Lower Extremity Biomechanics, Kinematics, and Pathology

Comprehensive vocabulary flashcards covering gait mechanics, biomechanical planes, joint kinematics, foot deformities, lower limb pathology, and musculoskeletal principles.

Kinesiology

The study of human movement, integrating both anatomical and mechanical components.

Newton's First Law (Law of Inertia)

The physical principle stating that an object remains at rest or in uniform motion unless acted upon by an external force.

Kinematics

The branch of mechanics that describes the spatial and temporal characteristics of motion (position, velocity, acceleration, displacement, angles, and range of motion) without reference to the forces causing it.

Kinetics

The branch of mechanics that analyzes the internal and external forces acting on a biological system that produce, arrest, or modify movement.

Cardinal Planes of Motion

The three mutually perpendicular anatomical reference planes: Coronal (Frontal) Plane, Sagittal Plane, and Axial (Transverse) Plane.

Talocrural Joint

A uniaxial mortise joint formed by the distal tibia, fibula, and trochlea of the talus that moves primarily in the sagittal plane to produce dorsiflexion and plantarflexion.

Ankle Joint Rockers

The three pivotal roll-over mechanisms of stance: heel rocker (heel strike to foot flat), ankle rocker (tibial advancement over a flat foot), and forefoot rocker (pivot over metatarsal heads into propulsion).

Subtalar Joint Axis of Rotation

A triplanar axis angled on average $42^\natural$ from the horizontal plane and $16^\natural$ from the sagittal plane.

Open-Chain Subtalar Joint Pronation

A triplanar motion where the talus is stationary and the calcaneus simultaneously everts, abducts, and dorsiflexes.

Closed-Chain Subtalar Joint Pronation

Triplanar weight-bearing motion wherein the calcaneus everts while the talus adducts and plantarflexes, accompanied by internal rotation of the tibia and fibula.

Midtarsal Joint (Chopart's Joint)

The functional articulation between the rearfoot and forefoot comprising the talonavicular and calcaneocuboid joints, functioning around longitudinal and oblique axes.

Midtarsal Joint Osseous Locking Mechanism

The stabilization process where subtalar joint supination causes the axes of the midtarsal joint to cross/converge and the cuboid's superior border to lock against the calcaneus, converting the midfoot into a rigid lever.

Windlass Mechanism

The mechanical effect in which dorsiflexion of the hallux tightens the plantar aponeurosis around the metatarsal head, elevating the medial longitudinal arch by approximately $6\,mm$ and stabilizing the forefoot for propulsion.

Vertical Ground Reaction Force Curve

The characteristic bimodal 'double-hump' force curve during stance phase representing loading response, midstance unloading, and terminal stance push-off.

Foot Posture Index (FPI)

A 6-item clinical evaluation tool used to quantify static standing foot posture from $-12$ (highly supinated) to $+12$ (highly pronated).

Navicular Drop

A clinical measure of sagittal plane foot pronation defined as the vertical distance change of the navicular tuberosity between subtalar joint neutral and relaxed weight-bearing.

Navicular Drift

The displacement of the navicular tuberosity in the transverse plane during weight-bearing, reflecting medial bulging at the talonavicular joint.

Supination Resistance Test

A manual assessment determining the amount of force required to resupinate the subtalar joint in a weight-bearing patient, categorized as Easy, Average, or Difficult.

First Ray

The functional anatomical unit composed of the first metatarsal and medial cuneiform, rotating about an oblique axis inclined $45^\circ$ to both sagittal and frontal planes.

Hallux Limitus

A condition characterized by reduced sagittal motion at the first metatarsophalangeal joint, classified as functional ($>50^\circ$ non-weight-bearing but $<12^\circ$ weight-bearing) or structural.

Hallux Rigidus

Osteoarthritis of the first metatarsophalangeal joint characterized by joint space narrowing, periarticular osteophytes, and painful, severe loss of dorsiflexion.

Reverse Morton's Extension

A supportive pad placed under the second through fifth metatarsal heads to offload the first metatarsal head and promote first ray plantarflexion.

Hallux Valgus

A progressive forefoot deformity characterized by lateral deviation of the great toe exceeding $15^\circ$ alongside medial deviation of the first metatarsal.

Rearfoot Varus

A structural deformity where the calcaneus is inverted relative to the ground when the subtalar joint is in neutral position and the midtarsal joint is maximally pronated.

Forefoot Varus

A congenital osseous deformity in which the forefoot is inverted relative to the rearfoot when the subtalar joint is in neutral position and the midtarsal joint is locked.

