Ischiofemoral impingement syndrome provoked by labor: An unusual case of complete sciatic mononeuropathy

Abstract

Peripheral neuropathies are a recognized complication of labor in the post-partum period. Herein, we describe an uncommon presentation of sciatic mononeuropathy due to ischiofemoral impingement during labor. A 29-year-old, gravida 4 para 2, female presented post-partum with acute left lower limb paresthesia and left foot drop, following spontaneous vaginal delivery of twins. Neurological examination demonstrated no activation of the left sciatic-innervated muscles and sensory loss in the same distribution. Electromyography (EMG) demonstrated an acute complete left sciatic mononeuropathy. MRI of the lumbosacral plexus and sciatic nerve showed a narrowed quadratus femoris space with mild edema of the muscle, consistent with ischiofemoral impingement syndrome. In addition, there was flattening of the sciatic nerve as it passed through the ischiofemoral space. She was treated conservatively, and at 7-month follow-up, there was marked improvement in muscle strength with ongoing sensory impairment. Repeat EMG demonstrated reinnervation in all sciatic-innervated muscles. This case highlights the risk of a sciatic mononeuropathy secondary to ischiofemoral impingement in the peripartum setting. Future studies are needed to determine if women with a narrow ischiofemoral space at baseline are at increased risk for peripheral nerve injury during labor.

Background and aims

Post-partum peripheral nerve injury is a recognized complication with a reported incidence of just under 1%. ¹ The lateral femoral cutaneous nerve is the most commonly involved nerve, followed by the femoral and peroneal nerves. ² Sciatic mononeuropathy in the post-partum period has been infrequently described, characterized by pain, sensory loss, and weakness in a tibial or peroneal nerve distribution. Risk factors for the development of neuropathy during the peripartum and post-partum period include nulliparity, a prolonged second stage of labor, instrumental usage, and short stature.^1,2 Prior reported cases of sciatic neuropathies associated with childbirth have been largely iatrogenic in nature. Most recently, in 2020, Kim et al. published the first report of a case of sciatic neuropathy following vaginal delivery. ³ Therein, the authors postulate that the etiology of this patient’s neuropathy may have been secondary to prolonged nerve entrapment while in the lithotomy position.

We describe an uncommon presentation of sciatic mononeuropathy following spontaneous vaginal delivery of twins. In addition, we propose a novel association between labor and the development of symptomatic ischiofemoral impingement (IFI).

Case report

A 29-year-old Caucasian multiparous female (gravida 4 para 2) presented with acute onset of painless left lower limb weakness following the spontaneous vaginal delivery of twins. The first stage of her labor was 1 h 24 min, while the second stage of her labor was 39 min. She received routine epidural anesthesia with no known immediate complications. As the effect of the epidural waned over the following 24 h, the patient reported painless left foot drop and paresthesias of the left lower limb to the level of the knee. Examination revealed 0/5 strength (Medical Research Council scale, MRC) of dorsiflexion, plantar flexion, inversion, eversion, and toe flexion/extension, and an absent left Achilles reflex. Sensory examination revealed absent pinprick sensation over the dorsum of the left foot, more pronounced on the medial aspect and first two digits (superficial peroneal and medial plantar sensory distribution).

On day 13 following her presentation, the patient underwent electrodiagnostic testing. Nerve conduction studies (NCS) showed a low-amplitude left peroneal compound muscle action potential (CMAP) (0.3 mV compared to 5.5 mV on the right side); normal bilateral tibial CMAP; absent left peroneal sensory nerve action potential (10 μV on the right side); and a low-amplitude left sural sensory response (5 μV compared to 18 μV on the right side). Left-sided needle electromyography showed no activated motor unit potentials in the sciatic-innervated muscles. There were no abnormalities on needle examination of the proximal L5 and S1 muscles, nor in the lower lumbar paraspinals. There were no fibrillation potentials. These findings are in keeping with an acute complete left sciatic neuropathy with no evidence of reinnervation. An MRI of the lumbosacral plexus and entire nerve path demonstrated a narrowed quadratus femoris space (measuring 8 mm) with mild edema of the muscle, consistent with ischiofemoral impingement syndrome (Figure 1(a)–(c)). In addition, there was flattening of the sciatic nerve as it passed through the ischiofemoral space, with enlargement, fascicular T2 hyperintensity, and enhancement of the nerve both proximal and distal to the site of impingement, extending all the way through the thigh (Figure 1(c)). The posterior thigh compartment muscles demonstrated evidence of subacute denervation changes with mild edema and atrophy, visible on the MR images (Figure 1(d)). The patient was treated conservatively. She underwent physical therapy.

Figure 1.

