Table 2.

Micro-anatomical characteristics of key fascial planes and their potential relevance to regional anesthesia

Fascia	RA technique of interest	Mean thickness and structure	Mean HA content (µg)	Nerve fibers
Fascia lata	Fascia iliaca block	805 to 944 µm with anterior to posterior thickness gradient	35.4 ± 3	+
Pectoral fascia	Interpectoral plane block Pectoserratus plane block	297 µm with cranio-caudal thickness gradient	NI	+
Rectus sheath	Rectus sheath block	densely packed fibrous bundles interspersed with small amounts of adipose tissue	29.1 ± 0.2	NI
Fascia transversalis	Transversalis fascia plane block Quadratus lumborum plane block	thin layer composed by an elastic system comprising three distinct fiber types—oxytalan, elaunin, and elastic fibers	NI	NI
Thoracolumbar fascia	Erector spinae plane block Retrolaminar plane block Quadratus lumborum plane block	Up to 1500 µm. Two-layers with a trilaminar structure with each lamina separated by thin, loose connective tissue rich in type I collagen	NI	±

RA regional anesthesia, NI no information

+ confirmed in histological studies

± not confirmed in all histological studies