Shoulder complex movements represent care fully orchestrated motion of all of its components. The bones of the hip involved are the femur and pelvic girdle which form a ball and socket joint. 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. If you reach your hands behind you — think about putting something in your back pocket — you’re practicing extension. An anterior view of the right acromioclavicular joint including many surrounding ligaments. Stretched structures are shown as thin elongated arrows; slackened structures are shown as a wavy arrow. The very cooperative nature of shoulder muscles increases the versatility, control, and range of active movements. As we look at the strength of the muscles in the shoulder joint complex and what movements are strongest with them, adduction is the strongest movement in the shoulder complex. Between these crests is the intertubercular (bicipital) groove, which houses the tendon of the long head of the biceps brachii. Tissues That Stabilize the Sternoclavicular Joint, • Anterior and posterior sternoclavicular joint ligaments, • Sternocleidomastoid, sternothyroid, sternohyoid, and subclavius muscles. • Angles: inferior, superior, and lateral, • Supraglenoid and infraglenoid tubercles. Keep your elbows against your body and move your forearms towards your body. An issue with just one of these parts can affect your range of motion. Motions of the right scapulothoracic joint. This absorption mechanism apparently works well because significant age-related degenerative arthritis is relatively rare at this joint.35, The tremendous stability at the SC joint is due to the arrangement of the periarticular connective tissues and, to a lesser extent, the interlocking of the articular surfaces. These four stretches can help relieve…. FIGURE 5-9. The dashed lines show the capsular attachments around the glenohumeral joint. 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. An anterior view of the sternum with left clavicle and ribs removed. All rights reserved. Retraction occurs as the concave articular surface of the clavicle rolls and slides posteriorly on the convex surface of the sternum (Figure 5-15). Buy Membership for Rheumatology Category to continue reading. This muscle is the largest of the quadriceps group (often called quads) which also…, The adductor pollicis is a large triangular muscle located in the hand. The articular disc at the SC joint separates the joint into distinct medial and lateral joint cavities (see Figure 5-11).178 The disc is a flattened piece of fibrocartilage that attaches inferiorly near the lateral edge of the clavicular facet and superiorly at the sternal end of the clavicle and interclavicular ligament. Common conditions affecting range of motion, Pendulum and Codman Exercises for Shoulder Rehabilitation. A close-up view of the right coracoid process seen from above. The mechanics of this interesting motion are further described later in this section on shoulder kinematics. The interclavicular ligament spans the jugular notch, connecting the medial end of the right and left clavicles. 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 … The trapezoid ligament extends in a superior-lateral direction from the superior surface of the coracoid process to the trapezoid line on the clavicle. FIGURE 5-3. This motion occurs as a natural component of lowering the arm down to the side. 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). Sternoclavicular joint. The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. This joint, and associated ligaments, firmly attaches the scapula to the clavicle. The clavicular facet on the acromion forms part of the acromioclavicular joint (see Figure 5-16, B). This extensive ligament consists of two parts: the trapezoid and conoid ligaments. Posterior aspect of the right proximal humerus. Abduction occurs when you have arm movement away from the middle of your body. The head faces medially and superiorly, forming an approximate 135-degree angle of inclination with the long axis of the humeral shaft (Figure 5-8, A). STUDY. Shoulder flexion is movement of the shoulder in a forward motion. An articular disc of varying form is present in most AC joints. Each movement has a different range of motion. The clavicle, through its attachment to the sternum, functions as a mechanical strut, or prop, holding the scapula at a relatively constant distance from the trunk. The superior border extends from the superior angle laterally toward the coracoid process. Downward rotation—From an upward rotated position, the inferior angle of the scapula rotates in an inferior-medial direction. 