Anatomy and Physiology, Support and Movement, Joints (2023)

At the end of this section, you can:

• Describe the bones that articulate with each other to form selected synovial joints
• Discuss the movements available at each joint.
• Describe the structures that support and prevent excessive movement in each joint.

Each synovial joint in the body is specialized to perform specific movements. Allowable movements are determined by the structural classification of each joint. For example, a multi-axis ball joint has much higher mobility than a single axis ball joint. However, the ligaments and muscles that support a joint can limit the total range of motion available. Therefore, the ball and socket joint of the shoulder has little ligament support, giving the shoulder a very wide range of motion. Rather, movements in the hip joint are limited by strong ligaments that limit your range of motion but provide stability when standing and carrying.

This section examines the anatomy of selected synovial joints in the body. The anatomical names of most joints are derived from the names of the bones that articulate at that joint, although some joints, such as the elbow, hip, and knee, are exceptions to this general naming scheme.

spinal joints

In addition to being held together by intervertebral discs, adjacent vertebrae also articulate with each other at synovial joints formed between the superior and inferior articular processes, called the zygapophyseal (facet) joints.Figure 9.3🇧🇷 These are flat joints that allow limited movement between the vertebrae. The orientation of the articular processes in these joints varies in different regions of the spine and serves to determine the types of movement available in each region of the spine. The cervical and lumbar regions have the greatest ranges of motion.

In the neck, the articular processes of the cervical vertebrae are flattened and often point upwards or downwards. This alignment provides the cervical spine with wide ranges of motion for flexion, extension, lateral flexion, and rotation. In the thoracic region, the overlapping and downward-projecting spinous processes, together with the attached rib cage, severely limit flexion, extension, and lateral flexion. However, the flattened and vertically positioned thoracic condyles allow the greatest range of rotation within the vertebral column. The lumbar region allows considerable extension, flexion, and lateral flexion, but the alignment of the condyles greatly prevents rotation.

The joints formed between the skull, the atlas (C1 vertebra) and the axis (C2 vertebra) are different from the joints in other vertebral areas and play an important role in the movement of the head. The atlanto-occipital joint is formed by the joints between the superior articular processes of the atlas and the occipital condyles at the base of the skull. This joint has a pronounced U-shaped curvature oriented along the anteroposterior axis. This allows the skull to rock back and forth, causing flexion and extension of the head. This moves the head up and down as if nodding.

The atlantoaxial joint between the atlas and the axis consists of three joints. The paired superior articular processes of the axis articulate with the inferior articular processes of the atlas. These articulation surfaces are relatively flat and oriented horizontally. The third joint is the pivot joint formed between the dens, which project upward from the body of the axis, and the internal aspect of the anterior arch of the atlas (Figure 9.14🇧🇷 A strong band runs behind the burrows to hold it in place against the front arc. These joints allow the atlas to pivot on its axis and move its head to the right or left, as if shaking its head "no."

Figure 9.14 Atlantoaxial joint The atlantoaxial joint is a joint articulated between the dental portion of the axis (C2 vertebra) and the anterior arch of the atlas (C1 vertebra), with the tooth supported by a ligament.

Ear-jaw joint

The temporomandibular joint (TMJ) is the joint that allows opening (lowering the lower jaw) and closing (lowering the lower jaw) of the mouth, as well as side-to-side and protraction/retraction movements of the jaw. This joint involves the articulation between the mandibular fossa and the articular tubercle of the temporal bone with the condyle (head) of the mandible. Between these bony structures, which fill the space between the skull and the jaw, is a flexible articular disc (Figure 9.15🇧🇷 This disc serves to smooth the movements between the temporal bone and the mandibular condyle.

The movement of the temporomandibular joint during opening and closing of the mouth includes sliding and hinge movements of the mandible. With the mouth closed, the mandibular condyle and articular disc lie in the mandibular fossa of the temporal bone. As the mouth opens, the mandible rotates downward and is simultaneously pulled forward, causing the condyle and articular disc to slide forward from the mandibular fossa to the downwardly projecting articular tubercle. The net result is forward and downward movement of the condyle and mandibular depression. The temporomandibular joint is supported by an external ligament that anchors the lower jaw to the skull. This ligament spans the space between the skull base and the lingula on the medial side of the mandibular ramus.

