Breaking a sternum takes serious force in a healthy adult. The flat, shield-like bone at the center of your chest is backed by ribs, cartilage, and layers of muscle, and it’s built to absorb and distribute impact. Sternal fractures account for roughly 3 to 8 percent of all blunt trauma cases, which tells you something about how uncommon they are relative to other fractures from high-energy events like car crashes. But the threshold isn’t fixed for everyone, and there are surprisingly common scenarios where the sternum cracks under loads most people wouldn’t expect.
What the Sternum Is Built To Do
Your sternum is a roughly six-inch-long bone that sits in the middle of your chest wall, connecting to the upper ribs through cartilage and forming a protective cage around the heart, lungs, and major blood vessels. It’s made of three parts: the manubrium at the top (where your collarbones attach), the body in the middle, and the small xiphoid process at the bottom. In adults, these segments are usually fused or connected by dense cartilage, giving the bone a blend of rigidity and slight flex.
That flexibility matters. A purely rigid structure would shatter under a sudden blow. Instead, the sternum bends slightly under load and transfers force outward through the rib cage. The surrounding muscles, especially the pectorals and intercostals, also absorb some energy before it reaches the bone. In a young, healthy person, the sternum can withstand substantial compressive force from the front. But as you age, the cortical bone thins and the marrow space changes composition, reducing the load the sternum can handle before it cracks.
Car Crashes Are the Leading Cause
Motor vehicle collisions are responsible for the majority of sternal fractures. The mechanism is straightforward: in a frontal crash, your chest decelerates against the seatbelt or the steering wheel, concentrating force directly over the sternum. What’s interesting is that seatbelts, while saving lives, have shifted the pattern of chest injuries. A case report documented a sternal fracture in a seatbelt-restrained passenger during a moderate-speed crash, even without contact with any hard surface inside the vehicle. The seatbelt itself delivered enough focused force to crack the bone.1PubMed. Case report: sternal fracture from a seatbelt
Modern vehicle safety systems have dramatically reduced severe and fatal injuries overall, but thoracic injuries like rib and sternal fractures haven’t declined at the same rate. Research into seatbelt design has found that newer cars are reducing injuries in several body regions, yet the effect doesn’t hold as clearly for the chest.2PubMed. The effect of seatbelt pre-tensioners and load limiters in the reduction of MAIS 2+, MAIS 3+, and fatal injuries in real-world frontal crashes Advanced belt load limiters, which allow the seatbelt to give slightly under peak force, can cut severe chest injuries substantially. Studies have shown that a belt load limited to about 4 kilonewtons can reduce the most serious thoracic injuries by 75 to 85 percent compared to an unrestricted belt.3STAPP Car Crash Conference. Comparison of Thoracic Injury Risk in Frontal Car Crashes for Occupant Restrained without Belt Load Limiters and Those Restrained with 6 kN and 4 kN Belt Load Limiters Still, not every vehicle on the road has that technology, and even with it, high-speed crashes can overwhelm any safety system.
CPR Breaks Sternums More Often Than People Realize
This one surprises most people. Cardiopulmonary resuscitation requires pressing hard and fast on the sternum, typically at a depth of about two inches, at a rate of around 100 to 120 compressions per minute. That’s a lot of repeated mechanical stress on a bone that may already belong to an older adult with weakened bone density. A study that looked at this systematically using post-mortem examinations found that chest compressions caused skeletal chest injuries in about 86 percent of men and 91 percent of women. Sternum fractures specifically occurred in roughly 59 percent of men and 79 percent of women who received CPR.4PubMed. Frequency and number of resuscitation related rib and sternum fractures are higher than generally considered
Those numbers are higher than what most medical professionals casually estimate, and they underscore an uncomfortable reality: effective CPR is inherently violent to the chest wall. The study also found that the percentage of patients injured and the number of injuries increased with age. Changes in resuscitation guidelines over the years, which have pushed for harder and deeper compressions to improve survival, may have contributed to the rising injury rates. None of this means CPR should be performed more gently. A cracked sternum is vastly preferable to dying of cardiac arrest. But it does mean that if someone survives CPR, chest pain from fractures is an expected and common aftermath rather than a rare complication.
Sports and Unusual Mechanisms
Outside of car crashes and CPR, sternal fractures show up in high-impact sports, though they’re rare enough that each case tends to get written up individually. A case series of elite-level athletes found sternal fractures in competitors from rugby, judo, show-jumping, and MotoGP motorcycle racing.5PubMed Central. Management of Vertical Sternal Fracture Nonunion in Elite-Level Athletes The fracture pattern in athletes can differ from the typical transverse crack seen in car crashes. Some athletes develop vertical sternal fractures from repeated axial loading or sudden muscular contraction forces, which are harder to detect and slower to heal. In those cases, the sternum isn’t overwhelmed by a single massive blow but gradually fails under repetitive stress that exceeds its ability to remodel.
Falls, particularly in older adults, are another common mechanism. A direct fall onto a hard surface or even a fall that transmits force through outstretched arms can sometimes fracture the sternum. For most healthy young people, though, the chest wall is resilient enough that everyday falls and impacts won’t come close to the breaking threshold.
