Ak Dutta Anatomy Pdf Upper Limb

[Marlys Stotesberry]

Thearticular surfaces are covered with fibrocartilage (as opposed to hyaline cartilage, present in the majority of synovial joints). The joint is separated into two compartments by a fibrocartilaginous articular disc.

The sternoclavicular joint is required to be both mobile (to accommodate the movements of the upper limb) and strong (to form a stable connection between the upper limb and the trunk).

Dislocation of the sternoclavicular joint is rare and requires significant force. The costoclavicular ligament and the articular disc are highly effective at absorbing and transmitting forces away from the joint into the sternum.

In adolescents, the epiphyseal growth plate of the sternal end of the clavicle has not fully closed. In this population, the dislocation is usually accompanied by a fracture through the plate.

Acting in conjunction with the pectoral girdle, the shoulder joint allows for a wide range of motion at the upper limb; flexion, extension, abduction, adduction, external/lateral rotation, internal/medial rotation and circumduction. In fact, it is the most mobile joint of the human body. This shoulder function comes at the cost of stability however, as the bony surfaces offer little support. Instead the surrounding shoulder muscles and ligamentous structures offer the joint security; the capsule, ligaments and tendons of the rotator cuff muscles. Because of this mobility-stability compromise, the shoulder joint is one of the most frequently injured joints of the body.

The glenohumeral joint is the articulation between the spherical head of the humerus and the concave glenoid fossa of the scapula. Being a synovial joint, both articular surfaces are covered with hyaline cartilage.

The glenoid fossa is a shallow pear-shaped pit on the superolateral angle of scapula. The concavity of the fossa is less acute than the convexity of the humeral head, meaning that the articular surfaces are not fully congruent. Congruency is increased somewhat by the presence of a glenoid labrum, a fibrocartilaginous ring that attaches to the margins of the fossa. The labrum acts to deepen the glenoid fossa slightly, it is triangular in shape and thicker anteriorly than inferiorly. The surface of the humeral head is three to four times larger than the surface of glenoid fossa, meaning that only a third of the humeral head is ever in contact with the fossa and labrum.

This incongruent bony anatomy allows for the wide range of movement available at the shoulder joint but is also the reason for the lack of joint stability. Instead, joint security is provided entirely by the soft tissue structures; the fibrous capsule, ligaments, shoulder muscles and their tendons.

The shoulder joint is encircled by a loose fibrous capsule. It extends from the scapula to the humerus, enclosing the joint on all sides. The internal surface of the capsule is lined by a synovial membrane.

The capsule remains lax to allow for mobility of the upper limb. It relies on ligaments and muscle tendons to provide reinforcement. The anterior capsule is thickened by the three glenohumeral ligaments while the tendons of the rotator cuff muscles spread over the capsule blending with its external surface. These tendons form a continuous covering called the rotator capsule. It is comprised of the supraspinatus superiorly, infraspinatus and teres minor posteriorly, subscapularis anteriorly and the long head of triceps brachii inferiorly.

Two weak spots exist in this reinforced capsule. The first is the rotator interval, an area of unreinforced capsule that exists between the subscapularis and supraspinatus tendons. The second is the inferior capsular aspect, this is the point where the capsule is the weakest. The loose inferior capsule forms a fold when the arm is in the anatomical position. It becomes stretched, and least supported, when the arm is abducted.

Several ligaments limit the movement of the GH joint and resist humeral dislocation. These are the coracohumeral, glenohumeral and transverse humeral ligaments. Glenohumeral and transverse humeral are capsular ligaments while coracohumeral is an accessory ligament.

The transverse humeral ligament extends horizontally between the tubercles of the humerus. It covers the intertubercular sulcus and the long head tendon of the biceps brachii muscle, preventing displacement of the tendon from the sulcus. The coracohumeral ligament extends between the coracoid process of the scapula to the tubercles of the humerus and the intervening transverse humeral ligament, supporting the joint from its superior side. It acts to limit inferior translation and excessive external rotation of the humerus.

