Axial skeleton · Thorax
Sternum
The sternum is the flat midline bone at the front of the chest. It joins the clavicles and the costal cartilages of the upper ribs and completes the anterior wall of the thoracic cage.
- Latin (TA)
- Sternum
- Type
- Flat bone: an elongated, flattened plate of spongy bone
- Side
- Midline — single
- Model size
- 18.3 cm longest
Rotate the bone to inspect every surface. Blue dots are landmarks — tap one.
3D model: Z-Anatomy (CC BY-SA 4.0), derived from BodyParts3D © DBCLS (CC BY-SA 2.1 JP). Adapted by PharmaWallah. Credits & licence
Landmarks
3 of 9 marked on the modelTap a landmark to find it on the bone and read what it is.
The broad, roughly quadrilateral upper part of the sternum.
Where: Top of the sternum, behind which lie the great vessels arising from the aortic arch.
Why it matters: Articulates with the clavicles and the first costal cartilages, and with part of the second costal cartilages.
The shallow notch in the middle of the upper border of the manubrium.
Where: Superior border of the manubrium, in the midline, between the clavicular notches.
Why it matters: Easily felt at the root of the neck; the trachea can be felt just above it. Attachment of the interclavicular ligament.
Related: Interclavicular ligament.
Viva: What can you feel through the jugular notch?
An articular notch at each upper lateral corner of the manubrium.
Where: Superolateral angle of the manubrium, on each side of the jugular notch.
Why it matters: Articulates with the sternal end of the clavicle at the sternoclavicular joint, the only bony joint between the upper limb and the axial skeleton.
Related: Sternoclavicular joint.
Marked on the model at the point Z-Anatomy places this label.
The forward-projecting angle at the junction of the manubrium and the body.
Where: Manubriosternal joint, felt as a transverse ridge a short distance below the jugular notch.
Why it matters: The second costal cartilage joins the sternum at this level, so it is the starting point for counting ribs and intercostal spaces. It lies roughly at the level of the intervertebral disc between T4 and T5, marking the boundary between the superior and inferior mediastinum.
Related: Manubriosternal joint; second costal cartilage.
Viva: Why is the sternal angle a useful landmark?
Marked on the model at the point Z-Anatomy places this label.
The long, flat middle part of the sternum.
Where: Between the manubrium above and the xiphoid process below.
Why it matters: Gives attachment to the costal cartilages of the second to seventh ribs along its sides.
Notches along the lateral borders of the sternum for the costal cartilages.
Where: Lateral borders: the second at the sternal angle (shared by manubrium and body), the third to sixth on the body, and the seventh at the junction of the body and xiphoid process.
Why it matters: Sites of the sternocostal joints with the costal cartilages of the true ribs.
Related: Sternocostal joints.
Viva: Where does the seventh costal cartilage join the sternum?
Marked on the model at the point Z-Anatomy places this label.
The small, thin, lowest part of the sternum.
Where: Below the body, in the epigastric region, lying in a slight hollow.
Why it matters: Cartilaginous in the young and usually ossified in older adults; its shape varies and it may be split or perforated. It gives attachment to the diaphragm, rectus abdominis and linea alba.
Related: Xiphisternal joint.
Classification & region
Flat bone: an elongated, flattened plate of spongy bone (containing red marrow) between thin layers of compact bone.
- Manubrium
- The broad upper part, with the jugular notch above and the clavicular notches at its upper corners.
- Body
- The long middle part, formed by fused segments (sternebrae) whose lines of fusion show as transverse ridges; its sides carry notches for costal cartilages.
- Xiphoid process
- The small, thin lower tip, cartilaginous in the young and ossifying later in life; its shape varies.
Hold it in the anatomical position
- The broad manubrium is uppermost, with the jugular notch at its top; the narrow xiphoid process points downwards.
- The anterior surface faces forwards; it is slightly convex and shows transverse ridges on the body. The posterior surface is smoother and slightly concave.
- The clavicular notches face upwards and laterally at the upper corners of the manubrium; the costal notches line the lateral borders.
Orientation (a midline bone has no side)
- Superior vs inferior: the wide manubrium with the jugular notch is superior; the xiphoid process is inferior.
- Anterior vs posterior: the anterior surface is slightly convex, with transverse ridges across the body; the posterior surface is slightly concave.
- Confirm with the sternal angle, a ridge where the manubrium meets the body, which projects forwards.
The sternum lies in the midline with mirror-image right and left halves, so it has no side; you orient it instead.
Articulations
- With the clavicle at the Sternoclavicular joint, synovial saddle-type joint with an articular disc — Clavicular notch of the manubrium..
