Lower Extremities

Introduction

  • Focus on understanding joints and motions of the feet and ankles.

Ankle Structure

  • The ankle comprises four bones:

    • Calcaneus: Main heel bone.

    • Talus: Sits atop the calcaneus.

    • Tibia: Larger shinbone.

    • Fibula: Smaller shinbone.

  • The ankle itself is not a single joint but consists of multiple joints:

    • Subtalar Joint: Between the calcaneus and talus, allows for inversion/eversion.

    • Talocrural Joint: The "true" ankle joint, formed by the tibia and fibula with the talus, allows for dorsiflexion/plantar flexion.

    • Distal Tibiofibular Joint: Where the tibia and fibula meet, limited movement (syndesmosis joint).

Ankle Motion

  • Talocrural Joint: Mainly responsible for dorsiflexion (toe-up) and plantar flexion (toe-down).

  • Subtalar Joint: Responsible for inversion (foot rolling inward) and eversion (foot rolling outward).

    • Inversion: Calcaneus moves inwards.

    • Eversion: Calcaneus moves outwards.

  • Distal Tibiofibular Joint: No substantial motion; stabilizes the ankle.

Foot Structure

  • The foot contains 26 bones, including:

    • Metatarsals: Form the length of the foot where the arch is.

    • Phalanges: Each toe is made up of these bones.

      • Proximal, Middle, and Distal Phalanx labeled by position.

  • The big toe has only two phalanges (proximal and distal); others have three.

Tarsals and Joints

  • Tarsals: Seven total, key ones include calcaneus and talus.

  • Tarsometatarsal Joint: Between tarsals and metatarsals, allows for sliding action without significant motion.

  • Metatarsophalangeal Joint (MTP): Allows for flexion, extension, as well as abduction and adduction.

    • Proximal Interphalangeal Joint (PIP): Between the first and second phalanges of the toes.

    • Distal Interphalangeal Joint (DIP): Between the second and third phalanges of the toes.

Foot Arches

  • Medial Longitudinal Arch: Runs from the front to the back along the inside of the foot.

  • Lateral Longitudinal Arch: Smaller arch on the outer edge.

  • Transverse Arch: Across the width of the foot from metatarsals.

  • Arches facilitate force dissipation when walking/running:

    • Pes Planus: Flat feet due to a fallen medial longitudinal arch.

    • Pes Cavus: High, rigid arches that do not collapse or absorb force well.

Impact of Arches on Activity

  • Arches affect overall mechanics:

    • Normal Arch: Some give when weight-bearing helps dissipate force.

    • Pes Planus: Increased risk of lower extremity injuries due to lack of force absorption; tend to overpronate.

    • Pes Cavus: Higher risk for ankle sprains and stress injuries due to rigidity and poor shock absorption.

Muscle Groups

  • Dorsiflexors: Muscles responsible for moving toes up, mainly located at the front of the leg.

    • Key Muscles: Tibialis Anterior, Extensor Digitorum Longus, Extensor Hallucis Longus.

  • Plantar Flexors: Muscles for pointing toes down, located on the back of the leg.

    • Components known as Triceps Surae:

      • Gastrocnemius: Superficial muscle, crosses the knee and ankle, involved in actions like running.

      • Soleus: Underneath gastrocnemius, mainly for plantar flexion.

      • Plantaris: Small muscle, less significant function.

  • Evertors: Muscles that pull the ankle outwards, include Peroneus Longus and Peroneus Brevis.

  • Unlocking the Knee: Function of the Popliteus muscle helping in knee flexion after full extension.

Knee Joint

  • Tibiofemoral Joint: Main joint of the knee.

  • Consists of:

    • Condyles: Lateral and medial, where weight-bearing occurs.

    • Meniscus: Cushioning between femur and tibia.

  • Primarily a hinge joint allowing flexion and extension but also permits some rotation.

Important Concepts

  • Screw Home Mechanism: Describes the last few degrees of knee extension where tibia rotates externally.

  • Valgus and Varus Forces: Important for understanding joint injuries

    • Valgus: Force from outside to inside the knee; can damage MCL.

    • Varus: Force from inside to outside knee; less common injury type.

  • Patellofemoral Pain Syndrome: Caused by muscle imbalances especially in the quadriceps, leading to misguided patellofemoral tracking.

Hip Joint Fundamentals

  • Hip Structure: A ball-and-socket joint offering stability and movement.

  • Pelvic Bone: Comprised of three fused bones: ilium, ischium, and pubis.

  • Movements: Flexion, extension, abduction, adduction, internal and external rotation.

  • Pelvic Possibilities: Both anterior and posterior pelvic tilts occur during hip motions.