Download biomechanics of elbow joint

Biomechanics of elbow joint
By reem basodan
Table of content
ANATOMY OF THE ELBOW
Passive Stabilizers
 Osteology
 Articulation
 Ligaments
Active Stabilizers
 Muscles
BIOMECHANICS OF THE ELBOW
Elbow Stability and Stabilizing Structures
passive Stabilizers
 Passive Bony Stabilizers
 Passive Soft Tissue Stabilizers
 Interplay Between Passive Stabilizers
Active Stabilizers
 Force Transmission through the Elbow
Function
 Supination and Pronation
 Flexion and Extension
 Range of Motion
Elbow injuries
The elbow is a critical element for a functional upper extremity. The upper extremity
consists of a linked system between the shoulder, elbow, wrist, and hand. The primary
functions of the elbow are to position the hand in space, act as a fulcrum for the
forearm, and allow for powerful grasping and fine motions of the hand and wrist.
ANATOMY OF THE ELBOW
Passive Stabilizers
Osteology
The distal humerus comprises two condyles forming the articular surfaces of the
capitellum laterally and trochlea medially. The more prominent medial epicondyle
is an attachment point for the ulnar collateral ligament and flexor–pronator group. The
less prominent lateral epicondyle is an attachment point for the lateral collateral
ligament and extensor–supinator group. Anteriorly, the coronoid and radial fossa
accommodate the coronoid process of the ulna and radial head, respectively, during
flexion. Posteriorly, the olecranon fossa accommodates the olecranon process of the
ulna during extension (Fig. 1).
The proximal radius includes the cylindrical shaped radial head, while proximal ulna
provides the elbow articulation with an inherent stability, especially in full extension.
(Fig. 1).
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FIGURE 1. Bony landmarks of anterior, medial, and lateral distal humerus and
proximal ulna and radius
Articulation:
The elbow joint is highly congruous and is made up of the articulation between the
radius, ulna, and humerus bones.
The ulnohumeral joint is a hinge (ginglymus) joint with motion of flexion and
extension.
The proximal radioulnar and radiohumeral joints are pivoting joints (trochoid)
allowing rotation.
The trochlea of the distal humerus is a pulley-shaped surface that is larger medially
than laterally, and it articulates with the sigmoid notch of the proximal ulna. Laterally,
the capitellum articulates with the radial head.
The proximal radius has a cylindrical head with hyaline cartilage covering both the
depression for articulation with the capitellum and also at the outside circumference
of the radial head.
The proximal ulna consists of the coronoid and olecranon process (Fig. 1). These
make up the saddle-shaped, ellipsoid articular surface of the sigmoid notch.
The carrying angle of the elbow is formed by the longitudinal axis between the
humerus and ulna when the elbow is in full extension. In females, the average valgus
angle is 13° to 16°, whereas in males, it is 11° to 14°. The joint capsule normally has
a thin anterior portion. The anterior capsule becomes taut in extension and lax in
flexion.(figure 2)
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figure 2. carrying angle
Ligaments:
The triangular medial (ulnar) collateral ligament :
The anterior bundle (is the significant component of the medial collateral ligament
complex), posterior bundle (Bardinet ligament) is a posterior capsular thickening and
is best defined at 90° flexion, and transverse segment (ligament of Cooper)
contributes little to elbow stability. (Fig. 3)
Figure 3 .The medial (ulnar) collateral ligamentous complex is composed of the
anterior oblique bundle, the posterior oblique bundle, and the transverse
ligament.
The lateral (radial) collateral ligament complex :
The Radial collateral ligament the origin of the ligament is close to the axis of rotation
and is therefore uniformly taut throughout flexion-extension movement
The annular ligament It originates and inserts on the anterior and posterior margins of
the lesser sigmoid notch. The anterior insertion becomes taut during supination and
the posterior origin becomes taut in pronation
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The lateral ulnar collateral ligament functions as the primary lateral stabilizer of the
ulnohumeral joint (functions in stabilizing varus) stress, and deficiency of this
ligament results in posterolateral rotatory instability.
The accessory lateral collateral ligament functions to stabilize the annular ligament
during varus stress at the elbow.
The oblique ligament have limited functional importance.
The quadrate ligament is a stabilizer of the proximal radioulnar joint during
pronosupination (Fig. 4).
FIGURE 4. A, Medial elbow view shows the components of the medial collateral
ligament complex. B, Anterior view. C,Lateral view shows the radial collateral
ligament complex.
