Most arthroscopies are conventionally done using a 30-degree scope (30DS), which gives good field of view. This is used both for diagnostic and therapeutic procedures. For certain procedures 70-degree scopes (70DS) are used where visualisation with a conventional 30DS is insufficient and an increased field of view is required around corners. There have been studies done in past which have compared field of view of a 30DS and a 70DS. There has been no study so far that has compared blind spot created directly in front of a 30DS and 70DS. The aim of this study was to determine and compare blind spot created while doing arthroscopy using a 30DS and a 70DS.

A small box with a cannula at one end held firmly using plaster of Paris in horizontal position was made. This box was used to help hold 30DS and 70DS firmly in position while doing calculations. A scale was positioned on front of the scope to calculate the size of blind spot created at various distances. The 30DS and 70DS scopes were placed directly in contact with the scale at 0mm to start and markings on scale were used to calculate the diameter of blind spot created at various distances by moving the scopes at 5mm increment.

Our study shows that with a 30DS there is no blind spot in the front. With a 70DS there is a significant blind spot that increases in size linearly as the distance of scope increases from the object in vision. It goes up to 4.4cm in diameter when the 70DS is at a distance of 5cm. The 70DS however provides a very wide field of vision was compared to 30DS.

A 70DS provides a very large field of view and gives excellent visualization of structures around corners, but also has a significant blind spot directly in front of the scope tip which can be as large as 4.4cm at a distance of 5cm from the object in vision. Knowledge of this will help surgeons while using a 70DS and help avoid any missed pathology.