Exam 1 Summer - Allie W.pdf

Exam 1 Summer Sunday, May 14, 2017 1:49 PM Body Planes: Sagittal Plane: Divides the body into right and left halves Frontal Plane: Divides the body into front and back Transverse Plane: Divides the body into "slices". Perpendicular to the Sagittal a...

Exam 1 Summer Sunday, May 14, 2017 1:49 PM Body Planes: Sagittal Plane: Divides the body into right and left halves Frontal Plane: Divides the body into front and back Transverse Plane: Divides the body into "slices". Perpendicular to the Sagittal and Frontal Planes If a motion occurs PARALLEL to a particular plane, the motion is occurring within that body plane. Motions: ○ Knee Flexion: sagittal plane Plantarflexion Distal part of the foot moves away from the motion anterior aspect of the tibia parallel to the sagittal ○ Rotation of Foot: transverse plane plane motion Dorsiflexion Distal part of the foot moves toward the anterior ○ Abduction of the Arm: frontal aspect of the tibia parallel to the sagittal plane plane motion Abduction The foot is rotated away from the mid-line of the body parallel to the transverse plane FlexED: knee is in a flexed position FlexION: motion of the knee to obtain Adduction The foot is rotated toward the mid-line of the body the flexed position parallel to the transverse plane Inversion The foot or part of the foot is tilted so that the Positions: plantar surface is facing the mid-line of the body parallel to the frontal plane Anatomical Foot is at 90º relative to the Eversion The foot or part of the foot is tilted so that the Neutral leg plantar surface is facing away from the mid-line of Plantarflexed Distal part of the foot is in a the body parallel to the frontal plane stationary attitude away from Pronation Triplane motion that includes Abduction, Eversion, the tibia parallel to the sagittal and Dorsiflexion. Functionally shortens the limb. plane (< 90º) Supination Triplane motion that includes Adduction, Inversion, Dorsiflexed Distal part of the foot is in a Plantarflexion. Functionally lengthens the limb. stationary attitude towards the tibia parallel to the sagittal plane (> 90º) Joints and Motion Axis of Motion: is perpendicular to the motion around the axis ○ Angle of Axis of Motion determines the number of body planes that the motion occurs in Sagittal Plane Axis of Motion: ○ Perpendicular to the sagittal plane ○ Parallel to the frontal and transverse planes Transverse Plane Axis of Motion: ○ Perpendicular to the transverse plane ○ Parallel to the frontal and sagittal planes Frontal Plane Axis of Motion: ○ Perpendicular to the frontal plane ○ Parallel to the transverse and sagittal planes Biomechanics Page 1 Fixed Structural Positions structural position of the foot that is fixed in the position described. Generally an abnormality/deformity. Uses the suffix "-us". Varus The foot Adductus If the foot or part of or part of the foot is internally the foot is rotated, parallel to inverted, the transverse plane, parallel to with its distal aspect the frontal facing toward the plane mid-line of the body. "Pigeon toed" Valgus The foot or part of the foot is Abductus If the foot or part of everted, the foot is rotated parallel to externally, parallel to the frontal the transverse plane, plane with its distal aspect facing away from the mid-line of the body Gait Cycle Definition: The interval of time Talipes The foot is positioned from heel strike of one foot to heel Calcaneus above a transverse plane strike by the same foot on the next which runs through the step. Observed one foot at a time heel. Terms: Walking on the ○ Heel Off = Heel Lift heels ○ Toe Off = Propulsion (main Dorsiflexed goal of gait) structurally ○ Forefoot Loading: increasing Talipes The foot is positioned or decreasing weight present Equinas below a transverse plane on the forefoot (metatarsal which runs through the heads) heel ○ Full Forefoot Loading: all the Walking on the toes body weight present on the Plantar flexed forefoot (metatarsal heads) structurally Phases: Biomechanics Page 2  Phases: Swing Phase - 38% ○ Stance Phase: Closed Kinetic Chain - Motions 62% ○ Foot Pronates  Weight bearing portion of gait  This functionally SHORTENS the limb to help cycle the foot clear the ground just after toe off  Begins: heel strike  Destabilizes the osseous structures of the foot  Ends: toe off  Also minimizes the energy used for ground  Three sub-phases: Contact clearance as the non-weight bearing limb Period, Midstance Period, and passes the weight bearing limb Propulsive Period ○ Foot Supinates ○ Swing Phase: Open Kinetic Chain - 38%  Functionally LENGTHENS the limb  Non weight bearing portion of  Stabilizes the osseous structures of the foot, gait cycle preparing the foot for heel strike  Begins: toe off  Ends: heel strike Subtalar Joint (motion vs. position) Stance Phase - 62% Contact Period - 27% ○ Begins: Heel strike of observed foot  Foot is supinated at heel strike  Subtalar Joint pronates to absorb shock and act as the mobile adapter  Leg internally rotates - therefore the heel everts ○ Ends: Toe off of the OPPOSITE foot ○ Forefoot loading is occurring in the foot that is finishing the contact period. At the same time, toe off is occurring in the opposite foot Midstance Period - 40% Propulsive Period - 33% ○ Begins: right after toe off of ○ Begins: Heel lift of observed foot OPPOSITE foot (full forefoot  Subtalar joint is supinated allowing the foot to act as a rigid loading of observed foot) lever  Subtalar joint is  Leg is continuing to externally rotate pronated and moves to  Just before toe off: supination allows the □ Subtalar joint pronates SLIGHTLY foot to act as a rigid □ Body weight shifts from lateral to medial so the lever by causing "piling metatarsal heads 1, 2, and 3 load heavily up" of tarsal bones to ○ Ends: Toe off of observed foot increase rigidity. ○ Note: If the subtalar joint is pronated during propulsive phase, the  Leg externally rotates - foot and leg muscles must work harder, causing fatigue and slight heel inversion hypermobility (mobile adaption) when the subtalar joint SHOULD ○ Ends: Heel lift of observed BE supinated as the rigid lever. foot  Causes increase shearing forces Biomechanics Page 3 Biomechanics Page 4 First MPJ Range of Motion Planes of Motion - under normal circumstances there is no frontal plane Minimum ROM for 65-75º motion - therefore anytime the hallux is inverted/everted, there will be normal locomotion subluxation of