Collateral Ligament (MCL) – At the inside of the knee, the MCL prevents side to side movement of the femur.
  • Lateral Collateral Ligament (LCL) – At the outside of the knee, the LCL prevents side to side movement of the femur.
  • Posterior Cruciate Ligament (PCL) – At the back of the knee, prevents the femur from sliding forward on the tibia, or the tibia from sliding backward on the femur.

There are a variety of causes of side knee pain. The cause can be determined by whether the pain is medial (inside knee) or lateral (outside knee).

Causes of Lateral Knee Pain

Lateral knee pain is often caused by being active in a sport or at work. Certain causes can also be attributed to aging or poor health and obesity. Here’s a look at more specific causes for lateral knee pain.

Lateral Meniscus Injury

This is an injury of the cartilage tissue at the lateral side of the joint. This is caused by awkward knee twisting especially if the knee is bent while the foot was planted. Gradual onset from wear and tear is also a cause.

Symptoms include:

  • Pain in the knee joint
  • Swelling in the knee
  • Difficulty straightening the knee

Lateral Collateral Ligament (LCL) Injury

This is an injury to the ligament on the outer side of the knee. This is caused by a sudden twisting or awkward fall where the lower leg is forced inwards, and/or a blow to the inside of the knee.

Symptoms include:

  • Outer knee pain, swelling in the outer region of the knee
  • Bruising
  • Instability
  • Locking or catching of the knee with movement

Iliotibial Band Syndrome (ITBS)

Iliotibial band syndrome (ITBS) is a very common and occasionally stubborn knee injury among distance runners and cyclists, which causes outer knee pain. Typically, this knee pain and inflammation comes on gradually and is most prominent when participating in irritating activities.

Symptoms include:

  • Knee pain while walking or running due to inflammation on the lateral part of the knee joint.
  • Lateral Knee Arthritis

A result of wear and tear of the outer side of the knee joint, bone spur formation, loss of joint space, and inflammation. This is caused by aging, previous injuries or surgeries, and/or obesity.


  • Dull, nagging, achy pain in the knee, stiffness (particularly in the morning), and creaky/noisy knees.

There are a few other possible causes of outer knee pain. These are much less common but should still be considered.

Proximal Tibiofibular Joint Dislocation

Proximal tibiofibular joint dislocation is one of the most unusual causes of lateral knee pain. It affects the joint between the top of the shin bone (tibia) and the fibula, the small, thin bone that runs down the outer side of the shin, just below the knee joint on the outer side.

It takes a large force to dislocate the joint, such as a car accident, but it can also partially dislocate usually due to a fall when the foot is plantar-flexed (toes pointing down), which often also damages the tibiofibular ligament.

Symptoms usually include outer knee pain, instability especially during deep squats, and sometimes an obvious deformity at the side of the knee. There may also be associated with damage to the peroneal nerve leading to pins and needles or numbness around the outer knee.

Nerve Problems

Pressure along the path of the peroneal nerve can also cause outer knee pain. The peroneal nerve branches off from the sciatic nerve and runs down the outer side of the lower leg to the foot. Nerve pain is often associated with tingling, pins and needles, and or numbness.

Damage to the peroneal nerve usually occurs when there is a blow to the side of the knee, which squashes the nerve where it sits just below the skin. Alternatively, there may be pressure higher up the nerve where the sciatic nerve branches off from the lower part of the lumbar spine.

The pain can travel down the nerve and may result in pain on the outside of the knee, with or without associated back pain.

Causes of Medial Knee Pain

Medial knee pain typically occurs because of a deterioration of cartilage. It can also follow a sports injury or other type of trauma to the knee.

Medial Meniscus Injury

The meniscus is cartilage that provides a cushion between bones in a joint. They serve as cushions between the thigh and shin bones.

A meniscus can tear or become damaged if the knee is rotated or put under pressure, most commonly during sports or athletic activities.

Symptoms include:

  • Stiffness
  • Sharp pain when twisting the knee
  • Locking knees
  • Sense of imbalance

Medial Collateral Ligament (MCL) Injury

The medial collateral ligament (MCL) runs along the outside of the inner knee to stabilize the joint. If the ligament overstretches, an MCL sprain may occur.

The MCL can also tear partially or fully. An MCL injury most commonly occurs after force is applied to the outer knee, such as in contact sports.

Symptoms include:

  • Swelling
  • Instability while standing or walking
  • Locking knees
  • A popping sound at the time of impact


Osteoarthritis is a degenerative disease that breaks down cartilage, causing the bones in the joints to grind together.

If one experiences inner knee pain while putting pressure on the joint, such as when walking up and down stairs or sitting down in a chair, they may have osteoarthritis. Because this pressure causes the pain, symptoms may get more severe as the day goes on.

Rheumatoid Arthritis

Rheumatoid arthritis is an auto-immune disease that can also cause inner knee pain. Rheumatoid arthritis causes inflammation in the joints, so people with rheumatoid arthritis may experience severe inner knee pain in the morning, with symptoms decreasing throughout the day.

Medial Plica Irritation

Plica is small folds in the joint lining. Medial plica covers the inner knee. Overuse, such as from repeatedly flexing the knee, can irritate the medial plica.

This causes the folds to thicken and become stuck between the bones. In addition to dull inner knee pain, one may experience locking knees and possibly a cracking sound.

Treatment for Pain on Side of the Knee

The best course of treatment for lateral and medial knee pain will depend on the underlying cause of the outer knee pain. It will usually include a combination of exercises, physical therapy and rest from aggravating activities and may also include knee injections involving stem cells or platelet rich plasma (PRP).

Stem cells and PRP can help reverse the degenerative effects of certain causes of knee pain such as arthritis. It is also effective in healing ligament and muscle tears and will prevent a patient from needing surgery in more severe knee injuries.


Knee pain is very common and can stem from a large number of issues. When the pain is coming from the sides of the knee it is easier to identify the cause. Whether the pain is medial (inner knee) or lateral (outer knee), there are many possibilities of what it could be from. This article should help identify and explain many potential causes and treatments.

In severe instances, pain may not go away with conventional treatments. This is when the regenerative effects of stem cells or PRPs should be considered.

Dr. Matthew HC Otten

Dr. Matthew HC Otten

Director of Regenerative Orthopedic and Sports Medicine
Fellowship-trained & Board Certified in Sports medicine
Director Angiography at Harvard Clinical Research Institute
Michigan State University Alumni


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