The sternum, or breastbone, is the flat bone running down the center of your chest that connects your ribs and protects everything behind it: the heart, great vessels, and portions of the lungs. It plays a central role in breathing mechanics, serves as a crucial site for emergency vascular access, and provides the route through which cardiac surgeons reach the heart. For something so structurally simple at first glance, the sternum turns up across a surprising range of medical contexts, from congenital chest-wall deformities and traumatic fractures to bone marrow biopsies and forensic age estimation.
How the Sternum Is Built
The sternum has three parts. The manubrium sits at the top and connects to the collarbones and the first two pairs of ribs. Below it is the body (sometimes called the mesosternum or gladiolus), which is the longest section and attaches to ribs three through seven via cartilage. At the bottom is the xiphoid process, a small piece of cartilage that gradually hardens into bone over your lifetime. Together, these three sections form the keystone of the anterior chest wall.
In early embryonic development, the sternum begins as two separate cartilage bands on either side of the midline. These bands migrate toward the center and fuse. Bone then develops within each cartilage segment through individual growth centers called sternebrae. Some segments end up with two ossification centers rather than one, reflecting the sternum’s paired embryonic origin. Fusion of these segments proceeds from the bottom upward, the reverse of the order in which they first appeared.1PubMed. Postnatal development of the human sternum The manubrium and body often never fuse completely, remaining connected by a fibrocartilage joint. In a forensic study of Thai adults, about half of the sterna examined showed fusion at this joint, with the earliest complete fusion seen around age 30 and some individuals retaining a mobile joint into their eighties.2PubMed Central. Forensic age-at-death estimation using the sternal junction in Thai adults: an autopsy study
Sternal Foramina and Other Normal Variations
Because the sternum forms from two separate halves that must meet and merge, the process occasionally leaves gaps. The most common of these is the sternal foramen, a small hole in the bone body or xiphoid process. A meta-analysis covering more than 16,000 subjects found that roughly 9% of people have a foramen somewhere in the sternum or xiphoid, with about 6.5% located in the sternal body and about 3% in the xiphoid process.3PubMed Central. Prevalence and morphometry of sternal and xiphoid foramen: a meta-analysis on 16,666 subjects The foramen is more common in men than in women, and prevalence varies by population, running higher in South American and African study groups and lower in North American cohorts.
These holes are almost always harmless and discovered by accident on a CT scan done for some other reason. The average foramen measures under 6 mm across. But awareness matters for two reasons. First, a sternal foramen on imaging can be mistaken for a lytic bone lesion, potentially prompting an unnecessary biopsy or workup for cancer. Radiologists familiar with normal sternal variants can avoid that confusion.4PubMed. Frequency of sternal variations and anomalies in living individuals evaluated by MDCT Second, and more ominously, a foramen in the wrong spot means there is nothing between a needle and the structures directly behind the bone. That risk becomes relevant during sternal bone marrow aspiration, which we’ll return to below.
Beyond foramina, the xiphoid process itself comes in multiple shapes. Studies from Ethiopia found that about 83% of xiphoid processes end as a single tip, while roughly 16% are bifurcated and a small number trifurcated.5PubMed Central. Anatomical variations of the sternum: sternal foramen and variant xiphoid morphology in dried adult human sternum in Ethiopia These variants also have no clinical consequences on their own but add to the list of normal appearances that a radiologist or surgeon should recognize.
Congenital Chest-Wall Deformities
When sternal development goes more significantly wrong, the results are visible deformities of the chest wall. The two most common are pectus excavatum (“funnel chest,” where the sternum is sunken inward) and pectus carinatum (“pigeon chest,” where it juts forward). A much rarer malformation is the sternal cleft, where the two embryonic halves of the sternum fail to fuse entirely, leaving a gap in the middle of the chest.
Pectus Excavatum
Pectus excavatum is by far the more common deformity. The depression in the chest is not just cosmetic. The sunken sternum can press on the heart and lungs, and studies using cardiac MRI and exercise testing have documented measurable effects. In a study of over 300 patients, about a third showed reduced aerobic fitness on exercise testing, roughly one in six had a depressed right ventricular ejection fraction, and about one in five had a depressed left ventricular ejection fraction. Importantly, the deeper the deformity, the worse these cardiac measures tended to be.6PubMed. The Severity of Pectus Excavatum Defect Is Associated With Impaired Cardiopulmonary Function In a separate cohort of nearly 400 patients who underwent exercise testing before surgery, abnormal oxygen consumption was present in about two thirds.7PubMed Central. Cardiopulmonary Outcomes After the Nuss Procedure in Pectus Excavatum
The Nuss procedure, in which a curved metal bar is placed behind the sternum to push it forward, has become the standard surgical correction. The same study that documented widespread abnormal exercise performance found consistent improvements in cardiopulmonary function after surgery, adding weight to the argument that pectus excavatum is a functional problem, not merely an aesthetic one.
