Comparison of success rate of ultrasound-guided sciatic and femoral nerve block and neurostimulation in children with arthrogryposis multiplex congenita: a randomized clinical trial

Summary

Background and objectives

Arthrogryposis multiplex congenital is hallmarked with immobile joints and muscle fibrosis. The main objective of this study was to compare the success rate of ultrasound-guided sciatic and femoral nerve blocks with nerve stimulations in children diagnosed with distal arthrogryposis multiplex congenita.

Method

Sixty children aged 8 months to 2 years posted for foot surgery were randomly assigned to group NS and group US of 30 each. Under general anesthesia, femoro-sciatic block was performed with nerve stimulator guidance in group NS and ultrasound guidance in group US.

Results

Group NS: 23 of 30 (76.7%) children showed ankle movement with sciatic neurostimulation. In 7 (23.6%), distal motor response could not be elicited and the block was abandoned. Out of 23 children who could be given femoral block, in 12 (52%) patients quadriceps contractions were not elicited and fascia iliaca block was given. All 23 blocks were successful. CHIPPS score at 1, 4, 6, 8, and 10 h was 1.05 ± 0.90, 1.82 ± 1.18, 3.36 ± 1.65, 2.23 ± 2.02, and 1.18 ± 1.14, respectively. Group US: In 29 of 30 patients (96.6%), sciatic nerve was visualized with ultrasonography. All 29 children received femoral block, and they were successful. The odds of success in group US were 8.9 (95% confidence interval [1.0, 77.9]) as compared with NS group. The difference in success rate was statistically significant (P = 0.026). The analgesic duration difference in the US and NS groups was a mean 7.62 ± 0.57 h in group NS and 8.60 ± 0.66 h in group US (statistically significant [P < 0.001]). CHIPPS score at 1, 4, 6, 8, and 10 h was 0.79 ± 0.96, 1.61 ± 0.92, 2.96 ± 1.04, 2.36 ± 2.54, and 1.14 ± 1.01, respectively. The difference between the CHIPPS score was not statistically significant.

Conclusion

Ultrasonography significantly increases the success rate of sciatic and femoral block in arthrogryposis.

Introduction

The conspicuous features of arthrogryposis multiplex congenita are the presence of immobile joints and contractures because of muscle fibrosis [1]. This is a rare disorder with a frequency of about 1 in 3000 live births [1, 2]. The life span of affected individuals depends on the disease severity and associated malformations but is usually normal. These children present to pediatric anesthesiologist for multiple corrective surgeries including those of the lower extremities. It is known that nerve blocks are the potential effective means [3] to treat perioperative pain in these procedures. However, the immobile joints and muscle contractures make response to nerve stimulation difficult to elicit. Ultrasound guidance does not depend on these end points and logically may improve the success rate. However, replacement of normal muscle fibers with fibrous tissue might change the echogenicity of the muscles and might possibly interfere with nerve identification especially in transverse section. Previous experiences with nerve blocks in this population are present in the literature only in the form of case reports using loss of resistance technique [4] or ultrasound guidance [5]. The comparative success rate of neurostimulation (more easily available modality in our setting) and ultrasound-guided sciatic and femoral nerve block is not known in children affected with distal arthrogryposis multiplex congenita.

We hypothesized that ultrasound guidance may improve the success rate of these blocks. This study was designed to test our hypothesis. The primary objective was to compare the success rate of nerve stimulation–guided sciatic and femoral nerve block with that of ultrasound guidance in children with distal arthrogryposis multiplex congenita. Secondary objective was to compare the duration of analgesia with either modality.

Methods

This was a prospective, randomized, parallel, and blinded study conducted after the approval of the Ethics Committee of the hospital. Written informed consent from patient's parents or guardians for participation was obtained. Sixty children aged 6 months to 5 years diagnosed with distal arthrogryposis multiplex congenita [6] were recruited. They were posted for surgical correction of congenital vertical talus. They were excluded from study if they had coagulopathies, cardiac, and renal disorders. They were randomly allocated with a ratio of 1 : 1 into two groups: group NS (neurostimulation) and group US (ultrasound) of 30 each to receive sciatic and femoral nerve block. Randomization was performed by sealed envelopes prepared by the statistical staff. This study was performed in All India Institute of Physical Medicine and Rehabilitation Centre, India, in the year 2009. The anesthesiologist performing the block was given randomly generated group allocations within sealed opaque envelopes. Both groups received sciatic block followed by femoral nerve block. Group NS received the block under nerve stimulation guidance and group US under ultrasound guidance. Patients in whom a sciatic block could not be performed, femoral block was not attempted. Children were fasted for 6 h for solids, 4 h for breast milk, and 2 h for water prior to the procedure Oral midazolam 0.5 mg·kg⁻¹ was given 30 min before induction of anesthesia with O₂, nitrous oxide, and halothane to all. After securing vascular access, halothane was stitched off and all the patients received propofol 2–3 mg·kg⁻¹ to facilitate laryngeal mask airway placement. Anesthesia was maintained with 50% N₂O in O₂ and 2–3 mg·kg^−1·h⁻¹ of propofol infusion in all the patients. The patients were allowed to breath spontaneously through the laryngeal mask airway. S_pO₂, NIBP, ECG, and ETCO2 were monitored all throughout the procedure. All the blocks were performed by the same anesthesiologist having extensive experience in neurostimulation and ultrasound use. Fentanyl 2 mg·kg⁻¹ was given if sciatic nerve stimulation response could not be elicited (group NS) after three attempts (each pass was accounted as an attempt) or if nerve could not be convincingly visualized with ultrasound guidance in group US.

