Saphenous Nerve and Sural nerve injuries are a potential complication of all endothermal
treatments both endovenous laser and radiofrequency ablation.
This presentation discusses this problem.
It is mainly of concern to doctors, nurses and vascular technologists, but members of
the public mainly also find it of interest.
My own interest in this subject was stimulated by colleague and friend Dr Ted King in Chicago.
Ted has done a lot of clinical research on the saphenous nerve and sural nerve and their
anatomical relationship to the great saphenous vein and the small saphenous vein.
Ted has kindly helped to direct my reading of the medical literature and he has generously
shared the findings of his own research that was presented to the European Venous Forum
in June 2010.
Nerve injury may occur in over a third of laser treatments of the great saphenous vein
and nearly one in twenty small saphenous vein treatments.
A recent study from Germany has even suggested that saphenous nerve injury is more likely
after endovenous laser than after surgical stripping.
The study authors have proposed that in some cases the nerve may have been injured by the
needle during administration of the tumescent local anaesthetic.
Here are the mechanisms by which the nerve might possibly be injured.
Firstly, the nerve might injured by the needle during the cannulation of the vein itself.
This is probably very rare but it is possible that the nerve could be transected by the
needle.
Similarly, a needle stick injury might occur during the administration of local anaesthetic
causing a neurotemesis.
Finally, the thermal ablation could cause the direct transfer of heat energy to the
nerve causing a thermal neuropraxia -- a burn injury.
These are the possible strategies to avoid nerve injury.
Firstly, the nerve and vein can be imaged in transverse section to identify a site of
cannulation where the nerve and vein are sufficiently far apart to minimise the risk of thermal
energy transfer.
Secondly, the vein and nerve can be imaged in transverse section during the cannulation
to ensure that the vein is cannulated directly and that the needle tip does not impinge on
the nerve.
Thirdly, the nerve, vein and needle tip can be kept in view during tumescent anaesthetic
administration by scanning in transverse section at all times.
Lastly, the needle should be withdrawn immediately and the thermal ablation terminated immediately
if pain is felt in the sensory distribution of the nerve at risk.
In fact, performing these treatments under local anaesthetic is much safer than under
general anaesthetic for this very reason.
When pain occurs, the treatment should be terminated or the needle withdrawn, making
the possible risk of nerve injury less likely.
Here you can see that the saphenous nerve and the great saphenous vein are very close
and in contact in the distal calf.
The two lie within the saphenous fascia superficial to the tibia.
In this case the nerve lies anterior to the vein.
This would not be a good site for cannulation.
Even if the needle tip is kept in view and the vein is cannulated cleanly by which I
mean the needle tip is not allowed to stray near the nerve, it is likely that the nerve
would be injured by administration of local anaesthetic fluid.
As this video clip shows, distally the nerve and vein and nerve are in contact as the probe
moves more proximally, the vein and nerve are separated by 10mm or more.
The vein can be easily identified by the fact that it collapses flat with pressure from
the transducer probe.
The probe is moved proximally and distally . Here once again we can see the probe moving
more distally, and the vein and the nerve coming into contact with each other -- the
vein collapsing on pressure.
Here is the appearance of the Sural Nerve in relation to the small saphenous vein.
The anatomy and ultrasound appearance of the sural nerve have been very nicely described
by Ricci.
This video clip shows that further proximally the vein and nerve are separated by 10mm or
more.
As the probe moves more distally, the vein and the nerve are in close contact.
The vein here is collapsing on light pressure from the transducer probe showing that the
nerve and the vein are in contact here.
As the probe is moved more proximally, the vein and the nerve separate -- here by more
than a centimetre.
The nerves have an oval appearance and they are "speckled" with areas of hyper- and hypo
echogenicity.
The view of the nerve is improved by altering the angle of insonation and by using higher
frequency transducers.
This summary draws on Dr Kings conclusions presented to the European Venous Forum in
June 2010.
Identification of the Saphenous nerve and the Sural nerve and their zones of contact
with the great saphenous vein and the small saphenous vein can be accomplished with practice.
In the absence of ultrasound visualization of the nerve, the great saphenous vein should
be cannulated at a distance of no less than 19 cm above the medial malleolus and the small
saphenous no less than 26 cm above the plantar surface of the heel.
My practice is to visualise the nerve and vein in transverse section throughout the
cannulation procedure, thereby minimising the risk of needle stick injuries at this
stage as well as during the administration of tumescent local anaesthesia again ensuring
that the local anaesthetic solution is generously administered between the nerve and vein and
minimising the risk of direct needle injury to the nerve.
Well I hope you have found this video interesting.
Please share your opinion below and don't forget to subscribe.
Thank you for watching