the first MPJ and gait Transverse Axis Allows pure sagittal plane When weight bearing 20-30º motion (plantarflexion and hallux only dorsiflexion) dorsiflexes Axis of motion is First metatarsal (1st 45º perpendicular to the Ray) MUST plantar sagittal plane flex to increase the ROM of the 1st MPJ Vertical Axis Allows pure transverse (required for plane motion (adduction propulsion) and abduction ) Axis of motion is Tibia - during 45º perpendicular to the propulsion transverse plane Foot - plantar flexed 20º at the ankle The First Ray Functional metatarsal unit consisting of the first metatarsal and first cuneiform bones. Articulations 1st metatarsal with 1st cuneiform and 2nd metatarsal 1st cuneiform with navicular 2nd cuneiform and 2nd metatarsal Axis The first metatarsal cuneiform joint and first cuneiform navicular joint move about a common axis ○ Axis passes anterior, lateral and plantar through the foot 45 º with the frontal and sagittal planes Slight (clinically insignificant) angle with the transverse plane Motion Nearly all motion occurs in the frontal and sagittal planes with clinically insignificant transverse plane motion With dorsiflexion - the first ray inverts With plantar flexion - the first ray everts Amount of dorsiflexion and plantar flexion is = to amount of inversion and eversion Biomechanics Page 5  Minimum ROM Unknown Gait During forefoot loading First ray must dorsiflex to remove excess stress from the sesamoids Contact period pronation First ray must dorsiflex to compensate for eversion of calcaneus Propulsion First ray must plantar flex to contact with the ground First ray must plantar flex to allow 60-75º dorsiflexion of the first MPJ Fifth Ray Very stable articulation Articulation Fifth metatarsal with the cuboid Axis Very closely mirrors the subtalar joint axis Therefore motion around the subtalar joint greatly affects motion around the fifth ray axis 2 Midtarsal Joint Consists of two joints which function together about two common axis of motion ○ Talo-navicular Joint ○ Calcaneo - cuboid Joint (most stable in the foot) Axis - Each axis is a supination/pronation (triplanar) general joint Both axis pass obliquely through the foot in an anterior, medial and dorsal direction The two axis allow the forefoot to develop large ranges of motion in each body plane Biomechanics Page 6  Longitudinal 15º from the transverse plane Midtarsal 9º from the sagittal plane Joint (LMTJ) Motion is primarily in the frontal plane Primarily allows for inversion and eversion of the forefoot as supination and pronation of the LMTJ occurs -- Forefoot can compensate from eversion of the rearfoot Very small amounts of abduction and adduction, dorsiflexion and plantar flexion occur about the LMTJ. Clinically not visible Minimum ROM is 4-6º Allows for compensation to occur for subtalar joint pronation Oblique 52º from the transverse plane Midtarsal 57º from the sagittal plane Joint (OMTJ) Allows for major amounts of adduction and abduction as well as dorsiflexion and plantar flexion to occur with supination and pronation of the forefoot around the OMTJ The amount of inversion and eversion is insignificant Pronation = dorsiflexion + abduction Supination = plantarflexion + adduction Here no transverse plane motion can occur without sagittal plane motion and vice versa This allows the forefoot to LOCK on the rearfoot during forefoot landing with both the heel and the forefoot are in contact with the Single axis model ground ○ Mean axis that allows for Minimum ROM - unknown midtarsal joint motion ○ Motion occurring around this MTJ axis consists of the navicular and the cuboid moving with the calcaneus relative to the talus Motions Pronation and supination Subtalar Joint Biomechanics Page 7  Motions Pronation and supination Subtalar Joint Movement is mostly in the frontal and One common axis of motion transverse planes with less in the sagittal Articulations Inferior surface of the talus and plane the superior surface of the Minimum ROM = 4-6º inversion of the calcaneus calcaneus. (with supination of the STJ) Three articulations at the Minimum ROM = 4-6º eversion of the calcaneus anterior, middle and (with pronation of the STJ) posterior facets Total ROM = 8-12º of frontal plane motion is required at the subtalar joint for normal Axis Passes obliquely through the locomotion subtalar joint Passes FROM the lateral, plantar Neutral The position of the subtalar joint when twice as and posterior aspect of the heel much inversion of the calcaneus as eversion of the forward TOWARDS the anterior, calcaneus can be obtained dorsal and medial aspects Midline between 42º from the transverse plane ○ 20º inversion and 10º eversion 16º from the sagittal plane Technically the position of the subtalar joint when 48º from the frontal plane it is neither pronated or supinated Lower Limb/Transverse Plane Contact Subtalar Joint pronates Period Tibia internally rotates, but farther and faster than the femur Thigh internally rotates Knee internally rotates Midstance Subtalar Joint supinates and Tibia externally rotates Propulsive Thigh externally rotates Periods Just prior to toe off the tibia externally rotates faster than the thigh causing the knee to externally rotate Ankle Joint Biomechanics Page 8 Ankle Joint Articulations Consists of the trochlea of the talus and its articulations with the distal tibia and fibula Trochlea of the talus is slightly wider anteriorly than posteriorly Trochlea of the talus is also slightly curved so that the concavity is medial Axis Passes medial to lateral From: lateral, plantar and posterior To: medial, dorsal and anterior Motion Primary motion is sagittal plane dorsiflexion and plantarflexion Some abduction occurs with dorsiflexion (transverse plane motion) Some adduction occurs with plantarflexion (transverse plane motion) Minimum ROM for normal locomotion 10º dorsiflexion - required when knee extends just prior to heel lift in STANCE phase 20º plantar flexion (for 1st MPJ dorsiflexion during propulsion) - needed for toe off and propulsion Knee Joint Hip Motion Motions Sagittal plane motion during stance phase of Motion Hip extends during the contact and gait midstance periods Flexion during the contact period Hip flexes early in propulsion and Extension from the beginning of continues to flex through the propulsive midstance period until immediately prior period to heel lift Transverse plane motion Flexion again just prior to propulsion and