It is often recommended not get over around 2 cortisone injections for a tendinitis. Why are cortisone injections deleterious for tendons?
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One study published in 1996 in the Clinical Journal of Sport Medicince said that there are insufficient published data to determine the comparative risks and benefits of corticosteroid injections. Most side effects are temporary, but skin atrophy and depigmentation can be permanent.
In a further study published in 2002 in Foot and Ankle Clinics we read:
Intimidation with adverse effects of peritendinous corticosteroid injections is based on case reports only rather than convincing data from controlled clinical studies.
Although a complete tendon rupture with loading after steroid injection has been reported, no reliable proof exists of the deleterious effects of peritendinous injections; conclusions in literature are based mainly on uncontrolled case reports that fail under scientific scrutiny, whereas scientifically rigorous studies have not been performed.
Although corticosteroid injections are one of the most commonly used treatment modalities for chronic tendon disorders, there is an obvious lack of good trials defining the indications for and efficacy of such injections, and subsequently, many of the recommendations for the use of local corticosteroid injections do not rely on sound scientific basis. Thus, there is an obvious need for high-quality basic science studies and controlled clinical trials in examining the effects corticosteroids on various tendon disorders.
Based on above studies, the effect of local corticosteroid injection(s) for tendon disorders is unknown. The extent of the tendon problem, the duration of the symptoms, and the phase of healing at the time of injection are factors that may modify the efficacy and side effect profile of this procedure. More studies need to be conducted to determine how these factors influence outcomes.
NHS has provided the following advice about corticosteroid injections:
Corticosteroids can be injected around injured tendons to reduce pain and inflammation.
While these injections can help reduce pain, they aren't effective for everyone and the effect sometimes only lasts a few weeks.
The injections can be repeated if they help, but a gap of at least six weeks between treatments, and a maximum of three injections into one area, is usually recommended because frequent injections can cause side effects. Possible side effects include the weakening of the tendon (which can increase the risk of rupturing or tearing), and thinning and lightening of the skin.
Effects of cortisone ie. glucocorticoids (GCs) are very variable.
One effect of GC is the inhibition of collagen formation. Collagen is the main ingredient of tendons. Collagen units form the backbone for tendons and makes them as strong as they are. As every tissue in human reproduces all the time so do tendons by forming new collagen as the old molecules deteriorate. If collagen formation is blocked this naturally leads to possible rupture of tendon.
It is also important to note that GCs should never be injected IN tendon. Instead injection should be put as peritendinous to avoid imminent rupture. Of course in long run repeated peritendinous injections may lead to rupture.
peritendinous = surrounding the tendon.