Biomechanics of the shoulder complex
List the ligaments of the shoulder
1. Acromioclavicular ligament 2. coracoacromial ligament 3. subdeltoid bursa and subacromial bursa capsular ligament 4. inferior coracoid bursa 5.coracoclavicular(trapezoid and conoid ligament ) 6. Superior Transverse ligament
Primary Function of the AC joint
1. allow scapula additional ROM on the thorax 2. Allow for adjustments of the scapula (tipping & int/ext rotation) in order to follow the changing shape of the thorax as arm movement occurs. 3. allows transmission of forces from the upper extremity to the clavicle
Joint that is formed by the junction of the lateral clavicle (acromial end) and the acromion process (acromion) of the scapula. (2) This joint is what kind of joint?
AC Joint Gliding/Planar synovial joint
scapular plane
Approximately 30 degrees forward of the frontal plane In line with the normal resting position of the scapula as it lies on the posterior rib cage; movements in the scapular plane are in line with the scapular, which is at an angle of 30 to 45 degrees from the frontal plane A shoulder angle about halfway between the sagittal plane and the frontal plane, which represents approximately 30-45 degrees of shoulder flexion. This angle is in line with the orientation of the scapula as it rests naturally against the rib cage and helps protect the shoulder joint during overhead movements.
These ligaments contribute to horizontal stability, of the AC joint making them crucial for what? (2) Both portions also limit ____ of the scapula.
Coracoclavicular Ligaments (I.E. Conoid and Trapezius ligaments) preventing superior dislocation of the AC Joint (2) Rotation
The Coracoclavicular ligaments run from the _____ process to the underside of the ______, near the AC Joint.
Coracoid ; Clavicle
T or F; The conoid and trapezoid ligaments come in contact with the AC joint
False; they do not
The ___ joint is of particular interest when understanding the mechanism of shoulder injuries because it is osteologically predisposed to instability.
Glenohumeral Joint (GH)
congruent
Having the same size, shape and measure. Two figures are congruent if all of their corresponding measures are equal.
angle of inclination/inclination angle
The angle of depression formed by the meeting of a line drawn through the shaft of the femur with a line passing through the long axis of the femoral neck; normally about 125° in the frontal plane. Trig definition: angle formed by the intersection of a line and the x-axis.
longitudinal
along the length of the body the axis running lengthwise; in the direction of the long axis of the body any plane that sections an element parallel to its long axis
Because of the relatively large surface area of the humeral head in relation to the fossa, the GH joint itself has limited bony ____, (B) and consequentially heavily depends on what for structural support
congruency Surrounding Soft Tissue
trapezoid ligament
connects the clavicle to the coracoid process from coracoid process of scapula to the trapezoid line of the clavicle
coracoclavicular ligament
connects the clavicle to the coracoid process of the scapula, helping to limit the relative motion between the clavicle and scapula; splits into two ligaments (trapezoid and conoid ligaments)
Acromioclavicular Joint
one of four joints that comprises the Shoulder complex. formed by the junction of the lateral clavicle and the acromion process of the scapula. is a gliding, or plane style synovial joint. attaches the scapula to the clavicle serves as the main articulation that suspends the upper extremity of the arm.
types of synovial joints
plane, hinge, pivot, condyloid, saddle, ball and socket
intra-articular
within a joint
Ligaments of the AC joint
-Acromioclavicular -Coracoclavicular (Conoid & Trapezoid)
diarthrodial joints
A freely movable joint, such as the shoulder. This kind of joint has a joint capsule, a synovial membrane, cartilage, and ligaments.
Joint that attaches the scapula to the clavicle and serves as the main articulation that suspends the upper extremity from the trunk
AC (Acromioclavicular) Joint
scapular rotation
Inferior angle is the point of reference for rotation. ~Upward rotation: Inferior angle moves up and away from the vertebral column. ~Downward rotation Return to anatomical position Inferior angle moves towards vertebral column
The __joint is the only bony attachment site of the upper extremity to the axial skeleton.
SC
Motion of the AC Joint are described as ____movement with respect to the _____, including
Scapula; clavicle Upward/Downward Rotation about an axis directed perpendicular to the scapular plane facing anteriorly and medially. Internal/External Rotation about an approximately vertical axis Anterior/Posterior tipping or tilting about an axis directed laterally and anteriorly.
articulation between the lateral end of the clavicle and a small facet on the acromion of the scapula.
AC Joint
The articular facets of this joint are considered to be incongruent, meaning what?
AC Joint (Acromioclaviular) meaning the articular facets of the joint vary in their configuration
This ligament of the AC joint serves to reinforce the joint capsule and serves as the primary restraint to posterior translation and posterior axial rotation at the AC joint.
Acromioclavicular
The GH joint is comprised of a ball and socket synovial joint, where the head of the humerus (convex or concave surface) articulates with the glenoid fossa (convex or concave surface) of the scapula.
Convex Concave
Ligament of the shoulder which is composed of the conoid and trapezoid ligaments
Coracoclavicular Ligaments
This combined ligament is the primary support ligament of the AC Joint
Coracoclavicular Ligaments
scapular tipping
The inferior angle of the scapula moving away from the thorax while its superior border moves toward the thorax Inferior border of scapula moves posteriorly Superior border of scapula moves anteriorly Sagittal plane motion around a lateral axis Anterior/Posterior Tipping Posterior tipping on forward flexion Anterior tipping with extension
arthokinematics
The motions of joints in the body
T or F; The disc of the AC Joint is variable in size between individuals at various ages within an individual and between sides of the same individual.
