Biomech unit 4 Upper limb & Spine - deck 2 Flashcards
Specifically in the sagittal plane what is shoulder elevation termed ?
Shoulder elevation is termed forward flexion when the arm moves forward and backward extension or backward elevation when the arm moves backwards
Recall - Shoulder elevation is the term used to describe the movement of the humerus away from the side of the thorax in any plane
Specifically what is shoulder elevation termed in the coronal/ frontal plane ?
Shoulder elevation is called abduction when the arm moves away from the trunk and adduction as it moves towards the trunk
Note some authors use the terms elevation and depression interchangeably with abduction and adduction. (think for adduction you can term it shoulder depression)
What is true shoulder adduction limited by ?
The trunk
How can further shoulder adduction be achieved and overcome the limitation of the trunk being in the way ?
With slight forward flexion allowing you to adduct the arm in front of the trunk or with slight backward extension allowing you to adduct the arm behind the trunk (Fig. B)
What is the normal range in degrees of forward flexion and extension ?
- Forward flexion - 180 degrees
- Backward extension - 60 degrees
With the arm moving in front of the trunk what is the range of abduction and adduction possible ?
- Abduction = 180 degrees
- Adduction = 75 degrees
What 2 main factors decrease the range of motion in all planes of shoulder joint movements ?
- Increasing age
- Physical inactivity
Define what internal and external rotation of the shoulder joint is
Both are rotation about the longitudinal axis of the humerus. The difference is most easily described using examples:
- Consider a subject standing in the position shown in (Fig. A) with their arm by their trunk and elbow flexed at 90° - Internal rotation moves the forearm closer to the trunk and external rotation moves the forearm away from the trunk.
- Now consider a subject with their arm elevated and elbow still flexed to 90° as shown in (Fig. B) - Internal rotation moves the hand downwards and external rotation moves the hand upwards
What is the range of motion of internal and external rotation of the shoulder in degrees ?
Usually 90 degrees of internal or external rotation so 180 degrees in total
What is motion motion of the shoulder joint in the transverse (horizontal) plane is termed?
Horiztonal flexion and extension
Define what horizontal flexion and extension of the shoulder joint in the transverse plane is
- Horizontal flexion = the forward motion of the arm in the transverse plane (fig. A)
- Horizontal extension = the backward motion of the arm in the transverse plane (fig. B)
Starting from a position of 90 degrees of abduction (that is with the upper arm parallel with the ground) what is the range of motion in degrees for horizontal flexion and extension ?
- Horizontal flexion = 135 degrees
- Horizontal extension = 45 degrees
What are all 3 of the synovial articulations of the shoulder joint are prone to?
Dislocation
Which of the 3 synovial articulations of the shoulder joint is the most prone to dislocation and what type of dislocation is this termed as?
An anterior dislocation of the glenohumeral articulation
Describe what an anterior dislocation of the glenohumeral articulation is
It is is when the head of the humerus slips forward off the shallow glenoid fossa
Describe how an anterior dislocation of the glenohumeral articulation of the shoulder joint commonly occurs ?
If the arm suffers a heavy blow when the shoulder is abducted and horiztonally extended
- In this position the arm pivots about the acromion and the ligaments and muscles act to prevent the humeral head slipping forward.
- But if the blow is too heavy or the ligamental muscles too weak then a dislocation occurs.
When the arm is abducted and extended horizontally (the position most commonly causing anterior glenohumeral dislocations) what type of lever is the arm and shoulder functioning as ?
A first class lever in the same manner as a crowbar
Appreicate this:
With the arm fully extended the effort force is working a very large mechanical advantage over the resistance force enabling even a comparatively small external force to cause a dislocation. This can of course be likened to the action of a crowbar.
e.g. if the distance from the acromion to the point of application of the external force (dF) is 50 cm and the distance from the acromion to the point of application of the resultant of all the resistant force (dR) is 5.0 cm, then calculate the mechanical advantage (MA) and state what this means about how much more the resistance force would have to be compared to the applied force
MA = df / dr ==> = 10
Thus, in this case the mechanical advantage is 10, and the magnitude of the resistance force must be ten times that of the applied force
Bony landmarks of the humerus
What is the elbow joint formed by?
The distal surface of the humerus and the proximal articular surfaces of the forearm bones, the radius and ulna
What are the 3 articualtions of the elbow joint and what type of articulations are they ?
The 3 articualtions are:
- The humeroradial articulation
- The humeroulnar articulation
- The proximal radioulnar articulation
They are all synovial articualtions
What is the humeroradial articulation of the elbow joint formed by ?
