Intrapartum injuries to the lumbosacral plexus generally involve the lumbar part of the plexus. This is due to its position above the pelvic brim rendering it susceptible to compression by the fetal head. Risk factors include short maternal stature and cephalopelvic disproportion.
Postpartum Neuropathies Summary
|Nerve||Site of compression||Symptoms||Signs||Additional features|
|Lateral cutaneous nerve (L2-3)||Under the inguinal ligament or against the ASIS||Neuropathic pain or paraesthesia lateral thigh, often worse with standing or walking||sensory loss lateral thigh||Associated with prolonged hip flexion (lithotomy)|
|Femoral (L2-4)||Under the inguinal ligament or against the ASIS||Altered sensation in the femoral distribution, difficulty with climbing stairs||sensory loss in nerve distribution, knee extension weakness, decreased patellar reflex||Associated with prolonged hip flexion, bilateral in 25%.|
|Obturator (L2-4)||Lateral wall of lesser pelvis||Groin pain and difficulty walking||Sensory loss inner thigh, weakness of hip adduction and internal rotation||bilateral in 25%, commonly associated with femoral nerve injury|
|Lumbosacral plexus (L4-S3)||Posterior pelvic brim against the sacral ala||Abnormal sensation in the lumbosacral distribution. Tripping due to foot drop||Sensory loss lateral aspect of the leg and dorsum of the foot, weakness of dorsiflexion and eversion||Usually unilateral|
|Lumbosacral trunk / furcal nerve (L4-5) part of the lumbosacral plexus||Compression from fetal head on pelvic brim||Tripping due to foot drop||Sensory loss foot and lateral aspect of the leg. Weak dorsiflexion, eversion, and inversion.||Usually unilateral. Associated with arrested labour.|
|Common peroneal (L4-5, S1-2)||Head of fibula||Tripping due to foot drop||Sensory loss in nerve distribution, weakness of dorsiflexion and eversion||Associated with poor lithotomy positioning|
Upper Lumbar Lesions
Upper lumbar plexus lesions display symptoms in the iliohypogastric, ilioinguinal, genitofemoral, femoral, and obturator nerves. The patient may have reduced strength of hip flexion and knee extension (L2-4) due to weakness of psoas, iliacus, pectineus, sartorius, and quadriceps. Some patients may have a weakness of thigh adduction due to involvement of adductor longus, brevis, anterior half of magnus, and gracilis. There may be sensory loss in the lower abdomen, inguinal region, thigh excluding posteriorly, and the lower medial leg. The knee reflex is from L3-4 and may be reduced.
Lumbosacral Trunk Lesions
This is the most common lesion. The trunk is not protected by the psoas muscle, leaving it vulnerable to compression on the pelvic brim by the fetal head. Symptoms include a foot drop due to weakness of the anterior compartment of the leg with involvement of the tibialis anterior, extensor hallucis longus, and extensor digitorum longus. The patient may also have weak ankle dorsiflexion, eversion, inversion, and toe flexion. There may be buttock pain and gluteal and hamstring weakness. Sensory loss can be seen in the lateral leg and dorsum of the foot in an L5 dermatomal pattern. The ankle jerk is typically normal as this is supplied by S1, as is plantarflexion.