More than a dozen ligaments attach to the femur, the long bone of the thigh. They cluster around two major joints: the hip at the top and the knee at the bottom. Each one anchors to a specific bump, groove, or rough patch on the bone’s surface, and together they keep both joints stable through walking, running, and twisting movements.
Ligaments at the Hip Joint
The femur’s ball-shaped head fits into a deep socket in the pelvis, and several ligaments reinforce this joint from the outside while one works from the inside.
Ligament of the Head of the Femur
This short, sturdy band runs from the pelvis to a small pit near the top of the femoral head called the fovea. All of its fibers converge onto the upper half of the fovea, where the bone surface is noticeably rougher than the smooth lower portion. Beyond holding the hip together, this ligament carries a small artery that supplies blood to the femoral head, a role that is especially important during childhood when the bone is still growing. In adults, the ligament offers limited mechanical support, but it contains nerve receptors that detect pain and position, helping the brain sense where the hip is in space.
Capsular Hip Ligaments
Three thick bands reinforce the hip’s outer capsule and all originate from the pelvis before attaching along the femur’s neck and the bony ridges near it. The iliofemoral ligament fans out from the front of the pelvis and attaches along a ridge between two bony bumps (the greater and lesser trochanters) at the top of the femur. It is the strongest ligament in the body and prevents the hip from extending too far backward when you stand upright. The pubofemoral ligament wraps from the pubic bone to the lower part of the femoral neck, resisting excessive outward rotation. The ischiofemoral ligament spirals from the back of the pelvis to the base of the greater trochanter, limiting inward rotation. Together, these three ligaments essentially screw the femoral head deeper into its socket as you straighten your leg.
Cruciate Ligaments Inside the Knee
The two cruciate ligaments sit deep inside the knee joint, crossing each other in an X pattern. Both attach to the femur on its lower end, within a notch between the two rounded condyles.
The anterior cruciate ligament (ACL) anchors to the inner wall of the lateral (outer) femoral condyle. It prevents the shinbone from sliding forward and is the ligament most commonly torn during sports that involve sudden stops or direction changes. The posterior cruciate ligament (PCL) attaches to the inner wall of the medial (inner) femoral condyle, close to the cartilage surface. Cadaver studies show its attachment begins roughly 6 mm from the cartilage rim. The PCL is made of two distinct bundles and prevents the shinbone from sliding backward. It is thicker than the ACL and tears less frequently, typically requiring a direct blow to the front of the knee.
Collateral Ligaments on Each Side
The collateral ligaments run along the inner and outer edges of the knee, preventing it from buckling sideways.
The medial collateral ligament (MCL) originates from the medial epicondyle, a bony bump on the inner side of the femur’s lower end. It is a broad, flat band that runs down to the shinbone and resists forces that push the knee inward. The MCL also has deep fibers that connect to the meniscus cartilage inside the joint, which is why a hard blow to the outside of the knee can damage both structures at once.
The lateral collateral ligament (LCL) originates just above and behind the lateral epicondyle on the outer side of the femur, specifically about 1.4 mm above and 3.1 mm behind the epicondyle’s most prominent point. Unlike the MCL, the LCL is a cord-like structure that does not attach to the meniscus. It resists forces that push the knee outward.
The Anterolateral Ligament
The anterolateral ligament (ALL) is a relatively recent addition to anatomical textbooks, though surgeons have been aware of structures in this area for decades. It sits on the outer front of the knee and helps control rotational stability, particularly the inward twisting of the shinbone. A study of 52 cadaver specimens found the ALL in every single one. Its femoral attachment overlaps with the LCL origin in all cases, sitting either directly on the lateral epicondyle (23% of specimens), slightly behind and above it (58%), or completely behind and above it (19%). None attached in front of the epicondyle. Injury to the ALL may explain why some patients still feel rotational instability after ACL reconstruction.
The Medial Patellofemoral Ligament
The medial patellofemoral ligament (MPFL) connects the inner edge of the kneecap to the medial femoral condyle, near the medial epicondyle. Think of it as a leash that keeps your kneecap centered in its groove as you bend and straighten the knee. When the MPFL tears, the kneecap can slip sideways out of position, a painful event called patellar dislocation. This is one of the most common reasons young, active people experience a dislocating kneecap, and surgical reconstruction of the MPFL involves drilling a small tunnel into the femur to anchor a replacement graft.
Posterior Knee Ligaments
The back of the knee has its own set of reinforcing ligaments woven into the joint capsule. The oblique popliteal ligament is an extension of the hamstring tendon on the inner side of the knee. It runs from the inner shinbone upward and outward toward the lateral femoral condyle, where it blends into the back of the joint capsule. This ligament tightens when the knee is fully straight and helps lock it in extension so your muscles can briefly relax during standing. The arcuate popliteal ligament reinforces the outer back corner of the knee and arches over the muscle that sits behind the joint, contributing to what surgeons call the posterolateral corner, a complex area that resists combined backward and rotational forces.
How These Ligaments Work Together
No single ligament works in isolation. At the hip, the three capsular ligaments spiral in the same direction so that standing upright passively tightens them all, reducing the muscular effort needed to stay balanced. At the knee, the cruciates handle front-to-back sliding, the collaterals handle side-to-side forces, and the ALL and MPFL fine-tune rotation and kneecap tracking. Damage to one ligament shifts extra load onto the others, which is why a torn ACL gradually increases stress on the meniscus and cartilage if left untreated.
The femur’s surface is shaped to accommodate all of these attachments. Its epicondyles, condyles, trochanters, and ridges are not random bumps but precisely located anchor points that have been sculpted by the pull of ligaments over millions of years of bipedal walking. When surgeons reconstruct a torn ligament, placing the new graft at the exact anatomical footprint on the femur is one of the most important factors in restoring normal joint mechanics.