Week 7 Elbow biomechanics

Humero-ulnar joint

-largest, strongest joint at elbow

-between trochlea of humerus and trochlear notch of ulna

-limited movement

Humero-radial joint

Humeral Capitulum and Radial Head, No joint Motion

Humero-ulnar provides

stability from tight fit between trochlea and trochlear notch

Humero-radial joint provides stability between connection of

radial head and capitulum

During flexion-extension there is a near lateral axis of rotation through the

radial head and capitulum

Medial capitulum extends a bit more which causes

carrying angle

Carrying angle of the elbow

The angle formed by the long axis of the humerus and ulna, resulting in an abducted position of the forearm relative to the humerus.

Normal cubitus Valgus angle of the Elbow

13º

who was greater carrying angles

women

1 multiple choice option

Carrying angle increases with

age and dominant arm

Excessive Cubitus Valgus

20-25 degrees

Excessive Cubitus Valgus can cause

ulnar nerve damage

2 multiple choice options

cubitus varus

angulation of the elbow positioning the forearm closer to the body (medial)

Elbow ligaments

ulnar collateral ligament

radial collateral ligament complex

annular ligament

Articular capsule surrounds

Humero-ulnar and humero-radial joints

Proximal Radio-ulnar joint

Lowest intracapsular pressure occurs at

80° of elbow flexion

position of comfort of the elbow

80 degrees of flexion

open packed position of the humero-ulnar joint

70 degrees flexion, 10 degrees supination

Intra-articular inclusions

Fat pads, fibroadipose meniscoids, connective tissue rims

If rims hypertrophy they can get

pinched in joint lines

Ligaments give multiplanar stability to the elbow but primarily in the

frontal plane

MCL of the elbow aka

Ulnar collateral ligament

Anterior fibers of the MCL

-Strongest, stiffest ligament

Resists valgus/abduction

Anterior fibers of the MCL resists

valgus/abduction

Anterior fibers of the MCL connection

Medial epicondyle to coronoid process

Anterior fibers of the MCL are taut when

throughout the ROM

Anterior fibers of the MCL stabilize

sagittal plane movements

Posterior MCL fibers

thickening posterior capsule

resist valgus and extreme flexion

Posterior MCL fibers connect

Medial epicondyle to olecranon

Posterior MCL fibers resist

valgus forves

Posterior MCL fibers taut in

flexion

Transverse MCL fibers

do not cross joint

no load or limitation of movement

Transverse MCL fibers connection

Olecranon to coronoid process

static stabilizer of the Elbow

MCL

Elbow dynamic stabilizers

Muscles crossing joint (Aconeus, triceps, bicep, brachialis) and on lateral side ( EDC, ECRL/B) and on medial side (FCU, FDS, pronator, FCR) and Proprioception

LCL consists of

annular lig, RCL, accessory collateral lig, LUCL

LCL resists

varus forces

LCL is taut in

full flexion

RCL blends with

annular ligament, supinator and ECRB muscles

LUCL attaches to

supinator crest

LUCL Job

Guywire for the elbow because of attachment to ulna with anterior MCL fibers

LUCL sling supports

radial head to prevent excessive ER of the proximal forearm relative to the humerus.

If the LUCL ruptures, it results in...

posterior lateral rotary instability (PLRI)

Elbow flexion functional movements

pulling, eating, grooming, lifting, telephone

elbow extension functional movements

Throwing, pushing and reaching activities

Elbow flexion functional ROM

30-130º

Humero-ulnar joint Open chain flexion

concave ulna rolls and slides anteriorly

Humero-ulnar joint Open chain extension

concave ulna rolls and slides posteriorly

Humero-ulnar joint FIXED chain extension

Convex humerus rolls posterior and slides anterior

Humero-ulnar joint FIXED chain flexion

Convex humerus rolls anterior and slides posterior

Elbow close packed position

extended and supinated

Humero-radial open chain flexion arthrokinematics

concave Radial head rolls and slides anteriorly

Humero-radial open chain extension arthrokinematics

radial head rolls and slides posteriorly

Humero-radial closed chain flexion arthrokinematics

Convex humerus rolls anterior and slides posterior

Humero-radial closed chain extension arthrokinematics

humerus rolls posterior and slides anterior

Humero-radial joint: Pronation/supination

Radial head spins under the capitulum

Forearm AoR runs through

longitudinally radius

Pronator teres line of pull compresses

the radial head against the capitulum during PRO/SUP

screw home mechanism of the elbow

natural proximal migration of the radius and associated increased joint compression of the humeroradial joint during active pronation

Most susceptible to degeneration than any other joints of the elbow

humero-radial joint

forearm joints

proximal radioulnar joint and distal radioulnar joint

Central band between the radius and ulna

Interosseous membrane

Interosseous membrane central band runs

radius to ulna at 20° angle

IM central band has the same tensile strength as

patellar tendon

Im is the attachment site for

extrinsic muscles of the forearm

Proximal force transmitter

IM

80% of compression force that crosses the wrist through

Radiocarpal joint

Radiocarpal joint

pertaining to the joint between the radius and wrist

High likelihood of fractures of Radius through

FOOSH

20% of compression on the wrist through the

ulnocarpal joint

As radius gets pushed up it

pulls fibers taut and transfers force to the ulna and cross through the Humeral-ulnar joint

Tears of the Interosseous membrane result in a

proximal drift of the radius

proximal drift of the radius can cause what

degeneration of the humero-radial joint

Distraction slacken the

IM

distraction forces go through the

radius

Muscles such as the brachioradialis keep

radius against capitulum

Full supination

radius and ulna are parallel

full pronation

radius crosses over ulna

Axis of the forearm

runs from radial head→ulnar head

Pronation and supination allow rotation of the independent hand without

rotation of the ulna or humerus

PRUJ

Radial head in radial notch of the ulna

Pruj function

Fibroosseus ring of annular ligament

75% of PRUJ

Annular ligament

25% of PRUJ

radial notch of the ulna

DRUJ

Convex ulnar head, concave radial ulnar notch, articular disc

TFCC aka

articular disc

Anterior and posterior aspects of the discs are continuous

with the capsular ligaments

Primary stabilizer of the DRUJ

TFCC

Tears of the TFCC result in

dislocation, instability, limited/painful pronation, supination, and motions at the wrist, RA

Other structures that stabilize the DRUJ

Pronator quadratus, tendon of the ECU, distal oblique fibers of the IM

Normal Translation of the DRUJ

.25 inch

Supination functional activities

eating, drinking, shaving

pronation functional activities

coin grab, chair, typing on keyboard

Supination and pronation functional arc

100º 50/50 of both

pronation deficits results

Shoulder IR and abduction

supination deficits

Shoulder ER and adduction

Both pronation and supination require movement at the

DRUJ and PRUJ and a spin movement at the humeroradial joint

PRUJ Tissues limiting supination

-Pronator teres

-FCR

-Extrinsic finger flexors

PRUJ supination arthrokinematics

Radial head spins around ulna in the annular ligament

DRUJ Tissues limiting supination

-Pronator quadratus

-TFCC

-Interosseous membrane