K and B unit 01

The study of movement & the active & passive structures involved

Biomechanics – evaluates the motion of a living organism and the effects of force, internal or external, on the organism

Kinetics – Describes the effect of forces

Kinematics – describes motion without respect to forces

• Manual muscle testing
• Evaluation of mechanics of injury
• Therapeutic exercise prescription
• Joint mobilization
• Assessment of gait and posture

• Translatory - Movement along a straight pathway (unconstrained segment)
• Each point on the segment moves through the same distance at the same time
• Doesn’t occur in a pure sense in the body

• Rotary Motion - occurs around a fixed axis.
• Each point moves through the same angle at the same time.
• The human body rarely has a fixed axis and so an instantaneous axis of rotation is used to determine where the axis is during the range of motion of a joint

Curvilinear

Anatomic position - serves as our reference position

Fundamental - Same as Anatomic but hands face medially

Osteokinematics describes the motion of bones; typically around an axis or along an axis.

These motions occur in one of 3 Planes of motion

Axes of rotation with regard to planes of motion

• Mediolateral axis – Sagittal plane
• Anteroposterior axis – Frontal plane
• Vertical Axis – Horizontal plane

• Joint surface
• Tissue bulk
• Connective tissue
• Bony limitation

• Flexion/Extension
• Abduction/Adduction
• Rotation

• Protraction /Retraction of scapula
• Elevation /Depression of scapula
• Upward rotation / Downward rotation of scapula

• Circumduction
• Pronation / Supination (at ankle and subtalar joint)

• Roll - Movement in which points, at equal intervals, on a moving joint surface contact points on the opposing surface.
• Example: Ball rolling on the ground

• Glide - Movement in which a single contact point on the moving surface contacts numerous points on the opposing surface
• Example:Tires sliding on an icy road

• Spin - Rotation around a stationary mechanical axis
• Example:A top spinning or the stationary axel of a car

• Where spin occurs
• Forearm pronation/supination
• Shoulder flexion/extension
• Hip flexion/extension
• SC joint rotation

True

Because if only roll took placethe moving bone wouldtend to dislocate, and If only glide took place, the moving bone would tend to impinge and prevent full ROM.

• 1. Decide which direction the shaft of the bone is traveling
• -Roll is always in the direction of bone movement (distal aspect of shaft -

Example: If the tibia moves anterior then roll will also be anterior

2. Determine which joint surface is relatively fixed (stable) -

If the convex segment is fixed and the concave segment is movingRoll and Glide occur in SAME direction

-If the concave segment is fixed and the convex segment is movingRoll and Glide occur in the OPPOSITE direction

• Shoulder Abduction What direction is the upper arm traveling?
• Superior
• What bone is relatively fixed?
• Scapula

The fixed bone has what type of joint surface?

ConcaveWhat are the resulting arthrokinematics?Superior Roll and Inferior Glide (Roll / Glide Opposite)

Elbow Flexion What direction is the forearm traveling? Anterior

• What bone is relatively fixed? HumerusThe fixed bone has what type of joint surface?
• Convex
• What are the resulting arthrokinematics?

Anterior Roll and Anterior Glide (Roll / Glide Same)

The fit of the joint Can be

• Close-packed
• Open-packed

• Joints become maximally congruent
• Most ligaments and capsule are pulled taught
• Provides stability
• Arthrokinematic motions are very limited

• All other positions from close-packed position
• Ligaments and capsule
• slacken Allows for mobility

Force – a push or pull exerted by one object or substance on another

Internal and external

Point of application – Center of Mass (COM) or gravity (COG)

in the overall human body this point occurs around (COM) at S2 (2nd sacral vertebra)

true

Direction – line of gravity (LOG) is the direction of the force of gravity

Magnitude – determined by the distance from the center of the earth

Base of support (BOS) is the contact that the body has with the ground

Stability is determined by where the LOG falls in relationship to the BOS

hence a wider base of support or a lower center of gravity makes you more stable.

