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7 Articular System

Joints, simply defi ned, are the meeting

places between bones. Th is simple defi nition describes a joint as any place

in the skeleton where one skeletal element contacts another skeletal element. It is important to understand that, as a part of this defi nition,

the bones never contact each other directly. Instead, there is always some other connective tissue between the bony contact

surfaces. Joints come in a wide variety of structural junctions, with an accompanying variety of functions.

Because joints have various functions and those

functions do not always deal with movement, it is illogical to defi ne joints by their movements. Th e best

method for classifying joints is based on their structure. Because the structure of joints includes the connective tissues between the neighboring bones, a

classifi cation based on the structure of those tissues

is logical. At the simplest level, there are two basic

ways bones connect with one another to form joints.

Either they are connected by solid masses of connective tissue, or they are bound together by a connective

tissue capsule, which surrounds a lubricated cavity between the adjoining bones.

Joints formed by a solid core of connective

tissue between the neighboring bones are called

synarthroses. Th ere are two subcategories of

synarthroses — fi brous joints, which have connective tissue cores of connective tissue proper, typically dense irregular connective tissue, and cartilage

joints, which use some form of cartilage as the

connecting tissue between the bones. Th e capsular joints, with their lubricated cavity, are called

diarthroses or synovial joints. Th ere are numerous subcategories of diarthroses, each

based on the structure and function of their

articular surfaces.

In addition to joints, this chapter will

also illustrate other closely related synovial

structures — bursae and synovial (tendon)

sheaths.

Find more information

about arthrology in

123

REAL ANATOMY

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tissue binding the neighboring bones can vary considerably. Examples of fi brous joints are depicted on this and the facing

page. Gomphoses and sutures (the four different suture types are shown on the opposite page) have a very thin membrane

of collagenous connective tissue anchoring neighboring bony structures to one another. On the other hand, the syndesmoses between the tibia and fi bula — both the interosseous membrane and the tibiofi bular ligaments at the distal end — have

considerably more binding connective tissue. There is also an example of another syndesmosis, the interspinous ligament,

in the next section.

Fibrous joints are synarthrotic joints that

bind bone to bone with collagenous connective tissue. The amount of connective

Synarthrosis - Fibrous Joints

 1 Periodontal membrane

 2 Crown of tooth

 3 Root of tooth

 4 Gingiva

 5 Mandible

 6 Tibia

 7 Fibula

 8 Interosseous membrane

 9 Anterior tibiofibular ligament of tibiofibular syndesmosis

10 Patellar ligament (cut)

Dento-alveolar syndesmosis or gomphosis

Sagittal section of tooth in mandible

Crural skeleton – tibia and fi bula

Anterior view

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Squamous-type suture

Squamous or temporoparietal suture

Denticulate-type suture

Lamboidal or parieto-occipital suture

Serrate-type suture

Coronal or frontoparietal suture

Plane-type suture

Internasal suture

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Sagittal section of head and trunk

Medial view

Synarthrosis - Cartilaginous Joints Like the fi brous joints, the

cartilaginous joints join

neighboring skeletal ele-

 1 Intervertebral disc (symphysis)

 2 Nucleus pulposus of intervertebral disc

 3 Anulus fibrosus of intervertebral disc

 4 Pubic symphysis

 5 Manubriosternal synchondrosis

 6 Spheno-occipital synchondrosis

 7 Epiphysial cartilage or primary cartilaginous joint

 8 Sternocostal (synchondrosis)

 9 Sternocostal (typically synovial but can be symphysial)

10 Interchondral (synovial)

 11 Interchondral (synchondrosis)

12 Costochondral (synchondrosis)

13 Interspinous ligament (vertebral syndesmosis)

14 Nuchal ligament (vertebral syndesmosis)

15 Anterior longitudinal ligament (vertebral syndesmosis)

16 Posterior longitudinal ligament (vertebral syndesmosis)

17 Body of vertebra

18 Spinous process of vertebra

19 Lamina of vertebra

20 Psoas major muscle

21 Aorta

22 Inferior vena cava

ments with a solid mass of connective tissue, but the uniting tissue is some type of cartilage instead of collagenous connective tissue proper. The three types of cartilaginous joints are: 1) synchondroses, 2) symphyses, and 3) epiphysial cartilages

or primary cartilaginous joints. The photos on these facing pages depict the different categories of cartilaginous joints. A few

syndesmoses from the fi brous joint category are also evident.