Why Some People’s Sternums Break More Easily
Age is the single biggest risk factor. As cortical bone thins with age, the sternum becomes more vulnerable to fractures from forces that a younger person’s chest would absorb without issue. This is the main reason CPR causes sternal fractures in the majority of recipients, since most people receiving CPR are older adults. It’s also why the average age of sternal fracture patients in trauma studies tends to be in the early sixties.
Osteoporosis lowers the bar even further. A case report described a man on long-term steroid therapy who suffered a sternal insufficiency fracture from minimal trauma, meaning the bone broke under forces that wouldn’t normally be enough to cause a fracture.6PubMed Central. Sternal insufficiency fracture related to steroid-induced osteoporosis: A case report Steroid-induced bone loss is particularly insidious because it can affect relatively young people who wouldn’t otherwise be at risk. Insufficiency fractures of the sternum are diagnostically tricky because the patient often can’t recall a specific injury, and the pain gets attributed to something else.
Prior surgery through the sternum also changes the equation. Median sternotomy, the vertical cut through the sternum used in open heart surgery, is one of the most common major surgical incisions in the world. After the procedure, the sternum is wired back together, but it never quite returns to its pre-surgical strength. In a study of 288 consecutive sternotomies, about 8 percent resulted in sternal fractures, and the rate was significantly higher when an internal mammary artery was harvested during the surgery.7PubMed. Poststernotomy fractures and pain management in open cardiac surgery If the cut is even slightly off-center, the thinner side of the split sternum can fracture under the closing wires themselves.8PubMed. Faulty sternotomy and complications after median sternotomy In patients with osteoporotic bone, closing wires can cut through the sternum rather than holding it together, and surgeons sometimes use wider load-spreading techniques to avoid this.9European Journal of Cardio-Thoracic Surgery. A biomechanical study of median sternotomy closure techniques
How Sternal Fractures Get Diagnosed
Diagnosing a sternal fracture can be more complicated than you’d expect. A regular chest X-ray taken from the front often misses the fracture because the sternum is a flat bone that overlaps with the spine on that view. A lateral X-ray is better, and older data showed that plain lateral films could identify most sternal fractures. But imaging technology has moved on significantly. Modern multidetector CT scans with reconstructed images in multiple planes now offer accuracy around 97 percent for sternal fractures, compared to about 77 percent for lateral radiography.10PubMed. Sternal fracture in the emergency department: diagnostic value of multidetector CT with sagittal and coronal reconstruction images Older CT scanners without those reconstructions actually performed worse than plain films, which led to earlier research concluding that X-rays were superior.11PubMed. CT findings of sternal fracture
An emerging option, particularly in emergency settings, is point-of-care ultrasound. Ultrasound can detect cortical disruption at the sternal surface quickly and without radiation. In pediatric cases following indirect trauma, ultrasound identified fractures immediately and allowed management without additional imaging.12PubMed. Faster diagnosis, smarter care? Point of care ultrasound for pediatric sternal fractures secondary to indirect trauma: a case series There are even case reports of ultrasound detecting sternal fractures that CT missed entirely.13Journal of Emergency Medicine Case Reports. Detection of Sternum Fracture with POCUS Despite Normal Computed Tomography Findings: A Case Report The limitation is that ultrasound is operator-dependent, so its accuracy depends heavily on who’s holding the probe.
The Real Worry With a Broken Sternum
A sternal fracture by itself is painful but rarely dangerous. The real concern is what else might be injured. The heart sits directly behind the sternum, and any force strong enough to crack the bone could potentially bruise the heart muscle. Blunt cardiac injury ranges from mild bruising that causes transient abnormalities on an electrocardiogram to serious damage that can affect heart function.
But the risk of significant cardiac injury depends a lot on the type of sternal fracture. When the sternum breaks in combination with other chest injuries like pulmonary contusions, broken ribs, or hemothorax, the picture is more worrisome. A study of 380 sternal fracture patients found blunt cardiac injury in about 5 percent of cases, and these patients tended to have higher overall injury severity and concurrent lung injuries. Pulmonary co-injuries were the strongest predictor of cardiac damage.14PubMed Central. Blunt Cardiac Injury in Patients With Sternal Fractures
By contrast, when the sternal fracture is isolated, meaning no other significant injuries, the risk of meaningful cardiac damage drops dramatically. In a study of 88 patients with isolated sternal fractures, no cases of clinically significant cardiac injury were identified, even though blood markers were drawn in the majority of patients.15PubMed Central. The Association between Blunt Cardiac Injury and Isolated Sternal Fracture This distinction matters for clinical decision-making: a person who walks into the emergency room after a minor crash with a sore sternum and no other injuries is in a very different risk category than someone pulled from a high-speed wreck with multiple chest injuries.
Retrosternal hematoma, a collection of blood behind the sternum, is another sign that raises the level of concern. Research has found that the presence of a retrosternal hematoma on CT significantly increases the odds of having a concomitant chest injury, with an odds ratio above five. Fractures of the manubrium, the thicker upper segment, are also associated with higher rates of additional injury.
