Clinical applications
Hyaluronan is a naturally occurring mucopolysaccharide, which consists of a polyrepeating disaccharide structure [(1→3)-β-D-GlcNAc-(1→4)-β-D-GlcA-]. It is found in all tissues and body fluids of vertebrates, like synovial fluid, vitreous body, umbilical cord, skin, etc., where it plays some important physical and biological roles. For its unique viscoelastic nature and high capacity for holding water along with its biocompatibility and non-immunogenicity, hyaluronan has been used in several clinical applications. All the applications of hyaluronan were classified by Balazs Endre A. as viscosurgery, viscosupplementation, viscoaugmentation, viscoseparation, and viscoprotection. There are also some other applications, for example, drug delivery, tissue engineering, etc.
Viscosurgery
Hyaluronan can be used in ophthalmic surgery to protect eye tissues and maintain space during surgical manipulation. It can also be applied in other surgeries, such as arthroscopic surgery, otosurgery, endoscopic mucosal resection, etc.
Ophthalmic Surgeries
Since the first visco-elastic agent was successfully used in cataract surgery in 1979, HA-based ophthalmic viscosurgical devices (OVD) have sprung up on the market, and all of them have good clinical efficacy. In the case of cataract surgery, viscoelastic HA is used to maintain operative space (depth of the anterior chamber) and to protect the endothelial layer of the cornea or other tissues from physical damage. In transplantation surgery, HA is very useful in protecting implants from mechanical damage and dehydration.
Not cataract surgery, but HA can also be used in many other ophthalmic surgeries, such as phacoemulsification, intraocular lens (IOL) implantation, penetrating keratoplasty, glaucoma, intraocular foreign body extraction and ocular trauma surgery, and so on.
Arthroscopic Surgery
HA solution can used in arthroscopic surgery to protect tissues from mechanical damage and to create and maintain space for its high elastic and viscous properties. The first application of hyaluronan in arthroscopic viscosurgery was reported in 1989. At the time of surgery, HA solution was used to distend the capsule in the temporomandibular joints to protect the surfaces of the menisci, cartilage, and soft tissues from mechanical damage, and a favorable prognosis confirmed the mechanical protective ability of HA.
Otosurgery
In an animal experiment, HA solution was used as viscosurgical implants during the treatment of perforated tympanic membranes, influencing the healing process favourably. The healing was faster and the scar formation was reduced. The viscosurgical use of HA implants to aid middle ear surgery and the healing of tympanic membranes was advocated by Claude Laurent in 1988. It has been reported that HA can be applied in otosurgical procedures as an alternative to myringoplasty. The application of HA solution could prevent the formation of granulation tissue and adhesions and promote re-epithelialization of the wounded area.
Endoscopic Mucosal Resection (EMR)
Using submucosal injection of HA during EMR has the advantage of reducing the risk of perforation and accomplishing complete en bloc resection. Mucosal elevations created by submucosal injection of HA remained for a longer time with a clearer margin compared with those made by saline injection. Some study results also suggested that an appropriate concentration of HA could make the EMR procedure easier and more reliable than saline and other kinds of viscous materials such as dextrose and glycerol.
Viscosupplementation
Viscosupplementation refers to a procedure that involves the use of HA solution to supplement or replace synovial fluid in joints with pathological conditions to alleviate pain and promote the healing of intra-articular wounds. The viscosupplementation should improve the physiological environment of an osteoarthritic joint by restoring the protective viscoelasticity of synovial fluid, reducing friction, and improving mobility.
Studies have confirmed the satisfactory effect of HA in treating lameness in racehorses and osteoarthritis (OA) in human knees, hips, shoulders, temporo-mandibular joints, and so forth. The use of HA solution in OA treatment is considered to be the most successful medical application of HA.
Viscoaugmentation
Viscoaugmentation means the use of hyaluronan (HA) to fill and augment the intercellular spaces in connective tissues of the skin, sphincter muscles, vocal cords, and pharyngeal tissues.