Major Synovial Joints of the Body

Anatomy of Selected Synovial Joints

By the end of this section, you will be able to:

• Describe the bones that articulate together to form selected synovial joints
• Discuss the movements available at each joint
• Describe the structures that support and prevent excess movements at each joint

 

Each synovial joint of the body is specialized to perform certain movements.

• The movements that are allowed are determined by the structural classification for each joint.
  • For example, a multiaxial ball-and-socket joint has much more mobility than a uniaxial hinge joint.
• However, the ligaments and muscles that support a joint may place restrictions on the total range of motion available.
  • Thus, the ball-and-socket joint of the shoulder has little in the way of ligament support, which gives the shoulder a very large range of motion.
  • In contrast, movements at the hip joint are restricted by strong ligaments, which reduce its range of motion but confer stability during standing and weight bearing.

 

This section will examine the anatomy of selected synovial joints of the body.

• Anatomical names for 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 joints are exceptions to this general naming scheme.

 

 

Articulations of the Vertebral Column

In addition to being held together by the intervertebral discs, adjacent vertebrae also articulate with each other at synovial joints formed between the superior and inferior articular processes called zygapophysial joints (facet joints).

• These are plane joints that provide for only limited motions between the vertebrae.
• The orientation of the articular processes at these joints varies in different regions of the vertebral column and serves to determine the types of motions available in each vertebral region.
  • The cervical and lumbar regions have the greatest ranges of motions.
  • In the neck, the articular processes of cervical vertebrae are flattened and generally face upward or downward.
    • This orientation provides the cervical vertebral column with extensive ranges of motion for flexion, extension, lateral flexion, and rotation.
  • In the thoracic region, the downward projecting and overlapping spinous processes, along with the attached thoracic cage, greatly limit flexion, extension, and lateral flexion.
    • However, the flattened and vertically positioned thoracic articular processes allow for the greatest range of rotation within the vertebral column.
  • The lumbar region allows for considerable extension, flexion, and lateral flexion, but the orientation of the articular processes largely prohibits rotation.
  • The articulations formed between the skull, the atlas (C1 vertebra), and the axis (C2 vertebra) differ from the articulations in other vertebral areas and play important roles in movement of the head.

 

The atlanto-occipital joint is formed by the articulations between the superior articular processes of the atlas and the occipital condyles on the base of the skull.

• This articulation has a pronounced U-shaped curvature, oriented along the anterior-posterior axis.
  • This allows the skull to rock forward and backward, producing flexion and extension of the head.
  • This moves the head up and down, as when shaking your head “yes.”

 

The atlantoaxial joint, between the atlas and axis, consists of three articulations.

• The paired superior articular processes of the axis articulate with the inferior articular processes of the atlas.
  • These articulating surfaces are relatively flat and oriented horizontally.
• The third articulation is the pivot joint formed between the dens, which projects upward from the body of the axis, and the inner aspect of the anterior arch of the atlas.
  • A strong ligament passes posterior to the dens to hold it in position against the anterior arch.
• These articulations allow the atlas to rotate on top of the axis, moving the head toward the right or left, as when shaking your head “no.”

 

The atlantoaxial joint is a pivot type of joint between the dens portion of the axis (C2 vertebra) and the anterior arch of the atlas (C1 vertebra), with the dens held in place by a ligament.

 

 

Temporomandibular Joint

The temporomandibular joint (TMJ) is the joint that allows for opening (mandibular depression) and closing (mandibular elevation) of the mouth, as well as side-to-side and protraction/retraction motions of the lower jaw.

• This joint involves the articulation between the mandibular fossa and articular tubercle of the temporal bone, with the condyle (head) of the mandible.
• Located between these bony structures, filling the gap between the skull and mandible, is a flexible articular disc.
  • This disc serves to smooth the movements between the temporal bone and mandibular condyle.

 

Movement at the TMJ during opening and closing of the mouth involves both gliding and hinge motions of the mandible.