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. Thus, the shoulder complex provides seven DOF for the arm movement: Excessive tightness in the posterior bundle of the costoclavicular ligament, the posterior capsular ligament, and the scapular retractor muscles limit the extremes of clavicular protraction. The leg action in running is one that takes place in a sagittal plane about a frontal axisand involves the hip, knee and ankle joints. The SC joint is enclosed by a capsule reinforced by anterior and posterior sternoclavicular ligaments (see Figure 5-11).177 When active, muscles add further stability to the joint: anteriorly by the sternocleidomastoid, posteriorly by the sternothyroid and sternohyoid, and inferiorly by the subclavius. The shoulder complex consists of multiple joints that are stabilized by connective tissue, all of which allow for range of motion during movement: Glenohumeral Joint Sternoclavicular Joint The dashed line shows the capsular attachments of the glenohumeral joint. Unit X – The Neck and Shoulder Complex Objectives: At the completion of Unit 10 the student will be able to: 1. Superior and inferior acromioclavicular joint ligaments. costoclavicular Proximal attachments of muscles are in red, distal attachments in gray. A fully depressed clavicle elongates and stretches the interclavicular ligament and the superior portion of the capsular ligaments. This is medial rotation — also referred to as internal rotation — and the normal range of motion for a healthy shoulder is 70 to 90 degrees. The large and rounded greater tubercle has an upper, middle, and lower facet, marking the distal attachment of the supraspinatus, infraspinatus, and teres minor, respectively (see Figure 5-7, B and Figure 5-9). The glenohumeral, or shoulder, joint is a synovial joint that attaches the upper limb to the axial skeleton. Proximal attachments of muscle are shown in red. Identify the bony structures and key landmarks of the neck and shoulder complex. Rarely does a single muscle act in isolation at the shoulder complex. TThe multiarticular complex of the shoulder gives rise to the dynamic movement potential of the arm at the glenohumeral joint. The right side shows the first seven ribs and clavicle. The slope of the glenoid fossa is inclined upward about 4 degrees relative to a horizontal axis through the body of the scapula.26 This inclination is highly variable, ranging from a downward inclination of 7 degrees to an upward inclination of nearly 16 degrees. Then 3 of each, etc. Last medically reviewed on September 13, 2018, Shoulder popping, also known as crepitus, has several possible causes. 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). The right acromioclavicular joint. Posterior aspect of the right proximal humerus. Distal attachment of muscles is shown in gray. (The axis of rotation is shown in Figure 5-13 as intersecting the sternum because, by convention, the axis of rotation for a given motion intersects the convex member of the joint.) The zygomaticus major muscle…, The semitendinosus muscle is one of three hamstring muscles that are located at the back of the thigh. The joints of the right shoulder complex. Glenohumeral joint (Articulatio glenohumeralis) The glenohumeral, or shoulder, joint is a synovial joint that attaches the upper limb to the axial skeleton. Complete an ascending ladder of the 3-movement complex, increasing by 1 rep per round. The crisscrossing of fibers assists with stabilizing the joint through all motions, except for a downward movement of the clavicle (i.e., depression). The dashed line around the clavicular facet shows the attachments of the capsule at the sternoclavicular joint. (The term elevation is frequently used in the literature without differentiation between abduction and flexion.) 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. An anterior-lateral view of the articular surfaces of the right sternoclavicular joint. The coracoclavicular ligament provides an important extrinsic source of stability to the AC joint (see Figure 5-17). Angle A: The orientation of the clavicle deviated about 20 degrees posterior to the frontal plane. The AC joint is a gliding or plane joint, reflecting the predominantly flat contour of the joint surfaces. Find out why it is sometimes accompanied by pain while other times it's not, as…, Few would suspect the cause of shoulder pain to be something as typical and inactive as sitting at our desks. So, perform 1 back squat, 1 shoulder press, 1 deadlift. FIGURE 5-11. The dashed line around the ends of the clavicle show attachments of the joint capsule. The articular surfaces at the AC joint are lined with a layer of fibrocartilage and often separated by a complete or incomplete, Kinesiology of Mastication and Ventilation. The concavity within the fossa is filled with the thick subscapularis muscle. Clavicular fractures are most common in males under 30 years old—most often as the result of contact-sport or road-traffic accidents. A maximum of 15 to 30 degrees of motion have been reported in each direction.27,140,179 The horizontal plane motions of the clavicle are strongly associated with protraction and retraction motions of the scapula. With your arms at your sides, palms facing your body, bend your elbows 90 degrees. The posterior surface of the scapula is separated into a supraspinatous