Temporomandibular joint dislocation can occur when the mouth is opened wide (eg, during a large bite) or after a blow to the jaw, causing the mandibular condyle to move on (anteriorly) the articular tubercle . In that case, the person would not be able to close his mouth. Temporomandibular joint disease is a painful condition that can result from arthritis, wear and tear of the articular cartilage that covers the bony surfaces of the joint, muscle fatigue from overuse or teeth grinding, damage to the disc within the joint, or injury to the joint. jaw . Temporomandibular joint disorders can also cause headaches, difficulty chewing, or even the inability to move the jaw (locking). Pharmacological pain agents or other therapies, including bite protection, are used as treatments.

Figure 9.15 TMJ The temporomandibular joint is the connection between the temporal bone of the skull and the condyle of the mandible, with a disc articulation between these bones. During mandibular depression (opening of the mouth), the mandibular condyle moves forward and downward from the mandibular fossa to the articular tubercle.

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Watch thisVideofor more information on the ATM. Opening the mouth requires a combination of two movements at the temporomandibular joint, an anterior sliding movement of the articular disc and mandible, and a downward rocking of the mandible. What is the initial movement of the lower jaw during opening, and how much mouth opening does this create?

shoulder joint

The shoulder joint is called the glenohumeral joint. This is a ball-and-socket joint formed by the articulation between the head of the humerus and the glenoid cavity of the scapula (Figure 9.16🇧🇷 This joint has the greatest range of motion of any joint in the body. However, this freedom of movement is due to a lack of structural support and therefore the improved mobility is offset by a loss of stability.

Figure 9.16 Glenohumeral joint The glenohumeral (shoulder) joint is a ball-and-socket joint that provides the greatest range of motion. It has a loose joint capsule and is supported by ligaments and the muscles of the rotator cuff.

The large range of motion of the shoulder joint is made possible by the articulation of the large, rounded humeral head with the small, flat shoulder socket, which is only one-third the size of the humeral head. The socket formed by the glenoid fossa is slightly deepened by a small labrum of fibrocartilage called the glenoid labrum, which runs around the outer edge of the fossa. The joint capsule surrounding the glenohumeral joint is relatively thin and loose to allow large movements of the upper extremity. Some structural support for the joint is provided by thickenings of the joint capsule wall that form weak intrinsic ligaments. These include the coracohumeral ligament, which runs from the coracoid process of the scapula to the anterior humerus, and three ligaments, each called the aglenohumeral ligament, located anterior to the joint capsule. These ligaments help strengthen the walls of the superior and anterior capsule.

However, the main support for the shoulder joint is provided by the muscles that cross the joint, specifically the four rotator cuff muscles. These muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) arise from the scapula and attach to the greater or lesser tubercles of the humerus. As these muscles cross the shoulder joint, their tendons encircle the humeral head and fuse with the anterior, superior, and posterior walls of the joint capsule. The thickening of the capsule resulting from the fusion of these four muscle tendons is called the rotator cuff. Two bursae, the subacromial bursa and the subscapularis bursa, help prevent friction between the tendons of the rotator cuff muscles and the scapula as these tendons cross the glenohumeral joint. In addition to their individual actions of moving the upper extremity, the rotator cuff muscles also serve to hold the humeral head in position within the glenoid fossa. Constantly adjusting the force of their contraction to resist the forces applied to the shoulder, these muscles act as "dynamic ligaments" and thus provide the main structural support for the glenohumeral joint.

Shoulder joint injuries are common. Repetitive use of the upper extremity, particularly with abduction, such as throwing, swimming, or racquet sports, can lead to acute or chronic inflammation of muscle or tendon bursae, glenoid labral tear, or rotator cuff degeneration or tear. Because the humeral head is strongly supported by muscles and ligaments around its anterior, superior, and posterior sides, most humeral dislocations occur in an inferior direction. This can occur when force is applied to the humerus when the upper limb is fully abducted, e.g. B. when you jump to catch a baseball and land on your hand or elbow. Inflammatory reactions to any shoulder injury can cause scar tissue to form between the joint capsule and surrounding structures, reducing mobility of the shoulder, a condition known as adhesive capsulitis ("frozen shoulder").

INTERACTIVE LINK

Watch thisVideofor a shoulder joint anatomy tutorial. What movements are possible at the shoulder joint?