• External
• Gravity
• Bouyancy
• Air resistance
• Friction

• Internal
• Elasticity
• Muscle contraction

Inertia is the property of an object that resists both initiation and change in motion

Is proportional to its mass

Application – Walkers

Acceleration is proportional to the net unbalanced forces and inversely proportional to its mass

Acceleration is in the direction of the unbalanced force

Is related to the Law of Inertia based on mass

All forces come in pairs that are applied to contacting objects, are equal in magnitude and opposite in direction

Impact on PT is in things like Ground reaction force

When two or more forces act:on the joint of interest in the same plane and in the same line (if tails were extended would overlap)

Results of linear force systems

Traction/Distraction: net force moves a bony segment away from its adjacent bony segment

Compression: two segments are pushed together

Shear: a force that moves or attempts to move one object on another

Concurrent Force System

When two forces are applied to the same object are not collinear but intersect

Most forces acting on the body are concurrent

Graphically you can understand how forces interact with each other by using the parallelogram method

It is a graphical way to determine a resultant force vecotor. From two other forces.

Normal force – forces perpendicular to the bone shaft where the muscle attaches

May cause translation or rotation

Tangential force – forces acting parallel to the bone shaft where the muscle attaches

May occur as a compression or distraction within the joint

Force through the COM will cause translation

Force away from the COM with a fixed axis will cause rotation

Torque

Torque = Force x moment arm

Definition – A rigid segment that rotates around an axis, which produces torque

What’s NeededTwo forces – Load (L) and Effort (acts to move the lever in the opposite direction of the Load)

Two moment arms are associated with levers, may have different lengths

Axis

1st Class levers: Axis is in between the effort and load forces

Common Example: teeter totter

Uncommon in the human bodyExample – Atlanto-Occipital jt

Second Class Levers: load force is between the axis and the effort force

Common Example: Wheel barrow

Unusual in human bodyExample – Raising heels off of ground

Third class levers: effort force is between the axis and the load force

Examples: Shovel

• Most musculoskeletal levers in body are 3rd class
• Example – bicep curls

Open Chain – distal segment is free to move while the proximal segment is fixed

Closed Chain – proximal segment is free to move while the distal segment is fixed

Whenever the foot or hand is contacting an object, certain joints may NOT be in closed chain position

• Three types:
• Synarthrosis
• Amphiarthrosis
• Diarthrosis

Joint Material – Dense, irregular connective tissue

Available Motion – negligible

Examples – Interosseous membrane

Joint Material – hyaline cartilage or fibrocartilage

Available Motion – minimal

Examples – Intervertebral disk, pubic symphysis

Joint Material – true joint space filled with synovial fluid, surrounded by a capsule

Available Motion – extensive

Examples – will be listed on a different slide

RequiredSynovial fluid – provides nutrition to articular surface

Articular cartilage – allows for near frictionless movement

Articular capsuleCapsular ligaments

Not RequiredMenisci & Labra – increase stability (increase congruence), provide shock absorption, & facilitate motion

• Uniaxial – movement in one plane
• Hinge
• Pivot

• Biaxial – movement in two planes
• Condyloid
• Saddle

• Triaxial – movement in three planes Ball and socket
• Random - Plane

• Hinge: Humeroulnar joint
• Pivot: Proximal radioulnar
• Condyloid: Metacarpophalangeal
• Saddle: 1st Carpometacarpal joint
• Ball and socket: Glenohumeral
• Plane: Intercarpal joints

• Bone
• Compact
• Trabecular

• Dense
• Regular
• Irregular

• Cartilage
• Hyaline
• Fibrocartilage

• Cells
• Chondroblast - Found in cartilage
• Creates mostly Type II collagen

• Fibroblast - Found in tendon, ligament, and bone
• Creates mostly Type I collagen

• Osteoblast - Found in bone
• Creates mostly Type I collagen and hydroxyappatite

Extracellular Matrix (ECM) – Function of connective tissue is primarily determined by the ECM

• Two parts
• Interfibrillar
• Fibrillar

Glycoprotein – carbohydrate covalently bound to protein. They Fasten various components of the ECM together

Proteoglycans – similar to glycoproteins; differ in the number of carbohydrates attached. Distinguished by their protein core and their attached Glycosaminoglycans (GAG)

• Glycosaminoglycans (GAG) - Attract water through their GAGs.
• Proportion of GAGs determine how much water is contained in connective tissue

Regulate collagen fibril size

Are increased in tissues subjected to alternating cycles of compression

Collagen

Type I Collagen - Most common, it has a high tensile strength. Found in ligaments, tendons, fascia, and fibrous capsules.

