Anatomy, Joints

A joint is a region where 2 bones make contact. Joints may be classified histologically or functionally. Histological classification is based on the predominant connective tissue type composing the joint, either fibrous, cartilaginous, or synovial. Functional classification is based on the amount of movement the joint permits. The 3 functional joint types include the immovable synarthrosis, slightly moveable amphiarthrosis, and freely moveable diarthrosis. The 2 joint classification schemes correlate: synarthroses are fibrous, amphiarthroses are cartilaginous, and diarthroses are synovial.

Joints, comprised of bones and connective tissue, embryologically develop from mesenchyme. Bones may develop directly through intramembranous ossification or indirectly via endochondral ossification. Each joint has unique vascular and innervation schemes with recognizable patterns. Muscles stabilize joints. Muscle strength directly correlates with joint stability, particularly in synovial joints.

Many pathophysiological conditions affect joints, with histological class determining the kind of pathology that develops. Joint diseases are common across all ages. A thorough understanding of joint structure and function is of great clinical significance.