Hoja de repaso: Lower Limb Anatomy and Biomechanics

📋 Course Outline

1. Knee joint anatomy, stability, and ligamentous structures
2. Muscles acting on the knee and their functions
3. Hip joint movements and their biomechanical constraints
4. Knee joint movements and meniscal-ligament interactions
5. Tibio-fibular joints anatomy, ligaments, and mobility
6. Foot osteology and plantar arches for weight distribution
7. Ankle joint ligaments, movements, and injury mechanisms
8. Muscles acting on the ankle and foot with movement functions

📖 1. Knee joint anatomy, stability, and ligamentous structures

🔑 Key Concepts & Definitions

• Fémoro-tibial articulation : a hinge joint formed by the femoral condyles and the tibial plateaus, characterized by plane articular surfaces that are non-congruent, meaning they do not fit perfectly together.

• Fémoro-patellaire articulation : a joint between the femoral trochlea and the posterior surface of the patella, also with plane surfaces that are non-congruent, resulting in a less precise fit.

• Ligament croisé antérieur : a ligament that provides stability during knee flexion, preventing anterior displacement of the tibia relative to the femur.

• Ligament croisé postérieur : a ligament that stabilizes the knee by preventing posterior displacement of the tibia, especially in flexion.

📝 Essential Points

• The knee joint comprises two articulations: the femoro-tibial and the femoro-patellaire, both featuring plane, non-congruent surfaces that do not fit tightly together. Stability during flexion is primarily maintained by the cruciate ligaments, with the anterior cruciate ligament preventing forward movement of the tibia and the posterior cruciate ligament preventing backward movement. Lateral stability is secured by collateral ligaments. The joint capsule is thin and loose overall, except posteriorly, and is interrupted anteriorly by the patella. It is reinforced at the femoro-tibial level by fibrous sleeves, contributing to the joint's structural integrity.

💡 Key Takeaway

Understanding the dual articulation and the specific ligamentous arrangements reveals how the knee maintains stability despite the low congruence of its articular surfaces, allowing for both mobility and stability.

📖 2. Muscles acting on the knee and their functions

🔑 Key Concepts & Definitions

• Fléchisseur : A muscle that acts to bend the knee joint, including biarticular muscles such as the hamstrings and the gastrocnemius.
• Face médiale : The inner side of the thigh or knee, where muscles like the semi-tendinosus pass and contribute to medial knee structures.

📝 Essential Points

• The quadriceps femoris is a biarticular extensor muscle originating from the os coxal and inserting on the patella, also acting as a hip flexor.
• The ischio-jambiers group includes the biceps femoris long head, semi-tendinosus, and semi-membranosus muscles; they are biarticular, acting as hip extensors and knee flexors.

💡 Key Takeaway

The knee's movement and stability depend on coordinated action of biarticular muscles crossing hip and knee joints.

📖 3. Hip joint movements and their biomechanical constraints

🔑 Key Concepts & Definitions

Hip flexion refers to the movement that decreases the angle between the thigh and the pelvis, primarily involving muscles that lift the leg forward. It is greater when the knee is flexed, because this position relaxes the ischio-jambiers and reduces tension in ligamentous structures.

Hip extension describes the movement that increases the angle between the thigh and the pelvis, involving muscles that move the leg backward. Its range is limited to about 10° when the knee is flexed due to the proximity of the ischio-jambiers and the tension in the ilio-femoral ligament; this range increases to approximately 20° with the knee extended, but is limited by the ilio-femoral ligament wrapping around the femoral neck.

Hip abduction involves moving the leg away from the body's midline, reaching approximately 30°. This movement is blocked by the femoral neck impinging on the acetabular rim and tension in the ilio- and pubo-femoral ligaments. Hyperlordosis can increase the rotation, affecting the range.

Hip adduction is the movement of bringing the leg toward the midline, also reaching about 30°. It requires combined flexion or extension of the hip to avoid blockage by the opposite limb and depends on the strength of powerful muscles.

📝 Essential Points

• Hip flexion is more extensive when the knee is flexed because of the relaxation of the ischio-jambiers and the reduction of ligamentous tension.

• Hip extension is limited to roughly 10° with the knee flexed due to the proximity of the ischio-jambiers and the tension in the ilio-femoral ligament; this range increases to about 20° when the knee is extended, but the movement remains limited by the ilio-femoral ligament wrapping around the femoral neck.

