Cartilaginous Joints

Cartilaginous joints are joints in which two bones are united by cartilage (either hyaline cartilage or fibrocartilage). They have no joint cavity and permit little to no movement compared to synovial joints. They are structurally intermediate between fibrous joints and synovial joints.

Classification

Cartilaginous joints are divided into two types based on the type of cartilage present and the degree of movement allowed:

Feature	Primary (Synchondrosis)	Secondary (Symphysis)
Cartilage type	Hyaline cartilage	Fibrocartilage
Movement	None (except bone growth)	Slight (amphiarthrosis)
Location	Not necessarily midline	Midline of the body
Tendency to ossify	Yes (temporary) or no (permanent)	Less likely to ossify

1. Synchondrosis (Primary Cartilaginous Joint)

Bones are joined by hyaline cartilage
Functionally classified as a synarthrosis (immobile)
Subclassified as temporary or permanent

Temporary Synchondroses

These exist during growth and are eventually replaced by bone (synostosis):

Epiphyseal growth plates (physis) between the diaphysis and epiphysis of long bones - injury to these in a growing child can cause shortening or deformity of the bone
Y-shaped triradiate cartilage connecting the ilium, ischium, and pubis - completely ossified by ~age 25
Spheno-occipital synchondrosis at the base of the skull

Permanent Synchondroses

These persist throughout life:

Costochondral junctions (ribs to costal cartilage)
First sternocostal joint (1st rib to manubrium)
- Note: The 2nd through 7th sternocostal joints are synovial joints

2. Symphysis (Secondary Cartilaginous Joint)

Bones are united by a fibrocartilage disk and supported by periarticular ligaments
Functionally classified as amphiarthrosis (slightly mobile)
Located in the midline of the body
Fibrocartilage is much stronger than hyaline cartilage due to thick collagen fibers, making symphyses efficient at firmly uniting adjacent bones
Fibrocartilage of a symphysis is less likely to ossify than hyaline cartilage of a synchondrosis

Examples:

Pubic symphysis - narrow fibrocartilaginous joint connecting the two pubic bones; ends of pubic bones are covered by a thin layer of hyaline cartilage attached to the fibrocartilage disk; reinforced by several ligaments (anterior and posterior pubic ligaments)
Intervertebral discs - classified as wide symphyses; fibrocartilaginous joints between vertebral bodies
Manubriosternal joint - symphysis at the sternal angle (angle of Louis); filled with fibrocartilage (note: this particular symphysis is synarthrotic)
Sacrococcygeal articulation - amphiarthrodial symphysis homologous with intervertebral discs; may be partially or completely obliterated in old age
Mandibular symphysis (in early life; fuses by ~age 2)

Pubic Symphysis - Anatomy

Pubic symphysis - axial cadaveric section showing the joint, pubic bones, anterior pubic ligament, posterior pubic ligament, obturator muscles, rectus muscle, and fat

Fig. 1.41a - Axial cadaveric section of the pubic symphysis showing the fibrocartilage joint space and surrounding reinforcing ligaments.

Pubic symphysis - axial MRI showing joint, pubic bones, posterior pubic ligament and fat

Fig. 1.41b - Axial MRI of the pubic symphysis. The gap between the two pubic bones is bridged by the fibrocartilage disc; a small amount of fluid may normally be present.

Functional Classification Summary

Functional Class	Movement	Structural Type	Examples
Synarthrosis	Immobile	Synchondrosis (hyaline)	Epiphyseal plates, 1st sternocostal joint, costochondral
Amphiarthrosis	Slightly mobile	Symphysis (fibrocartilage)	Pubic symphysis, intervertebral discs, sacrococcygeal

Comparison with Other Joint Types

Fibrous joints - united by dense fibrous connective tissue (e.g., skull sutures, tibiofibular syndesmosis, gomphosis of teeth)
Cartilaginous joints - united by cartilage, no joint cavity
Synovial joints - freely mobile, have a fluid-filled joint cavity lined by synovial membrane; bones do not fuse

Clinical Points

Growth plate injuries in children (fracturing through a temporary synchondrosis) are classified by the Salter-Harris system and can disrupt normal longitudinal bone growth
Symphysis pubis dysfunction (commonly in pregnancy due to relaxin-mediated ligament laxity) causes pain and widening of the pubic symphysis
Intervertebral disc degeneration involves the fibrocartilage of symphyseal joints and is a major cause of back pain
The manubriosternal joint can be used as a surface landmark (sternal angle / angle of Louis) to identify the 2nd rib and the level of T4/T5 vertebra

Sources: Imaging Anatomy: Bones, Joints, Vessels and Nerves, Vol. 3; Forensic Anthropology: A Comprehensive Introduction, 2nd Ed.

This is a shared conversation. Sign in to Orris to start your own chat.