1. The Snapping Medial Antebrachial Cutaneous Nerve A New Entity of Snapping Elbow
Alper Cesmebasi, MD1,2, Shawn W O’Driscoll, MD, PhD3, Jay Smith, MD4,5,
John A Skinner, MD4, and Robert J Spinner, MD1,3.
1Department of Neurologic Surgery, Mayo Clinic, Rochester, MN, USA,
2Department of Anatomical Sciences, St George’s University, Grenada, West Indies,
3Department of Orthopedics, Mayo Clinic, Rochester, MN, USA,
4Department of Radiology, Mayo Clinic, Rochester, MN, USA,
5Department of Physical Medicine and Rehabilitation, Mayo Clinic, Rochester, MN , USA
32nd Annual Meeting of the American Association of Clinical Anatomists
11 June 2015
test

2. Snapping Phenomenon
Snapping occurs when a structure dislocates over a bony prominence resulting in a palpable sensation, sometimes with an audible noise
The snapping phenomenon have been described in a number of joints and may be symptomatic or asymptomatic
Snapping of a neural structure may be associated with friction neuritis or neuropathy with entrapment

3. Snapping Ulnar Nerve
Snapping elbow is a condition where flexion elicits a painful, popping sensation
The most frequent etiology of snapping elbow is anterior dislocation of the ulnar nerve
Childress (1956) describes ulnar nerve hypermobility
Type A- Incomplete dislocation leaving the nerve prone to direct trauma
Type B- Complete dislocation of the nerve leaving it prone to friction neuritis

4. * Figure from Childress HM: Recurrent ulnar-nerve dislocation at the elbow. J Bone Joint Surg Am 38: , 1956.

5. Snapping Ulnar Nerve
Snapping ulnar nerve may present with sensory changes along the medial aspect of the forearm and 4th/5th digits and hypothenar weakness.
Complaints:
Transient to more permanent pain and numbness with elbow flexion
Lose of grip and motor tasks in ipsilateral hand

6. Snapping Triceps
Ulnar nerve dislocation may also occur secondary to medial triceps snapping
In snapping triceps, the triceps pushes the ulnar nerve over the medial epicondyle resulting in two separate snaps
Failure to treat snapping triceps may result in persistent symptoms

7. Snapping Triceps

8. Methods
Review of the records of four patients with snapping of the medial antebrachial cutaneous nerve (MABC) over the medial epicondyle with elbow flexion
All patients underwent preoperative dynamic ultrasound and surgical exploration of the medial elbow

9. Review
Four patients (one male and three females) with complaints of a popping sensation in the elbow, pain over the medial aspect of the forearm, and ulnar neuritis
Physical examination demonstrated a dislocating structure in all cases
EMG was normal in three patients
Preoperatively, all patients underwent dynamic ultrasound and were found to have a snapping structure
Retrospective review of the ultrasounds revealed the snapping structures as snapping MABCs.

10. Results (History/Physical)
Case 1
Case 2
Case 3
Case 4
Age/Sex
16 yo F
9 yo M
32yo F
17yo F
Affected Side
Right
Left
Duration
21 mo
15 mo
36 mo
Symptoms
Medial elbow pain
Yes
Posteromedial forearm pain
Popping/Snapping
Motor symptoms No
Physical Examination
Snapping structure
Medial epicondyle tenderness
Dislocating ulnar nerve
Yes*
Dislocating triceps

11. Results (Workup/Treatment)
Case 1
Case 2
Case 3
Case 4
Electrophysiological Testing
Ulnar nerve
Normal
N/A
Ultrasound Findings
Dislocation of ulnar nerve No
Yes
Dislocation of triceps
Intraoperative Findings
Snapping ulnar nerve
Snapping triceps
Snapping MABC
Prior Surgical Treatment
Treatment
MABC transposition
Mobilization
Ulnar transposition
Revision
Medial triceps resection

12. Case Illustration
Case 2: 9 yo M with 15 month history of right posteromedial elbow and medial forearm pain
Injury sustained by a fall on an outstretched hand during wrestling practice
Sx: persistent popping/snapping sensation with elbow flexion and numbness /pain on flexion