Type II Collagen - Possess less tensile strength as type I. Helps maintain the general shape and consistency of structures. Found mainly hyaline cartilage and center of intervertebral disk

• ElastinHave more give when stretched. Readily return to their original shape after being deformed.
• Found in small quantities in load bearing tissues

Load: external force(s) applied to a structure

Deformation: caused by a force that acts upon a structure

• Tensile – pull apart
• Compressive – push together
• Torsional – twisting
• Shear – surfaces try to slide past each other
• Combination – bending; tensile and compression on opposite sides

Stress is a measure of load that is in an object

Equal to force / cross sectional area

Strain is a relative deformation (change in length, width, or shape) of a structure

Plotting the stress against the strain – gives information about the properties of the material.

Toe region - Slack of tissues is taken up

Elastic region - Slope of elastic region is referred to as Young’s Modulus or Modulus of Elasticity. Is a measure of the material’s stiffness. In the elastic region - Fibers are elongated and resist the force – influenced by the type of collagen, fibril size, and cross-linking between fibrils

Yield point - Marks the end of the elastic region and the start of the plastic region.

Plastic region - Permanent deformation after load is removed. Progressive failure as stress continues

Ultimate failure point

Early part of plastic range

At failure point

Materials where the stress-strain curve changes as a function of time

true

Creep - is a progressive strain of a material under a constant load over time.

Tendons or ligaments demonstrate creep through tensile loads.

Bone or cartilage demonstrate creep through compressive loads.

If the strain is held constant, the stress decreases with time.

Compact, Cortical or Lamellar

Trabecular, Spongy or Cancellous

Central Canal- runs parallel to bone, and contain nerves, veins, and arteries, around this is are the Lamella- Concentric layers of bone that surround central canal, each layer contains collagen fibers at a 45 degree angle and each layer runs opposite to the one beneath.

Within this is the Lacunae- small cavities between adjacent lamella. They are connected by canaliculi, which allow nutrients to pass through them.

Lamellae not arranged in concentric layers. Arranged in lines corresponding to where max stress is applied in the body

Can have more force applied before failure

Can elongate further before failure

• Compressive loading will cause hyptertrophy in trabecular bone
• Dependent on rate, frequency, duration, and magnitude microfractures can occur do to
• High repetitions with a low load
• Low repetitions with a high load

Collagen fibers are nearly parallel; when straightened not all fibers will be affected the same due to the nearly parallel arrangement.

Cross-sectional area, composition of the tendon, and the length of the tendon determine the amount of force that can be resisted.

Transition regions (muscle to tendon; tendon to bone) render tendons more susceptible to injury due to changes in composition.

In response to a tensile force, tendons have a moderate ↑ in thickness & strength

Are similar to tendons mechanically. The more variable collagen orientation make ligaments more able to function in a range of load directions without being damaged.

Handle tensile forces from multiple directions

Intermittent tension will cause an increase in thickness and strength to ligaments

In order for cartilage to withstand compressive forces it must have an intact collagen network and proteoglycan/GAG matrix.

The compressive load is supported by both the fluid components and solid components of cartilage Upon being loaded in compression, fluid will be “squeezed” out of the solid component region and with the removal of the load the fluid will enter via an osmotic gradient

Behavior to tensile stresses is similar to tendons and ligaments.

Resistance to shear stresses is dependent on the collagen present

Some level of loading or exercise is appears to be beneficial for cartilage – The magnitude or frequency is yet to be determined

Immobilization can be due to a inflammation, cast, bed rest, weightlessness, or denervation If immobilization is due to inflammation, a loose pack joint position will be assumed. Capsule, ligaments, tendon, and muscle will adapt to this position in as short as just a few weeks. Muscles develop contractures; ligaments and capsules will have one side lengthen and one side shorten

Effects on Ligaments and Tendon

Have a decrease in their collagen content and cross-linking, i.e. weaken

Can loose 50% of tensile strength in 8 weeks

Recovery may take over a year to regain strength

Graded reloading is necessary to restore tendon and ligament strength

Effects on Articular Surfaces and Bone

Cartilage will atrophy

Proteoglycan synthesis is decreased

Greater deformation when subjected to compressive loads

Bone can have a regional osteoporosis

Due to less collagen formed and an increase in bone resorption

• Decreased number and size of GAG molecules
• Fibers don’t align themselves as readily to imposed tensile forces
• Adhesions are more likely to form between connective tissue

• Sarcolemma: cell membrane
• Sarcoplasm: – contains myofilaments, which are composed of actin and myosin
• Non-contractile proteins:
• Contractile proteins: - Myosin, Actin

• Contractile proteins
• Contains a rod-like tail and two globular heads
• Hinge joints occur between the myosin head and tail
• ATPase activity: found on Myosin – referred to as the thick filament myosin heads

