Medial Collateral Knee Ligament Injury

Background

Medial collateral ligament (MCL) injuries of the knee are very common sports-related injuries. The MCL is the most commonly injured knee ligament. Injuries to the MCL occur in almost all sports and in all age groups.

NextEpidemiologyFrequencyUnited States

The incidence of MCL injuries is impossible to determine because of the wide spectrum of injury severity. Many MCL injuries are minor and may never be evaluated by a physician.[1]

PreviousNextFunctional Anatomy

The medial aspect of the knee has been divided into 3 distinct layers based on cadaver dissection. The first layer is the deep fascia, which consists of the sartorius fascia anteriorly and a thin fascial layer posteriorly. The thin posterior fascia covers the popliteal fossa and the heads of the gastrocnemius muscle. The second layer includes the superficial MCL, also known as the tibial collateral ligament. This ligament attaches proximally to the medial femoral epicondyle and to the tibia distally, approximately 4-5 cm distal to the joint line. The parapatellar retinaculum and patellofemoral ligament are within this layer.

The third layer is the knee joint capsule, which attaches proximally and distally at the articular margins. The capsule is divided into thirds from anterior to posterior. The anterior third of the capsule is the thinnest portion. It is attached to the anterior horn of the medial meniscus and is reinforced by the medial retinaculum. The middle third of the capsule consists of the deep medial collateral ligament. It is firmly attached to the mid body of the medial meniscus. Proximal to the meniscal attachment, it is termed the meniscofemoral ligament. Distal to its meniscal attachment, it is termed the meniscotibial ligament. The posterior third of the capsule includes the posterior oblique ligament (POL) and the oblique popliteal ligament. The POL has 3 arms, the superficial, tibial, and capsular.

See the figure below.

The medial and lateral collateral ligaments of the knee. Courtesy of Randale Sechrest, MD, CEO, Medical Multimedia Group PreviousNextSport Specific Biomechanics

The superficial MCL has been shown through serial cutting studies to provide the primary restraint to valgus loads at all degrees of flexion. It is also an important restraint to anterior tibial translation when the anterior cruciate ligament is injured. The superficial MCL acts as a primary restraint to external rotation of the tibia.

Stability of the medial side of the knee is provided by dynamic and static restraints. The static restraints are the superficial MCL and the joint capsule, including the deep MCL and the POL. The semimembranosus muscle, the pes anserine muscles, and the vastus medialis muscle provide dynamic stability. The muscles of the pes include the sartorius, gracilis, and semitendinosus. These muscles flex and internally rotate the tibia. The semimembranosus has 4 attachments: direct, tibial, inferior, and capsular.[2, 3]

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Lateral Collateral Knee Ligament Injury

Background

Lateral collateral ligament (LCL) injuries result from a varus force across the knee. A contact injury, such as a direct blow to the medial side of the knee, or a noncontact injury, such as a hyperextension stress, may result in a varus force across the knee injuring the LCL. In terms of functionality, the LCL has often been grouped with the popliteofibular ligament and the popliteus tendon as the posterolateral corner (PLC).

See the figure below.

The medial and lateral collateral ligaments of the knee. Courtesy of Randale Sechrest, MD, CEO, Medical Multimedia Group NextFunctional Anatomy

The LCL is a round ligament that originates close to the lateral epicondyle and inserts onto the fibular head.

PreviousNextSport-Specific BiomechanicsVarus stress

The LCL is the primary restraint to varus stress across the knee.

External tibial rotation

The PLC, which includes the LCL, popliteofibular ligament, and popliteus tendon, is the primary restraint to external rotation stress across the knee.

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Meniscus Injuries

Background

Our understanding of the meniscus has changed radically in the last century. In 1887, Sutton described the meniscus as "the functionless remains of a leg muscle."[1] Not until 1948 did Fairbanks appreciate that "meniscectomy is not wholly innocuous," in his classic report of postmeniscectomy radiographic changes.[2] Research and knowledge of the meniscus has continued. The critical importance of the meniscus of the knee joint is now understood.

Note the contrasting images below.

Magnetic resonance imaging scan showing a normal meniscus. Magnetic resonance imaging scan showing a torn medial meniscus.

For patient education resources, see the Foot, Ankle, Knee, and Hip Center and Arthritis Center, as well as Knee Pain and Knee Injury.

