Elbow Complex Biomechanics Flashcards
Proximal Radioulnar Joint
Head of radius in radial notch of ulna
Distal Radioulnar Joint
Head of ulna in ulnar notch of radius; TFC is articular disc
Proximal Elbow complex
Hinge joint, uniaxial diarthrodial, 1 DF
Superior and Inferior RU joint
Pivot Joint, uniaxial diarthrodial, 1 DF
Elbow joint capsule
Large, lose, weak anterior and posterior
Cross contamination of infections possible at 3 joints
MCL
Anterior, Posterior, and Oblique bands
Anterior protects valgus best at 20-120 flexion
Oblique helps ulnar nn and anchors ant/post bands
LCL
Resists varus and distractive forces
Weaker than medial
Annular Ligament
Stabilizes head of radius to ulna
Very strong
Interosseous membrane
Fibers in all directions for strength
Humeroulnar joint kinematics
Concave on convex
Same glides and rolls
Humeroradial joint kinematics
Concave on convex
Same glides and rolls
Proximal Radioulnar joint Kinematics
Radial Head longer A-P when supinated
Radial Head longer M-L when pronated
Spins on capitulum in relation to radial groove
Distal Radioulnar joint Kinematics
Concave radius on convex ulna
Anterior roll and glide pronation
Posterior roll and glide supination
Axis of motion at elbow
Carrying angle
5-15 Degrees
Cubital valgus when >15
Cubital Varus when <5
Carrying angle disappears when…
Pronation combines with full elbow extension/flexion
Due to position of the lever
Open Pack position
Joint capsule and ligaments have greatest laxity
Greatest amount of accessory mobility present
Closed Pack position
Joint capsule and ligaments are most taut
Most often position of greatest joint congruency
Extension ROM
0 degrees normal May have 5-10 degrees Hard end feel Humeroulnar closed pack Humeroradial open pack
Flexion ROM
135-145 AROM
150-160 PROM
Soft/Hard endfeel
Humeroulnar joint closed pack at 70 degrees
Humeroradial joint closed pack at 90 degrees
Active Insufficiency
Agonist muscles too short or too long to produce effective tension
Passive insufficiency
Antagonist Muscle is on stretch and is too short to allow further passive ROM
Spurt Muscle
Mobility muscle
Increased rotary component and angle of pull
Proximal insertion
Shunt Muscle
Decreased rotary component, decreased angle of pull
Increased compressive force
Distal insertion
Biceps
Spurt muscle
MA greatest between 80-100
Brachioradialis
Shunt muscle
MA greatest between 100-110
Brachialis
Spurt muscle
MA greatest at 100
Work horse muscle
Triceps
Medial head is work horse
Synergistically w/ biceps during resistive forearm supinatoin
Anconeus
Initiates elbow extension
Active w/ forced finger flexion and extension
Draws capsule out to prevent impingement
Pronation ROM
85 degrees
Supination ROM
90 degrees
Proximal RU joint open pack position
35 supination, 70 elbow flexion
Proximal RU joint closed pack position
5 supination, extension
good for stabilization
Lateral Epicondylitis
Repetitive use, primarily ECRB
Tensile stress leads to microtears
Medial Epicondylitis
Repetitive use, primarily pronater teres, FCR, FCU
Nursemaids elbow
Longitudinal traction force
Radial head extracted from annular ligament then pinches it
Medial Collateral Ligament Sprain
Increased tensile stress leads to increased carrying angle
Increased compression of radial head on capitulum
Avascular necrosis when prolonged