• Hip abduction can reach approximately 30°, but this movement is blocked by the femoral neck impinging on the acetabular rim and tension in the ilio- and pubo-femoral ligaments. Hyperlordosis can increase the rotation, influencing the abduction range.

• Hip adduction also reaches about 30°, requiring combined flexion or extension to avoid blockage by the opposite limb. Its range depends on the strength of the muscles involved, which are described as powerful.

💡 Key Takeaway

Hip joint movements are intricately limited by bony impingements and ligament tensions, which define the functional range and influence movement capacity.

📖 4. Knee joint movements and meniscal-ligament interactions

🔑 Key Concepts & Definitions

• Ligt croisé : Intracapsular but extrasynovial ligaments that connect femoral condyles to the tibial intercondylar fossae, facilitating knee stability during movement.
• Face axiale : The surface orientation of certain structures, such as the femoral condyles and ligaments, aligned with the axial plane of the joint.
• Face axiale of condyles : The surface of the femoral condyles oriented in the axial plane, involved in the biomechanics of knee movement.

📝 Essential Points

• During knee flexion, the femoral condyles roll within the tibial cavities, causing posterior displacement of the menisci due to pressure from the condyles. This movement allows the knee to bend smoothly while maintaining joint stability. As the knee flexes, the cruciate and collateral ligaments relax, and the synovial fluid shifts posteriorly within the joint, accommodating the motion.

• In contrast, knee extension involves anterior movement of the menisci, which slide forward as the collateral ligaments tense to stabilize the joint. Simultaneously, the cruciate ligaments exert forward pressure on the menisci, aiding in their anterior shift. During this extension, the patella enhances the efficiency of the quadriceps muscle, with the tibia rotating outward and the femur moving forward, optimizing the joint’s biomechanical function.

💡 Key Takeaway

Knee movements involve complex biomechanical interactions characterized by dynamic shifts of the menisci and tension adjustments in the ligaments, ensuring stability and efficiency during flexion and extension.

📖 5. Tibio-fibular joints anatomy, ligaments, and mobility

🔑 Key Concepts & Definitions

• Proximal tibio-fibular joint : an arthrodial joint characterized by limited mobility, involving a capsule and reinforced by anterior and posterior tibio-fibular ligaments.
• Distal tibio-fibular joint : a joint forming part of the ankle mortise, classified as an amphiarthrosis with limited movement, which is linked to ankle motion.
• Anterior tibio-fibular ligament : a ligament situated near the biceps femoris tendon, connecting the fibular head to the tibia.
• Posterior tibio-fibular ligament : a broader and longer ligament than the anterior, attaching from the medial malleolus to the fibula.

📝 Essential Points

• The proximal tibio-fibular joint is an arthrodial joint with limited mobility, stabilized by a capsule and the anterior and posterior tibio-fibular ligaments.
• The distal tibio-fibular joint contributes to the ankle mortise structure, functioning as an amphiarthrosis with limited movement that correlates with ankle motion.
• The anterior tibio-fibular ligament is located near the biceps femoris tendon and connects the fibular head to the tibia.
• The posterior tibio-fibular ligament is broader and longer than the anterior ligament, attaching from the medial malleolus to the fibula.

💡 Key Takeaway

Tibio-fibular joints provide essential stability and slight mobility to unify leg bones, crucial for ankle function.

📖 6. Foot osteology and plantar arches for weight distribution

🔑 Key Concepts & Definitions

• Talus bone : a tarsal bone with a narrowed neck and a trochlea that forms the ankle mortise with the tibial and fibular malleoli, playing a central role in ankle articulation.

• Calcaneus bone : the posterior tarsal bone that bears weight at the tuberosity, serving as a key support point for the foot's arches.

• Plantar arches : three internal, external, and anterior arches of the foot that rest on the ground at the calcaneal tuberosity and the heads of metatarsals 1 and 5, functioning to distribute weight and absorb shock during gait.

• Metatarsal bones : five long bones in the midfoot; metatarsal 2 is the longest and serves as the foot's axis, while metatarsal 1 is short, robust, and articulates with the medial cuneiform and hallux.

