Knee injections

A number of different anti-inflammatory injectable preparations are available to administer to the knee including corticosteroids, hyaluronic acid (viscosupplementation) and platelet rich plasma (PRP). These products can all be administered to the knee joint, and the corticosteroid and PRP can be administered to the soft tissue around the outside of the knee as well. The common goal with these agents is to achieve a knee that is less swollen and painful, and in the case of viscosupplementation, possibly prolong the longevity of the native knee.

Corticosteroids are medications that are related to cortisone, a type of steroid that is a powerful anti-inflammatory agent. These steroids are different to the body building type of steroid (anabolic steroids) and instead medications of this class powerfully reduce inflammation. Cortisone is one type of corticosteroid, and whilst it is not a “pain killer”, because it can reduce inflammation, it can decrease pain proportionate to the amount arising from inflammation. It has a long history of use, is relatively inexpensive compared to other injectable knee preparations, but its benefit is usually short lived. Thus, corticosteroid injections are usually used for severe bouts of inflammation, in a degenerate or inflammatory arthritis of the knee joint or acute strain or episode of inflammation around the outside of the knee. While the inflammation can recur, corticosteroid injections can provide weeks to months of relief when used properly, and occasionally, can permanently resolve tissue inflammation localised to a small area, such as bursitis and tendonitis.

A distinct benefit of a corticosteroid injection is that the relief of localised inflammation in a particular body area is often more rapid and powerful than commonly used non-steroidal anti-inflammatories (NSAID’s) such as Mobic, Celebrex or Nurofen. A single injection also can avoid certain side effects that can accompany many oral NSAID’s, notably gastrointestinal ulcers, renal impairment and hypertension (high blood pressure). Other advantages include the rapid onset of the medication’s actions, dependability, minimal side effects and easy administration under local anaesthetic in the doctor’s office. If corticosteroid injections are used repeatedly inside the knee joint (intra-articular), this can result in overall thinning of the remaining cartilage, increased inflammation in the joint (arthritis) due to a reaction to the corticosteroid, and very rarely introduction of infection into the joint or if used repeatedly for peritendinous injections outside the knee (extra-articular), can be associated with increased risk of tendon rupture.

With life’s wear and tear, the articular cartilage of the knee can begin to thin, resulting in osteoarthritis (OA) leading to the onset of mechanical symptoms including stiffness, swelling and pain. The knee normally produces a lubricating fluid called synovial fluid which has a high concentration of Hyaluronic Acid (HA) which is a lubricating and anti-inflammatory agent normally made by the knee joint. As we age and/or develop OA, the quality of our synovial fluid decreases with a diminishing concentration of HA, losing the ability to protect the joint effectively and as a result, cartilage can break down and become worn and frayed. To address this, HA preparations, can be injected into the knee joint, in order to try and improve the quality of the knee’s synovial fluid by increasing the concentration of HA and making it more viscous, hence the term viscosupplementation. Viscosupplementation is best indicated for use in the middle stages of knee osteoarthritis, when the knee is sufficiently worn to be symptomatic, but the cartilage is not yet fully eroded (bone on bone). To increase the likelihood of correctly choosing who will benefit from viscosupplementation, patients require up to date imaging with plain X-rays taken whilst standing, and if possible an MRI. Whilst these products are usually quite expensive to purchase, if patients have been appropriately selected, they will often experience reduced pain and swelling for up to 6 to 12 months and potentially experience the dual benefit of both symptomatic improvement and prolongation and preservation of joint function.

There are many preparations on the market, with some requiring multiple injections on a weekly basis over a number of weeks, and others as a one off injection such as “Synvisc–One”. The injection is performed using local anaesthesia under sterile conditions as a walk in – walk out procedure. You may notice a local reaction, such as pain, warmth, and slight swelling immediately after the injection but these symptoms generally do not last long. Rarely, patients may develop a local allergy-like reaction in the knee, becoming red, warm, swollen and painful. If this occurs, other possible causes include infection and bleeding and prompt medical assessment is necessary to establish the cause and appropriate treatment. Whilst the viscosupplementation can begin to benefit the knee immediately by acting as a lubricant and a shock absorber, the peak anti-inflammatory and symptomatic benefit usually occurs somewhere between the sixth and twelfth week, with patients enjoying improvement in knee function for somewhere between six to twelve months. If successful, viscosupplementation can be repeated one or two times each year with a view to both improving the way the knee feels and as part of a global approach to helping delay the rate of wear progression.

Platelet rich plasma (PRP) has been used most widely for enhancing and accelerating healing of extra articular structures (ligaments, tendons, muscles) with tears, both in the acute setting (sports injuries) and for chronic injuries (such as tendinosis). PRP has also recently become a product of interest for the symptomatic management of the arthritic and inflamed knee, but it’s role here is as yet unclear, with a small number of early positive reports on its ability to decrease pain and swelling, comparing favourably to other mid to longer term agents such as hyaluronic acid (viscosupplementation). Blood is made up mainly of a liquid called plasma, containing three main types of cells, red cells, white cells, and platelets. Platelet rich plasma (PRP) is an injectable product made up of a patients’ own blood, which has been manipulated to have a higher concentration than normal of platelets and a lower concentration of the other (red and white) blood cells. Whilst platelets are best known for helping blood to clot, they also contain hundreds of proteins called growth factors including platelet derived growth factor, insulin like growth factor and connective tissue growth factor, which are very important in the healing of injuries. Thus PRP is plasma with many more platelets and a greater concentration of growth factors, which can be five to ten times greater than usual.

To develop a PRP preparation, blood must first be drawn from a patient, platelets are separated from other red and white blood cells and platelet concentration is increased during a process called centrifugation before adding them back to the remaining blood plasma. Whilst it is not exactly clear how PRP works, laboratory studies have shown that the increased concentration of growth factors in PRP can potentially improve the quality and speed of the healing process. PRP can be carefully injected into the injured area (ie. quadriceps or patella tendon) or the actual knee joint, and can be done as a standalone procedure or in conjunction with surgery for tendinosis or focal arthritis such as microfracture (Bone Marrow Stimulation). Treatment with PRP appears to hold promise for chronic tendon injuries, but for all other conditions, current research is suggestive rather than conclusive, and the medical community needs more scientific evidence before it can determine whether PRP therapy is truly effective or not. Thus, even though the role of PRP therapy is still questionable, as the risks associated with it (pain at injection site, infection, tissue damage, nerve injuries) appear to be no different from that associated with cortisone or hyaluronic acid (viscosupplementation), patients are able to embark on this course of therapy, as an alternative to other types of knee injections, under “experimental conditions”.