The connection between femoroacetabular impingement (FAI) and osteoarthritis (OA) continues to be a topic of debate for both clinicians and biomechanists1. The study by Chinzei et al. adds additional fuel to that conversation in the form of a head-to-head comparison of cartilage tissues taken from patients with FAI and OA. Real-time qRT-PCR (quantitative reverse transcription polymerase chain reaction) results from the comparison indicated that cartilage samples from the FAI samples were more actively engaged in responding to inflammation and degeneration than were the OA tissues, and that the response was dependent on the degree of mechanical impingement. The reverse was found to be true for synovial and labral tissues.
The interpretation of the authors’ results is limited by the lack of the inclusion of “normal” cartilage tissue samples to serve as a comparison group. This limitation is not unique to the work of Chinzei et al.; for obvious ethical reasons, it is unreasonable to extract tissue samples from well-functioning joints. The short window of post-mortem cell viability usually precludes real-time qRT-PCR analysis of cadaveric specimens, and gene-expression results from cultured cells are likely to vary from cells in an in vivo environment because of mechanical and environmental factors.
Another challenge to establishing the link between FAI and OA is due to the disparity in the typical age of onset. FAI has a notably earlier onset age (for example, in the study by Chinzei et al., the average age of the FAI group was forty-two years, whereas it was sixty-nine years for the OA group). While this anecdotally suggests disease progression, it prevents establishing equivalently aged comparison groups for the RT-PCR studies.
Thus, we are left with our present conundrum in trying to connect the dots in establishing FAI as a mechanical precursor to OA. From a mechanical perspective, it “just makes sense” that the repeated, localized, high-magnitude concentrations of mechanical stress induced in the cartilage consequent to FAI could lead to premature tissue degradation and trigger an osteoarthritic response. Both prospective and retrospective imaging-based studies2-4 have provided evidence in support of that perspective. On the other hand, it is still unclear which FAI cases will progress to OA, and more importantly, which FAI cases should be treated to result in improved patient outcomes5.
The results of this study are intriguing, as they attempt to unravel potential molecular mechanisms underlying an FAI-OA connection. They represent a first step in identifying a biological phenotype that may elucidate the metabolic state of pre-OA tissues. The authors’ finding that the variation in catabolic and anabolic cytokine activity in FAI cartilage is associated with impingement angle suggests that it may indeed be possible to identify a threshold level of FAI that would progress to OA. There were notable limitations to the study, which the authors have pointed out. Nonetheless, the article makes a compelling case that additional studies in this area may add clarity to the ongoing challenge of translating observations of the associations between FAI and OA into guidelines for effective clinical practice.
↵* The author received no payments or services, either directly or indirectly (i.e., via his institution), from a third party in support of any aspect of this work. Neither the author nor his institution has had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, the author has not had any other relationships, or engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
- Copyright © 2016 by The Journal of Bone and Joint Surgery, Incorporated