Bio-mechanics of the Elbow Joint

Biomechanics Lecture for DPT students & Physical Therapists

1. Biomechanics of the Elbow Dr. Abid Ullah PT Lecturer FIMS Abbottabad Email: [email protected]

2. Objectives At the end of this lecture, you must be able to To identify the structure of the elbow & forearm, including joint type, articular shape & surrounding tissues To describe joint motion occurring at the elbow, including physiological & accessory movement, muscle actions & factors checking elbow stability To understand the stability mechanisms of the elbow complex & the possible mechanism of injury

3. Contents Function of elbow complex Joint structure of elbow complex Kinematic of the elbow Muscle action at the elbow Stability of the elbow complex Common injuries at the elbow

4. Function of the elbow Two major function of the extremity joints are mobility and stability The function of the elbow joint are To add mobility of the hand in space by Shorting / lengthening the arm Rotating the arm Combination of the above To provide control & stability For skilled hand motion For forceful upper extremity motion

5. Joint structure of elbow Joints at elbow complex Humeroulnar joint (HUJ) Humeroradial joint (HRJ) Proximal radioulnar joint (proxi-RUJ) Note: The above three joints are enclosed in the same joint capsule

6. Humeroulnar joint Proximal component: Hourglass-shaped trochlea ( trochlea= pulley) Olecranon fossa Coronoid fossa coronoid = like crown Distal component: ulna

7. Cont… Joint type: hinged Motion: Elbow flexion/ extension Elbow flexion with anterior glide of trochlea notch of the ulna on the trochlea of humerus Elbow extension with posterior glide of the trochlea notch of the ulna on the trochlea of the humerus DOF= 1 Rest position: 70 d& 10 deg of forearm supination Closed packed position: full elbow extension

8. Cont…

9. Humeroradial joint Proximal component: Humerus Radial fossa Ball-shaped capitulum Distal component: cup-shaped superior aspect of the radial head ( Fovea) Joint type: ball & 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 spining Medially/laterally on the capitulum of the humerus

10. 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 Resting position: 70 deg of elbow flexion & 35 deg of forearm supination.

11. Muscle action at the elbow Elbow flexors Brachialis Single joint muscle Participate all flexion activities Biceps brachi Long head: two joint muscle most effective when shoulder extended & forearm supinated short head : single joint muscle Muscle action Affective as a flexor b/w 80-100 of elbow flexion or forearm supinated Forearm supination Shoulder flexion as shoulder extended Factor affecting the strength of the biceps brachii Elbow position: moment arm & muscle length Shoulder position: long head only Brachioradialis : activate when Joint stability is needed Speed of flexion motion increases Forearm is pronated

12. Cont…

13. Elbow extensor 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 triceps brachii Elbow position: moment & muscle length Shoulder position: long head only Anconeus Acts as elbow extensor Stabilize elbow during forearm pronation & supination Against valgus stress

14. Cont…

15. Cont… Forearm pronators Pronator quadratus Active during all pronation activities Pronator teres To be active during fast pronation or pronationagainst resistance To stablize proximal radioulnar joint To approximate humeroradial joint Elbow position dose not affect the activity of pronators Forearm supinators Supinator : Bicep brachii: active during fast supination with elbow flexed or supination against resistance

16. Carrying angle Synonyms: cubitus angle 10-15 deg valgus angle when the elbow is fully extended & the forearm is fully supinated Disappear when the elbow is extended & forearm is pronated Decrease when the elbow is flexed Female has greater than male The trochlea of the humerus extends farther distally than dose the capitulum The outer lip of the trochlea extends father distally than does the inner lip Anomaly Cubitus valgus i.e cubitus angle is grater than 15, resulting the forearm deviating outwards Cubitus varus resulting the forearm deviating toward the midline

17. Cont…

18. Kinematics of the elbow Elbow flexion & extension Joints involved Humeroulnar joint Humeroradial joint Plane of motion: sagittal plane Axis of rotation Not fixed point Closed to a line through the center of the trochlea & capitulum Not perpendicular to the longitudinal axis of the humerus (4-8 deg of valgus) Palpation: slightly distal to the connecting line b/w the lateral & medial epicondyles of the humerus

19. Osteokinematic moments Range of motion Elbow flexion : 0-145 deg Somewhat hyperextension , especially in female Functional range: 30-130 deg Closed kinematic chain motion Pull-up push-up push& pull

20. Arthrokinematic movement 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 5-10 deg Posterior glide of the ulna on the humerus with elbow extension Especially in the last 5-10 deg

21. Cont…

22. Factors checking elbow flexion Soft tissue approximation at anterior humerus Corocoid process into coronoid fossa Radial head into radial fossa Passive tension of triceps tightness of the posterior joint capsule Factors checking elbow extension Olecranon process into Olecranon fossa Passive tension of the elbow flexors Passive tension of the collateral ligaments Tightness of the anterior capsule

23. Forearm pronation & supination Joint involved Proximal radioulnar joint Distal radioulnar joint Humeroradial joint Plan of motion: Transverse plane Axis of motion Passing through the center of the radial head & the distal ulnar head Not parallel to the longitudinal axis of the forearm

24. Cont… Osteokinematic movements Motion: the radial head rotate within the annular ligament & spin on the capitulum of the humerus Range of motion (ROM) pronation 0-70 degree Supination 0-85 degree Note: pure motion occur as the elbow is held on 90 degree of flexion. If the elbow is extended, shoulder rotation occur simultaneously with forearm rotation Functional range: 50 degree pronation to 50 degree of supination Close kinematic chain motion Open the door knob

25. Cont… Arthokinematic movements ( convex on concave) Anteromedial gliding of the radius on ulna with forearm supination Posterolateral gliding of the radius on ulna with forearm pronation

26. Cont… Factors checking forearm pronation Ulna on radius Quardrate ligaments Posterior radioulnar ligament Oblique cord Factors checking forearm supination Anterior radioulnar ligaments Quadrate ligament Oblique cord Interosseous membrane

27. Stability of the elbow complex Factors affecting elbow stability Bony configration Coronoid process prevent anterior displacement Olecranon process prevent posterior displacement Humeroradial joint provides resistance to valgus stress Tension of ligaments Medial collateral ligament From the medial epicondyle of the humerus to coronoid process ( anterior fibers, the strongest)and to the olecranon process of ulna ( posterior fibers) as well as form form the olecranon process to the corocoid process of the ulna ( transverse fibers)

28. Cont… Tension of ligaments Medial collateral ligament Against valgus stress Taut at full extension ( anterior fiber) or full flexion ( posterior fiber) Lateral collateral ligament Against varus stress Taut at full flexion Anterior oblique ligament Prevent hyperextension Taut at extension Posterior oblique ligament Taut at flexion

29. Common injury at the elbow Direct stress Longitudinal compression stress fracture of radial head, coronoid or Olecranon process and supracondylar fracture Posterior stress posterior dislocation of the elbow

30. Repeated stresses Repeated wrist motions forearm pronated repeated tensile stress on extensor Carpi radialis brevis tennis elbow ( lateral epicondylitis) Repeated varus motion as forearm supinated Repeated tensile stress on Pronator teres, flexor carpi radialis Golfer’s elbow ( medial epicondylitis)