• The actin filament is made up of three separate protein molecules:
• Actin molecules (G-actin) form a twisted pearl strand, referred to as F-actin
• Tropomyosin hides the actin-myosin binding site Troponin has 3 isoforms

Structural proteinsC-protein – holds the myosin tails in correct spatial arrangement

Titin – links myosin (M-line) to Z-line

α-Actinin – attaches actin to Z-line

Z-line to Z-line; composed of two bands

BandsA-band: composed of myosin filaments and areas of overlap with actin fibers; lies at the center of the sarcomere

H-zone: lies in the middle of the A-band; contains only myosin tails

I-band: composed of actin filaments; part of two adjacent sarcomeres, bisected by Z-line

Action potential (AP) enters cell

Ca+2 is released in response to AP, which binds to troponin

Troponin moves tropomyosin to uncover the binding site for myosin

Binding of myosin to actin is referred to as a cross-bridge and is what is required for tension to develop in muscles

Endomysium – surrounds the muscle fiber

Perimysium – surrounds bundles of muscle fibers called a fascicle

Epimysium – surrounds the whole muscle

Two factors

Length of the muscle fibers

Size of the muscle’s moment arm

Joint range of motion (ROM) is determined by two properties.

• Sarcomeres in series.
• Muscle architecture

Muscle shortening is proportional to the length of the muscle fibers

Typically muscles can shorten to ~50% of its length

• There is a wide variety of muscle lengths in the human body
• Sartorius vs. Bicep brachii

Length of the muscle fibers is a function of the muscle architecture

• Fiber architecture can be divided into two main classifications
• Parallel
• Pennate

Parallel – muscle fibers are approximately parallel to the length of the whole muscle

Pennate – muscle fibers are oriented obliquely to the long axis of the muscle

Muscles with greater moment arms have to shorten more than muscles with smaller moment arms to achieve the same ROM for the same joint angle

• Muscle size
• Muscle moment arm
• Stretch
• Contraction velocity
• Muscle recruitment
• Fiber types

Anatomic cross-sectional area is a cross-section of the muscle at the widest part

Physiologic Cross- Sectional Area (PCSA) is the cross-sectional area of the muscle that is perpendicular to the orientation of the muscle fibers

A muscle with a greater moment arm will be able to produce greater torque around a joint than a muscle with a smaller moment arm if they contract with the same force

After 90°, the tangential component of the total muscle force produces a distraction force

There is a sarcomere length at which actin and myosin are optimally overlapped for cross-bridge formation, this is the resting length of the muscle

Changing the sarcomere width beyond the optimal length decreases the number of cross-bridges Active tension may still be developed, however, it is less due to fewer cross-bridges between actin and myosin

• CE = contractile elements
• PE = parallel elements
• SE = series elements

Passive Tension – tension developed in the parallel & series elastic components

Active Tension – the tension developed by cross-bridge formation

Passive Insufficiency - A muscle can’t stretch enough to achieve full range of motion at all joints it crosses

Occurs with multiarticulate muscles

Muscle is being moved by someone (i.e. therapist) or something else (i.e. antagonist muscle) – it takes a passive role in being lengthened

Active insufficiency – a muscle can’t develop full force due to the actin-myosin overlap, which decreases ROM for the distal joints the muscle crosses

Occurs with multiarticulate muscles

Muscle is causing the change in length or change in ROM – taking an active role

• Causes
• Decrease in cross-bridge formation
• Change in moment arm at different joints
• Passive tension of antagonist muscle

Types of Muscle Contraction

Isometric – tension is generated by myosin and actin binding but no movement occurs

Concentric – tension is generated; actin is pulled into the H-zone; shortening of the muscle occurs

Eccentric – tension is generated; actin is pulled away from the H-zone; lengthening of the muscle occurs

This is the relationship between velocity of contraction and force produced

When shortening contraction speed increases, force that can be produced decreases

When lengthening contraction speed increases, force that can be developed is able to increase to a certain point


In a dynamic contraction you have to consider both the velocity and the length of the muscle in order to determine force production

We don’t move with constant velocity so force changes with a change in velocity & change in length

A motor unit consists of an alpha motor neuron and all of the muscle fibers associated with that neuron

Size of a motor unit can vary from a few muscle fibers to 1000s of fibers

Fine control is provided by small motor units

Gross movement is provided by large motor units

Smaller motor units are recruited first

If additional force is required, larger motor units will be recruited

Partly due to energy conservationWhat does that mean?

