The entrapment of the MN occurs between the transverse carpal ligament and carpal bones, with subsequent CSA enlargement which occurs at the level of proximal carpal tunnel (the level of pisiform), the MN size appears to be not affected at more proximal level above the carpal tunnel (the level of pronator quadratus) .
Many sonographic studies had compared MN dimensions between CTS patients and controls and found that CSA at the proximal carpal tunnel was higher in CTS patients than control group. Accordingly, the CSA difference (PS-PQ) was also higher in CTS patients than the control group [16,17,18,19].
Sonographic median nerve FR was also assessed as a differentiating parameter for neuropathy and a cutoff value of 3 was accepted to be significant for CTS [16, 17, 20].
The current study showed that CTS patients had statistically significant higher values of CSA at the pisiform, CSA difference (PS-PQ) and FR at the hamate.
In the current study, the CSA at the pisiform, CSA difference (PS-PQ), and FR in the non-surgically treated patients were lower than that of the surgically treated patients, these differences were statistically insignificant and this might be due to small population size.
Surgical approaches for carpal tunnel release include longitudinal approach mini-palm or extended open, double incision, transverse mini incision, and endoscopic carpal tunnel release. The longitudinal approaches permit the surgeon to extend the incision when there is an indication for more release [21,22,23].
To date, there is no publication assesses the impact of preoperative median nerve ultrasonography on surgical decisions.
In the current study, the data of median nerve ultrasonography was analyzed retrospectively on the light of the operative notes, and it was found that the mini-palm longitudinal approach had to be extended in five patients for adequate decompression; and all these five patients had median nerve CSA difference (PS-PQ) > 7 with significant-high correlations.
This CSA difference could be recommended as a cutoff value at which surgeon should put in mind that surgical field extension might be demanded.
External neurolysis means the removal of fibrotic tissue outside a nerve trunk. Median nerve neurolysis is not a routine step in primary carpal tunnel release; however, external neurolysis could be needed if fibrous adhesions are found intra operatively .
Asami A et al. studied external neurolysis of the median nerve in severe CTS cases who had no electro-physiologic reaction; they found that all patients regained some degree of hand function post-operatively, so they recommended external neurolysis for severe CTS to achieve satisfactory results .
There is no consensus on specific preoperative advisory measures to recommend planning external neurolysis.
In the current study, twelve patients needed intraoperative external neurolysis of the median nerve to free the nerve trunk from surrounding fibrous tissue that was seen adherent to the superficial epineurium; all of them had median nerve flattening ratio > 4 with significant-high correlations. This value could be assigned as a cutoff value at which surgeon should put the possible need of median nerve external neurolysis in mind.
The high FR may reflect severe nerve compression, and long-standing severe compression may lead to fibrosis around the nerve.
The flattening ratio was correlated significantly with both motor distal latency and motor amplitude, this could reflect the reliability of the flattening ratio as a parameter of the severity of carpal tunnel syndrome.
The need for either neurolysis or wound extension might consider choosing a traditional open longitudinal approach rather than endoscopic or “minimal-incision” as transverse approach to permit possible approach extension.
The current study could define cutoff values of flattening ratio > 4 for the possible need for external neurolysis and cutoff values of CSA difference (PS-PQ) > 7 for possible need for wound extension.
Five patients out of eight with flattening ratio > 4.2 were found to need intraoperative wound extension for adequate decompression. Although the correlation was significant and reasonable, this might require a larger sample size study for more accurate evaluation.
To the best of the authors’ knowledge, no study up to date was conducted to evaluate the implication of the ultrasonographic data of median nerve dimensions on surgical carpal tunnel release.