A doctor may suggest injections as a treatment for osteoarthritis, an inflammatory condition of joint cartilage and bone.

When knees are sore, stiff, and swollen from osteoarthritis, several treatment options are available.

Treatment for osteoarthritis (OA) of the knee may start with non-medicinal interventions, such as exercise or weight loss. Another option is over-the-counter (OTC) pain relief medication. Options include acetaminophen (Tylenol), aspirin, or ibuprofen (Motrin, Aleve).

If these treatments do not resolve symptoms, injections are available to help achieve the desired effects. The United States Food and Drug Administration (FDA) has approved two injections to treat OA of the knee: Hyaluronic acid and corticosteroids.

In this article, we provide an in-depth examination of both types of injection, their uses, and their possible side effects.

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Hyaluronic acid injections can help to lubricate the joint and protect the knee against wear and tear.

Hyaluronic acid is a gel-like substance that is naturally present in the synovial fluid surrounding the joints.

This substance provides lubrication and cushioning. It acts as a shock absorber and helps the bones move smoothly instead of grinding against one another.

People with OA have reduced amounts of hyaluronic acid in their joint fluid. Hyaluronic acid injections can help restore normal levels. These injections not only lubricate the joint, but they may also reduce inflammation and protect the cartilage from further wear and tear.

A doctor or another healthcare provider will inject between one and five shots into the knee. The number of shots depends on the brand of hyaluronic acid. Injections occur at weekly intervals.

Before giving an injection, the doctor may perform an aspiration, removing some of the fluid from the knee joint with a needle to reduce swelling.

After injections, avoid putting too much weight on the knee. Do not jog or run, stand for long periods of time, or lift heavy objects.

Side effects

Typical side effects from hyaluronic acid injections include:

  • pain in the knee
  • bruising
  • warmth
  • slight swelling

These side effects should resolve after a few days. Applying a bag of ice to the knee can help relieve discomfort and prevent swelling after the shots.

In rare cases, people might experience more serious side effects, such as bleeding, infection, or allergic reaction.

Call a doctor right away if any of these symptoms occur:

  • severe swelling in the knee
  • rash
  • redness or warmth in the knee
  • severe pain

The pain of OA may not start to ease up until several weeks after the injections.

The pain relief effects of the injection typically last for about 6 months. Once this wears off, a person will require another round of shots or different treatment.

Most insurers will cover the second round of injections if they also covered the initial treatment, and it helped relieve the pain.

Hyaluronic acid injections do not stop or reverse arthritis. However, they may temporarily ease pain and improve mobility in some people. Those with mild OA are likely to see the greatest benefit from hyaluronic acid injections.

Steroid medicines act in a similar way to the hormone cortisol. Cortisol works on the immune system to reduce inflammation throughout the body, also serving to relieve pain.

The FDA have approved five different steroid medicines to treat OA. All of them are about equally effective.

The FDA have also recently approved an extended release corticosteroid injection of triamcinolone acetonide (Zilretta). A person can have it only once, but its anti-inflammatory effects may last longer.

People will need to visit a doctor for the injection. Doctors sometimes use ultrasound to guide the placement of the needle into the space around the joint. Ultrasound is a scan that uses sound waves to create images of the inside of the body.

The doctor may also give an injection of anesthetic pain relief alongside the injection, which will provide immediate relief. The steroid should start taking effect within a few days.

Corticosteroids work faster than hyaluronic acid injections, but their effects do not last as long. In some people, corticosteroid injections can help relieve pain and improve movement in the joint. Others do not find any pain relief from these shots.

People with a extensive damage in the knee are less likely to see results. Even if the pain does improve, it may start to return from a few weeks to a few months after the shot.

Side effects

Although the FDA considers corticosteroid shots to be safe, people might experience side effects, such as:

  • crystal flares, or irritation in the joint similar to gout
  • nerve damage
  • in rare cases, infection
  • an increase in blood sugar levels, a side effect particularly common in people with diabetes
  • thinning of the bones near the knee

If the effects wear off, people receiving the injection may not be able to have another shot right away. Doctors only recommend receiving corticosteroid injections once every 3–4 months.

Receiving shots too frequently can increase the risk of adverse effects, such as damage to soft tissues in the knee. The pain relief from the injection will also not be as effective and wear off more quickly.

If injections every few months are not frequent enough to relieve the pain, another type of treatment may be necessary.

Talking to a doctor about injections

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Speak to a doctor about whether knee injections will help your presentation of OA.

People who think they might have OA of the knee should ask a doctor if knee injections are an effective next step.

Two other types of injections are available. Although these treatments are still experimental and not yet FDA-approved for arthritis of the knee, some doctors may be able to use them.

Platelet-rich plasma (PRP) injections

These injections use cells called platelets. These help wounds heal and blood clot. The doctor takes the platelets from the individual's own blood. Once inside the knee joint, platelets release growth factors, which are substances that help fix damaged tissues.

PRP injections may relieve OA pain and improve function, although researchers must provide further evidence before this treatment enters the mainstream.

Stem cell injections

These injections repair damaged cartilage using cells that can develop into any type of tissue. Stem cell injections can help reduce swelling and relieve pain.

Before turning to injections, more conservative treatments are available, like physical therapy, heat, ice, and weight loss. Insurers will often not cover injections for osteoarthritis until they receive evidence confirming that a person has attempted conservative treatment without success.

Takeaway

Two main injections are available to treat OA in the knee.

Hyaluronic acid injections replace a naturally-occurring lubricant in the fluids around the knee joint. Corticosteroid injections provide an anti-inflammatory medication directly to the knee joint.

In either case, the effects wear off and a top-up will likely be necessary. However, a person should not receive steroid injections more than once in a 3–4 month period as this increases the risk of side effects.

Other experimental injections are under examination, such as PRP and stem cell injections. However, these are not yet mainstream treatments.

Speak to a doctor to assess whether knee injections are right for you.