Unit 4 - Biomechanics of the upper limb & spine Flashcards
What 2 bones make up shoulder girdle?
Clavicle & scapula
What 4 articulations make up the shoulder joint & what type of articulations are they?
3 synovial: - glenohumeral - acromioclavicular - sternoclavicular 1 bone-on-muscle-on-bone joint: - scapulothroacic
What type of joint is the glenohumeral?
Ball (humeral head) & socket (glenoid fossa of scapula)
What structures aid stability of the glenohumeral joint?
Glenoid labrum (thick cartilagenous rim)
Capsule
Rotator cuff
What muscles make up the rotator cuff & what is its function?
Muscles:
- Subscapularis
- Infraspinatus
- Supraspinatus
- Teres minor
Pushes on humeral head, providing dynamic restraints to anterior, posterior & inferior displacement
What structures stabilise the AC joint?
Superior & inferior AC ligaments which prevent joint being pulled apart
2 parts of the coracoclavicular ligament which limits movement of clavical
RoM limited to a few degrees during arm abduction (restricted by thorax & muscle attachments)
How much does the clavicle elevate during arm elevation?
~4 degrees for every 10 of arm elevation (for first 90 of arm elevation - past 90 clavicle elevation is negligible)
Why does the clavicle rotate?
During arm elevation/depression clavicle rotates about longitudinal axis due to attachment of costoclavicular ligament
Why is the scapulothoracic articulation not a true joint?
No direct bony/ligamentus connections
What 2 muscles separate scapula from posterior thorax?
Serratus anterior:
- originates on upper 8/9 ribs & inserts on anterior surface of scapula along vertebral boarder
- helps hold scapula against thorax (preventing winging) & is a strong abductor (for pulling/pushing)
Subscapularis:
- originates from subscapular fossa & inserts on lesser tubercle of humerus
- medially rotates humerus
What is the range of motion of the shoulder in the sagittal plane?
Forward flexion - 180
Backward extension - 60
What is the range of motion of the shoulder in the coronal plane?
Abduction - 180
Adduction - 75
Internal rotation - 90
External rotation - 90
What is the range of motion of the shoulder in the transverse plane?
Horizontal flexion - 135
Horizontal extension - 45
What is the most common type of shoulder dislocation?
Anterior dislocation of glenohumeral joint
Heavy blow when arm abducted & extended. If blow too heavy/muscles too weak –> dislocation
Arm & shoulder acting as 1st class lever with resistance to dislocation at a disadvantage
What 3 articulations make up the elbow joint?
Humeroradial
Humeroulnar
Proximal radioulnar
How much extension & flexion are possible at the elbow?
Extension - 0
Flexion - 140 (40 between arm & forearm when fully flexed)
Humeroradial/ulnar articulations allow hinge movement - axis of rotation through middle of trochlea
What articulation in the elbow allows for pronation & supination?
Describe hoe it comes about
Proximal radioulnar
Rotation of radial head in radial notch of unla in pivot-like manner (occurs in annular ligament - ligamentous sling wich binds through radius to ulna)
Longitudinal axis passes through radial head & distal unla articular surface - rotation about this axis results in migration of distal radius around ulna
What is the max RoM for pronation & supination of forearm?
Pronation - 70
Supination - 80
How is stability achieved at the elbow?
Olecranon process holding trochlea like a spanner & nut (for anterior-posterior stability)
2 collateral ligaments:
- medial (ulnar): most important, preventing abduction
- lateral: provides limited resistance to adduction. Aided by anconeus muscle located on lateral aspect of elbow (weakness doesn’t cause problem as valgus stability more important)
What bones make up the carpals?
Scaphoid Lunate Triquetrum Pisiform Trapezium Trapezoid Capitate Hamate
What is the function of the pisifrom?
Is the insertion point of flexor carpi ulnaris (flexes & adducts wrist)
Increases lever arm of flexor carpi ulnaris - decreasing the force required from the muscle
What articulations are involved in the wrist?