Thigh internally rotates through the through propulsion contact period Transverse plane motion Thigh externally rotates through the Internally rotates during the contact midstance and propulsive periods period The thigh and the pelvis are rotating Externally rotates during the midstance the same direction but the thigh and propulsive periods moves quicker Upper Trunk Motions Opposite the direction of the pelvis When the pelvis internally rotates, the trunk on the same side externally rotates When the pelvis externally rotates, the upper trunk on the same side internally rotates NOTE: when the talus internally rotates with the leg, the calcaneus everts and when the talus externally rotates with the leg, the calcaneus inverts Biomechanics Page 9 Mechanical Advantage and Levers Resistance (R): force acting at its application Lever system: bones are the levers which are rotated about point having a vector in the opposite direction an axis by means of muscles and external forces of the effort ○ A way to transmit energy Resistance Arm (RA): moment arm for ○ Energy derived from muscular contraction is resistance - distance from the axis of rotation transmitted by the bones to move body segments to the resistance vector Lever: a rigid bar that revolves around an axis or a fulcrum Mechanical Advantage ○ Three types: first, second and third class ○ Positive: when the effort arm is greater Point of application of effort: point at which contracting than the resistance arm muscle is attached to the moving bones  Magnifies force Effort (E): force acting at its point of application  Ex: second class lever represented by a vector - vector is always the muscle.  EA > RA Effort Arm (EA): movement arm for the effort - distance ○ Negative: when the resistance arm is from the axis of rotation to the point of muscle attachment greater than the effort arm Point of acceleration of resistance: Center of gravity of the  Magnifies speed mass of the lever. Can change with weight (mass) of  Ex: first class lever and third class external object applied to lever changes levers ○ Curling 15 pounds vs. 100 pounds  RA > EA Lever Types ○ Type 3 is most common in the foot. Sometimes it is more like class 1 (usually) and sometimes it is more like class 2 Type 1 Type 2 Type3 Articular Stability Newton's Laws of Motion Vectors: represented by arrows indicating direction of a ○ 1st Law: the net moment acting on the mass vector and the length of the arrow indicates the magnitude is equal to the moment of inertia times the of the force. angular acceleration ○ Acceleration is also considered a vector.  INERTIA: tendency of something to ○ Vectors have magnitude and direction remain at rest ○ Vector Polygon: when all vectors are on the same plan  Moment Vectors: (magnitudes of ○ Net force: the resultant vector sum of the forces that forces) x (lever arm) act upon a given mass ○ 2nd Law: F=MA Linear motion: the vector representing the motion is in one  Foot generally has no acceleration direction when in contact with the ground Axial force: the vector representing force along one axis or  Only times of acceleration are initial are linear in nature (rotational forces) contact or final propulsion off of the Rotational Motion ground ○ Example: weight on the end of a rope traveling in a □ Making accelerations negligible circle.  Net force is near zero  Tension exerts a force ○ 3rd Law: To every action there is an equal  Velocity of the mass has direction and opposite reaction Biomechanics Page 10  Small amounts of force can result in osseous Skeletal Stability instability. These forces are restricted by muscle Bone in static stance is in near balance which the bones tension on the bone. Two forces act on weight move slowly and slightly bearing bones. ○ Forces compress the bones against each other at ○ Compression force: pushing bones together the joints - Compression = GOOD! ENHANCES osseous STABILITY ○ Tension of the ligaments resists motion at weight ○ Rotational force: rotating bone abnormally bearing joints against its axis of motion ENHANCES ○ Because equilibrium is not perfect, motion occurs INSTABILITY stretching the ligaments Angulation Forces Static positions - last for less than 1 minute ○ When angulation of forces at a joint is small, ○ Requires momentary muscle contraction to re- compression is usually achieved. establish osseous position and relieve tension on  Supinated foot - decreased angulation the ligaments of forces, increased stability Abnormal motion occurs whenever a joint moves ○ When angulation is large, less joint excessively or in any direction outside the normal plane compression achieved and more rotational of motion force is seen creating instability ○ Any motion in a direction outside its normal plane  Pronated foot (flat foot): increases of motion causes instability and is called angulation of forces- decreases hypermobility stability ○ Hypermobility causes momentary subluxation of a ○ Muscle activity helps keep angulation of joint forces low, increasing stability Subluxation: state of partial dislocation - joint margins  If angulation of forces increases, compress on one side and separate on the opposite side muscles must work harder to maintain ○ Causes trauma to the joint and results in stability functional adaptation or degenerative joint  Decreases overall efficiency of gait and disease causes muscle imbalance Biomechanics Page 11  Static Stance Definition ○ A state of bipedal support of body weight during which all bones of the foot remain nearly motionless ○ Ends with any significant movement of the bones of the foot ○ Usually brief - interrupted by muscle contractions that relieve fatigue Distribution of Body Weight ○ Supported by each foot equally where each foot has a Base of support specific distribution of weight throughout that foot ○ Because of the forces described, the between forefoot and rearfoot majority of body weight is supported by ○ 1/4 of body weight supported by each forefoot (met the feet anterior to the ankle joint, so heads) the base of the support is made up of:  The first metatarsal head supports 2 parts of the  Lateral margins of both feet total weight of the forefoot  Posterior margins of both feet  Each lesser metatarsals supports 1 part each of  The metatarsophalangeal joints of the total weight on the forefoot both feet  2:1:1:1:1 relationship  The toes do not bear weight ○ 1/4 of body weight supported by each heel without muscle function