Articulations

An articulation is a joint, a place where bones or bones and cartilage come together. There are three types of joints based on the amount of movement they allow: synarthrotic, amphiarthrotic, and diarthrotic. Note that these types refer to the physiology of the joints.

Synarthrotic joints are immovable because the bones are held tightly together with fibrous connective tissue or cartilage. There are three types of synarthroses. Sutures exist between bones of the skull and are held together with collagenous connective tissue continuous with the periosteum. A synchondrosis is an articulation held together by cartilage. The joints between the ribs and the sternum are synchondrotic. Some synchondroses are very slightly moveable. A gomphosis is a joint in which a peg is held tightly in a socket. An example is the joint between a tooth and the alveolar process.

Slightly moveable joints are termed amphiarthrotic. There are two types of amphiarthroses. Symphyses are slightly movable joints with a pad of fibrocartilage between bones held together by ligaments. The joints between the vertebrae and between the os coxae are symphyses. A syndesmosis is an amphiarthrotic joint that lacks cartilage, but has a ligament holding the bones together. An example is the articulation between fibula and the tibia.

Diarthroses are freely movable joints. They are also called synovial joints. The epiphyses of the bones are covered with articular cartilage. An articular capsule holds the two bones together. The articular capsule is made of an outer layer of ligaments and an internal synovial membrane. The membrane secretes synovial fluid into the synovial cavity between the bones. There are six different kinds of diarthrotic joints in the body. They are listed, discussed, and pictured in your textbook.

Exercise 12.1

Label the structures in Figure 12.1.

Figure 12.1 Articulations

Articular capsule Articular cartilage (X2) Fibrocartilage pad Fibrous connective tissue Ligament (X2) Periosteum Suture Symphysis Synovial cavity Synovial joint Synovial membrane

Exercise 12.2

As you continue reading, label the structures in Figure 12.2.

An example of a synovial articulation is the knee joint. Let us examine it in more detail.

To cushion and hold the condyles of the femur and tibia there are two fibrocartilage pads located between the bones. These pads are the lateral and medial menisci (sing. -meniscus). Note that the menisci are thick toward the outside and thin in the middle to provide a socket for the condyles of the femur. The menisci are held together by the transverse ligament.

The bones are held together by four main ligaments. The innermost of these ligaments are the anterior and posterior cruciate ligaments. The word "cruciate" comes from the Latin word crux which means cross. Note that the cruciate ligaments form a cross (an X) on the knee. The fibular collateral ligament is on the lateral surface and joins the lateral epicondyle of the femur to the head of the fibula. (However, the two bones do not articulate as they have no direct connection.) The tibial collateral ligament lies medially and connects the medial epicondyle of the femur to the tibia. There are additional ligaments in the knee joint which we will not discuss.

Anterior to the femur and tibia is the patella. The patella lies inside the quadriceps femoris tendon. Between the patella and the leg bones is a cavity, the suprapatellar bursa, lined with synovial membrane. The fluid in this bursa acts as a shock absorber in protecting the knee joint.

The knee joint is held together almost entirely by soft tissue such as ligaments, synovial membranes, and cartilages. There are no bony projections to prevent dislocations in any direction, thus knee injuries are common among athletes.

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ANTERIOR

POSTERIOR

POSTERIOR

Figure 12.2 Right Knee

Synovial Joint5
MIDSAGGITAL

Anterior cruciate ligament (X2) Fibular collateral ligament Head of fibula Lateral condyle of femur Lateral meniscus Medial condyle of fémur Medial meniscus Menisci Patella (X2) Patellar ligament Posterior cruciate ligament (X2) Quadriceps femoris tendon Suprapatellar bursa Synovial membrane Tibial collateral ligament Transverse ligament

CHAPTER 12 REVIEW

1. _ The three types of joints are:

4. __Another name for a diarthrotic joint is a (4) joint.

5. __What kind of membrane lines a bursa?

6. __What does this membrane secrete?

7. __What kind of tissue holds suture together?

8. _ True or false. The pads between vertebrae and the pads in the knee joint are made of the same material, fibrocartilage.

9. _ The (9) capsule holds diarthrotic joints together.

10. _ True or false. A symphysis is not moveable.

11. _ Name the pads located in the knee joint.

12. _ Name the two ligaments which form a cross in the knee joint.

13. _ Name a sesamoid bone.

14. _ What is the function of a bursa?

Classify each of these joints as syndesmosis, synchondrosis, suture, symphysis, or synovial:

16. _ shoulder

17. _ joint between parietal bones

18. _(_ joint between os coxae

19. _ fibulo-tibial joint

20. _ joint between the epiphysis and diaphysis in the long bone of a child

21. __atlo-occipital joint

22. __intervertebral joint

24. __joint between the ulna and the radius

CHAPTER

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