Radiocarpal
Midcarpal
Carpometacarpal
Intercarpal
Describe the radiocarpal joint
Condyloid joint - oval shaped condyle of radius fits into eliptical depression between lunate & scaphoid
Allows flexion, extension, abduction, adduction & circumduction
Describe the range of motion at the wrist
Flexion: 80-90 (40% at radiocarpal & 60% at midcarpal)
Extension: 70-80 (67% at radiocarpal & 33% at midcarpal). Most critical movement
Abduction: 15-20
Adduction: 35
What articulations are found in the hand?
Carpometacarpal Intermetacarpal Metacarpophalangeal Proximal interphalangeal Distal interphalangeal
Describe 1st carpometacarpal joint
Saddle joint between trapezium & 1st metacarpal at base of thumb
Most freely moving CMC joint & allows thumb to oppose fingers giving great dexterity
All CMC joints surrounded by joint capsule & reinforced by ligaments
Describe intermetacarpal joints
Irregular articulations formed by prox ends of adjacent metacarpals
Share joint capsules of CMC joints
Describe metacarpophalangeal joints
Condyloid - rounded distal heads of metacarpals & concave prox ends of phalanges
Forms the knuckles
Each enclosed in a capsule & stabilised by strong collateral ligaments (MCP of thumb strengthened by additional dorsal ligament)
What type of joints are DIP & PIPs?
Hinge joints allowing only flexion/extension
Describe the range of motion in the:
- Metacarpals?
- MCPs?
- DIP/PIPs?
Metacarpals - 2nd & 3rd immobile while a small amount of flexion/extension is allowed in 4th & 5th
MCPs - allow flex/extension & add/abduction. Max flex ~90 & extension varies between individuals depending on ligament laxity
PIPs - flexion 100-110
DIPs - flexion 90
(extension for both depends on ligament laxity)
Describe the range of motion at the thumb
MCP does not allow as much flexion as fingers (30-90) but has more extension
CMC joint:
- flexion (thumb across palm) - 15
- extension (thumb away from side of palm) - 20
- abduction (thumb away from palm) - 60
- small degree of rotation
What is the interaction between hand and wrist movements?
As wrist changes positions it alters lengths of tendons crossing from forearm into wrist
When wrist straight fingers can be easily clenched however if wrist is flexed it becomes difficult to fully flex fingers (and vice versa)
What common features do unfused vertebrae have (bar C1 & 2)?`
Vertebral body - flat round central body
Neural arch - arch of bone that forms spinal foramen
Spinous process - projects inferoposteriorly
2x transverse processes - project laterally
At what points to adjacent vertebrae articulate?
Vertebral body via intervertebral disc
2x facet joints - synovial joints either side of the arch
Describe the nucleus pulposus
Lies in centre of intervertebral discs
Formed by strongly hydrophilic gel enmeshed in random collagen matrix
Gel produces high water content & elevated nucleus pressure which balances compressive stress
If applied stress increases, water is driven out of disc until new equilibrium is reached (disc rehydrates when stress decreases)
Describe the annulus fibrosis
Tough layer that surrounds nucleus pulposus composed of collagen fibres forming concentric layers (lamellae) with alternating orientations
Arrangement resists high bending & torsional loads
How are C1 & C2 different to other vertebrae?
C1 (atlas) - no body, composed of a ring withing which an oval fossa articulates with axis
C2 (axis) - has dens which protrudes superiorly & forms small synovial joint with oval fossa of atlas
At which points of the thoracic vertebrae do the ribs articulate with?
Head of each rib with vertebral body
Tubercle of each rib with transverse process
Describe motion in the spine:
- flexion-extension?
- lateral bending?
- rotation?
Flexion-extension:
- varies between different regions (cervical>thoracic)
- extent of flexion & extension also varies between regions
Lateral bending:
- similarly cervical has greatest Rom & thoracic least
- no lateral bending between C1 & 2
Rotation:
- decreases down spine
- greatest between C1 & 2
How can you explain higher load on spine when sitting compared to standing?
Moment arm of upper body weight about lumbar spine increases during sitting due to backward tilt of pelvis
This moment must be counter balanced by extension moment produced by posterior back muscles (producing compressive load)
