Musculoskeletal Statics Sept 17

8/13/2019 Musculoskeletal Statics Sept 17

1/27

Anatomy & Terms

Anatomical planes

Three planes are defined Coronal

Sagittal

Transverse/Axial

1


2/27

Anatomy & Terms

Plane of rotation

We will simplify to 2D most of the time

What direction is the primary motion?

2


3/27

Ant ropometryte s us size, weig t

and shape

3From Winter, 1990


4/27

Anatomy & Terms

4From Winter, 1990


5/27

5


6/27

Equivalent Mechanical Components

Bone assume rigid beam

Muscle/tendon/ligament tension only cables

Joints 1D, 2D or 3D motion hinge, ball andsocket, sliding connection

6


7/27


7


8/27


8


9/27


9


10/27


10


11/27


11


12/27


12


13/27

13

Si i i ti M t


14/27

Simp i ications: Muscu os e etaProblems

We will assume

The point of joint rotation is known The location of muscle/tendon/ligament insertion is

known

The line of action of muscle tension is known (what angle

it inserts into the bone) Segment weights and centers of gravity are known

Friction within joints is negligible (synovial fluid)

Any dynamic aspects are ignored (this class)

14


15/27

Specific Examples

15


16/27

Mechanics of the Elbow Hinge joint

What are the possiblereactions?

Is the weight causing

motion in 3D?

What if we simplify to 2D?

Now what type of support

is it?

What are the reactions?

y

x

z

Jx, Jy, JzMx, My

Pin

Jx, Jy


17/27

Mechanics of the Elbow Major muscle group

(biceps, brachialis, brachioradialis

shown)

Why do I need to pick

one?

Biceps is the major

contributor

W is the weight of the forearm

W0is the dumbbell


18/27

Mechanics of the Elbow

Given:

Length of the arm c Location of the center of mass b

Insertion angle of the biceps 90when arm is at 90

Insertion location of the biceps a

The biceps is the major muscle to maintain equilibrium

18

Make sure you know

what axis these

dimensions are being

given along

Can you solve this for

the reactions at thejoint and the

magnitude of the

muscle force?


19/27

Mechanics of the Elbow

Given:

Length of the arm c Location of the center of mass b

Insertion angle of the biceps 90when arm is at 90

Insertion location of the biceps a

The biceps is the major muscle to maintain equilibrium

19

Make sure you know

what axis these

dimensions are being

given along

Can you solve this for

the reactions at thejoint and the

magnitude of the

muscle force?


20/27

20


21/27

Mechanics of the Shoulder Shoulder is a ball and socket

joint

Very shallow socket, more like a

golf ball on a golf tee

Allows for wide range of

motion

In a horizontal position as

shown

Major muscle group is deltoid

Assume all bones are onerigid structure

21

Scapula

Deltoid

HumerusUlna

Radius


22/27

Mechanics of the Shoulder FBD in 2D

Joint is a pin connection

Note: book chose to draw

joint reactions opposite

musclethats ok, just meansa positive number is as

drawn on FBD

22


23/27

23


24/27

Mechanics of the Knee Knee is a hinge joint

Also known as tibiofemoral

joint

In lifting position shown

Major muscle group is the

quadriceps Force from quad transmitted

through quad tendon, over

patella, through patellar

tendon, to the tibia Like a cable and pulley

Patellar tendon has same

tension as quad tendon

24

Femur FibulaTibia

Patella

Patellar

tendonQuadriceps

tendon


25/27

Mechanics of the Knee We could also look at the

patellofemoral joint

The larger the tension in the

quad muscle, the larger the

force the join exerts on the

patella (compression) Look at patella

Can analyze as a concurrent

system of forces

25


26/27

26


27/27

Documents

Musculoskeletal Statics Sept 17