Active Stabilizers
Muscles.
The muscles crossing the elbow joint can be divided into four main groups (table 1).
Posteriorly, the elbow extensors cross the elbow joint, and are innervated by the radial
nerve. Laterally, the wrist and finger extensors and the supinator are found and
innervated by the radial nerve. Medially, the flexor–pronator group and are innervated
by the medial and ulnar nerves. Anteriorly, the elbow flexors cross the joint, and are
innervated by the musculocutaneous nerve.
BIOMECHANICS OF THE ELBOW
Elbow Stability and Stabilizing Structures
 passive Stabilizers
The passive and active stabilizers provide biomechanical stability in the elbow joint.
The passive stability results from both the highly congruent articulation between the
humerus and ulna and the soft tissue constraints. The active stability is caused by joint
compressive forces provided by the muscles
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Passive Bony Stabilizers
The ulnohumeral joint is a highly congruous joint and is a dominant factor as a
passive bony stabilizer.
The contact areas in the elbow joint vary with the type of applied stress. In a
laboratory study, contact areas of the elbow have been shown to occur at four facets in
the sigmoid fossa, two at the coronoid and two at the olecranon (Fig. 5). With varus
and valgus loads, the contact changes medially and laterally, respectively.
FIGURE 5.
Four separate areas of contact in the sigmoid fossa. Contact moves toward the center
of the sigmoid during flexion.
The carrying angle orientation changes from a valgus orientation in extension to varus
orientation in flexion. [For simplicity, one may assume that the ulnohumeral joint is a
pure hinge joint, and that the axis of rotation coincides with the trochlea so that the
change in carrying angle with flexion is caused by anatomic variations of the
articulation].(figure 2)
Passive Soft Tissue Stabilizers.
It is include the medial and lateral collateral ligament complexes and the anterior
capsule. The lateral collateral ligament originates from the lateral condyle at the point
where the axis of rotation of the elbow passes through. This ligament has a fairly
uniform tension throughout range of motion, because it originates at the axis of
rotation .The medial collateral ligament consists of two main components ,As the
point of origin of the different components of the medial complex do not occur at the
axis of rotation, the different components are not uniformly taut during elbow flexion
and extension .
Interplay Between Passive Stabilizers
The contributions of the articular geometry and ligaments to varus and valgus loads
were studied .
In 90° elbow flexion, the medial collateral ligament is the primary stabilizer to valgus
stress
In extension, the medial collateral ligament, anterior capsule, and bony fit
(articulation) are fairly equally resistant to valgus stress.
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With the elbow in both flexion and extension ,the bony articulation provides much
of the stability to varus stress.
Eighty-five percent of the resistance of the joint to distraction is caused by the
anterior capsule in extension, whereas only 8% of resistance is caused by the anterior
capsule in 90° elbow flexion. With elbow flexion, 78% resistance to traction is
provided by the medial collateral ligament complex.
 Active Stabilizers
Muscles crossing the elbow joint and their function
have been previously described (Table 1). The line of
pull and contraction of muscles across the elbow
joint create forces within the joint at the humerus,
radius, and ulna. These balanced forces likely
function as dynamic stabilizers of the joint.
From the muscles crossing the elbow joint, the
brachialis and triceps muscles have the largest work
capacity and contractile strength.
maximal isometric elbow flexion, when the elbow is
fully extended can produce joint compression forces
of as much as two times body weight.
Figure 6
Force Transmission Through the Elbow
Although the elbow is not considered to be a weight bearing joint , it regularly
sustains large load during daily activities. For example, research show that:
Compressive load during activities such as dressing and eating=300N,1700 N when
the body is supported by arm when raising from chair ,and 1900 N when pulling table
across the floor.
During moderate activities ,Humeroulnar forces up to 1600N,humeroradial forces up
to 800 N.
During push-up exercise peak force in each elbow reach 45% of body weight.
During hand medially rotated, greater posterior and varus force are generated more
than during hand in natural or laterally rotated position.
Since the attachment of triceps tendon of (figure 6)ulana is closer to elbow joint
center than the attachment of the brachialis on the ulna and biceps on the radius, the
extensor moment arm is shorter than the flexor moment arm. This mean that the
elbow extensor must generate more force than elbow flexor to produce the same
amount of joint torque. The following Sample problem illustrates the relationship
between moment arm and torque at elbow joint.
