From the Guidelines

Hyaluronic acid (HA) is used for various medical applications, including intra-articular injections for the treatment of knee osteoarthritis 1.

Intra-articular HA injections are commonly used to treat knee osteoarthritis, although the evidence supporting its effectiveness is inconsistent 1.
The American Academy of Orthopaedic Surgeons recommends against the routine use of HA in patients with knee osteoarthritis due to the lack of consistent evidence supporting its benefits 1.
However, other guidelines, such as the OARSI and ESCEO guidelines, conditionally recommend the use of intra-articular hyaluronic acid (IAHA) for patients with knee OA, depending on their comorbidity profiles and response to other treatments 1.
IAHA may be recommended for patients with contraindications to NSAIDs or those who are still symptomatic despite the use of NSAIDs 1.
The typical dose and treatment duration of HA injections may vary, but a common regimen is 2-4 mL of a 1% sodium hyaluronate solution, administered over 3-5 injections, spaced 1 week apart.
It is essential to note that the evidence supporting the use of HA is not strong, and its effectiveness may vary depending on the individual patient and their specific condition 1.

From the FDA Drug Label

INDICATIONS: For use as a lubricant to prevent further irritation, or to relieve dryness of the eye. For use in dogs and cats.

Hyaluronic acid (HA), in the form of sodium hyaluronate, is used as a lubricant to:
- Prevent further irritation
- Relieve dryness of the eye
It is specifically indicated for use in dogs and cats 2

Hyaluronic acid (HA) is used for various purposes, including:

Treatment of osteoarthritis (OA) in humans and animals, as it has been shown to alleviate symptoms and reduce pain 3, 4
Treatment of dry eye disease (DED), with artificial tears containing HA being effective in improving signs and symptoms of DED 5, 6
Ophthalmic, dermal, burns, wound repair, and other health conditions, due to its anti-arthritic effects and role in lubrication and viscoelasticity 4
Cosmetics, as it is important in various anatomical structures and is widely used in therapeutics and cosmetics areas 7

HA can be administered in various forms, including:

Intraarticular viscosupplementation, which has been shown to be effective in reducing pain and improving symptoms of OA 3
Artificial tears, which are used to treat DED and have been shown to be effective in improving signs and symptoms of the disease 5, 6
Topical treatments, which are used to treat various health conditions, including skin and wound repair 4

The concentration and molecular weight of HA appear to play a critical role in its effectiveness, with:

Concentrations ranging from 0.1% to 0.4% being used in artificial tears for DED treatment 5, 6
Molecular weight being an important factor in the formulation of HA products, with different molecular weights being used for different applications 4, 7