Participation in recreational activity or competitive sports could place individuals at higher risk of overuse and traumatic injuries (Yang, Bowling, Lewis et al. 2005). In studies of OA
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risk factors, various definitions of injury are seen. Some studies used a simple and non-specific definition of injury, in which impaired weight bearing was considered as evidence of injury (Muthuri, McWilliams, Doherty et al. 2011). Such non- specific definition included both severe and less severe injuries. In other studies, injury definition was more specific as defined by the type of injury such as anterior cruciate ligaments rupture (ACL), meniscal tear, articular cartilage damage or fracture.
In one of the earliest studies of OA risk factors (Felson et al. 1997), non-specific knee injury was not found to be a risk factor for knee OA (aOR: 0.7, 95% CI: 0.1 - 3.2). Similarly, a 4-year prospective study of women from the Chingford cohort (Hart et al. 1999) did not show a significant association between injury and the risk of knee OA. The reason why these studies failed to show any significant associations was mainly due to the inclusion criteria and inadequate follow-up. For instance, participants with knee OA at baseline were excluded from studies. Thus, injured participants who had possibly developed knee OA before baseline were not accounted in the risk assessment, and the follow-up for the remaining injured participants possibly was not long enough to develop knee OA.
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However, studies with long-term follow-up and large sample size have shown a strong relationship between injury and the increased risk of knee OA. A cohort study of 8000 Finnish people found the risk of knee OA was five-fold higher at 22 years follow-up in participants with baseline knee injuries (aOR: 5.1 95%CI: 1.4 - 19.0) (Toivanen, Heliovaara, Impivaara et al. 2010). A prospective study of 1321 former medical students followed for 36 years also showed that the baseline joint injury was associated with a three-fold increase in the risk of symptomatic knee OA (RR: 2.95, 95% CI: 1.35 – 6.45). This association was even stronger when injuries during follow-up were added into the analysis (RR: 5.17, 95% CI: 3.07 to 8.71) (Gelber, Hochberg, Mead et al. 2000).
Similarly, a strong association was found in a prospective cohort study of 1436 adults aged 40 years old and over, in which participants with acute knee injuries were at a 7-times higher risk of knee OA compared to uninjured counterparts. (Wilder, Hall, Barrett Jr et al. 2002). NHANES I data also indicated a significant increase in the risk of radiographic knee OA in participants with acute knee injuries (Davis, Ettinger, Neuhaus et al. 1989). In this study, acute injury was defined as a history of fracture, severe knee twisting that was
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associated with swelling for ≥2 weeks, or any other knee injuries associated with pain for most days of a month.
Previous injuries have been reported also as the potential reason for the increased risk of knee OA in former football players and ex-weight lifters (Kujala et al. 1995). A high prevalence of radiographic knee OA was reported in male football players who sustained ACL injury 14 years earlier (von Porat, Roos and Roos 2004). A long term follow-up study of female footballers with ACL injury also showed similar findings, where radiographic changes, pain and functional limitation were highly prevalent at 12 years post-injury (Lohmander, Ostenberg, Englund et al. 2004).
Specifically, ACL injury is a strong risk factor for developing knee OA. A review of OA risk factors in patients with ACL rupture has shown a substantial increase in the prevalence of knee OA at 20 year follow-up in both surgically (14%-37%) or non-surgically treated participants (60%-100%) (Louboutin, Debarge, Richou et al. 2009). This was confirmed by a meta- analysis study, in which the risk of knee OA was significantly higher in ACL injured participants treated non-operatively (RR: 4.98, 95%CI: 2.45 - 10.15) and operatively (RR: 3.62, 95%CI: 2.40 - 5.47) (Ajuied, Wong, Smith et al. 2014). A systematic review of 20 studies also found the presence of OA
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biomarkers in ACL deficient or reconstructed participants (Harkey, Luc, Golightly et al. 2015).
The worst clinical outcomes are seen when ACL injury is associated with chondral or meniscal injury (Shelbourne and Gray 2000). A systematic review of 31 studies with a minimum follow-up of 10 years has revealed the prevalence of knee OA in subjects with isolated ACL rupture was 0%-13% as compared to 21%-48% in subjects with combined ACL and meniscal injuries (Oiestad, Engebretsen, Storheim et al. 2009).
Meniscal tear regardless of treatment types and extent of damage is also another significant contributor to the risk of knee OA. Numerous studies have reported the relationship between meniscal injury and the increased risk of radiographic and symptomatic knee OA (Englund and Lohmander 2004; McDermott and Amis 2006; Englund, Niu, Guermazi et al. 2007; Salata, Gibbs and Sekiya 2010). In surgically treated subjects, the risk of symptomatic knee OA has been reported as 7 times higher for degenerative meniscal tear and 3 times higher for traumatic tear during a 16 year follow-up (Englund, Roos and Lohmander 2003). Similarly, in non-surgically treated subjects, minor and severe degenerative meniscal tears have been found to substantially increase the risk of
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knee OA in middle aged and older people (Englund, Guermazi, Roemer et al. 2009). A systematic review of partial meniscectomy studies also indicated a substantial increase in the risk of knee OA 8-16 years after arthroscopy (Petty and Lubowitz 2011). Total meniscectomy is associated with even worse long-term clinical and radiographic outcomes than partial or limited meniscectomy (Englund, Roos, Roos et al. 2001; Papalia, Del Buono, Osti et al. 2011). Hence, meniscal injury has a key role in increasing the risk of knee OA.
Overall, the current evidence conveys a strong association between knee injury and the increased risk of knee OA. This has been confirmed by a meta-analysis of 20,997 participants from 24 observational studies included 7 cohort studies, 5 cross-sectional studies and 12 case controlled studies. The overall pooled OR for the association between injury and the risk of knee OA was 4.20 (95%CI 3.11 - 5.66), with the OR of 5.95 (95%CI: 4.57 - 7.75) for specified injury and OR of 3.12 (95%CI: 2.17 - 4.50) for non-specified injury (Muthuri et al. 2011).
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