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Watch thisVideoto learn about the anatomy of the shoulder joint, including the bones, joints, muscles, nerves, and blood vessels. What is the cross-sectional shape of the glenoid labrum and what is the significance of this shape?

elbow joint

The elbow joint is a uniaxial hinge joint formed by the humeroulnar joint, the joint between the trochlea of ​​the humerus and the trochlear notch of the ulna. The humeroradial joint and the proximal radioulnar joint are also associated with the elbow. All three joints are enclosed in a single joint capsule (Figure 9.17).

The elbow joint capsule is thin on its anterior and posterior sides, but thickened at its outer edges by strong intrinsic ligaments. These ligaments prevent lateral movement and overstretching. On the medial side is the triangular-ulnar collateral ligament. It originates from the medial epicondyle of the humerus and inserts on the medial surface of the proximal ulna. The strongest part of this band is the front part, which resists hyperextension of the elbow. The ulnar collateral ligament can be injured by frequent and vigorous stretching of the forearm, as seen in baseball pitchers. Reconstructive surgical repair of this ligament is known as Tommy John surgery, after the former major league pitcher who was the first person to receive this treatment.

The lateral aspect of the elbow is supported by the radial collateral ligament. This arises from the lateral epicondyle of the humerus and then fuses with the lateral side of the pulley. The annular ligaments surround the radial head. This ligament supports the radial head when it articulates with the radial notch of the ulna at the proximal radioulnar joint. This is a hinged joint that allows rotation of the radius during supination and pronation of the forearm.

Figure 9.17 Elbow joint (a) The elbow is a joint that only allows flexion and extension of the forearm. (b) It is supported by the radial and ulnar collateral ligaments. (c) The pulley supports the head of the radius at the proximal radioulnar joint, the joint that allows rotation of the radius.

INTERACTIVE LINK

Watch thisanimationto learn more about the anatomy of the elbow joint. What structures give the elbow its primary stability?

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Watch thisVideoto learn more about the anatomy of the elbow joint, including the bones, joints, muscles, nerves, and blood vessels. What are the functions of articular cartilage?

the hip joint

The hip joint is a multiaxial ball-and-socket joint between the femoral head and the acetabulum (Figure 9.18🇧🇷 The hip supports the weight of the body and therefore requires strength and stability when standing and walking. For these reasons, its range of motion is more limited than that of the shoulder joint.

The acetabulum is the socket part of the hip joint. This space is deep and has a large articulation area for the femoral head, providing stability and strength to the joint. The acetabulum is further deepened by the acetabular labrum, a fibrocartilaginous labrum attached to the outer edge of the acetabulum. The surrounding joint capsule is strong, with several thickened areas that form intrinsic ligaments. These ligaments originate from the hip bone at the edges of the acetabulum and attach to the femur at the base of the neck. The ligaments are the iliofemoral ligament, the pubofemoral ligament, and the ischiofemoral ligament, all of which spiral around the head and neck of the femur. The ligaments are tightened by straightening the hip, pulling the femoral head forcefully into the socket into an upright, upright position. Very little additional extension of the thigh is allowed beyond this upright position. These ligaments stabilize the hip joint and allow it to stand upright with minimal muscle contraction. Within the joint capsule, the ligament of the femoral head (ligamentum teres) extends between the hip socket and the femoral head. This intracapsular ligament is usually loose and does not provide significant joint support, but does provide a pathway for a major artery that supplies the femoral head.

The hip is prone to osteoarthritis and was therefore the first joint for which a replacement prosthesis was developed. A common injury in older people, particularly those with weakened bones due to osteoporosis, is a "hip fracture," which is actually a fracture of the femoral neck. This can result from a fall or cause the fall. This can happen when one lower extremity takes a step and the entire weight of the body shifts to the other extremity, fracturing the femoral neck and causing a fall. Any associated disruption in the blood supply to the femoral neck or head can lead to necrosis of these areas, resulting in bone and cartilage death. Femur fractures often require surgical treatment, after which the patient may require mobility assistance for an extended period, either from family members or in a long-term care facility. Consequently, the health costs associated with "broken hips" are significant. Hip fractures are also associated with increased morbidity (disease) and mortality (death). Hip fracture surgery followed by prolonged bed rest can lead to life-threatening complications, including pneumonia, infection of pressure sores (bedsores), and thrombophlebitis (deep vein thrombosis; blood clots), which can lead to pulmonary embolism ( blood clots in the lungs).

