The use of regional anesthesia for nerve block in diabetic patients with peripheral neuropathy is currently made on a case-by-case basis, also remains underlying uncertainty regarding the preferred technique and the likelihood of block-related nerve injury. For this many diabetic patients with otherwise healthy nerves may receive general anesthesia instead of regional anesthesia, thus giving up the benefits associated with the latter technique, including a decrease in health complications and superior analgesia following the operation. Ultrasound is used to identify the target nerve and guide needle insertion for nerve blocks, may be a useful tool to detect the presence and severity of neuropathy prior to block placement, a recent study demonstrated a statistically significant increase in the sonographic cross-sectional area of the posterior tibial nerve (PTN) in all diabetic patients who had abnormal motor transmission on nerve conduction studies. For regional anesthesiologists, the ultimate goal of detecting peripheral neuropathy and in particular, diabetic neuropathy by US is to avoid nerve injury. To do so, the association between US-detected diabetic neuropathy and block-related nerve damage must be first established, hence the purpose of this study. We aim to examine whether the cross-sectional area of PTN as assessed by preoperative US can predict nerve injury as assessed by worsening nerve conduction studies following PTN block inpatients scheduled to receive an ankle block. A further subgroup analysis will be performed in diabetic patients.
We hypothesize that the cross sectional area of the PTN will correlate with motor conduction velocity on nerve conduction studies (NCS) following PTN block in patients with peripheral neuropathy. All eligible patients will undergo NCS to confirm or exclude distal neuropathy. Patients without neuropathy will be excluded from further participation in this study. Also excluded will be diabetic patients with neuropathy caused by genetic, metabolic and inflammatory diseases as well as toxic agents and drug induced. A systematic US examination of the PTN will be performed for all patients. After Block administration at surgery day the block successes will be assessed and for the purposes of the present study, patients in whom the block was not successful will be excluded from further intervention and data analyses. Eight weeks after surgery, all study patients will return to hospital for repeat NCS and US.