Biomechanics Elbow Flashcards
joints that comprise the elbow
humero-ulnar joint
humero-radial joint
proximal radio-ulnar joint
distal radio-ulnar joint
most of structural stability of elbow comes from which joint
humero-ulnar
humero-ulnar joint
- type of joint
- motions allowed
modified hinge joints
mostly flexion/extension
cubital valgus
- other name
- normal range
- excessive value
- cubital varus (other name)
carrying angle
normal = 13 +/- 6
excessive > 20
cubital varus = gunstock deformity
ligaments of the elbow
ulnar collateral ligament -anterior and posterior fibers radial collateral ligament lateral ulnar collateral ligament annular ligament
UCL anterior fibers
-function
limit
- valgus
- extension
- flexion
UCL posterior fibers
-function
limit
- valgus
- flexion
radial collateral ligament
-function
limits
- varus
- external rotation (supination)
lateral UCL
-function
limits
- varus
- ER (supination)
- flexion
annular ligament
-function
limits
- radial distraction
- ER (supination)
what type of force can lead to a UCL rupture
valgus force (force to lateral side of elbow)
“Tommy John” repair
-what is repaired
UCL
what does ORIF stand for?
open reduction, internal fixation
humero-ulnar arthrokinematics
-what is the rule (open chain)
concave on convex
humero-radial joint arthrokinematics
- ____ sagittal stability
- provides _____ of resistance against valgus forces
- what moves on what?
minimal sagittal stability
provides 50% of resistance
concave fovea of radius rolls and slides across convex capitulum in flexion/extension
interosseus membrane
-function
binds radius and ulna together
stable attachment for muscles
transmist force proximally through upper limb
radiocarpal joint stability
when load bearing through the hand occurs, muscles contract that are attached to the radius, causing compressing with contraction
-this adds to the stability of the RC joint
pronation/supination of forearm
- occurs at which joints
- hand and wrist connect firmly to _____
- how does pronation occur?
occurs at proximal and distal radio-ulnar joints
hand and wrist connect firmly to radius, not ulna
distal end of radius crosses over fixed ulna for pronation
triangular fibrocartilage complex
- function
- components
primary stabilizer of the distal radio-ulnar joint
-holds ulnar head firmly against ulnar notch of radius in pronation/supination
components
-articular disc
-capsular ligaments
-ulnar collateral ligament
radio-ulnar arthrokinematics of supination and pronation
distal
-concave ulnar notch of radius rolls and slides over convex ulna
-concave on convex
proximal
-radial head rotates in the annular ligament/radial notch of unla
-primarily spin
humero-radial arthrokinematics of supination and pronation
concave fovea of radius “spins” against convex capitulum of humerus
elbow flexors
- what are they?
- which has greatest force potential
- which has greatest mechanical advantage
biceps brachii brachialis brachioradialis greatest force potential -brachialis -greatest PSCA greatest mechanical advantage -brachioradialis -moment arm
at what angle do the following occur for elbow flexion
- maximum elbow torque
- maximum force
- maximum moment arm
torque -80-100 force -70-85 moment arm -80-110 (except brachioradialis)
synergistic relationship between biceps brachii and posterior deltoid
simultaneous shoulder extension can increase elbow flexion capability
elbow extensor muscles
- what are they
- which has greatest force potential
- which has greatest mechanical advantage
triceps -long head -medial head -lateral head anconeus greatest force -LH trices -PCSA greatest mechanical advantage -triceps
unique function of each of the elbow extensors
anconeus
-first to initiate, stays on at low level, assists with elbow stabilization
medial head
-initiates after anconeus, stays on
-workhorse muscle
lateral and long heads come on last
-reserve muscles for maximal extension force
which muscles are the primary elbow stabilizers?
-similar to…
elbow extensors
similar to quadriceps in the knee
to pronate/supinate, the muscle must attach…
on both sides of axis of rotation
-humerus or ulnar attachment proximally –> radius or hand distally
must have an internal momemt arm that produces rotation around pronation/supination axis
functional association between forearm pronators/supinators and shoulder IR/ER allows…
nearly 360 degree movement of hand in space
forearm supination stronger with shoulder in…
ER
when is supination strongest
- why
- function of triceps during supination
strongest in 90 elbow flexion
optimizes biceps brachii
triceps co-contract to prevent elbow flexion
which are stronger: pronators or supinators
supinators produce 25% more torque
left-hand dominant person has a disadvantage with things such as using a screwdriver
