The sternum consists of the manubrium, body, and xiphoid process (Figure 5-2). Large forces through the clavicle often cause fracture of the bone before the SC joint dislocates. FIGURE 5-11. The acromioclavicular (AC) joint is the articulation between the lateral end of the clavicle and the acromion of the scapula (Figure 5-16, A). The head of the humerus is much larger than the glenoid fossa, giving the joint a wide range of movement at the cost of inherent instability. The longitudinal diameters, The SC joint is enclosed by a capsule reinforced by, Anterior and posterior sternoclavicular joint ligaments, Sternocleidomastoid, sternothyroid, sternohyoid, and subclavius muscles. Human muscle system - Human muscle system - The shoulder: The shoulder is a complex ball-and-socket joint comprising the head of the humerus, the clavicle (collarbone), and the scapula. costoclavicular A, Elevation and depression. In addition, skin The right humerus showing a 135-degree “angle of inclination” between the shaft and head of the humerus in the frontal plane (A) and the retroversion of the humeral head relative to the distal humerus (B). The arthrokinematics for protraction and retraction of the clavicle occur along the SC joint’s transverse diameter (see Figure 5-12). The…, The ankle bones include the calcaneus, cuboid, external cuneiform, internal cuneiform, middle cuneiform, navicular, and talus. The lateral or acromial end of the clavicle articulates with the scapula at the oval-shaped acromial facet (see Figure 5-3; inferior surface). The shoulder is composed of 4 joints- The shoulder joint also is […] With the arm resting by the side, the medial or vertebral border runs almost parallel to the spinal column. Additional movements of the scapula will be defined as the chapter unfolds. The articular structures of the shoulder complex are designed primarily for mobility, allowing us to move and position the hand through a wide range of space. Each degree of freedom is associated with one of the three cardinal planes of motion: The osteokinematics of the right sternoclavicular joint. These structural features, in conjunction with the coracoclavicular ligament’s near-vertical orientation, suggest an important role in suspending the scapula (and upper extremity) from the clavicle. This rotation, known as retroversion (from the Latin retro, backward, + verto, to turn) aligns the humeral head within the scapular plane for articulation with the glenoid fossa (see Figure 5-4; angle C). The muscles in the shoulder aid in a wide range of movement and help protect and maintain the main shoulder joint, known as the glenohumeral joint. Located at the superior and inferior rim of the glenoid fossa are the supraglenoid and infraglenoid tubercles. ... Movement of the shoulder would be limited to 30 degrees of shoulder flex/abd. The head of the humerus, nearly one half of a full sphere, forms the convex component of the glenohumeral joint (Figure 5-7). Angle C: Retroversion of the humeral head about 30 degrees posterior to the medial-lateral axis at the elbow. This chapter describes several of the important muscular synergies that exist at the shoulder complex and how weakness in one muscle can affect the force generation potential in others. Traditional Terminology for Describing the Primary Movements at the Scapulothoracic Joint. Movement of the Shoulder Complex The development of a measurement technique based on proposed ISB standards Lianne Jones, Cathy Holt, Amy Bowers Cardiff University, Cardiff, Wales, UK FIGURE 5-10. An anterior-lateral view of the articular surfaces of the right sternoclavicular joint. Flexion - Movement of the arm through the saggital plane that raises the arm. Rarely does a single muscle act in isolation at the shoulder complex. FIGURE 5-12. The right humerus showing a 135-degree “angle of inclination” between the shaft and head of the humerus in the frontal plane. The vertical axis of rotation is shown through the sternum. Includes: shoulder girdle and shoulder joint. This gives rise to the alternate name for the shoulder joint – the glenohumeral joint. Like most synovial joints, the articulating surfaces are covered with hyaline cartilage. Movement Anatomy: Shoulder Complex. Upper, middle, and lower facets on the greater tubercle, The most proximal articulation within the shoulder complex is the, Before the kinematics of the sternoclavicular and acromioclavicular joints are described, the movements at the scapulothoracic joint must be defined (. The joints of the right shoulder complex. If you hug yourself, your shoulders are adducting. To reduce the disproportion in surfaces, the glenoid fossa is deepened by a fibrocar… The motions are elevation and depression in a near frontal plane (purple), protraction and retraction in a near horizontal plane (blue), and posterior clavicular rotation in a near sagittal plane (green). The scapula also has three borders. CHAPTER 6 Biomechanics of the Shoulder Eiji Itoi, MD, PhD, Bernard F. Morrey, MD, Kai-Nan An, PhD Because of its component parts, a description of the biomechanics of the shoulder complex is rather involved. An electromagnetic movement sensor (Isotrak), which makes three dimensional measurements of shoulder movement and measures the ranges of flexion, extension, abduction in the neutral position, abduction preceded by external … Muscles work in “teams” to produce highly coordinated actions that are expressed over multiple joints. The shoulder is a complex joint system — three bones and five joints — that can move in multiple directions. The jugular notch is located at the superior aspect of the manubrium, between the clavicular facets. FIGURE 5-2. The transverse diameters (blue) extend roughly in the horizontal plane between anterior and posterior points of the articular surfaces. Movement at the Shoulder Complex occurs as a result of movement at each of these four joints. Because each of the individual shoulder complex joints defined previously has three DOF, one would expect the shoulder complex to have 12 DOF in its entirety. The articulations between the bones make up the shoulder joints. If you reach your hands behind you — think about putting something in your back pocket — you’re practicing extension. The depth of the supraspinatous fossa is filled by the supraspinatus muscle. The axes of rotation are shown in the anterior-posterior direction near the head of the clavicle. Shoulder adduction occurs when you move your arms towards the middle of the body. This extensive ligament consists of two parts: the trapezoid and conoid ligaments. 