More energy is expended when a large motor unit is recruited since is activates 1000s of muscle fibers

Type I - Don’t fatigue easily; often referred to as stability or postural muscles; force production is limited

Type IIa - Characteristics are between those of Type I and Type IIb

Type IIb - Fatigue easily; can generate tremendous amounts of force

Prime mover (agonist) – the muscle whose role is to produce a desired motion

Antagonist – opposes the movement of the agonist

Co-Contraction: provides stability


Synergist – assist the agonist to perform the desired motion. Can help produce the desired motionor. Can stabilize a segment to allow the agonist to produce the motion

• Flexor carpi radialis and ulnaris are agonists for wrist flexion;
• extensor digitorum is the antagonist;
• flexor digitorum is a synergist by helping produce wrist flexion

• Flexor digitorum profundus will cause wrist flexion
• so the extensor digitorum will act as a synergist and eliminate wrist flexion
• so the profundus can produce finger flexion

Muscle Spindle – within muscles; is sensitive to stretch and will contract the muscle in order to avoid injury

Golgi Tendon Organ – within tendons, is sensitive to tension, will cause relaxation of muscle in order to prevent injury

In shortened position -

• Decrease in number of sarcomeres
• Increase in connective tissue
• Muscle atrophy
• Prevention of the above effects need only ~30 minutes of daily ROM activities

In lengthened position

• Increase in the number of sarcomeres
• May have a decrease in strength

• Fiber number and fiber type changes
• Loss of muscle fibers
• Decrease in type II fibers Increase in type I fibers
• Connective tissue changes
• Increased connective tissue

??

• Sternoclavicular joint (SC jt)
• Acromioclavicular joint (AC jt)
• Scapulothoracic joint not a true physiologic joint
• Glenohumeral joint (GH jt)

• The SC joint has incongruent joint surfaces
• Joint Type: Saddle (2 physiologic DOF; 1 non-physiologic: rotation)

• Joint DiskShock Absorber
• Improves joint surface contact

• MotionElevation/Depression
• Arthrokinematics: Roll/Glide opposite

• Protraction/Retraction
• Arthrokinematics: Roll/Glide same

• Rotation
• Arthrokinematics: Spin

• Articular disc
• Anterior SC ligament Restricts retraction
• Posterior SC ligament Restricts protraction
• Interclavicular ligament Restricts depression

• Costoclavicular ligament
• Restricts: ElevationProtraction, Retraction

Muscle: Sternocleidomastoid, sternohyoid, sternothyroid – stretched in depression

Depression can cause a pinching of nerves & arteries

Joint Type: Plane: has 3 DOF

Joint Disk: May only be partial disk

Degeneration is common

Motion: Helps fine tune the position of the scapula after motions have occurred at the SC joint

• Motion: Upward Rotation/Downward Rotation
• Plane: Frontal

Winging - Plane: Horizontal

Tipping - Plane: Sagittal

Stabilizing tissues

Articular disc

Superior AC ligament - Restricts downward rotation

Inferior AC ligament - Restricts upward rotation

Coracoclavicular ligament - Restricts upward rotation

Muscles: Deltoid & Trapezius – surround the joint

Interface between scapula and thorax

• Position
• Superior angle = rib 2, inferior angle = rib 7

Medial border = ~2 inches from spinous processes

Bony connections: SC and AC joints

???

• Elevation/Depression
• Protraction/Retraction
• Upward / Downward Rotation

• Joint type – Ball and Socket
• Position
• Glenoid fossa: Lateral
• Slightly anteriorSuperior

• Humeral head:
• Medial
• Posterior
• superior

Stabilizing tissue

Glenoid labrum – increases the joint congruency

Rotator cuff muscles – dynamic stabilizers, attach to the capsule

Biceps brachii – long head – blends with the superior capsule

Capsular ligaments:

Superior restricts: Adduction, External rotation

Middle restricts: external rotation horizontal abduction

• Inferior – has three bands
• Anterior restricts: Abduction, External rotation
• Axillary pouch restricts: abduction
• Posterior restricts: Abduction, Internal rotation

• Adequate size of the glenoid fossa
• Humeral head retroversion
• Intact capsule and labrum
• Shoulder girdle muscle control

• Gravity
• Superior capsule
• Coracohumeral ligament
• Passive tension of supraspinatus

