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The Elbow Complex

Functions of the Elbow Complex
Joint Structure of the Elbow Complex
Kinematics of the Elbow
Muscle Action at the Elbow
Stability of the Elbow Complex
Common Injuries at the Elbow

 

Objectives: After studying this topic, the students will be able to

  1. to identify the structures of the elbow and the forearm, including joint type, articular shape, and the surrounding tissues
  2. to describe joint motions occurring at the elbow, including physiological and accessory movements, muscle actions, and factors checking elbow motions
  3. to understand the stability mechanism of the elbow complex and the possible mechanisms of injury

  1. Neumann DA (2002).  Elbow and Forearm Complex.  In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby.  Chapter 6, pp. 133-171
  2. Smith LK et al., 1996. Chapter 5
  3. Jazrawi LM et al. (2001).  Biomechanics of the Elbow.  In Nordin M & Frankel VH: Basic Biomechanics of the Musculoskeletal System.  Philadelphia: Lippincott Williams & Wilkins. Chapter 13, pp.340-357

Functions of the Elbow Complex

 

Two major functions of the extremity joints are mobility and stability.  The functions of the elbow joints are

  • to add mobility of hand in space by
  • shortening and/or lengthening the arm
  • rotating the forearm
  • combination of the above both
  • to provide control and stability
  • for skilled hand motions
  • for forceful upper extremity motions
    1. Keep your arm straight and try to do any daily activities, e.g. eating, writing, opening the door, throwing a ball, walking, etc.  See which one is affected if elbow motion is restricted and which one is not.
    2. Try not to rotate your forearm and do any daily activities, e.g. eating, writing, opening the door, throwing a ball, walking, etc.  See which one is affected if forearm motion is restricted and which one is not.

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    Joint Structure of the Elbow Complex

     

    Joints at elbow complex

  • humeroulnar joint (HUJ)
  • humeroradial joint (HRJ)
  • proximal radioulnar joint (prox. RUJ)
  • Note:
    The above three joints are enclosed in the same joint capsule
  •  

    Humeroulnar joint

  • proximal component: humerus
  • hourglass-shaped trochlea
    trochlea =pulley
  • olecranon fossa
  • coronoid fossa
    cornoid = like crown
  • distal component:ulna
  • saddle-shaped trochlear fossa
  • coronoid process
  • olecranon process
  • joint type
  • hinged (ginglymus) or modified hinged (Morrey BF and Chao EY, 1976; Neumann DA 2003, p.137)
  • Note: The elbow complex, including both the humeroulnar and humeroradial joints, is considered entirely and therefore is treated as a trochleoginglymoid joint. (Jazrawi LM et al., 2001)
  • motion: elbow flexion/ extension
  • elbow flexion with anterior glide of the trochlea notch of the ulna on the trochlea of the humerus
  • elbow extension with posterior glide of the trochlea notch of the ulna on the trochlea of the humerus
  • DOF = 1
    Note: Some scholars refer the elbow joint to the whole elbow complex so that the degree of freedom of the elbow joint, they think, is equal to 2.
  • rest position: 70° of elbow flexion and 10° of forearm supination
  • closed packed position: full elbow extension
  • Joints at elbow complex
    Elbow Flexion/ Extension

     

    Humeroradial joint

  • proximal component: humerus
  • radial fossa
  • ball-shaped capitulum
  • distal component: cup-shaped superior aspect of the radial head (fovea)
  • joint type: ball-and-socket joint
  • motion: elbow flexion/ extension and forearm pronation/ supination
  • elbow flexion/ extension with anterior/ posterior glide of the radial head on the capitulum of the humerus
  • forearm pronation/ supination with the radial head spinning medially/ laterally on the capitulum of the humerus
  • DOF = 2
  • rest position: full elbow extension with forearm supination
  • Joints at elbow complex
    Elbow Flexion/ Extension
    Forearm pronation/ supination

     

    Proximal radioulnar joint

  • proximal component: concave radial notch of the ulna
  • distal component: convex rim of the radial head
  • joint type: pivot joint
  • motion: forearm pronation/ supination
  • forearm pronation with posterior glide of the radial head
  • forearm supination with anterior glide of the radial head
  • DOF = 1
  • rest position: 70º of elbow flexion and 35º of forearm supination
  • Note: The distal radioulnar joint structurally separate from the elbow complex but moves with proximal radioulnar joint as a functional unit.  Will be discussed in details on the page of "wrist complex".
  • Joints at elbow complex
    Forearm pronation/ supination

