Categorizing the distribution of the saphenous nerve in relation to the great saphenous vein

The long-term incidence of chronic post-surgical pain after coronary artery bypass surgery - A prospective observational study

BACKGROUND

Chronic post-surgical pain (CPSP) represents a significant issue for many patients following surgery; however, the long-term incidence and impact have not been well described following cardiac surgery. Our aim was to characterize CPSP at least 5 years following coronary artery bypass grafting (CABG) surgery.

METHODS

This prospective observational study investigated a cohort of patients from a larger trial investigating cognitive outcomes following CABG surgery, with 89 of 148 eligible patients (60.1%) assessed for CPSP at a mean (standard deviation [SD]) of 6.8 [1.2] years. Questionnaires interrogated pain presence, intensity, location, neuropathic characteristics, Geriatric Depression Scale scores (GDS) and instrumental activities of daily living (IADL).

RESULTS

CPSP was described in 21/89 (23.6%), with 10 rating it as moderate to severe. Six of the CPSP patients (29%) met criteria for neuropathic pain (6.7% overall). The highest rate of CPSP was associated with the leg surgical site (chest 12/89 [13.5%], arm 8/68 [11.8%] and leg (saphenous vein graft-SVG) 11/37 [29.7%]; χ2  = 6.523, p = 0.038). IADL scores were significantly lower for patients with CPSP (mean [SD]: 36.7 [1.6] vs. no CPSP 40.6 [0.6]; p = 0.006). Patients had GDS scores consistent with moderate depression (GDS >8) in 3/21 (14.3%) with CPSP, versus 3/68 (4.4%) non-CPSP patients (χ2  = 3.20, p = 0.073).

CONCLUSIONS

This study identified a CPSP incidence of 23.6% at a mean of 6.8 years after CABG surgery, with the highest pain proportion at SVG harvest sites. CPSP was associated with neuropathic pain symptoms and had a significant impact on IADLs. This emphasizes the need for long-term follow-up of CABG patients.

SIGNIFICANCE

This study highlights the impact of CPSP 7 years following cardiac surgery and highlights the effect of surgical site, neuropathic pain and the importance of including pain assessment and management in the long-term follow-up of cardiac surgical patients. Strategies to address and prevent chronic pain following cardiac surgery should be further explored.

Distribution, course, and spatial relationships of the saphenous nerve: A 3D neuroanatomical map for nerve stimulation

The overall objective of this study was to construct a 3D neuroanatomical map of the saphenous nerve based on cartesian coordinate data to define its course in 3D space relative to bony and soft tissue landmarks. Ten lower limb embalmed specimens were meticulously dissected, digitized, laser scanned, and modelled in 3D. The course of the main branches, number of collateral branches, and relationship of saphenous nerve to the great saphenous vein were defined and quantified using the high-fidelity 3D models. In 60% of specimens, the saphenous nerve was found to have three branches in the leg, infrapatellar, anterior, and posterior. In 40% of specimens, the posterior branch was absent. Three landmarks were found to consistently localize the anterior branch: the medial border of tibia at the level of the tibial tuberosity, the medial border of tibia at the level of the mid-point of leg, and the mid-point of the anterior border of the medial malleolus. The posterior branch, when present, had variable branching patterns but did not extend as far distally as the medial malleolus in any specimen. Anatomically, the anterior and posterior branches at the level of the tibial tuberosity could be most advantageous for nerve stimulation due to their close proximity to the bifurcation of the saphenous nerve where the branches are larger and more readily localizable than distally. Additionally, the tibial tuberosity is a prominent landmark that can be easily identified in most individuals and could be used to localize the anterior and posterior branch using ultrasound or other imaging modalities. These findings will enable implementation of highly realistic computational models that can be used to simulate saphenous nerve stimulation using percutaneous and implanted devices.

Frequency-Dependent Effects on Bladder Reflex by Saphenous Nerve Stimulation and a Possible Action Mechanism of Tibial Nerve Stimulation in Cats

Purpose

The present study determined the effects of saphenous nerve stimulation (SNS) at different stimulation frequencies on bladder reflex and explored a possible action mechanism of tibial nerve stimulation (TNS) on bladder activity in cats.