fossa and an infraspinatous fossa by the prominent spine. Protraction—The medial border of the scapula slides anterior-laterally on the thorax away from the midline. When you raise your arm out from the sides of your body, it’s an abduction of your shoulder. A normal range of motion for shoulder flexion is 180 degrees. The dashed line around the ends of the clavicle show attachments of the joint capsule. Primary movements at the scapulothoracic joint are traditionally described as elevation and depression, protraction and retraction, and upward and downward rotation. Relative Strength of Shoulder Joint Movements. Axial rotation of the clavicle is mechanically linked with the overall kinematics of abduction or flexion of the shoulder and cannot be independently performed with the arm resting at the side. This gives the shoulder complex a huge range of motion and makes it a very versatile joint. 18.1 and 18.2).The mobility provided by three joints working together gives the shoulder complex a wide range of movement. The head of the humerus, nearly one half of a full sphere, forms the convex component of the glenohumeral joint (Figure 5-7). To make the subject at once comprehensive and relevant to the clinician, the structure and function of the sternoclavicular and acromioclavicular… FIGURE 5-8. There are few published data on the ranges of available motion at the shoulder and no clinical technique for the assessment of three dimensional movement. The study of the upper extremity begins with the shoulder complex, a set of four articulations involving the sternum, clavicle, ribs, scapula, and humerus (Figure 5-1). • The clavicle and the scapula are important osseous structures that provide origination sites for many of the shoulder muscles. Flexion - Movement of the arm through the saggital plane that raises the arm. The ST joint involves the gliding movement of the scapula along the rib cage during upper extremity movements and does not include a physical bone-to-bone attachment. The shoulder is composed of 4 joints- The shoulder joint also is […] B, A posterior view of the joint opened up from behind, showing the clavicular facet on the acromion and the disc. According to DePalma,35 the incomplete discs are not structural anomalies but rather indications of the degeneration that often affects this joint. Proximal attachments of muscle are in red, distal attachments in gray. Proximal attachments of muscles are shown in red, distal attachments in gray. The sternoclavicular (SC) joint is a complex articulation, involving the medial end of the clavicle, the clavicular facet on the sternum, and the superior border of the cartilage of the first rib (Figure 5-11). FIGURE 5-1. The ability of your shoulders to move in a normal range depends on the health of your: Your shoulders have the ability to move more than most joints. The vertical axis of rotation is shown through the sternum. The sternum consists of the manubrium, body, and xiphoid process (Figure 5-2). The costal facets, located on the lateral edge of the manubrium, provide bilateral attachment sites for the first two ribs. A normal range for abduction, starting with your palms at your sides, is around 150 degrees in a healthy shoulder. With the arm in the anatomic position, the long axis of the clavicle is oriented slightly above the horizontal plane and about 20 degrees posterior to the frontal plane (Figure 5-4; angle A). A weakened, painful, or unstable link anywhere along the chain significantly decreases the effectiveness of the entire complex. The GH joint is of parti… The shoulder complex involves 3 physiological joints and one floating joint: 1. Each degree of freedom is associated with one of the three cardinal planes of motion: sagittal, frontal, and horizontal. The very cooperative nature of shoulder muscles increases the versatility, control, and range of active movements. 4. FIGURE 5-2. Shoulder complex. The osteokinematics of the clavicle involve a rotation in all three degrees of freedom. The manubrium possesses a pair of oval-shaped clavicular facets, which articulate with the clavicles. PLAY. Identify the key joint structures of the neck and shoulder region. FIGURE 5-12. 12 Stretches to Help Relieve Tight Shoulders. The acromioclavicular (AC) joint is the articulation between the lateral end of the clavicle and the acromion of the scapula (Figure 5-16, A). Your doctor will diagnose a potential issue through a series of tests, which may include: If you’re worried about the range of motion of your shoulder, you should mention the issue to your doctor. Lateral and slightly posterior to the costal facet is the distinct costal tuberosity, an attachment for the costoclavicular ligament. The disc not only strengthens the articulation but functions as a shock absorber by increasing the surface area of joint contact. 