Is there an increased risk of nitrogen narcosis when scuba diving with a syndesmosis injury that is not healing?

No: But there is a chance of worsening a non-healing injury.

No: The development of nitrogen narcosis is related only to depth and bottom time in air breathing divers, and to depth, time and gas mix in nitrox divers. Your syndesmosis is not a factor.

Agree with the : Physiology described by dr. Nichol. This injury would have no impact on nitrogen narcosis. I would question the wisdom of diving with an unhealed injury. Have you had surgery on that ankle? If yes, that would be even more reason not to be diving - unhealed surgical site.

Not really: Nitrogen narcosis happens from breathing high partial pressures of Nitrogen. This can occur from diving to depths usually more than 100 FSW (feet of sea water) while still breathing air which is 79% Nitrogen. It has nothing to do with this or other musculoskeletal injuries.

Nitrogen narcosis: short answer is no. The narcosis had to do with time at a certain depth while breathing nitrogen rich gas such as normal air (21%Oxygen, 79%Nitrogen). Diving other enriched oxygen mixtures mitigate that risk but limits within certain other limits.