Bill Sellers

Email:wis@mac.com

This lecture can be found at:

http://mac-huwis.lut.ac.uk/~wis/lectures/

In previous lectures you have learnt about the general principles of musculoskeletal function.

This lecture will cover specific details of the functional anatomy of the upper limb to

illustrate the points made previously and as useful information in its own right.In the course

of the lecture I will move distally down the limb from the pectoral girdle to the phalanges.

This is not an exhaustive coverage but will cover the main functional anatomical features of

the joints and musculature including ranges of movement and the major actions of the

muscles.

Figure 1.The sternoclavicular joint

synovial joint with an articular disk.Its range of movement is shown in figure 1.It is an

a dynamic ligament.This means that the joint almost never dislocates –when the forces

acting on the joint get too great the clavicle tends to break.

Figure 2.The acromioclavicular joint

two parts have perpendicular fibres to prevent excessive movement both medially and

anteriorly.

Figure 3.Movements of the scapular

Between the two of them the sternoclavicular and acromioclavicular joints allow a large

range of movements of the scapular as shown in figure 3.There is no specific joint between

the scapular and the thoracic cage although the movements all consist of the blade of the

mobility of the shoulder is actually due to the mobility of the scapular.The limb girdle for the

lower limb (the pelvis)is firmly fixed to the axial skeleton and so sacrifices mobility to gain

increased stability and better load bearing capacity.

Figure 4.Muscles acting on the scapular

With such a complex array of possible movements it should come as no surprise that there

are quite a large number of muscles that act on the scapular.The main ones are shown in

figure 4.These muscles do not tend to act in isolation and because they tend to be muscular

sheets rather than fusiform or strap muscles the precise action depends on which fibres within

the muscle are activated (this is because the fibres in sheet muscles rarely run in parallel

throughout the whole of the muscle).

Figure 5.Dorsal aspect of the arm

mobility a large number of muscles.Figure 5 shows the main extensors of the shoulder but

note that triceps is also an elbow extensor and only the long head acts as a shoulder extensor.

Figure 6.Ventral aspect of the arm

The flexors of the shoulder are on the ventral aspect (figure 6).Note that the very important

a pure flexion is required then other muscles need to act antagonistically for adduction (e.g.

adduction and medial rotation and would require antagonistic action in other muscles for pure

extension.Latissimus dorsi and pectoralis major often act together to produce very powerful

adduction since their extension and flexion components cancel each other although this

would still leave the medial rotation component.

Figure 7.Superior view of the shoulder

If we look down on the shoulder from above (figure 7)we can see the medial and lateral

rotators,and the abductors.Deltoid is a triangular (delta)shaped muscle which has all three

actions depending on which fibres you look at.Its main action is as an abductor though.

abductors.

Figure 8.Shoulder abduction

Shoulder abduction (figure 8)is a more complex activity than might originally be thought.If

you start from the anatomical position and begin to abduct the arm the initial 10 °is

performed entirely by supraspinatus because initially the fibres of deltoid are in the wrong

direction to help.After that the much larger deltoid takes over the work.Abduction continues

for about 110 °at the glenohumeral joint but subsequent abduction takes place by upward

rotation of the scapular.The full range of abduction (180 °)can also only take place if the arm

is medially rotated.

Figure 9.The glenohumeral joint

The extreme mobility of the glenohumeral joint means that it cannot be stabilised by the

normal,passive elastic mechanisms of ligaments.Instead it has active stabilisation from the

short muscles that surround the joint –the so called rotator cuff muscles (figure 9).You can

see from the joint shape and locations of the muscles that there is little to support the joint

inferiorly and indeed dislocations of the shoulder are almost always in this direction.

Figure 10.The elbow joint

The elbow joint is a complex of three joints that share the same synovial sheath (figure 10).

humeroradial and humeroulnar joints allow flexion and extension at the elbow whilst the

superior radioulnar,humeroradial,and the more distal inferior radioulnar joints allow the

the ulna that produces an apparent rotation of the wrist around a longitudinal axis.The elbow

flexors and extensors can be seen in figures 5 and 6.Triceps is the main extensor and

this action stops it being an effective flexor of the pronated forearm.

Figure 11.Pronation and supination

11).When they contract they role the radius anteriorly across the ulna.The converse action,

supination,is mainly produced by biceps brachii with some help from supinator.Biceps

brachii is a much larger muscle than the other three and this means that the action of

supination tends to be much stronger than pronation.Supination of the right arm is the action

used to drive screws into a substrate and produces more torque than unscrewing which uses

pronantion.

Figure 12 Superficial extensors in the forearm

The forearm contains a large number of muscles.Dorsally these are primarily extensors of

the wrist and fingers as shown in figure 12.They do attach to the common extensor origin on

the lateral epicondyle of the humerus so you might expect them to have an action at the

elbow but because this attachment point is so close to the centre of rotation of the elbow their

Similarly there are superficial flexors in the ventral compartment (see figure 5)which

originate on the common flexor origin on the medial epicondyle of the humerus whose effect

at the elbow is minimal and whose primary actions are more distally at the wrist and hand.

to tense the palmar aponeurosis.It is therefore a prime candidate (in those of us who have

one)for surgical removal for use as a tendon repair material elsewhere in the body.

