The Effect of Time after Shear Injury on the Subsynovial Connective Tissue and Median Nerve within the Rabbit Carpal Tunnel

Abstract

Background The most prominent nonneurological finding in the common compression neuropathy carpal tunnel syndrome (CTS) is fibrosis of the subsynovial connective tissue (SSCT). Recently, a rabbit model of CTS has been developed, based on the hypothesis that SSCT injury and subsequent fibrosis cause nerve compression. The purpose of this study was to evaluate the effects in this model at earlier and later time points than have heretofore been reported. Methods Sixty rabbits were operated on and observed at two different time periods: 6 and 24 weeks. Nerve electrophysiology (EP), SSCT histology, and SSCT mechanical properties were assessed. Results There was no significant difference in median motor nerve amplitude or latency at either time point. The total cell density in the SSCT was significantly higher at 6 and 24 weeks compared to controls. The mean size of the collagen fibrils in the SSCT was higher 6 and 24 weeks after surgery compared to controls. Both the ultimate load and the total energy absorption of the SSCT were significantly higher at 6 and 24 weeks compared to controls. Conclusions In this model, there were signs of SSCT fibrosis and histology changes at 6 weeks, which persist after 24 weeks. Thus, this model leads to sustained SSCT fibrosis, which is one characteristic of human CTS. However, no significant EP changes were found at these two time points, which is in contrast to the findings reported previously for this model at 12 weeks. The significance of the differences in EP findings will be the subject of future studies.

Development of a hyperelastic material model of subsynovial connective tissue using finite element modeling

“…Similar observations have been made in CTS animal models (Moriya et al, 2011; Vanhees et al, 2013; Yoshii et al, 2009b). Results of this study do, however, refine the analysis, allowing for a more detailed description of how the mechanical behavior is different.…”

“…Characterization of the SSCT stiffness is particularly important, as it surrounds tendons and median nerve in the carpal tunnel and influences the relative kinematic behavior between them. In previous studies, mechanical interactions between tendons, median nerve and SSCT were evaluated in normal and CTS tissues of both humans and rabbits (Vanhees et al, 2013; Vanhees et al, 2012; Yamaguchi et al, 2008; Yoshii et al, 2009a; Yoshii et al, 2008). SSCT behavior has been evaluated in both an in situ cadaver model (Filius et al, 2014; Vanhees et al, 2012) and through direct mechanical characterization of isolated tissue samples (Osamura et al, 2007).…”

Transforming Growth Factor-β (TGF-β) Expression Is Increased in the Subsynovial Connective Tissue in a Rabbit Model of Carpal Tunnel Syndrome

“…In this study, TGF-β1 was overexpressed at 6, 12 and 24 weeks after a single shear injury to the SSCT, CTGF was overexpressed at 6 weeks, and both CTGF expression and fibroblast density returned to normal at 24 weeks. Furthermore, in our previous studies, electrophysiological evaluations were performed in the same rabbit model [11] , [12] . The median nerve distal motor amplitude was decreased in 12 weeks after a single shear injury [11] , but not in the 6 and 24 weeks [12] .…”

“…Buprenorphine SR (0.15 mg/kg) was given subcutaneously once before surgery for pain, and postoperatively as needed. SSCT fibrosis was created by a surgical intervention described previously [11] , [12] . Briefly, two volar incisions were made, proximal and distal to the carpal tunnel, and the flexor digitorum superficialis (FDS) tendon of the middle digit was cut at the musculotendinous junction.…”

“…Therefore, recently, a rabbit model for CTS has been developed to understand the pathomechanism of idiopathic CTS as previously described [11] , [12] . Briefly the model is created by surgically stretching SSCT, thereby disrupting the normal elasticity of the tissue.…”