Ulnar nerve dislocation is an uncommon cause of pain and paresthesias in the ulnar nerve distribution. It occurs if the ulnar nerve subluxates and then dislocates over the anterior aspect of the medial epicondyle during flexion and extension of the elbow.
Ulnar nerve dislocation occurs in 16% of normal individuals 1. As the elbow is flexed or extended, the ulnar nerve dislocates over the anterior aspect of the medial epicondyle. A "snap" may be heard or felt. This motion may eventually result in ulnar neuropathy with characteristic pain and paresthesias along the ulnar nerve distribution.
Ulnar nerve dislocation is separate entity from snapping triceps syndrome, which is more uncommon. The nerve may dislocate in snapping triceps syndrome as well.
Ultrasound is the imaging modality of choice since it can dynamically image the relationship between the ulnar nerve and medial epicondyle during elbow flexion and extension.
To evaluate 2-3:
- the transducer is placed transversely over the medial epicondyle, over the entrance to the cubital tunnel
- the patient flexes the elbow
- there is normally some movement of the ulnar nerve toward the apex of the medial epicondyle
- dislocation occurs if there is translation of the ulnar nerve over the medial epicondyle
- a snap may be heard or felt with the movement
- evaluation of the ulnar nerve distal to the neuropathy may reveal a swollen and hypoechoic nerve, characteristic ultrasound findings in ulnar neuropathy.
- ulnar neuropathy may be seen on standard elbow MRI, but a diagnosis of ulnar nerve dislocation can only be suggested with elbow MR in both the flexed and extended positions
Possible differential considerations include
- 1. Childress HM. Recurrent ulnar-nerve dislocation at the elbow. Clin. Orthop. Relat. Res. 1975; (108): 168-73. Pubmed citation
- 2. Jacobson JA. Fundamentals of Musculoskeletal Ultrasound: Expert Consult-Online and Print, 2e (Fundamentals of Radiology). Saunders. ISBN:1455738182. Read it at Google Books - Find it at Amazon
- 3. Lee KS, Rosas HG, Craig JG. Musculoskeletal ultrasound: elbow imaging and procedures. Semin Musculoskelet Radiol. 2010;14 (04): 449-60. doi:10.1055/s-0030-1263260 - Pubmed citation
- 4. Xarchas KC, Psillakis I, Koukou O, Kazakos KJ, Ververidis A, Verettas DA. Ulnar nerve dislocation at the elbow: review of the literature and report of three cases. (2007) The open orthopaedics journal. 1: 1-3. doi:10.2174/1874325000701010001 - Pubmed