Ligament Anatomy

Cruciate Ligaments of the Knee Joint

The anterior (Anterior cruciate ligament, ACL) and posterior (Posterior cruciate ligament, PCL) cruciate ligaments connect the femur and tibia. They cross inside the joint in an "X" shape and are responsible for knee stability in the sagittal plane.

• Anterior Cruciate Ligament (ACL): Originates from the lateral femoral condyle (in the posterior part of the intercondylar notch) and attaches to the anterior part of the tibial plateau. Its primary function is to prevent anterior displacement of the tibia. It is frequently injured (typically during sudden deceleration or directional changes with a fixed foot) and has virtually no potential for spontaneous healing.
• Posterior Cruciate Ligament (PCL): Runs from the inner surface of the medial femoral condyle downward and backward, attaching to the posterior intercondylar area of the tibia. It prevents the tibia from displacing posteriorly. It consists of dense collagen bundles possessing high strength and elasticity to absorb loads. Two bundles are distinguished: the anterolateral and posteromedial, whose tension adapts to the knee flexion angle. Unlike the ACL, this ligament is capable of repair. It is vascularized by branches of the middle genicular artery and innervated by the tibial nerve.

Medial Collateral Ligament (MCL)

The MCL is a key structure for internal knee stabilization. It protects the joint from valgus loads, preventing the tibia from deviating inward. The ligament originates from the medial epicondyle of the femur and courses downward, attaching to the tibia on average 8 cm below the joint line level.

Anatomically, the MCL is divided into two layers:

1. Superficial layer: Longer and wider, it undertakes the major portion of the stabilizing function.
2. Deep layer: Short, located closer to the joint cavity. Its fibers are integrated into the joint capsule and blend into the medial meniscus.

Ligamentous Apparatus and Patellar Stability

The stability of the patellofemoral articulation (patella and femur) depends on the knee flexion angle and the coordinated action of ligaments and muscles.

• Static stabilization: With the joint extended and flexed up to 30°, prevention of lateral displacement of the patella is provided by the medial patellofemoral ligament (MPFL).
• Dynamic stability: Achieved through the oblique fibers of the medial head of the quadriceps femoris muscle (VMO). Restoring the tone of this muscle provides good chances for conservative treatment in instability.

Patellar dislocation is more common in women. This is due to anatomy: a wider pelvis creates an increased Q-angle (normally 15°–20° in women, while in men it is 12°–15°). A typical indirect injury mechanism involves a fixed foot, slight knee flexion, and internal femoral rotation.

Ligaments of the Spinal Segment

Biomechanically, the intervertebral disc is considered a hemijoint. The nucleus pulposus acts as the joint cavity containing fluid, the hyaline cartilage plates of the vertebral bodies serve as the articular surfaces, and the anulus fibrosus functions as the capsule.

Each spinal segment is reinforced by its own ligamentous apparatus, which includes:

• Anterior and posterior longitudinal ligaments (lig. longitudinale anterius et posterius).
• Ligamentum flavum (lig. flavum).
• Interspinous and supraspinous ligaments (lig. interspinale, lig. supraspinale).

Degeneration of these structures and the disc itself begins with the depolymerization of glycosaminoglycans in the nucleus pulposus followed by the enzymatic destruction of collagen by cathepsins. The thoracic spine is additionally fixed by the ribs and has limited mobility, so maximum dynamic loads fall on its middle and lower parts.

Class and exam questions

What else to study on this topic

• Characteristics of spinal cord blood supply in the thoracic region (anterior radiculomedullary artery).
• Sympathetic innervation of the spine: stellate ganglion and splanchnic nerve.
• The role of cathepsin enzymes in the pathogenesis of intervertebral disc degeneration.
• Factors of spinal instability: developmental anomalies (spina bifida, lumbarization) and autoimmune disorders.
• Complications of acute patellar dislocation: formation of osteochondral fragments.

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.