Clinical Significance of Parabens Flocculation on the Anti Inflrammmatory Effects of Corticosteroid Injection Osteoarthritic Knees

Corticosteroid injections have been used to treat inflammatory conditions for many decades (Storz 1973; Roszental, Zurakowski and Blazar 2008). In order to maximize the effectiveness on the synovial tissue, the concentrated form of corticosteroids is typically mixed with an anesthetic preparation. The corticosteroid suspension in a large volume of anesthetic can then disperse throughout the entire joint more effectively, especially in larger joints such as the knee (Centeno and Moore 1994). In addition, the anesthetic provides immediate relief to the area and can help verify that the injected site was the source of pain (Cole and Schumacher 2005). Typical preparations of anesthetic medications are sold in multi-use vials. The anesthetic solution usually contains a paraben preservative, except in the single vials used for spinal injections, because the use of paraben preservatives is contraindicated in spinal injections (Centeno and Moore 1994).

Celestone and Kenalog are two corticosteroid products that are commonly used for intra-articular injections. If co-administration of a local anesthetic is desired, the suspension of Celestone or Kenalog is commonly mixed with 1% or 2% Lidocaine hydrochloride from multi-use vials containing parabens in Orthopedic and Rheumatology clinics.

The orthopedic literature relating to injections rarely addresses the use of the anesthetic commonly used in injections. Flocculation occurs significantly when parabens are present, but the influence on the efficacy of the corticosteroid is unknown (Philipose et al. 2011; Hwang et al. 2016). There is abundant evidence that flocculation occurs when steroids are mixed with anesthetic solutions containing parabens however, the clinical significance of this phenomenon has not been reported. (Skedros and Pitts 2008b; Andreson, Deodhar and O'Rourke 2005; Skedros and Pitts 2008; Lutt, O'Rouke and Deodhar 2007; Cole and Schumacher 2005).

Cole and Schumacher (2005) suggest that flocculation can result from a chemical incompatibility between corticosteroid and other agents. Flocculation that occurs when corticosteroid is mixed with an anesthetic containing parabens may reduce the anti-inflammatory effect of the steroid. There are two possible mechanisms in which the corticosteroid preparation may be less effective. Flocculation may cause the corticosteroid to precipitate, thus reducing dispersal within the injected area (Centeno and Moore 1994). Additionally, flocculation may result from corticosteroid bonding with another molecule (such as methylparaben) within the anesthetic preparation, making it chemically less effective. The purpose of this study is to identify whether corticosteroid use with anesthetics containing parabens reduces clinical effectiveness relative to paraben-free preparations.

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