3. Stretched structures are shown as thin elongated arrows; slackened structures are shown as a wavy arrow. Movement Anatomy: Shoulder Complex. The lateral or axillary border runs from the inferior angle to the lateral angle of the scapula. The ball of your upper arm fits into your shoulder socket. The shoulder joint complex is composed of three joints—the sternoclavicular, acromioclavicular, and glenohumeral joints ().As a group, they attach the upper limb to the scapula and sternum (Figs. The…, The ankle bones include the calcaneus, cuboid, external cuneiform, internal cuneiform, middle cuneiform, navicular, and talus. Trauma or disease often limits shoulder motion, causing a significant reduction in the effectiveness of the entire upper limb. FIGURE 5-6. A, An anterior view showing the sloping nature of the articulation. It’s held there with muscles, tendons, and ligaments. The clavicle elevates and depresses, protracts and retracts, and rotates around the bone’s longitudinal axis (Figure 5-13). Proximal attachments of muscle are shown in red. A close-up view of the right coracoid process seen from above. Muscles work in “teams” to produce highly coordinated actions that are expressed over multiple joints. Your shoulder is made up of many different moving parts. A normal range of motion for shoulder extension to the highest point you can lift your arm behind your back — starting with your palms next to your body — is between 45 and 60 degrees. The shoulder joint is formed by the articulation of the head of the humerus with theglenoid cavity(or fossa) of the scapula. This is lateral rotation — also referred to as external rotation — and the normal range of motion for a healthy shoulder is 90 degrees. The transverse diameters (blue) extend roughly in the horizontal plane between anterior and posterior points of the articular surfaces. This series of joints provides extensive range of motion to the upper extremity, thereby increasing the ability to reach and manipulate objects. The costal facet of the clavicle (see Figure 5-3; inferior surface) rests against the first rib. Before the kinematics of the sternoclavicular and acromioclavicular joints are described, the movements at the scapulothoracic joint must be defined (Figure 5-10). Angle C: Retroversion of the humeral head about 30 degrees posterior to the medial-lateral axis at the elbow. This rotation occurs as a natural component of raising the arm upward. For each complex, use the same set of dumbbells for all three movements. The rounded and prominent medial or sternal end of the clavicle articulates with the sternum (see Figure 5-3). The clavicular facet on the acromion faces medially and slightly superiorly, providing a point of attachment with the corresponding acromial facet on the clavicle. Because the shoulder is such a unique joint it is also prone to particular problems. Both parts of the coracoclavicular ligament are of similar length, cross-sectional area, stiffness, and tensile strength.31 As a whole, the entire ligament is stronger and absorbs more energy at the point of rupture than most other ligaments of the shoulder. B, Protraction and retraction. Anterior view of a mechanical diagram of the arthrokinematics of roll and slide during elevation (A) and depression (B) of the clavicle around the right sternoclavicular joint. The primary purpose of these movements is to place the scapula in an optimal position to accept the head of the humerus. A, Elevation and depression. 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. When one looks from above, it is evident that the. The arthrokinematics of protraction around the SC joint are similar to those of retraction, except that they occur in an anterior direction. 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. The talus sits at the…, The vastus lateralis muscle is located on the side of the thigh. Maximums of approximately 45 degrees of elevation and 10 degrees of depression have been reported.27,140 Elevation and depression of the clavicle produce a similar path of movement of the scapula.73. The joint therefore must be firmly attached while simultaneously allowing considerable range of movement. The scapula articulates with the head of the humerus at the slightly concave glenoid fossa (from the Greek root glene, socket of joint, + eidos, resembling) (see Figure 5-5, B). The other two are the semimembranosus muscle…. FIGURE 5-5. Retraction—The medial border of the scapula slides posterior-medially on the thorax toward the midline, such as during “pinching” of the shoulder blades together. The longitudinal axis is indicated by the dashed green line. C, Upward and downward rotation. Flexion/Extension, Adduction/abduction. Scapulothoracic (ST) joint - known as a "functional joint". Sharp crests extend distally from the anterior side of the greater and lesser tubercles. During shoulder movements such as lifting, certain muscle groups help to move the shoulder, while other muscle groups help to stabilize the shoulder complex. Large forces through the clavicle often cause fracture of the bone before the SC joint dislocates. The axes of rotation are shown in the anterior-posterior direction near the head of the clavicle. Motions of the right scapulothoracic joint. 