Anatomy and Physiology 2e · Joints
Cartilaginous Joints
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Cartilaginous joints are the body's cushion joints: bones held together by cartilage, with no joint cavity between them. Where fibrous joints lock bones in place with tough connective tissue, cartilaginous joints use cartilage to bond bones while allowing a small, controlled amount of give. They are the joints of the midline skeleton — spine, ribcage, pelvis — strong yet slightly flexible.
There are exactly two types. Synchondroses are joined by Hyaline cartilage Smooth, firm cartilage; the most common type in the body Full entry → and are immovable (synarthroses); the growth plates of children's long bones are the best-known examples. Symphyses are joined by Fibrocartilage Cartilage reinforced with collagen fibers, built for compression Full entry → and are slightly movable (amphiarthroses); the joints between vertebral bodies and the Pubic symphysis Fibrocartilage joint between the two pubic bones Full entry → are the classics. Because cartilage is living tissue that grows, remodels, and can be damaged, these joints sit at the center of everyday topics: bone growth in children, back pain from intervertebral discs, and pelvic changes in pregnancy. Details here are standard reference concepts — verify against your current text.
Why this matters
- Bone growth happens at a joint: Children's long bones lengthen at the epiphyseal plates — synchondroses. Growth-plate damage can alter how a limb grows, which is why pediatric bone injuries near joints are taken seriously.
- Back pain is a cartilaginous-joint problem: The intervertebral discs are symphyses between vertebral bodies; their structure (fibrocartilage with a soft center) explains both their shock-absorbing job and the disc problems that cause so much pain.
- The pelvis is designed to give: The pubic symphysis normally allows only slight movement, but pregnancy hormones relax its connective tissue and widen it for childbirth — a real-world example of a "slightly movable" joint becoming more movable.
- Ribcage mechanics: The joints where ribs meet the sternum include synchondroses; their rigidity keeps the chest wall stable while still allowing the small motions of breathing.
- A bridge to bone: Growth plates ossify into synostoses — the clearest example of joints changing class over a lifetime.
The college version
Core Concepts
Cartilage as the binding material
Two features define a Cartilaginous joint Joint where bones are united by cartilage, with no joint cavity Full entry →: bones united by cartilage, with no joint cavity. The cartilage type determines the joint type. Hyaline cartilage — smooth and glassy, the type that caps joint surfaces in synovial joints — forms synchondroses. Fibrocartilage — hyaline-like tissue reinforced with collagen fibers, built for compression and tension — forms symphyses. The theme is the same as in fibrous joints: strength over mobility, with a little more give in the material itself.
Synchondroses: hyaline bridges
A Synchondrosis Immovable cartilaginous joint joined by hyaline cartilage Full entry → is a cartilaginous joint in which the bones are joined by hyaline cartilage. Because hyaline cartilage is firm and not compressible like fibrocartilage, synchondroses permit no movement; functionally they are synarthroses.
The most important synchondroses are the epiphyseal (growth) plates of growing long bones — discs of hyaline cartilage between the shaft (diaphysis) and ends (epiphyses) of a child's femur or humerus. These joints do not move, but they grow: new cartilage forms on the epiphyseal side while bone replaces it on the shaft side, lengthening the bone. When growth ends, the plate ossifies into an epiphyseal line and the joint becomes a synostosis. Other synchondroses include the first sternocostal joint (first rib to the manubrium) and the costochondral joints where ribs meet their costal cartilages.
Symphyses: fibrocartilage cushions
A Symphysis Slightly movable cartilaginous joint joined by fibrocartilage Full entry → is a cartilaginous joint in which bones are joined by fibrocartilage, usually with a thin hyaline layer capping each bone. Fibrocartilage absorbs compression, so symphyses take heavy loads while permitting slight movement; functionally they are amphiarthroses — the "slightly movable" middle ground.
The standard examples are the intervertebral discs between adjacent vertebral bodies (each disc cushions the spine and lets it bend a little at every level), the pubic symphysis, and the manubriosternal joint of the sternum. Each is a weight-bearing or force-spreading joint where a rigid bond would transmit too much shock and a freely movable joint would be too unstable.
The design logic: strength with a little give
The pattern shows in the midline. The spine must be a strong column that still bends, twists, and absorbs shock — so each vertebral joint is a symphysis: strong, slightly movable, cushioned. The pubic bones must resist walking forces while the pelvic ring flexes slightly — again a symphysis. The ribcage must be stable yet move with every breath — a mix of synchondroses and slightly movable sternal joints. Wherever the body needs controlled flexibility under load, it builds a cartilaginous joint.