NextEpidemiologyFrequencyUnited StatesMeniscal injuries may be the most common knee injury. The prevalence of acute meniscal tears is 61 cases per 100,000 persons.The overall male-to-female incidence is approximately 2.5:1. The peak incidence of meniscal injury for males is in those aged 31-40 years. For females, the peak incidence is in those aged 11-20 years. In patients older than 65 years, the rate of degenerative meniscal tears is 60%. Surgical procedures of the meniscus are performed on an estimated 850,000 patients each year.[3] International

Estimates indicate that at least twice the number of meniscus procedures in the United States are performed worldwide.

PreviousNextFunctional Anatomy

The menisci are 2 semilunar wedges in the knee joint positioned between the tibia and the femur. They are essentially extensions of the tibia that act to deepen the articular surfaces of the otherwise relatively flat tibial plateau to accommodate the relatively round femoral condyles. The superior surfaces are concave and in contact with the femoral condyles; the inferior surfaces are flat and conform to the tibial plateaus. The peripheral, convex borders of the menisci are thick and attach to the joint capsule; the opposite border tapers inward to a thin, free edge centrally. Therefore, menisci have a triangular shape in cross section. Each covers approximately two thirds of the corresponding articular surface of the tibia. The medial and lateral menisci each have distinct, individual anatomic characteristics.[4, 5, 6]

The medial meniscus is semicircular or C-shaped and approximately 3.5 cm in length from anterior to posterior. It is asymmetric with a considerably wider posterior horn than anterior horn. Peripherally, the medial meniscus is continuously attached to the joint capsule, with the middle portion being more firmly attached via connection with fibers of the deep medial collateral ligament. It is anchored to the tibia by the coronary (meniscotibial) ligaments.

The posterior horn of the medial meniscus inserts in the posterior intercondylar fossa directly anterior to the posterior cruciate ligament. The anterior horn attachment is more variable, distributed in a 6- to 8-mm area anterior to the anterior cruciate ligament (ACL) tibial attachment in the anterior intercondylar fossa. Some anterior fibers attach over the anterior periphery of the tibial articular surface, and some posterior fibers of the anterior horn merge with the transverse meniscal ligament that connects to the lateral meniscus.

The lateral meniscus is more nearly circular or O-shaped and covers a larger portion of the tibial plateau surface than the medial meniscus. Its length from anterior to posterior is slightly less than the medial meniscus, and it has an almost uniform width. There is attachment to the joint capsule peripherally, except in the region of the middle one third, where there is no attachment but rather a hiatus for the popliteal tendon.

Unlike the medial meniscus, there is no attachment of the lateral meniscus to the lateral collateral ligament, but the lateral meniscus is anchored to the tibia via coronary (meniscotibial) ligaments. Posteriorly, the lateral meniscus is uniquely attached to the medial femoral condyle by meniscofemoral ligaments. These ligaments are highly variable and pass anterior (ligament of Humphrey) and/or posterior (ligament of Wrisberg) to the posterior cruciate ligament. The posterior attachment to the tibia is just anterior to the medial meniscus attachment in the posterior intercondylar fossa. The anterior horn inserts anterior to the lateral tibial spine and in close proximity to the ACL tibial insertion. Some fibers actually may blend into the ACL.

Despite their attachments, both menisci have mobility. The medial meniscus, with excursion of approximately 5 mm, is half as mobile as the lateral meniscus, whose mobility may exceed 10 mm. The anterior horns are more mobile than the posterior horns. This mobility allows for improved conformity of the tibiofemoral joint. Because the posterior horn of the medial meniscus has the least movement, it is at greatest risk for disruption.

The microanatomy of the meniscus is dense fibrocartilage composed of cells and an extracellular matrix of collagen fibers in network. The cells are termed fibrochondrocytes because they appear to be a mixture of fibroblasts and chondrocytes. These cells are responsible for the synthesis and maintenance of the extracellular fibrocartilaginous matrix.

The most abundant component of the menisci is collagen (75%)—mainly type I collagen (>90%) but it also contains types II, III, V, and VI. Collagen fibers are arranged mostly along a longitudinal or circumferential direction, with some interwoven radial and oblique fibers. The circumferential fibers are related directly to the menisci's functional ability to dissipate compressive loads. The other fibers act primarily as ties to enhance structural rigidity and to help prevent longitudinal splitting. The extracellular matrix also includes proteoglycans, glycoproteins, and elastin.

