Cartilage and bone markers and inflammatory cytokines are increased in synovial fluid in the acute phase of knee injury (hemarthrosis) – a cross sectional analysis
Swärd P, Frobell R, Englund M, Roos H & Struglics A. Osteoarthritis and Cartilage. 2012, 20: 1302-1308.
Acute knee injuries, including anterior cruciate ligament (ACL) tears, are known to increase an athlete’s risk of developing osteoarthritis (OA). Rate of OA incidence seems to be at an increased risk, despite whether an athlete gets ACL surgery or not. There are various biomechanical as well as biochemical theories as to why this may be. One biochemical theory being that the acute inflammatory process that follows a knee injury propagates OA. Therefore the purpose of this study was to investigate the biochemical markers within 1 month of an acute knee injury (i.e. any rotational injury with hemarthrosis) and compare them to healthy knees, as well as to see if time from injury affects concentrations. Synovial fluid (SF) was aspirated once and analyzed in 111 acutely injured knees at varying time points within the 1 month window post-injury based on when the injured knee was seen. SF concentrations of specific markers for cartilage (i.e., aggregan), bone (i.e., osteopontin, osteonectin), and all pro-inflammatory cytokines (signalling proteins; i.e., IL-1β, IL-6, IL-8, and TNF-α) were significantly higher at all time points when compared to the healthy controls. This study also found a time-dependent response of certain cartilage markers being higher in the days immediately following knee injury. Markers remained elevated when compared to healthy controls, but started to become lower the longer it was from the time of injury.
An early inflammatory response in acutely injured knees may start a cascade of events that lead to irreversible changes to the entire joint environment. Clinically it is important to take this into consideration for future research as well as when applying rehabilitation techniques, recommending interventions, or modifying activities of daily living. While this study finds some interesting elevations of biomarkers, the question still remains “what can we do clinically about this.” Unfortunately I think it is still too early to tell. There is not enough evidence to stop doing rehabilitation in days immediately following injury or to make treatment modifications due to these elevated markers, but clearly these biomarkers are an issue that warrants more attention. Within 1 month of an acute knee injury, there may be no evidence of structural changes, but this provides a unique window of opportunity to intervene and help a patient maintain a better long-term quality of life. Biochemically the knee is altered and this may be the lone condition needed to start the development of OA. Other studies have found that some markers remain elevated as much as 1 year post-injury (Beynnon et al). Is there anything that we may be able to do as clinicians to help these athletes? Are there things that we can implement to help return these biochemical levels to normal?
Written by: Nicole Cattano
Reviewed by: Stephen Thomas