Sacral plexus catheter analgesia in a patient with traumatic sacral fractures and Tarlov cysts

Summary

We report the use of a sacral plexus catheter for continuous local anaesthetic infusion in a patient with a unilateral sacral ala fracture following a fall from a horse. Although sacral plexus blockade has been well described for lower limb surgery, an ultrasound‐guided continuous catheter technique for conservatively managed fractures has not been described. Despite appropriate oral analgesia, the patient reported severe pain, particularly in the right gluteal region, which meant she was unable to sit upright or take deep breaths. A sacral plexus catheter was inserted with ultrasound guidance and an initial bolus of 30 ml levobupivicaine 0.25% was delivered followed by infusion of 8 ml.h⁻¹ levobupivicaine 0.125%. Daily follow‐up and assessment were provided by the acute pain team. We judged the procedure to be a success as measured by an improvement in mobilisation, deep breathing, cough and patient satisfaction.

Introduction

The incidence of fractures in the UK continues to rise due to, among other factors, an ageing population. Osteoporosis accounts for most pelvic fractures, but patients with malignancy are also at risk. The incidence of pelvic fractures has been estimated to be between 25–92 per 100,000 per year 1. Pelvic fractures are rarely treated surgically, and conservative strategies include rest and oral analgesia 1. Undisplaced fractures of the sacrum are also often managed conservatively, with analgesia and physiotherapy as the mainstay of treatment 2. They are associated with severe pain, high opioid consumption with their associated side‐effects, and reduced mobilisation. Poor mobility following sacral fracture has a significant impact on morbidity and mortality, as well as increasing hospital length of stay 1.

The sensory supply to the pelvis arises from the lumbar and sacral plexus. The sacral plexus arises from the L5–S4 nerve roots with a contribution from L4. The L4 and L5 roots fuse together to form the lumbosacral trunk which crosses the sacral ala, where it joins the S1 nerve root. The S1–S4 nerve roots emerge from their corresponding sacral foramina and form a wide plexus which terminates in the sciatic and pudendal nerves. This plexus lies in the pelvic cavity deep to the sacral fascia. Its relations are the iliac vessels, ureters and bowel anteriorly, and the piriformis muscle posteriorly. The sacral plexus innervates the entire pelvis other than the iliac crest and the pubis, which are supplied by the ilioinguinal and obturator nerves, respectively, and derived from the lumbar plexus 3.

Report

A 68‐year‐old woman suffered a right sacral ala and a left pubic ramus fracture following a fall from a horse. She suffered with chronic back pain caused by Tarlov cysts 4, and her regular medication included gabapentin, naproxen and amitriptyline. A computed tomography (CT) scan shortly after the injury demonstrated a stable sacrum but with multiple undisplaced fractures into the cysts. Following discussion with orthopaedic surgeons, radiologists and physiotherapists, a plan was agreed for conservative management with rest and oral analgesia. This included paracetamol and 10 mg oral morphine sulphate every 2 h, which was ineffective. She was subsequently referred to the acute pain team due to severe pain in the right posterior hip/gluteal region together with lower back paraesthesia. She had normal perianal sensation. She was unable to tolerate physiotherapy or comfortably sit beyond 45 degrees, mobilise, take a deep breath or cough. The possibility of providing analgesia via a sacral plexus catheter was discussed, including the associated risks, such as inadequate analgesia due to the lack of evidence for the technique and the rarity of its use. Despite this and other risks, such as infection, bleeding and nerve damage, she was keen to explore an option that may negate the requirement for oral opioids and which might improve analgesia.

A sacral plexus catheter was inserted using an ultrasound‐guided parasacral technique, targeting the sacral plexus immediately caudal to the posterior inferior iliac spine (PSIS) 5. She was positioned in the lateral decubitus position, based on a previously described technique 6. A full aseptic technique was used, including preparation of the skin with chlorhexidine 0.5%. The PSIS and the greater trochanter were identified and the curvilinear ultrasound transducer placed at the midpoint of the two until the iliac bone was visualised (Fig. 1). The ultrasound transducer was then moved in an inferomedial direction until the continuity of the iliac bone was disrupted. This is where the sacral plexus exits the pelvis below the piriformis muscle 6.

Figure 1.