Figure 13 Middle and deep flexors in the forearm

The deeper muscles in the flexor compartment are extrinsic hand muscles – they are powerful

flexors of the fingers.Their force is transmitted to the hand through long tendons.Somewhat

to let the FDP tendon pass through it.

Figure 14.Middle and deep extensors in the forearm

The arrangement in the extensor compartment is somewhat similar although the extensor

muscles are smaller than the flexors (figure 14).Flexors are used to produce the clenched-fist

power grips whereas there is not much need for forced extension.

Figure 15.Joints of the hand

Moving to the hand there are a large number of complex joints at the wrist and between the

allowing adduction,abduction (also known as ulnar and radial deviation),flexion and

extension.The exact ways that the wrist bones move to produce these composite movements

is complex but flexion occurs mostly at the midcarpal joint and extension is mostly at the

radiocarpal joint.The radiocarpal joint also provides most of the adduction and abduction.

between the distal row of carpal bones and the five metacarpals.The first CMC joint is the

best example of a sellar (saddle-shaped)joint which allows flexion,extension,adduction and

abduction of the first ray.The other four are under tight ligamentous control and only allow a

first MCP joint has little mobility but the other four allow flexion,extension,adduction and

abduction.

Figure 16.The bones of the hand [Netter 1997]

More distally still are the simple hinge joints of the phalanges (see figure 16):the five

proximal and distal interphalageal joints and the four middle interphalangeal joints since the

first ray only has two phalanges.

Figure 17.Wrist cross-section [Snell 1986]

When we look at the muscles that act over the wrist joint (figure 17)we get a complex

picture because as well as the specific wrist muscles (FCR,FCU,ECR,ECU and PL)all the

tendons from the extrinsic hand muscles also pass this joint and so have an effect depending

on the relative position of their tendon to the joint centre.The primary movers of the wrist

(FCR,FCU,ECR,ECU)also act the 4 corners of the joint so all produce a dual action.Thus

FCR produces wrist flexion and radial deviation,FCU flexion and ulnar deviation,ECR

extension and radial deviation,and ECU extension and ulnar deviation.Thus to produce pure

flexion,extension,abduction or adduction requires the activation of the correct two muscles:

the two flexors produce flexion together because the adduction and abduction actions cancel

out etc.If finger movements are required without corresponding wrist movements then the

wrist only muscles need to act antagonistically to avoid the unwanted wrist movement.

You can also see from figure 17 that the median nerve shares a rather small and inextensible

space with the extrinsic finger flexors.This is the carpal tunnel where tendonitis can cause

swelling which presses on the median nerve producing pain and in severe cases paralysis of

some of the intrinsic hand muscles:carpal tunnel syndrome.

Figure 18.Various types of grip [Aiello &Dean 1990]

The primary role of the hand itself is grasping and manipulation.Figure 18 shows the variety

of grips that have been classified.A and B are simple grips,C,D and E are precision grips

and F,G and H are power grips.It is suggested that the precision grips are unique to humans

among the primates.

Figure 19.The superficial intrinsic hand muscles [Jacob 1996]

These fine movements are controlled by the intrinsic hand muscles in conjunction with the

more powerful extrinsic hand muscles of the forearm.Figure 19 shows the superficial palmar

move the first and fifth digits respectively.As you might imagine movements of the fifth

digit are not terribly important but the relatively large thenar eminence muscles are very

important for the various movements of the thumb.The first ray is rotated 90 °to the other

rays so that flexion of the thumb moves it medially across the palm of the hand,abduction

moves it anteriorly,perpendicular to the palm,extension moves it laterally in the plane of the

palm and adduction moves it posteriorly perpendicular to the palm.The special movement,

opposition,is the combined flexion and adduction that brings the palmar surface of the tip of

the first digit towards the palmar surfaces of the tips of any of the other four digits.

muscles and the extensor digitorum comunalis tendons.They allow a controlled transfer of

power from the FDP to the EDC when flexing and extending the fingers and also allow

flexing of the MCP joint whilst keeping the IP joints extended.

Figure 20.Palmar and dorsal interossei [Jacobs 1996]

(palmar)and adduct (dorsal)the MCP joints of the fingers.The first dorsal interosseous

muscle is very important fin pincer or pinch grips.These are shown in figure 20.

Figure 21.The extensor mechanism of the hand [Snell 1986]

The tendon arrangement around the fingers is complex as illustrated in figure 21.As

previously mentioned the FDP tendon pierces the FDS tendon to attach to the base of the

distal phalanx and the lumbricals attach the FDP tendon to the EDC.The EDC tendon

connects to the lumbricals,the dorsal interossei and to all three phalanges and is known as the

of a pen top whilst holding the pen in one hand,but none of the movements are entirely

independent because single muscles act over several joints at once.

Bibliography