Axial T2W (a, c, d) and an axial SPGR post-gadolinium-enhanced (b) image from the patient’s pelvic MRI are shown. The top images (a, b) are above the ischiofemoral space, whereas the bottom images are at the level of the quadratus femoris space (c) and at the level of the mid thighs (d). There is enlargement, T2 hyperintensity, and enhancement of the left sciatic nerve proximally (a, b, solid arrows) with abrupt tapering of the nerve as it passes through the ischiofemoral and quadratus femoris spaces (c, solid arrow). The quadratus femoris space itself is narrowed to approximately 8 mm (c). More distally at the level of the mid thighs, there is mild T2 hyperintensity of the posterior thigh muscles (d, arrows). The hamstring muscle origins (c, dashed arrow), lesser trochanter (c, arrowhead), and quadratus femoris (b, dashed arrow) are denoted. The right sciatic nerve appears normal.

At 7-month follow-up, the patient reported significant improvement in her strength, with residual sensory deficit. On examination, she had MRC grade 4-/5 foot dorsiflexion and eversion, 4/5 foot inversion, 5/5 foot plantar flexion, 3/5 toe extension, and 4-/5 toe flexion, and an ongoing absent Achilles reflex. Sensory loss was confined to the area between the first and second metatarsals. Repeat NCS were relatively unchanged. Repeat needle electromyography demonstrated chronic neuropathic changes with mildly to moderately reduced recruitment of long duration, high amplitude motor unit potentials, with occasional fibrillation potentials, in the left sciatic-innervated muscles. These findings correlated with her clinical improvement.

Interpretation

The sciatic nerve originates from the ventral rami of spinal nerves at L4-S3 within the lumbosacral plexus, eventually converging into a single nerve. It then leaves the pelvis via the greater sciatic foramen, which is situated between the deeper gemelli, obturator internus, and the superficial piriformis muscles. After moving alongside or through the piriformis muscle, the sciatic nerve runs posteriorly to the obturator/gemelli complex and quadratus femoris muscle. The nerve then passes along the posterior surface of the quadratus femoris muscle, between the ischial tuberosity and the proximal femur, near the posterior capsule of the hip. Finally, it descends along the posterior compartment of the thigh, dividing into the tibial and common peroneal nerves.

During pregnancy, the gluteal muscles of the hip and pelvis region can become lax, resulting in elongation and strain, which can distort normal anatomy. Positioning during labor can further exacerbate these changes. IFI syndrome is impingement of soft tissues between the bony prominences of the ischial tuberosity and the lesser trochanter. It is characterized by decreased ischiofemoral and quadratus femoris spaces affecting the contents within these areas with prototypical quadratus femoris edema as was seen in our case. ⁴ In healthy controls, the ischiofemoral space measures between 15 and 31 mm, in contrast to the measurement of just 7.9 mm as is seen in this case. A recent meta-analysis of MRI exams found that using a cutoff of ≤15 mm for the ischiofemoral space yielded a sensitivity of 76.9%, and specificity of 81.0%, while a cutoff of ≤10.0 mm for the quadratus femoris space resulted in 78.7% sensitivity, and 74.1% specificity. ⁴

IFI syndrome is typically a chronic presentation with non-specific pain in the deep gluteal region, differing from our case who had a dramatic presentation. ⁵ Acute IFI syndrome has been previously reported as a result of either direct hip trauma or hip surgery. ⁶ To our knowledge, this is the first documented case of acute IFI syndrome due to childbirth. Our patient had no preceding symptoms, nor any history of hip surgery or trauma. We postulate that the patient’s variant anatomy with narrowing of the ischiofemoral space, the musculoskeletal pregnancy-related physiological changes, and the twin pregnancy, in the setting of patient positioning during labor, culminated in the development of IFI and subsequent sciatic mononeuropathy.

There is no definitive treatment strategy for IFI. Endoscopic decompression of sciatic neuropathies has been described, with some success, however this was for a variety of compressive etiologies and not definitively related to post-partum IFI. ⁷ Typically, conservative management is considered first-line. ⁸ Our patient did not have surgical intervention and had a good recovery. Now her condition is known, we have recommended against the prolonged lithotomy position for future pregnancies.

Clinicians should be familiar with the potential for the development of sciatic mononeuropathies during labor, even in the absence of traditional risk factors. EMG and MRI were particularly useful in our case, by confirming the diagnosis and localizing the pathological anatomical etiology. Future studies are needed to determine if women with a narrow ischiofemoral space are at increased risk for peripheral nerve injury during labor.

ORCID iDs

Jacqui-Lyn Saw https://orcid.org/0000-0003-1180-7929

Ajay Madhavan https://orcid.org/0000-0003-1794-4502

Michael D Ringler https://orcid.org/0000-0003-4870-4237