Sternoclavicular and Acromioclavicular Joint- Palastanga Flashcards
Classification of the sternoclavicular (sc) joint
Functionally a ball and socket but anatomically is a synovial double plane (or saddle)
Articular surfaces of the sternoclavicular joint
Medial end of clavicle with the clavicular notch at the superolateral angle of the sternum and adjacent upper medial surface of the 1st costal cartilage
What provides congruency to the sc joint
The inta-articular fibrocartilagenous disc
Joint surfaces give little congruency
Features of the intra-articular disc of the sc joint
Thinner centrally where may be perforated
Attached circumstantially to the joint capsule
Attached to superior and posteriorly to medial end of clavicle and inferiorly to 1st costal cartilage
Function of the intra-articular disc of sc joint
Increase congruency of the joint
Provide cushioning between articular surfaces
Ligamentous- fibrous around circumference so holds clavicle against sternum when subjected to forces from upper limb
What strengthens the SC joint capsule
Anterior sternoclavicular ligament
Posterior sternoclavicular ligament
Interclavicular ligament (between the 2 clavicles)
Costoclavicular ligament- very strong
What is limited by the costoclavicular ligament
Elevation of the capsule
Also compensates for the inferior weakening of the capsule
What confers the most stability to the SC joint
The integrity of it’s surrounding ligaments, particularly costoclavicular
Movement of the SC joint occurs i how many degrees of freedom
3
elevation/ depression
protraction/ retraction
axial rotation
Is really the lateral end of the clavicle that moves with small reciprocal movements at the SC joint
Describe elevation/ depression of the sc joint
Occurs at an axis which runs horizontally and anterolaterally through the costoclavicular ligament
Total angular range of 60degrees
Elevation- lateral end up medial end down
Depression- lateral end down medial end up
What limits elevation/ depression of the sc joint
Elevation- costoclavicular ligament and tone of subclavius
Depression- tension in interclavicular ligament and intra-articular disc
Describe protraction/ retraction of the sc joint
Axis of movement lies in a vertical plane running obliquely inferolaterally through middle part of costoclavicular ligament
Total angular ROM of 35degrees
Protraction- lateral end moves forward and medial end posteriorly
Retraction- lateral end moves backward and medial end anteriorly
Limits to pretraction/ retraction of the sc joint
Protraction (post movement of medial end)- poterior sternoclavicular and costoclavicular ligament
Retraction (ant movement of medial end)- anterior sternoclavicular and costclavicular ligament
How does axial rotation of the SC joint differ from elevation/depression/protraction/retraction
Axial rotation is entirely passive where others are brought about my active muscle movement
How is axial rotation at the SC joint brought about
By rotation of the scapula transferred via the coracoclavicular ligament
Cannot happen as a pure movement, is always accompanied by other movement of the joint
Degree of axial rotation of the SC joint and what allows this
40 to 60 degrees depending on position of clavicle
Allowed by relative incongruency of joint, intra-articular disc and relative laxness of capsule
Classification of the acromioclavicular (ac) joint
Synovial plane
Articular surfaces of the ac joint
Oval flat or slightly convex facet on lateral head of clavicle with similar flat or concave facet on anteromedial border of the acromion
How does the joint axis run through the ac joint
From anterolateral to posteromedial
Clavicular facet faces posterolaterally
Acromion facet faces anteromedially
What of the anatomy of the AC joint predisposes it to displacement of the acromion downwards and under the clavicle during dislocation?
Over-riding of the lateral end of the clavicle over the acromion and slope of their articular surfaces
Describe the intra-articular disc of the ac joint
Wedge-shaped fibrocatilagenous disc present in most, only rarely forms a complete partition
May not be present but when is is attached to the superior aspect of the joint capsule and hangs down
Function of the ac joint intra-articular disc
Partially compensates for the lack of congruity of the joint surfaces (but not by much)
What may strengthen the capsule of the ac joint
Debated whether or not is strengthened by the superior and inferior acromioclavicular ligaments, which may just be thickenings of the joint capsule
Strength of joint is mainly provided by the coracoclavicular ligament- an extracapsular accessory ligament
Where is the coracoclavicular ligament found
Sits medial to the ac joint and anchors the lateral end of the clavicle to the coracoid process
Separated into conoid and trapezoid (more lateral) parts which are usually continuous with eachother