Resultant force pulls the head of the humerus into the glenoid fossa


Deltoid contracts creates rotation and superior translation

Supraspinatus Produces a compressive force

Infraspinatus, Teres Minor, Subscapularis - Produce an inferior translation to counteract the superior translation of the deltoid contraction

• Flexion / Extension
• Arthrokinematics: Spin (both open & closed chain)
• Inferior / Posterior glide

• Abduction / Adduction
• Arthrokinematics: Roll / Glide Opposite (open chain)

• External / Internal rotation
• Arthrokinematics: Roll / Glide Opposite (open chain)

• Horizontal Adduction / Horizontal Abduction
• Arthrokinematics: Roll / Glide Opposite (open chain)

Combination of GH and STJ for abduction and flexion

Is a 2:1 ratio of movement between GH and STJ

Scapula has 60° upward rotation

GH contributes 120° of elevation, even if scapula is fixed

Total ROM is 180°

Assists in maintaining proper length tension relationships

Distributes motion between two joints

Maintains glenoid fossa in an optimal position

Early

• 0 – 90° arm elevation
• 60° GH abduction

30° upward rotation

• SC joint 20-25° elevation
• AC joint 5-10° upward rotation

• Late
• 90 – 180° arm elevation
• 60° GH abduction
• GH external rotation 30° STJ upward rotation
• SC joint 5° elevation
• AC joint 20 - 25° upward rotation
• Posterior clavicular rotation

• Trapezius
• Upper - Elevation, Retraction, Upward rotation

Tightness – elevation of shoulder girdle or asymmetrical head position

• Middle - Retraction
• Lower - Depression, Retraction

Weakness – due to chronic scapular elevation or reciprocal inhibition

Serratus Anterior- Protraction, Upward rotation

Weakness – winging

• Levator Scapula & Rhomboids
• ElevationRetraction
• Downward rotation

Tightness: in the levator scapula may cause headaches

• Pectoralis Minor
• Protraction
• Downward rotation
• Depression
• Anterior Tilt (Tip)

• Deltoid - Anterior
• Flexion
• Internal rotation
• Abduction
• Horizontal adduction

• Middle
• Abduction
• Posterior
• Extension
• External rotation
• Abduction
• Horizontal abduction

• Pectoralis Major
• Sternal head - Flexion, Extension (from 180 flexed position), Adduction, Internal rotation, Horizontal adduction

Clavicular head - Flexion, Internal rotation

Latissimus Dorsi - Extension, Adduction, Internal rotation, Shoulder depression

Teres Major - Internal rotation, Extension, Adduction

Coracobrachialis - Flexion, Adduction

Biceps Brachii – Long head - Flexion

Triceps Brachii – Long head - Extension, Adduction

Supraspinatus - Abduction

Weakness – significant abduction weakness and loss of endurance with abduction

Teres Minor - External rotation

Infraspinatus - External rotation

Subscapularis - Internal rotation, Flexion, Adduction, Horizontal adduction

Weakness – may contribute to anterior instability of the shoulder

Trapezius and Serratus Anterior form a force couple for upward rotation - Serratus pulls from the bottom while the upper trapezius pulls from the topIf one of the muscles becomes paralyzed but the other muscle is intact; ROM is affected

Flexion - With serratus anterior paralysis (trapezius intact): result is weak, partial ROM. Only 130°. With trapezius paralysis (serratus anterior intact): result is weak, full ROM. Unopposed retraction of trapezius only allows the scapula to upwardly rotate 1/3 of the normal motion.




Abduction - With serratus anterior paralysis (trapezius intact): result is weak, full ROMWith trapezius paralysis (serratus anterior intact): result is weak, partial ROM. Only 75°. Without the trapezius the scapula rests in a downward rotated position

Hinge

Carrying Angle - is the angle of the forearm in relation to the body.

• Valgus = distal part is abducted
• Varus = distal part is adducted

– Roll / Glide Same (open chain)

Roll / glide opposite (closed chain)

Articular capsule covers humeroulnar, humeroradial, and proximal radioulnar joints

Posterior-lateral = Varus force

Anterior-medial = Valgus force

• Annular ligament – surrounds radial head and
• Prevents dislocation of radial head (Nursemaid’s elbow)

Radiohumeral joint – will resist valgus forces

• Medial collateral ligament
• Anterior fibers
• Resists Valgus
• Resists Extension

• Posterior fibers
• Resists Valgus
• Resists Flexion

• Lateral collateral ligament
• Ulnar component - resists -Varus and Flexion

Radial component - resists - Varus