Transverse section of lumbar intervertebral disc

Inferior view

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Radiograph of juvenile wrist region

Anterior view

Joints of the thoracic cage

Anterior view

Epiphysial cartilage Fetal skeleton 200x

Posterior view

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Diarthroses or Synovial Joints Diarthroses differ from synarthroses

in one major way: instead of connecting neighboring bones by a solid mass

of connectve tissue, the bony connection consists of a double-layered connective tissue capsule that surrounds a lubricated

cavity between the bones. Within the capsule the ends of neighboring bony surfaces are covered by a smooth layer of hyaline cartilage. As a result of this design there is typically a much greater range of motion present in synovial joints, and they

form the joints of the skeleton that are responsible for the major movements of the body. The outer layer of the capsule, the

fi brous membrane, is continuous with the periosteum on the adjoining bones, while the inner layer of the capsule, the synovial membrane, attaches from the border of the articular cartilage on one bone to the border of the articular cartilage on the

other bone. Additionally, the synovial membrane secretes synovial fl uid, a lubricant that reduces friction between the mobile

cartilage-covered articular surfaces of the bones. The section through a fi nger joint below and the dissections of the knee

joint on the opposite page illustrate the basic features of a synovial joint. The pages that follow depict the major synovial

joints of the skeleton. One other key feature among synovial joints that is responsible for their varied range of motion is the

shape of the adjoining bone surfaces. It is this feature that anatomists use to describe the different types of synovial joints.

 1 Middle phalanx of index finger

 2 Proximal phalanx of index finger

 3 Fibrous membrane of joint capsule

 4 Synovial membrane of joint capsule

 5 Articular cartilage

 6 Joint cavity

 7 Collateral ligament

 8 Quadriceps tendon

 9 Patellar ligament

10 Suprapatellar bursa

 11 Synovial fold

12 Meniscus

13 Periosteum

14 Junction of periosteum (removed) with fibrous membrane

15 Junction of synovial membrane (removed) with articular cartilage

16 Femur with periosteum removed

17 Tibia with periosteum removed

18 Fibula with periosteum removed

19 Patella within quadriceps tendon

Proximal interphalangeal joint showing design of synovial joint

Frontal section, anterior view

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Dissection of knee showing design of synovial joint

Medial view

Dissection of knee showing design of synovial joint

Lateral view

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Ischium

20 Body of ischium

21 Ischial ramus

22 Ischial tuberosity

23 Ischial spine

24 Lesser sciatic notch

Pubis

25 Body of pubis

26 Pubic tubercle

27 Symphysial surface

28 Pubic crest

29 Superior pubic ramus

30 Pecten pubis or pectineal line

31 Obturator groove

32 Inferior pubic ramus

33 Obturator foramen

Left os coxae

Lateral view, anterior to left

Left os coxae

Medial view, anterior to right

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wider toward each end, the compact wall of bone becomes thinner and the medullary cavity accumulates spongy

bone. The proximal end consists of a short cantilevered neck capped by a smooth, round articular head. Projections of bone, the trochanters, form at the base of the cantilevered neck. The distal end consists of two large,

knuckle-like processes separated by an intermediate groove. The femur articulates with three bones: the os coxae,

patella, and tibia.