Pectus Carinatum
Pectus carinatum, the outward protrusion of the sternum, is less likely to compromise heart or lung function but often causes significant distress for the young people who have it. Unlike pectus excavatum, the first-line treatment is usually non-surgical. Custom-fitted compression braces, worn for several hours a day, gradually reshape the flexible chest wall. In a large series of 241 patients treated with two different brace designs, the overall success rate was about 90%, with most failures attributable to patients not wearing the brace consistently rather than to any shortcoming of the device itself.8PubMed. Dynamic Compression System versus Self-Adjustable Bracing for Pectus Carinatum: Clinical Outcomes and Cost Comparison The active bracing period averaged around five months. An earlier series using a custom aluminum brace reported good to excellent results in about 88% of patients who completed treatment.9PubMed. Dynamic compression system for the correction of pectus carinatum In both studies, the consensus was that a trial of bracing should come before anyone considers surgical resection.
Sternal Cleft
Sternal cleft is rare and far more urgent. Because the sternum never fused in utero, the heart and great vessels sit without a bony shield, covered only by skin and soft tissue. Surgeons recommend early repair, ideally in the newborn period when the chest wall is still flexible enough to allow the two sternal halves to be brought together and closed primarily.10PubMed Central. Reconstruction of Congenital Sternal Clefts: Surgical Experience and Literature Review If repair is delayed past the first few months of life, the chest becomes too rigid for simple closure, and more complex reconstructive techniques using cartilage grafts or prosthetic materials may be needed.11PubMed Central. Surgical repair of a sternal cleft malformation
Median Sternotomy and How Surgeons Close It
If you or someone you know has undergone open-heart surgery, the incision almost certainly went straight down the middle of the sternum. This approach, called a median sternotomy, was first described in 1897 but wasn’t widely adopted until 1957 and only became ubiquitous after coronary artery bypass grafting took off in the late 1960s.12PubMed. Median sternotomy It gives unrivaled access to the heart, aorta, and both lungs.
Closing the sternum afterward is deceptively important. The two halves need to stay aligned and stable while bone heals, yet every breath you take tugs on them. The traditional method uses stainless steel wires twisted around or through the bone. Biomechanical testing on cadavers has shown that standard steel wire provides the most stable closure compared with alternatives like Mersilene ribbon or steel bands, likely because twisting the wire generates more compression across the cut surfaces.13PubMed. Biomechanical study of sternal closure techniques
More recently, rigid plate fixation systems have challenged wire closure. In randomized multicenter trials, plates produced better bone healing scores at both three and six months. In one trial, 70% of patients with rigid plates had achieved full sternal union by six months, compared with just 24% of wire-closure patients.14PubMed. Sternal closure with rigid plate fixation versus wire closure: a randomized controlled multicenter trial A second multicenter trial confirmed faster healing and found zero sternal complications through six months in the plate group versus 5% in the wire group.15PubMed. Randomized, multicenter trial comparing sternotomy closure with rigid plate fixation to wire cerclage Another biomechanical approach, interlocking sternotomy (a zigzag cut that creates an interlocking jigsaw-like fit), showed dramatically less displacement than a straight cut in lab testing, though clinical studies in patients are still needed.16PubMed Central. Comparison of straight median sternotomy and interlocking sternotomy with respect to biomechanical stability
Wound Infections After Sternotomy
Sternal wound infection is one of the most feared complications of open-heart surgery. Although uncommon in absolute terms, it can be devastating when it occurs. The strongest risk factors identified across a large meta-analysis include diabetes, obesity, the use of both internal thoracic arteries as bypass grafts, chronic obstructive pulmonary disease, prolonged surgery, and extended time on a ventilator after the operation.17PubMed Central. Risk factors for sternal wound infection after open‐heart operations: A systematic review and meta‐analysis Congestive heart failure, kidney problems, and peripheral vascular disease also increase risk.