Figure 9.18 Hip joint (a) The ball and socket joint of the hip is a multi-axial joint that provides stability and a wide range of motion. (b-c) When standing, the supporting ligaments are taut and pull the femoral head toward the acetabulum.

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Watch thisVideofor a tutorial on the anatomy of the hip joint. What consequences can a femoral neck fracture have within the hip joint capsule?

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Watch thisVideoto learn about the anatomy of the hip joint, including the bones, joints, muscles, nerves, and blood vessels. Where is the articular cartilage thickest in the hip joint?

knee joint

The knee joint is the largest joint in the body (Figure 9.19🇧🇷 It actually consists of three joints. The patellofemoral joint is located between the patella and the distal femur. The medial tibiofemoral joint and the lateral tibiofemoral joint lie between the medial and lateral condyles of the femur and the medial and lateral condyles of the tibia. All of these joints are contained within a single joint capsule. The knee acts as a hinge joint, allowing the leg to bend and extend. This action is produced by rolling and sliding movements of the femur on the tibia. Also, some leg rotation is possible when the knee is bent, but not when it is straight. The knee is well designed to bear weight in its extended position, but it is susceptible to injuries associated with hyperextension, twisting, or impingement on the medial or lateral side of the joint, especially during weight bearing.

In the patellofemoral joint, the patella slides vertically in a groove on the distal femur. The patella is a sesamoid bone embedded in the tendon of the quadriceps femoris, the large muscle in the front of the thigh. The patella serves to protect the quadriceps tendon from rubbing against the distal femur. Continuing from the patella to the anterior tibia, just below the knee, is the patellar ligament. Working through the patella and patellar ligament, the quadriceps femoris is a powerful muscle that extends the leg at the knee. It also serves as a "dynamic band" for all-important support and stabilization of the knee joint.

The medial and lateral tibiofemoral joints are the joints between the rounded condyles of the femur and the relatively flat condyles of the tibia. During flexion and extension movements, the condyles of the femur roll and slide on the surfaces of the tibia. The rocking motion creates flexion or extension, while the sliding motion serves to keep the femoral condyles centered over the tibial condyles, ensuring maximum bone support and weight bearing for the femur in all knee positions. When the knee is fully extended, the femur rotates slightly medially with respect to the tibia. The rotation occurs because the lateral condyle of the femur is slightly smaller than the medial condyle. Therefore, the lateral condyle completes its rocking motion first, followed by the medial condyle. The resulting small medial rotation of the femur serves to "lock" the knee in its most stable, fully extended position. Knee flexion is initiated with a slight lateral rotation of the femur on the tibia, which "unlocks" the knee. This lateral rotation movement is generated by the popliteus muscle of the hind leg.

Between the articular surfaces of the femur and tibia are two articular discs, the medial meniscus and the lateral meniscus (see Fig.Figure 9.19b🇧🇷 Each is a C-shaped fibrocartilage structure, thin along its inner edge and thick along its outer edge. They are attached to the tibial condyles but not to the femur. While both menisci are free to move during knee movement, the medial meniscus shows less movement because it is anchored at its outer edge to the joint capsule and tibial collateral ligament. The menisci provide cushioning between the bones and help fill the space between the rounded femoral condyles and the flattened tibial condyles. Some areas of each meniscus lack arterial blood supply and therefore these areas heal poorly when damaged.

The knee joint has several ligaments that support it, especially in the extended position (cf.Figure 9.19C🇧🇷 Outside the joint capsule there are two external ligaments on the sides of the knee. The fibular collateral ligament (lateral collateral ligament) is on the lateral side and extends from the lateral epicondyle of the femur to the head of the fibula. The tibial collateral ligament (medial collateral ligament) of the medial knee extends from the medial epicondyle of the femur to the medial tibia. Crossing the knee, the tibial collateral ligament is firmly attached to the joint capsule and medial meniscus on its deep side, an important factor when considering knee injuries. In the fully extended knee position, both collateral ligaments are taut (tight) and therefore serve to stabilize and support the extended knee and prevent lateral or rotational movement between the femur and tibia.