Methods

Two bipolar nerve cuff electrodes were implanted on the saphenous nerve and the contralateral tibial nerve in 13 cats, respectively. Multiple cystometrograms were obtained to determine the effects of single SNS at different frequencies and that of combined SNS and TNS on the micturition reflex by infusing normal saline.

Results

SNS at 1 Hz significantly reduced the bladder capacity (BC) to 59.8%±7.7% and 59.3%±5.8% of the control level at the intensity threshold (T) and 2T, respectively (P<0.05), while that at 20 Hz significantly increased the BC to 130.6%±4.2% of the control level at 6T (P<0.05). The TNS and SNS at 20 Hz did not significantly change the BCs at 1T (P>0.05), while combined stimulation at 1T significantly increased the BC to 122.7%±1.9% of the control level and induced an inhibitory effect which was similar to that TNS at 2T.

Conclusions

The current study revealed that SNS reduced and increased BC depending on different stimulation frequencies. The combined SNS and TNS maximized the clinical efficacy at a low intensity. Also, SNS may be a potential therapeutic mechanism of TNS.

Sihler's staining of the cutaneous nerves of the leg and its implications for sensory reconstruction

INTRODUCTION

This study aimed to reveal the entire cutaneous nerve distribution pattern of the leg and provide a morphological basis for sensory reconstruction during skin flap transplantation.

MATERIALS AND METHODS

Twelve adult cadavers were fixed with formalin, and the whole leg skin with subcutaneous fat was removed close to the muscle surface. The cutaneous nerves were visualized using modified Sihler's staining to reveal the distribution and innervation density of the cutaneous nerves.

RESULTS

The saphenous nerve innervated the anterior part, 82.2% of the upper-middle region of the lateral part of the anterolateral leg, and the upper 63.4% of the medial posterior leg. The superficial peroneal nerve innervated 90.1% of the lateral lower one-third of the anterolateral leg. The medial sural cutaneous nerve covered 26.4% of the posterior leg. The lateral sural cutaneous nerve covered 42.3% (approximately 28.6% overlap with the saphenous nerve) of the upper-middle region of the anterolateral and posterolateral leg. The number of branches differed between certain cutaneous nerves in the leg. Communications were observed between the arborizations of the four cutaneous nerves mentioned above. The highest density of primary and secondary nerve branches was observed in the upper one-third of the lateral posterior leg. The upper one-third of the posteromedial leg contained the highest density of intracutaneous nerve branches and highest number of total nerve branches.

CONCLUSIONS

These results may be used to map sensory regions when designing leg skin flaps for reconstruction surgery to obtain improved sensory recovery.

Cutaneous Branch of the Obturator Nerve Extending to the Medial Ankle and Foot: A Report of Two Cadaveric Cases

The area of skin supplied by the cutaneous branch of the obturator nerve (CBO) is highly variable. Although most introductory anatomy texts describe the CBO as innervating only a portion of the medial thigh, there are numerous reports in the literature of CBOs passing the knee to innervate the proximal, middle, or even distal leg. There are no previous reports of CBOs extending to the ankle and foot. Herein we describe 2 cases of CBOs extending at least to the medial foot. Both cases were discovered incidentally, during routine cadaver dissections by osteopathic and podiatric medical students in the anatomy laboratory of Western University of Health Sciences in California. In both instances, the anomalously long CBOs shared several characteristics: (1) they arose as direct branches of the anterior division of the obturator nerve, not from the subsartorial plexus; (2) they coursed immediately posterior to the great saphenous vein from the distal thigh to the distal leg, only deviating away from the saphenous vein just above the medial malleolus; and (3) they terminated in radiating fibers to the posterior half of the medial ankle and foot. In both cases, the saphenous branch of the femoral nerve was present but restricted to the area anterior to the great saphenous vein. It is likely that the variant CBOs carried fibers of the L4 spinal nerve and thus provided cutaneous innervation to the medial foot and ankle, a function most commonly reserved for the saphenous branch of the femoral nerve distal to the knee. Saphenous neuropathy is a common postoperative complication of saphenous cutdowns for coronary artery bypass grafts, so the potential involvement of a long CBO can add additional complexity to regional anesthetic blocks for foot and ankle surgery and procedures such as vein harvesting for coronary artery bypass grafts.