Technique of nerve stimulator–guided sciatic nerve block

With the patient in supine position and the thigh held flexed at 90°, the greater trochantor and ischial tuberosity were palpated and the midpoint of the line joining the two was marked as the puncture point. A 24-g, 5-cm insulated needle (Braun, Melsungen, Germany) connected to a nerve stimulator (B Braun Stimuplex Dig RC) was inserted medially and upward (cephalad) toward the ischial tuberosity. A current of 1.5 mA was used to locate the nerve. After eliciting plantar or dorsiflexion in the foot, the response (ankle joint movements) at 0.5 mA, 0.5 ml·kg⁻¹ of 0.25% bupivacaine was administered.

Technique of nerve stimulator–guided femoral nerve block

With the patient in supine position, thigh slightly abducted and externally rotated, and the inguinal ligament and the femoral artery were palpated. A 24-g, 5-cm insulated needle (Braun) connected to a nerve stimulator (B Braun Stimuplex Dig RC) was inserted at right angles to the thigh 0.5 cm lateral to femoral artery and distal to inguinal ligament. Quadriceps contractions at 0.5 mA were taken as the end point, and 0.7 ml·kg⁻¹ of 1% lignocaine was injected. In group NS, if we failed to elicit quadriceps contractions for femoral block, fascia iliaca block was given with loss of resistance technique.

Technique of ultrasound-guided sciatic nerve block

Children were placed in lateral position, with the operative leg nondependent and extended. The infragluteal area was scanned in the transverse plane using the Sonosite Micromax Ultrasound machine with 5–10 MHz, high-frequency probe. An inplane approach was used. Under sterile conditions, the nerve was located in between the gluteus maximus and biceps femoris at this level. When the sciatic nerve was indistinct, the entire length of thigh was scanned to identify the sciatic nerve, and the block was performed where the nerve was seen the best. 0.5 ml·kg⁻¹ of 0.25% bupivacaine was injected.

Technique of ultrasound-guided femoral nerve block

The probe was placed transversely along the inguinal ligament. The nerve was identified lateral to the artery. The needle was advanced from the lateral aspect of the inguinal ligament, toward the nerve under real-time guidance in an in plane approach. 0.7 ml·kg⁻¹ of 1% lignocaine was injected. All blocks were allowed to set up for 20 min before surgical incision. Block success rate (successful block) was defined as the absence of pain response to surgical stimulus (no increase in pulse rate and blood pressure by more than 20% of the basal rate after surgical stimulus). This is an accepted means of determining effective from ineffective blocks [7]. Bolus of fentanyl 2 mg·kg⁻¹ was administered as rescue analgesic if the block failed. Postoperatively, CHIPPS pain score was recorded at 1, 4, 6, 8, and 10 h by the second anesthesiologist on duty blinded to the block technique. Tramadol 2 mg·kg⁻¹ was administered as rescue analgesic in case of inadequate pain relief (CHIPPS > 4) in the immediate postoperative period. Patients in both the groups who could not be given blocks received Tramadol 2 mg·kg⁻¹ in the postoperative period. Duration of analgesia was defined as the time interval between the administration of the nerve block and the first dose of rescue analgesia. Failed blocks and patients in whom blocks could not be performed were excluded from statistical analysis. However, they were included in the study.

Statistical analysis

The sample size was calculated using the following assumptions: we believed based on our previous experience that the success rate of sciatic and femoral nerve block with neurostimulation in patients with distal arthrogryposis multiplex congenita is 60% and would increase to 100% with ultrasound-guided blocks. To achieve 90% power with P1 = 60% and P2 = 100% with alpha = 0.05, 30 patients would be required in each group (total 60). All data analyses were carried out according to a preestablished analysis plan. Proportions were compared using Fisher's exact test and 95% confidence interval presented. Statistical significance was defined as P < 0.05. Simple randomization was performed with sealed envelopes. The anesthesiologist who recorded the pain scores was blinded to the block technique.

Results

Sixty patients were recruited and all of them completed the study. The baseline demographics are shown in Table 1.