📝 Essential Points

• The foot comprises 26 bones organized into the tarsus, metatarsus, and phalanges, with the posterior tarsus formed by the talus and calcaneus. The talus features a narrowed neck and a trochlea that creates the ankle mortise with the tibia and fibula. The calcaneus supports weight at its tuberosity, which is a primary contact point with the ground. The plantar arches—internal, external, and anterior—rest on the ground at specific points: the calcaneal tuberosity and the heads of metatarsals 1 and 5. These arches are essential for distributing weight evenly and absorbing shocks during walking or running. The metatarsal bones include metatarsal 2, the longest bone that acts as the central axis of the foot, and metatarsal 1, which is shorter, sturdier, and articulates with the medial cuneiform and the hallux.

💡 Key Takeaway

The bony architecture of the foot, including its specific bones and arches, is highly specialized to optimize weight distribution and shock absorption during movement.

📖 7. Ankle joint ligaments, movements, and injury mechanisms

🔑 Key Concepts & Definitions

• Tarse : A group of bones in the foot forming the posterior part, including the talus and calcaneus; the talus articulates with the tibia and fibula forming the ankle joint.
• Dessus condyle fémorale lat  Te : The upper part of the lateral femoral condyle, serving as an origin point for muscles such as the lateral head of the gastrocnemius and the plantaris muscle.

📝 Essential Points

• Forced abduction (eversion) can cause bimalléolar fractures involving both medial and lateral malleoli and their collateral ligaments.
• The ankle joint (talo-crural) allows one degree of freedom: flexion and extension in the sagittal plane around a transverse axis.

💡 Key Takeaway

Ankle stability depends on complex ligamentous structures vulnerable to specific injury mechanisms linked to movement extremes.

📖 8. Muscles acting on the ankle and foot with movement functions

🔑 Key Concepts & Definitions

• Calcanéus (heel bone) : the large bone in the posterior part of the foot that serves as the insertion point for several muscles involved in foot movements.

📝 Essential Points

• The tibialis anterior originates from the anterior and lateral surfaces of the tibia and the interosseous membrane. It functions as a dorsiflexor, adductor, and supinator of the foot, contributing to upward foot movement and medial rotation.

• The long fibular muscle arises from the fibula and tibia. It acts as a plantar flexor and evertor of the foot, serving as an abductor and lateral rotator, and works antagonistically to the tibialis anterior.

• The triceps surae group, composed of the gastrocnemius and soleus muscles, inserts on the calcaneus via the Achilles tendon. These muscles are powerful plantar flexors, supporting body weight during standing and movement.

• Short extensor muscles of the foot, such as the short extensor of the hallux and toes, originate from the calcaneus. They assist in extending the toes and dorsiflexing the foot.

💡 Key Takeaway

The movements of the ankle and foot result from the coordinated actions of multiple muscles with specific origins, insertions, and functions, enabling complex and precise foot positioning.

📊 Synthesis Tables

Knee Joint Ligaments and Stability

Ligament	Function
Anterior cruciate ligament	Prevents anterior displacement of tibia during flexion
Posterior cruciate ligament	Prevents posterior displacement of tibia, stabilizes in flexion
Collateral ligaments	Secure lateral stability

⚠️ Common Pitfalls & Confusions

1. Confusing the congruence of articular surfaces with joint stability.
2. Misunderstanding the role of cruciate ligaments in knee stability.
3. Assuming the joint capsule is uniformly thick and tight.
4. Overlooking the importance of menisci in load distribution.
5. Mixing up the actions of biarticular muscles crossing hip and knee.
6. Confusing hip joint movement limitations with those of the knee.
7. Misinterpreting the role of tibio-fibular joints in ankle stability.

✅ Exam Checklist

1. Identify the articulations of the knee joint.
2. Describe the functions of the anterior and posterior cruciate ligaments.
3. Explain the movement range of hip flexion and extension.
4. Describe the biomechanical interactions during knee flexion and extension.
5. Identify the bones forming the foot arches.
6. Explain the role of the talus in ankle movement.
7. List muscles involved in dorsiflexion of the foot.
8. Describe the ligamentous structures stabilizing the tibio-fibular joints.
9. Explain the movement limitations of the hip joint.
10. Identify the muscles acting on the ankle and their functions.