731 Benchmark 4

Lower Extremity Joints

Structure of the Joints of the Lower Extremity

• Pelvis, Hip, Knee, Ankle, and Foot

  • Joint Types

  • Ball and Socket Joint

    • Degrees of Freedom: 3 degrees of freedom

    • Shape and Features of Articular Surfaces:

    • Acetabulum: concave

    • Femoral Head: convex

    • Periarticular Tissues:

    • Ischiofemoral ligament

    • Iliofemoral ligament (Y ligament, strongest)

    • Pubofemoral ligament

  • Synovial Condyloid Joint

    • Degrees of Freedom: 2 degrees of freedom

    • Shape and Features of Articular Surfaces:

    • Femoral condyles: convex

    • Tibial Plateau: concave

    • Periarticular Tissues:

    • Anterior Cruciate Ligament (ACL)

    • Posterior Cruciate Ligament (PCL)

    • Lateral Collateral Ligament (LCL)

    • Medial Collateral Ligament (MCL)

    • Menisci of knee:

      • Coronary ligament

      • Transverse ligament

      • Medial meniscus (C shaped)

      • Lateral meniscus (O shaped)

  • Synovial Hinge Joint (Talocrural Joint, Proximal and Distal Tibiofibular Joints)

    • Degrees of Freedom: 1 degree of freedom

    • Shape and Features of Articular Surfaces:

    • Convex talus & concave tibia/fibula

    • Periarticular Tissues:

    • Deltoid ligament

    • Anterior talofibular ligament

    • Posterior talofibular ligament

    • Calcaneofibular ligament

  • Synovial Joint (Subtalar Joint) & Metatarsophalangeal Joint (Condyloid Joint)

  • Degrees of Freedom:

    • Subtalar: 1 degree (inversion/eversion)

    • Metatarsophalangeal: 2 degrees of freedom

    • Shape and Features of Articular Surfaces:

    • MTP: Metatarsal head (convex) and proximal phalanx (concave)

    • Periarticular Tissues:

    • Plantar aponeurosis (fibrous tissues connecting bones, providing support to arches)

Osteokinematics of Joints of the Lower Extremity

• Normative Range of Motion for both Distal-on-Proximal and Proximal-on-Distal Motions

Hip Joint

• Distal-on-Proximal (femoral-on-pelvic, open chain)

  • Flexion:

  • ~120° (knee flexed)

  • ~70–80° (knee extended)

  • Example: Lifting leg to tie shoe

  • Extension: ~20° beyond neutral

  • Example: Pushing leg backward during gait

  • Abduction: ~40–45°

  • Adduction: ~25°

  • Internal Rotation: ~35°

  • External Rotation: ~45°

• Proximal-on-Distal (pelvic-on-femoral, closed chain)

  • Anterior pelvic tilt → hip flexion

  • Posterior pelvic tilt → hip extension

  • Lateral pelvic tilt → hip abduction/adduction

  • Pelvic rotation → hip internal/external rotation

  • Example: Squat (pelvis rotates over fixed femurs)

Knee (Tibiofemoral Joint)

• Sagittal Plane

  • Flexion: ~130–150°

  • Extension: 5–10° beyond neutral

• Transverse Plane (only when flexed)

  • External Rotation: ~30°

  • Internal Rotation: ~15°

• Distal-on-Proximal: Tibia moves (e.g., kicking a ball)

• Proximal-on-Distal: Femur moves (e.g., sit-to-stand)

Talocrural (Ankle) Joint

• Plantarflexion: ~40–55°

• Dorsiflexion: ~15–25°

• Open Chain: Foot moves on leg

• Closed Chain: Tibia moves over fixed foot (e.g., squat)

Subtalar Joint

• Inversion: ~20–25°

• Eversion: ~10–15° (2:1 ratio)

Joint Stability and Mobility

Role of Bony Congruence, Periarticular Tissues, and Muscle Forces

• Bony Congruence:

  • Hip: Deep acetabulum + spherical femoral head → high stability

  • Knee: Flat tibial plateau + convex femoral condyles → low stability

  • Ankle: Talus wedged into mortise during dorsiflexion → high stability

• Periarticular Tissues:

  • Ligaments & capsule: Passive restraints to excessive motion

  • Labrum (hip) & menisci (knee): Increase surface contact and reduce stress

  • Example: Knee stability relies heavily on ACL, PCL, MCL, LCL due to poor bony fit

• Muscle Forces:

  • Provide dynamic stability

  • Examples:

  • Quadriceps stabilize knee during femoral-on-tibial motion

  • Plantarflexors stabilize ankle during stance phase of gait

Close-Packed and Loose-Packed Positions of Joints of the Lower Extremity

• Hip Joint

  • Closed Packed: Full extension

  • Open Packed: 30 degrees flexion, 30 degrees abduction, slight external rotation

• Knee Joint

  • Closed Packed: Knee straight

  • Loose Packed: Knee slightly bent

• Ankle Joint

  • Closed Packed: Toes pulled up (dorsiflexion)

  • Loose Packed: Toes pointed down (plantarflexion)

• Kneecap (Patellofemoral Joint)

  • Closed Packed: Knee bent

  • Loose Packed: Knee straight

Arthrokinematics of Joints of the Lower Extremity

Mechanics of Joint Movement

• Hip

  • Femoral-on-Pelvic (convex-on-concave):

  • Roll and slide in opposite directions

  • Example: Hip abduction → superior roll, inferior glide

  • Pelvic-on-Femoral (concave-on-convex):

  • Roll and slide in the same direction

• Knee

  • Tibial-on-Femoral (concave-on-convex):

  • Roll and slide in the same direction

  • Femoral-on-Tibial (convex-on-concave):

  • Roll and slide in opposite directions

  • Screw-Home Mechanism:

  • Tibial external rotation (open kinetic chain) or femoral internal rotation (closed kinetic chain) during the last ~30° extension

• Talocrural Joint

  • Open Chain (talus moves):

  • Dorsiflexion: anterior roll, posterior slide

  • Plantarflexion: posterior roll, anterior slide

  • Closed Chain (tibia moves):

  • Roll and slide in the same direction

Convex and Concave Surfaces Articulating Bones for Each Joint

• Hip:

  • Convex Surface: Femoral Head

  • Concave Surface: Acetabulum

• Knee:

  • Convex Surface: Femoral Condyles

  • Concave Surface: Tibial Plateau

• Talocrural Joint:

  • Convex Surface: Talus

  • Concave Surface: Tibia/Fibula Mortise

• Metatarsophalangeal Joint:

  • Convex Surface: Metatarsal Head

  • Concave Surface: Proximal Phalanx

Joint Motions and Degrees of Freedom

• Hip:

  • Flexion/Extension

  • Abduction/Adduction

  • Internal/External Rotation

  • Degrees of Freedom: 3

• Knee (Tibiofemoral Joint):

  • Flexion/Extension

  • Internal/External Rotation

  • Degrees of Freedom: 2

Periarticular Tissues

Ligaments of the Hip and Knee, Menisci of Knee, Labrum of Hip

• Hip

  • Iliofemoral Ligament: Resists extension

  • Pubofemoral Ligament: Resists abduction

  • Ischiofemoral Ligament: Resists internal rotation

• Menisci of Knee:

  • Coronary Ligament

  • Transverse Ligament

  • Acetabular Labrum: Deepens socket, reduces stress

  • Ligament of the Head of Femur

  • Transverse Acetabular Ligament

• Knee

  • ACL: Resists anterior tibial translation

  • PCL: Resists posterior tibial translation

  • MCL: Resists valgus stress

  • LCL: Resists varus stress

Joints in the Ankle and Foot

• Ankle Joints:

  • Talocrural Joint

  • Proximal Tibiofibular Joint

  • Distal Tibiofibular Joint

• Foot Joints:

  • Subtalar Joint (Rearfoot)

  • Transverse Tarsal Joint and Distal Intertarsal Joint (Midfoot)

  • Tarsometatarsal Joints

  • Intermetatarsal Joints

  • Metatarsophalangeal Joint

  • Interphalangeal Joints (Forefoot)

Joint Motions (Degrees of Freedom) for Ankle and Foot Joints

• Talocrural Joint:

  • Degrees of Freedom: 1 (plantarflexion and dorsiflexion)

• Subtalar Joint:

  • Degrees of Freedom: 1 (inversion/eversion)

• Metatarsophalangeal Joint:

  • Degrees of Freedom: 2 (flexion/extension, abduction/adduction)

Periarticular Tissues in the Ankle/Foot

• Deltoid Ligament: Strong medial ligament; resists eversion

• Anterior Talofibular Ligament: Most anterior ligament on lateral side; thin and weak, most injured

• Posterior Talofibular Ligament: Strongest of lateral ligaments; resists posterior displacement of the talus beneath the tibia and fibula

• Calcaneofibular Ligament: Provides lateral stability by resisting inversion

• Plantar Aponeurosis: Fibrous tissues connecting bones; provides support to the arches

Joint Mechanics

Histology, Material Properties, and Functions of Periarticular Tissues and Skin

• Dense Connective Tissues:

  • Tendon:

  • Function: Attach muscle to bone.