The femur is the longest bone of the body. The strong shaft forms a long cylindrical tube with

a slight forward bow. The strong wall of the shaft is thickest near the narrow center of the bone

where the medullary cavity is also the most spacious. As the shaft becomes progressively

Femur

Left femur

Anterior view, lateral to rigjt

Left femur

Posterior view, lateral to left

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 1 Head

 2 Fovea for ligament of head

 3 Neck

 4 Greater trochanter

 5 Trochanteric fossa

 6 Lesser trochanter

 7 Intertrochanteric line

 8 Intertrochanteric crest

 9 Quadrate tubercle

10 Shaft or body

 11 Linea apsera

12 Pectineal or spiral line

13 Gluteal tuberosity

14 Medial supracondylar line

15 Lateral supracondylar line

16 Medial condyle

17 Medial epicondyle

18 Adductor tubercle

19 Lateral condyle

20 Lateral epicondyle

21 Groove for popliteus

22 Patellar surface

23 Intercondylar fossa

Left femur

Lateral view, anterior to left

Left femur

Medial view, anterior to right

Left femur

Inferior view, lateral to right

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Left femur

Superior view, lateral to left

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with a fl at plateau-like superior surface largely covered with articular cartilage. The smaller distal end is more knoblike with a pronounced medial projection, the malleolus. The shaft has a strong anterior crest with sloping surfaces

to either side. The bone is easily palpable throughout its length. The tibia articulates with three bones — the femur,

fi bula, and talus.

The tibia is the large, medial bone of the leg skeleton. It is the second longest bone of the body,

only exceeded in length by the femur. Its strong shaft, consisting of thick walls of compact bone, is

triangular in cross-section. The shaft expands proximally into a fl uted extremity of spongy bone

Tibia

Left tibia

Anterior view, lateral to right

Left tibia

Posterior view, lateral to left

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 1 Superior articular surface

 2 Medial condyle

 3 Lateral condyle

 4 Fibular articular facet

 5 Anterior intercondylar area

 6 Posterior intercondylar area

 7 Intercondylar eminence

 8 Medial intercondylar tubercle

 9 Lateral intercondylar tubercle

10 Shaft or body

 11 Tibial tuberosity

12 Soleal line

13 Interosseous border

14 Anterior border

15 Posterior border

16 Medial malleolus

17 Malleolar groove

18 Malleolar articular facet

19 Fibular notch

20 Inferior articular surface

Left tibia

Lateral view, anterior to left Left tibia

Medial view, anterior to right

Left tibia

Superior view, lateral to left

Left tibia

Inferior view, lateral to right

Left tibia

Close-up of lateral view

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mal and distal ends, the shaft being totally surrounded with muscle. The fi bula articulates with two bones — the

tibia and talus.

The fi bula is the lateral bone of the leg skeleton. It is a slender, splint-like bone that is slightly

expanded at both ends. It plays no role in the weight-bearing function of the lower limb, but

serves as a signifi cant site of muscle attachment. It is not easily palpable except at its proxiFibula

 1 Head

 2 Articular facet for tibia

 3 Apex of head

 4 Neck

 5 Shaft or body

 6 Interosseous border

 7 Anterior border

 8 Posterior border

 9 Lateral malleolus

10 Articular facet for talus

 11 Malleolar fossa

12 Malleolar groove

Left fi bula

Anterior view, lateral to right

Left fi bula

Posterior view, lateral to left

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Left fi bula

Lateral view, anterior to left

Left fi bula

Medial view, anterior to right

Left fi bula

Inferior view, lateral to right

Left fi bula

Superior view, lateral to left

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that show a greater range in size and shape than their carpal counterparts in the hand. Distal to the tarsals are the

fi ve digital rays. The four lateral digits consist of a metatarsal bone and three phalanges. The large medial digit, the

hallux or great toe, has a metatarsal bone and only two phalanges. Two prominent sesamoid bones (bones that form

in tendons) are present on the plantar surface at the head end of the fi rst metatarsal.

Like the hand, the foot is a composite structure comprised of 26 bones, not

counting the small sesamoid bones that are found in certain tendons. The

proximal end of the foot is the tarsus or ankle. There are seven tarsal bones

Foot Skeleton

 1 Talus

 2 Calcaneus

 3 Navicular

 4 Medial cuneiform

 5 Intermediate cuneiform

 6 Lateral cuneiform

 7 Cuboid

 8 Metatarsal I

 9 Metatarsal II

10 Metatarsal III

 11 Metatarsal IV

12 Metatarsal V

13 Proximal phalanx

14 Middle phalanx

15 Distal phalanx

16 Sesamoid bones

Left foot

Dorsal view, lateral to right

Left foot

Plantar view, lateral to left

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Left foot

Medial view, anterior to right

Left foot

Anterior view, lateral to right

Left foot

Lateral view, anterior to left

Left foot

Posterior view, lateral to left

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one another. All the tarsal bones were photographed at the same scale so you can see their relative sizes.

