Hyaluronan, the sodium salt of hyaluronic acid, is a polysaccharide, more specifically a glycosaminoglycan (GAG), that is an essential component of the extracellular matrix (extracellular matrix, intercellular substance, ECM, ECM) in almost all vertebrates. Hyaluronic acid is almost ubiquitous (“found everywhere”). It occurs in higher concentrations mainly in the skin, cartilage, intervertebral discs and synovial fluid (“synovial fluid”) of joints. It is also a component of the vitreous humour of the eye. The synovial fluid is synthesized (formed) by special membrane proteins in close spatial relationship to the cell membrane and released into the joint cavity. It is used for lubrication (discharge of mucilaginous lubricating fluid) and protection (protection) of all internal surfaces of joints. Hyaluronan also has an antiphlogistic effect, i.e. anti-inflammatory. Hyaluronic acid therapy is usually useful when simpler measures do not lead to the desired result and there is no reason for surgery yet. Exogenously supplied hyaluronic acid has a beneficial effect on articular cartilage metabolism:
- Leads to improved viscoelasticity.
- Protects the collagen-proteoglycan matrix as well as chondrocytes (cartilage cells) and pain receptors
- Improves the transsynovial flow of metabolites to the cells and of degradation products out of the joint
- Improves the milieu for the cells and the sensory system
Indications (areas of application)
The hyaluronic acid preparations are used for the treatment of:
- Gonarthrosis (osteoarthritis of the knee joint).
- Coxarthrosis (hip joint arthrosis)
- Ankle joint arthrosis
- Osteoarthritis of the thumb saddle joint (for symptomatic therapy).
- Big toe metatarsophalangeal joint (for hallux limitus and rigidus – the toe is limited in its mobility; it is a preliminary stage of hallux rigidus).
Contraindications
- Inflammatory joint diseases such as ankylosing spondylitis or chronic polyarthritis.
- Venous or lymphatic congestion in the leg
If the preparation contains chicken protein, chicken protein intolerance is a contraindication.
The procedure
Hyaluronic acid is injected directly into the abnormal joint. The therapy is performed on a course basis. Therapy effects are usually seen several weeks later and often last for months.
Origin of hyaluronic acid
The origin of hyaluronic acid preparations varies: on the one hand, hyaluronic acid is obtained from rooster combs and thus contains foreign protein, on the other hand, there is fermentatively obtained hyaluronic acid, which is free of chicken egg protein. Recently, there is also hyaluronic acid produced by genetic engineering.
Scientific studies
Most scientific studies have been conducted on patients with gonarthrosis. To date, there are no consistent conclusions about symptom reduction with hyaluronic acid therapy. A meta-analysis in the Journal of Bone and Joint Surgery confirmed the therapeutic effect and safety of intraarticular injections of hyaluronic acid for the treatment of knee joint osteoarthritis. According to other studies, the application of hyaluronic acid produces little, if any, improvement in symptoms. Likewise, a structure-modifying effect cannot be proven. The evidence (empirical proof) of hyaluronic acid therapy is given as level 1a or 1b in the EULAR guideline. Other guidelines (OARSI, AAOS) rate the efficacy as low.
Potential complications
- Joint infections (risk is very low).
- Pain at the injection site or bleeding (about 8%).
Other indications
- After arthroscopic meniscectomy (surgical removal of the menisci by knee arthroscopy), hyaluronic acid therapy in the sense of viscosupplementation neither accelerates mobility after surgery nor reduces pain.
Benefit
Hyaluronic acid therapy is a proven effective therapy for the treatment of osteoarthritis. It leads to improvement in pain intensity and joint mobility.
