Hyaluronic Acid Gel Injections in the Knee Are Absorbed by the Body
Yes, hyaluronic acid (HA) gel injections in the knee are absorbed by the body over time, which is why they typically provide temporary relief lasting up to 6 months before requiring repeat injections.
Absorption and Duration of Effect
Hyaluronic acid injections are administered as a course of treatment for knee osteoarthritis, with the following characteristics:
- Standard regimen consists of 3-5 weekly injections of approximately 20 mg HA per injection 1
- Pain relief and functional improvement typically last up to 6 months after completing the injection course 1
- The body gradually metabolizes and eliminates the injected hyaluronic acid, necessitating repeat courses for continued benefit
Mechanism and Efficacy
Hyaluronic acid works through several mechanisms in the knee joint:
- Protects against damage to articular cartilage
- Reduces friction between joint surfaces
- Provides pain relief
- Reduces risk of adhesion and contractures 2
However, current guidelines from the American College of Rheumatology/Arthritis Foundation (2019) conditionally recommend against hyaluronic acid injections for knee osteoarthritis 3. This recommendation is based on:
- Limited evidence of benefit in high-quality trials
- Meta-analyses showing that when limited to trials with low risk of bias, the effect size of hyaluronic acid injections compared to saline injections approaches zero 3
- Potential for harm associated with these injections
Safety of Repeated Injections
Despite the conditional recommendation against their use, research shows that repeated courses of HA injections appear to be safe:
- Common adverse events include joint swelling and arthralgia
- Serious adverse events are rare
- Repeated courses have not shown increased safety risks compared to initial injections 4
Clinical Application
In clinical practice, hyaluronic acid injections may still be considered when:
- Other interventions have failed to provide adequate symptom relief
- The patient has had inadequate response to nonpharmacologic therapies, topical and oral NSAIDs, and intraarticular steroids 3
Best results are typically seen in:
- Patients with mild to moderate knee OA
- Those without active joint effusion at baseline
- Patients over 60 years with functional impairment 1
Important Considerations
- Higher molecular weight HA products may provide better pain relief compared to lower molecular weight preparations 1
- Effects are generally slower in onset but longer-lasting than corticosteroid injections 1
- The complete absorption of HA necessitates repeat courses, typically after 6 months, if the treatment is beneficial 1
While guidelines conditionally recommend against HA injections for knee OA, they acknowledge that in the context of shared decision-making, this treatment may be viewed more favorably than offering no intervention when other alternatives have been exhausted 3.