Exam 3 ankle

Ankle Complex Anatomy

• Key Components:

  • Subtalar Joint: Located underneath the talus.

  • Ankle Joint: Comprised of the following:

    1. Tibiotalar Joint:

       • Formed by tibia articulating with the talus.

       • Main source of movement.

       • Mortise and tenon structure; cartilage helps hold it together.

    2. Tibiofibular Joint:

       • Tibia and fibula connected by fibrous tissue (syndesmosis).

    3. Fibulotalar Joint:

       • Fibula articulates with the talus.

• Weight Bearing:

  • The ankle joint can support up to 5 times body weight.

• Main Joints of the Ankle Complex:

  • Distal Tibiofibular Joint

  • Talocrural Joint

  • Subtalar Joint

Ankle and Foot Labelling and Movement

• Ankle Complex:

  • Consists of the ankle joint and subtalar joint.

  • Offers 6 degrees of freedom; considered multi-axial/tri-axial.

• Ankle Joint (Talocrural Joint):

  • Darthrotic Joint:

    • Freely movable.

    • Hinge joint action, allowing dorsiflexion (internal rotation) and plantar flexion (external rotation) in the sagittal plane.

• Subtalar Joint Movement:

  • Eversion and Inversion in the coronal plane.

  • Pronation and Supination occur in the oblique plane.

Gait Mechanics

• Subtalar Joint Movements During Gait:

  • Inversion:

    • Calcaneus turns inwards, stabilizing the ankle.

    • Ligaments, muscles, and tendons become taut.

    • Happens during initial contact and terminal phases of gait.

  • Eversion:

    • Calcaneus turns outward during loading response and midstance, transitioning foot and ankle from lever to shock absorber.

Functions of the Foot and Ankle

• Major Functions:

  • Support body weight.

  • Shock absorption.

  • Maintain balance.

  • Transfer ground reaction forces.

  • Compensate for proximal joint and muscle misalignments.

  • Serve as a substitute for hand functions in cases of upper extremity loss.

• Tendon Functions:

  • Flexor Tendons: Located on the bottom of toes.

  • Extensor Tendons: Located on the top of toes.

• Inversion (30 degrees on frontal plane):

  • Plantar surface faces toward the body's midline.

• Eversion (20 degrees on frontal plane):

  • Plantar surface faces away from the body's midline.

Range of Motion (ROM)

• Movements include:

  • Plantar Flexion

  • Dorsiflexion

  • Eversion

  • Inversion

  • Abduction

  • Adduction

• Open Chain Movements:

  • Pronated (Calcaneus): Eversion, abduction, dorsiflexion; leg and talus held stable.

  • Supinated (Calcaneus): Inversion, adduction, plantar flexion; leg and talus remain stable.

• Closed Chain Movements:

  • Pronation: Adduction and plantar flexion of the talus with internal rotation of the leg. Inversion of the calcaneus and knee flexion.

  • Supination: Abduction and dorsiflexion of the talus with external rotation of the leg. Inversion of the calcaneus and knee extension.

Ankle Arthrodesis vs. Total Ankle Replacement

• Historical Perspective:

  • Before 1970: Arthrodesis was standard.

  • After 1970: Introduction of Total Ankle Replacement (TAR).

• Advantages of TAR:

  • Preservation of Motion: Maintains natural ROM whereas arthrodesis fuses the joint.

  • Improved Gait Mechanics: More natural walking patterns, reducing adjacent joint strain.

  • Lower Risk: Decreased stress on nearby joints, mitigating arthritis.

Indications and Design of TAR

• Indications for TAR:

  • Osteoarthritis

  • Post-traumatic arthritis

  • Avascular necrosis

  • Rheumatoid arthritis

• Challenges and Complications:

  • Limping, arthritis, malleolar impingement, limb length discrepancy, loosening.

• 3-Component Design of TAR:

  • Types: Buechel-Pappas and STAR TAR allow for more degrees of freedom.

  • Less constraint compared to two-component implants.

Buechel-Pappas (BP) Total Ankle Replacement

• Design Details:

  • T-Shape for insertion

  • Semi-constrained, three-component system with a mobile bearing

    • Allows multidirectional motion, reducing stress on the implant.

• Components:

  • Tibial Component: Anchored to the tibia.

  • Talar Component: Designed to articulate with the bearing.

  • Mobile Bearing: Provides flexibility for natural joint mechanics.

• Biomechanical Focus:

  • Aims to reduce shear and rotational forces on the implant.

Deltoid Ligaments and Ankle Sprains

• Deltoid Ligaments:

  • Bind medial malleolus to tarsal bones.

  • Components include:

    • Tibionavicular ligament

    • Tibiocalcaneal ligament

    • Anterior and Posterior Tibiotalar ligaments

• Ankle Ligament Sprains:

  • Account for ~8% of sports injuries.

  • Signs and Symptoms:

    • Pain, swelling, bruising, joint instability, "pop" sensation.

• Sprain Grades:

  • Grade 1: Stretch of ligament; full 90-100% usage.

  • Grade 2: Partial tear; 50% usage.

  • Grade 3: Complete tear; instability.

Conceptual Design Phase

PDR (Product Requirement Document)

• The PDR outlines essential requirements for the total ankle replacement (TAR) based on the literature review.

Key Considerations from Literature Review

• Identifies critical needs for effective TAR based on existing research.

Brainstorming and Concept Development

• Number of Components: Determine how many components are necessary for optimal function.

• Geometry: Analyze the shape and configuration of components for correct articulation and motion.

• Bearing Surface: Choose appropriate materials and design for bearing surfaces to ensure durability and low wear.

• Fixation: Develop strategies for securing implant components to the bone, considering mechanical stability.

• Materials: Select biocompatible materials that support longevity and functionality of the ankle replacement.