A hematoma block is a type of local anesthesia where a numbing medication is injected directly into the pool of blood that forms around a broken bone. When a bone fractures, blood collects at the break site, creating a natural pocket called a hematoma. By injecting anesthetic into that pocket, the medication spreads along the fracture and numbs the surrounding nerves, allowing a doctor to realign the bone without putting you under general anesthesia or heavy sedation.
How a Hematoma Block Works
When a bone breaks, especially if the pieces shift out of alignment, blood leaks from the bone and surrounding tissue and pools around the fracture. This collection of blood is the hematoma. The key insight behind the technique is that this blood-filled space connects directly to the fracture line and the nerves running through it.
A doctor inserts a needle into that hematoma, typically from the back (dorsal) side of the limb, angled toward the fracture. To confirm the needle is in the right spot, they pull back on the syringe. If blood mixed with small fat droplets from the bone marrow comes back, they know they’ve reached the fracture hematoma. They then slowly inject the anesthetic, which spreads through the hematoma and temporarily blocks the nerves from sending pain signals. This preserves normal sensation and movement in the rest of the hand or limb while numbing only the fracture area.
When It’s Used
Hematoma blocks are most commonly used for displaced fractures of the distal radius, the bone on the thumb side of your forearm near the wrist. This is one of the most frequent fractures seen in emergency departments, often resulting from a fall onto an outstretched hand. When the broken bone pieces are angled or shifted, they need to be manually pushed back into alignment, a procedure called closed reduction. The hematoma block numbs the area enough for this to happen.
The technique is also used for other fractures near joints, including certain ankle fractures, where a natural hematoma forms and the bone needs repositioning before casting or surgical fixation. In some cases, it’s used before inserting pins through the skin to hold bone fragments in place.
What the Procedure Feels Like
The injection itself involves a brief needle stick near the fracture, which can be uncomfortable since the area is already tender. A standard approach uses about 10 to 20 mL of local anesthetic, often lidocaine, injected through a relatively thin needle. Once the medication is in, you’ll typically wait several minutes for the area to go numb. During the bone reduction, you may still feel pressure or a deep aching sensation, but the sharp pain is significantly dulled. Motor function and sensation in your fingers or toes are generally preserved throughout.
Hematoma Block vs. Sedation
The main alternative to a hematoma block is procedural sedation, where you receive intravenous medications that make you drowsy or briefly unconscious while the bone is set. Both approaches work about equally well at getting the bone back into proper alignment, with no significant difference in reduction failure rates between the two methods in either adults or children.
Pain during the actual manipulation is roughly comparable between the two approaches. Where the hematoma block shows a measurable advantage is afterward: patients who received a hematoma block reported less pain following the reduction compared to those who had sedation. Sedation, meanwhile, carries a higher rate of side effects like nausea, vomiting, and breathing difficulties, particularly in adults.
The practical differences are significant too. Sedation requires an IV line, monitoring equipment, fasting beforehand in some cases, and a recovery period while the medications wear off. A hematoma block requires none of that. For children with wrist fractures, studies have found that using a hematoma block produces alignment, pain control, and patient satisfaction comparable to sedation while significantly cutting down time spent in the emergency department.
Use in Children
Hematoma blocks are used in children as young as five for displaced wrist fractures. In a study of 52 children aged 5 to 16, those who received a hematoma block had outcomes equivalent to those who received sedation, with similar bone alignment before and after the reduction. Some children received a mild anti-anxiety medication alongside the block for comfort. Only one child in the study needed to be converted from a hematoma block to full sedation because the block didn’t provide enough relief. The reduced need for monitoring and shorter emergency department stays make it a practical choice in pediatric settings.
Safety and Risks
The most persistent concern about hematoma blocks, dating back to the 1980s, is that inserting a needle into a fracture site could introduce bacteria and cause a bone infection (osteomyelitis). In practice, this risk has proven very low. In one study of 42 fractures treated with a hematoma block, a single case of local skin infection occurred (about 2.3%), with no cases of deep bone infection. Multiple prospective studies over the years have found no infections at all. The fear of turning a closed fracture into something resembling an open one has not been supported by the clinical evidence.
A rarer but more serious concern is systemic toxicity from the anesthetic itself. Local anesthetics like lidocaine work by blocking nerve signaling. If too much enters the bloodstream, it can affect the brain and heart. Isolated case reports describe neurological symptoms like lightheadedness or, in rare instances, seizures after a hematoma block. These events are uncommon, and staying within established dosing limits minimizes the risk. The fracture hematoma is a confined, blood-rich space, which means the anesthetic can be absorbed into the circulation more readily than it would from a typical skin injection.
When a Hematoma Block May Not Be Appropriate
The technique depends on having a closed fracture with an intact hematoma around it. Open fractures, where the bone has broken through the skin, disrupt this contained blood pool and also raise the infection risk of inserting a needle into an already-exposed wound. Fractures that are several days old may also be poor candidates, since the hematoma begins to organize and harden over time, making it difficult for the anesthetic to spread effectively. In cases where multiple fractures need attention or the injury is too complex for a simple closed reduction, sedation or general anesthesia is typically a better fit.