13. Case Illustration
Physical Exam: tenderness over the right posterior medial epicondyle; snapping triceps and ulnar nerve were noted
Imaging (US): Snapping ulnar nerve and fascial slip thought to be the medial triceps
Dx: Snapping triceps with ulnar nerve dislocation
Plan: Ulnar nerve decompression with possible transposition; partial resection of the medial triceps

14. Case Illustration (Patient 2)

15. Case Illustration (Patient 2)

16. Medial Antebrachial Cutaneous Nerve
The MABC arises from the medial cord of the brachial plexus and divides into anterior and posterior branches
Damage to the posterior branch is more common due to its relative close proximity to the medial epicondyle

17. Variations in MABC
Race and Saldana (1991) noted variations in number and distribution
Arborization of 5-8 branches 2 cm proximal to medial epicondyle
3-7 branches sent to the deep fascia overlaying the medial epicondyle and olecranon
Tanaka and Lourie (2013) noted variations in course of the MABC
MABC pierces the deep fascia on average 9.2 cm proximal to the medial epicondyle
Posterior branches cross the medial epicondyle 3.2cm proximal to 5.8cm distal to it

18. Medial Antebrachial Cutaneous Nerve
Snapping of the MABC has not been previously described.
Presents with posteromedial elbow and medial forearm sensory changes with no motor weakness
Given its location and variability, the constellation of symptoms can be easily understood
Snapping structures may also carry over the MABC

19. Misdiagnosis Snapping MABC may be misdiagnosed
Results in treatment which delays appropriate diagnosis and treatment

20. Dynamic Ultrasound Dynamic imaging plays key role in diagnosis
Concurrent snapping structures should warrant suspicion of snapping MABC
Prior elbow pathologies warrant a high degree of clinical suspicion (i.e. history of ulnar transposition with persistent symptoms)
Prospectively identification of snapping MABC may be difficult due to a number of factors
Easily overlooked for other common pathologies
Regional anatomy may camouflage the MABC due its size
Excess transducer pressure may preclude distinguishing snapping structures

21. Snapping MABC

22. Conclusions
Snapping MABC is a new differential diagnosis of snapping elbow syndrome.
Patients may present with snapping pain and ulnar distribution symptoms.
Snapping MABC may be concurrent with snapping triceps and ulnar nerve.
Awareness of this entity can help avoid misdiagnoses.

23. References
Calfee RP, Manske PR, Gelberman RH, Van Steyn MO, Steffen J, Goldfarb CA: Clinical assessment of the ulnar nerve at the elbow: reliability of instability testing and the association of hypermobility with clinical symptoms. J Bone Joint Surg Am 92: , 2010.
Childress HM: Recurrent ulnar-nerve dislocation at the elbow. J Bone Joint Surg Am 38: , 1956.
Dellon AL, MacKinnon SE: Injury to the medial antebrachial cutaneous nerve during cubital tunnel surgery. J Hand Surg Br 10:33-36, 1985.
Guillin R, Marchand AJ, Roux A, Niederberger E, Duvauferrier R: Imaging of snapping phenomena. Br J Radiol 85: , 2012.
Jacobson JA, Jebson PJ, Jeffers AW, Fessell DP, Hayes CW: Ulnar nerve dislocation and snapping triceps syndrome: Diagnosis with dynamic sonography-report of three cases. Radiology 22: , 2001.
Masear VR, Meyer RD, Pichora DR: Surgical anatomy of the medial antebrachial cutaneous nerve. J Hand Surg Am 14: , 1989.
Race CM, Saldana MJ: Anatomic course of the medial cutaneous nerves of the arm. J Hand Surg Am 16:48-52,
Spinner RJ, Goldner RD: Snapping of the medial head of the triceps and recurrent dislocation of the ulnar nerve. Anatomical and dynamic factors. J Bone Joint Surg Am 80: , 1998.
Spinner RJ, O'Driscoll SW, Jupiter JB, Goldner RD: Unrecognized dislocation of the medial portion of the triceps: another cause of failed ulnar nerve transposition. J Neurosurg 92:52-57, 2000.
Stahl S, Rosenberg N: Surgical treatment of painful neuroma in medial antebrachial cutaneous nerve. Ann Plast Surg 48: , 2002.
Tanaka SK, Lourie GM: Anatomic course of the medial antebrachial cutaneous nerve: a cadaveric study with proposed clinical application in failed cubital tunnel release. J Hand Surg Eur Vol 40: , 2015.

24. Questions & Discussion