Table 1. Shows the demographic data, success rate for sciatic nerve block, and duration of analgesia

Variable	Group NS	Group US	P value
There were no significant differences between groups in age. For success rate, Fisher's exact probability test (one tailed) was applied, the difference was statistically significant. The difference was statistically significant for duration of analgesia.
Age (months)	12.17 ± 3.96	11.69 ± 3.83	0.6
Sex	M = 19/F = 11	M = 24/F = 8
Weight (kg)	9.72 ± 2.33	8.97 ± 1.32	0.1
Success rate	23 (76.3%)	29 (96.6%)	0.026
Duration of analgesia	7.62 ± 0.57	8.60 ± 0.66	≤0.001

Block success rate

Group NS: 23 of 30 (76.7%) children showed ankle movement with nerve stimulation technique. We were unable to elicit the neurostimulation response in 7 (23%) patients; in six of these seven patients, no response could be elicited at all, and in one patient there was inability to elicit response at 0.5 mA. These seven cases received 2 mg·kg⁻¹ fentanyl. Out of 23 children who could be given femoral nerve block, in 12 (52%) patients quadriceps contractions were not elicited and fascia iliaca block was given with loss of resistance method. All 23 patients had effective blocks. CHIPPS score at 1, 4, 6, 8, and 10 h was 1.05 ± 0.90, 1.82 ± 1.18, 3.36 ± 1.65, 2.23 ± 2.02, and 1.18 ± 1.14, respectively. Total intravenous tramadol consumption at the time of first onset of pain was 582 mg.

Group US: In 29 of 30 (96.7%) patients, sciatic nerve was visualized with ultrasound guidance. In one case, we could not convincingly identify the sciatic nerve and was considered as failed block. Figure 1 shows the ultrasound scan of this particular case. This case received a bolus of fentanyl. The femoral nerve was visualized in the remaining 29 children, and they received femoral block. In all the 29 patients, the blocks were effective. CHIPPS score at 1, 4, 6, 8, and 10 h was 0.79 ± 0.96, 1.61 ± 0.92, 2.96 ± 1.04, 2.36 ± 2.54, and 1.14 ± 1.01, respectively. Total Intravenous tramadol consumption at the time of first onset of pain was 520 mg.

Figure 1. Transverse scans at the infragluteal level. Note the three echogenic structures resembling a nerve.

Statistical significance

The difference in the success rate was statistically significant (P = 0.026) between the two groups (Table 1). The odds of success in group US were 8.9, and 95% confidence interval value was (1.0, 77.9) as compared with NS group.

Duration of analgesia

Analgesia time was 7.62 ± 0.57 h in group NS and 8.60 ± 0.66 h in group US. The difference was statistically significant (P < 0.001). CHIPPS score showed no statistically significant difference (Table 1).

Discussion

Ultrasound guidance results in greater success rate and longer duration of sciatic and femoral blocks than neurostimulation in our study population. Nerve stimulation technique has its limitations. The distal motor responses are difficult to obtain in patients with arthrogryposis because the joints are immobile and fussed [8]. This explains our failure to elicit the ankle joint movement in 6 of 30 patients. In one case, distal motor response could be elicited at 1.5 mA but could not at 0.5 mA. This probably indicates inability to locate the nerve than immobility of the ankle joint itself. Improper needle placement could have been ruled out by assessing with ultrasound guidance; however, it was not a part of the study. It is exceedingly important to note the abnormality in the muscle tissue and its probable consequence on the echogenicity. This syndrome complex is characterized by fibrosis of the affected muscles, almost absence of limb musculature, with replacement by fibrous and fatty tissue [1] which in turn changes the echogenicity of the muscles. When observed in infragluteal transverse scan, they appear akin to nerves as shown in Figure 1. In speculation, this explains the failed block in group US. Femoral block was given to provide analgesia for the tourniquet pain and the medial aspect of the foot, which is supplied by saphenous nerve (branch of femoral nerve). It is interesting to note that an immobile and fixed knee joint and noncontractile quadriceps muscle made elicitation of quadriceps contractions response difficult. In certain cases, the absence of patella was an additional concern. This explains our failure to obtain the patellar flexion response in 12 of 23 patients. These children were given fascia iliaca block with loss of resistance technique, which is in accordance with Ion et al. case report [4]. In this case report, the authors have remarked upon the difficulty in palpation of the femoral artery because of contractures in groin and several unsuccessful attempts to locate the femoral nerve. They had successfully resorted to fascia iliaca block by loss of resistance technique.

Sciatic block was the primary block and femoral block was the supplementary block; hence, we used local anesthetic with a longer duration for the primary block. The increase in duration of ultrasound-guided sciatic nerve was in accordance with other studies [9].

In conclusion, there was a statistically significant increase in the success of sciatic and femoral nerve block with ultrasound guidance as compared with neur-ostimulation technique in children with distal arthrogryposis multiplex congenita. Ultrasound guidance also prolonged the duration of the block in the postoperative period by an hour, which clinically is not very significant.

Acknowledgments

This research was carried out without funding.

Conflict of interest

No conflicts of interest declared.