elbow biomechanics and Pathomechanics.pptx

Biomechanics and
Pathomechanics of Elbow Joint
- kaustubh maktedar 1st MPT

Ligaments of the Elbow
• Medial (ulnar) collateral ligament :
• The medial collateral ligament
complex consists of bundles of
fibers that may be differentiated
into anterior, posterior, and
transverse portions.
• Function :
• Providing medial support to the
elbow against valgus stress.
• Limiting end range elbow
extension.

Lateral (radial) collateral ligament :
• The lateral collateral ligament
complex, a fan-shaped ligament on
the lateral surface of the elbow, is
composed of the lateral collateral
ligament, the lateral ulnar collateral
ligament, and the annular ligament.
• Function :
This complex provides stability to the
lateral aspect of the elbow against varus
and supination forces, stabilizes the
humeroradial joint, resists longitudinal
distraction, and prevents posterior
translation of the radial head.

Humeroulnar Articulation
Characteristics :
The humeroulnar (HU) articulation is a modified
hinge joint. The primary motions at this
articulation are flexion and extension.
Arthokinematics : During flexion/extension the
concave fossa slides in the same direction in
which the ulna moves, so with elbow flexion, the
fossa slides around the trochlea in an anterior
and distal direction. With elbow extension, the
fossa slides in a posterior and proximal direction.

Humeroradial Articulation
• Characteristics : The humeroradial (HR) articulation
is a hinge-pivot joint. The laterally placed, spherical
capitulum at the distal end of the humerus is
convex. The concave boney partner, the head of
the radius, is at the proximal end of the radius.
Flexion/extension and pronation/supination occur
at this articulation.
• Arthrokinematics :
• As the elbow flexes and extends, the concave
radial head slides in the same direction as the bone
motion, so with elbow flexion, the concave head
slides anteriorly, and with elbow extension, it slides
posteriorly. With pronation and supination of the
forearm, the radial head spins on the capitulum.

Proximal ( superior ) Radioulnar Articulation
Characteristics : The convex rim of the radial head
articulates with the concave radial notch on the ulna
and the annular ligament. This ligament encircles the
rim of the radial head and stabilizes it against the
ulna. The primary motion is pronation/ supination.
Arthrokinematics : As the forearm rotates into
pronation and supination, the convex rim of the
radial head slides opposite the bone motion, so with
pronation, the head slides posteriorly (dorsally) on
the radial notch, and with supination, it slides
anteriorly (volarly). It also slides in the annular
ligament, and the proximal surface spins on the
Capitulum.

• Elbow flexion and extension take place at the humeroulnar and
humeroradial articulation.
• The normal range of flexion-extension is from 0° to 146° with a functional
range of 30° to 130°.
• The normal range of forearm pronation-supination averages from 71° of
pronation to 81° of supination.
• Most activities are accomplished within the functional range of 50°
pronation to 50° supination
ROM

Long Axes of the Humerus and Forearm
When the upper extremity is in the anatomical position (shoulder in
external rotation, elbow in extension and fully supinated), the long axis
of the humerus and the long axis of the forearm form an acute angle
medially when they meet at the elbow. The angulation in the frontal
plane is caused by the configuration of the articulating surfaces at the
humeroulnar joint. The medial aspect of the trochlea extends more
distally than does the lateral aspect, which shifts the medial aspect of
the ulna trochlear notch more distally and results in a lateral deviation
(or valgus angulation) of the ulna in relation to the humerus. This
normal valgus angulation is called the carrying angle or cubitus valgus

• The angle is less in children
as compared to adults and
greater in females as
compared to males,
averaging 10° and l3° of
valgus.

Elbow Flexion
• Biceps brachii. The biceps is a two-joint
muscle that crosses both the shoulder and
elbow and inserts close to the axis of
motion on the radius, so it also acts as a
supinator of the forearm.
• It functions most effectively as a flexor of
the elbow between 80° and 100° of flexion.
• For the optimal length-tension relationship,
the shoulder extends to lengthen the
muscle when it contracts forcefully for
elbow and forearm function

• If, sufficient elbow and shoulder
flexion occur together, the biceps
brachii may be so shortened that it
can generate little force. This is known
as active insufficiency.
• In contrast, shoulder extension
lengthens the biceps brachii and
increases the biceps contractile force
during elbow flexion.