The talus is the second largest and most proximal of the tarsal bones. It forms the ankle joint with the

distal end of the leg skeleton. It consists of a cuboid body, a distally directed neck capped by a convex,

oval head, a proximolateral facet for the fi bular malleolus, and a proximal trochlea for the tibia. It articulates with four bones — the tibia, fi bula, calcaneus, and navicular.

The next four pages depict the tarsal bones.

Like the carpals, this is a complex series of

bones that form numerous articulations with

Tarsal Bones - Talus

 1 Head

 2 Navicular articular surface

 3 Anterior facet for calcaneus

 4 Neck

 5 Middle facet for calcaneus

 6 Sulcus tali

 7 Body

 8 Trochlea of talus

 9 Lateral malleolar facet

10 Lateral process

 11 Medial malleolar facet

12 Posterior process

13 Groove for flexor hallucis longus

14 Lateral tubercle

15 Medial tubercle

16 Posterior calcaneal articular facet Left talus

Inferior view, lateral to right

Left talus

Lateral view, anterior to left

Left talus

Posterior view, lateral to right

Left talus

Superior view, lateral to left

Left talus

Medial view, anterior to right

Left talus

Anterior view, lateral to left

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 1 Calcaneal tuberosity

 2 Calcaneal tubercle

 3 Sustentaculum tali

 4 Groove for flexor hallucis longus

 5 Calcaneal sulcus

 6 Tarsal sinus

 7 Anterior talar articular surface

 8 Middle talar articular surface

 9 Posterior talar articular surface

10 Groove for fibularis longus

 11 Fibular trochlea

12 Articular surface for cuboid

Its distal end forms a series of articular surfaces with neighboring bones. Its posterior or proximal end is

box-like and forms a roughened calcaneal tubercle at the posterior surface. The calcaneus articulates

with two bones — the talus and the cuboid.

The calcaneus is the largest

bone of the foot and its long axis

parallels the long axis of the foot.

Tarsal Bones - Calcaneus

Left calcaneus

Anterior view, lateral to right

Left calcaneus

Superior view, lateral to left

Left calcaneus

Posterior view, lateral to left

Left calcaneus

Medial view, anterior to right

Left calcaneus

Inferior view, lateral to right

Left calcaneus

Lateral view, anterior to left

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The cuboid bone, like its name suggests, has a cube shape when viewed from above, but has ridges and

grooves on its plantar surface. It is the lateral bone in the distal series of tarsal bones and articulates with

the fourth and fi fth metatarsals. With a good imagination one can visualize the hull of a ship when observing the navicular bone. This ship-shaped bone is an intermediate bone between the talus and the three

cuneiforms on the medial aspect of the foot.

Tarsal Bones - Cuboid and Navicular

Left cuboid

Superior view, lateral to left

Left cuboid

Inferior view, lateral to right

Left cuboid

Anterior view, lateral to right

Left cuboid

Posterior view, lateral to left

Left cuboid

Medial view, anterior to right

Left cuboid

Lateral view, anterior to left

Left navicular

Superior view, lateral to left

Left navicular

Inferior view, lateral to right

Left navicular

Anterior view, lateral to right

Left navicular

Posterior view, lateral to left

Left navicular

Medial view, anterior to right

Left navicular

Lateral view, anterior to left

Cuboid

 1 Groove for fibularis longus

 2 Cuboid tuberosity

 3 Calcaneal process

 4 Articular surface for calcaneus

 5 Articular surface for navicular

 6 Articular surface for lateral cuneiform

 7 Articular surface for fourth metatarsal

 8 Articular surface for fifth metatarsal

Navicular

 9 Tuberosity

10 Articular surface for talus

 11 Articular surface for cuboid

12 Articular surface for medial cuneiform

13 Articular surface for intermediate cuneiform

14 Articular surface for lateral cuneiform

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of the ankle. They articulate with the three medial metatarsal bones. Their wedge shapes contribute to the

formation of the transverse arch of the foot.

