The light bulb sign is a radiological finding observed on plain radiographs in the context of posterior shoulder dislocation. [1] It refers to the abnormal, rounded appearance of the humeral head, which resembles a "light bulb," due to internal rotation of the arm following dislocation. [2]
In posterior shoulder dislocation, the humeral head is displaced posteriorly out of the glenoid cavity. This injury is frequently associated with internal rotation where the humeral head rotates internally, altering its usual elliptical contour to a more rounded shape, creating the "light bulb" appearance. On anteroposterior (AP) radiographs, the humeral head no longer overlaps the glenoid, further emphasizing its abnormal shape.
Posterior shoulder dislocations typically result from trauma such as seizures or electric shocks, which cause forceful contraction of the internal rotator muscles of the shoulder. [3] [4]
The light bulb sign is best observed on an AP radiograph of the shoulder. [5] Key features include:
The scapula, also known as the shoulder blade, is the bone that connects the humerus with the clavicle. Like their connected bones, the scapulae are paired, with each scapula on either side of the body being roughly a mirror image of the other. The name derives from the Classical Latin word for trowel or small shovel, which it was thought to resemble.
The humerus is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rounded head, a narrow neck, and two short processes. The body is cylindrical in its upper portion, and more prismatic below. The lower extremity consists of 2 epicondyles, 2 processes, and 3 fossae. As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck due to its tendency to fracture, thus often becoming the focus of surgeons.
The rotator cuff is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles are:
Shoulder problems including pain, are one of the more common reasons for physician visits for musculoskeletal symptoms. The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed. This instability increases the likelihood of joint injury, often leading to a degenerative process in which tissues break down and no longer function well.
The human shoulder is made up of three bones: the clavicle (collarbone), the scapula, and the humerus as well as associated muscles, ligaments and tendons.
The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle is made up of three distinct sets of muscle fibers, namely the
A joint dislocation, also called luxation, occurs when there is an abnormal separation in the joint, where two or more bones meet. A partial dislocation is referred to as a subluxation. Dislocations are often caused by sudden trauma on the joint like an impact or fall. A joint dislocation can cause damage to the surrounding ligaments, tendons, muscles, and nerves. Dislocations can occur in any major joint or minor joint. The most common joint dislocation is a shoulder dislocation.
The teres minor is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the greater tubercle of the humerus and the posterior surface of the joint capsule.
The shoulder joint is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint. It involves an articulation between the glenoid fossa of the scapula and the head of the humerus. Due to the very loose joint capsule, it gives a limited interface of the humerus and scapula, it is the most mobile joint of the human body.
The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of the clavicle, scapula, and coracoid. Some mammalian species have only the scapula.
The glenoid labrum is a fibrocartilaginous structure attached around the rim of the glenoid cavity on the shoulder blade. The shoulder joint is considered a ball-and-socket joint. However, in bony terms the 'socket' is quite shallow and small, covering at most only a third of the 'ball'. The socket is deepened by the glenoid labrum, stabilizing the shoulder joint.
A separated shoulder, also known as acromioclavicular joint injury, is a common injury to the acromioclavicular joint. The AC joint is located at the outer end of the clavicle where it attaches to the acromion of the scapula. Symptoms include non-radiating pain which may make it difficult to move the shoulder. The presence of swelling or bruising and a deformity in the shoulder is also common depending on how severe the dislocation is.
A dislocated shoulder is a condition in which the head of the humerus is detached from the glenoid fossa. Symptoms include shoulder pain and instability. Complications may include a Bankart lesion, Hill-Sachs lesion, rotator cuff tear, or injury to the axillary nerve.
Shoulder surgery is a means of treating injured shoulders. Many surgeries have been developed to repair the muscles, connective tissue, or damaged joints that can arise from traumatic or overuse injuries to the shoulder.
A Bankart lesion is a type of shoulder injury that occurs following a dislocated shoulder. It is an injury of the anterior (inferior) glenoid labrum of the shoulder. When this happens, a pocket at the front of the glenoid forms that allows the humeral head to dislocate into it. It is an indication for surgery and often accompanied by a Hill-Sachs lesion, damage to the posterior humeral head.
A Hill–Sachs lesion, or Hill–Sachs fracture, is a cortical depression in the posterolateral head of the humerus. It results from forceful impaction of the humeral head against the anteroinferior glenoid rim when the shoulder is dislocated anteriorly.
Humeral avulsion of the glenohumeral ligament (HAGL) is defined as an avulsion of the inferior glenohumeral ligament from the anatomic neck of the humerus. In other words, it occurs when we have disruption of the ligaments that join the humerus to the glenoid. HAGL tends to occur in 7.5-9.3% of cases of anterior shoulder instability. Making it an uncommon cause of anterior shoulder instability. Avulsion of this ligamentous complex may occur in three sites: glenoid insertion (40%), the midsubstance (35%) and the humeral insertion (25%). Bony humeral avulsion of the glenohumeral ligament (BHAGL) refers when we have HAGL with bony fracture.
Cunningham shoulder reduction was originally published in 2003 and is an anatomically based method of shoulder reduction that utilizes positioning, voluntary scapular retraction, and bicipital massage. It is designed for true anterior/subcoracoid glenohumeral dislocations in patients who can fully adduct their humerus. This is distinct from anteroinferior/subglenoid glenohumeral dislocations for which alternative techniques should be used. The method is one of several techniques used for shoulder reduction.
Yergason's test is a special test used for orthopedic examination of the shoulder and upper arm region, specifically the biceps tendon.
Glenolabral articular disruption (GLAD) lesion is a type of shoulder injury. It is difficult to diagnose clinically, and requires surgical repair to correct the damage to the shoulder.