Sternal nonunion, where the breastbone fails to heal after being surgically divided or fractured, carries real and sometimes serious dangers. Though it is relatively uncommon, it is linked to a high rate of ongoing health problems, with chronic pain and audible clicking being the complaints that most often drive patients to seek help.​ The risks extend well beyond discomfort, however. An unstable sternum can set the stage for deep wound infections, impair breathing mechanics, and in rare cases involving broken fixation wires, even threaten the heart and major blood vessels.
What Sternal Nonunion Actually Means
The sternum is the flat bone running down the center of your chest, and surgeons routinely split it lengthwise during open-heart procedures (a median sternotomy). After surgery, the two halves are wired back together and expected to fuse over several months. When that fusion never happens and the bone edges remain separated by fibrous tissue instead of new bone, the result is sternal nonunion. The same thing can happen after a traumatic sternal fracture that fails to knit. In either case, the chest wall loses a critical piece of its structural integrity, and that instability is the root of nearly every complication that follows.
Who Is Most at Risk
Several patient-level and surgical factors raise the odds that the sternum won’t heal properly. Diabetes, emergency surgery, and the need for a return trip to the operating room all increase the chance of postoperative sternal complications, including nonunion, wound breakdown, and infection.1PubMed. Effectiveness of Various Sternal Closure Devices Post Adult Cardiac Surgery Age matters too. A study looking at sternal healing in otherwise low-risk patients found that being older than 45 roughly doubled the predicted risk of the sternum remaining ununited on imaging.2PubMed Central. Analysis of sternal healing after median sternotomy in low risk patients at midterm follow-up
Obesity, chronic obstructive pulmonary disease, osteoporosis, and heavy coughing after surgery are also commonly cited contributors. Anything that puts repeated mechanical stress on the healing bone or compromises blood supply and tissue repair can tip the balance from slow healing to no healing at all. Even the material used to control bone bleeding during surgery can play a role, as discussed later in this article.
Pain, Clicking, and the Toll on Daily Life
The most immediate and consistent danger of sternal nonunion is chronic pain. When the two halves of the sternum shift against each other during routine movements like reaching overhead, rolling in bed, or coughing, the result is a grinding or clicking sensation that patients describe as deeply unsettling. Pain and sternal clicking are the two most common reasons people with nonunion seek evaluation and treatment, and the condition is associated with a high rate of ongoing illness and disability.3PubMed Central. Late complications of chest wall reconstruction: management of painful sternal nonunion
A large survey of cardiac surgery patients gives some sense of how often these symptoms come up. Of nearly 2,000 respondents, about 2.3% reported a sensation of movement or clicking in their sternum during body movements or coughing. Having tenderness when the sternum was pressed was strongly linked to these symptoms.4Thoracic and Cardiovascular Surgeon. Symptoms of Sternal Nonunion Late after Cardiac Surgery What makes this data interesting is that none of those symptomatic patients actually had a clinically unstable sternum or confirmed nonunion on imaging. That suggests the line between incomplete healing that causes symptoms and full-blown nonunion is blurry, and that even partial instability can reduce quality of life.
The pain often becomes self-reinforcing. People guard their chest, avoid deep breathing, and limit upper-body activity, which can lead to deconditioning, stiffness, and loss of independence. For someone who has just been through major cardiac surgery, these restrictions layer on top of an already difficult recovery.
The Infection Risk, Including Mediastinitis
An unstable sternum is not just a mechanical problem. The constant micro-motion between bone fragments creates an environment where bacteria can gain a foothold, and what starts as a superficial wound issue can progress into something far more dangerous. Instability of bone fragments predisposes a patient to nonunion and malunion, and can subsequently lead to deep sternal wound infections that progress to mediastinitis, an infection of the tissues in the central chest cavity.5European Journal of Cardio-Thoracic Surgery. Primary sternal plating in high-risk patients prevents mediastinitis
Mediastinitis after cardiac surgery is one of the most feared complications in the field. It can involve the space around the heart, great vessels, and trachea, and historically has carried mortality rates in the range of 10 to 25 percent depending on the series. Treatment typically requires surgical debridement, prolonged intravenous antibiotics, and sometimes reconstruction with muscle flaps. Preventing sternal instability in the first place is one of the key strategies surgeons use to keep this complication from developing.