• With the mouth closed, the mandibular condyle and articular disc are located within the mandibular fossa of the temporal bone.
• During opening of the mouth, the mandible hinges downward and at the same time is pulled anteriorly, causing both the condyle and the articular disc to glide forward from the mandibular fossa onto the downward projecting articular tubercle.
• The net result is a forward and downward motion of the condyle and mandibular depression.
• The temporomandibular joint is supported by an extrinsic ligament that anchors the mandible to the skull.
  • This ligament spans the distance between the base of the skull and the lingula on the medial side of the mandibular ramus.

 

Dislocation of the TMJ may occur when opening the mouth too wide (such as when taking a large bite) or following a blow to the jaw, resulting in the mandibular condyle moving beyond (anterior to) the articular tubercle.

• In this case, the individual would not be able to close his or her mouth.
• Temporomandibular joint disorder is a painful condition that may arise due to arthritis, wearing of the articular cartilage covering the bony surfaces of the joint, muscle fatigue from overuse or grinding of the teeth, damage to the articular disc within the joint, or jaw injury.
• Temporomandibular joint disorders can also cause headache, difficulty chewing, or even the inability to move the jaw (lock jaw).
• Pharmacologic agents for pain or other therapies, including bite guards, are used as treatments.

 

Temporomandibular Joint The temporomandibular joint is the articulation between the temporal bone of the skull and the condyle of the mandible, with an articular disc located between these bones.  During depression of

the mandible (opening of the mouth), the mandibular condyle moves both forward and hinges downward as it travels from the mandibular fossa onto the articular tubercle.

 

Watch this video: 

TMJ joint

 

Elbow Joint

The elbow joint is a uniaxial hinge joint formed by the humeroulnar joint, the articulation between the trochlea of the humerus and the trochlear notch of the ulna.

• Also associated with the elbow are the humeroradial joint and the proximal radioulnar joint.
• All three of these joints are enclosed within a single articular capsule.

 

The articular capsule of the elbow is thin on its anterior and posterior aspects, but is thickened along its outside margins by strong intrinsic ligaments.

• These ligaments prevent side-to-side movements and hyperextension.
• On the medial side is the triangular ulnar collateral ligament.
  • This arises from the medial epicondyle of the humerus and attaches to the medial side of the proximal ulna.
    • The strongest part of this ligament is the anterior portion, which resists hyperextension of the elbow.
  • The ulnar collateral ligament may be injured by frequent, forceful extensions of the forearm, as is seen in baseball pitchers.
    • Reconstructive surgical repair of this ligament is referred to as Tommy John surgery, named for the former major league pitcher who was the first person to have this treatment.
  • The lateral side of the elbow is supported by the radial collateral ligament.
    • This arises from the lateral epicondyle of the humerus and then blends into the lateral side of the annular ligament.
  • The annular ligament encircles the head of the radius.
    • This ligament supports the head of the radius as it articulates with the radial notch of the ulna at the proximal radioulnar joint.
    • This is a pivot joint that allows for rotation of the radius during supination and pronation of the forearm.

 

Elbow Joint (a) The elbow is a hinge joint that allows only for flexion and extension of the forearm. (b) It is supported by the ulnar and radial collateral ligaments. (c-d) The annular ligament supports the head of the radius at the proximal radioulnar joint, the pivot joint that allows for rotation of the radius.

 

Hip Joint

The hip joint is a multiaxial ball-and-socket joint between the head of the femur and the acetabulum of the hip bone.

• The hip carries the weight of the body and thus requires strength and stability during standing and walking.
  • For these reasons, its range of motion is more limited than at the shoulder joint.

 

The acetabulum is the socket portion of the hip joint.

• This space is deep and has a large articulation area for the femoral head, thus giving stability and weight bearing ability to the joint.
• The acetabulum is further deepened by the acetabular labrum, a fibrocartilage lip attached to the outer margin of the acetabulum.
• The surrounding articular capsule is strong, with several thickened areas forming intrinsic ligaments.
  • These ligaments arise from the hip bone, at the margins of the acetabulum, and attach to the femur at the base of the neck.
  • The ligaments are the iliofemoral ligament, pubofemoral ligament, and ischiofemoral ligament, all of which spiral around the head and neck of the femur.
  • The ligaments are tightened by extension at the hip, thus pulling the head of the femur tightly into the acetabulum when in the upright, standing position.
    • Very little additional extension of the thigh is permitted beyond this vertical position.
    • These ligaments thus stabilize the hip joint and allow you to maintain an upright standing position with only minimal muscle contraction.
  • Inside of the articular capsule, the ligament of the head of the femur (ligamentum teres) spans between the acetabulum and femoral head.
    • This intracapsular ligament is normally slack and does not provide any significant joint support, but it does provide a pathway for an important artery that supplies the head of the femur.