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Sample problem :
How much force must be produced by the brachioradialis and biceps(Fm) to maintain
the 15 N forearm and hand in
position shown below, given moment arm of 5 cm for
the muscle and 15 cm for the force arm/hand weight? What is the magnitude of the
joint reaction force?
Known
Wt=15N
dwt =15 cm
r
dm =5 cm
A
wt
solution:
torque is the product of of force and prepenicular distance from its line of action to the
center of rotation.
torque at elbow created by arm muscle must equal
torque at elbow created by forearm/hand weight,net elbow Torque=0
∑Te=0
∑Te=(Fm)(dm)-(wt)(dwt)
0=(Fm)(5cm) - (15N)(15cm)
Since the arm is stationary, the sum of the acting vertical
forces must be =0.(upward is positive direction)
∑Tv=0
∑Tv= Fm – wt -R
∑Tv= 45N-15N-R
R=30 N
Function
Supination and Pronation
The primary motion of the forearm is supination and
pronation, with the axis of rotation passing from the proximal radial head to the
convex articular surface of the ulna at the distal radioulnar Joint( In ADL 50°
pronation and 50° supination).
Flexion and Extension
In elbow flexion and extension (in ADL 30° to 130° ) ,the deviation of joint rotation is
minimal, and elbow motion can be thought of as a uniaxial joint except at the
extremes of flexion and extension.With this simplification, the axis of rotation can be
thought of a line passing from the inferior medial epicondyle through the center of the
lateral epicondyle.
The elbow is often mistakenly thought of as a simple hinge joint because of the
congruous and stable ulnohumeral articulation. Studies have shown that in addition to
flexion and extension, the ulnohumeral joint also has 6° axial rotation secondary to
the obliquity of the trochlear groove .
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Range of Motion:
Normal elbow range of motion is from 0° to 150°, and forearm rotation averages 75°
pronation and 85° supination.
Factors limiting extension :
- include the impact of the olecranon process on the olecranon fossa
- tension of the anterior bundle of the medial collateral ligament, and the flexor
muscles.
Factors limiting flexion :
-include the impact of the coronoid process against the coronoid fossa
- the impact of the radial head against the radial fossa, and the tissue tension from the
capsule and triceps muscle.
Pronation and supination motions are restricted more by the passive stretch of
antagonistic muscles than by ligaments, although the quadrate ligament has been
shown to provide static constraint to pronosupination motion.
Elbow enjureis:
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Lateral epicondylitis, commonly known as tennis elbow. The amount of force
to which the lateral aspect of the elbow is subjected during tennis play
increase with poor technique and improper equipment.
Medial epicondylitis is commonly known as golfer's elbow Elbow injuries in
pitchers can be related to the large rotational force - called "torque" - needed
to slow down the cocking of the arm and accelerate the forearm, hand, and ball
forward. From the cocked position, the ulnar collateral ligament (UCL) pulls
the forearm forward with the rotating upper arm. Injury or stretching of UCL
can result in valgus instability , repeated valgus overload during repetitive
throwing provoke bony changes. This seen in individual who throw
repetitively.
Elbow sprain and dislocation: forced hyper extension of elbow----posterior
displacement of ulna resulting in dislocation .continued hyperextension----cause distal humerus to slide over the ulna. The mechanism in adult is
typically falling on an outstretched hand or a forceful ,twisting elbow. In
children radial head subluxation is generally results from a sudden pull on the
upper limb, such as that exerted by an adult to prevent the child from falling;
in children aged 1 to 3years it is referred as nursemaid's elbow.
Radial tunnel syndrome (happens when the radial nerve is squeezed where it
passes through a tunnel near the elbow).
Olecranon bursitis is the inflammation of a small sac of fluid located on the
tip of the elbow .
Elbow arthritis may be surgically treated with a procedure called
interposition arthroplasty. The term "interposition" means that new
tissue is placed between the damaged surfaces of the elbow joint
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Cubital tunnel syndrome is a condition that affects the ulnar nerve where it
crosses the inside edge of the elbow.
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Refernces:
1.Fornalski S, Gupta R, Lee T. Anatomy and Biomechanics of the Elbow Joint.
Techniques in Hand and Upper Extremity Surgery 7(4):168–178, 2003
2.Churchill livingstone.(1982).The elbow.biomechanics of elbow=forearm
comlex.31-47.
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