Static Stance - Conditions ○ 1/2 of body weight supported by the bones of the ○ Legs and the sagittal bisection of the midfoot (arches) ○ Axis of Loading: Loading axis must extend between the calcaneus are perpendicular to the center of the trochlea of the talus and the second ground and parallel to each other ○ The subtalar joints of both feet are in intermetatarsal space for normal distribution neutral. Heel bisection perpendicular to  If you shift the axis medially the first and second metatarsals bear more than 50% of the weight the ground ○ The midtarsal joints are locked in their (Abducted forefoot would cause this) fully pronated positions - forefoot is  If you shift the axis laterally the lateral metatarsal perpendicular to heel bisection head will bear more of the weight (adducted ○ The plantar surface of the forefoot rests forefoot would cause this) Gastrocnemius upon the ground fully, all met heads ○ In order for the forefoot to bear 1/4 of the total weight bear weight, and the forefoot is placed on the foot, the gastrocnemius must fire perpendicular to a vertical bisection of the heel ○ This places tension on the Achilles tendon which places ○ No muscle support is needed to keep a plantarflexory force on the foot causing the metatarsal structural integrity heads to bear weight ○ Force exerted by the Achilles tendon must EXCEED the ○ Contraction of the gastrocnemius muscle force of the load on the tibia before the forefoot will exerts a plantar flexion moment force at the ankle joint, loading the forefoot bear weight Biomechanics Page 12 Dynamic Gait Ligaments ○ Emergency stability needed when a Bones sudden unanticipated motion of one or ○ Bones of the foot are moving while they bear weight more joints occurs - muscle provides ○ Can also occur if the center of weight is outside the normal little initial resistance base of support during static stance ○ Sudden motion beyond the full range of ○ Loss of postural equilibrium causes foot and bone motion, or outside the normal planes of movement as compensation for position occurs. motion, or both ○ 2nd Law of Motion - F=ma ○ Subluxation of a joint starts tension in  The faster a person walks or the heavier that person the ligaments and joint capsule of the is the greater the forces acting on the joints of the involved joint foot during gait ○ As ligaments lengthen -- resistance to ○ All forces at work during dynamic gait: the emergency rotational forces  Ground reactive forces interacting with the force of increases mass, acceleration and muscle tension at the joints ○ Stretch on ligaments and capsule of the foot. stimulates proprioceptors which through  2 components of force interacting at a joint are reflex cause muscle contraction of □ Compression (linear) = stability muscles that stabilize the joint - causing □ Bending (tension) = Instability stabilization  Foot function normally during stance phase achieves ○ Functions during emergency instability joint stability by bone compression, muscle  Decelerate motion of subluxing contraction but LITTLE/NO ligament tension joint (ligaments do NOT play a role in stability during  Increased contraction of muscles dynamic gait) responsible for stabilizing joint Muscles  Keep joint integrity intact until ○ Phasic Activity: muscles undergo contraction at certain muscle function reestablishes the periods of the gait cycle to exert their actions and resists joint rotation movements at joints and ground reactive forces. ○ Ligament failure ○ Example  Ligament Sprain - small tear (Strain  Pronated foot has increase in instability and increase = stretched fibers) in rotational motion. The angle of forces that interact  Ligament Rupture across a joint also increase  Avulsion Fracture  Muscle needs to work harder (phasic activity is  Joint damage due to compression interrupted) of articular surfaces  Opposite for a supinated foot - too stable  Total joint dislocation Kinetic Instability during Locomotion Causes internal tissue damage which Why we use orthotic devices eventually manifests in external symptoms - Primary cause of mechanical trauma to the foot corns, calluses, neuromas ○ Hypermobility = abnormal motion of the bone caused by Subluxation also results in ligament strain, un-resisted forces at a time when the joint should be muscle fatigue, joint deformities stable ○ Hallux abducto valgus, hammer toes,  Most common to have hypermobility during the hallux limitus propulsive phase when the foot should be stable ○ Young feet - subluxation can lead to ○ Subluxation = partial dislocation of a joint resulting in abnormal bone structure since juvenile hypermobility bone is adaptable Abnormal shifting of weight bearing bones in the hypermobile ○ Adult feet - subluxation can result in foot results in excessive shearing forces between bones and degenerative joint disease such as surrounding soft tissues which are fixed against shoe gear traumatic arthritis due to adult bone being slow to adapt Biomechanics Page 13 Compensatory function of the foot Compensation - change of structure, position, or function of one part in an attempt by the body to adjust to a deviation of structure, position, or function of another part ○ Normal compensation  Motion in which the foot moves to adjust for irregularities of the supporting terrain or deviations in the position of any part of the trunk or lower extremities  Necessary to maintain postural equilibrium  Accomplished by the subtalar and midtarsal joints ○ Abnormal compensation  Motion in which the foot moves to adjust for abnormal structure of function of the trunk and lower extremity  Structural or positional abnormalities can create a recurrent or persistent demand for compensation that may result in pathology  Accomplished by pronation or supination of the subtalar or midtarsal joint or both  Subtalar joint - primary joint for compensation because of the triplane motion  Midtarsal joint - secondary joint for compensation because of the triplane motion  Compensation will only occur in one plane, but it will cause abnormal motion in the other two body planes □ Pronatory compensation and supinatory compensation - describe direction Normal Compensation Midtarsal for rearfoot - STJ pronation ○ Compensation for subtalar pronation (rearfoot Subtalar joint eversion) = forefoot inversion (supination of the ○ Pronation = eversion of the rearfoot LMTJ) (calcaneus) ○ Must have the same number of degrees of forefoot ○ Supination = inversion of the rearfoot inversion as rearfoot eversion for compensation to (calcaneus) occur ○ As the STJ moves, the forefoot ○ If the forefoot cannot invert the same number of attempts to remain in contact with degrees as the rearfoot everts then the rearfoot is the ground - which is dependent on only partially compensated motion available at the midtarsal ○ Result - 1st ray dorsiflexes (inverts), MTJ unlocks, joint foot bears weight primarily on 2nd metatarsal head ○ "The calcaneus is the window to the Midtarsal for Rearfoot - STJ supination subtalar joint" ○ Forefoot cannot compensate for rearfoot supination Midtarsal Joint ○ Osseous restraining mechanism of the MTJ prevents ○ Midtarsal joint locks on the rearfoot eversion of the forefoot on the rearfoot when the when both the longitudinal and STJ is supinated oblique axis are maximally pronate  Allows locking mechanism of midtarsal joint  Locking primarily occurs during during midstance midstance  Involves the calcaneo-cuboid joint laterally ○ So ROM and locking position of the ○ As the calcaneus inverts with STJ supination, the MT are factors that determine the forefoot also inverts MTJ's ability to compensate fore ○ The MTJ axis are loaded and maximally pronated rearfoot position thus locked - no more forefoot motion can occur Biomechanics Page 14  Midtarsal for terrain ○ When terrain beneath the foot is tilted so the foot is inverted  If angle of tilt does not exceed amount of inversion available at the forefoot then forefoot only compensates. NO rearfoot involvement  If angle of tilt exceeds the amount of inversion available at the forefoot, then the rearfoot inverts the extra degrees required for compensation ○ When the terrain beneath the forefoot is tilted so that the forefoot is everted - the forefoot and rearfoot will evert together  Because MTJ is locked on the rearfoot due to lateral pressure, they will move together to compensate  However, because with STJ pronation, we will free some eversion of the forefoot and the forefoot ends up everting slightly more than the rearfoot Subtalar joint for terrain ○ A sudden demand for subtalar supination can result in instability leading to equilibrium loss and possible lateral instability  "I've fallen and I can't get up syndrome" ○ Demand for subtalar joint eversion follows the example given for the midtarsal joint compensation involving STJ eversion Abnormal Compensation Compensation at the MTJ or STJ to an abnormal structural or positional deviation in the lower extremity The deviation causing compensation is constant causing a persistent abnormal compensation of the foot Usually one or both of the following ○ Abnormal locomotor function of the foot ○ Abnormal position of the foot or part of the foot Pathologies Forefoot Varus (fixed Structural Compensation seen is STJ inversion) inversion of pronation through the forefoot midstance and on the propulsion (should be rearfoot when supination) the MTJ is Result: instability so locked muscles will fire and (maximally become ineffective - pronated) fatigue - hypermobility - subluxaton - pathology Biomechanics Page 15  Rearfoot Varus Rearfoot Compensation seen is STJ neutral STJ pronation during position is midstance to equalize inverted ground reactive forces across the plantar heel (STJ should be supinated) Forefoot Supinatus Soft tissue contracture causing forefoot to be inverted on the Compensation results in rearfoot supination of the LMTJ Usually caused by influence of tight gastro/soleus complex and its creating osseous effects on the foot instability of the forefoot Note: Equinus - usually will have forefoot supinatus Rigid Plantar Flexed The first Compensation results in First Ray metatarsal is supination of the STJ during structurally contact period (should be a plantarflexed pronating) Result - muscle imbalance and lateral instability Torque When forces produce a turning effect, this is also observed as a moment Torque develops between the ground and the foot during the stance phase of gait At heel strike, the leg is internally rotating Friction from the ground stops the foot so it cannot internally rotate with the tibia, so STJ pronation occurs instead STJ motion results from the torque that develops as the leg internally rotates on a foot which cannot rotate STJ is a torque converter Forefoot contact with the ground prevents rotation of the foot STJ pronation decreases torque but internal torque develops between the ground and the sole of the foot This initial internal torque peaks at early contact period as the forefoot loads Torque is virtually eliminated at the end of the contact period As the leg externally rotates at the start of the midstance period, internal torque again begins to develop Second torque reaches a peak at a point just prior to heel lift. This peak is larger than the first peak Forces Biomechanics Page 16 Forces Ground Reactive Forces: All motion of the foot produces forces against the ground, with the ground responding ( 3rd Law) Vertical  Foot supports body weight as the center of gravity of the body passes in linear progression above the foot Forces  NOT constant during the stance phase of gait  Contact phase of gait - center of gravity starts behind the foot and forces increase as the center of gravity progresses forward  Two peaks of center of gravity □ End of contact period - 1st peak - when body weight is supported by one foot. Heel and metatarsals are loaded -- Results from elevation of center of body weight as it is lifted over the weight bearing limb Ground reactive forces greater than body weight □ Midway through Propulsion - 2nd peak - all weight is being supported by the ball of one foot From kinetic energy from the falling trunk and muscle function that elevates the heel and provides a push to the center of gravity during propulsion ("what goes up must come down")  If abnormal foot, then trauma from instability or compensation is common Shear  Shear Force - occurs when stress causes one part to slide over another because of a blow or other significant Forces impact □ Occurs at two points during the stance phase of gait (contact and propulsion - mirrors vertical)  Posterior Heel strike causes posterior shearing which results from the moving foot suddenly being stopped by friction from the ground as contact is made Imparts a posterior shear force to the soft tissue of the heel Calcaneus slides anterior relative to the leg All this causes shear between