Ultrasound image of the sacral plexus. The ultrasound transducer is positioned in an inferomedial direction on a line between the posterior superior iliac spine and greater trochanter.

The block was performed in‐plane, from left lateral to medial, and a catheter was placed. A bolus of 30 ml levobupiviciane 0.25% was injected and an infusion of 8 ml.h⁻¹ levobupiviciane 0.125% commenced. Immediate analgesia was observed, and the patient was able to sit comfortably. The pain intensity was now described as ‘bearable’. The infusion rate was titrated over the course of the next 3 days to 12 ml.h⁻¹. The catheter remained in situ for 7 days. The patient was then able to mobilise with the physiotherapists and reported that deep breathing and coughing were much less painful. No significant motor block was elicited at any point.

Discussion

We have described successful ultrasound‐guided sacral plexus catheter insertion for infusion of local anaesthesia in a patient with severe unilateral pain following sacral ala fracture. Ultrasound‐guided sacral plexus catheter placement has not previously been described, neither has the use of a sacral plexus catheter for the management of acute pain following pelvic fracture. The potential consequences of pelvic fractures are chronic pain, neurological damage, morbidity and mortality. The current mainstay of treatment for patients not requiring surgery is mobilisation and analgesia 2. Novel strategies include treatment with parathyroid hormone and sacroplasty, which involves injection of cement under CT or X‐ray guidance 2, but these are likely to have a role in long‐term healing and chronic pain rather than the acute setting.

The role of regional analgesia for fracture analgesia is well‐recognised. It has been shown to improve the outcomes of patients with neck of femur and rib fractures 7, 8, 9. Although we report a novel indication, ultrasound‐guided sacral plexus blocks have been described for surgical anaesthesia of the hip joint in conjunction with a lumbar plexus block 6. Parasacral approaches to the sacral plexus and sciatic nerve have also been widely reported 5. Potential advantages include unilateral analgesia with minimal unilateral motor block, reduced opioid consumption, reduced opioid side‐effects and the facilitation of mobilisation.

Sacral fractures can be accompanied by other fractures of the pelvis 2, such as a contralateral fracture of the pubic ramus. This was observed in our case and, clearly, a unilateral sacral plexus technique will not provide analgesia for an area innervated by the ilio‐inguinal nerve on the contralateral side. However, the patient's focus of severe pain was in the posterior hip, and the pain from the pubic ramus was managed effectively with multimodal analgesia. Currently, there is no evidence on the complications of continuous ultrasound‐guided sacral plexus blockade. In addition to risks common to all perineural techniques, such as local anaesthetic toxicity and unintentional intravascular injection, rectal perforation has been reported 5. Given the depth of the target, there is more risk of haematoma with parasacral blockade in comparison with more superficial blocks (such as femoral nerve blockade), due to relatively incompressible blood vessels 5.

Other analgesic options included oral opioids, patient‐controlled analgesia (PCA) or a lumbar epidural catheter. Oral opioids or intravenous patient‐controlled analgesia have side‐effects such as dizziness or respiratory depression, which may increase the risk of falls and further injury. Other adverse effects include constipation, urinary retention and nausea and vomiting. Increasingly, there is a trend to reduce peri‐operative opioid prescribing. Both acute and chronic opioid prescriptions have been implicated in impaired bone healing and an increased risk of fracture non‐union 10. Epidural analgesia is associated with rare but potentially catastrophic risks, such as bleeding, infection and nerve damage. There is a significant failure rate and sacral analgesia is not always achieved, even when sited at a low lumbar space. Although mobilisation of patients with epidural analgesia is possible, it seems logical that our unilateral technique may result in preserved motor function.

As with any case report, there are factors limiting generalisability. The severity of pain observed could have been due to pre‐existing Tarlov cysts, and a sacral catheter may not be routinely required for other patients with similar injuries. We are also unable to compare our technique with others, and have not demonstrated reproducibility, especially given that sacral plexus blockade can be technically challenging 5. As a large proportion of the pelvis is innervated by branches of the sacral plexus, we have since provided analgesia with sacral plexus blockade for several patients with acetabular fractures.

In conclusion, we have demonstrated that continuous sacral plexus analgesia is feasible for unilateral sacral fracture pain and we argue that regional anaesthesia may have a significant future role in the analgesic management of pelvic fractures.