Treatment and How Long Recovery Takes
The vast majority of sternal fractures heal on their own with conservative management: pain control, activity modification, and time. A 13-year retrospective study found a treatment failure rate of only about 1 percent, and failures were actually more common in the group that underwent surgical treatment, suggesting that operating on simple sternal fractures doesn’t improve outcomes and can introduce its own complications.16PubMed Central. Traumatic Sternal Fractures can be Safely Treated Conservatively – A 13-Year Retrospective Cohort Study In a systematic review of treatment outcomes, all patients eventually showed sternal healing, and 98 percent reported pain relief.17PubMed Central. Current treatment and outcomes of traumatic sternal fractures-a systematic review
Typical healing time is around 10 to 12 weeks, though the first few weeks are the most uncomfortable. Deep breathing, coughing, laughing, and rolling over in bed can all produce sharp pain at the fracture site. Adequate pain control matters not just for comfort but because people who can’t take deep breaths due to chest pain are at risk for lung complications like pneumonia.
Surgery gets reserved for cases with significant displacement, overlap of the fracture fragments, or instability that isn’t resolving. The fixation approach has evolved; plates are more commonly used than wires for traumatic sternal fractures. Fixation of sternal fractures occurs in a small minority of cases overall, estimated at 3 to 8 percent of blunt trauma patients who sustain the fracture, with most of those healing without surgical intervention. A survey-based study found that patients who did undergo sternal fixation reported better long-term quality of life across most domains compared to those managed without surgery, though the difference in anxiety and depression scores was not significant.18PubMed. Sternal fixation for traumatic sternal fractures demonstrates better long-term quality of life outcomes than nonoperative management: A survey analysis The catch is that patients selected for surgery tend to have more displaced or complicated fractures, so the comparison isn’t apples-to-apples.
When Healing Goes Wrong
Most sternal fractures heal without lasting problems, but a small percentage develop nonunion or malunion. Nonunion means the fracture doesn’t bridge with new bone, typically diagnosed when a fracture shows no healing progress after three to six months. The hallmark symptoms are persistent pain that worsens with deep breathing or coughing, and a clicking sensation at the fracture site when the two halves move against each other.19PubMed Central. Traumatic sternal fractures: a narrative review Malunion is when the bone heals but in the wrong position, leaving a noticeable step-off that you can sometimes feel through the skin.
Both conditions can require operative repair if they’re causing significant pain or functional limitation. The surgery typically involves debriding the nonunion site, realigning the fragments, and fixing them with plates. While the outcomes are generally good, the procedure itself is morbidity-prone because the sternum has limited blood supply and sits over the mediastinum, making infection a serious concern.20PubMed Central. Late complications of chest wall reconstruction: management of painful sternal nonunion Elite athletes face a particular challenge with sternal nonunion because their sport often involves exactly the kind of repetitive loading that prevents healing. The athletes treated in one case series all required surgical fixation and a prolonged period away from competition before returning.5PubMed Central. Management of Vertical Sternal Fracture Nonunion in Elite-Level Athletes
Sternal Fractures in Children
Children’s sternums are more flexible than adults’, which is both protective and deceptive. The cartilaginous component of a child’s chest wall is proportionally greater, making the sternum more pliable under impact. This means it takes more force to fracture the bone, but it also means that force can transmit through the sternum to the heart and lungs without leaving an obvious external sign of injury. When a child does sustain a sternal fracture, it often results from indirect mechanisms rather than direct blows. Ultrasound has shown promise as a first-line diagnostic tool in pediatric sternal fractures, partly because it avoids radiation exposure and partly because the thinner soft tissue in children makes the sternal surface easier to visualize.12PubMed. Faster diagnosis, smarter care? Point of care ultrasound for pediatric sternal fractures secondary to indirect trauma: a case series In the reported cases, all children recovered fully with conservative management and had no complications at follow-up.
The relative rarity of pediatric sternal fractures means that when one is found, clinicians tend to look more carefully for underlying causes. A sternal fracture in a child from a low-energy mechanism raises questions about bone health, and in some contexts, about the possibility of non-accidental injury. The index of suspicion and the workup differ meaningfully from the adult population, where the mechanism is usually obvious.
Why the Sternum Looks the Way It Does
The human sternum is broader and flatter than what you’d find in most primates, and that shape traces back to how our ancestors moved. Comparative studies of primate skeletons have found that the manubrium and sternum body are broader in apes and humans than in monkeys, correlating with the wider, barrel-shaped rib cage that evolved alongside upright posture and suspensory locomotion.21PubMed. Manubriosternal Morphology of Anthropoid Primates Even among monkeys, the species that hang and swing from branches tend toward wider sterna and rib cages, supporting the idea that sternal shape tracks locomotor style.22The FASEB Journal. Sternum Morphology and Locomotor Adaptation in Anthropoid Primates The broad, flat sternum we ended up with is well-suited to distributing forces across a wide chest wall, which happens to be useful both for absorbing frontal impacts and for providing a stable anchor for the muscles involved in arm movement and breathing. It’s an evolutionary legacy that, incidentally, makes the bone harder to break than a narrower or thinner alternative would be.