Task Analysis Of Baseball Diamond Concept For Port Position In Laparoscopy

DR.D. PARIVALLAL
FMAS  + DMAS


The first technique to learn in laparoscopic surgery is the BASEBALL DIAMOND CONCEPT FOR PORT POSITION IN LAPAROSCOPY.  Common problem beginners encounter is where should port to be inserted.  If one port in the wrong position, the surgeon will struggle throughout the surgery due to bad Ergonomics.  The wrong port position is one of the most common causes of stressful surgery and may lead to conversion and complications.

There are 3 principles in baseball diamond concept

FIRST PRINCIPLE:

Laparoscopic instruments work on lever action.  Generally, all laparoscopic instruments should behave like type 1 lever ( half of the instruments should be in and half out). It means fulcrum in center and load is equal and opposite to the force applied. In type 2 lever, a fulcrum is very close to loading arm i.e., port very near to target of dissection hence the maximum length of the instrument is outside which results in tissue tear and avulsions. In type 3 lever.  fulcrum is very close to forcing arm i.e., port very far from the target of dissection hence the maximum length of the instrument is inside the body which results in overshooting. 

ELEVATION  ANGLE:

It is defined as an angle between the instruments and body of the patient. Elevation angle Ideally should be 60 degrees.
If the port is very close to the target of dissection ( type 2 lever), elevation angle will be 90 degrees then surgery cannot be performed as an instrument will not lift the tissue.

If the port is very far from the target of dissection (type 3 lever), elevation angle will be less than 10 degrees then the handle of the instrument will touch the body of the patient. 

Steps  to achieve the 1st principle\:
Step 1: Find out the target of dissection, for example, calot’s triangle in cholecystectomy
Step 2: Choose the correct length of instruments
Pediatrics: 28 cms
Adult: 36 cms
Morbid Obese: 45 cms 
Step 3: keeping the target at the center, draw 2 arc
1st arc 18cm from the target
2nd arc 24 cm from the target

SECOND PRINCIPLE

The telescope should be in the middle of working instruments.

AZIMUTH ANGLE:

It is defined as the angle between the telescope and working instruments i.e., contralateral port position. Ideally, it should be 30 degrees ( normal range 15 to 45 degree)

Benefits:

Linear parallax – Depth perception will be good
Motion parallax – object near will appear to move more and vice versa
Relative size – object far will appear to be small and vice versa
Aerial gradient – object near will appear to have better contrast and color
Texture gradient – near object appear to have detailed surface
Correct shadow – shadowing as the cue for depth

THIRD PRINCIPLE

MANIPULATION ANGLE:

It is defined as the angle between two working hand instruments should be 60 degrees +/- 15 degree

Steps  to achieve the 3rd principle

After creating the Pneumoperitoneum, Put the tip of the index finger over the target of dissection and put the tip of thumb over the site of telescope. Position of anatomical snuffbox will give a rough estimation of working port position on both sides in adults.