Most meniscal tissue is avascular and depends on passive diffusion and mechanical pumping to provide nutrition to the fibrocytes within the meniscal substance. Arnoczky and Warren demonstrated the important vascular anatomy of the menisci.[7, 8] The limited peripheral blood supply originates from the medial and lateral inferior and superior geniculate arteries. Branches from these vessels give rise to a perimeniscal capillary plexus within the synovium and joint capsule, which, in turn, supplies the meniscus periphery.

Studies have shown that 10-30% of the periphery of the medial meniscus and 10-25% of the lateral meniscus receives a vascular supply; the remainder receives its nutrition from the synovial fluid from passive diffusion and mechanical pumping. A few terminal branches of these vessels, along with the middle geniculate artery through the synovial covering of the anterior and posterior horn attachments, supply increased vascularity to the meniscal horns. The potential for vascular ingrowth is essential for successful meniscal healing and surgical repair. Various zones of the meniscus are described based on the blood supply; the red zone is the well-vascularized periphery, the red-white zone is the middle portion with vascularity peripherally but not centrally, and the white zone is the central avascular portion.

The neuroanatomy of the meniscus is not well described. However, the distribution of neural elements has been demonstrated in essentially the same anatomic distribution as the vascular supply. The anterior and posterior horns are the most richly innervated, and the body innervation follows the pattern along the periphery. Although not entirely clear, these nerve endings are believed to play a role in sensory feedback and proprioception. The greater innervation of the horns of the meniscus reflects the need for feedback at the extremes of flexion and extension, when the meniscal horns are compressed and neural elements are activated.[4, 5, 6]

The meniscus has unique anatomic properties. An understanding of this anatomy is essential to comprehending its important functions, which include load bearing, load and force distribution, joint stability, joint lubrication, and proprioception.[4, 5, 9] One of the primary functions is to provide load bearing across the knee joint. Fifty percent of the compressive load in the knee is transferred by the menisci in extension, whereas up to 85% of the load is transferred at 90° of flexion. The collagen orientation makes this load bearing possible by converting the compressive forces to tensile forces.

Load and forces are distributed across a much larger surface area because of the menisci, which (1) decrease focal contact pressure by increasing the contact area and (2) protect the underlying articular cartilage. Resection of 15-34% of a meniscus may increase contact pressure by more than 350%. Normal knees have 20% better shock-absorbing capacity than meniscectomized knees.

Joint stability is increased because of meniscal structure, which allows increased congruence and conformity between the femoral condyles and tibial plateaus.[4, 5] The wedge-shaped meniscus attached to the tibia serves as a secondary stabilizer. For example, the posterior horn acts as a shim to resist anterior tibial translation relative to the femur. Meniscectomy alone may not increase knee laxity, but it has been shown that in association with ACL deficiency, anterior laxity is increased. Meniscal lubrication occurs by fluid exudation across the surface, much like articular cartilage.

The classification of meniscal tears provides a description of pathoanatomy. The types of meniscus tears are (1) longitudinal tears that may take the shape of a bucket handle if displaced, (2) radial tears, (3) parrot-beak or oblique flap tears, (4) horizontal tears, and (5) complex tears that combine variants of the above.

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Iliotibial Band Syndrome

Background

Iliotibial band (ITB) syndrome (ITBS) is the most common cause of lateral knee pain among athletes.[1, 2, 3, 4, 5, 6] ITBS develops as a result of inflammation of the bursa surrounding the ITB and usually affects athletes who are involved in sports that require continuous running or repetitive knee flexion and extension.[1, 2, 3, 7, 8, 9, 10] This condition is, therefore, most common in long-distance runners and cyclists. ITBS may also be observed in athletes who participate in volleyball, tennis, soccer, skiing, weight lifting, and aerobics.[11]

For excellent patient education resources, visit eMedicineHealth's Osteoporosis Center. Also, see eMedicineHealth's patient education articles Knee Pain, Knee Injury, Tendinitis, and Running.

See also the following on Medscape Reference:

Iliotibial Band Friction Syndrome [in the Orthopedic Surgery section]

Physical Medicine and Rehabilitation for Iliotibial Band Syndrome

See also the following Medscape resource:

CME Medical Interventions Effectively Treat Overuse Injuries in Adult Endurance Athletes

NextEpidemiologyFrequencyUnited States

ITBS is the most common cause of lateral knee pain in runners. Although few studies are available regarding the incidence of ITBS in athletes, some studies cite this condition with an incidence as high as 12% of all running-related injuries.[12] Several studies of US Marine Corps recruits undergoing basic training determined the incidence of ITBS among this group to vary from 5.3 to 22.2%.

International

Data are not available regarding the international incidence of ITBS.