Clinical Relevance
• Clinicians affect a patient’s elbow flexion
strength by varying the position of the elbow
or shoulder joint.
• shoulder hyperextension is a useful position
in which to exercise a patient with weakness
of the biceps brachii, since the resulting
muscle stretch enhances the muscle’s force
output.

Brachialis :
• The brachialis is a one-joint muscle that
inserts close to the axis of motion on the
ulna, so it is unaffected by the position of
the forearm or the shoulder; it participates
in all flexion activities of the elbow.

Brachioradialis :
• With its insertion a great distance
from the elbow on the distal radius,
the brachioradialis mainly functions
to provide stability to the joint.
• The brachioradialis contributes to
pronation and supination only as an
accessory muscle when resistance is
provided to the motion.
• Innervation : Radial nerve.

Torque
• Two forces that are equal in magnitude, opposite in direction,
parallel, and applied to the same object at different points are known
as a force couple. A force couple will always produce pure rotary
motion of an object (if there are no other forces on the object).
• The strength of rotation produced by a force couple is known as
torque (τ), or moment of force, and is a product of the magnitude of
one of the forces and the shortest distance (which always will be the
perpendicular distance) between the forces:
• τ = (F)(d)

Moment Arm
• The moment arm for any force vector will always be the length of a
line that is perpendicular to the force vector and intersects the joint
axis (presuming a two-dimensional perspective). In other words, the
moment arm will always be the shortest distance between a force
vector and the axis of rotation.
• The length of the moment arm is directly related to the angle of
application of the force on the segment. The angle of application of
a vector is the angle made by the intersection of the force vector
and the segment to which it applied, on the side of the joint axis
under consideration.
• The moment arms are maximal when the force is applied
perpendicular to the segment and at their minimum when the
forces lie closest to being parallel to the segment.

• Brachialis :
• Its moment arm (MA) is greatest at
slightly more than 100° of elbow
flexion, at which point its ability to
produce torque is greatest.
• Because the brachialis is inserted on
the ulna, it is unaffected by changes
in the forearm position brought
about by rotation of the radius. Being
a one-joint muscle, it is not affected
by the position of the shoulder.

• The moment arm of the biceps is largest between 80° and 100°of
elbow flexion, and therefore the biceps is capable of producing its
greatest torque in this range.
• The functioning of the biceps is affected by the position of the
shoulder because both heads of the muscle cross both the shoulder
and the elbow. If full flexion of the elbow is attempted with the
shoulder in full flexion, especially when the forearm is supinated, the
muscle’s ability to generate torque is diminished

• Brachioradialis :
• The brachioradialis is inserted at a
distance from the joint axis, and
therefore the largest component of
muscle force goes toward compression
of the joint surfaces and hence toward
stability.
• The peak moment arm for the
brachioradialis occurs between 100°
and 120° of elbow flexion. The
brachioradialis does not cross the
shoulder and therefore is unaffected
by the position of the shoulder.

• According to the length–tension
relationship, a muscle’s ability to produce
force improves as the muscle is
lengthened and diminishes as the muscle
is shortened. Thus when the elbow is
extended, the elbow flexors are
lengthened, facilitating force production.
• However, in the extended position, the
moment arms for the flexors are quite
small thereby decreasing the muscles’
capacity to generate a torque. Thus the
effect of elbow joint position on the length
of the elbow flexors is quite different from
its effect on muscle moment arm.

Classes Of Lever
• A lever is any rigid segment that rotates around a fulcrum.
• In a lever system, the force that is producing the resultant torque (the
force acting in the direction of rotation) is called the effort force (EF).
Because the other force must be creating an opposing torque, it is
known as the resistance force (RF).
• The moment arm for the effort force is referred to as the effort arm
(EA), whereas the moment arm for the resistance force is referred to
as the resistance arm (RA).

• A first-class lever is a lever system in which the
axis lies somewhere between the point of
application of the effort force and the point of
application of the resistance force.
• A second-class lever is a lever system in which
the resistance force has a point of application
between the axis and the point of application of
the effort force, which always results in the effort
arm being larger than the resistance arm.
• A third-class lever is a lever system in which the
effort force has a point of application between
the axis and the point of application of the
resistance force, which always results in the
resistance arm being larger than the effort arm.

Mechanical Advantage
• Mechanical advantage (M Ad) is a measure of the mechanical
efficiency of the lever system.
Mechanical advantage of a lever is the ratio of the effort arm (moment
arm of the effort force) to the resistance arm (moment arm of the
resistance force),
• M Ad = EA/RA
• Or when the effort arm is larger than the resistance arm, the
mechanical advantage will be greater than one.

