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Ultrasound interventional pain management during pregnancy

The sacroiliac joint is the source of pain in 50 per cent of the patients during pregnancy.

Non-obstetric painful syndromes are a common problem during pregnancy, It has been estimated that 90 per cent of women would experience some form of pain during the gestation period. The main reason for the occurrence of pain is musculoskeletal changes that accompany pregnancy. With the start of pregnancy, there is a release of a large number of certain hormones namely, oestrogen, progesterone, relaxin and prolactin, which have a known effect on the collagen remodeling and increase joint laxity and hyper-mobility.

Furthermore, weight gain, fluid retention, the position of the gravid uterus and anterior pelvic tilt during pregnancy will lead to additional mechanical effects on the musculoskeletal system, which intensify the painful syndromes.

The most common pain syndromes that happen because of pregnancy may include low back, pelvic girdle and radicular leg pain. It also includes abdominal cutaneous nerve entrapment, carpal tunnel syndromes and De Quervain’s tenosynovitis. Parturients may complain from neuralgia of the occipital, intercostal, pudendal, obturator and lateral femoral cutaneous nerves.

Furthermore, pregnant women may present with small joint arthralgia and foot pain secondary to tarsal tunnel syndrome or plantar fasciitis. Moreover, physiological changes with pregnancy may exaggerate already existing chronic painful conditions such as migraine, cervical or lumbar disc disease, lumbar spondylosis and facet joint arthropathy.

Conservative treatment with non-pharmacological remedies such as physiotherapy and body supports are the first line to treat pregnancy-induced pain. However, many of the patients may not be contented and require pharmacological treatment. It is well known that an untreated painful condition might constitute a higher risk to the foetus compared to medications.

Careful assessment of the parturient condition should be performed before prescribing medications as nearly all medications given to the mother will cross the placenta and reach the foetus. The effect of the drug on the foetus depends on the drug category, gestational age and duration of exposure. Possible side effects of the medications may include congenital anomalies, growth retardation, intrauterine foetal death, neonatal intoxication and neonatal abstinence syndrome. Therefore, the non-systemic administration of medications is considered a safer solution.

Interventional pain management is a relatively new specialty. The basic principle for interventional treatment is to identify precisely the source of pain, whether nerve, muscle, tendon or joint, and deliver the medications directly to the diseased part through a minimally invasive procedure.

This procedure gives permanent or long-term pain relief and at the same time, avoids systemic administration of the drug. This treatment method hypothetically matches the requirement for pain relief during pregnancy. Procedures can be done under CT, X-Ray or ultrasound. However, during pregnancy, only ultrasound-guided procedures are performed. Common painful pregnancy conditions and their interventional treatments include:

Sacroiliac joints dysfunction

Back pain during pregnancy is considered one of the most common problems. The patient can suffer from mild, moderate or severe pain. Previous works showed that one-third of the parturients would present with severe back pain (pain score > 6/10). Pain typically started during the second or third trimester; however, some patients will have severe pain from the beginning of pregnancy. There are multiple pain generators in the back, yet, the sacroiliac joint is the source of pain in 50 per cent of the patients. If parturient is complaining of sacroiliac joint pain, she may present with one or all of the following: (1) Low back pain with maximum tenderness over the posterior superior iliac spine, (2) Groin pain, (3) Hip and lateral thigh pain and/ or (4) posterior calf pain. The patient might present with unilateral or bilateral pain, and the pain could be axial or radiating to the legs. Clinical diagnosis can be made when there are > three positive provocation tests. In general, there is no need for imaging to support the diagnosis of sacroiliac joint dysfunction unless it is absolutely indicated. In case refractory pain did not respond to conservative management, interventional treatment should be offered to the patient.

An ultrasound-guided sacroiliac joint injection can be safely done during pregnancy. The procedure can be performed in a prone, lateral or sitting position (Figure 1) based on the pregnancy duration and operator experience. As the pain is mainly due to the laxity of the supportive ligaments, the majority of the medications should be deposited extra-articular rather than intra-articular. Medications consist of local anaesthetic, either lidocaine or bupivacaine and corticosteroids, which usually administered during pregnancy for foetal lung maturation.

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Fig 1: Injection of the left sacroiliac joint injection in 32 weeks patient patients in sitting position.

 

Carpal tunnel syndrome

The compression of the median nerve at the wrist below the flexor retinaculum is another pregnancy related painful condition. It has an incidence of between 2.3 to 35 per cent. Parturient usually present during the second or third trimester with numbness, tingling and throbbing sensation, which may worsen at night. If the condition becomes severe, additionally, there will be a difficulty for hand gripping and performing fine motor hand skill. The pain ranges from mild to severe, and the patient may complain from one or both hands. Fluid retention is the main reason for the occurrence of carpal tunnel syndrome. Predisposing factors include obesity, gestational diabetes and hypertension as they may lead to more fluid retention.

Carpal tunnel syndrome can be diagnosed clinically by positive Tinel’s sign and Phalen’s manoeuvre. The diagnosis is usually confirmed by nerve conduction and electromyography (EMG); however, recently, a simple bedside test using ultrasound can be used. The measurement of the cross-sectional area (CSA) of the median nerve could be diagnostic. The typical CSA of the median nerve is up to 0.09 cm2, and it had been documented that a CSA of the median nerve ≥ 0.13 cm2 confirms the diagnosis of carpal tunnel syndrome.

The interventional injection will be offered to the patient if she has two positive diagnostic tests with a documented enlarged median nerve by ultrasound (in case of failure of medical treatment). The injection of local anaesthesia with corticosteroids is done under ultrasound either in a longitudinal or transverse plane approach. The author prefers to use the in-plane transverse ulnar approach as this ensures the placement of injectable below the flexor retinaculum with less chance of injury to the median nerve (Figure 2).

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Fig 2: Injection of the right carpal tunnel in transverse ulnar approach.

Besides, during pregnancy, there is no inflammation and adhesion between the median nerve and the flexor retinaculum, and there is no need for further dissection above the wrist.

Meralgia paresthetica

Pregnant women present with a painful burning sensation in the lateral or anterolateral aspect of the thigh. This condition appears during pregnancy due to compression of the lateral femoral cutaneous nerve (LFCN) below the fascia lata, at the level of the inguinal ligament. It is a pure sensory nerve with the absence of any motor symptoms. The pain is usually aggravated by prolonged sitting, standing or sleeping on the affected side. A clinical neurological examination will demonstrate loss of sensation in the affected area with normal reflexes and motor function.

Ultrasound-guided injection of the LFCN can be conveniently done in pregnant patients. The nerve and its branches will be located above the sartorius muscle when the high-frequency ultrasound probe inserted above the inguinal ligament with the heal of the probe just lateral to the anterior superior iliac spine. A small volume of local anaesthetic and corticosteroids are sufficient to alleviate the pain.

Conclusion

Pregnancy is associated with multiple painful conditions secondary to hormonal, musculoskeletal changes and fluid retention. Interventional procedures are safe and effective treatment modalities. Awareness among healthcare professionals with this new management approach will improve patients care and decreases the side effects of medications during pregnancy.

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