The Effects of Hypertonic Dextrose Injection on Connective Tissue and Nerve Conduction Through the Rabbit Carpal Tunnel

Abstract

Objective To investigate the effects of hypertonic dextrose injection on the subsynovial connective tissue (SSCT) in a rabbit model. We hypothesized that dextrose injection would induce proliferation of the SSCT, hinder median nerve conduction, and alter SSCT mechanical properties similar to what is observed in patients with carpal tunnel syndrome (CTS). Design Randomized, controlled prospective study. Setting Not applicable. Participants New Zealand white rabbits (N=28) weighing 4.0 to 4.5kg. Intervention One fore paw was randomly injected with 0.1ml of 10% dextrose solution. The contralateral paw was injected with a similar amount of 0.9% saline solution as a control. Animals were sacrificed at 12 weeks after injection. Main Outcome Measures Animals were evaluated by electrophysiology (EP), mechanical testing, and histology. EP was evaluated by distal motor latency and amplitude. Shear force was evaluated when the middle digit flexor digitorum superficialis tendon was pulled out from the carpal tunnel. The ultimate tensile load and the energy absorption were also measured. Tissue for histology was evaluated qualitatively. Results EP demonstrated significant prolongation of distal motor latency. The energy absorption and stiffness were also significantly increased in the dextrose group. Histologically, the dextrose group showed thickening of the collagen bundles and vascular proliferation within the SSCT compared to the saline group. Conclusions These results are consistent with the findings in CTS patients and suggest that hypertonic dextrose injection has the potential to create a novel animal model in which to study the evolution of CTS.

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.…”

Tendon Injury Produces Changes in SSCT and Nerve Physiology Similar to Carpal Tunnel Syndrome in an in Vivo Rabbit Model

“…With regard to EP testing, a previous study [23] had shown that the normal rabbit median nerve motor latency was 1.74±0.25 ms and the normal motor amplitude was 1.71±0.6 mV. Based on these data, a sample size of 12 would be more than sufficient to detect a difference of 25% in either value, which we thought would be a clinically important difference.…”

“…The use of hypertonic dextrose to induce SSCT fibrosis in an animal model of CTS has been previously reported [14,23]. This model is based on the concept of proliferative therapy or prolotherapy, in which an irritant, in this case a hypertonic solution, is injected in order to initiate neovascularization and to stimulate collagen synthesis.…”

“…The rabbit model is frequently used to study CTS [3,7,14,22,23] because the anatomy of the carpal tunnel is similar in humans and rabbits: all the digital flexors and the median nerve are within a well-defined tunnel, with a ligament bridging radial and ulnar carpal bones to form a canal, and there is a well-developed SSCT. Rats, while also commonly used [10], do not have an SSCT [3]; in dogs, the FDS tendons are outside the tunnel [3].…”

“…Throughout testing, the specimen was kept moist by spraying saline solution. The ultimate tensile load was measured, and the energy absorption and the stiffness were calculated [23]. The ultimate tensile load and energy absorption were defined as the maximum load and the area under the load/displacement curve, respectively.…”