• When a muscle is contracting concentrically (actively shortening), the
muscle must be moving the segment to which it is attached in the
direction of its pull. Therefore, the muscle will be the effort force.
• When a muscle is contracting eccentrically (actively lengthening), the
muscle must be acting in a direction opposite to the motion of the
segment; that is, the muscle must be the resistance force. When a
muscle is contracting eccentrically, it generally serves to control (slow
down) the acceleration of the segment produced by the effort force.

Elbow Extension
• Triceps brachii :
• The long head of the triceps brachii
crosses both the shoulder and elbow;
the other two heads are uniaxial. The
long head functions most effectively
as an elbow extensor if the shoulder
simultaneously flexes. This maintains
an optimal length–tension relationship
in the muscle.
• Innervation : Radial Nerve C6, C7 and
C8.

• Activity of the long head of the triceps is affected by changing
shoulder joint positions because the long head crosses both the
shoulder and the elbow. The long head’s ability to produce torque
may diminish when full elbow extension is attempted with the
shoulder in hyperextension. In this instance, the muscle is shortened
over both the elbow and shoulder simultaneously.
• Maximum isometric torque is generated at a position of 90° of elbow
flexion.

• The triceps is active
eccentrically to control elbow
flexion as the body is lowered
to the ground in a push-up.
• The triceps is active
concentrically to extend the
elbow when the triceps acts
in a closed kinematic chain,
such as in a push-up.

Clinical Relevance
• Tricep weakness in individuals with tetraplegia :
• Individuals with tetraplegia at the level of C6 lack active control of the
triceps brachii, innervated at the level of C7 and C8.
• Despite the absence of elbow extension strength, the individual is able to
bear weight on the upper extremity by locking the elbow in extension.
• Grover et al. demonstrate that an elbow flexion contraction of
approximately 25° prevents a patient with C6 tetraplegia and complete loss
of triceps brachii strength from performing a sliding transfer. Thus the
prevention of elbow flexion contractures is an essential element in the goal
of independent function for individuals with C6 tetraplegia.

Asymmetrical tonic neck reflex :
• The ATNR is a normally occurring motor reflex in infants. The reflex is manifested
in the upper extremities by a change in muscle tone in each upper extremity,
determined by the rotation of the head and neck. As the head is turned to one
side, there is an increase in motor tone in the extensor muscles of the upper
extremity to which the head is turned.
• This reflex usually is integrated as normal motor development unfolds during the
first year, before the child can perform many independent activities of daily living.
However, in some children with developmental delays and impaired motor
control, the reflex may continue to be evident even as the child becomes ready
for some functional independence.
• In this case, the abnormal presence of an ATNR may interfere with the child’s
ability to gain independence in activities such as self-feeding. As the child looks at
the hand with the food in it, the extensor tone increases in that limb, increasing
the difficulty of flexing the elbow and bringing the food to the mouth.

Anconeus :
• The anconeus muscle stabilizes the
elbow during supination and
pronation and assists in elbow
extension
• Innervation : Radial Nerve

Supinator :
• The proximal attachment of the
supinator at the annular and
lateral collateral ligaments.
• may function to stabilize the
lateral aspect of the elbow.
• Unlike the biceps brachii, its
effectiveness as a supinator is
not influenced by the elbow
position.
• Innervation : Posterior
interosseous nerve.
Forearm Supination

Biceps brachii.
• The biceps muscle acts as a supinator if the elbow simultaneously
flexes or if resistance is given to supination when the elbow is in
extension.
Brachioradialis :
• The brachioradialis contributes to pronation and supination only as an
accessory muscle when resistance is provided to the motion. It
cannot function alone as a rotator or stabilizer of the forearm joints
when other forearm muscles are paralyzed.

Forearm Pronation
Pronator teres :
• The pronator muscle pronates as
well as stabilizes the proximal
radioulnar joint and helps
approximate the humeroradial
articulation.
• Innervation : Median nerve.

Pronator quadratus :
• The pronator quadratus is a one-
joint muscle and is active during
all pronation activities.
• Innervation : Median nerve.

