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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor=William J Gibson
|QuestionAuthor=William J Gibson (Reviewed by  {{YD}}) and  {{AJL}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Anatomy
|MainCategory=Anatomy
Line 8: Line 8:
|MainCategory=Anatomy
|MainCategory=Anatomy
|SubCategory=Musculoskeletal/Rheumatology, General Principles
|SubCategory=Musculoskeletal/Rheumatology, General Principles
|MainCategory=Anatomy
|MainCategory=Anatomy
|MainCategory=Anatomy
|MainCategory=Anatomy
|MainCategory=Anatomy
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|MainCategory=Anatomy
|MainCategory=Anatomy
|SubCategory=Musculoskeletal/Rheumatology, General Principles
|SubCategory=Musculoskeletal/Rheumatology, General Principles
|Prompt=A newborn female was born via normal vaginal delivery to a 32 year old prima gavid woman. The pregnancy was complicated by gestational diabetes for which the mother took insulin before meals. The child now has an adducted, pronated left arm with flexion of the wrist.  The right arm is normal. Damage to which of the following nerves most likely caused this patient’s condition?
|Prompt=A 3-week-old girl is brought to the physician's office for asymmetric movement of her upper extremities. The mother reports that the girl is a first-born child. The girl weighed 4600 g at birth and is a product of a difficult assisted vaginal delivery with forceps. The pregnancy was complicated by gestational diabetes for which the mother was administered insulin before meals. On physical examination, the girl now has an adducted, medially rotated, and pronated left arm with flexion of the wrist and fingers, while the right arm is normal. Damage to which of the following nerves most likely caused this patient’s condition?
|Explanation=The patient in this vignette is suffering from Erb’s Palsy, a condition in which the upper trunk of the brachial plexus is injured.  Erb’s palsy is caused primarily by severe traction of the shoulder (shoulder dystocia) during birth. The most commonly involved root is C5 (aka Erb's point: the union of C5 & C6 roots)[8] as this is mechanically the furthest point from the force of traction, therefore, the first/most affected. The nerve roots normally involved are C5 and partly C6. Symptoms include paralysis of the biceps (through the musculocutaneous nerve); the brachioradialis (through the radial nerve); and the deltoid (through the axillary nerve). The effect is called "Erb's palsy" (see image). Typically, an affected person's arm hangs at the side with the hand rotated medially, like a waiter preparing to accept a tip; hence the colloquial name "waiter's tip hand". Some babies recover on their own, while others require surgical intervention for proper shoulder function.
|Explanation=[[Erb’s palsy]] (waiter's tip palsy) classically results from an injury to the nerve roots C5 and C6. Although injury to C7 nerve roots may be observed in Erb's palsy, less than 50% of patients have C7 nerve root injury. Patients are typically unable to abduct (deltoid and supraspinatus) or laterally rotate (infraspinatus) their shoulders due to involvement of C5 nerve root. Also, patients cannot supinate their arm (supinator) or flex their elbow (biceps and brachioradialis muscles) due to involvement of both C5 and C6. Finally, patients cannot extend their wrists (extensors) or their fingers (extensors) due to involvement of C6 (and possibly C7) nerve roots. Consequently, patients typically present similarly to the patient in the vignette with an adducted, pronated arm and flexed wrists and fingers.
[[File:Erb_palsy.jpg | centered | 400px]]
 
|AnswerA=Axillary Nerve
[[Erb’s palsy]] is often caused by shoulder dystocia at birth that results from severe traction of the shoulder during delivery. Risk factors for shoulder dystocia may be either maternal, fetal, or labor-related. Maternal factors include post-dates pregnancy, abnormal pelvic anatomy, gestational diabetes, short stature, obesity, and previous shoulder dystocia. The most important fetal factor is macrosomia (weight at birth > 4000 g). Labor-related factors include use of forceps of vacuums for delivery assistance and protracted labor.  
|AnswerAExp='''Incorrect:''' The axillary nerve is not typically directly damaged in Erb’s palsy.   However, the axillary nerve can no longer conduct nerve signals as the cervical roots that give rise to it are disrupted (C5-C6).  The axillary nerve innervates the deltoid muscle, which is responsible for abducting the arm.  Thus, patients with Erb’s palsy cannot abduct the affected arm.
 
