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Difficulty: MediumLabor, Delivery, and Puerperium

A medical student is reviewing maternal lower extremity neuropathies that can occur as complications of labor, operative positioning, or fetal descent. Match each classic postpartum clinical presentation with the specific compromised nerve.

  • A patient develops weakness in knee extension, an absent patellar reflex, and numbness over the anterior thigh after a 3-hour second stage of labor in a hyperflexed lithotomy position.Femoral nerve neuropathy
  • A patient exhibits a noticeable foot drop and sensory loss over the lateral lower leg and dorsum of the foot following prolonged compression of the lateral knee against hard stirrups.Common fibular (peroneal) nerve neuropathy
  • A patient complains of weakness in leg adduction and numbness isolated to the medial aspect of the thigh following prolonged descent of a macrosomic fetus through the maternal pelvis.Obturator nerve neuropathy
  • A patient experiences fecal incontinence and severe perineal numbness despite an intact anal sphincter complex on examination, following a difficult forceps-assisted delivery.Pudendal nerve neuropathy

Answer

1 matches with Femoral nerve neuropathy, 2 matches with Common fibular (peroneal) nerve neuropathy, 3 matches with Obturator nerve neuropathy, and 4 matches with Pudendal nerve neuropathy.
Each neuropathy is correctly identified by combining its specific neuroanatomical distribution (motor and sensory deficits) with its classic intrapartum risk factor (e.g., hyperflexed hips compressing the femoral nerve, hard stirrups compressing the common fibular nerve, fetal head compressing the obturator nerve, and operative stretching of the pudendal nerve).

Step-by-Step Solution

1
Analyze the first clinical presentation: weakness in knee extension, absent patellar reflex, and anterior thigh numbness after prolonged hyperflexion of the hips.
Identify this as femoral nerve neuropathy.
The femoral nerve innervates the anterior thigh compartment (quadriceps) and provides sensation to the anterior thigh. It is classically compressed under the inguinal ligament when hips are hyperflexed in the lithotomy position.
2
Analyze the second presentation: foot drop, lateral lower leg sensory loss, and history of compression against hard stirrups.
Identify this as common fibular (peroneal) nerve neuropathy.
The common fibular nerve wraps around the lateral fibular neck, making it susceptible to external compression from poorly padded stirrups. Injury causes weakness in foot dorsiflexion and eversion.
3
Analyze the third presentation: weakness in leg adduction and medial thigh numbness following fetal descent.
Identify this as obturator nerve neuropathy.
The obturator nerve exits through the obturator foramen along the lateral pelvic wall, where it can be directly compressed by a large fetal head descending through the pelvis, affecting the medial thigh sensory and motor (adductor) distribution.
4
Analyze the fourth presentation: fecal incontinence and perineal numbness without anatomical sphincter disruption following forceps delivery.
Identify this as pudendal nerve neuropathy.
The pudendal nerve provides motor supply to the external anal sphincter and sensory supply to the perineum. It can be stretched excessively during vaginal delivery, particularly with operative assistance, leading to functional incontinence despite an intact sphincter.

Key Concept

Maternal obstetric neuropathies result from distinct mechanisms of nerve compression or stretch during labor and delivery, with each compromised nerve presenting with a classic and predictable pattern of motor and sensory deficits.
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Topics

Labor, Delivery, and Puerperium

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