     

    Carrying angle

  • synonym: cubitus angle
  • 10-15º  valgus angle when the elbow is fully extended and the forearm is fully supinated
  • disappear when the elbow is extended and the forearm is pronated
  • decreased when the elbow is flexed
  • female > male
  • The trochlea of the humerus extends farther distally than does the capitulum
    The outer lip of the trochlea extends father distally than does the inner lip
  • anomaly
  • cubitus valgus i.e. cubitus angle >15º, resulting the forearm deviating outwards
  • cubitus varus resulting the forearm deviating towards the midline
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    Kinematics of the Elbow

     

    Elbow flexion and extension

  • joint involved
  • humeroulnar joint (principal joint)
  • humeroradial joint
  • plane of motion: sagittal plane
  • axis of rotation
  • not a fixed point
  • close to a line through the centers of the trochlea and capitulum
  • not perpendicular to the longitudinal axis of the humerus (4-8º of valgus)
  • palpation: slightly distal to the connecting line between the lateral and medial epicondyles of the humerus
  • osteokinematic movements
  • range of motion (ROM)
  • elbow flexion: 0-145º
  • somewhat hyperextension, especially in female
  • functional range: 30-130º
  • closed kinematic chain motions: motion occurs when the hand is fixed and the elbow moves
  • pull-up (引體向上)
  • push-up (伏地挺身)
  • push and pull
  • elbow adduction with elbow flexion
  • 6° adduction from full extension to full flexion (Morrey & Chao, 1976)
  • < 1° from full extension to full flexion (London et al., 1981)
  • no clinical significance (An et al., 1984)
  • arthrokinematic movements (concave on convex joint)
  • distraction /compression of the ulna to the humerus
  • anterior glide of the ulna on the humerus with elbow flexion
  • especially in the last 5-10º
  • posterior glide of the ulna on the humerus with elbow extension,
  • especially in the last 5-10º
    1. Use your left thumb and index to palpate the olecranon and coronoid processes of your right ulnar bone. Try to bend your right elbow and feel the the motions of both processes.
    2. Do the above trial on your friend's.
    3. Place one hand on the medial aspect of your friend's upper arm as close to his/her elbow as possible. Place the other hand on the lateral aspect of your friend's forearm. Similarly, as close to the elbow joint as possible. Push the forearm medially and feel the medial gliding of the forearm. DO NOT push too hard!!
  • factors checking elbow flexion
  • soft tissue approximation at anterior humerus (most important)
  • coronoid process into coronoid fossa
  • radial head into radial fossa
  • passive tension of the triceps
  • tightness of the posterior joint capsule
  • factors checking elbow extension
  • olecranon process into olecranon fossa (most important)
  • passive tension of the elbow flexors
  • passive tension of the collateral ligaments
  • tightness of the anterior capsule
  • Humeroulnar Joint

     

    Forearm Pronation/ Supination

  • joint involved
  • proximal radioulnar joint
  • distal radioulnar joint
  • humeroradial joint
  • plane of motion: transverse plane
  • axis of rotation
  • passing through the center of the radial head and the distal ulnar head
  • not parallel to the longitudinal axis of the forearm
  • osteokinematic movements
  • motions: the radial head rotates within the annular ligament and spins on the capitulum of the humerus
  • range of motion (ROM)
  • pronation: 0-70º
  • supination: 0-85º
  • Note: Pure motions occur as the elbow is held in the 90° of flexion. If the elbow is extended, shoulder rotation occurs simultaneously with forearm rotation.
  • functional range: 50º of pronation to 50º of supination
  • closed kinematic chain motions
  • open the door knob
  • open the can
  • arthrokinematic movements (convex on concave)
  • anteromedial gliding of radius on ulna with forearm supination
  • posterolateral gliding of radius on ulna with forearm pronation


    1. Use your left thumb and index to palpate the head of the radius of your right arm. Try to rotate your right forearm and feel the the motion of the radial head.
    2. Try the above trial on your friend's.
  • factors checking forearm pronation
  • ulna on radius
  • quadrate ligaments
  • posterior radioulnar ligament
  • oblique cord
  • factors checking forearm supination
  • anterior radioulnar ligament
  • quadrate ligament
  • oblique cord
  • interosseous membrane
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    Muscle Action at the Elbow

