A trocar is a pointed medical instrument designed to puncture body cavities and create an access point for draining fluid, releasing gas, or inserting surgical tools. It consists of two main parts: a sharp inner rod called an obturator that does the piercing, and a hollow outer sleeve called a cannula that stays in place after the obturator is removed. The spelling “trochar” is a common variant, but “trocar” is the standard medical term. While most people encounter the word in the context of laparoscopic surgery, trocars are also used in veterinary emergencies and in mortuary science.
How a Trocar Works
The basic principle is simple. The sharp obturator punches through tissue, and the cannula acts as a tunnel that keeps the opening from collapsing. Once the obturator is withdrawn, the hollow cannula provides a stable port for passing instruments, cameras, or fluids in and out of the body. A snap-lock mechanism holds the two pieces together during insertion so they don’t separate at the wrong moment.
In laparoscopic surgery, trocars also need to maintain an airtight seal. The abdomen is inflated with carbon dioxide gas to create working space for the surgeon, and any air leak would cause the cavity to deflate. Modern trocars use rubber valves and, in some designs, inflatable balloons at the tip to keep gas from escaping. Over time, these valves can wear out and tear, especially with repeated insertion and removal of instruments, which is one reason many hospitals use single-use disposable trocars.
Trocar Sizes
Laparoscopic trocars come in eight marketed size categories: 3, 3.5, 5, 8, 10, 11, 12, and 15 millimeters. The number refers to the inner diameter of the cannula, which determines what instruments can fit through it. A 5 mm trocar is common for a camera or small grasping tool, while a 12 mm port allows larger instruments or the removal of tissue specimens.
The actual dimensions are somewhat larger than the label suggests. A study measuring trocars sold in North America found that 5 mm ports had a true inner diameter averaging 6.2 mm and an outer diameter of 8.5 mm, while 12 mm ports averaged 13.0 mm on the inside and 15.2 mm on the outside. The skin incision needed is larger still: about 13 mm for a “5 mm” port and roughly 24 mm for a “12 mm” port. Trocars marketed in the same size category from different manufacturers can vary enough to affect which instruments fit through them and how large an incision the surgeon needs to make.
Bladed Versus Bladeless Designs
The sharpened tip of a trocar comes in two main styles. Bladed trocars have a small cutting edge that slices through tissue layers. Bladeless trocars use a conical tip that pushes and separates tissue fibers rather than cutting them. The theory behind bladeless designs is that spreading tissue apart rather than cutting it should leave a smaller wound and lower the risk of hernias forming at the port site later.
The clinical evidence is mixed. One large review found that port-site hernias occurred in 1.5% of cases using 12 mm bladed trocars compared to just 0.12% with bladeless ones. A meta-analysis of eight randomized trials involving 720 patients found significantly less bleeding with bladeless trocars. However, bladeless ports require more force to push through the abdominal wall, which some surgeons find harder to control. And at least one animal study found no meaningful difference in the size of the tissue defect left behind by the two designs.
How Trocars Enter the Abdomen
Getting the first trocar safely into the abdomen is the most critical step in any laparoscopic procedure, because the surgeon is working without a camera view at that point. There are two main approaches.
In the closed technique, the surgeon first inserts a thin needle (called a Veress needle) through a small incision near the belly button. Carbon dioxide flows through this needle to inflate the abdomen. A low initial gas pressure below 10 mmHg with a free flow of gas confirms the needle is in the right place. Once the abdomen is inflated, the needle is removed and the first trocar is pushed through the same incision.
In the open technique, sometimes called the Hasson technique, the surgeon cuts through the abdominal wall layer by layer, visually confirming entry into the abdominal cavity before placing the trocar. No sharp instruments pass blindly into the body. Most surgeons (about 77% in one survey) prefer this open approach for its perceived safety, though neither method has been established as a definitive gold standard.
A third option, the optical trocar, includes a built-in window at its tip. The surgeon places a tiny camera inside the trocar and watches on a screen as the instrument passes through each tissue layer, rotating it gently with steady pressure. This lets the surgeon see exactly when the trocar enters the abdominal cavity.
Risks of Trocar Insertion
Trocar-related injuries are uncommon but can be serious. Data from a Finnish study found an overall rate of major trocar injuries at 1.4 per 1,000 procedures. Intestinal injuries occurred in about 0.6 per 1,000, urological injuries in 0.3 per 1,000, and vascular injuries in 0.1 per 1,000 cases. Major vascular injury, the most feared complication, has been reported at rates between 0.2% and 0.5% across studies, with the aorta, iliac arteries, and vena cava being the most commonly affected vessels. The risk is higher in very thin patients because there is less distance between the abdominal wall and major blood vessels.
Bowel injuries are particularly dangerous because they often go unrecognized during the procedure itself, delaying diagnosis. Port-site hernias, where tissue bulges through the hole left by a trocar, are another known complication, especially with larger 12 mm ports.
Disposable Versus Reusable Trocars
Disposable trocars are made of plastic and used once. Reusable trocars are typically stainless steel and can be sterilized between procedures. Disposable models offer consistent sharpness and a fresh seal every time, but they generate medical waste and cost more per procedure. Reusable trocars are more economical over time, though their valves wear out and may need replacement, and they can require more insertion force as they age.
Re-sterilizing single-use trocars to save money is generally not recommended because their design makes it difficult to fully clean internal spaces, creating an infection risk. Many surgical departments use a hybrid approach: reusable instruments as the default, with disposable backups available when a reusable trocar has a technical problem during a case.
Trocars Outside of Surgery
Trocars play a role well beyond the operating room. In veterinary medicine, a trocar and cannula are used as emergency treatment for bloat in cattle. When a cow’s rumen fills with trapped gas and distends dangerously, a veterinarian (or in a true emergency, a farmer) punctures the animal’s flank with a trocar to release the pressure. The procedure takes seconds in a crisis and can be lifesaving. The cannula is left in place afterward to allow continued gas escape. The main risk is contamination of the abdominal cavity with stomach contents if the trocar is placed incorrectly, which can lead to peritonitis.
In mortuary science, a specialized trocar is used during the embalming process. This version is a long, pointed, hollow tube inserted into the chest and abdominal cavities to aspirate internal gases and fluids. Preserving fluid is then distributed through the same instrument to reach all the body’s cavities evenly.