BioMechanics Exam 3 Flashcards
Glenohumeral motion arthrokinematic goal
Combine rotation (roll) and translation (slide) to keep humeral head centered on glenoid
Eliminate unwanted slide with active and passive restraints
Passive restraints of glenohumeral joint
Bony geometry
Labrum
Capsuloligamentous structures
Long head of bicep
Negative intra-articular pressure
Arm abduction
Rotator cuff muscles down and deltoid up
Major abductors of humerus
Supraspinatus
-Initiates abduction
Lateral deltoid
-Most active after 30 degrees of abduction
-Superior dislocating component neutralized by infraspinatus, subscapularis, and teres minor
Phase one of GH abduction
Setting phase initiated by supraspinatus
Phase two of GH abduction
The scapula has greater motion, approaching a 1:1 ratio with the humerus
Phase three GH joint abduction
Later in range, the glenohumeral joint again dominates the motion
What muscle is susceptible to damage from impingement?
Supraspinatus
Know how the roll slide mechanism can prevent impingement
When the supraspinatus pulls, a roll is created by abduction and is countered with slide action
Requires external rotation of humerus to clear greater tuberosity
Requires upward rotation of scapula to elevate lateral end of acromion
Know how the roll slide mechanism can lead to impingement?
When the supraspinatus pulls, a roll is created by abduction and is not countered with slide action
Primary impingement
Structural stenosis of subacromial space
Secondary impigment
Functional stenosis of subacromial space due to abnormal arthrokinematics
Hip
Attaches hip to trunk
Deeper labrum at hip
Hips are weight bearing joints
Shoulder
Attaches arms to trunk
Parts of hip
Ilium, sacrum, ischium, pubis
acetabulum
Makes pelvic bowl
Has parts of the ilium, ischium and the pubis
Is socket
Horse shoe shape
Only posterior head of femur attaches to the socket
Fovea capitis
head of femur dimple to make the joint more stable
Is an attachment point for ligamentum teres
Affects ligamentum teres attachment and size
Ligamentum teres
Provides stability for hip
Ligament between the femoral head and the acetabulum.
Does not exist in the shoulder
The hip joint
Is a ball and socket joint, made up of the top of the thigh bone called the femoral head (the ball) and the part of the pelvis called the acetabulum (the socket).
Fovea brevis
Small fovea capitis diameter
Smaller, narrower ligamentum teres
Less stable hip
Fovea magnus
Large fovea capitis diameter
Fovea plane
Shallow fovea capitis
Ligament has less surface area
Fovea profunda
Deep fovea capitis
Fovea capitis Index Equation
Ratio between diameter of femoral head to diameter of fovea capitis
Has small clinical role to predict hip issues
Good to take several pictures under different magnification
Angles of the acetabulum
Angle of acetabular torsion
Center Edge Angle of the acetabulum
Angle of acetabular torsion
Orientation of medial and front and down
Center edge angle (CEA)
Average range: 25-40 degrees
Function: Provide lateral stability of the pelvis (pushing in opposition to pelvis that is being pushed outward from wedged sacrum) and to prevent superior dislocation
Angle created with vertical line through vertical head of femur to the superior edge of the acetabulum
Measure of how deep the acetabulum is a way to evaluate risk of dislocation
CEA of less than 15 degrees
Certain dislocation
CEA of 15-25 degrees
Possible dislocation
Hip abductors
Gluteus minimus
Gluteus medius
Center of gravity is in-front of the hip which causes a lever
Hip abductors causes pelvis to go back up to keep it stable
Single leg raise (SLR)
2 BW
Way to evaluate lower back issues
Do you have pain/numbness at the knee?
Single leg stance (SLS)
3x BW
Just picking your leg up
Walking = 5x BW
Running = 10x BW
Trendelenburg sign
Pelvis tips when one leg is lifted up
Shows issue with hip abductors
Angulation of Femur
Two angulations made by the neck of the femur and the femoral shaft
Angle of inclination and angle of torsion
Angle of inclination of femur
In frontal plane
Between femoral head and neck and the femoral shaft
Angle created from the intersection of a line down the shaft of the femur and the neck of the femur
AOI of the femur approximates 125 degrees
With a normal angle of inclination, the greater trochanter lies at the level of the center of the femoral head
Angle of torsion
In the transverse plane
Between the femoral head and neck and an axis through the distal femoral condyles
Coxa valga
Excessive angle over 125 degrees clinical, 140 degrees technical angle of inclination
Lengthens the limb
Reduces the moment arm of the hip abductors which makes force greater
Reduces the load on the femoral neck
Increases the load on the femoral head
Hip would dislocate since this angle is higher than normal
Coxa vara
110 degrees and below technical
Below 125 degrees clinical
Shortens the limb
Increases the moment arm of hip abductors
Increases the load on the femoral neck
Reduces the load on the femoral head
Angle of torsion
An axis through the femoral head and neck in the transverse plane
SCFE Slipped capital femoral ephysis
Caused by someone moving through coxa valga and normal
Issue with childhood obesity
Get change in angle from added weight or from trauma
Happens on bilateral and unilateral sides
Symptom is groin pain while walking
Are treated with a hip brace, growth plates
Deviations from normal angle of torsion
10-15 degrees males
18-20 degrees female
Born with extreme anteversion of 40 degrees
Angle moves back towards these values
Retroversion
0-9 degrees
Excessive anteversion
21-more degrees