2. The posterior surface of the scapula is separated into a supraspinatous fossa and an infraspinatous fossa by the prominent spine. An anterior-lateral view of the articular surfaces of the right sternoclavicular joint. But the movement also improves overhead mobility, hits your entire shoulder complex, and even works your traps and upper and mid back, says Gaddour. Muscles may weaken as a result of disease or injury affecting the neuromuscular or musculoskeletal systems. The acromion extends in a lateral and anterior direction, forming a horizontal shelf over the glenoid fossa. The scapula and humerus tend to follow this plane when the arm is naturally raised overhead. An articular disc of varying form is present in most AC joints. Angle A: The orientation of the clavicle deviated about 20 degrees posterior to the frontal plane. The shoulder complex, composed of the clavicle, scapula, and humerus, is an intricately designed combination of three joints that links the upper extremity to the thorax. The AC joint is surrounded by a capsule that is directly reinforced by superior and inferior ligaments (Figure 5-17).36,105 The superior capsular ligament is reinforced through attachments from the deltoid and trapezius. The subscapular fossa is located on the anterior surface of the scapula (see Figure 5-5, B). This gives the shoulder complex a huge range of motion and makes it a very versatile joint. The very cooperative nature of shoulder muscles increases the versatility, control, and range of active movements. Elevation—The scapula slides superiorly on the thorax, as in the shrugging of the shoulders. To allow so much movement the joints need to be 'free' to move, therefore the shoulder should be 'unstable' compared to other joints of the body; However a series of complex ligaments and muscle keep it in joint. The right clavicle and acromion have been removed to expose the top of the right glenohumeral joint. Buy Membership for Rheumatology Category to continue reading. Anterior (A) and superior (B) aspects of the right humerus. Last medically reviewed on September 13, 2018, Shoulder popping, also known as crepitus, has several possible causes. Axial (Longitudinal) Rotation of the Clavicle: The third degree of freedom at the SC joint is a rotation of the clavicle around the bone’s longitudinal axis (see Figure 5-13). Proximal attachments of muscles are shown in red, distal attachments in gray. The vertical axis of rotation is shown through the sternum. Retraction occurs as the concave articular surface of the clavicle rolls and slides posteriorly on the convex surface of the sternum (Figure 5-15). The position of the scapula on the thorax provides a base of operation for the glenohumeral joint, the most distal and mobile link of the complex. If you’re concerned about the rotation or range of motion of your shoulder or you’re feeling pain during normal movement, you should consult with your doctor. At rest the scapula is normally positioned against the posterior-lateral surface of the thorax, with the glenoid fossa facing about 35 degrees anterior to the frontal plane (see Figure 5-4; angle B). Interaction Among the Joints of the Shoulder Complex. Osteologic Features of the Proximal-to-Mid Humerus, • Upper, middle, and lower facets on the greater tubercle. The ligament has two distinct fiber bundles running perpendicular to each other.178 The anterior bundle runs obliquely in a superior and lateral direction, and the posterior bundle runs obliquely in a superior and medial direction (see Figure 5-11). Distal attachment of muscles is shown in gray. The longitudinal axis is indicated by the dashed green line. Your shoulder joint is a complex system made up of five joints and three bones: This system of joints and bones allows your shoulder to move in different directions. Why Do My Shoulders Click, Pop, Grind, and Crack? Interestingly, researchers have shown that the dominant shoulder in elite baseball pitchers possesses greater humeral retroversion than the nondominant limb.24 This difference (which was not present in a control group of nonpitchers) was theorized to occur as an osseous adaptation to the large torsional stress generated during pitching. Before the kinematics of the sternoclavicular and acromioclavicular joints are described, the movements at the scapulothoracic joint must be defined (Figure 5-10). Angle B: The orientation of the scapula (scapular plane) deviated about 35 degrees anterior to the frontal plane. 18.1 and 18.2).The mobility provided by three joints working together gives the shoulder complex a wide range of movement. The groove separates the proximal attachments of the lateral and medial head of the triceps (see Figure 5-9). Your shoulder is made up of many different moving parts. Proximal attachments of muscles are in red, distal attachments in gray. FIGURE 5-17. Located at the lateral end of the clavicle is the acromioclavicular joint. Keep your elbows against your body and move your forearms towards your body. The dashed line shows the capsular attachments of the glenohumeral joint. In contrast, the lateral end of the spine gains considerable height and flattens into the broad and prominent acromion (from the Greek akros, meaning topmost, highest). Up to this point, we have discussed the arthrology and kinematics of each joint of the shoulder complex. Shown in red, distal attachments of muscles are shown as wavy arrows for shoulder adduction when. Or incomplete articular disc products are for informational purposes only is made up of many different parts... 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