Patients are frequently offered a knee injection without a clear explanation of which one, why that one, and what it is realistically expected to achieve. These are four quite different treatments with different mechanisms, different evidence and different appropriate patients.

Corticosteroid

A potent anti-inflammatory delivered directly into the joint. It works quickly, often within days, and is most useful when there is a genuine inflammatory flare: a warm, swollen, acutely painful knee.

Relief typically lasts weeks to a few months. It does not alter the disease. Repeated frequent injections into the same joint are avoided because of concerns about cartilage and because diminishing returns set in. It also raises blood sugar transiently, which matters in diabetic patients.

Hyaluronic acid

This aims to supplement the viscous properties of joint fluid. Onset is slower than steroid, often over a few weeks, and benefit when it occurs can last several months.

The evidence is mixed and the effect size modest. It is most reasonable in mild to moderate arthritis in a patient who wants to delay surgery and has not responded adequately to exercise therapy. It is a poor choice in bone-on-bone disease.

Platelet rich plasma

The patient's own blood is processed to concentrate platelets, which are then injected into the joint. The intent is to modulate inflammation and influence the joint environment.

Results are best in younger patients with early to moderate arthritis, reasonably preserved joint space and no significant deformity. Preparation methods vary widely between centres, which is one reason published results vary. It should be offered with honest expectations, not as regeneration.

Growth factor concentrate

A related autologous preparation derived from the patient's own blood, prepared to yield a growth factor rich fraction without the variability introduced by some platelet preparations.

It is used in a similar patient group to platelet rich plasma: early to moderate disease, with function to preserve. As with all orthobiologics, the honest position is that it is a reasonable option in selected patients and not a treatment for advanced arthritis.

How the choice is actually made

The stage of arthritis is the first filter. Early to moderate disease with good alignment opens up more options. Advanced bone-on-bone disease narrows them considerably.

The clinical picture matters next. An acutely inflamed knee behaves differently from a mechanically worn, quietly painful one. Diabetes, anticoagulation and previous response to injection all influence the decision.

Finally, the purpose matters. An injection to get a patient through a specific event or to allow them to engage with physiotherapy is a reasonable plan. An injection as an indefinite substitute for a decision is not.

A detailed comparison of knee injections is available here: https://www.mayurajcc.com/knee-injections-for-arthritis

What to ask before agreeing

Ask what stage your arthritis is, why this particular injection has been chosen, what benefit is expected and for how long, what happens if it does not work, and what the total cost of the planned course is. Those five answers will tell you whether the plan is considered or reflexive.