- With the first costal cartilage at the First sternocostal joint, primary cartilaginous joint (synchondrosis) — Costal notch on the manubrium..
- With the second to seventh costal cartilages at the Sternocostal joints, synovial plane joints — Costal notches of the body (the second at the sternal angle, the seventh at the xiphisternal junction)..
- With the manubrium and body (within the sternum) at the Manubriosternal joint, secondary cartilaginous joint (symphysis) — Lower border of the manubrium and upper border of the body..
- With the xiphoid process (within the sternum) at the Xiphisternal joint, cartilaginous; often ossifies with age — Lower end of the body..
Muscle and ligament attachments
| Structure | Type | Where on the bone |
|---|---|---|
| Sternocleidomastoid (sternal head) | origin | Anterior surface of the manubrium. |
| Pectoralis major (sternocostal head) | origin | Anterior surface of the sternum. |
| Sternohyoid | origin | Posterior surface of the manubrium. |
| Sternothyroid | origin | Posterior surface of the manubrium, below sternohyoid. |
| Transversus thoracis | origin | Posterior surface of the lower body and the xiphoid process. |
| Diaphragm (sternal part) | origin | Posterior surface of the xiphoid process. |
| Rectus abdominis | insertion | Xiphoid process (with the adjacent costal cartilages). |
| Linea alba | other | Xiphoid process. |
| Interclavicular and sternoclavicular ligaments | ligament | Jugular notch and the margins of the clavicular notches. |
Functions
- Completes the front of the thoracic cage and protects the heart, great vessels and other mediastinal structures.
- Anchors the costal cartilages of the true ribs, so the ribs and sternum move together in breathing.
- Gives the only bony attachment of the upper limb to the trunk, through the sternoclavicular joints.
- Contains red bone marrow throughout life.
Clinical & practical relevance
- Sternal marrow aspiration: because the sternum contains red marrow and lies just under the skin, marrow can be sampled from it, though the iliac crest is the more usual site.
- Median sternotomy (splitting the sternum in the midline) is the standard approach for many heart operations.
- The sternal angle is used at the bedside to count ribs and find intercostal spaces, for example when placing chest leads or examining the heart.
Identification tips
- The sternum is shaped like a sword: handle (manubrium), blade (body), tip (xiphoid).
- Find the jugular notch, slide down to the ridge of the sternal angle, then move sideways: you are on the second costal cartilage.
- Seventh costal cartilage = xiphisternal junction.
Common student mistakes
- Counting ribs from the jugular notch or the clavicle: the first rib is hard to feel, so count from the second at the sternal angle.
- Calling the first sternocostal joint synovial: it is a synchondrosis.
- Thinking the sternum articulates directly with ribs: it articulates with the costal cartilages.
Common exam questions
Name the parts of the sternum.Show answer
Manubrium, body and xiphoid process.
What is the sternal angle and what is its importance?Show answer
The angle at the manubriosternal joint; the second costal cartilage joins at this level, so it is used to count ribs, and it marks the level of the T4–T5 disc.
Which costal cartilages articulate with the manubrium?Show answer
The first, and the upper part of the second.
What type of joint is the manubriosternal joint?Show answer
A secondary cartilaginous joint (symphysis).
How does the first sternocostal joint differ from the others?Show answer
It is a primary cartilaginous joint (synchondrosis); the second to seventh are synovial joints.
Why is the sternum used for bone marrow sampling?Show answer
It is superficial and contains red marrow throughout life.
Name the muscles attached to the xiphoid process.Show answer
Diaphragm (posterior surface), transversus thoracis, and rectus abdominis; the linea alba is also attached.
Revision summary
- Three parts: manubrium, body, xiphoid process.
- Manubrium: jugular notch, clavicular notches, first costal notch.
- Sternal angle = manubriosternal joint = level of the second costal cartilage.
- Costal notches 2–7; the seventh at the xiphisternal junction.
- Sternoclavicular joint: saddle-type synovial with an articular disc.
- Red marrow throughout life.
Test yourself on the sternum
Spotting questions on bones, sides and landmarks — untimed, with explanations.
Joints of the sternum
References
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 5th ed. Philadelphia: Elsevier; 2023.
- Moore KL, Dalley AF, Agur AMR. Moore's Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
- Federative International Programme for Anatomical Terminology (FIPAT). Terminologia Anatomica. 2nd ed. FIPAT.library.dal.ca; 2019. fipat.library.dal.ca/TA2
- Kervyn G, Zielinski M, Vinent L, et al. Z-Anatomy: the libre 3D atlas of anatomy. Models derived from BodyParts3D, The Database Center for Life Science (CC BY-SA 2.1 JP). CC BY-SA 4.0. www.z-anatomy.com/
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