Cannula & Obturator

Arthroscope, or for that matter any endoscope, is a delicate device. It needs to be protected against all damaging forces that it might encounter. Precisely for this reason, the Arthroscope should not be inserted through small incisions directly. To enable the entry of scope without damaging, it is inserted inside a Cannula. Cannula is a hollow, tube that can accommodate the scope inside it.

At the start of procedures, a small incision of 2-3mm is made in the skin and then this incision is deepened to reach the interiors of the capsule using combination of cannula and obturator/trocar. Obturator/Trocar are solid rods with blunt/sharp tip respectively. Generally, obturator/trocar are slightly thicker in diameter than the Arthroscope. Either obturator/trocar is inserted in the cannula and this assembly is pushed through the shallow incision in skin to pierce the muscles, other soft tissue and finally the capsule. Once the assembly has reached and is communicating with the joint space, obturator/trocar is disengaged from the cannula and withdrawn, leaving the cannula in place. Now, the scope is inserted in place of obturator and the procedure is carried out.

In the earlier years, trocar was preferred because of the ease it offers while piercing the joint. Over the years, though, use of trocar is avoided and an obturator is used instead. The explanation for this shift is that the sharp tip of the trocar causes much more damage to the soft tissue while piercing than the blunt tip of obturator.

In addition to protection of scope, the cannula also performs another vital function and this is to provide irrigation. This irrigation is nothing but the fluid that distends the joint during surgical procedure and also helps clean up the debris. It washes the joint. Cannula allows the inflow/outflow of fluids from the joint. Cannula/Sheath (as it is commonly called among surgeons) comes with built-in valves. These valves provide for the attachment of tubing for irrigation. The irrigation fluid flows in the space that is present in between the inner wall of cannula and the outer wall of scope.