Biomechanics Lecture 01

Biomechanics Lecture 01 ( Upper Extremity)

Biomechanics of Upper extremity

Structure of shoulder

• Most complex joint in human body
• Include 5 different articulations

1)      Glenohumeral joint

2)      Strenoclavicular joint

3)      Acromioclavicular joint

4)      Coracoclavicular joint

5)      Scapulothoracic joint

1.Sternoclavicular joint

• Saddle joint type
• Fibro cartilaginous disc improve the fit
• Synovial diarthroidal joint
• Major axis of rotation for the movement of clavical and scapula
• Rotation occur during shrugging of shoulders,

Elevation of arms above head

Close pack position : max. shoulder elevation

2. Acromioclavicular joint

• Irregular joint
• Allow limited motion in three plane
• Rotation occur at AC joint during arm elevation

Close pack position : arm abducted at 90 degree

3. Coracoclavicular joint

• This joint is a syndyesmosis ( joint surface is bound by ligament)
• Coracoid process of scapula and inferior surface of clavicle bound together by coracoclavicular ligament
• This joint permits little movement

4. Scapulothoracic joint

• Region between anterior scapula and thoracic wall is referred to scapulothoracic joint, as scapula can move in both saggital and frontal plane.

Functions of muscles attaching to scapula

1)      Either stabilize shoulder region e.g lifting suitcase

2)      Or facilitate movement of upper extremity through appropriate positioning of glenohumeral joint ex. Rhomboids during overhead throw

5. Glenohumeral joint

• Ball and socket joint
• Most freely moving joint in human body
• Hemispherical head of humerus 3 to 4 times surface area as the shallow glenoid cavity
• Glenoid fossa is also less curved as compare to head of humerus,
• G. Fossa are of different shapes…..oval/peer

Glenohumeral joint

All planes movement.

To increase stability:

• There is labrum at the periphery of the G. Fossa.
• Many ligaments merge with joint capsule.
• 4 muscle RC merge with it.

RC are anterior,post and sup to joint.

RC and biceps provides stability to joint prior to the mov.

Movement in glenohumeral joint

• Flexion
• Extension
• Abduction
• Adduction
• Horizontal adduction, abduction
• Medial rotation and lateral rotation
• circumduction

Characteristics of glenohumeral joint

Factors providing stability to glenohumeral joint

1. Glenoid labrum
2. Ligaments
3. Rotator cuff
4. Negative pressure within joint capsule
5. Closed pack position

1.Glenoid labrum

• The glenoid fossa is encircled by the glenoid labrum
• It is a fibrocartilaginous rim attached around the margin of the glenoid cavity in the shoulder blade. The shoulder joint is considered a ball and socket joint.
• It deepens the fossa and adds stability
• On cross section the labrum is triangular.
•  It is the primary attachment for the glenohumeral ligaments and gives rise to the long head of biceps superiorly.
•   The glenoid labrum is approximately 9mm thick, thus serves to deepen the glenoid socket.  It conforms perfectly to the curvature of the humeral head and increases glenoid depth by 50%.

2. Ligaments

Glenohumeral ligaments

–      Superior-Restraint lateral rotation below 45

–      Middle-limits lateral rotation 45-90ᵒ

–      Inferior- has two parts

• Anterior ….above 90 limits lateral rotation
• Posterior….above 90 limits medial rotation

–      Coracohumeral ligament

–      Capsular ligament

3. Rotator cuff muscles and Jt. Stability

• The four muscles that make up the rotator cuff are:

–      supraspinatus,

–      infraspinatus,

–      subscapularis,

–      teres minor

Referred to as SITS

• Rotator cuff surround the shoulder from posterior, superior and anterior side
• Contraction of theses muscles pulls the head of humerus toward glenoid fossa contributing to joint stability.

4. Closed pack position

Abduction and lateral rotation.

Ø  Shoulder joint

Ø  Most complex

Ø  Shoulder region has 5 articulations

Ø  GH,AC,SC,ST,CC

Ø  SHOULDER GIRDLE:

Ø  Sternoclavicular and acromioclavicular

Bursae

• Cushion and reduce friction between layers of collagenous tissue
• Important bursae around shoulder are:

–      Subscapularis bursae

–      Subcoracoid bursae

–      Subacromial bursae