Biomechanics of the elbow and forearm

Question 1

Bone structure of the elbow and the forearm

Answer 1

• Distal Humerus
• Proximal Ulna
• Proximal Radius

Question 2

Articulations and supporting structures of the elbow and the forearm

Answer 2

• Humeroulnar articulation
• Humeroradial articulation
• Superior Radioulnar joint

Question 3

Elbow movement

Answer 3

• Flexion and extension
• Pronation and supination

Question 4

VALGUS

Answer 4

Lateral deviation of a distal segment with respect to proximal segment

Question 5

VARUS

Answer 5

medial deviation of a distal segment with respect to proximal segment

Question 6

Functional AROM of the elbow

Answer 6

The arc of movement required for most ADLs is 30◦ to 130◦ (100 degrees) in flexion-extension. 50◦ of pronation and 50◦ of supination.

Question 7

Humerus shaft and distal end

Answer 7

• Non-uniform geometry
• Increase the area of contact.
• 30° anterior curve – distal humerus
• The structure of these bones in to increase the congruency.
• 6 degrees of tilt

Question 8

Elbow joint, different compartment

Answer 8

• Humeroulnar
• Humeroradial
• Proximal radioulnar

Question 9

how is called the elbow joint and what does it mean

Answer 9

• Called a trochoginglymus joint
• Elbow joint complex contains both a hinge and pivot joint

Question 10

Humeroulnar joint

Answer 10

Ginglymus joint (hinge)
Flexion-extension
Joint space asymmetrical

Question 11

the bone shape of the humeroulnar joint favours which movement?

Answer 11

Bone shape favors flexion excursion vs. extension excursion

Greater contact with elbow
in flexion
- Greater flexion, less stress

Question 12

Superior radioulnar

Answer 12

Trochoid joint (pivot)
Pronation and supination
No support from bone structure—soft tissues only

Question 13

Interosseous membrane

Answer 13

Interosseous membrane an important static longitudinal stabilizer of the forearm (less contribution to forearm rotation)

Question 14

tension in supination and pronation

Answer 14

• Tension is least in pronation
• Tension is greatest in supination or neutral
• Increased tension helps stabilize the forearm in positions most often used for powerful grasp or heavy lifting

Question 15

3 PRIMARY STATIC CONSTRAINTS (elbow stabilisation)

Answer 15

• Ulnohumeral articulation
• Anterior bundle of the medial collateral ligaments
• Lateral collateral ligaments

more ligaments

Question 16

4 SECONDARY CONSTRAINTS: (more tissues)

Answer 16

• Radiocapitellar articulation
• Common origin of the flexors
• Common origin of the extensors
• Capsule
• more tissue

Question 17

Stabilization of elbow bones

Answer 17

• Congruent articular surfaces
• Radial Head stabilizes with stress in valgus direction.
• Olecranon stabilizes with stress in valgus direction.
• Coronoid stabilizes with stress in varus direction.

Question 18

Medial collateral ligaments and the Lateral collateral ligaments are important for

Answer 18

medial = Important stabilizer with valgus stress
lateral = Stabilize with varus stress

Question 19

Flexion/extension

Answer 19

• 1 DOF
• Medial-Lateral axis

Question 20

carrying angle of the flexion / extension

Answer 20

• Carrying angle 5 to 10°
• the valgus angle between the longitudinal axes of humerus and ulna
• trochlea extends further distally then does the capitulum.
• trochlea is asymmetric
  (its outer lip extending farther distally than does the inner lip)

Question 21

Bone on bone congruency:

Answer 21

all the distal and proximal bone are in relation together.

Question 22

pronation / supination

Answer 22

• ulna = doesn’t move and the radius does all the rotation work
• Rotation about a longitudinal axis passing through the radial head and the distal ulnar articular surface. (Lateral to medial)
• Application: poignée de porte

Question 23

the biceps in the pronation

Answer 23

Biceps less active with arm in full pronation

Question 24

Elbow angle affects what

Answer 24

affects the amount of muscle force parallel and perpendicular to forearm

Question 25

Moment arms of primary flexors =

Answer 25

• Sum of multiple muscles that cross the elbow joint.

Question 26

Each muscle will have its optimum leverage and length through the elbow’s range of motion.

Answer 26

• Better leverage with longer moment arms for producing movement.
• Muscle length also influence it.
• Flexion = shorter muscle = decrease the ability to create forces
• Extension = longer muscle = increase the force

Question 27

Maximum elbow strength

Answer 27

= max torque
= sum (lever arm x muscle force)

Question 28

• Moment arm vs. length of muscle

Answer 28

• Optimal range ~70-90degrees of elbow flexion
• 75-90 degrees of elbow flexion for maximum strength (greater in males than females and decrease with aged)

Question 29

What is the optimal muscle origin-insertion for ideal force production?

Answer 29

• Muscle with shorter lever arm = work harder to produce flexion
• Muscle B = decrease range of motion, more force
• Muscle A = more range of motion, less force

Question 30

Active insufficiency

Answer 30

• When a muscle crosses more than one joint, it will influence each joint
• At shortest length, muscle at weakened length
• Called active insufficiency for multi-joint muscle
• Bicep: shoulder flexion, elbow flexion, supination

Question 31

Valgus stress and pitching

Answer 31

• Valgus torque 64Nm
• Highest at late cocking and acceleration phase
• Professional pitchers 290N of force across elbow joint
• Ligamentous tensile strength 260N

Question 32

Epicondylitis

Answer 32

• Lateral epicondylitis (tennis elbow)
• Medial epicondylitis (golfer’s elbow)

Question 33

Shoulder vs. elbow

Answer 33

• Articulating surfaces of the elbow guide & restrict motion
• Collateral ligaments stabilize the elbow (ML) and contribute to limits of extension
• Muscles play a role in stabilizing the elbow, but main function is to produce motion
• Shoulder relies heavily on muscles for stability
• Ligaments provide support primarily at end ranges of motion