Biomechanics Exam 2

1. Single jt capsule that encloses the HU jt, HR jt, and the superior RU jt.
2. Formed bt the convexity of the trochlea on the distal end of the humerus ART with the concavity of the trochlear notch on the ulna
3. ART Surfaces are congruent --> increases with increasing jt loads as a result of the deformation of the articular cartilage
a. Provide most of elbows structural stability
4. Motion occurs in sagittal plane in the form of FLX and EXT

1. Formed by the ART bt the sup surface of the radial hd(concave) with the convexity of the capitulum on the distal humerus
2. In full EXT
a. The SUP surface of the radial hd is only going to ART with a portion of the capitulum
b. The contact bt the SUP surface of the radial hd with the capitulum will increase as the elbow flexes
3. With given loads thru this jt in posns of FLX, we are going to have less pressure per unit of surface area

· Angulation formed in frontal plane of the elbow by the long axis of the humerus aligned parallel to the ulna
· Evident in the anatomical position
· The angulation is valgusàdistal segment moves away from the midline relative to the proximal segment
“Cubitus valgus”

• from 13-15 degrees; larger in females which may or may not be statistically significant
• In men: average is 5-10 degrees
• In females: average is 10-15, some sources say 20 degrees

• If the valgus angulation is more than the normative valuesàcubitis valgus deformity
• If it is less than normal or varusàcubitis varus deformity
• associated with fractures in the distal humerus
• “gun stock” deformity

• Look at bony architectureà”tongue and groove fit” bt humerus, radius and ulna
• This fit makes LAT and MED gliding bt the ART surfaces nearly impossible
• Reciprocal convex-concave surfaces guide FLX and EXT at the elbow
• The radial hd plays a role in limiting valgus excursion at the elbow
  o When removing radial hd-->30% decrease in stability

O Surround three jts
o Loose ANT and even more loose POST
o During the movements of FLX and EXT of the elbow, these folds will unfold and refold to allow movement to occur

O Folds with flexion, Like an accordian
o Unfolds with extension

O Folds with extension
o Unfolds with flexion

Larger of the two (LCL)
Reinforces the capsule MED and functioning as a whole, fxs to resist valgus stresses to the elbow-->Deviation of ulna away from the midline with respect to the long axis of the humerus

Attaches distally to the coronoid process (AMCL)
· strongest and stiffest fibers of the three
· provides most of the resistance against a valgus force “ABD force”
· some fibers are taut throughout the ROM bc the ANT fibers fall on both sides of the axis of rotation
· most anterior pt is taut in EXT of the elbow
· midpart of AMCL is taut in the midrange of FLX
· post part of the AMCL becomes progressively taut with FLX
· most fibers will be taut when elbow is extended or near full EXT

(PMCL) attaches to the olecranon process and fxs to resist excessive valgus forces
· will become taut after 60 to 90 degrees of FLX and is most taught at the extreme of elbow FLX
· plays a role in resisting distraction forces to the jt typically found in athletes (pitchers, tennis)

Span MED aspect of the trochlear notch
· does not attach to humerus; runs from olecranon to coracoid process

O Runs from the lat epicondyle of the humerus to insert on the annular ligament

Will remain taut throughout the entire FLX/EXT movt

Stabilizes against excessive varus(ADD) stresses and against excessive compression bt the ART surfaces of the HR jt.

Primary LAT stabilizer for the elbow jt
· has a significant role in resisting varus stressed
· taut in FLX and EXT by acting a stabilizer throughout the ROM
· most taut in extreme FLX