The articulation between the capitellum of the distal humerus and the head of the radius
What is the humeroulnar articulation formed by ?
The articulation between the trochlea of the distal humerus and the reciprocally shaped trochlear fossa of the proximal ulna.
What is the proximal radioulnar articulation formed by ?
The head of the radius and the radial notch of the proximal ulna.
What 2 articulation in the elbow joint are responsible for allowing the elbow to flex and extend in a hinge-like mannor ?
The two articulations that include the humerus, the humeroradial and humeroulnar
State what the axis of rotation for flexion and extension of the elbow passes through and is parallel to
The axis of rotation passes through the middle of the trochlea and is roughly parallel to the line joining the lateral and medial epicondyles of the humerus.
State the range of flexion and extension of the elbow joint
The full range of flexion-extension is 140 degrees:
- 140 degrees of flexion
- 0 degrees of extension
What movements does the radioulnar articulation allow for in the elbow joint ?
It allows rotation of the forearm about a longitudinal axis. This rotation is termed pronation and supination
If the elbow is pronated what way does the hand face when the elbow is extended with the upper arm inline alongside the trunk?
The hand faces posteriorly
If the elbow is pronated what way does the hand face if the elbow is flexed 90 degrees?
The hand faces downwards
Specifically what bony landmarks are responsible for pronation and supination of the elbow ?
Pronation and supination are achieved by rotation of the head of the radius in the radial notch of the ulna in a pivot-like manner (Fig. A)
(this is essentially talking about the bony landmarks that make up the radioulnar articulation)
What does Pronation and supination are achieved by the rotation of the head of the radius in the radial notch of the ulna in a pivot-like manner occur inside ?
It occurs inside the ligamentous sling which binds the radius to the ulna, the annular ligament (Fig. B)
State what the axis is which pronation and supination occur around and also describe what happens to the radius and ulnar in relation to eachother during pronation and supination of the elbow joint
- The longitudinal axis passes through the radial head and the distal ulna articular surface.
- The rotation about this axis results in the migration of the distal end of the radius around the distal end of the ulna.
State the range of motion of pronation and supination of the elbow joint
The total range of pronation-supination is 150 degrees:
- 70 degrees of pronation
- 80 degrees supination
How does the max range of motion possible in the elbow joint compare to the actual range of motion required for most daily activities?
- The required ranges for various daily activities is much less than that which the elbow can achieve.
- Around 100 degrees of flexion motion is required from 30 to 130 degrees (to achieve all the daily tasks shown) and around 100 degrees of pronation and supination motion is required (to achieve all the daily tasks shown) from around 50 degrees pronation and 50 degrees supination.
Note - Would learn this bit not the specific degrees from the table
What 3 things contribute to the stability of the elbow joint ?
The bony structure, the ligaments and the muscles
In waht direction does the olecranon process of the elbow joint resist and how?
The olecranon process, which in profile resembles the end of a spanner, it holds the trochlea like a nut resisting forces in the anteroposterior and posteroanterior directions
What direction of forces does the olecranon process of the elbow joint not resist?
Forces acting in a lateral and medial direction.
What is the side to side (forces acting in medial and lateral directions) stability of the elbow joint provided by ?
The two collateral ligaments:
- The ulnar or medial collateral ligament
- The lateral collateral ligament
Which of the two collateral ligaments of the elbow is the most important and state why
. The ulnar or medial collateral ligament
It is more important than the lateral collateral ligament because the lateral collateral provides only limited resistance whereas the medial provides more resistance to the movement it prevents
State specifically the direction of forces which the medial and lateral collateral ligaments of the elbow resist
- The medial collateral resists abduction forces
- The lateral collateral provides only limited resistance to adduction forces
Due to the limited resistance to adduction by the lateral collateral ligament what assists the ligament in this function?
The anconeus muscle (located on the lateral aspect of the elbow.)
State the origin and insertion of the anconeus muscle
- Origin on the lateral epicondyle of the humerus
- Insertion on the olecranon and superior portion of the ulna shaft
Why is the apparent weakness of the elbow joint to adduction not a problem ?
- Because valgus stability is much more important functionally than varus stability.
- This is easily appreciated if you consider the forces acting during a throwing or hammering action or a fall on an outstretched arm.
The stability of the elbow joint means that dislocations are much less common than dislocations of the shoulder. However, what is the typical way in which a dislocation of the elbow may occur ?
A fall on a outstretched arm in almost full extension can result in an anterior dislocation, whereby the distal end of the humerus slides forward over the coronoid process.