Screw Home Mechanism
• The arthrokinematics at the humeroradial joint involve a spin of the fovea of the
radial head against the rounded capitulum of the humerus. The arthrokinematics
during active pronation under the power of the pronator teres muscle.
Contraction of this muscle as well as others inserting into the radius can generate
significant compression forces on the humeroradial joint, especially when the
joint is near extension. This compression force is associated with a proximal
migration of the radius, which is greater during active pronation than during
supination.Because the interosseous membrane as a whole is relatively slackened
in pronation, it is likely less able to resist the proximal pull on the radius imparted
by pronator muscle contraction. The natural proximal migration of the radius and
associated increased joint compression of the humeroradial joint during active
pronation has been referred to as the “screw home” mechanism of the elbow.

Based on location, the humeroradial joint is
mechanically linked to the kinematics of both
the elbow and forearm. Any motion
performed at the elbow or forearm requires
movement at this joint. A postmortem study
of 32 cadavers (age at death ranging from 70
to 95 years) showed more frequent and
severe degeneration across the humeroradial
than the humero-ulnar joint.The increased
wear on the lateral compartment of the
elbow can be explained in part by the
frequent and complex arthrokinematics (spin
and roll-and-slide), combined with varying
amounts of muscular-produced compression
force.

Supracondylar Fracture
• Simple supracondylar fractures are typically seen in younger children, and
are uncommon in adults; 90% are seen in children younger than 10 years of
age, with a peak age of 5-7 years.
Mechanism :
• There are two types of supracondylar fractures: extension (95-98%) and
flexion (<5%) types.
• Extension type supracondylar fractures typically occur as a result of a fall
on a hyper-extended elbow. When this occurs, the olecranon acts as a
fulcrum after engaging in the olecranon fossa. The humerus fractures
anteriorly initially and then posteriorly. They result in an extra-articular
fracture line, and (when displaced) posterior displacement of the distal
component.

• The Gartland classification of supracondylar fractures of the humerus is
based on the degree and direction of displacement, and the presence of intact
cortex. It applies to extension supracondylar fractures rather than the
rare flexion supracondylar fracture.

Type I: undisplaced or minimally
displaced

Type II: displaced but with intact
cortex

Type III: completely displaced

• There are three main complications.
• malunion: resulting in cubitus varus (varus deformity of the elbow, also
known as gunstock deformity)
• ischemic contracture (Volkmann contracture) due to damage/occlusion to
the brachial artery and resulting in volar compartment syndrome
• damage to the ulnar nerve, median nerve, or radial nerve
• most commonly insured at the time of injury is the anterior interosseous
nerve (AIN; a branch of the median nerve), followed by the radial nerve
and then the ulnar nerve. Ulnar nerve injury is more common in flexion
type fractures.

Medial epicondyle fracture
Epidemiology :
• Medial epicondylar avulsion fractures are the most common
avulsion injury of the elbow and are typically seen in children
and adolescents 4. Medial epicondyle fractures are often
associated with elbow dislocation and make up
approximately 12-20% of all pediatric elbow fractures.

• posterior elbow dislocation transmitting force to the medial epicondyle via the
ulnar collateral ligament (most common; accounts for two-thirds of cases of
medial epicondylar fractures 3)
• fall on an outstretched hand with the elbow in full extension, resulting in
sudden traction on the flexor-pronator muscle group of the forearm.

Lateral Condyle Fracture
Epidemiology
•They represent ~12.5% (range 5-20%) of elbow
fractures in children and are the second most
common pediatric elbow fracture
after supracondylar fractures.
•They occur in school-age children, with a peak
at 6 years.

Mechanism :
• These occur either after fall onto an outstretched hand.
• Two theories exist regarding mechanism of injury: push-off
and pull-off theories2.
• The push-off theory suggests there is a direct force
upwards and outwards causing the radial head to impact
the capitellum2.
• The pull-off theory suggest the lateral condyle avulses due
to the extensor carpi radialis longus and brevis creating a
varus stress on a supinated forearm

Complications
• stiffness
• delayed union
• non-union
• fracture displacement
• cubitus valgus (>10%) with tardy ulnar nerve palsy, cubitus varus
(>20%)
• avascular necrosis (osteonecrosis)
• fishtale deformity
• lateral overgrowth

Posterolateral Rotatory Innstability
• O’Driscoll is credited with the description and detailing of
posterolateral rotatory instability (PLRI). Osborne and
Cotterill were the first to appreciate fully the importance of
the lateral ligamentous complex in recurrent instability and
describe the findings of PLRI. The rotatory instability
develops due to injury to lateral UCL that happens with a
combination of axial compression, valgus stress and
supination (or external rotation).

