Chapter 6 - Elbow and Forearm complex Flashcards
Elbow joints
1) humero-ulnar joint
2) humeroradial joint
forearm joints
1) proximal radio-ulnar joint
2) distal radio-ulnar joint
“carrying angle” of the elbow
normal cubitus valgus(elbow medially) = 15 degrees
- excessive cubitus valgus = 30 degrees
- cubitus varus = 0 degrees
medial collateral ligament
anterior, posterior, transverse fiber bundles
- anterior fibers = most resistance to valgus force; taut near full extension
- posterior fibers = become taut in extreme flexion
Fall on outstretched arm injures which ligament
medial collateral ligament
nerve susceptible to injury with valgus stretch
ulnar nerve
repetitive, valgus producing forces
pitching baseball, volleyball spike
“position of comfort”
80 degrees, capsule most compliant
- ligaments most relaxed
- accomodates swelling and inflammation
lateral collateral ligament
resists varus-directed force
- taut in full flexion
lack of flexion may be caused by:
- paralysis of flexor muscles
- contracture due to immobilization
- loss of joint integrity from arthritis or fracture
lack of extension may be caused by:
- flexion contracture due to immobilization
- spasticity of elbow flexors
- paralysis of triceps
- scarring anterior elbow area
- loss of joint integrity from arthritis or fracture
range needed to have full functional ability
30-130 degrees
elbow extension requires extensibility:
dermis, flexor muscles(biceps, brachialis), anterior capsule, anterior fibers of MCL
elbow flexion requires elongation of:
- posterior capsule
- extensor muscles
- ulnar nerve
- posterior fibers of MCL
arthrokinematics of humeroradial joint
- roll and slide(same direction) of concave fovea and convex capitulum
function interosseous membrane
dissipates force from radius to ulna to prevent radial fracture
- 80% of compression force through hand transmits through the lateral side of the carpus and the radius
- not aligned to resist distally applied forces on the radius
structures preventing “pulled elbow”
- oblique cord
- annular ligament
- brachioradialis
necessary AROM at forearm to be functional with most ADL’s
50 degrees in each direction
arthrokinematics for supination
- spinning of radial head within fibro-osseous ring of annular ligament/radial notch of ulna
- concave ulnar notch of radius rolls and slides in similar directions on head of ulna
arthrokinematics of pronation
- similar to supination
- full pronation exposes articular surface of ulnar head
structures preventing supination
- palmar capsular ligament
- pronator teres
structures preventing pronation
- dorsal capsular ligament
- biceps on bicipital tuberosity
Elbow flexors(biomechanics)
- dominant side shows significantly higher levels for flexion, but not extension, pronation/supination
- flexor torques 70% greater than extension torques
- flexor torques are 20-25% greater with forearm supinated versus pronated(longer moment arm for biceps)
- maximal flexor torque occurs at about 90 degrees of flexion
elbow extension
- triceps produces majority of total extensor torque
- anconeus is first to initiate movement
- medial head of triceps is next(workhorse)
- lateral head is active for moderate to high levels of effort
- long head is activated last
elbow extensors(biomechanics)
- maximal elbow extension torque at about 90 degrees
- muscle length, not leverage, determines maximal torque in elbow extensors
supinator muscles
primary: supinator, biceps(high power - recruited last)
- if biceps contracts, then elbow triceps and posterior deltoid may have to contract to stabilize
- supination torque is greatest around 90 degrees
- supinators produce 25% greater isometric torque than pronators
pronator muscles
primary: pronator quadratus, pronator teres
- pronator quadratus = most active and consistently used
- pronator teres = involved with higher power actions
