Introduction Overuse tendinopathy is one of the most common diseases in the orthopaedic region. Hyaluronic acid (HA) and Platelet-rich plasma (PRP) injection into or around the tendon seemed to be an option for difficult-to-treat tendinopathy according to recent research, however the mechanisms of these materials were not well known. The purpose of this study was to evaluate the tendon and chondrogenic markers after injecting HA and PRP for a murine overuse supraspinatus tendinopathy model.
Material and Methods Tendinopathy models were made by 6-week forced decreased treadmill running according to Soslowsky’s methods [Soslowsky, 2006]. They were divided into 4 groups; Time 0 after running protocol (time 0), and 1 week after running protocol with 3 different treatments (No injection [rest], HA injection [HA] and PRP injection [PRP]). HA or PRP were injected once transcutaneously into subacrominal space just after the end of the running protocol. PRP were made by double spinning methods from allograft. Supraspinatus tendons were harvested under anaesthesia and mRNAs were extracted by Tissue Fibrous RNeasy kit (Qiagen). Tendon markers (decorin, Col1α1, Col3α1, tenascin-C, tenomodulin, scleraxis) and chondrogenic markers (byglican, aggrecan, Col2α1, SOX9) were detected by real time RT-PCR. Relative mRNAs compared to control rats (without running) were calculated. One-way ANOVA and post-hoc Tukey were used for statistical analysis.
Results Tendon marker: scleraxis, tenomodulin, decorin, and Col3α1 were not significantly different among the 4 groups. Tenascin C in rest, HA and PRP were significantly decreased compared to time 0. Col1α1 was significantly increased in HA compared to time 0 [Table 1]. Chondrogenic markers: aggrecan, Col2α1 and SOX9 were not significantly different among the 4 groups. Biglycan in rest, HA and PRP were significantly decreased compared to time 0 [Table 2].
Discussion There were no significant differences between the treatment groups. Thus, we could not find any superiority of the HA and PRP injection, but only HA group showed significant increase of Col1α1. HA might be the best choice to create new type collagen in the early stage.
Col2a1 and Sox9 were increased after 4 week running in a previous report [Archambault, 2007]. However we could not detect these chondrogenic changes. Cook et al.  reported that degenerative changes were more severe in the proximal side near insertion. Possible reasons for this were the small number of samples or that the specimens we examined were only middle of tendon substance. Different times and different places of tendon might produce different results.
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