|AnswerB=Radial Nerve
[[File:Erb.jpg | 600px]]
|AnswerBExp='''Incorrect:''' The radial nerve is not typically directly damaged in Erb’s palsy. However, the radial nerve can no longer conduct efferent nerve signals to the wrist extensors, as the cervical roots that give rise to the radial nerve are disrupted (C5-C6).
|AnswerA=Axillary nerve
|AnswerC=C5-C6
|AnswerAExp=The [[axillary nerve]] originates from the nerve roots C5 and C6. It is not directly damaged in [[Erb’s palsy]]. The [[axillary nerve]] innervates the deltoid muscle, disallowing patients with [[Erb’s palsy]] to abduct the affected arm.
|AnswerCExp='''Correct:''' The superior trunk of the brachial plexus is most often injured in Erb’s palsy at the eponymous Erb’s point, the union of the C5 and C6 nerve roots (see image). The patient will typically exhibit the classic "waiter's hand" appearance due to paralysis of the biceps, deltoid and wrist extensors.
|AnswerB=Radial nerve
|AnswerD=C6-C7
|AnswerBExp=The radial nerve is not directly damaged in [[Erb’s palsy]]. However, the radial nerve is unable to conduct efferent nerve signals to the wrist extensors, as the radial nerve originates from the C5 and C6 cervical nerve roots.
|AnswerDExp='''Incorrect:'''  C6 is often affected in Erb’s palsy, but C7 is not. Lesions of the C7 nerve root will affect the triceps and finger extension.
|AnswerC=C5-C6 nerve roots
|AnswerCExp=[[Erb’s Palsy]] classically results from an injury to the nerve roots C5-C6. Patients typically present with an adducted, pronated arm with flexion of the wrist and fingers.
|AnswerD=C6, C7 nerve roots
|AnswerDExp=While C6 is often affected in [[Erb’s palsy]], C7 is usually not involved. On the other hand, C5 is frequently involved in Erb's palsy. Lesions of the C7 nerve root would affect the triceps and finger extension.
|AnswerE=C8-T1
|AnswerE=C8-T1
|AnswerEExp='''Incorrect:'''  The C8-T1 nerve roots give rise to the Ulnar nerve. The Ulnar nerve is responsible for medial wrist and finger flexion. Lesion of the Ulnar nerve can occur due to fracture of the medial epicondyle of the humerus. This type of lesion will cause weakness of handgrip and radial deviation of the hand on wrist flexion.
|AnswerEExp=The ulnar nerve originates from the C8-T1 nerve roots. The ulnar nerve is responsible for medial wrist and finger flexion. Lesion of the ulnar nerve typically results from a fracture of the medial epicondyle of the humerus. Lesion of the C8-T1 nerve roots is called [[Klumpke’s palsy]].
|EducationalObjectives=[[Erb’s Palsy]] clasically results from an injury to the nerve roots C5-C6. Patients typically present with an adducted, pronated arm with flexion of the wrist and fingers. [[Erb’s palsy]] is often caused by shoulder dystocia at birth that results from severe traction of the shoulder during delivery. Assisted delivery, macrosomia, and gestational diabetes are 3 risk factors for shoulder dystocia.
|References=Chatfield J. ACOG issues guidelines on fetal macrosomia. American College of Obstetricians and Gynecologists. Am Fam Physician. 2001; 64(1):169-70.<br>
Chater M, Camfield P, Camfield C. Erb's palsy - Who is to blame and what will happen? Paediatr Child Health. 2004;9(8):556-60.<br>
Modanlou HD, Dorchester WL, Thorosian A, et al. Obstet Gynecol. 1980;55(4):420-4.<br>
Nath RK, Kumar N, Avila MB, et al. Risk factors at birth for permanent obstetric brachial plexus injury and associated osseous deformities. ISRN Pediatr. 2012;E-pub.<br>
 
First Aid 2014 page 413
|RightAnswer=C
|RightAnswer=C
|WBRKeyword=Brachial plexus, Brachial, Plexus, Nerve, Erb's, Palsy, Erb's Palsy, Arm, Upper Limb, Muscle, Limb
|WBRKeyword=Brachial plexus, Nerve, Erb's palsy, Erb palsy, Waiter's tip palsy, Palsy, Shoulder dystocia, Dystocia, Delivery, Gestational diabetes, Macrosomia, Normal vaginal delivery
|Approved=Yes
|Approved=Yes
}}
}}