The posterior joint capsule of the knee is thickened by intrinsic ligaments that help resist hyperextension of the knee. There are two intracapsular ligaments in the knee, the anterior cruciate ligament and the posterior cruciate ligament. These ligaments are anchored below the tibia at the intercondylar crest, the rough area between the tibial condyles. The cruciate ligaments are named according to their attachment to this anterior or posterior tibial region. Each band runs diagonally upward to join the interior of a femoral condyle. The cruciate ligaments get their name from the X-shape they form when crossed (cruciate means "crossed"). The posterior cruciate ligament is the strongest ligament. It serves to support the knee during bending and loading, such as when descending a slope. In this position, the posterior cruciate ligament prevents the femur from sliding forward from the top of the tibia. The ACL tightens when the knee is extended, thus resisting hyperextension.

Figure 9.19 Knee joint (a) The knee joint is the largest joint in the body. (b)-(c) It is supported by the tibial and peroneal collateral ligaments, which lie on the sides of the knee outside the joint capsule, and by the anterior and posterior cruciate ligaments, which lie within the capsule. The medial and lateral menisci provide cushioning and support between the femoral and tibial condyles.

INTERACTIVE LINK

Watch thisVideoLearn about knee flexion and extension as the femur rolls and glides over the tibia to maintain stable interosseous contact in all knee positions. The patella slides along a groove in front of the distal femur. The lateral ligaments on the sides of the knee contract in the fully extended position to stabilize the knee. The posterior cruciate ligament supports the knee when it is flexed, and the anterior cruciate ligament contracts when the knee is fully extended to resist hyperextension. What ligaments support the knee joint?

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Watch thisVideoto learn more about the anatomy of the knee joint, including the bones, joints, muscles, nerves, and blood vessels. Which ligament in the knee prevents the tibia from sliding too far forward in relation to the femur and which ligament prevents the tibia from sliding too far back?

DISORDERS OF...

joints

Knee injuries are common. Since this joint is supported primarily by muscles and ligaments, injuries to these structures cause knee pain or instability. A posterior cruciate ligament injury occurs when the knee is bent and the tibia moves backward, such as when B. falls and lands on the tibial tuberosity or when his shin hits the dashboard without wearing a seat belt in a car accident. . Injuries are more common when forces are applied to the straight knee, especially when the foot is planted and immobile. Anterior cruciate ligament injuries can be caused by a hard blow to the front knee that causes hyperextension, or when a runner makes a rapid change of direction that causes twisting and hyperextension of the knee.

A worse combination of injuries can occur with a blow to the lateral side of the straight knee (Figure 9.20🇧🇷 A moderate blow to the lateral knee will open the medial aspect of the joint, causing stretching or injury to the tibial collateral ligament. Since the medial meniscus is attached to the tibial collateral ligament, a stronger blow can tear the ligament and also damage the medial meniscus. This is one of the reasons why the medial meniscus is injured 20 times more than the lateral meniscus. A hard blow to the side of the knee creates a "terrible triad" injury, in which there is sequential injury to the tibial collateral ligament, medial meniscus, and anterior cruciate ligament.

Arthroscopic surgery has greatly improved the surgical treatment of knee injuries and has shortened subsequent recovery times. This procedure involves making a small incision and inserting an arthroscope, a thin instrument that allows you to see inside the joint, into the joint. Small surgical instruments are also inserted through additional incisions. With these tools, a surgeon can remove or repair a torn meniscus or reconstruct a torn cruciate ligament. The current anterior cruciate ligament replacement procedure involves the use of part of the patellar ligament. Holes are drilled at the cruciate ligament attachment points on the tibia and femur, and the patellar ligament graft, with small areas of bone attached still intact at each end, is inserted into these holes. The bone-to-bone junctions at each end of the graft heal quickly and strongly, allowing for speedy recovery.

Figure 9.20 Knee injury A severe blow to the lateral side of the extended knee causes three consecutive injuries: tibial collateral ligament tear, medial meniscus injury, and anterior cruciate ligament tear.