A pilot feasibility study of treating overactive bladder patients with percutaneous saphenous nerve stimulation

AIMS

Effective long-term treatment of overactive bladder (OAB) remains a significant clinical challenge. We present our initial experience with a new bladder neuromodulation method that electrically targets the saphenous nerve (SAFN).

METHODS

A total of 18 OAB patients (female, 55-84 years) were provided with percutaneous SAFN stimulation. The SAFN was targeted with a needle electrode inserted below the medial condyle of the tibia. Activation of the SAFN was confirmed by the patient's perception of paresthesia radiating down the leg. Electrical stimulation was applied for 30 min and subsequently repeated weekly for 3 months. The effects of stimulation were assessed by a 4-day bladder diary and quality-of-life questionaire (OAB-q).

RESULTS

Percutaneous SAFN stimulation was confirmed in all 16 patients who completed the study, and no adverse events were reported. Positive response to SAFN stimulation was achieved in 87.5% (14 of 16) of patients, as determined by either a minimum 50% reduction in bladder symptoms or a minimum 10 point increase in the HRQL total score.

CONCLUSIONS

Electrical activation of the SAFN was consistently achieved using anatomical landmarks and patient feedback. The procedure was well tolerated and, based on our small cohort of patients, appears efficacious, and safe. This pilot study provides early feasibility data that points to a promising new intervention for treating OAB.

A finite element modeling study of peripheral nerve recruitment by percutaneous tibial nerve stimulation in the human lower leg

Percutaneous tibial nerve stimulation (PTNS) is a clinical therapy for treating overactive bladder (OAB), where an un-insulated stainless steel needle electrode is used to target electrically the tibial nerve (TN) in the lower leg. Recent studies in anesthetized animals not only confirm that bladder-inhibitory reflexes can be evoked by stimulating the TN, but this reflex can also be evoked by stimulating the adjacent saphenous nerve (SAFN). Although cadaver studies indicate that the TN and major SAFN branch(es) overlap at the location of stimulation, the extent to which SAFN branches are co-activated is unknown. In this study, we constructed a finite element model of the human lower leg and applied a numeric axon model (MRG model) to simulate the electrical recruitment of TN and SAFN fibers during PTNS. The model showed that up to 80% of SAFN fibers (located at the level of the needle electrode) can be co-activated when electrical pulses are applied at the TN activation threshold, the standard therapeutic amplitude. Both the location of the inserted electrode and stimulation amplitude were important variables that affected the recruitment of SAFN branches. This study suggests further work is needed to investigate the potential therapeutic effects of SAFN stimulation in OAB patients.

Frequency-dependent inhibition of bladder function by saphenous nerve stimulation in anesthetized rats

AIMS

Percutaneous tibial nerve stimulation (PTNS) is an effective neuromodulation therapy for treating overactive bladder (OAB). The therapeutic effects are achieved by repeatedly applying electrical stimulation through a percutaneous needle electrode that is used to target the tibial nerve (TN). Anatomical studies indicate there can be multiple saphenous nerve (SAFN) branches located near the site of electrical stimulation, and therefore we investigated the possibility of evoking a bladder-inhibitory reflex by electrically activating the SAFN.

MATERIALS AND METHODS

Acute experiments were conducted in 26 urethane-anesthetized rats. Changes in bladder contraction rate (BCR) and bladder capacity were measured in response to 10-min SAFN stimulation trials. Electrical pulses were applied at 25 µA and at stimulation frequencies between 2 Hz and 50 Hz.