PreviousNextFunctional Anatomy

The ITB is the condensation of fascia formed by the tensor fascia lata and the gluteus medius and minimus muscles. The ITB is a wide, flat structure that originates at the iliac crest and inserts at the Gerdy tubercle on the lateral aspect of the proximal tibia. This band serves as a ligament between the lateral femoral condyle and the lateral tibia to stabilize the knee. The ITB assists in the following 4 movements of the lower extremity:

Abducts the hipContributes to internal rotation of the hip when the hip is flexed to 30°Assists with knee extension when the knee is in less than 30° of flexionAssists with knee flexion when the knee is in greater than 30° of flexion

The ITB is not attached to bone as it courses between the Gerdy tubercle and the lateral femoral epicondyle. This lack of attachment allows it to move anteriorly and posteriorly with knee flexion and extension. Some authors hypothesize that this movement may cause the ITB to rub against the lateral femoral condyle, causing inflammation. Other investigators hypothesize that injury of the ITB results from compression of the band against a layer of innervated fat between the ITB and epicondyle. Furthermore, a potential deep space is located under the ITB as it crosses the lateral femoral epicondyle and travels to the Gerdy tubercle. This bursa may become inflamed and cause a clicking sensation as the knee flexes and extends. The inflamed bursa may add another component to ITB tendinitis.

See also the following on Medscape Reference:

Bursitis in Emergency Medicine

Bursitis [in the Orthopedic Surgery section]

Tendonitis

PreviousNextSport-Specific Biomechanics

In runners, the posterior edge of the ITB impinges against the lateral epicondyle of the femur just after foot strike in the gait cycle.[7, 8] This friction occurs at or slightly below 30 º of knee flexion.[2, 3, 7] Downhill running and running at slower speeds may exacerbate ITBS as the knee tends to be less flexed at foot strike.[13, 14]

In cyclists, the ITB is pulled anteriorly on the pedaling downstroke and posteriorly on the upstroke. The ITB is predisposed to friction, irritation, and microtrauma during this repetitive movement because its posterior fibers adhere closely to the lateral femoral epicondyle.

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Medial Condylar Fracture of the Elbow

Background

Medial condylar fractures of the elbow, demonstrated in the images below, are rare in adults and children; prompt recognition of these sometimes elusive injuries is imperative so that complications can be averted.

Milch classification of condylar fractures. NextEpidemiologyFrequencyUnited States

Trauma to the elbow has a high potential for complications and residual functional disability. Luckily, fractures of the humeral condyles are uncommon in adults. Medial condylar fractures are less common than fractures of the lateral condyle. Together, these injuries account for approximately 5% of all distal humerus fractures in adults.

During adolescence, the distal humerus is the second most common site of physeal injury (second only to the distal radius). Supracondylar fractures account for approximately two thirds of distal humeral injuries in children. In children with elbow fractures, isolated medial condyle fractures are uncommon and account for approximately 1-2% of all distal humerus fractures. In children, medial condyle fractures occur at a peak age of 8-12 years.

Fracture of the medial epicondyle of the elbow, as seen in the image below, is common and occurs in approximately 10% of pediatric elbow fractures. Most of these injuries occur in males aged 10-14 years.

Medial epicondylar fracture PreviousNextFunctional Anatomy

The elbow joint is composed of the bony articulation between the humerus, ulna, and radius. The distal end of the humerus can be divided into the medial and lateral condyles. The articular portion of the medial condyle is the trochlea, and the articular portion of the lateral condyle is the capitulum. The epicondyle is considered part of the nonarticular portion of the condyle. The dividing point for the distal humerus, separating the medial and lateral condyles, is the capitulotrochlear sulcus.

Distinguishing between the articular and nonarticular surface of the condyles is important in the diagnosis and management of condylar fractures. By definition, fractures that involve only the intra-articular surface have no muscular attachments and can only be repositioned by pressure of the opposing articular surface or by open reduction and internal fixation. Fractures that extend beyond the joint capsule have attached muscle and ligaments. The position of the fracture fragment is often influenced by its muscular attachment.

The stability of the elbow is enhanced by its surrounding ligamentous structures. The medial collateral ligament and the lateral collateral ligament (ie, ulnar collateral ligament, radial collateral ligament) provide further stability of the elbow. The radiocapitellar joint is supported by the radial collateral and annular ligaments.

