Biomech unit 4 Upper limb & Spine - deck 3 Flashcards
During common daily activities what can the elbow joint forces be as high as?
2000 N which is almost 2.5 to 3 times body weight.
e.g. For example, the action of pulling an object, such as a table, can generate a joint force of about 1900 N, and during dressing and eating activities these can be around 300 N
Why are elbow joint forces so high?
- Because of the large muscle forces that need to be generated to perform these activities act to pull the two sides of the joint together.
- The muscle forces need to be large since the muscles generally have small moment arms compared to the moment arms of the externally applied forces
e.g. pic shown - Notice that the moment arm of the weight of the dumbbell and the moment arm of the weight of the forearm and hand are both several times larger than the moment arm of the biceps muscle force
Do worked example on pg. 160
What is the function of the wrist joint ?
It allows the hand to move relative to the forearm and it transmits loads between the forearm and hand.
What is the wrist joint formed by ?
- The distal radius
- The structures within the ulnocarpal space
- The carpal bones
- And proximal ends of the metacarpals
What is the mneumonic for remembering the carpal bones of the hand ?
So, Long, To, Pinky, Here, Comes, The, Thumb
(goes from lateral to medial proximal row and then medial to lateral distal row - starts at scaphoid ends at Trapezium)
What are 7 of the 8 carpal bones are arranged into?
2 rows:
- Proximal row
- Distal row
List the carpal bones which make up the proximal row
- Scaphoid
- Lunate
- Triquetrum
List the carpal bones which make up the distal row
- Hamate
- Capitate
- Trapezoid
- Trapezium
What is the 8th carpal bone which is not part of the proximal or distal rows - state its exact position
- The pisiform does not form part of the rows
- It is positioned anteriorly to the triqeutrum
Which of the carpal bones can be easily palpated ?
The pisiform - It projects anteriorly on the little finger side of the hand as a small rounded elevation
What inserts on to the pisiform bone ?
The flexor carpi ulnaris muscle
What is the function of the flexor carpi ulnaris muscle ?
It flexes and adducts the wrist
What can be easily palpated when the wrist is flexed ?
The tendon of the flexor carpi ulnaris muscle
What other bone and tendon arrangement can the arrangement of the pisiform and tendon of the flexor carpi ulnaris muscle be likened to and why?
The arrangement of the pisiform and the flexor carpi ulnaris is comparable to the arrangement of the patella and the knee extensor muscles in that the pisiform increases the lever arm of the flexor carpi ulnaris
Is the wrist a relatively stable joint ?
Yes
What structures provide the stability of the wrist joint ?
The intricate ligamentous structures and the precise opposition of the multifaceted (many sided) articular surfaces rather than from any inherent bony stability, such as that found in the hip joint.
Numerous articulations between what bones is motion of the wrist joint dependant on ?
Numerous articulations formed between the carpal bones and between the carpal bones and adjacent bones of the hand and forearm.
What are the 4 main joints formed by the numerous articualtions that make up the wrist joint?
- The radiocarpal joint
- The midcarpal joints - The midcarpal joint is formed by the scaphoid, lunate, and triquetral bones in the proximal row, and the trapezium, trapezoid, capitate, and hamate bones in the distal row.
- The carpometacarpal joints - articulate the distal row of carpal bones and the proximal bases of the five metacarpal bones.
- The intercarpal joints - articulations between the individual carpal bones
What type of joint is the radiocarapl joint ?
It is a condyloid joint - whereby an oval-shaped condyle fits into an elliptical (oval) depression
What are the attachements of the inter-articular disc (articular cartilage) which occupies the ulnocarpal space?
It is attached at its apex to the styloid process of the ulna and at its base to the ulnar notch of the radius
What movements does the wrist joint allow ?
Flexion & extension, Abduction & adduction:
- flexion results in the hand tilting forwards
- extension results in the hand tilting backwards
- abduction results in the hand tilting outwards
- adduction results in the hand tilting inwards
What percetange of flexion and extension is accounted for on average by the radiocarpal and midcarpal joints in the wrist ?
- Approx 60% of flexion occurs at the midcarpal joint, 40%, in the radiocarpal joint
- The opposite for extension - 67%, of extension occurring in the radiocarpal joint and 33%, at the midcarpal joint
What bones form the hand ?
The metacarpals and phalanges
How many metacarpal and phalange bones are there in the hand ?
- 5 metacarpals (one at the base of each digit)
- 14 phalanges (3 for each finger except the thumb which has 2)
What bones form the first CMC joint in the hand and why is this joint of great significance?
It is formed by the articulation between the trapezium and the first metacarpal, at the base of the thumb
It is of great significance because it is the most freely moving CMC joint. It allows the thumb to oppose the fingers giving the human hand much greater dexterity than the forepaw of any other animal and allows us to manipulate our environment so effectively
Pic shows opposition of the thumb
What type of joint is the first CMC joint and what movements does this joint allow?
- It is a saddle joint - the articulating surfaces resembling reciprocally shaped saddles
- It allows the first metacarpal to flex and extend, and abduct and adduct.