 

The hip is prone to osteoarthritis, and thus was the first joint for which a replacement prosthesis was developed.

• A common injury in elderly individuals, particularly those with weakened bones due to osteoporosis, is a “broken hip,” which is actually a fracture of the femoral neck.
  • This may result from a fall, or it may cause the fall. This can happen as one lower limb is taking a step and all of the body weight is placed on the other limb, causing the femoral neck to break and producing a fall.

  Any accompanying disruption of the blood supply to the femoral neck or head can lead to necrosis of these areas, resulting in bone and cartilage death.

• Femoral fractures usually require surgical treatment, after which the patient will need mobility assistance for a prolonged period, either from family members or in a long-term care facility.
  • Consequentially, the associated health care costs of “broken hips” are substantial.
  • In addition, hip fractures are associated with increased rates of morbidity (incidences of disease) and mortality (death).
  • Surgery for a hip fracture followed by prolonged bed rest may lead to life-threatening complications, including pneumonia, infection of pressure ulcers (bedsores), and thrombophlebitis (deep vein thrombosis; blood clot formation) that can result in a pulmonary embolism (blood clot within the lung).

 

 

Hip Joint (a) The ball-and-socket joint of the hip is a multiaxial joint that provides both stability and a

wide range of motion. (b–c) When standing, the supporting ligaments are tight, pulling the head of the femur into the acetabulum.

 

Watch these videos: 

Hip Anantomy

Total Hip replacement procedure

Total Hip Replacement Surgery

 

 

Ankle and Foot Joints

The ankle is formed by the talocrural joint.

• It consists of the articulations between the talus bone of the foot and the distal ends of the tibia and fibula of the leg (crural = “leg”).
• The superior aspect of the talus bone is square-shaped and has three areas of articulation.
  • The top of the talus articulates with the inferior tibia.
  • This is the portion of the ankle joint that carries the body weight between the leg and foot.
  • The sides of the talus are firmly held in position by the articulations with the medial malleolus of the tibia and the lateral malleolus of the fibula, which prevent any side-to-side motion of the talus.
• The ankle is thus a uniaxial hinge joint that allows only for dorsiflexion and plantar flexion of the foot.

 

Additional joints between the tarsal bones of the posterior foot allow for the movements of foot inversion and eversion.

• Most important for these movements is the subtalar joint, located between the talus and calcaneus bones.
  • The joints between the talus and navicular bones and the calcaneus and cuboid bones are also important contributors to these movements.
  • All of the joints between tarsal bones are plane joints.
  • Together, the small motions that take place at these joints all contribute to the production of inversion and eversion foot motions.
• Like the hinge joints of the elbow and knee, the talocrural joint of the ankle is supported by several strong ligaments located on the sides of the joint.
  • These ligaments extend from the medial malleolus of the tibia or lateral malleolus of the fibula and anchor to the talus and calcaneus bones.
  • Since they are located on the sides of the ankle joint, they allow for dorsiflexion and plantar flexion of the foot.
  • They also prevent abnormal side-to-side and twisting movements of the talus and calcaneus bones during eversion and inversion of the foot.
• On the medial side is the broad deltoid ligament.
  • The deltoid ligament supports the ankle joint and also resists excessive eversion of the foot.
• The lateral side of the ankle has several smaller ligaments.
  • These include the anterior talofibular ligament and the posterior talofibular ligament, both of which span between the talus bone and the lateral malleolus of the fibula, and the calcaneofibular ligament, located between the calcaneus bone and fibula.
  • These ligaments support the ankle and also resist excess inversion of the foot.