     

    Elbow flexors

  • brachialis
  • single joint muscle
    not affected by position of forearm or shoulder
  • participates all flexion activities

  • biceps brachii
  • long head: two-joint muscle
    most effective when shoulder extended and forearm supinated
  • short head: single-joint muscle
  • muscle actions 
  • effective as a flexor between 80-100º of elbow flexion or forearm supinated
  • forearm supination
  • shoulder flexion as shoulder extended
  • factors affecting the strength of the biceps brachii
  • elbow position: moment arm and muscle length
  • shoulder position: long head only
  • brachioradialis: activates when
  • joint stability is needed
  • speed of flexion motion increases
  • forearm is pronated
  • elbow flexion strength
  • generates maximum isometric force at 65° of flexion
  • force of flexion as forearm supinated > in neutral > pronated
  •  

    Elbow extensors

  • triceps brachii
  • long head: from lateral border of scapula
  • two joint muscle
  • most effective as shoulder flexed
  • medial and lateral heads
  • one joint muscle: from posterior surface of humerus
  • insertion: olecranon
  • factors affecting the strength of the triceps brachii
  • elbow position: moment arm and muscle length
  • shoulder position: long head only
  • anconeus
  • acts as elbow extensor
  • stabilize elbow during forearm pronation and supination
  • against valgus stress
  • elbow extension strength: generates maximum isometric force at 90° of elbow flexion
  •  

    Forearm pronators

  • pronator quadratus: most important
  • activates during all pronation activities
  • pronator teres
  • to be active during fast pronation or pronation against resistance
  • to stabilize proximal radioulnar joint
  • to approximate humeroradial joint
  • elbow position does not affect the activity of pronators
  •  

    Forearm supinators

  • supinator: most important
  • biceps brachii:active during fast supination with elbow flexed or supination against resistance regardless of elbow position
  • elbow position does not affect the activity of pronators
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    Stability of the Elbow Complex

     

    Factors Affecting Elbow Stability

  • bony configuration
  • coronoid process prevents anterior displacement
  • olecranon process prevents posterior displacement
  • humeroradial joint provides resistance to valgus stress

  • tension of ligaments
  • medial collateral ligament
  • from the medial epicondyle of the humerus to the coronoid process (anterior fibers, the strongest) and to the olecranon process of the ulna (posterior fibers) as well as from the olecranon process to the coronoid process of the ulna (transverse fibers)
  • against valgus stress
  • taut at full extension (anterior fibers) or full flexion (posterior fibers)
  • lateral collateral ligament
  • against varus stress
  • taut at full flexion
  • anterior oblique ligament
  • preventing hyperextension
  • taut at extension
  • posterior oblique ligament
  • taut at flexion flexion
  • less functional because its insertion is attached at the annular ligament
  • muscle contraction (dynamic stability)
  • anconeus: against varus stress
  • cocontraction of antagonists: to increase compression forceand produce joint approximation
  • What if
  • a varus stress happens?
  • a valgus stress happens?
  • an anterior stress happens?
  • a posterior stress happens?
  •  

    Factors affecting the stability of the proximal radioulnar joint

  • What is the instability?
  • bony configuration is no help
  • tension of ligament
  • annular ligament: against distraction of the radius and preventing dislocation of radial head
  • inerosseous membrane: prevents separation or longitudinal shift of radius and ulna
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    Common Injuries at the Elbow

     

    Direct stress

  • longitudinal compression stress à fracture of radial head, coronoid or olecranon process and supracondylar fracture
  • distraction stress à nurse maid’s elbow (pulled elbow)
  • posterior stress à posterior dislocation of the elbow
  •  

    Repeated stresses

  • repeated wrist motions as forearm pronated à repeated tensile stress on extensor carpi radilais brevis à tennis elbow (lateral epicondylitis)
  • repeated wrist motions as forearm supinated à repeated tensile stress on pronator teres, flexor carpi radialis à golfer’s elbow
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    Established on 09/30/2002 and Last Updated 10/22/2004 © 2004 Huei-Ming Chai, PhD PT          All Right Reserved