Many WLS patients find it difficult to visualise how the gastric band works and how its interaction with the body can occasionally cause either loss of restriction or excessive restriction; this page (and the following one) aim to clarify the scenarios you may encounter.
Adjustable gastric bands come in about half a dozen different makes (e.g. the Swedish Adjustable Gastric Band or SAGB, Inamed's Lap-Band, MID's MIDband, Ethicon's RealizeBand, Cousin's BioRing, Helioscopie's Heliogast, etc.), but all are basically very similar and individual surgeons usually choose their preferred item based on familiarity and cost considerations; often marketing factors such as a good relationship with a particular company rep, or special pricing offers, are decisive. Of course if a surgeon experiences technical problems or materiel failures with a given product, he or she is likely to change manufacturers.


All AGBs consist of an inflatable ring (the actual "band") which is usually of one piece with the tube or catheter which eventually connects it to the (separate) access port. The band and tube part is generally made of medical silicone and also incorporates a flange which allows the surgeon to sling the open-ended band around the stomach and close it to form a ring shape. The port is made of a metal alloy or toughened plastic and also has a thick rubber membrane facing to the skin which can withstand at least a thousand perforations by specially designed needles (your fill provider should have a so-called "non-coring" Huber tip - ordinary needles are likely to cut out a tiny core of membrane material while penetrating it and so lead to leaks).


Whereas the gastric band is located around the top of the stomach inside the abdominal cavity, the tube or catheter part is led out through a small opening made by the surgeon, into the tissue layer underneath the outer muscle layer and skin but outside the abdominal cavity. The port component is also placed there, through a separate external incision (patients will have a small visible scar near it) and connected with the open end of the tubing or catheter - this is why, if necessary, the port can be replaced (or a disconnection corrected) under local anaesthesia. The port component usually incorporates quite a long outlet also made of metal or tough plastic, so that the connecting end of the soft silicone tubing is protected against inadvertent puncture if a needle misses the port. 


Because the port membrane is only about 3mm in diameter and very thick, and the port chamber underneath it quite small, any attempt to access the internal part of the system for a fill/defill will only succeed if the needle approaches the membrane at exactly the right angle  - even a few degrees of skew are likely to result in failure. This is why port access, especially in patients with a thick abdominal wall, can be quite challenging and may require several attempts. It can even happen that the port component turns over in its tissue pocket (often called a "flipped port"),   the port may then have to be operatively repositioned (usually under local anaesthesia).