Kinesiology; Elbow and Forearm Biomechanics principles (Done)

Synergist Muscle Function

-Anterior deltoid stabilizes shoulder in slight flexion, allows long head of triceps to lengthen across shoulder and exert max torque at the elbow towards extension. -Posterior deltoid acts as important synergist with biceps with lifting activities: allows biceps to lengthen across shoulder during activation.

Efficient Use of Muscles

-Biceps recruited primarily During high power activities *note activity of triceps, EPL, and supinator. -Body automatically recruits supinator only for low power task to conserve energy. -Biceps PCSA 3x that of supinator. -Triceps stabilizes elbow, and ulna in particular during high power tasks with elbow in flexion

Biceps VS. Supinator

-Biceps very effective as supinator at 90 degrees of flexion -Tendon has greatest moment arm -Biceps becomes less of supinator with elbow in extension -Less active with low power supination activities -Supinator activity not influenced by elbow angle - is relentless supinator

Internal MA of Biceps and Triceps

-Both produce maximum torque with elbow at 90 degrees of flexion. -Largest internal MA's different: -Biceps: 90 degrees. -Triceps: near full extension. -Muscle length, not leverage, very influential in determining where in the range max muscle torque occurs in the triceps

Muscles that move the Elbow

-Brachioradialis. -Biceps. -Brachialis. -Pronator teres/quadratus. -Triceps. -Anconeus. -Supinator

C5-6 Quadriplegia

-Clients use concentric contraction of biceps and brachialis, and brachioradialis to help "push up" body. -Distal segment must be fixed in order for them to do this. -Also rely on latissimus dorsi, serratus anterior, deltoid, pectoralis major, trapezius, rhomboids to stabilize shoulder

Interosseous Membrane: Compression Forces

-Compression force through hand transmitted through radius and interosseous membrane. -Orientation of IOM fibers transfers load to ulna and causes it to migrate proximally....more load goes to trochlea, less to capitulum and radial head.

The Elbow

-Creates working relationship between shoulder and forearm. -Open and closed chain functions

The triceps

-Elbow extensor. -Due to attachment on ulna, it does not contribute to forearm pronation or supination *unlike its antagonist the biceps. -Major stabilizer of elbow in closed chain activities. -Also contributes to control of forearm and hand to counteract force of gravity

Closed Kinematic Chain Motion at the Elbow

-Elbow must be in FULL extension in order for the body to rely on joint for stability. -Slight flexion........Body has to rely on flexors and extensors that cross the elbow joint for stability. -Elbow "middle of chain"...if unstable, function compromised

Triceps and quadriplegia continued

-FLEXION CONTRACTORS OF ELBOW VERY DETRIMENTAL TO FUNCTION!! -Must prevent this to ensure this client population can rely on passive elbow extension for independence with transfers and weight shifts.

IOM with Distraction Forces

-IOM not aligned to resist distally applied forces. -Distraction force tightens annular ligament and slackens interosseous membrane. -Forces transmitted primarily through radius. -Brachioradialis can help disperse load through radius and humerus. -Carry load across shoulder to reduce forces on annular ligament

Moment Arms and Function

-In general, elbow flexors generate the most torque (moment) in flexion. -Biceps peak force output at 100 degrees of flexion. -Brachialis 80 degrees of flexion. -Brachioradialis 110-120 degrees of flexion. -This position demands maximum torque of muscles as result of large external moment created by gravity on FA *in sitting or standing positions

Triceps and quadriplegia

-Individuals with C6 quadriplegia lack triceps *C7-C8.* -Elbow extension maintained passively by locking elbow in extension *weight bearing force.* -Pull of pectoralis major places shoulder and wrist anterior to axis of elbow. -Creates posterior line of force at elbow by adducting and internally rotating humerus. -This places humerus over elbow and locks it in place

Elbow joint capsule

-Lax at about 80 degrees flexion. -Position of comfort in presence of joint effusion/swelling.

Proximal radioulnar joint

-Lies within capsule of joint. -Pivot joint. -side of head of radius articulates with radial notch of ulna. -ANNULAR LIGAMENT: forms ring around head of radius. -Radial head rotates within this ligament. -Shallow cup of radial head pivots/spins on capitulum.

Elbow Flexor Moment Arms

-MAs vary considerably throughout elbow motion. -Brachialis: optimal at 90-100 degrees flexion. -Biceps: optimal at 90-100 degrees flexion. -Brachioradialis: Large MA with FA in neutral, smaller with FA in pronator/supination

Axis of rotation/Carrying angle

-More distal trochlea creates carrying angle: Ulna deviates laterally from humerus. -Axis of rotation goes through lateral epicondyle.

Ulna

-Olecranon process: "tip of elbow" trochlear notch. -"Cubital tunnel" area between olecranon and medial epicondyle contains ulnar nerve, articulates with trochlea of humerus.

Biceps vs. Supinator continued

-REST FOREARM IN LAP. -Palpate biceps tendon. 1. Slow with no resistance to supination -----Supinator main mover. 2. Resist supination (rapid) - biceps tendon increases tension markedly. -This is used to determine if supinator innervated after radial nerve injury. -If supinator weak/inactive, biceps tendon becomes pronounced with slow active supination

Humeroradial Articulation

-Radial head. -Capitulum of humerus. -Radial head only articulates on very small portion of capitulum with elbow extension. -Capitulum oriented anteriorly. -Contact increases with elbow flexion. -Forearm rotation also changes joint surface contact.

