The most prominent structure on the outside of your knee is the iliotibial band, a thick strip of connective tissue that runs down the entire outer thigh and attaches to the shinbone just below the knee. But it’s not the only one. Several tendons and ligaments overlap on the lateral (outer) side of the knee, each playing a different role in stability and movement.
The Iliotibial Band
The iliotibial band, commonly called the IT band, is the structure most people are feeling when they notice a tight, rope-like band on the outer knee. It originates at the hip bone and runs the full length of the outer thigh before inserting on a small bony bump called Gerdy’s tubercle, located on the outer surface of the upper shinbone. It functions almost like an extended tendon for two hip muscles: the gluteus maximus and the tensor fasciae latae. Through this connection, it helps stabilize both the hip and the knee during standing, walking, and running.
The IT band does more than just connect two points. It also sends deeper fibers that anchor to the thighbone and the outer joint capsule of the knee. This layered attachment system is what gives the outer knee so much lateral stability, preventing your knee from buckling sideways when you’re upright. It’s also why IT band problems tend to produce broad, diffuse pain across the entire outer knee rather than one pinpoint spot.
The Biceps Femoris Tendon
Just behind and slightly below the IT band, the biceps femoris tendon crosses the outer knee. This is one of the three hamstring muscles, and its tendon attaches primarily to the head of the fibula, the smaller bone on the outer side of your lower leg. You can often feel this tendon as a firm cord at the back-outer corner of your knee, especially when you bend your knee against resistance.
The biceps femoris actually has two parts. The long head originates at the sitting bone of the pelvis and travels the full length of the back of the thigh. The short head starts partway down the thighbone. Both merge into a common tendon that fans out into multiple attachment points on the fibular head and surrounding tissues. Beyond bending the knee, this muscle rotates the lower leg outward, which is why injuries to it can make pivoting or turning feel unstable.
The Popliteus Tendon
Deeper than both the IT band and the biceps femoris sits the popliteus tendon. This smaller tendon runs from the back of the upper shinbone, passes through a gap in the joint capsule, and inserts into a groove on the outer surface of the thighbone. You can’t feel it through the skin because it lies underneath the other lateral structures, but it plays a critical role in knee stability.
The popliteus tendon is one of the key stabilizers of the posterolateral corner of the knee, the area where the back and outer sides meet. It resists the lower leg from rotating outward too far and acts as a secondary check against the shinbone sliding backward on the thighbone. Injuries to this tendon are less common than IT band problems but can cause significant instability, particularly during cutting or pivoting movements.
The Lateral Collateral Ligament
While not a tendon, the lateral collateral ligament (also called the fibular collateral ligament) deserves mention because it runs right alongside these tendons and is frequently the source of outer knee pain. This cord-like ligament connects the outer thighbone to the fibular head, and its primary job is preventing the knee from bowing outward. It works together with the popliteus tendon and a smaller ligament called the popliteofibular ligament to form the main stabilizing trio of the outer knee.
IT Band Syndrome: The Most Common Outer Knee Problem
Of all the structures on the outside of the knee, the IT band is the one most likely to cause trouble. IT band syndrome is one of the leading causes of lateral knee pain, particularly in runners and cyclists. It develops when the lower portion of the IT band repeatedly slides over the bony prominence of the outer thighbone during bending and straightening of the knee. Over time, this friction irritates the tissue and produces inflammation.
The pain typically starts as a vague ache across the outer knee that appears partway through a run or after finishing one. As the condition worsens, the pain sharpens, becomes more localized, and starts earlier in activity. Eventually it can bother you even at rest. Hills, longer strides, and sitting with a bent knee for extended periods tend to make it worse. Risk factors include high weekly running mileage, training on tracks, tightness in the IT band itself, and weakness in the hip abductor muscles that control pelvic stability.
On physical exam, the tenderness is usually located about 2 centimeters above the joint line on the outer knee. Pressing on this spot with the knee bent to about 30 degrees reproduces the pain, because that’s the angle where the IT band is under maximum stress against the bone.
How IT Band Pain Differs From a Meniscus Tear
Outer knee pain doesn’t always come from a tendon. A lateral meniscus tear can produce pain in a similar area, and the two conditions are sometimes confused. The key differences are location and behavior. IT band pain sits slightly above the joint line and develops gradually from overuse without a specific injury event. It rarely involves swelling, though a small fluid-filled sac can form under the band over time.
A lateral meniscus tear, by contrast, produces pain right at the joint line and is often accompanied by swelling, fluid buildup, and mechanical symptoms like clicking, catching, or a popping sensation in the knee. In younger people, meniscus tears usually follow a specific traumatic event. When the distinction isn’t clear from a physical exam, an MRI can help rule out a meniscus tear or a lateral collateral ligament injury.
Managing Outer Knee Tendon Pain
Most IT band problems respond to a combination of rest, targeted stretching, and strengthening of the hip abductors. Because hip weakness contributes to abnormal tension on the IT band, exercises like side-lying leg raises and clamshells are staples of rehabilitation. Foam rolling the outer thigh can reduce tightness, and temporarily reducing running volume or avoiding downhill routes helps calm the irritation.
Surgery is rarely needed. It’s generally reserved for cases where several months of conservative treatment haven’t worked, the pain is significantly limiting daily activities or sports participation, or structural abnormalities like limb alignment issues are contributing to the problem. For the biceps femoris and popliteus tendons, injuries are less common and typically occur in the context of more complex knee trauma rather than repetitive overuse.