d. Capsule. The "typical" synovial articulation is surrounded by a sleeve of
dense FCT known as the capsule. The capsule encloses the articulation.
e. Ligaments. Primarily, ligaments hold bones together. Ligaments also may
help restrain motion in certain directions and stabilize the articulation.
f. Muscles. Skeletal muscles apply the forces to produce a given motion.
See table 4-1 for a summary of the structures in a "typical" synovial
articulation, the tissues composing each structure, and the actions attributed
to each structure.
4-10. CLASSIFICATION OF SYNOVIAL JOINTS
Synovial joints are further classified according to the kind of motion and the
number of axes of motions used.
a. Uni-Axial Synovial Joints.
(1) In uni-axial synovial joints, motion occurs in only one plane. The joints of
the fingers (interphalangeal) flex and extend in the sagittal plane. These are commonly
referred to as hinge joints.
(2) If a single rotatory (rotational) motion occurs around a post-like structure,
the joint is a pivot joint. The atlas vertebra rotating around the dens (tooth like
projection) of the axis vertebra at the top of the neck (base of the skull) is a pivot joint.
b. Bi-Axial Synovial Joints. In bi-axial synovial joints, motion between the
bones occurs in two planes. Here the surface in contact is curved or rounded in two
(1) The proximal phalanx of a finger can flex and extend and move from side
to side on the rounded head of the metacarpal bone. This is the MP or
(2) When the two surfaces are curved in directions at right angles to each
other, a shape similar to that of a cowboy's saddle is formed. This type of synovial joint
is called a saddle joint. In the human body, the saddle joint is located at the base of the