The type of bacteria involved depends on the depth of infection. Superficial infections that don’t meet full surgical-site-infection criteria are typically caused by skin bacteria, while deeper, more serious infections are commonly driven by Staphylococcus aureus and gut-origin organisms.18PubMed. Sternal wound infection after cardiac surgery: incidence and risk factors according to clinical presentation When deep sternal infection leads to osteomyelitis (bone infection) and partial destruction of the sternum, reconstruction may require advancing a flap of pectoralis muscle to fill the defect and provide vascularized tissue for healing.19Scientific Reports. Reconstruction of sternal defects after sternotomy with postoperative osteomyelitis, using a unilateral pectoralis major advancement muscle flap
Sternal Fractures From Trauma
The sternum can fracture from blunt chest trauma, most commonly in motor vehicle crashes (particularly from seatbelt loading) and falls. The fracture itself heals with time and pain management, but the real clinical question is always the same: did the heart get bruised too? Because the sternum sits right in front of the heart, blunt cardiac injury is the concern that drives the workup.
The reassuring finding across several studies is that isolated sternal fractures, those without other major injuries, very rarely cause clinically significant cardiac damage. In one multicenter review, only about 4% of patients with sternal fractures had ECG abnormalities, and only 2% had an elevated troponin level.20PubMed Central. Investigation of myocardial contusion with sternal fracture in the emergency department: multicentre review A study looking at prolonged heart monitoring in 129 patients with isolated sternal fractures found that only a single patient (under 1%) suffered a cardiac-related complication, and no patients required any cardiac procedure.21PubMed. Evaluating the Need for Prolonged Telemetry Monitoring in Patients With Isolated Sternal Fractures Another study of 88 patients with isolated sternal fractures found no cases of clinically significant cardiac injury at all, even though initial ECG abnormalities popped up in a small number of patients and resolved within hours.22PubMed Central. The Association between Blunt Cardiac Injury and Isolated Sternal Fracture
The practical takeaway is that if your sternal fracture is truly isolated (no other chest injuries, no hemodynamic instability), a normal ECG and normal troponin level are highly reassuring. Routine prolonged cardiac monitoring for everyone with a sternal fracture is being increasingly questioned.
Bone Marrow Aspiration and Emergency Intraosseous Access
The sternum is a common site for bone marrow aspiration, particularly in adults, because it remains rich in hematopoietic marrow throughout life. However, the procedure carries a small but genuine risk that does not exist at other aspiration sites: the needle can penetrate through the back wall of the sternum and strike the ascending aorta or other mediastinal structures. A Japanese safety analysis found that this risk is real, concluding that sternal bone marrow aspiration carries an inherent danger of aortic laceration, particularly in older patients of short stature whose sterna may be thinner.23PubMed. Risk factors concerning sternal bone marrow aspiration and patient safety in Japan Case reports of fatal pericardial tamponade following sternal aspiration, while extremely rare, have been documented.24PubMed Central. Professional accountability in a sternal bone marrow aspiration: a forensic case report The presence of a sternal foramen, as discussed earlier, would further reduce the margin of safety. This is one reason imaging studies have emphasized identifying sternal foramina before planned procedures.25PubMed Central. MDCT evaluation of sternal variations: Pictorial essay
In emergency medicine, the sternum serves a different role as a site for intraosseous (IO) access, which is the placement of a needle into the bone marrow space to deliver fluids and medications when an IV line cannot be established. The sternum turns out to be the fastest IO site for fluid delivery. A cadaveric study measured a mean flow rate of about 94 mL per minute through the sternal IO route, compared with about 57 mL per minute through the upper arm bone and about 31 mL per minute through the shin bone.26Journal of Trauma and Acute Care Surgery. Intraosseous infusion rates under high pressure: A cadaveric comparison of anatomic sites That makes the sternal site roughly three times faster than the tibial site, a meaningful difference in a trauma resuscitation where every minute of delayed fluid replacement counts.27PubMed Central. Sternal Intraosseous Devices: Review of the Literature Specialized sternal IO devices are designed with depth guards to prevent the needle from penetrating too far, mitigating the very risk that makes sternal bone marrow aspiration hazardous.