Broken Wires and Threats to the Heart
When steel wires are used to close the sternum and the bone fails to unite, the ongoing motion can fatigue and eventually snap those wires. Broken sternal wires are not always benign leftovers. In rare but dramatic cases, wire fragments can migrate. One reported case involved a fractured sternal wire segment that punctured the heart, traveled to the right lung, and eroded into a bronchus, causing massive coughing up of blood.6PubMed. Intravascular migration of fractured sternal wire presenting with hemoptysis
In another case, a patient with broken sternal wires and an unstable sternum developed bleeding around the heart from a penetrating injury caused by a jagged wire fragment. Surgical re-opening revealed a 3.5-centimeter laceration on the right ventricle that corresponded to where a fractured wire was projecting into the pericardial space.7PubMed Central. Fractured sternal wire causing a cardiac laceration That report emphasized that patients with broken wires and an unstable sternum need careful evaluation because these situations can become life-threatening if left untreated.
These cases are genuinely rare, but they underscore a broader point: sternal nonunion is not a static condition. Metal hardware under cyclic stress will eventually fail, and when it does, the consequences can escalate unpredictably. Any new chest pain, unexplained bleeding, or change in symptoms in someone with known sternal instability warrants prompt medical attention.
How Sternal Nonunion Affects Breathing
The sternum anchors the ribs and provides the rigid front wall of the chest that your respiratory muscles push against when you breathe. When that anchor is loose, the mechanics of breathing change. Paradoxical motion, where the unstable segment moves inward during inhalation instead of outward, reduces the efficiency of each breath. This is especially problematic for patients who already have reduced lung function from cardiac disease, obesity, or COPD.
Data from patients with sternal fractures who underwent surgical fixation shows that respiratory complications like pneumonia and respiratory insufficiency can occur in about a fifth of cases even when the bone is successfully stabilized.8European Journal of Orthopaedic Surgery & Traumatology. Osteosynthesis of sternal fractures with double locking compression plate fixation In patients whose sternum never heals and who can’t generate an effective cough, the risk of retained secretions and lower respiratory tract infections is a persistent concern throughout recovery and beyond.
Diagnosing the Problem
Sternal nonunion is diagnosed through a combination of history, physical exam, and imaging. The hallmark physical finding is palpable motion at the sternal edges when gentle pressure is applied. Patients often describe clicking with certain movements, and pressing on the sternum reproduces their pain. Confirmation comes from imaging: plain chest X-rays can show a persistent gap or wire displacement, while CT scans offer much more detail about the degree of separation, the presence of bone bridging, and any associated soft tissue abnormality.3PubMed Central. Late complications of chest wall reconstruction: management of painful sternal nonunion
One diagnostic wrinkle is that sternal healing after sternotomy is surprisingly slow even under normal circumstances. In a randomized trial comparing closure methods, only about a quarter of patients closed with conventional wire had evidence of sternal union at six months.9The Annals of Thoracic Surgery. Sternal Closure With Rigid Plate Fixation Versus Wire Closure: A Randomized Controlled Multicenter Trial That means imaging done “too early” can make normal slow healing look like nonunion, complicating decisions about whether and when to intervene.
Surgical Treatment Options
When sternal nonunion causes significant symptoms or poses infection risk, surgical repair is the definitive treatment. The approach generally involves re-opening the chest, clearing away the fibrous tissue between the bone edges, freshening the bone surfaces, and securing them with more robust fixation than the original wire closure provided.
Rigid plate fixation has become the leading method for both preventing and treating sternal nonunion. In one series, 14 patients who received titanium plates for established nonunion all went on to heal their sternums without developing mediastinitis.10PubMed. Rigid fixation for the prevention and treatment of sternal complications Another approach adds autologous bone graft, harvested from the patient’s own iliac crest, to the plating procedure. A case series using this combination reported lasting results with no patients requiring further intervention after an average follow-up of 18 months.11PubMed Central. Sternal fixation and autologous bone grafting for post sternotomy non-union
The decision to operate is a balance between the severity of symptoms and the risks of another chest surgery. For patients with mild clicking but no pain or instability, observation may be reasonable. For those with chronic pain limiting daily activity, recurrent infections, or evidence of wire migration, repair is usually the right call.
Does the Original Closure Method Matter
Quite a bit, as it turns out. The traditional approach of twisting steel wires around the sternal halves has been the standard for decades, but it has known limitations. Wires concentrate force along a narrow line of contact with bone, which can lead to the wire cutting through soft or osteoporotic bone over time.
