Edematous Anconeus Epitrochlearis: another potential site of ulnar nerve compression

Figure 1 - anatomy of the anconeus epitrochlearis

The incidence of the often forgotten anconeus epitrochlearis muscle has been reported to be as high as 34% in the literature (1).   The anconeus epitrochlearis muscle takes the same course as the cubital tunnel retinaculum (the fibrous covering of the ulnar nerve forming the tunnel), running from the medial cortex of the olecranon to the inferior surface of the medial epicondyle.¹ The muscle thus runs superficial to the ulnar nerve and serves to keep the nerve in position.  The fibrous retinaculum is in fact postulated to be the remnant of the anconeus epitrochlearis.  Although the muscle may be unilateral, it was found to be bilateral in one of four patients with cubital tunnel syndrome in a study by Masear et al.²

Identification of the muscle can be done done via Ultrasound, however is more accurately demonstrated with MR imaging (figure

Figure 2 - T1 weighted MR demonstrating the muscle and the relationship with the ulnar nerve

2).  It is important to distinguish the muscle from the ulnar head of the flexor carpi ulnaris, which occurs more distally and merves with the humeral head of that muscle.

Swelling/edema of this muscle has been shown to cause compression of the ulnar nerve; a condition is referred to as Edematous Anconeus Epitrochlearis³ (figure 3).  Treatment for said condition has varied from excision of the mass⁴ (or splitting the muscle) to anterior transposition⁵ (figure 4 & 5).

Figure 3 - T2 Axial Fatsat MR image demonstrating swelling within the ulnar nerve

The obvious importance of the existence of this potential structure for manual therapist is the knowledge of its addition to the differential diagnosis of ulnar nerve compression symptoms.  Failure of conservative care warrants the appropriate referral for surgical consult….in this case, the rarity of the condition may cause it to be over looked even by the surgical community.

Figure 4 - The anconeus epitrochlearis muscle compresses the ulnar nerve (Ulnar N.) against the medial epicondyle. This is the left elbow with the hand being to the right in the photograph. The anconeus epitrochlearis is seen extending from olecranon to the inferior surface of the medial epicondyle (ME).

Figure 5 - Operative photograph of the ulnar nerve after anconeus epitrochlearis has been reflected

1. MasearVR, Hill JJ Jr, Cohen SM. Ulnar compression neuropathy secondary to the anconeus epitrochlearis muscle. J Hand Surg [Am] 1988; 13: 720–724.

2.  JeonIH, Fairbairn KJ, Neumann L, Wallace WA. MR imaging of edematous anconeus epitrochlearis: another cause of medial elbow pain? Skeletal Radiol 2005; 34: 103–107.

3.  Chalmer J. (1978) Unusual causes of peripheral nerve compression. Hand 10:168-175

4.  Vanderpool DW, Chalmers J, Lamb DW, Whiston TB. (1968) Peripheral compression lesion of the ulnar nerve. J Bone Joint Surg [Br] 50 : 792-803

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