True
upper extremity
arm, forearm, wrist, hand
The articular facets of the AC Joint can be
flat, reciprocally concave-convex, or reversed (reciprocally convex-concave)
during adduction and extension the scapula moves
in downward rotation relative to the acromion about 30 degrees
During abduction and flexion the scapula moves
in upward rotation in relation to acromion about 30 degrees
incongruent
incompatible; inconsistent; not harmonious
how many joints make up the shoulder complex? (2) List them
(1) Four (2) sternoclavicular, acromioclavicular, glenohumeral, scapulothoracic
articular facets of the AC joint are considered to be ______, meaning what? (2) the articular facets may be
(1) Incongruent (they vary in configuration) (2)
the more lateral portion of the coracoclavicular ligament. (2) It is ___ in shape
(1) Trapezoid Ligament (2) quadrilateral in shape.
Acromioclavicular ligament
(1) connects the clavicle to the acromion process (2) quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the acromial end of the clavicle and the adjoining part of the upper surface of the acromion
(1) The AC Joint has a thin capsule lined with _____. (2) The capsule is (strong or weak) and is strengthened by ____ ____ both inferiorly and superiorly, which in turn are reinforced through attachments from the _____ and _______. (3) Without the superior and inferior ____ ____, the AC Joint capsule would not be strong enough to maintain the integrity of the joint.
(1) synvoium (2) Weak; Capsular Ligaments ; Deltoid; Trapezius (3) Capsular Ligaments;
it is estimated that only __% of the humeral head articulates with the glenoid fossa at any one time during movements. (B) surrounding passive structures (such as____), (C)as well as the active structures (____) (D) work cooperatively in a healthy shoulder to maintain ___stability throughout movements.
(A) 25% (B) Passive Structures - labrum, joint capsule, and ligaments (C) Active Structures - muscles and associated tendons (D) Dynamic
(A) An area most often involved in the cases of shoulder pain is the subacromial space. (B) includes the theoretical space between the ___ ___ and the ___of the humerus.
(A) Subacromial space (B) coracoacromial arch; Head of Humerus
fan shaped component of the coracoclavicular ligament. (B) It is located more ____ than the trapezoid ligament 1. Medially 2. Laterally 3. Centrally 4. Inferiorly
(A) conoid ligament (B) (1) Medially
The ST joint involves the ___movement of the scapula along the rib cage during upper extremity movements and (B) does not include a physical bone-to-bone attachment. T or F
(A) gliding (B) True
articulation between the lateral end of the clavicle and a small facet on the acromion of the scapula
AC Joint
The Acromioclavicular ligament of the AC joint serves to reinforce the ____ _____ and also serves as the primary restraint to _______ ______ and _____ _____ rotation at the AC Joint
Joint Capsule Posterior Translation Posterior Axial Rotation
Close-packed position
The joint position in which contact between the articulation structures is maximal. unique position of most joints of the body where the articular surfaces are most congruent and the ligaments are maximally taut joint orientation for which the contact between the articulating bone surfaces is maximum
T or F; The inclination of the articulating surfaces (facets) of the AC joint varies from individual to individual. (2) The closer the surfaces (were) to vertical, the more prone the joint was to
True (2) Wearing effects of shearing forces
Why are the intra-articular movements of the AC joint not predictable?
because of the variable articular configuration of the joint (I.E. the inclination of the articulating surfaces) observed between people.
Why would the AC joint capsule not be strong enough to maintain the integrity of the joint without the superior and inferior capuslar ligaments?
because the joint capsule is strengthened by inferior and superior capsular ligaments. (The ligaments are in turn reinforced through attachments from the delt and traps)
coracoacromial ligament
extends across the space between the coracoid process and the acromion
Acromion process
extension of the scapula, which forms the superior (highest) point of the shoulder
The "ball" of the humerus is held in place on the "tee" or socket of the shoulder blade, called the ___ by a number of small but important ____ and ____ which create an airtight hold by doing what?
glenoid Tissues (ligaments and capsule) tissues wrap around the joint like a tight fitting glove
conoid ligament
ligament running from the coracoid process of the scapula to the conoid tubercle of the clavicle
What is the most critical role of the coracoclavicular ligament
producing the longitudinal rotation of the clavicle necessary for full ROM during elevation of the upper extremity.
subdeltoid bursa
sac that helps to reduce friction between the greater tubercle and the acromion (5) when the arm is raised in the abducted position. decreases friction between deltoid muscle & the joint capsule Forms a cushion between the deltoid muscle and the greater trochanter when the arm is abducted
Facet
small, smooth, nearly flat articular surface
The AC Joint capsule and ligaments surrounding the joint work together to provide what?
stability and to keep the clavicle in contact with the acromion process of the scapula.
Movement of the Scapulothoracic Joint are generally considered to be a combination of ______and _____motion.
sternoclavicular and acromioclavicular
Scapula Inferior Angle
teres major origin