Collectively, the forearm musculature originates from the bony epicondyle prominences. The wrist flexors originate from the medial epicondyle, and the wrist extensors originate from the lateral epicondyle. Because the forearm musculature traverses the elbow joint, some inherent stability to the joint is conferred by muscular contraction.

The structures of the upper arm and elbow are located in either the anterior or posterior compartments. The anterior compartment contains the biceps brachii, brachialis, and coracobrachialis muscles. The anterior compartment also contains the brachial artery, median nerve, musculocutaneous nerve, and ulnar nerve. The ulnar nerve passes behind the medial condyle as it enters the forearm. Because of its location and relatively tight tethering to the epicondyle, the ulnar nerve can be injured when the medial humeral condyle is fractured. The posterior compartment contains the triceps brachii muscle and the radial nerve.

The bony anatomy of the elbow in the pediatric population deserves special mention. Many of the challenges encountered in diagnosing elbow fractures in pediatric patients involve proper knowledge of the ossification centers of the elbow. In general, ossification of the growth centers begins at an earlier age in girls than in boys. Although variation exists, ossification of the growth centers of the elbow occurs at the following times:

Capitellum - 11 monthsMedial epicondyle - 4-6 yearsRadial head - 5-6 yearsOlecranon - 6-8 yearsTrochlea - 9-10 yearsLateral epicondyle - 10-12 yearsPreviousNextSport Specific Biomechanics

By definition, the elbow is a true hinge joint that is very stable to all motions except varus and valgus stress. The articulation of the trochlea of the humerus and the olecranon of the ulna defines the plane of flexion and extension at the elbow. The elbow also allows for pronation and supination at the radiocapitellar articulation. The radiocapitellar joint does provide some stability against valgus stress by acting as a buttress to prevent medial elbow opening. Stability is further enhanced by the strength of the ulnar collateral ligament, the principal stabilizing ligament of the elbow that resists valgus stress.

The radial-collateral ligament protects the joint from posterolateral rotary instability and is usually injured during elbow dislocation. The wrist extensor tendons that originate on the lateral intermuscular septum of the arm and the lateral epicondyle provide the elbow with stabilization against varus stress.

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Acromioclavicular Joint Injury

Background

Injuries in and around the shoulder are common in today's athletic society. Proper knowledge of the different problems and treatment options for shoulder disorders is necessary to get patients back to their preinjury state.

Acromioclavicular (AC) joint injuries are common and often seen after bicycle wrecks, contact sports, and car accidents. The acromioclavicular joint is located at the top of the shoulder where the acromion process and the clavicle meet to form a joint. Several ligaments surround this joint, and depending on the severity of the injury, a person may tear one or all of the ligaments. Torn ligaments lead to acromioclavicular joint sprains and separations.[1]

The distal clavicle and acromion process can also be fractured. Injury to the acromioclavicular joint may injure the cartilage within the joint and can later cause arthritis of the acromioclavicular joint.

This article discusses the anatomy of the acromioclavicular joint, the diagnosis of disorders of this joint, and the different treatment options.

For excellent patient education resources, see eMedicineHealth's First Aid & Injuries Center. Also, see eMedicineHealth's article on Shoulder Dislocation.

NextEpidemiologyFrequencyUnited States

Injuries to the acromioclavicular joint are the most common reason that athletes seek medical attention following an acute shoulder injury. Glenohumeral dislocations (see Shoulder Dislocation) are the second most common injuries seen. Men in their second through fourth decades of life have the greatest frequency of acromioclavicular joint injuries, which are most often incomplete tears of the ligaments.[1]

PreviousNextFunctional Anatomy

The normal width of the acromioclavicula joint is 1-3 mm in younger individuals; it narrows to 0.5 mm or less in individuals older than 60 years.

The acromioclavicular joint is made up of 2 bones (the clavicle and the acromion), 4 ligaments, and a meniscus inside the joint.

The acromioclavicular joint is surrounded by a thin joint capsule and 4 small ligaments. These ligaments mostly give joint stability to anterior and posterior translation, as well as provide horizontal stability to the joint.

Another set of ligaments also provides vertical stability to the acromioclavicular joint. These ligaments are called the coracoclavicular ligaments, which are found medial to the acromioclavicular joint and go from the coracoid process on the scapula to the clavicle.

Different injuries result in different tears of the 2 coracoclavicular ligaments (the conoid and the trapezoid). Torn acromioclavicular joint ligaments and/or torn coracoclavicular ligaments are seen in acromioclavicular joint sprains. The meniscus that lies in the joint may also be injured during sprains or fractures around the acromioclavicular joint. The acromioclavicular capsular ligaments provide most of the joint stability in the anteroposterior (AP) direction. The conoid and trapezoid ligaments aid in providing superior-inferior stability to the joint. Compression of the joint is restrained mainly by the trapezoid ligament.

