Biomechanics of the Upper Extremity

Shoulder Complex

• permits upper extremity movement and weight bearing

• Very mobile, relies on muscle for stability

Sternoclavicular Joint

• True joint

• saddle-shaped, synovial joint

• connects the clavicle to the manubrium

• only connection of the UE to the axial skeleton

• where most movement happens

Full arm abduction and elevation

• closed pack position of the sternoclavicular joint

1st Principle

• Elevation and Depression of the SC joint

2nd Principle

• Protraction and Retraction of the SC joint

Acromioclavicular Joint

• True joint

• Connects the clavicle and scapula

• Serves as the fine-tuning of the SC joint

• Transmission of forces from UE to axial skeleton

• Plane Synovial Joint

Anterior-posterior tilting of AC

• happens when the clavicle is depressed/elevated

• happens with the same action of the SC

Internal-External rotation of AC

• occurs when the clavicle is protracted/retracted

Upward-downward rotation of AC

• occurs during abduction/flexion or adduction/extension

• the clavicle also moves posteriorly and anteriorly rotates

Scapulothoracic Joint

• False joint

• Provides shoulder region stability

• aligns the fossa and glenohumeral head

• Maintains the length tensions relationship of the deltoid muscle

• Increases the ROM of the shoulder

• Permits elevation of the body

Glenohumeral Joint

• True joint

• Connects the scapula and humerus

• Most freely moving joint, little bony stability

• Ball-and-socket joint

External rotation of humerus

• happens with full shoulder abduction

Internal rotation of humerus

• happens with full flexion

Scaption

• shoulder abduction that happens in the 30°-40°

• Most functional shoulder abduction motion occur in the scapular plane

Full abduction + Full External rotation

• Closed-pack position of the GH Joint

20-30° horizontal adduction + 55° flexion

• Open-packed position of the GH Joint

Bursa, Supraspinatus, Biceps tendon

• What are the contents of the subacromial space?

Scapulohumeral Rhythm

• GH motion + scapular rotation, which permits higher shoulder flexion/abduction with elevation reaching 150-180°

• 2(GH):1(S) variable

• First 30°, GH

Deltoid

• the muscle that pulls upward in the Deltoid-Rotator Cuff Mechanism

Supraspinatus

• muscle that pulls to keep the humerus in the glenoid fossa, in the Deltoid-Rotator Cuff Mechanism

Infraspinatus, Teres Minor, Subscapularis

• muscle that pulls downward for a good roll and slide for abduction in the Deltoid-Rotator Cuff Mechanism

Proximal Radio-Ulnar Joint

• motion is pronation/supination

• part of the forearm complex

Elbow Joint

• humeroulnar + humeroradial joint

• uniaxial hinge joint (flexion and extension)

145° (120-160°)

• ROM of elbow in flexion

30-130°

• functional range of elbow flexion

Radioulnar Joint

• proximal + distal radioulnar joints

• one degree of freedom (pronation/supination)

90°

• ROM of forearm supination

• Firm end-feel

80-90°

• ROM of forearm pronation

• Hard/Firm end-feel

Ulna

• the rigid base for forearma and wrist function

• stays stationary

Ulnar deviation and supination

• What is the coupling motion when the wrist flexes?

Radial deviation

• What is the coupling motion when the wrist extends?

• Flexor Carpi Ulnaris and Extensor Carpi Ulnaris

• Flexor Carpi Radialis and Extensor Carpi Radialis Longus

• Antagonist muscle for Flexion/Extension

Flexor Carpi Ulnaris and Extensor Carpi Ulnaris

• Synergists for ulnar deviation

Flexor Carpi Radialis and Extensor Carpi Radialis Longus

• Synergists for radial deviation

5th

• most mobile digit

3rd

• least mobile digit

Tenodesis

• wrist extension = finger flexion

• wrist flexion = finger extension

• provides grasping mechanism

Wrist flexion

• has twice the work capacity than its counterpart movement

30-40°

• there is 3x more grip in this ROM of the wrist extension, compared to 40° flexion

Radial Deviation

• has slightly higher work capacity than its counterpart movement

20° extension, 10° ulnar deviation

• Wrist at the functional hand position

45° MCP flexion, 30-45° PIP flexion, 10-20° DIP flexion

• Hand at the functional hand position

Intrinsic-plus position

• MCP flexion

• IP extension

• interossei and lumbricals at shortest

• caused by muscle contracture (rheumatoid arthritis)

Intrinsic-minus position

• claw hand

• IP flexion

• MCP extension

• Paralysis in the lumbricals and interossei

Power Grips

• uses entire hand to hold

• Full-hand Prehension

  • partially flexed fingers and palm.

  • Thumb adducted or in position which provides counterpressure

• Isometric contraction

Hook Grip

• carry or support an object

• does not use thumb

• FDS and FDP

  • FDP for more distal load

Flexor Digitorum Superficialis

• main muscle in hook grip

Cylindrical Grip

• for cylindrical objects

• fingers and palm flexed to grasp object

• fingers are adjacent and parallel

• thumb is usually flexed and adducted

• Wrist in neutral or sometimes ulnar deviation

FDP, FDS, Interossei

• muscle for cylindrical grip

Spherical Grasp

• for round objects

• greater spread of fingers

• MCP abducted, partially flexed

• Thumb in opposition and flexed at MCP or IP

FDS, FDP, thenar muscles, interossei

• muscles for spherical grip

extensor digitorum

• during spherical grasp

• contracts against flexor for controlled release of object

Fist Grip

• Distal palmar prehension pattern

• thumb is closer to the digits

• closing a fist over a comparatively narrow object

• fingers parallel to one another

• thumb over and adducted against the object/in opposition to fingers

FDP, FDS

• muscles for fist grip

Lateral Prehension

• extensor muscle predominates

• not powerful

• not used in in-hand manipulation

• object held in between extended fingers

Precision Grips

• accuracy and fine touch

• Finger-thumb precision

  • on the flexor surface of the fingers

  • thumb adducted

Lateral Pinch Grip

• key grip

• contact between thumb pad and radial index finger

• least precise

FDP, FDS, 1st dorsal interossei, FPL, FPB, AdP

• muscles for lateral pinch grip

Three-prong Chuck

• pad-to-pad/palmar prehension

• thumb opposes distal pads of digits

• joint of thumb and fingers are relatively extended

FDS, FDP, interossei, thenar muscles

• muscles for three-prong chuck

Tip Prehension Grip

• tip-to-tip grip

• most precise but most easily disturbed

• small objects

• thumb nearly full flexion and opposing finger MCP joint to UD

  • allows fingertips to meet thumb facing radial

FDP, FPL, interossei

muscle for tip prehension grip