  • Histology: Dense regular connective tissue; high proportion of type 1 collagen fibers arranged in parallel.

  • Material Properties: Less stiff than bone, high tensile strength in direction of fibers.

  • Ligament:

  • Function: Binds bones together at the joint.

  • Histology: Dense regular connective tissue.

  • Material Properties: Little elasticity; high tensile strength to resist tension.

  • Joint Capsule:

  • Function: Bind bones together at joint.

  • Histology: Dense irregular connective tissue.

  • Material Properties: Resists multidirectional tension.

• Articular Cartilage

  • Hyaline:

  • Characteristics: Proteoglycan-rich; resists compressive loads.

  • Function: Distributes and disperses compressive forces between articulating bones.

  • Fibrocartilage:

  • Includes: Menisci/labrum; resists compression and tension.

  • Function: Supports and stabilizes joints; provides resistance and shock absorption.

• Skin:

  • Function: Regulate body temperature; source of sensory information; protection from external threats.

  • Histology: Composed of 3 layers (epidermis, dermis, subcutaneous).

  • Material Properties: Loaded primarily in tension, compression, and shear; exhibits stiffness and elasticity in multiple directions.

Classification of Joints According to Structure and Function

• Fibrous: Immobile (synarthroses)

• Cartilaginous: Slightly mobile

• Synovial: Freely mobile (diarthroses)

Definitions

• Osteokinematics: Describes the movement of a segment relative to the three cardinal planes.

• Arthrokinematics: Describes the passive motions that occur between joint surfaces during movement, including roll, slide, and spin. Not observable; occurs inside the joint.

Relationship Between Joint Structure and Movement Capacity

• Example:

  • Hip: Deep socket = stable joint; allows for 3 degrees of freedom.

  • Knee: Shallow surfaces = mobile joint but unstable.

Axes of Rotation and Fundamental Movements

• Hip:

  • Axes: 3 (anterior/posterior, medial/lateral, vertical)

  • Movements: Flexion/Extension, Abduction/Adduction, Internal/External Rotation

• Knee:

  • Axes: Medial/Lateral Axis (flexion/extension), Nutritional Axis (rotation)

• Ankle:

  • Axis: Oblique medial/lateral axis through malleoli

Open and Closed Kinematic Chain Movements

• Open Chain (Distal-on-Proximal):

  • Foot moving in space

  • Examples:

  • Sitting and kicking a ball

  • Lying down and lifting your leg

  • Ankle pumping while sitting

  • Joint Behavior:

  • One joint moves at a time

  • Easier to isolate muscles

  • More shear forces

• Closed Chain (Proximal-on-Distal):

  • Foot is on the ground

  • Examples:

  • Squat

  • Sit-to-stand

  • Walking, stairs

  • Joint Behavior:

  • Multiple joints move together

  • Greater compressive forces

  • Greater joint stability

Fundamental Movements Associated with Arthrokinematics

• Roll: New point on one surface contacts new point on the other.

  • Example: Femoral condyle rolling on tibia during knee flexion

• Slide: Same point on one surface contacts new points on the other.

  • Example: Tibia sliding anteriorly during knee extension

• Spin: Rotation around a fixed axis.

  • Example: Supination (looking at phone)

Close-Packed and Loose-Packed Positions at a Joint

• Closed Packed: Joint is maximally stable; minimal joint play.

• Open Packed: Joint is most mobile; maximum joint play; ligaments and capsule slack.

  • Example:

  • Talocrural joint: Full dorsiflexion (closed packed) ~10 degrees plantarflexion.

Relationship Between Joint Stability and Range of Motion

• More stability = less range of motion

• More range of motion = less stability

• They have an inverse relationship

Application of Joint Mechanics to Clinical Examples

• Example Case: Patient demonstrates decreased abduction range of motion of the hip.

  • Likely lacking arthrokinematic motion: Inferior slide

• Another Example: What arthrokinematic motion occurs at the knee when standing up from a seated position?

  • Anterior roll and posterior slide.