Biomechanics Exam 2

1. What are the characteristics of the HU Joint Articular Surfaces?

1. Compound jt capsule that encloses the HU jt only. 2. Formed by the concavity of the trochlea on the distal end of the humerus ART with the convexity of the trochlear notch on the ulna. 3. ART Surfaces are incongruent --> decreases with increasing jt loads as a result of the deformation of the articular cartilage. 4. Motion occurs in frontal plane in the form of ADD and ABD.

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

The correct features of the HU Joint Articular Surfaces include a single joint capsule enclosing various joints, congruent articular surfaces providing structural stability, and motion occurring in the sagittal plane. The incorrect answers provided misrepresent these characteristics by introducing incorrect descriptions of the joint capsule, articular surfaces, load effects on the cartilage, and the plane of motion.

Explanation

The correct features of the HU Joint Articular Surfaces include a single joint capsule enclosing various joints, congruent articular surfaces providing structural stability, and motion occurring in the sagittal plane. The incorrect answers provided misrepresent these characteristics by introducing incorrect descriptions of the joint capsule, articular surfaces, load effects on the cartilage, and the plane of motion.

2. What are the articicular surfaces in the HR joint?

3. The contact between the sup surface of the radial head and the capitulum decreases as the elbow flexes.

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

4. Increased pressure per unit of surface area is observed with given loads in positions of flexion.

2. Only the sup surface of the radial head makes contact with a small portion of the capitulum in full extension.

When articulating surfaces in the HR joint, it is important to note that the correct contact is made between the concave articular surface of the radial head and the convexity of the capitulum on the distal humerus. This contact increases as the elbow flexes, distributing pressure evenly and reducing pressure per unit of surface area.

Explanation

When articulating surfaces in the HR joint, it is important to note that the correct contact is made between the concave articular surface of the radial head and the convexity of the capitulum on the distal humerus. This contact increases as the elbow flexes, distributing pressure evenly and reducing pressure per unit of surface area.

3. What is the Carrying Angle?

An angulation that is only visible when the arm is at a 90-degree abduction angle from the body

· 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”

An angulation formed in the sagittal plane of the elbow by the long axis of the humerus aligned parallel to the radius

A angulation that is varus in nature and leads to the distal segment moving closer to the midline relative to the proximal segment

The carrying angle refers to the angulation formed in the frontal plane of the elbow where the humerus aligns parallel to the ulna, making it more evident in the anatomical position. This angulation is valgus in nature, meaning the distal segment moves away from the midline relative to the proximal segment, a condition known as 'Cubitus valgus'. The incorrect answers provided do not accurately describe the concept of the carrying angle.

Explanation

The carrying angle refers to the angulation formed in the frontal plane of the elbow where the humerus aligns parallel to the ulna, making it more evident in the anatomical position. This angulation is valgus in nature, meaning the distal segment moves away from the midline relative to the proximal segment, a condition known as 'Cubitus valgus'. The incorrect answers provided do not accurately describe the concept of the carrying angle.

4. What is the average carrying angle?

20-25 degrees

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

8-10 degrees

3-5 degrees

The average carrying angle ranges from 13-15 degrees, with it being larger in females. In men, the average is around 5-10 degrees, while in females it averages around 10-15 degrees, according to various sources.

Explanation

The average carrying angle ranges from 13-15 degrees, with it being larger in females. In men, the average is around 5-10 degrees, while in females it averages around 10-15 degrees, according to various sources.

5. What are the implications of deviations from the average carrying angle?

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

Bone growth

Infection

Nerve damage

6. What are the stabilizing structures of the elbow?

The ulnar collateral ligament provides stability primarily in rotational movements of the elbow.

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

The brachialis muscle helps stabilize the elbow joint during flexion and extension.

The synovial fluid within the elbow joint cavity acts as the primary stabilizing structure.