Pain on the outer side of the knee — lateral knee pain — is common, and pinning down the cause can be challenging. The area contains many structures that cross the joint: tendons, ligaments, nerves, and the joint capsule. So what causes pain on the outside of the knee, and how do we make a diagnosis?
Common causes of pain on the outside of the knee
Knee osteoarthritis
Osteoarthritis can affect the outer (lateral) compartment as well as the inner one. Symptoms include outer-knee pain, swelling, restricted movement, crepitus, and occasional giving way. It usually affects people over 50, though younger people with a previous knee injury — such as an ACL tear — can develop it earlier.
Torn lateral meniscus
The lateral meniscus can tear during an acute twist, or from degeneration. Symptoms often include outer-knee pain, swelling, locking, and a feeling of giving way.
LCL sprain
The lateral collateral ligament connects the outer femur to the tip of the fibula, providing stability and preventing the knee from falling outwards. LCL injuries usually follow a direct blow to the inside of the knee, forcing it outward. Symptoms include a pop, pain, swelling, and instability. Because this ligament lies near the common peroneal nerve, an injury can also cause numbness, tingling, and weakness in the lower leg.
IT band friction syndrome
The iliotibial (IT) band is a long band of connective tissue on the outside of the leg, running from the pelvis across the knee to the outer shin. Pain occurs when the back of the band rubs against the femur, causing pain and focal swelling. It’s common in runners — though cyclists and walkers get it too. The pain typically starts within minutes of activity and worsens as you continue, sometimes enough to make you stop.
Less common causes of pain on the outer side of the knee
Common peroneal nerve injury
This nerve crosses the outer side of the knee before supplying the lower-leg muscles. As with an LCL injury, a blow to the inside of the knee can stretch or tear it. Typical symptoms are pain, numbness, and tingling on the outer lower leg and the top of the foot — a form of nerve damage worth recognising.
Proximal tibiofibular joint injury
This small joint connects the top of the shin bone to the fibula. Injury to it occurs acutely after high-force trauma, or gradually through degeneration. Symptoms include outer-knee pain and a sense of instability during deep squats, and the joint is often tender and looser when moved.
Biceps femoris tendonitis
The biceps femoris tendon forms a tendon that crosses the outer knee to attach to the fibula. Biceps femoris tendonitis usually comes from excessive running and jumping. The pain sits on the outer knee, worse at the start of movement and easing as you continue, and the tendon is tender. It can sometimes lead to snapping of the biceps femoris tendon.
How is lateral knee pain diagnosed?
See a sports medicine doctor for a diagnosis and management plan. Your doctor asks about your symptoms, then examines limb alignment, knee movement, and ligament stability, and carefully palpates the joints and tendons. Investigations confirm the cause: weight-bearing X-rays assess arthritis, MRI examines the joint, tendons, and ligaments, and ultrasound provides more detailed views of the tendons. Our knee pain location chart can help you narrow down the likely source of your pain.
When to see a doctor about pain on the outer side of the knee
See a doctor if you have any of the following:
- Outer-knee pain after trauma
- Pain that hasn’t settled after a few weeks of simple treatment such as ice and ibuprofen
- Mechanical symptoms such as locking or giving way
- Nerve symptoms such as numbness or tingling, which suggest nerve damage
Frequently asked questions about pain on the outer side of the knee
What is the most common cause of pain on the outside of the knee?
In runners and other active people, IT band friction syndrome is among the most common — an overuse problem that causes pain that starts soon after you begin running. In older people, lateral-compartment osteoarthritis is common. Because several structures overlap here, an accurate diagnosis matters.
How do I know if it’s my IT band or my meniscus?
IT band pain is an overuse pain that comes on predictably a few minutes into running and eases with rest, without true locking. A lateral meniscal tear more often follows a twist and can cause locking, catching, or giving way. An examination — and imaging if needed — tells them apart.
Can outer knee pain be a trapped nerve?
It can. The common peroneal nerve wraps around the outer knee, and an injury there can cause pain with numbness, tingling, or weakness spreading into the outer lower leg and foot. Nerve-type symptoms are a reason to get it assessed.
When should I worry about pain on the outside of my knee?
See a doctor for outer-knee pain after a significant injury, pain that doesn’t settle in a few weeks, locking or giving way, or numbness and tingling. These point to a structural or nerve cause that benefits from an accurate diagnosis.
Final word from Sport Doctor London about pain on the outer side of the knee
Pain on the outside of the knee is common in athletes and runners, and it can have many possible causes — from the IT band and lateral meniscus to the LCL and the nerves around the knee. Because so many structures overlap here, an early, accurate diagnosis is the key to the right treatment.
If you have persistent outer-knee pain, Dr Masci can assess you in London, including ultrasound in clinic. Contact the team here or call +44 (0) 203 488 0350.
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