Forefoot Supinatus

An acquired, soft-tissue, triplanar contracture in which the forefoot is inverted relative to the rearfoot around the longitudinal midtarsal axis, reducible manually.

Forefoot Equinus

A sagittal plane deformity where the entire forefoot is fixed in a plantarflexed relationship to the rearfoot across the midtarsal joint.

Ankle Equinus

A sagittal limitation defined as less than $10^\circ$ of ankle joint dorsiflexion when the subtalar joint is in neutral and the midtarsal joint is locked.

Tailor's Bunion (Bunionette)

A lateral bony prominence or soft tissue hypertrophy of the fifth metatarsal head, often linked with excessive subtalar joint pronation or an increased 4th-5th intermetatarsal angle.

Freiberg's Disease

Avascular necrosis and subsequent osteochondrosis/flattening of a metatarsal head, occurring most commonly at the second metatarsal.

Iselin's Disease

A traction apophysitis of the fifth metatarsal base at the insertion of the peroneus brevis tendon in skeletally immature children.

Hammer Toe

A lesser digital deformity characterized by hyperextension of the metatarsophalangeal (MTP) joint, flexion of the proximal interphalangeal (PIP) joint, and neutral alignment of the distal interphalangeal (DIP) joint.

Claw Toe

A digital contracture presenting with hyperextension of the MTP joint coupled with flexion at both the PIP and DIP joints.

Mallet Toe

A sagittal digital deformity featuring isolated flexion contracture at the distal interphalangeal (DIP) joint with neutral PIP and MTP joints.

Flexor Stabilization

A digital deformity etiology where deep digital flexors (FDL) fire earlier and longer during late stance to stabilize an excessively pronated forefoot, overpowering the interossei.

Extensor Substitution

A digital deformity mechanism in which the extensor digitorum longus overpowers weak lumbricals and tibialis anterior during swing phase, leading to toe clawing.

Polydactyly

A congenital condition involving the presence of supernumerary digits, categorized in the foot by the Venn-Watson classification.

Syndactyly

A congenital condition characterized by soft tissue or osseous fusion (webbing) between adjacent digits, most frequently seen between the second and third toes.

Digital Formulae

Categorization of relative toe lengths across populations, including Egyptian (hallux longest), Greek (second toe longest), Roman (equal length digits 1 and 2), Germanic, and Celtic.

Metatarsus Adductus

A transverse plane congenital deformity characterized by medial deviation of the metatarsals relative to the midline of a neutrally aligned hindfoot.

Femoral Anteversion

Anterior orientation of the femoral neck relative to the femoral condyles; considered excessive when exceeding $35^\circ$, predisposing to in-toeing gait and internal hip rotation.

Q-Angle (Quadriceps Angle)

The angle formed between a vector from the ASIS to the central patella and a vector from the central patella to the tibial tubercle, influencing lateral patellofemoral tracking.

Genu Varum

A frontal plane angular knee deformity ('bowlegs') where the mechanical axis shifts medial to the knee center, increasing loading across the medial tibiofemoral compartment.

Genu Valgum

A frontal plane knee deformity ('knock-knees') where the mechanical axis passes lateral to the knee center, shifting compressive load to the lateral compartment.

Blount's Disease

A localized growth disturbance of the posteromedial proximal tibial physis and epiphysis leading to progressive, pathological tibia vara and internal tibial torsion.

Coxa Vara

A hip deformity defined by a decreased angle of inclination between the femoral neck and shaft ($<120^\circ$, e.g., $90^\circ$), increasing the abductor moment arm while elevating bending and shear stress across the femoral neck.

Coxa Valga

A hip deformity defined by an abnormally large femoral neck-shaft angle ($>135^\circ\text{--}140^\circ$, e.g., $150^\circ$), reducing the effective abductor moment arm and predisposing to hip subluxation/dislocation.

Patellofemoral Joint Compression Force

The resultant compressive force pressing the patella into the femoral trochlea, which increases dramatically with knee flexion as the quadriceps and patellar tendon angles decrease.

Stress-Strain Relationship (Bone Mechanics)

The mechanical curve plotting applied stress (load per unit area) against strain (proportional deformation), detailing elastic behavior, yield point, plastic deformation, and failure point.

Viscoelasticity

The mechanical property of biological tissue whereby stiffness and ultimate strength vary depending on the strain rate or loading speed.

Close-Packed Position

The specific position of maximum articular congruency, maximal capsule/ligament tension, and greatest structural stability for a joint.

Loose-Packed Position

A joint posture where articulating surfaces are in minimal congruency, periarticular tissues are slack, and joint play/mobility is maximized.