Latest revision as of 00:41, 28 October 2020
Author [[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.) and Alison Leibowitz [1])]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Anatomy
Sub Category SubCategory::Musculoskeletal/Rheumatology, SubCategory::General Principles
Prompt [[Prompt::A 3-week-old girl is brought to the physician's office for asymmetric movement of her upper extremities. The mother reports that the girl is a first-born child. The girl weighed 4600 g at birth and is a product of a difficult assisted vaginal delivery with forceps. The pregnancy was complicated by gestational diabetes for which the mother was administered insulin before meals. On physical examination, the girl now has an adducted, medially rotated, and pronated left arm with flexion of the wrist and fingers, while the right arm is normal. Damage to which of the following nerves most likely caused this patient’s condition?]]
Answer A AnswerA::Axillary nerve
Answer A Explanation [[AnswerAExp::The axillary nerve originates from the nerve roots C5 and C6. It is not directly damaged in Erb’s palsy. The axillary nerve innervates the deltoid muscle, disallowing patients with Erb’s palsy to abduct the affected arm.]]
Answer B AnswerB::Radial nerve
Answer B Explanation [[AnswerBExp::The radial nerve is not directly damaged in Erb’s palsy. However, the radial nerve is unable to conduct efferent nerve signals to the wrist extensors, as the radial nerve originates from the C5 and C6 cervical nerve roots.]]
Answer C AnswerC::C5-C6 nerve roots
Answer C Explanation [[AnswerCExp::Erb’s Palsy classically results from an injury to the nerve roots C5-C6. Patients typically present with an adducted, pronated arm with flexion of the wrist and fingers.]]
Answer D AnswerD::C6, C7 nerve roots
Answer D Explanation [[AnswerDExp::While C6 is often affected in Erb’s palsy, C7 is usually not involved. On the other hand, C5 is frequently involved in Erb's palsy. Lesions of the C7 nerve root would affect the triceps and finger extension.]]
Answer E AnswerE::C8-T1
Answer E Explanation [[AnswerEExp::The ulnar nerve originates from the C8-T1 nerve roots. The ulnar nerve is responsible for medial wrist and finger flexion. Lesion of the ulnar nerve typically results from a fracture of the medial epicondyle of the humerus. Lesion of the C8-T1 nerve roots is called Klumpke’s palsy.]]
Right Answer RightAnswer::C
Explanation [[Explanation::Erb’s palsy (waiter's tip palsy) classically results from an injury to the nerve roots C5 and C6. Although injury to C7 nerve roots may be observed in Erb's palsy, less than 50% of patients have C7 nerve root injury. Patients are typically unable to abduct (deltoid and supraspinatus) or laterally rotate (infraspinatus) their shoulders due to involvement of C5 nerve root. Also, patients cannot supinate their arm (supinator) or flex their elbow (biceps and brachioradialis muscles) due to involvement of both C5 and C6. Finally, patients cannot extend their wrists (extensors) or their fingers (extensors) due to involvement of C6 (and possibly C7) nerve roots. Consequently, patients typically present similarly to the patient in the vignette with an adducted, pronated arm and flexed wrists and fingers.

Erb’s palsy is often caused by shoulder dystocia at birth that results from severe traction of the shoulder during delivery. Risk factors for shoulder dystocia may be either maternal, fetal, or labor-related. Maternal factors include post-dates pregnancy, abnormal pelvic anatomy, gestational diabetes, short stature, obesity, and previous shoulder dystocia. The most important fetal factor is macrosomia (weight at birth > 4000 g). Labor-related factors include use of forceps of vacuums for delivery assistance and protracted labor.


Educational Objective: Erb’s Palsy clasically results from an injury to the nerve roots C5-C6. Patients typically present with an adducted, pronated arm with flexion of the wrist and fingers. Erb’s palsy is often caused by shoulder dystocia at birth that results from severe traction of the shoulder during delivery. Assisted delivery, macrosomia, and gestational diabetes are 3 risk factors for shoulder dystocia.
References: Chatfield J. ACOG issues guidelines on fetal macrosomia. American College of Obstetricians and Gynecologists. Am Fam Physician. 2001; 64(1):169-70.
Chater M, Camfield P, Camfield C. Erb's palsy - Who is to blame and what will happen? Paediatr Child Health. 2004;9(8):556-60.
Modanlou HD, Dorchester WL, Thorosian A, et al. Obstet Gynecol. 1980;55(4):420-4.
Nath RK, Kumar N, Avila MB, et al. Risk factors at birth for permanent obstetric brachial plexus injury and associated osseous deformities. ISRN Pediatr. 2012;E-pub.

First Aid 2014 page 413]]

Approved Approved::Yes
Keyword WBRKeyword::Brachial plexus, WBRKeyword::Nerve, WBRKeyword::Erb's palsy, WBRKeyword::Erb palsy, WBRKeyword::Waiter's tip palsy, WBRKeyword::Palsy, WBRKeyword::Shoulder dystocia, WBRKeyword::Dystocia, WBRKeyword::Delivery, WBRKeyword::Gestational diabetes, WBRKeyword::Macrosomia, WBRKeyword::Normal vaginal delivery
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