PreviousNextSport-Specific Biomechanics

When a person falls onto their shoulder, the force pushes the tip of the shoulder down. The clavicle is usually kept in its anatomic position, whereas the shoulder is driven down, which injures the different ligaments or causes a fracture. When the ligaments are injured they are either sprained or, in more severe cases, torn.

Acromioclavicular joint sprains have been classified according to their severity. In a type I sprain, a mild force applied to these ligaments does not tear them. The injury simply results in a sprain, which hurts, but the shoulder does not show any gross evidence of an acromioclavicular joint dislocation. Type II sprains are seen when a heavier force is applied to the shoulder, disrupting the acromioclavicular ligaments but leaving the coracoclavicular ligaments intact. When these injuries occur, the lateral clavicle becomes a little more prominent.

In type III sprains, the force completely disrupts the acromioclavicular and coracoclavicular ligaments. This leads to complete separation of the clavicle and obvious changes in appearance. The lateral clavicle is very prominent. A few more types of acromioclavicular joint sprains have been classified, but types I–III are the most common (see below).

Classification of acromioclavicular joint injuries.

An acromioclavicular joint sprain is more common than a fracture after an injury. However, fractures of the distal clavicle and the acromion process may occur, so the healthcare provider must be aware of such injuries and ready to diagnose and treat them as well (see Clavicular Injuries).

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Shoulder Dislocation

Background

Shoulder dislocations may occur from a traumatic injury or from loose capsular ligaments. Different conditions may affect the stabilizing structures of the shoulder and, thus, negatively affect patients with shoulder dislocations.[1]

Note the images below.

Normal shoulder. Anterior dislocation.

This article focuses on glenohumeral joint dislocation. Although acromioclavicular (AC) joint separations are sometimes called shoulder dislocations by nonmedical persons, these are not true shoulder dislocations. Shoulder dislocations occur when the head of the humerus comes out of its socket, the glenoid.

For patient education resources, see the Breaks, Fractures, and Dislocations Center and Sports Injury Center, as well as Shoulder Dislocation and Shoulder Separation.

Related Medscape Reference topics include the following:

Acromioclavicular InjuryAcromioclavicular Joint SeparationsDislocation, ShoulderSuperior Labrum LesionsNextEpidemiologyFrequencyUnited States

The shoulder is the most commonly dislocated joint in the body.[1, 2, 3]

Although most shoulder dislocations occur anteriorly, they may also occur posteriorly, inferiorly, or anterior-superiorly.

Patients with a previous shoulder dislocation are more prone to redislocation.

Other factors that show a clear correlation to redislocation are the age of the patient and concomitant rotator cuff tears and fractures of the glenoid.

Younger patients (teenagers and those aged 20 years) have a much higher frequency of redislocation than patients in their 50s and 60s.[4] Many physicians believe that age is less of a predisposing risk factor for redislocation than activity level.

Patients who tear their rotator cuffs or fracture the glenoid during their shoulder dislocation have a higher incidence of redislocation than patients without these problems.

PreviousNextFunctional Anatomy

Shoulder stability is maintained by the glenohumeral ligaments, the joint capsule, the rotator cuff muscles, the negative intra-articular pressure, and the bony/cartilaginous anatomy.

The main stabilizers of the shoulder joint are the ligaments and the capsule complex. Multiple ligaments are present, but the inferior glenohumeral ligament is the most important and the one most commonly injured during an anterior shoulder dislocation. The injury may be a tear of the ligament/capsule off one of its bony attachments, and/or it may cause a stretch injury to these structures.

Tears in the rotator cuff muscles may also lead to shoulder instability. Four rotator cuff muscles are present in the shoulder. They are found superficial to the glenohumeral ligaments and the bones. Large tears may lead to shoulder instability, even with intact glenohumeral ligaments. Instability of the shoulder can also occur from injury to the nerves that control the shoulder muscles, specifically the axillary nerve.

PreviousNextSport-Specific Biomechanics

The shoulder is a very mobile joint; therefore, it is often placed in awkward positions during sports. Thus, the force from a fall or a blow may be sufficient to cause shoulder damage. If the force is strong enough, the athlete tears the ligaments/tendons, fractures the glenoid or humerus, and dislocates the shoulder.

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