Elbow Dislocation
• Elbow dislocation is the second most common large joint
dislocation in adults and the most common in children.
• If an elbow dislocation is associated with a fracture (fracture-
dislocation), it is called "complex." An isolated dislocation
without fracture is "simple.“
• The most common associated fracture in adults is a radial
head fracture, although coronoid process fracture is also
common. When all of these occur together in a severe
posterior dislocation, it is known as the terrible triad of the
elbow .

Clinical Presentation
• Patients typically present complaining of a painful, swollen joint
after a fall on an outstretched hand; also commonly occurs in the
context of motor vehicle accidents, violence, and sporting events.
• In posterior dislocations the affected elbow is commonly held in
mid-flexion, whereas patients with anterior dislocations tend to
adopt a position of forearm supination with extension at the
elbow.
• Inspection may reveal a prominent olecranon posteriorly, and the
ipsilateral forearm may appear "shortened" compared to the
contralateral extremity.
• Range of motion will be decreased.

Mechanism
• Posterior dislocations typically occur following a fall onto an extended arm,
either with hyperextension or a posterolateral rotatory mechanism.

Complications
• Ulnar nerve :
most common neuropraxia associated with posterior
dislocation.
• Median nerve :
anterior interosseous branch typically involved may be
entrapped during closed reduction of a posterior dislocation.
• Radial nerve
• Brachial artery :
associated with anterior dislocations.

Distraction Injuries
Pulled elbow :
• A tensile force of sufficient
magnitude exerted on a pronated
and extended forearm may cause
the radius to be pulled inferiorly
out of the annular ligament. This
injury is common in children
younger than 5 years and rare in
adults. Lifting a small child up into
the air by one or both hands or
yanking a child by one hand is the
usual causative mechanism, and
therefore the injury is referred to
as either nursemaid’s elbow or
pulled elbow.

Tennis Elbow
• Lateral epicondylitis, also known as tennis elbow, is an overuse
syndrome of the common extensor tendon and predominantly affects
the extensor carpi radialis brevis (ECRB) tendon.
• Clinical Presentation :
• Patients often present with lateral elbow pain, tenderness and
swelling, which is frequently exacerbated when they grasp objects
during wrist extension with resistance.

Golfer’s Elbow
• Golfer’s elbow, also known as medial epicondylitis, medial
epicondylalgia, or medial epicondylosis, involves the common
flexor/pronator tendon at the tenoperiosteal junction near the medial
epicondyle. It is associated with repetitive movements into wrist
flexion, such as swinging a golf club, pitching a ball, or work-related
grasping, shuffling papers, and lifting heavy objects.

Etiology of Symptoms
• The most common cause of epicondylalgia is excessive repetitive use
or eccentric strain of the wrist or forearm muscles. The result is
microdamage and partial tears, usually near the musculotendinous
junction when the strain exceeds the strength of the tissues and
when the demand exceeds the repair process. Initially there may be
signs of inflammation followed by the formation of granulation tissue
and adhesions.
• With repetitive trauma, fibroblastic activity and collagen weakening
occurs. Recurring problems are seen because the resulting immobile
or immature scar is re-damaged when returning to activities before
there is sufficient healing or mobility in the surrounding tissue.

Cubital tunnel syndrome
• The cubital tunnel is an osseous/fibrous tunnel posterior to the
medial epicondyle of the humerus associated with the origin of the
flexor carpi ulnaris muscle.
• The cubital tunnel is a potential site of entrapment of the ulnar nerve,
resulting in “cubital tunnel syndrome.”
• Ulnar nerve compression results in loss of intrinsic hand function and
paresthesia on the medial aspect of the hand.

Myositis Ossificans
• The terms myositis ossificans and heterotopic or ectopic bone
formation are often used interchangeably to describe the
formation of bone in atypical locations of the body.
Etiology of Symptoms :
• Although not a common phenomenon, the sites most frequently
involved are the elbow region and thigh
• In the elbow, heterotopic bone formation most often develops in
the brachialis muscle or joint capsule as the result of trauma, such
as a comminuted fracture of the radial head, a fracture dislocation
(supracondylar or radial head fracture) of the elbow, or a tear of
the brachialis tendon.

• Patients with neurological impairments, specifically traumatic brain
injury or spinal cord injury, and patients with burns to the extremities
are also prone to develop this complication. It also may develop as
the result of aggressive stretching of the elbow flexors after injury and
a period of immobilization.
• After the acute inflammatory period, heterotopic bone formation is
laid down in muscle between, not within, individual muscle fibers or
around the joint capsule within a 2- to 4-week period.

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