The superior, middle and inferior glenohumeral ligaments support the joint from the anteroinferior side. They have a weak stabilizing function, each acting to limit the maximum amplitude of certain arm movements;

The superior glenohumeral ligament extends from the supraglenoid tubercle of scapula to the proximal aspect of the lesser tubercle of humerus. Along with the coracohumeral ligament, it supports the rotator interval and prevents inferior translation of the humeral head, particularly during shoulder adduction.

The inferior glenohumeral ligament is a sling-like ligament extending between the glenoid labrum and the inferomedial part of the humeral neck. It is split into anterior and posterior bands, between which sits the axillary pouch. This is the strongest of the three GH ligaments, being thicker and longer than the other two. Both bands stabilize the humeral head when the arm is abducted above 90. The anterior band limits external rotation of the arm, while the posterior band limits internal rotation.

The glenohumeral joint has a greater range of movement (RoM) than any other body joint. Being a ball-and-socket joint, it allows movements in three degrees of freedom (average maximum glenohumeral active RoM is shown in brackets);

Activities of the arm rely on movement from not only the glenohumeral joint but also the scapulothoracic joint (acromioclavicular, sternoclavicular and scapulothoracic articulations). Together these joints can change the position of the glenoid fossa, relative to the chest wall. Thus repositioning the glenohumeral joint, and upper limb, within space. This provides for a greater range of motion available within the greater shoulder complex;

The prime flexors of the glenohumeral joint are the deltoid (anterior fibers) and pectoralis major (clavicular fibers) muscles. While coracobrachialis and the long head of biceps brachii assist as weak flexor muscles.

Extension is performed by the latissimus dorsi, teres major, pectoralis major (sternocostal fibers) and long head of triceps brachii muscles. Of note, is that these muscles have a stronger action when acting to extend the flexed arm.

The prime abductors of the arm are the supraspinatus and deltoid muscles. It is believed that the supraspinatus is important for movement initiation and early abduction, while the deltoid muscle is engaged from approximately 20 of abduction and carried the arm through to the full 180 of abduction. Contraction of the deltoid muscle applies a strong superior translation force to the humerus, this is countered by the action of the rotator cuff muscles, preventing superior humeral dislocation.

Internal rotation is primarily performed by the subscapularis and teres major muscles. Pectoralis major, deltoid (anterior fibers) and latissimus dorsi are also capable of producing this movement. The main lateral rotators are the infraspinatus and teres minor muscles, with help from the posterior fibers of the deltoid muscle. External rotation of the humerus moves the greater tubercle out from under the acromial arch, allowing uninhibited arm abduction to occur.

The rotator cuff muscles are four muscles that form a musculotendinous unit around the shoulder joint. These are the supraspinatus, infraspinatus, teres minor and subscapularis muscles. The function of this entire muscular apparatus is to produce movement at the shoulder joint while keeping the head of humerus stable and centralized within the glenoid cavity.

All four muscles are firmly attached around the joint in such a way that they form a sleeve (rotator capsule). Individually, each muscle has its own pulling axis that results in a certain movement (prime mover), while together they create a concavity compression. This is a stabilizing mechanism in which compression of the humerus into the concavity of glenoid fossa prevents its dislocation by translating forces.

Stroke is the leading cause of sensorimotor disability worldwide. Recently, neurorehabilitation therapies based on neural interfaces have paved the way toward new effective rehabilitation strategies exploiting neural plasticity mechanisms and have produced promising results even in extremely compromised patients. In this chapter, we review and discuss several aspects of the design and use of neural interfaces coupled with upper limb actuators (robotics and functional electrical stimulation (FES)) for motor rehabilitation after stroke. We first describe the burden of stroke and the limitations of currently used rehabilitation strategies. Secondly, we analyze different neural interfacing methods to reinforce the brain-to-muscle link leveraging previous neuroscientific findings on motor learning and functional neuroplasticity. We review current clinical trials using this technology and analyze its effect on the sensorimotor function of stroke patients, reported as clinical and neurophysiological parameters. Thirdly, we provide several guidelines for the optimal design of these systems to boost motor recovery. We conclude with some recommendations and thoughts for future development of this technology in stroke rehabilitation.

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