For entrapment neuropathies, US has proven to be a valuable tool in diagnosing the site of entrapment and the possible underlying etiology, and has become an important tool complementary to clinical electrophysiology (Beekman and Visser 2004; Bianchi et al. 1999; Cartwright and Walker 2013; Lee and Healy 2005; Martinoli et al. 2000; Nakamichi and Tachibana 2003). In the vicinity of the entrapment site, the nerve may be focally thickened. Thus, analysis of nerve cross-sectional areas plays a crucial role in US examinations. We measured the cross-sectional areas of the UN, SBUN and DBUN in US still images. The results we obtained for the UN are in agreement with existing studies of patients (Cartwright and Walker 2013; Kerasnoudis and Pitarokoili 2014; Peeters et al. 2004; Sugimoto et al. 2013). Measurements of the cross-sectional areas of the DBUN and SBUN have not yet been presented. Our data on these PD 0332991 may serve as a reference for further, more detailed US characterizations of UN branches within the UT (Table 1). We emphasize that these measurements are based on 21 cadaver specimens. Because there are no significant differences in the dimensions of the UN from existing data, we assume that our ex vivo measurements of the DBUN and SBUN might be similar to in vivo measurements.
The majority of UTSs are caused by local compressing masses or trauma and, thus, require surgical intervention (Chen and Tsai 2014). Conservative therapy is primarily indicated in UTS with mild sensory symptoms, subsequent to repetitive trauma, strain or direct pressure on the UT. Such lesions usually are type 2 according to Wu et al. (1985) and are located in zone 3 of the UT according to Gross and Gelberman (1985). In the conservative management of carpal tunnel syndrome, perineural injection of corticosteroids has proven to be successful (Marshall et al. 2007). Perineural injection of corticosteroids is not an established therapeutic option in the management of UTS. There are no clinical trials because feasibility studies are lacking. To our knowledge, our study is the first to prove that in cadavers, perineural injection of fluids into the UT can be performed without damaging blood vessels, tendons or the UN and its branches. Thus, our study can be the basis for designing potentially tolerable clinical trials with the prospect of ensuring delivery of the injection agent to the relevant nerve.
The UT is a confined space with densely packed contents. Exact positioning of the injection needle without image guidance could easily lead to an erroneous intra-neural or intra-vasal application of corticosteroids or could even cause a direct lesion on nerve fascicles (Frederick et al. 1992). The intra-neural application of a crystalline corticosteroid could have neurotoxic effects or even induce the formation of a nerve granuloma. An injection erroneously made into the ulnar artery or ulnar veins could give rise to such far-reaching complications as emboli and necrosis (Berthelot et al. 2013; Kim and Park 2014). Only US guidance allows constant visualization of the needle tip and, thus, controlled application of an injection fluid with adequate spatial resolution. It can help to reduce the number of needle passes required to position the needle tip correctly right at the neural sheath while avoiding blood vessels. As a consequence, a US-guided injection also makes it possible to decrease the volume of fluid injected (Koscielniak-Nielsen 2008; Porter and Inglefield 1993). The latter is of particular relevance in the UT. Because the anatomic boundaries of the UT are composed of tendons, ligaments and dense connective tissue, the UT walls do not elastically expand after injection of a large volume. In such an event, the large injection volume could increase the pressure on the nerve and thus aggravate the entrapment. With respect to previously published effective injection doses in carpal tunnel syndrome, we assume that technically an injection volume of 1 mL could contain a therapeutically effective dose of corticosteroids (Marshall et al. 2007).