Rigid plate fixation distributes force more evenly and holds the bone edges more securely. A multicenter randomized trial found that patients closed with rigid plates had sternal union rates of about 80% at six months, compared with roughly two-thirds of those closed with wire. Sternal complications through six months occurred in none of the plate patients versus 5% of wire patients.12Journal of Thoracic and Cardiovascular Surgery. Randomized, multicenter trial comparing sternotomy closure with rigid plate fixation to wire cerclage Sternal wound infections also trended lower with plates. Despite a slightly higher upfront cost for the hardware, total costs through six months were similar between the two approaches because the plate group had fewer complications and re-interventions.
An earlier, smaller trial showed an even starker gap at six months: 70% union with plates versus 24% with wire.9The Annals of Thoracic Surgery. Sternal Closure With Rigid Plate Fixation Versus Wire Closure: A Randomized Controlled Multicenter Trial These findings have gradually shifted surgical practice, particularly for patients at higher risk of healing problems, though wire closure remains common because it is fast, cheap, and adequate for many patients.
When Surgery Is Not the Right Move
Not every case of sternal nonunion leads to the operating room. For traumatic sternal fractures, non-operative management with pain control, breathing exercises, and gradual activity is sometimes preferred, particularly if the fracture is minimally displaced and the patient is not in respiratory distress. A large propensity-matched comparison found that patients managed without surgery after sternal fracture had shorter hospital stays but a higher mortality rate than those who underwent surgical fixation, at roughly 11% versus about 3%.13European Journal of Trauma and Emergency Surgery. Comparison of surgical fixation and non-operative management in patients with traumatic sternum fracture Interpreting that difference requires caution, because the surgical group was likely selected for reasons that also affected their outcomes, but the data suggest that leaving significantly unstable fractures alone is not without cost.
For post-sternotomy patients with mild symptoms, conservative strategies include wearing a sternal support vest, modifying activities to reduce stress on the chest, and managing pain with medication. Traditional sternal precautions, the familiar instructions to avoid pushing, pulling, or lifting more than a few pounds, are meant to protect the healing bone. But there is a growing recognition that overly strict activity restrictions may themselves contribute to long-term functional impairment. A review of the literature found that many patients remain functionally limited well after surgery, and suggested that some of those restrictions may be doing more harm than good.14PubMed Central. Sternal Precautions: Is It Time for Change? Precautions versus Restrictions – A Review of Literature and Recommendations for Revision The trend in cardiac rehabilitation is toward guided, individualized activity progression rather than blanket prohibitions.
Managing Chronic Pain After Sternotomy
For some patients, pain persists long after the bone has healed or been repaired, a condition increasingly recognized as chronic post-sternotomy pain syndrome. The pain may be skeletal, related to residual instability or hardware irritation, or neuropathic, caused by nerve damage sustained during surgery. Regional anesthesia techniques such as thoracic epidural analgesia and thoracic paravertebral blocks can reduce acute pain and opioid use in the early postoperative period, though the evidence on whether they prevent chronic pain is mixed. Newer options including erector spinae plane blocks, parasternal blocks, peripheral nerve stimulation, and cryoneurolysis (freezing targeted nerves) show promise but still need more study.15Current Pain and Headache Reports. A Review of Chronic Post-Sternotomy Pain Syndrome
This is an area where the science is still catching up with clinical need. Patients who develop chronic sternal pain after nonunion repair, or after wire removal, sometimes cycle through multiple analgesic strategies before finding adequate relief. A multimodal approach combining physical therapy, targeted nerve procedures, and judicious medication use tends to work better than any single intervention.
Why Bone Wax Deserves a Mention
One underappreciated contributor to sternal nonunion is bone wax, a material surgeons sometimes apply to cut bone surfaces to stop bleeding during sternotomy. An animal study comparing bone wax to a resorbable polymer alternative found that bone wax completely prevented new bone formation. X-rays showed nonunion in the bone wax group versus normal healing in the polymer group, and the polymer-treated bone was roughly twice as strong mechanically.16The Annals of Thoracic Surgery. The effects of a soluble polymer and bone wax on sternal healing in an animal model Histology showed only fibrotic scar tissue where bone wax had been applied, with no new bone growing at all.
This finding has practical implications for patients heading into cardiac surgery. If you have risk factors for poor healing, it may be worth discussing with your surgeon whether bone wax alternatives are available. Many centers have already moved toward resorbable hemostatic agents for exactly this reason, but the practice is not yet universal.