Specific Joints

Structural Classes of Synovial Joints

The amount of motion a joint allows is determined by the shape of the surfaces of the two articulating bones and the number of axes around which the bones move

plane, hinge, pivot, condylar, saddle, ball and socket

Plane Joint

Nonaxial joint

Two bones whose flat surfaces sit next to each other

Hinge Joint

Uniaxial joint

Convex surface of one bone fits into a concave depression of another bone

Pivot Joint

Uniaxial joint

The rounded surface of one bone fits into a groove on the surface of another bone

A ring-like ligament surrounds the rounded bone and holds it in the groove of the other bone

Condylar (Ellipsoid) Joint

Biaxial joint

The oval, convex surface of one bone fits into a shallow concave surface of another bone

Saddle Joint

Biaxial joint

Surface of each articulating bone has both convex and concave regions that complement each other

Ball-and-Socket Joint

Multiaxial joint

Articulating surface of one bone is ball-shaped, or spherical, and fits into a cup or socket formed by the articulating surface of the other bone

Elbow

hinge joint composed of 2 articulations

humeroulnar joint

humeroradial joint

Extrinsic ligaments support the articular capsule:

Radial (Lateral) Collateral Ligament—Supports the lateral side of the joint

Ulnar (Medial) Collateral Ligament—Supports the medial side of the joint

Anular Ligament—Stabilizes the radial head

Humeroulnar Joint

Between the trochlea of the humerus and the trochlear notch of the ulna

Humeroradial Joint

Between the capitulum of the humerus and the head of the radius

Knee

Largest diarthrosis in the body

Hinge joint that also allows some degree of rotation and lateral gliding

Can “lock out” in extension without causing muscle fatigue

Composed of two articulations:

Tibiofemoral Joint—Between the femoral and tibial condyles

Patellofemoral Joint—Between the patella and the patellar surface of the femur

Articular capsule covers all but the anterior surface of the knee joint, which is covered by the patella, the tendon of the quadriceps femoris muscle group, and the patellar ligament

Menisci and extrinsic ligaments that enhance stability:

Medial and Lateral Menisci

Tibial (Medial) Collateral Ligament

Fibular (Lateral) Collateral Ligament

Anterior Cruciate Ligament (ACL)

Posterior Cruciate Ligament (PCL)

Medial and Lateral Menisci

Pair of C-shaped fibrocartilage pads on the tibial condyles

Improve fit between bones

Shock absorption and cushioning

Tibial (Medial) Collateral Ligament

Links femur with the tibia and attaches to the medial meniscus

Fibular (Lateral) Collateral Ligament

Links femur with the fibula but does not attach to the lateral meniscus

Anterior Cruciate Ligament (ACL)

Runs from an anterior insertion site on the tibia to the posterior aspect of the femur

Prevents tibia from moving too far anteriorly

Posterior Cruciate Ligament (PCL)

Runs from a posterior position on the tibia to the anterior femur

Prevents tibia from moving too far posteriorly

Knee Injuries and the Unhappy Triad

Any activity that involves quick changes in direction can injure the knee

Contact sports, such as football or soccer, put athletes at greater risk, especially if their knee is struck from the side or from behind

Lateral blows often rupture the tibial collateral ligament, and puts pressure on the lateral meniscus, which may tear

The force of the blow also frequently ruptures the anterior cruciate ligament (ACL), forming the so-called Unhappy Triad

Surgery is required to repair the injury followed by physical therapy