The wedge-shaped cuneiforms are the distal tarsal

bones on the medial aspect

Tarsal Bones - Cuneiforms

Left lateral cuneiform

Superior view, lateral to left

Left lateral cuneiform

Inferior view, lateral to right

Left lateral cuneiform

Anterior view, lateral to right

Left lateral cuneiform

Posterior view, lateral to left

Left lateral cuneiform

Medial view, anterior to right

Left lateral cuneiform

Lateral view, anterior to left

Left middle cuneiform

Superior view, lateral to left

Left middle cuneiform

Inferior view, lateral to right

Left middle cuneiform

Anterior view, lateral to right

Left middle cuneiform

Posterior view, lateral to left

Left middle cuneiform

Medial view, anterior to right

Left middle cuneiform

Lateral view, anterior to left

Left medial cuneiform

Superior view, lateral to left

Left medial cuneiform

Inferior view, lateral to right

Left medial cuneiform

Anterior view, lateral to right

Left medial cuneiform

Posterior view, lateral to left

Left medial cuneiform

Medial view, anterior to right

Left medial cuneiform

Lateral view, anterior to left

Lateral cuneiform

 1 Articular surface for cuboid

 2 Articular surface for navicular

 3 Articular surface for middle cuneiform

 4 Articular surface for second metatarsal

 5 Articular surface for third metatarsal

 6 Articular surface for fourth metatarsal

Middle cuneiform

 7 Articular surface for navicular

 8 Articular surface for medial cuneiform

 9 Articular surface for lateral cuneiform

10 Articular surface for second metatarsal

Medial cuneiform

 11 Articular surface for navicular

12 Articular surface for middle cuneiform

13 Articular surface for second metatarsal

14 Articular surface for first metatarsal

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metatarsal bones are the most distinct. The fi rst metatarsal is short and thick compared to its counterparts, while the distinguishing feature of the fi fth metatarsal bone is the projecting tuberosity at its proximal end.

The fi ve metatarsal bones form the central portion of

the foot skeleton. The three central metatarsals most

closely resemble one another, while the fi rst and fi fth

Metatarsal Bones

 1 Base

 2 Shaft or body

 3 Head

 4 Tuberosity of first metatarsal

 5 Tuberosity of fifth metatarsal

Left metatarsal bones, numbered I to V from medial to lateral

Dorsal view, lateral to left

Left metatarsal bones, numbered I to V from medial to lateral

Plantar view, lateral to right

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part of the bone. From the base a narrow shaft projects to a rounded head with a trochlear articular surface. The middle and distal phalanges are short bones that can be easily distinguished by their distal

ends. The middle phalanges have a trochlear articular surface on their distal head, while the distal phalanges have a broad tuberosity at their distal ends.

Similar in number to the phalanges of the hand, the phalanges of the foot

are much smaller than those of the hand, with the exception of the large

fi rst toe. The proximal phalanges have broad bases that form the widest

Phalanges

 1 Base

 2 Shaft or body

 3 Head

 4 Trochlea

 5 Tuberosity of distal phalanx

Left phalanges

Dorsal view, lateral to left

Left phalanges

Plantar view, lateral to right

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border. The posterior surface of the bone is smooth and articulates with the femur, while the anterior surface of the

bone is rough by its attachment to the quadriceps tendon.

The patella is the largest sesamoid bone of the body. A sesamoid bone is a bone that forms

within a tendon. The patella occupies the posterior half of the quadriceps tendon just anterior

to the knee joint. It is a disc-like bone with a curved superior margin and a triangular inferior

Patella

 1 Base

 2 Apex

 3 Articular surface

 4 Anterior surface

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