A trocar is a hollow, pointed instrument used to puncture body cavities and create a channel for other tools, fluids, or gases to pass through. Its most common application today is in minimally invasive surgery, where it serves as the entry port for a camera and instruments during laparoscopic procedures. But trocars also play important roles in veterinary medicine, bone marrow biopsies, eye surgery, and embalming.
How a Trocar Works
At its simplest, a trocar has two main parts: a sharp inner rod (the obturator) that pierces tissue, and a hollow outer tube (the cannula) that stays in place after the puncture is made. Once the obturator is removed, the cannula acts as a stable tunnel into the body. A flexible valve sits on top of the cannula to prevent fluids or gases from leaking out while still allowing instruments to slide through. The valve needs to spring back shut each time an instrument is withdrawn, maintaining a tight seal with gaps smaller than 10 micrometers between the valve flaps.
Laparoscopic and Minimally Invasive Surgery
The most widespread use of trocars is in laparoscopic surgery, where surgeons operate through small incisions rather than opening the abdomen. The trocar creates a port, typically near the belly button, through which a camera and surgical instruments are inserted. Before surgery begins, the abdomen is inflated with carbon dioxide to give the surgeon room to see and work. The trocar’s seal keeps this gas from escaping, maintaining a stable pressurized space throughout the procedure.
There are two main approaches to placing the first trocar. In the open technique, the surgeon makes a small 1.5 to 2 cm incision, carefully cuts through layers of tissue, and then inserts the cannula under direct vision before inflating the abdomen. In the closed technique, a thin needle called a Veress needle is used to inflate the abdomen first, and then the trocar is pushed through the abdominal wall. Both methods are used routinely, though some surgeons prefer the open approach in patients who have had prior abdominal surgery or abdominal distention, where the risk of hitting internal structures is higher.
A newer option is the optical bladeless trocar, which has a clear tip that lets the surgeon watch through a camera as the trocar passes through each tissue layer. This direct visualization approach is significantly faster than the open technique, with entry times averaging about 72 seconds compared to 215 seconds. In a study of obese women undergoing laparoscopic surgery, the optical approach also resulted in less blood loss and showed a trend toward fewer minor injuries to surrounding tissue. Most laparoscopic procedures use multiple trocars, typically ranging from 5 mm to 12 mm in diameter, placed at different points across the abdomen so the surgeon can work from several angles.
Risks of Trocar Entry
The moment the trocar punctures the abdominal wall is one of the riskiest steps in laparoscopic surgery, because the sharp tip can potentially injure blood vessels or organs underneath. In obese patients, a meta-analysis found that entry-related vascular or organ injuries occurred in roughly 8 out of every 1,000 cases. Trocars equipped with optical viewing capability cut that rate considerably, with about 1 injury per 100 cases compared to 4 per 100 with non-optical devices. These numbers are small overall, but they explain why surgeons pay close attention to trocar design and insertion technique.
Eye Surgery
Miniature trocars are used in vitreoretinal surgery to access the interior of the eye. These work on the same principle as their larger counterparts: a tiny cannula is placed through the eye wall, and surgical instruments are passed through it. The valve on top is critical here because it prevents the fluid and gas inside the eye from leaking out, keeping intraocular pressure stable throughout the operation. Multiple trocars are typically placed so the surgeon can insert a light source, a cutting instrument, and an infusion line simultaneously.
Bone Marrow Biopsy
In hematology and oncology, a specialized trocar-style needle is used to collect bone marrow samples. The needle is designed to extract a cylindrical core of solid bone marrow tissue, usually from the back of the hip bone. This core sample allows doctors to examine the structure and cell composition of the marrow under a microscope, which is essential for diagnosing blood cancers, unexplained anemia, and other blood disorders.
Veterinary Emergency Use
In large animal medicine, trocars are used to relieve bloat in cattle and other ruminants. When gas builds up in the rumen and the animal cannot belch it out, the pressure can become life-threatening. A veterinarian inserts a trocar and cannula directly through the animal’s left flank into the rumen, releasing the trapped gas immediately. For severe cases involving thick, foamy gas, a larger-bore instrument (about 2.5 cm in diameter) is necessary because the standard size cannot vent the viscous foam quickly enough. The ideal insertion point is midway in the flank, about 5 to 10 cm below the bony projections of the lumbar spine.
Embalming and Mortuary Science
Outside of medicine, trocars are a standard tool in the funeral industry. During embalming, a long, pointed trocar is inserted through the abdomen to reach the thoracic and abdominal cavities. It serves two purposes: first, it aspirates gases and fluids from the organs and body cavities, with the sharp tip used to break up tissue so fluids can be removed effectively. Second, after aspiration is complete, concentrated embalming fluid is injected back through the same trocar to preserve and disinfect the internal cavities.
Disposable vs. Reusable Trocars
Modern surgical trocars come in both single-use disposable and reusable versions. Disposable trocars are made of plastic and are discarded after one procedure, which generates significant hospital waste from both the device and its packaging. Reusable trocars are made of metal with replaceable rubber valves and can be sterilized between cases. Their valves wear out faster than any other component, typically tearing at the rubber seal from repeated instrument insertion, which causes gas leaks during surgery.
Reusable trocars substantially reduce the cost of laparoscopic surgery without compromising patient safety, though they may require slightly more force during insertion. Many surgical departments now use a hybrid approach: reusable instruments as the standard, with a small backup stock of disposable ones available when technical problems arise.