Common Confusions
| Do not confuse | With | Difference |
|---|---|---|
| Synchondrosis | Symphysis | Synchondrosis uses hyaline cartilage and is immovable; symphysis uses fibrocartilage and is slightly movable |
| Epiphyseal plate | Epiphyseal line | The plate is growing hyaline cartilage (a synchondrosis, present in children); the line is the fused bone that remains (a synostosis, present in adults) |
| Cartilaginous joints | Synovial joints | Cartilaginous joints have no joint cavity; synovial joints are defined by their fluid-filled cavity |
| Cartilaginous joints | Fibrous joints | Cartilaginous joints are bound by cartilage; fibrous joints by dense connective tissue — neither has a cavity |
| Intervertebral disc | Vertebral body | The disc is the fibrocartilage symphysis between bodies; the body is the bone itself |
| "Symphysis" in everyday language | Symphysis as a joint class | Colloquially it can mean "growing together"; anatomically it is specifically a fibrocartilage joint (e.g., pubic symphysis) |
| Growth plates | Joints that move | They are synarthroses — they never move; their job is growth, not mobility |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Cartilaginous joints are the squishy connections between building blocks. Some are joined by a firm, smooth material (like your ribs meeting your breastbone) and don't move at all — but in kids, that same material is the "growing pad" that makes bones longer. Others are joined by a tough, springy cushion (like the pillows between your spine bones) that lets bones wiggle a little while holding heavy loads. No fluid-filled space — just strong, slightly bendy material between the bones.
Worked example
Follow a child's femur over time. At birth and through childhood the femur is not one solid bone: its shaft (diaphysis) and ends (epiphyses) are separated by epiphyseal plates of hyaline cartilage. Structurally each plate is a synchondrosis; functionally a synarthrosis — the femur does not flex there. The plate's real job is growth: cartilage cells multiply on the epiphyseal side while bone replaces cartilage on the shaft side, lengthening the bone by several centimeters per year.
Now consider what this means when a young athlete injures a knee. A blow to the knee may damage the growth plate rather than (or in addition to) the ligaments of the synovial knee joint. Because a damaged growth plate can stop lengthening on one side, the injured leg may end up shorter or angled compared with the other — which is why pediatric bone-and-joint injuries are assessed with special care and followed over time. Finally, growth finishes in the late teens: the plates ossify into epiphyseal lines, the synchondroses become synostoses, and the femur is one continuous bone. The joint that built the bone disappears into it.
Key takeaways
- Cartilaginous joints = bones bound by cartilage, no joint cavity — two types: synchondrosis (hyaline) and symphysis (fibrocartilage).
- Synchondroses are immovable (synarthroses), e.g., the epiphyseal plate; symphyses are slightly movable (amphiarthroses), e.g., intervertebral discs and the pubic symphysis.
- Growth plates are temporary joints: they ossify into epiphyseal lines (synostoses) when growth ends.
- Fibrocartilage is built for compression — that is why the spine's discs and the pubic symphysis can take heavy loads yet still move slightly.
- Cartilaginous joints live on the midline: spine, ribcage, sternum, pelvis — protection and load-bearing, not limb movement.
- Symphyses respond to pregnancy hormones: the pubic symphysis connective tissue relaxes and widens for childbirth — a classic clinical connection.
Check yourself
5 review questions from the chapter. Try each one, then open the answer.
What are the two types of cartilaginous joints, and what cartilage forms each?
Show answer
Synchondrosis (hyaline cartilage) and symphysis (fibrocartilage).
What is the functional classification of a synchondrosis? Of a symphysis?
Show answer
Synchondrosis: synarthrosis (immovable). Symphysis: amphiarthrosis (slightly movable).
Why is an Intervertebral disc Fibrocartilage cushion between adjacent vertebral bodies Full entry → classified as a symphysis?
Show answer
Because it is a fibrocartilage pad between two bones with no joint cavity — the defining features of a symphysis.
What happens to the epiphyseal plates when a person stops growing?
Show answer
They ossify into epiphyseal lines (synostoses); the joints disappear into solid bone.
Why can the pubic symphysis widen in pregnancy despite being "slightly movable"?
Show answer
Because pregnancy hormones relax the connective tissue of the joint, allowing it to widen for childbirth — its "slight movement" is normally small but is increased by that hormonal change.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Cartilaginous joint
- Joint where bones are united by cartilage, with no joint cavity
- Hyaline cartilage
- Smooth, firm cartilage; the most common type in the body
- Fibrocartilage
- Cartilage reinforced with collagen fibers, built for compression
- Synchondrosis
- Immovable cartilaginous joint joined by hyaline cartilage
- Symphysis
- Slightly movable cartilaginous joint joined by fibrocartilage
- Epiphyseal plate
- Hyaline-cartilage growth disc between the shaft and end of a growing long bone
- Intervertebral disc
- Fibrocartilage cushion between adjacent vertebral bodies
- Pubic symphysis
- Fibrocartilage joint between the two pubic bones
Sources & references
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