RESULTS

We report that SAFN stimulation at 20 Hz was most effective at reflexively decreasing the BCR (53.8 ± 5.4% from baseline) and also increasing the bladder capacity (145.8 ± 43.5% from baseline). In contrast, SAFN stimulation at other frequencies yielded inconsistent changes in bladder function. Carry-over effects were minimized by randomizing the sequence of SAFN stimulation trials and also by allowing the bladder to return to the baseline conditions.

CONCLUSIONS

With notable changes in both the BCR and bladder capacity, our findings provide evidence of a novel bladder-inhibitory reflex in anesthetized rats that is mediated by the SAFN. Further work is needed to determine the clinical relevance of this neural pathway.

A Randomized Controlled Trial Assessing the Effect of a Continuous Subcutaneous Infusion of Local Anesthetic Following Elective Surgery to the Great Toe

Local anesthetic use for wound infusions, single injection, and continuous nerve blocks for postoperative analgesia is well established. No study has investigated the effect of a continuous block of the saphenous and superficial peroneal nerves at the level of the ankle joint following first ray surgery. A double blind randomized controlled trial was designed. One hundred patients with hallux valgus and rigidus requiring surgical correction were recruited and randomized to receive a postoperative continuous infusion at the ankle of normal saline or ropivacaine for 24 hours. Pain scores were recorded on postoperative days 1 and 7. There were more females than males. Follow-up was 100%. There were no significant differences in demographic data between the 2 randomized groups. There was no significant difference between the absolute visual analog scale scores on day 1 (P = .14) and day 7 (P = .16); nor was there a significant difference in reduction in scores between days 1 and 7 (P = .70). This study has shown no benefit to postoperative analgesia with the use of a continuous infusion of ropivacaine at the ankle. We, therefore, cannot currently recommend its use in the way described. Further studies may still identify a role for continuous local anesthetic infusions at the ankle to improve postoperative analgesia.

LEVELS OF EVIDENCE

Level I : Prospective randomised control trial.

Optimal site for ultrasound-guided venous catheterisation in paediatric patients: an observational study to investigate predictors for catheterisation success and a randomised controlled study to determine the most successful site

Introduction

Venous catheterisation in paediatric patients can be technically challenging. We examined factors affecting catheterisation of invisible and impalpable peripheral veins in children and evaluated the best site for ultrasound-guided catheterisation.

Methods

Systolic pressure, age, sex, and American Society of Anaesthesiologists (ASA) physical status were determined in 96 children weighing less than 20 kg. Vein diameter and subcutaneous depth were measured with ultrasound. Logistic regression was used to evaluate the contribution of these factors to cannulation success with (n = 65) or without (n = 31) ultrasound guidance. Thereafter, we randomly assigned 196 patients for venous catheter insertion in the dorsal veins of the hand, the cephalic vein in the forearm, or the great saphenous vein. Success rates and vein diameters were evaluated by using Dunn tests; insertion time was evaluated by using Kaplan-Meier cumulative incidence analysis.

Results

Independent predictors of catheterisation were ultrasound guidance (odds ratio (OR) = 7.3, 95% confidence interval (CI) 2.0 to 26.0, P = 0.002), vein diameter (OR = 1.5 per 0.1 mm increase in diameter, 95% CI 1.1 to 2.0, P = 0.007), and ASA physical status (OR = 0.4 per status 1 increase, 95% CI 0.2 to 0.9, P = 0.03). Cephalic veins were significantly larger (cephalic diameter 1.8 mm, P = 0.001 versus saphenous 1.5 mm, P <0.001 versus dorsal 1.5 mm). Catheterisation success rates were significantly better at the cephalic vein than either the dorsal hand or saphenous vein (cephalic 95%, 95% CI 89% to 100%, P <0.001 versus dorsal 69%, 95% CI 56% to 82%, P = 0.03 versus saphenous 75%, 95% CI 64% to 86%).

Conclusions

The cephalic vein in the proximal forearm appears to be the most appropriate initial site for ultrasound-guided catheterisation in invisible and impalpable veins of paediatric patients.

Trial registry number

UMIN Clinical Trials Registry as UMIN000010961. Registered on 14 June 2013.