We have been using an ultrasound-guided procedure of mobilizing the nerve away from the deep surface of the flexor retinaculum by percutaneous hydrodissection, followed by fenestration and splitting the laminar layers of the flexor retinaculum.
In addition, the entire procedure was described and patients were shown how our technique differs from blind carpal tunnel steroid injection, ie, that hydrodissection (using the jet of injected isotonic fluid from the needle tip) is used to separate the median nerve from the deep surface of the flexor retinaculum along nearly its entire course within the carpal tunnel, which is a series of perforations of the flexor retinaculum is done along the long axis of the forearm from the distal to the proximal borders of the carpal tunnel.
Under ultrasonographic guidance with the probe oriented in the transverse (anatomic axial) plane of the carpal tunnel, a 30 gm needle was introduced nearly perpendicular to the skin surface at the entry point defined previously, pointing slightly proximal along line OP, and 1% lidocaine was injected from the skin along a track ending at the deep surface of the flexor retinaculum.
The distance of the midpoint of the line drawn from trapezial tubercule to the hamate hook to the flexor retinaculum at the level of the distal carpal tunnel (bowing of the flexor retinaculum) was also calculated.
Diagnostic ultrasonographical parameters in carpal tunnel syndrome demonstrated in previous studies can be listed as increased bowing of the flexor retinaculum, increased flattening ratio or above normal cross-sectional area of the median nerve in the carpal tunnel proximal (inlet), middle section, and outlet (distal) (10).
Etiologies include soft tissue masses, such as ganglion cysts, tendon pathology with thickening and mass effect, thickening of the flexor retinaculum
, or, less commonly, osseous abnormalities (Figure 13).