Sternal Pain, Tumors, and Tietze’s Syndrome
Pain in the sternal area sends many people to the emergency room convinced they are having a heart attack. The most common musculoskeletal culprit is costochondritis, an inflammation of the cartilage connecting the ribs to the sternum, which produces sharp chest pain that worsens with movement or deep breathing but carries no cardiac risk. A related but less common condition is Tietze’s syndrome, which involves not just pain but visible swelling of one of the sternal joints, usually the sternocostal or costochondral junction on one side. Diagnosis is clinical: tenderness on pressing the affected joint, sometimes elevated inflammatory markers, and imaging that rules out other causes.28PubMed Central. What do we know about Tietze’s syndrome? Both conditions are self-limiting in most cases, though Tietze’s can linger for months.
Tumors of the sternum are uncommon but worth knowing about. The most frequent primary sternal tumor is chondrosarcoma, a malignancy of cartilage. In one series of 36 patients who underwent sternal tumor excision, chondrosarcoma accounted for half the primary tumors, while breast cancer metastases represented about a fifth of all cases.29PubMed Central. Short and long-term results of sternectomy for sternal tumours For primary sternal sarcomas, complete surgical removal (partial or total sternectomy) can yield good long-term results, with one series reporting five-year survival of about 73%.30The Annals of Thoracic Surgery. Resection of sternal tumors: extent, reconstruction, and survival Reconstruction after sternectomy typically involves prosthetic mesh or bone cement to restore chest-wall stability and protect the organs beneath.
CPR Complications in Patients With Sternal Hardware
One modern wrinkle in sternal medicine involves people who have a Nuss bar in place for pectus excavatum repair. These curved metal bars sit behind the sternum and are designed to push it forward. If a patient with a Nuss bar goes into cardiac arrest, chest compressions become complicated. Finite-element simulation has shown that the bar’s metallic stiffness dramatically reduces the chest wall’s ability to deform, meaning that far more force than normal could be needed to achieve the recommended compression depth of 5 centimeters.31PubMed Central. Efficacy of standard chest compressions in patients with Nuss bars This doesn’t mean CPR shouldn’t be performed, but rescuers should know it may be less effective, and patients with Nuss bars are sometimes advised to carry medical alert identification.
The Sternum Across Species
The sternum’s shape tells a story about how an animal moves. In birds, sternum shape is tightly linked to flight style. Researchers analyzing sterna across modern bird species found that a large sternum with a deep, forward-projecting keel is essential for powered flight. Deeper keels correlated with slower but more powerful flight, the kind used by birds that carry heavy prey or take off from water. Wider, flatter sternal borders were associated with fast-flapping species like songbirds, while narrower sterna turned up in runners and other ground-dwelling birds.32PubMed Central. The relationship between sternum variation and mode of locomotion in birds
The evolutionary history of the mammalian sternum is itself surprisingly complex. For a long time, the sternum was treated as a single structure in evolutionary terms. Recent work combining developmental biology, genetics, and paleontology has revealed that the sternum of modern mammals was actually assembled from at least two pre-existing elements: the sternal bands (which attach to the ribs) and the interclavicle (which connects to the collarbone). These were independent bones throughout most of the evolutionary history of the mammalian lineage and only became fused into a single structure relatively recently in evolutionary time.33Current Biology. The therian sternum at the lateral somitic frontier: Evolutionary origin and structural variation of a composite structure Meanwhile, fossils of a 260-million-year-old predatory synapsid called Gorgonops show a segmented sternum with a configuration strikingly similar to the one in modern mammals, suggesting that the multipartite sternal plan appeared far earlier in the mammalian family tree than previously believed.34Scientific Reports. The earliest segmental sternum in a Permian synapsid and its implications for the evolution of mammalian locomotion and ventilation
Forensic Age Estimation From the Sternum
Forensic scientists have long used the sternum to estimate a deceased person’s age, because its joints fuse on a loose but predictable schedule. The joint between the manubrium and the sternal body fuses at an average age in the mid-fifties for both sexes, but the range is enormous: some individuals fuse as early as 30, while others never fuse at all even into their eighties. The joint between the sternal body and the xiphoid process follows a similar pattern, with the youngest fused specimens observed around age 30 and some remaining unfused into the late seventies.35PubMed Central. Forensic age-at-death estimation using the sternal junction in Thai adults: an autopsy study That wide variability means the sternum is useful for narrowing down an age range but nowhere near precise enough to pin down a specific year of death. Forensic teams typically combine sternal fusion data with other skeletal markers like pubic symphysis morphology and cranial suture closure to triangulate a more confident estimate.