bone and soft tissue as heel continues to move forward - also shear between shear and the ground The thicker the soft tissue the better able it is to distribute and absorb posterior shear forces If soft tissue is thin- may lead to soft tissue trauma  Anterior Caused by heel lift and the push off of propulsion. This imparts a linear acceleration of the center of gravity of the trunk in a forward direction Friction from the ground prevents posterior movement of the foot and an anterior shear is developed against the ball of the foot Reaches its peak at the moment when the opposite foot makes contact with the ground Soft tissue will be displaced anteriorly to the metatarsal heads Fat pad under the ball of the foot is important to disperse shear developed in propulsion Wasting or further anterior displacement of the fat pad makes dispersion of shear forces difficult. Result = soft tissue trauma, hemorrhage, fibrosis, and hyperkeratotic lesions, even ulceration Biomechanics Page 17 Shear Abnormal Shear Forces Lateral Shear ○ NOTE: two primary factors in stability are osseous structure and ○ Produced by side to side muscle activity -- muscle resists abnormal motion of bone motion of the trunk ○ Two primary causes of abnormal shearing between bones and soft ○ Peaks at the end of contact tissue period and peaks again during  Abnormal subtalar joint pronation propulsion □ If the STJ is pronated during propulsion, this allows for ○ Clinically insignificant excessive osseous motion which can lead to soft tissue ○ Primary caused by body trauma weight shifting from one  Hypermobility of weight bearing bones weight bearing foot to the □ Soft tissue is fixed against shoe gear. Any shear other between bone and soft tissue will cause soft tissue trauma Columns Lateral Column ○ Primarily the 4th and 5th metatarsals (cuboid maybe) Medial Column ○ Primary role: balance ○ Primarily the cuneiform, 1st, 2nd, and  Forefoot everts, calcaneus also everts to adapt to 3rd metatarsals terrain -- this motion maintains balance ○ Primary role: shock absorption and ○ Small range of motion which ensures the calcaneus and terrain adaptation - MOBILE ADAPTER lateral column move together for adaption to terrain ○ First ray dorsiflexes during contact and  Also ensures that the forefoot will remain locked on midstance to compensate for STJ the rearfoot due to OMTJ axis pronation pronation to alleviate stress on the ○ Contact and Midstance sesamoids  Medial = mobile ○ Large range of motion to compensate  Lateral = stable and adapt ○ Propulsion ○ Normally can dorsiflex as much as the  Medial = more stable calcaneus during subtalar joint pronation  Lateral = less stable Planal Dominance If an axis of a joint is deviated to become more perpendicular to a certain body plane, then motion in that plane will be the dominant motion ○ Transverse Plane - adduction, abduction ○ Frontal Plane - eversion, inversion ○ Sagittal Plane - dorsiflexion, plantar flexion Vertical OMTJ Axis If the OMTJ axis is deviated so that it is more vertically oriented, then the axis is more perpendicular to the transverse plane (closer to 90º) Planal dominance will then be seen in the transverse plane Result = more adduction and abduction of the forefoot on the rearfoot with pronation and supination of the OMTJ Normal 52º from the transverse plane 57º from the sagittal plane Biomechanics Page 18 STJ Axis IF the STJ axis is more vertically oriented, it is then more perpendicular to the transverse plane Result = more transverse plane motion Problem - for the STJ to convert torque from the leg rotation, you need frontal plane motion at the STJ Shear forces prevent abduction/adduction of the foot on the ground So ankle, knee, and hip will compensate for this deviation of axis Normal 42º from the transverse plane 16º from the sagittal plane 48º from the frontal plane STJ Axis If the STJ axis is deviated more horizontally then it is more perpendicular to the frontal plane Result = more frontal plane motion Increase inversion/eversion at the STJ BUT - more angulation is now possible between the bones at joints Increases instability, hypermobility and subluxation seen with STJ pronation Compensation and pathology will be seen STJ Axis If the STJ axis is deviated in the transverse plane Medially = greater pronation will occur Laterally = greater supination will occur Lateral Ankle Ligaments Provide emergency stability for ankle in response to subtalar inversion, preventing subluxation ○ Anterior Talo-fibular Ligament, Calcaneo- fibular ligament and Posterior Talo-fibular Ligament Short lateral column or forefoot valgus (eversion of the forefoot to rearfoot with STJ in neutral) can result in lateral instability ○ Forefoot valgus Biomechanics Page 19  Plantar Fascia Structure: Abductor Hallucis M., Abductor Digiti Minimi M., and plantar aponeurosis ○ Medial, Lateral and central bands of the plantar fascia. All attach to the plantar process of the calcaneus Windlass Mechanism ○ When we dorsiflex the digits, especially the hallux we see  Increase in height of the medial arch as medial slip tightens (plantarflexes the first metatarsal)  Shortening of the medial column  Inversion of the calcaneus due to tightening of the plantar fascia ○ Makes the plantar fascia a passive supinator of the STJ ○ No energy is expended by the mechanism to cause supination ○ One reason for continued supination into propulsion Locking Position of the Midtarsal Joint Elftman Two components of the Root Presented when the STJ is held in neutral position and -- NOT midtarsal joint (Talo-navicular pronation of midtarsal joint stops (load lateral column) widely and Calcaneo-cuboid) each Normal - forefoot plantar surface and rearfoot plantar held have two axis. Total of 4 axis surface as parallel today In pronation the T-N1 axis is Another way of describing this would be the plantar surface in line with the C-C1 axis of the forefoot is perpendicular to a vertical bisection of the resulting in an unlocked calcaneus midtarsal joint Midtarsal = maximally prone and STJ = neutral In supination each of the four Huson Midtarsal joint actually consists of the navicular and cuboid axis contribute movement to rotating around the talus along with the calcaneus align the foot and lock it at any given point during Nester and MTJ relate the navicular and cuboid move as a single unit. supination Findlow No matter what motion is occurring there is only a single axis of motion at all