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Watch thisVideofor more information on different knee injuries and knee diagnostic tests. What are the most common causes of anterior cruciate ligament injury?

ankles and ankles

The ankle is formed by the tetalocrural joint (Figure 9.21🇧🇷 Consists of the joints between the talar bone of the foot and the distal ends of the tibia and fibula of the lower leg (crural = "leg"). The upper surface of the talus bone is square and has three areas of articulation. The tip of the talus articulates with the lower tibia. This is the part of the ankle that carries the weight of the body between the lower part of the leg and the foot. The sides of the talus are held firmly in place by articulations with the medial malleolus of the tibia and the medial malleolus of the fibula, preventing any lateral movement of the talus. Thus, the ankle is a uniaxial hinge joint that allows only dorsiflexion and plantarflexion of the foot.

Additional joints between the tarsal bones of the hind foot allow inversion and eversion movements of the foot. The most important for these movements is the subtalar joint, located between the talus and the calcaneus. The joints between the talus and scaphoid bone and the calcaneus and cuboid also make important contributions to these movements. All the joints between the tarsal bones are flat. Together, the small movements that occur at these joints contribute to the creation of inversion and eversion movements of the foot.

Like the elbow and knee joints, the talocrural ankle joint is supported by several strong ligaments located on the sides of the joint. These ligaments extend from the medial malleolus of the tibia or the medial malleolus of the fibula and anchor to the talus and calcaneus bones. Because they are located on the lateral side of the ankle, they allow dorsiflexion and plantarflexion of the foot. They also prevent abnormal lateral and rotational movements of the talus and calcaneus during eversion and inversion of the foot. On the medial side is the broad deltoid ligament. The Delta Band supports the ankle and also resists excessive eversion of the foot. The lateral side of the ankle has several smaller ligaments. These include the anterior and posterior talofibular ligaments, which run between the talus bone and the lateral malleolus of the fibula, and the calcaneal-fibular ligament, which runs between the heel bone and fibula. These ligaments support the ankle and also resist excessive inversion of the foot.

Figure 9.21 Ankle The ankle is a uniaxial hinge joint that allows only dorsiflexion or plantarflexion of the foot. Movements at the subtalar joint between the talus and calcaneus combined with movements at other intertarsal joints allow eversion/inversion movements of the foot. The ligaments connecting the medial or lateral malleolus to the talus and calcaneus bones serve to support the talocrural joint and resist excessive eversion or inversion of the foot.

INTERACTIVE LINK

Watch thisVideofor a tutorial on ankle anatomy. What are the three ligaments on the lateral side of the ankle?

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Watch thisVideoto learn more about the anatomy of the ankle, including the bones, joints, muscles, nerves, and blood vessels. What type of joiner joint does the hock resemble?

DISORDERS OF...

joints

The ankle is the most injured joint in the body, with the most common injury being an inversion ankle sprain. A sprain is the stretching or tearing of the supporting ligaments. Excessive inversion causes the talus bone to tilt to one side, damaging the ligaments on the side of the ankle. The anterior talofibular ligament is the most frequently injured, followed by the calcaneal-fibular ligament. In severe inversion injuries, forced lateral movement of the talus not only tears the lateral ankle ligaments but also fractures the distal fibula.

Less common are eversion ankle sprains, in which the deltoid ligament on the medial side of the ankle is stretched. Forced eversion of the foot, such as when it lands badly after a jump or when a football player has one foot on the ground and is struck on the side of the ankle, can lead to a Pott's fracture and dislocation of the ankle. With this injury, the very strong delta ligament does not tear, but instead tears the medial malleolus of the tibia. This exposes the talus, which moves laterally and fractures the distal fibula. In extreme cases, the posterior edge of the tibia can also be cut.

Above the ankle, the distal ends of the tibia and fibula are connected by a strong syndesmosis formed by the interosseous membrane and ligaments at the distal tibiofibular joint. These connections prevent separation between the distal ends of the tibia and fibula and hold the talus in place between the medial and lateral malleolus. Injuries that result in lateral twisting of the leg on the supported foot can result in stretching or tearing of the tibiofibular ligaments, which can lead to a syndesmotic ankle sprain or "high ankle sprain".

Most ankle sprains can be treated with the RICE technique: rest, ice, compression, and elevation. Temporary restriction of joint mobility with a splint or cast may be necessary. More serious injuries involving torn ligaments or broken bones may require surgery.

INTERACTIVE LINK

Watch thisVideofor more information on ankle ligaments, ankle sprains and their treatment. During an inversion ankle sprain injury, all three ligaments that resist excessive inversion of the foot can be injured. In what order are these three ligaments injured?