Types of Injected Substances
Different injections have different goals. Some numb a structure for diagnosis, some reduce inflammation, and others attempt to influence pain or tissue biology with more variable evidence.
Local anesthetic
Local anesthetic medications such as lidocaine, bupivacaine, or ropivacaine may be used for diagnostic pain relief, immediate short-term symptom relief, or in combination with corticosteroid.
Relief from local anesthetic is temporary. The pattern and duration of relief can help determine whether the injected structure is the main pain generator.
Corticosteroid
Corticosteroid medications such as triamcinolone, methylprednisolone, betamethasone, or dexamethasone are used to reduce inflammation and provide short-term pain relief in selected conditions.
Common indications include knee osteoarthritis flare, hip osteoarthritis pain, shoulder glenohumeral arthritis, subacromial bursitis or rotator cuff-related pain, adhesive capsulitis, trigger finger, De Quervain's tenosynovitis, acromioclavicular joint arthritis, greater trochanteric pain syndrome, and pes anserine bursitis.
Hyaluronic acid
Hyaluronic acid is also called viscosupplementation, a gel injection, or a lubricating injection. It is most commonly used or discussed for knee osteoarthritis.
Hyaluronic acid is a component of normal synovial fluid. In osteoarthritis, synovial fluid properties may change. The goal of viscosupplementation is to improve lubrication and possibly reduce pain.
The evidence is mixed. Major guidelines do not recommend routine use for symptomatic knee osteoarthritis, and they recommend against use in hip osteoarthritis. Some patients with knee arthritis still report benefit, but results are variable. Recent network meta-analyses generally rank hyaluronic acid below PRP for knee osteoarthritis outcomes. Hyaluronic acid should not be presented as a treatment that repairs cartilage or reverses arthritis.
Soft-tissue indications
Hyaluronic acid may also have a role in selected soft-tissue conditions. Randomized trials and systematic reviews have studied HA for rotator cuff disease and partial-thickness tears, elbow tendinopathy, acute ankle sprain, Achilles tendinopathy, patellar tendinopathy, and trigger finger. Some pooled analyses show pain improvement, but the results are heterogeneous, the number of trials for several indications is small, and the best comparator treatment is not always clear.
For that reason, I consider hyaluronic acid an adjunctive or emerging soft-tissue injection rather than a routine first-line orthopaedic injection for ligament sprains, tendinopathy, or partial tendon tears. In my practice, when biologic injection therapy is appropriate for degenerative meniscal pathology, early knee arthritis, or selected chronic tendon problems, PRP is generally my preferred option based on the current literature.
Platelet-rich plasma
Platelet-rich plasma, or PRP, is prepared from the patient's own blood. The blood is processed to concentrate platelets, and the platelet-rich portion is injected into or around the painful structure.
PRP is used in some practices for selected cases of knee osteoarthritis, degenerative meniscal pathology, lateral epicondylitis, medial epicondylitis, partial-thickness rotator cuff tears, rotator cuff tendinopathy, patellar tendinopathy, plantar fasciitis, selected Achilles tendinopathy cases, and selected sports medicine injuries.
In my practice, when an injection is appropriate for degenerative meniscal pathology or early knee arthritis, I consider PRP the best injection option currently available. This position is based on recent comparative knee osteoarthritis studies in which PRP generally performs better than corticosteroid or hyaluronic acid for pain and function over medium-term follow-up, as well as newer meniscal injury literature showing improved pain and functional outcomes in selected patients.
Scientifically supported indications
The strongest injection-related evidence in my practice is currently for early knee osteoarthritis and degenerative meniscal pathology, particularly when the goal is symptom improvement rather than structural regeneration. PRP may also be considered for selected chronic tendon and enthesis-related problems where symptoms persist despite an appropriate rehabilitation program.
- Early knee osteoarthritis: Several network meta-analyses of randomized trials have found PRP to rank better than corticosteroid, hyaluronic acid, and placebo for pain and function at 3, 6, and 12 months. Some analyses also suggest that PRP combined with hyaluronic acid may perform well for pain relief.
- Degenerative meniscal pathology: Recent systematic reviews are encouraging for pain and functional improvement in selected patients, although MRI evidence of actual meniscal healing remains variable.
- Partial-thickness rotator cuff tears and rotator cuff tendinopathy: Systematic reviews of randomized trials suggest PRP may improve pain and function in selected patients, especially over longer follow-up. It should not be presented as a reliable solution for large or full-thickness tears that require surgical assessment.
- Lateral epicondylitis, commonly called tennis elbow: PRP may be more useful than corticosteroid for longer-term improvement, while corticosteroid can perform better in the very short term.
- Other chronic tendinopathies: PRP may be discussed for selected cases of patellar tendinopathy and plantar fasciitis. Evidence for Achilles tendinopathy is more mixed, so patient selection and expectations are especially important.
Evidence is still evolving. PRP preparation methods differ, platelet concentration varies, some systems produce leukocyte-rich PRP and others leukocyte-poor PRP, the number of injections varies, and cost is often out-of-pocket. PRP is not a proven method to regrow a severely damaged meniscus, reverse advanced arthritis, or reliably heal a full-thickness rotator cuff tear.
Stem-cell and cell-based injections
Cell-based treatments may be marketed as stem cells, mesenchymal stromal cells, bone marrow aspirate concentrate, BMAC, adipose-derived cell therapy, or regenerative cells.
These treatments attempt to use cells or cell-derived products to influence inflammation or tissue repair. Current evidence does not support presenting them as a reliable method to regrow cartilage, regenerate a meniscus, or reverse established arthritis. The ACR/Arthritis Foundation guideline strongly recommends against stem-cell injections for knee or hip osteoarthritis.
Prolotherapy
Prolotherapy commonly uses a hypertonic dextrose solution, sometimes combined with local anesthetic. It is intended to stimulate a local healing response in chronically painful ligaments, tendons, or entheses.
It may be discussed in selected chronic soft-tissue pain conditions, but evidence varies by condition and treatment protocols are not standardized.
NSAID injections
Injectable anti-inflammatory medication, such as ketorolac, may be considered in selected situations, especially when corticosteroid is not preferred or is poorly tolerated. The evidence and indications vary by condition.
Aspiration
Aspiration means removing fluid from a joint or bursa using a needle. It may be used for diagnostic testing, relief of pressure, evaluation for infection, evaluation for crystals such as gout or pseudogout, or reduction of a large effusion before corticosteroid injection.
If infection is suspected, aspiration and laboratory analysis are more important than simply injecting medication. Corticosteroid injection should generally be avoided when infection has not been excluded.