Knee injection can be either diagnostic or therapeutic:-
Diagnostic- If there is uncertainty about where pain is coming from then a local anaesthetic injection into the knee joint will only resolve pain coming from the knee. If the pain goes it is coming from the knee; if the pain does not go, it is not coming from the knee.
Therapeutic- usually a cortisone (Kenalog) and local anaesthetic is used and this reduces the inflammation in the knee joint. the success rate is around 70% but the duration of improvement is very variable (from a few hours to a long term improvement). where a cortisone injection (or two) has not worked Mr Ashworth has found that Ostenil and Synvisc (synthetic lubricants of hyaluronic acid) have about a 40-50% chance of significantly improving the knee pain.
The injection is performed in clinic under local anaesthetic
Allergy to the drugs used (Kenalog or Marcaine/Chirocaine)
Injury to a nerve (usually temporary symptoms of pain &/or Numbness)
Low risk of infection. However, if this happens it requires urgent treatment and admission to hospital