The biceps

-Shoulder flexion. -Elbow flexion. -Supination. -Biceps inactive when elbow and shoulder in flexion with forearm in pronation *due to active insufficiency. -In supination, acts as flexor and supinator. -Posterior deltoid acts as important synergist muscle with lifting activities: allows biceps to lengthen across shoulder during activation

Proximal radioulnar joint continued...

-Slight lateral and medial glides noted with forearm rotation. -Provides little stability to elbow "joint". -Annular ligament helps prevent inferior dislocation of radial head during distraction loads. -Closed packed = full supination or pronation.

Supination vs. Pronation

-Supination 25% greater torque than pronators. -Related to functional demands. -Using screwdriver with right hand: threads oriented to favor supination.

Synergist Muscle Function continued

-Triceps and pronator teres: triceps stabilizes elbow during high power pronation tasks. -Pronator teres would try and flex elbow otherwise. -Biceps and triceps: triceps stabilizes elbow *long head the shoulder also* during high power supination tasks. -Biceps would flex elbow otherwise, and possibly flex shoulder

Humeroulnar Articulation

-Trochlear notch of ulna. -Trochlea of humerus. -Note area of non articulating joint surface. -Close packed=full extension

Arthrokinematics

-Very little translator movement noted with elbow flexion and extension.

Fall on outstretched hand *FOOSH*

-With elbow in extension, FA in pronation = radial head fracture with possible ulna dislocation. -IOM disrupted; transfers load to proximal radius. -Elbow extension/FA supination: MCL rupture with possible radial head fracture

Ulnohumeral Joint

-With stable humerus, ulna rolls and slides anteriorly in flexion, rolls and slides posteriorly with extension.

The brachioradialis

-Works best with forearm in mid position. -Moment arm larger with more elbow flexion = muscle has more leverage. -Is also a FA rotator: FA in full pronation; brings FA back to neutral, FA in supination; brings FA back to neutral

Supinator

1 joint muscle; -Only muscle that supinates FA with elbow in extension

Brachialis

1 joint muscle; Powerhouse muscle for elbow flexion: only pure flexor (intricate part of anterior joint capsule)

Brachioradialis

1 joint muscle;Long fibers/small cross section area

Biceps

2 Joint muscle; Most effective with forearm in supination secondary to position of distal biceps tendon as elbow flexor

Open Packed Positions; Ulnohumeral

70 degrees elbow flexion, 10 degrees supination.

Open Packed Positions; Radioulnar (PRUJ)

70 degrees flexion, 35 degrees supination/pronation

Closed Packed Positions of the Elbow;Radio-humeral joint

80 degrees elbow flexion and 5 degrees supination.

Distal Humerus

Capitulum, trochlea, olecranon fossa. Epicondyles: Lateral-extensor muscle attachment site. Medial: flexor muscle attachment site.

Interosseous Membrane: Compression Forces continued

Closed chain tasks: 90% of weight bearing force transmitted through radius IOM fibers tighten and transfer load to proximal ulna

Elbow flexion

Elbow flexion strength decreases considerably with forearm in pronation (renders biceps essentially inactive. -Muscle torques 20-25% greater with FA in supination *biceps and brachioradialis have larger MA with elbow in flexion and FA in supination.* -Overcoming large loads recruits all flexors, regardless of FA position

Moment Arms and Function continued

Elbow flexors generate 70% more torque than elbow extensors Similar in LE: quadriceps generate more torque than hamstrings across knee ....related to function of muscle groups *having to work against gravity frequently during functional movements*

Closed chain

Elbow stable or in fixed position; allows force to be transmitted to hand or shoulder

Proximal Radioulnar joint (PRUJ)

Forearm rotation: Radial head spins on capitulum and glides slightly medial with pronation, lateral with supination.

Closed packed positions of the Elbow;Ulnar-humeral joint

Full elbow extension

Closed packed positions of the elbow; PRUJ

Full pronation or supination

Lateral collateral ligament

Important stabilizer of humeroradial joint with varus stress.

Supination

Less contact

Pronation

More contact

Forearm Rotators

Muscles that rotate forearm MUST: -Attach on both sides of the axis of rotation. -Produce an internal moment arm around the axis of rotation for pronation and supination. -MA greatest if line of force perpendicular to axis of rotation...no pronator or supinator has this "perfect" arrangement; pronator quadratus is close. -FA rotation closely tied to shoulder internal and external rotation: sup/ER, pro/IR

Head of radius

Point just distal to lateral epicondyle. -Articulates with capitulum

Closed Packed Positions of the Elbow

Position of stability differs in joints of elbow

Open chain

Positioning hand; Considerable loss of reaching function with loss of elbow extension

Pronator teres/quadratus

Quadratus powerful pronator, Pronator theres active against high load at 60 degrees elbow flexion.

Radiohumeral joint

Radial head glides and rolls in same direction as radius *anterior with flexion, posterior with extension*.

Anconeous

Short, small muscle. Contributes to elbow extension and stability

Elbow joint

Uniaxial. Hinge. -Good joint congruity overall. -Favors stability. -Strong structurally secondary to ligaments and joint structure. -Radiohumeral and ulnohumeral joints differ in positions of stability (closed packed)

Open Packed Positions; Radiohumeral

full elbow extension with full supination

Triceps

long head: 2 joint muscle. -Strongest muscle crossing elbow: peak ext torque at 90 degrees of elbow flexion