The knee is one of the most fascinating and crucial joints in the human body. It supports our entire weight, allowing us to walk, run, jump, and perform countless movements every day. For healthcare professionals and anyone experiencing knee discomfort, understanding the knee’s anatomy is invaluable. Its design is both intricate and delicate—enabling remarkable mobility while remaining vulnerable to injury. This article unpacks the key elements of knee anatomy, focusing on ligaments, tendons, and muscles, explaining how these components work together to facilitate movement and how they can be affected by injury.

The Structure of the Knee Joint: More Than Just a Simple Hinge

We often think of the knee as a simple hinge — like a door opening and closing — but the truth is far more complex. The knee is a synovial joint, more specifically a modified hinge, allowing not only bending and straightening (flexion and extension) but also slight rotation when the knee is bent.

The knee comprises three main bones: the femur (thigh bone), tibia (shin bone), and patella (kneecap). The femur and tibia form the main hinge joint (the tibiofemoral joint), which carries most of the body's weight, while the patella sits within the quadriceps tendon at the front, forming the patellofemoral joint. This combination allows smooth, controlled movement and stabilisation.

Covering the ends of these bones is articular cartilage, a slippery tissue that reduces friction. Between them sit the menisci—two moon-shaped pads of cartilage that act as shock absorbers, cushioning your steps and distributing your weight evenly across the knee. Surrounding these bones and cartilage are soft tissues, including ligaments and tendons, which provide stability and control movement. As Turner and Craig (1980) explained, “the osseous portions of the knee were discussed in relation to muscular actions,” emphasising how bone and muscle work closely together in this joint.

Knee Ligaments and Tendons: The Body’s Natural Stabilisers

Ligaments are strong bands of connective tissue that link bones together and restrict movements that might damage the joint. The knee has eleven such ligaments forming a network of stabilisers. The most familiar of these include the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), which cross inside the knee to control forward and backward movement of the tibia relative to the femur. On either side of the knee, the medial collateral ligament (MCL) and lateral collateral ligament (LCL) prevent sideways bending and provide crucial stability.

Less well-known are the ligaments of the posterolateral corner, a complex area at the back and outer part of the knee that helps control rotational movements. LaPrade et al. (2005) describe key posterolateral structures, including the lateral collateral ligament, popliteus muscle and tendon, specialised connective bands called popliteomeniscal fascicles, and the lateral gastrocnemius muscle—highlighting their intricate roles in knee stability.

Recently, attention has shifted toward the anterolateral complex at the front and outer side of the knee. Helito and Helito (2018) explain that this area includes the iliotibial band, the joint capsule, and a recently recognised ligament called the anterolateral ligament (ALL). The ALL’s anatomy is still debated, but it’s thought to play an important role in rotational stability, an area critical for athletes and injury prevention.

Meanwhile, tendons connect muscles to bones, allowing muscles to move the joint. The large quadriceps tendon joins the front thigh muscles to the patella, and the patellar tendon (often called a ligament in this context) links the patella to the tibia. Together, these tendons transfer the powerful contractions of muscles into movement and help keep the knee stable. Turner and Craig (1980) noted these soft tissues “divide the knee into medial and lateral compartments,” showing how the anatomy supports both motion and stability.

Knee ligament injuries, particularly ACL tears, are common and can cause pain, instability, and difficulty walking. While an X-ray can reveal bone fractures and cartilage damage, it often misses ligament injuries. Magnetic resonance imaging (MRI) is the best tool to diagnose issues with soft tissues like ligaments and tendons.

The Muscles Around the Knee: Dynamic Support in Action

Muscles around the knee don’t just move the joint—they also protect and stabilise it dynamically. The quadriceps at the front of the thigh straighten the knee, while the hamstrings at the back bend it and control rotational movements. Calf muscles, such as the gastrocnemius, cross behind the knee, offering additional support during movement.

This coordinated interplay of muscles, tendons, and ligaments is vital for smooth and safe knee function. The popliteus muscle, located at the back of the knee, plays a specialised role in “unlocking” the knee from full extension to allow bending. LaPrade and colleagues (2005) emphasise this by highlighting the popliteus and its associated ligaments as key stabilisers in the posterolateral knee.

When these muscles are out of balance—say, if the outer quadriceps are weak—it can place uneven stresses on the knee. This often leads to pain on the outer side of the knee, even without obvious swelling. Turner and Craig (1980) emphasise the importance of understanding “the interaction between structure and function,” which explains why muscle health is critical to knee wellbeing.

Why Understanding Knee Anatomy Matters—Especially for Women

Knowing the nuances of knee anatomy is not just academic; it has practical implications for diagnosing and managing pain. Women are more likely to experience certain knee injuries, such as ACL tears, due to anatomical and biomechanical factors. A wider pelvis changes the angle between the hip and knee (the Q-angle), which can increase stress on ligaments. Hormones may also affect the flexibility and strength of these connective tissues.

Understanding “what causes knee pain in females” helps clinicians offer personalised advice and treatment, targeting these unique risks. Moreover, conditions like mild osteoarthritis can be detected on X-rays by observing changes such as joint space narrowing or bone spur formation. These degenerative changes often develop alongside biomechanical stressors and require careful clinical evaluation.

Conclusion

The knee’s anatomy is a beautifully complex ballet of bones, cartilage, ligaments, tendons, and muscles. Each part plays a vital role in movement, stability, and injury protection. To truly understand knee pain or injury, it’s essential to appreciate this intricate interplay rather than looking for simple causes.

Advances in medical imaging and research continue to shed light on knee anatomy, improving diagnosis and enabling tailored treatment. Whether you are a clinician, athlete, or simply curious about your own body, unlocking the mysteries of knee anatomy paves the way to better knee health and mobility in the future.

References

Turner, A. B., & Craig, E. (1980). Knee Anatomy. Physical Therapy, 60(12), 1556-1560. https://doi.org/10.1093/ptj/60.12.1556

LaPrade, R. F., Kimber, K. A., Wentorf, F. A., & Olson, E. J. (2005). Anatomy of the posterolateral aspect of the goat knee. Journal of Orthopaedic Research, 24(2), 141-148. https://doi.org/10.1002/jor.20032

Helito, C. P., & Helito, P. V. P. (2018). An overview of anatomy and imaging of the anterolateral structures of the knee. Techniques in Orthopaedics, 33(4), 206-212. https://doi.org/10.1097/bto.0000000000000308