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. A normal range of motion for your shoulder depends on your flexibility and the overall health of your shoulder. Depression—From an elevated position, the scapula slides inferiorly on the thorax. Imagine your body is a cabinet, your arms are the cabinet doors and you’re shutting the doors. FIGURE 5-10. The muscles of the shoulder complex provide stability and movement. The scapula and humerus tend to follow this plane when the arm is naturally raised overhead. FIGURE 5-7. The costoclavicular ligament is a strong structure extending from the cartilage of the first rib to the costal tuberosity on the inferior surface of the clavicle. 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. tasks in this study to (1) test the reliability of the shoulder complex kinematic data duri ng functional tasks in asymp-tomatic subjects, (2) character ize functional tasks in terms of 3-D shoulder complex movements, and (3) examine the relationships between age and shoulder complex movements during the functional tasks. Joint surfaces vary, however, from flat to slightly convex or concave (see, The AC joint is surrounded by a capsule that is directly reinforced by. During shoulder abduction or flexion, a point on the superior aspect of the clavicle rotates posteriorly 20 to 35 degrees.62,84,115,194 As the arm is returned to the side, the clavicle rotates back to its original position. What can you tell us about the complex? This orientation of the scapula is referred to as the scapular plane. The jugular notch is located at the superior aspect of the manubrium, between the clavicular facets. The acromion extends in a lateral and anterior direction, forming a horizontal shelf over the glenoid fossa. Elevation of the clavicle occurs as its convex articular surface rolls superiorly and simultaneously slides inferiorly on the concavity of the sternum (Figure 5-14, A). Includes: shoulder girdle and shoulder joint. The right side shows the first seven ribs and clavicle. Rarely does a single muscle act in isolation at the shoulder complex. The articular surfaces at the AC joint are lined with a layer of fibrocartilage and often separated by a complete or incomplete articular disc. Note in A that the stretched costoclavicular ligament produces a downward force in the direction of the slide. ACL, anterior capsular ligament; CCL, costoclavicular ligament; PCL, posterior capsular ligaments. If you hug yourself, your shoulders are adducting. A force couple is defined as two equal but oppositely directed forces acting simultaneously on opposite sides of an axis that generates rotation. Depression of the clavicle occurs by action of its convex surface rolling inferiorly and sliding superiorly (see Figure 5-14, B). The largest of these shoulder … Muscles work in “teams” to produce highly coordinated actions that are expressed over multiple joints. Posterior (A) and anterior (B) surfaces of the right scapula. The motions are elevation and depression in a near frontal plane, Elevation and depression of the clavicle occur approximately parallel to the frontal plane, around a near anterior-posterior axis of rotation (see, The arthrokinematics for elevation and depression of the clavicle occur along the SC joint’s longitudinal diameter (see, Anterior view of a mechanical diagram of the arthrokinematics of roll and slide during elevation, Protraction and retraction of the clavicle occur nearly parallel to the horizontal plane, around a vertical axis of rotation (see, The arthrokinematics for protraction and retraction of the clavicle occur along the SC joint’s transverse diameter (see. The articulations between the bones make up the shoulder joints. Essentially all functional movements of the glenohumeral joint involve some movement of the clavicle around the SC joint. Shoulder adduction occurs when you move your arms towards the middle of the body. Your shoulder range of motion is, basically, how far you can move each shoulder in different directions without major joint pain or other issues. The shoulder is a complex joint system — three bones and five joints — that can move in multiple directions. The design of these structures promotes movement. The prominent lesser and greater tubercles surround the anterior and lateral circumference of the extreme proximal end of the humerus (see Figure 5-7, B). The depth of the supraspinatous fossa is filled by the supraspinatus muscle. The joints of the right shoulder complex. The superior and inferior surfaces of the right clavicle. It must be understood, however, that movement of the entire shoulder is the result of movement in each of its four joints. 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. The stretched costoclavicular ligament helps limit as well as stabilize the elevated position of the clavicle.

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