times Ontogenic Dysfunction Forefoot Varus Congenital resulting from retention of varus torsion of the talar head and neck (inverted) Uncompensated - No subtalar eversion to equalize ground forces on the forefoot. Excessive weight born on the LATERAL forefoot Partially Compensated - Some subtalar eversion but not enough to completely equalize ground reactive forces on the forefoot Compensated - Enough subtalar eversion to equalize ground forces of the forefoot. Pronation into propulsion Primary compensation site - STJ Forefoot Valgus Congenital resulting from excessive valgus torsion of the head and neck of the talus Biomechanics Page 20 Forefoot Valgus Congenital resulting from excessive valgus torsion of the head and neck of the talus relative to the body of the talus Can compensate at the midtarsal joint by dorsiflexing the first ray or at the STJ but supinating the STJ or both If MTJ - we may see lesion sub 2 If STJ - we see lesions sub 1 and/or 5 Equinus Foot cannot dorsiflex the 10º needed at midstance in relation to the tibia. Can be muscular or osseous Will see pronation at heel contact with equinus (should be supination) Commonly see patient walk with knee flexed to relieve tension on the gastrocnemius muscle Commonly also see early heel off in midstance - may be due to tight gastrocnemius or tight medial/lateral hamstrings Plantar flexed First Ray Plane of met heads 1 and 5 everted to the rearfoot. First ray plantar flexed in relation to met heads 2-5 May be due to contracture state of the Fibularis (peroneus) longus or tight medial slips of the plantar fascia Compensation is STJ supination Lesions commonly seen under 1 and 5 Abnormal STJ Loading Medial Loading - caused by external forces (widened base of gait for heavy lifting) Forces increased toward pronating STJ Obesity - increase force at center of mass (body weight) more medial toward pronation of the STJ Tibial valgus or heel valgus - eversion of the bone putting increased forces medial to the STJ and pronation of the STJ ("knock-kneed") Lateral Loading - STJ varus - forces directed laterally due to inverted nature of calcaneus Foot STJ pronates to get rest of foot to the ground Forefoot Valgus or plantarflexed first ray will direct forces laterally Oblique Toe Break MPJ Axis ○ The axis of motion for the lesser MPJs is the same as the first met.  Vertical and horizontal axis allowing sagittal and transverse plane motion ○ MPJs need ~ 62º +/- 10º of dorsiflexion of the lesser digits on the lesser metatarsal heads ○ 62º +/- 10º plantarflexion for metatarsals on the proximal phalanx ○ Need less motion of the lesser MPJs because lesser metatarsal heads and digits lift off the ground before the hallux ○ Because the line of the lesser MPJ's (2-5) is an oblique line this results in an oblique toe break when the digits dorsiflex during propulsion Biomechanics Page 21 Axis High Gear ○ A transverse axis made up of met heads 1 and 2 ○ Operates for high speed motion or propulsion, sprinting Low Gear ○ Oblique axis mad up of a line from met heads 2-5 ○ Operates for low speed power - uphill climb, carrying heavy loads Initially in propulsion we are low gear and shift medially to high gear for propulsion Autosupport Truss - supports a structure, braces it and makes it rigid Beam - resists bending ○ Causes internal compress (GOOD!) ○ Ends are not secure - foot can elongate during ○ Ends are secure - foot cannot elongate because contact and midstance of the ground, osseous structure and phasic ○ Foot at contact becomes a beam allowing for muscle activity, plus the windlass mechanism motion at joints to adapt to terrain without result in a rigid lever for efficient propulsion bending the foot abnormally Material Mechanics Deformation - the strain is a degree of deformation as a result of a load Loads ○ Elastic - based on its ability to return to its ○ Compression - force pushing a material more original shape after a load has been applied tightly together  Rubber band  Axis of loading through bones more parallel ○ Plastic - measure of how much the material to each other, more compression at joints deforms and remains deformed after a stress is  Supination of the STJ allows for piling up of applied -- Play-dough tarsal bones resulting in greater Young's Modulus compression at the joints of the foot  Supination increases height of medial arch in ○ ⎯⎯⎯⎯⎯= measure of elasticity the sagittal plane and increases transverse ○ Stress refers here to the amount of force per arch of the lesser tarsus - increases stability unit area of collision ○ Tension - stress on a material or structure ○ Strain is the amount of distortion (deformation) produced by pull of forces causing separation or with respect to original size extension Hook's Law  Tension on ligaments is what starts the ○ As stress increases - so does strain emergency action of ligaments (proportionately) ○ Shear - the stress on a material or structure ○ Applies to solids - not all body tissues follow this causing one material or structure to slide over law another material or structure Yield Point  Tends to cause ripping or tearing ○ Point where the load on a material causes the Stress - force generated in the substance of a material in material to submit or lose resistance to the load response to load -- Compression, Tension and Shear ○ Can cause the material to deform in response to Strain - the degree of deformation of matter as a result that load of the load on it -- Compression, Tension and Shear Failure Point ○ The ability of a structure to resist strain is ○ The point when a material in response to a load dependent on its elasticity, resilience, toughness deforms to the point when it no longer (resistance to fracture on impact) and reaction to performs its normal function damping (deformation to a degree - opposite of ○ Material may fail by deforming a great deal or reliance) more often, by fracturing Biomechanics Page 22 Bone Loading Anisotropic - Not having the same properties the Tension same in all directions ○ Bones are next resistant to tensile forces or loads ○ The forces of the loads are not in the same ○ Bones can fracture or fail under tensile force direction and are not of the same intensity ○ Example ○ Different loads are directed on the same bones  Pencil - bend it - fails on the tension side  Compression, tension, shear first Compression  Femur - 10,000-20,000 PSI ○ Bones are MOST resistant to compression Shear forces or loads ○ Bones are LEAST resistant to shear forces or ○ Bones are least likely to yield or fail under loads compression ○ Most fractures of throwing arms are due to shear ○ Example due to torque  Femur - 20,000-30,000 PSI ○ Example - Femur - 400 PSI Swing Phase Begins: toe off of the same foot Ends: heel contact of the same foot Normal gait - occupies the final 38% of the gait cycle Primary events ○ Transportation of the foot - transporting the foot from one stance phase to the next while maintaining forward momentum ○ Limb length adjustments  Shortening - during the first half of the swing phase the foot pronates at the STJ shortening the limb to help the foot clear the ground  Lengthening - during the last half of the sing phase the foot supinates at the STJ lengthening the limb to prepare for heel contact and shock absorption ○ Internal limb rotation  The swing phase limb is externally rotating for a moment after toe off but switches to internal rotation for the remainder of the swing phase  Note - this is open chain internal rotation… closed chain internal rotation causes different motions □ Open chain internal rotation - STJ can supinate □ Closed chain internal rotation - STJ pronates due to rotation + ground reactive forces ○ Subtalar joint pronation  The STJ is briefly and quickly pronated before toe off and into swing phase.  The majority of swing phase, the STJ is supinated ○ Ankle joint dorsiflexion  Slight dorsiflexion of the foot at the STJ accompanies ankle joint dorsiflexion to get the toes to clear the ground Biomechanics Page 23 Combined Forces Wolff's Law - structure/function ○ Interdependence between form and function Column ○ Bone is able to re-orient itself through a process of ○ Direct (concentric) Loading: straight down the rearrangement of its trabeculae and lamellae center system in response to mechanical tension and stress  Mostly causes compression co the Electrical Current column can bear more load ○ Bone responds by forming and resorbing bone in ○ Eccentric (excentric) Loading: Peripheral response to stress and electrical current loading ○ Positive current - Results in bone resorption, convex  Can cause shearing or tension resulting in stress or tension on bone will result in bone the column having a decreased ability to resorption support the weight or force ○ Negative current - Results in osteogenesis in bone, Beam - foot is a beam during midstance - ends are concave stress of compression on bone will cause not secure to help resist bending new bone formation ○ Dorsal load applied to a beam from dorsal to Compression sites get stronger, tension sites get weaker - plantar - the force passing through the beam very slow process will cause compression dorsally and tension plantarly Contact Phase ○ Adaption to surface terrain  STJ pronation cause the foot to become Begins: at heel contact a mobile adapter allowing the forefoot Ends: with full forefoot loading/toe off of the opposite foot to adjust easily to changes in surface Occupies 27% of the stance phase of gait terrain Primary events ○ Internal limb rotation ○ Subtalar Joint pronation  Leg is internally rotating causing the STJ  In normal gait, pronation of the STJ should ONLY to pronate allowing the STJ to be a occur during the contact period torque converter (internal rotation to  Open chain STJ pronation = dorsiflexion, eversion, frontal plane motion) abduction  Causes a decrease in shear forces  Closed chain STJ pronation ○ Hip extension □ Talus = abduction and plantarflexion  At the beginning of the contact period (abduction due to internal leg rotation) the hip is flexed but switches to □ Calcaneus = eversion (only motion possible extension as the contact phase due to the ground) continues  Progression of movements ○ Knee flexion □ Internal leg rotation causes the talus to abduct □ Abduction of the talus causes calcaneal  Flexion of the knee occurs during the eversion contact period and the action is □ Eversion of the calcaneus moves the calcaneus primarily a shock absorber out of the way and the talus plantarflexes ○ Ankle joint plantarflexion ○ Shock absorption  The ankle is plantarflexed from heel strike to forefoot contact during the  STJ pronation causes a reduction of shock through the leg and foot contact period  STJ pronation turns the foot into a mobile adapter to  The ankle was dorsiflexed just prior to dissipate shock contact and will also dorsiflex between forefoot contact and actual forefoot  The majority of the shock absorbed is at the knee where it is flexing during the contact period loading as the body moves forward on the foot Peaking vertical forces Midtarsal joint Biomechanics Page 24 ○ Peaking vertical forces ○ Midtarsal joint  Vertical ground reactive forces and  Forefoot is influenced by muscle activity until the forefoot shear forces peak just before the end of touches the ground when ground reactive forces take over the contact period. Due to:  At heel strike □ Knee extension to push the body □ Forefoot is supinated about the LMTJ axis due to the weight up and over the stance Anterior Tibialis M. limb □ Forefoot is pronated about the OMTJ axis due to the □ Toe off of the opposite limb Extensor Digitorum Longus M. and Peroneus Tertius causing full forefoot loading M. ○ Double limb support □ Heel is inverted as well  Contact period is a double limb support □ Mid tarsal joint is not fully locked allowing for mobile period with both limbs in contact with adaption the ground ○ Loading of forefoot ○ Center of gravity  Pronation of the OMTJ axis locks the forefoot partly so it is  Provide motion that gives the body prepared to bear weight linear acceleration □ The head of the 5th metatarsal is the first to contact □ Transverse plane - transverse the ground rotations of the trunk and skeletal  Ground reactive forces and the Tibialis Anterior M. relaxing portions in alternate transverse allows smooth loading from lateral to medial rotations about alternating weight  Because the calcaneus is everting (STJ pronation) and bearing limbs results in linear directing more of the body weight medially, the medial body movement column begins to dorsiflex as compensation for calcaneal □ Sagittal Plane - shifts the center of eversion -- supination of the LMTJ gravity anterior to the center of □ As the forefoot loads, the forefoot is pronated at the foot support. Like a controlled fall OMTJ and supinated about the LMTJ during the forward contact period Biomechanics Page 25