 

Ankle Joint The talocrural (ankle) joint is a uniaxial hinge joint that only allows for dorsiflexion or plantar flexion of the foot. Movements at the subtalar joint, between the talus and calcaneus bones, combined with motions at other intertarsal joints, enables eversion/inversion movements of the foot. Ligaments that unite the medial or lateral malleolus with the talus and calcaneus bones serve to support the talocrural joint and to resist excess eversion or inversion of the foot.

 

The ankle is the most frequently 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.
• Excess inversion causes the talus bone to tilt laterally, thus damaging the ligaments on the lateral side of the ankle.
  • The anterior talofibular ligament is most commonly injured, followed by the calcaneofibular ligament.
  • In severe inversion injuries, the forceful lateral movement of the talus not only ruptures the lateral ankle ligaments, but also fractures the distal fibula.
• Less common are eversion sprains of the ankle, which involve stretching of the deltoid ligament on the medial side of the ankle.
  • Forcible eversion of the foot, for example, with an awkward landing from a jump or when a football player has a foot planted and is hit on the lateral ankle, can result in a Pott’s fracture and dislocation of the ankle joint.
  • In this injury, the very strong deltoid ligament does not tear, but instead shears off the medial malleolus of the tibia.
  • This frees the talus, which moves laterally and fractures the distal fibula.
  • In extreme cases, the posterior margin of the tibia may also be sheared off.

 

Above the ankle, the distal ends of the tibia and fibula are united 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 maintain the talus locked into position between the medial malleolus and lateral malleolus.

• Injuries that produce a lateral twisting of the leg on top of the planted foot can result in stretching or tearing of the tibiofibular ligaments, producing a syndesmotic ankle sprain or “high ankle sprain.”
• Most ankle sprains can be treated using the RICE technique: Rest, Ice, Compression, and Elevation.
  • Reducing joint mobility using a brace or cast may be required for a period of time.
• More severe injuries involving ligament tears or bone fractures may require surgery.

 

 

Development of Joints

By the end of this section, you will be able to:

• Describe the two processes by which mesenchyme can give rise to bone
• Discuss the process by which joints of the limbs are formed

 

Joints form during embryonic development in conjunction with the formation and growth of the associated bones.

• The embryonic tissue that gives rise to all bones, cartilages, and connective tissues of the body is called mesenchyme.
• In the head, mesenchyme will accumulate at those areas that will become the bones that form the top and sides of the skull.
  • The mesenchyme in these areas will develop directly into bone through the process of intramembranous ossification, in which mesenchymal cells differentiate into bone-producing cells that then generate bone tissue.
  • The mesenchyme between the areas of bone production will become the fibrous connective tissue that fills the spaces between the developing bones.
• Initially, the connective tissue-filled gaps between the bones are wide, and are called fontanelles.
  • After birth, as the skull bones grow and enlarge, the gaps between them decrease in width and the fontanelles are reduced to suture joints in which the bones are united by a narrow layer of fibrous connective tissue.
• The bones that form the base and facial regions of the skull develop through the process of endochondral ossification.
  • In this process, mesenchyme accumulates and differentiates into hyaline cartilage, which forms a model of the future bone.
  • The hyaline cartilage model is then gradually, over a period of many years, displaced by bone.
  • The mesenchyme between these developing bones becomes the fibrous connective tissue of the suture joints between the bones in these regions of the skull.

 

A similar process of endochondral ossification gives rises to the bones and joints of the limbs.

• The limbs initially develop as small limb buds that appear on the sides of the embryo around the end of the fourth week of development.
• Starting during the sixth week, as each limb bud continues to grow and elongate, areas of mesenchyme within the bud begin to differentiate into the hyaline cartilage that will form models for of each of the future bones.
  • The synovial joints will form between the adjacent cartilage models, in an area called the joint interzone.
  • Cells at the center of this interzone region undergo cell death to form the joint cavity, while surrounding mesenchyme cells will form the articular capsule and supporting ligaments.
• The process of endochondral ossification, which converts the cartilage models into bone, begins by the twelfth week of embryonic development.
  • At birth, ossification of much of the bone has occurred, but the hyaline cartilage of the epiphyseal plate will remain throughout childhood and adolescence to allow for bone lengthening.
  • Hyaline cartilage is also retained as the articular cartilage that covers the surfaces of the bones at synovial joints.