Muscle:Anconeus

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Anconeus is a small, triangular muscle on the posterior aspect of the elbow, functioning as an assistant elbow extensor and stabiliser of the humeroulnar joint. Although a minor contributor to elbow extension, its trigger point (TrP) is a clinically significant and frequently overlooked source of local lateral epicondyle pain. An anomalous variant — the anconeus epitrochlearis — is an established cause of ulnar nerve compression neuropathy at the elbow.

Contents

Anatomy

The anconeus appears as an extension of the triceps between the lateral epicondyle and the olecranon process.

  • Origin: lateral epicondyle of the humerus
  • Insertion: lateral surface of the olecranon process and the dorsal surface of the proximal ulna

Innervation: Radial nerve; spinal roots C7 and C8 — the same innervation as all heads of the triceps brachii.

Primary actions:

  • Assists the triceps in extension of the forearm at the elbow
  • Stabilises the humeroulnar joint during forearm pronation and supination (acts jointly with the supinator and medial head of the triceps for elbow stabilisation)
  • EMG studies show activation by all index finger movements

Referred Pain Pattern

The single TrP in the anconeus muscle refers pain and tenderness locally to the lateral epicondyle.

Key clinical features:

  • Pain is local — centred on the lateral epicondyle; it does not project distally into the forearm or fingers
  • Must be distinguished from referred lateral epicondyle pain from Muscle:Triceps_Brachii TrP2 (which shares this referral zone) and from forearm extensor TrPs
  • Because the referral zone is entirely local, the anconeus TrP is easily overlooked and its contribution to "tennis elbow" presentations underappreciated

Activation and Perpetuating Factors

  • Repetitive or forceful elbow extension activities — racquet sports, golf, manual labour
  • Activities requiring elbow stabilisation during rapid forearm pronation/supination — hammering, screwdriving, wringing
  • Overuse as a stabiliser in patients with chronic elbow pathology
  • Concurrent triceps brachii TrP activity (the anconeus functions as a synergistic stabiliser and may be co-activated)

Symptoms

The patient complains of pain localised to the lateral elbow, centred on or just distal to the lateral epicondyle. Because the referral is local rather than projected, the patient may describe it simply as "elbow pain." There are no neurological symptoms from an uncomplicated anconeus TrP.

Clinical Examination

Functional Assessment

Test Positive finding Must be present / must be absent
Resisted elbow extension Pain localised to the lateral epicondyle Must be present: local lateral epicondyle pain on resisted elbow extension implicates the anconeus (or triceps TrP2). Must be absent: pain with resisted wrist extension or radial deviation (implicates forearm extensors, not anconeus); neurological signs (numbness, weakness in radial or median distribution).
Palpation between lateral epicondyle and olecranon Spot tenderness at the TrP in the midfibre region of the anconeus; no taut band palpable in this small muscle Must be present: spot tenderness with reproduction of the lateral epicondyle pain. Must be distinguished from joint-line tenderness (which lies more anteriorly).

Trigger Point Examination

  • The TrP lies in the midfibre region of the anconeus, between the lateral epicondyle and the olecranon process
  • Localise the TrP by flat palpation against the ulna, between the olecranon process and the lateral epicondyle
  • Tenderness reproducing the lateral epicondyle pain confirms involvement

Nerve Entrapment — Anconeus Epitrochlearis

An anomalous anconeus epitrochlearis muscle has been reported as a cause of ulnar compression neuropathy at the elbow. This variant muscle bridges from the medial epicondyle (epitrochlea) toward the olecranon, lying in the cubital tunnel region and compressing the ulnar nerve.

Clinical presentation:

  • Ulnar nerve symptoms: tingling and numbness in the fourth and fifth digits; weakness and clumsiness of intrinsic hand muscles
  • Ulnar nerve compression neuropathy confirmed by nerve conduction studies showing slowing at the elbow
  • Symptoms relieved by surgical excision of the anomalous muscle

Differentiation from cubital tunnel syndrome (without the anomalous muscle): The distinction can only be confirmed operatively or by advanced imaging, but the anconeus epitrochlearis should be suspected in cases of ulnar neuropathy at the elbow with atypical presentation or lack of response to conservative cubital tunnel management.

Differential Diagnosis

The anconeus TrP enters the differential primarily for lateral epicondyle pain. Because its referral is entirely local, it mimics any other cause of pain at the lateral epicondyle.

Condition Must be present to consider this diagnosis Must be absent Differentiating feature
Anconeus TrP Local lateral epicondyle pain; spot tenderness in the midfibre region of the anconeus between lateral epicondyle and olecranon; no neurological signs Distal referral to forearm or hand; neurological signs; forearm extensor weakness Pain and tenderness are strictly local; no neurological component; TrP palpation between lateral epicondyle and olecranon reproduces the pain
Triceps TrP2 (lateral head, medial border) Lateral epicondyle pain; taut band with spot tenderness 4–6 cm proximal to the lateral epicondyle in the distal medial head of triceps — TrP2 is proximal (in the arm); anconeus TrP is distal (at the elbow). Palpation locates the source accurately.
Lateral epicondylitis (tennis elbow — forearm extensor origin) Lateral epicondyle pain reproduced by resisted wrist extension and/or third finger extension; tenderness at the common extensor origin on the anterior face of the lateral epicondyle — Resisted wrist extension implicates forearm extensors, not anconeus. Anconeus pain is from elbow extension loading, not wrist.
Radial nerve entrapment (arcade of Frohse / posterior interosseous nerve) Lateral elbow pain; may include weakness of wrist and finger extension (motor involvement) or tingling in the radial sensory distribution Motor deficit absent in uncomplicated anconeus TrP — if present, nerve entrapment or posterior interosseous nerve palsy must be investigated Neurological signs distinguish nerve entrapment from a pure anconeus TrP
Olecranon bursitis Fluctuant swelling over the olecranon; localised posterior elbow swelling Fluctuant swelling is absent in a pure anconeus TrP Palpation: bursal swelling is superficial and fluctuant; anconeus TrP tenderness is muscular and does not fluctuate
Lateral compartment elbow arthritis Crepitus; loss of both flexion and extension; radiological changes Isolated activity-related pain without joint-line crepitus or ROM restriction suggests myofascial origin over arthritis Radiological assessment to exclude arthritis in refractory presentations

Treatment

Trigger Point Release

  • Ischaemic compression over the TrP region between the lateral epicondyle and olecranon
  • Stretch and spray: elbow flexion is the appropriate stretch; vapocoolant applied from proximal to distal over the lateral elbow region
  • The anconeus is too small for effective stand-alone stretch-and-spray technique in most patients — injection is often more efficient

Trigger Point Injection

  • Patient supine, elbow flexed approximately 45°, forearm pronated
  • The TrP is localised between the fingers against the ulna, between the olecranon process and the lateral epicondyle
  • The TrP is fixed between the fingers of the palpating hand; the needle is directed toward the ulna
  • The TrP is not especially close to the neurovascular bundle; however, excessively wide injection spread risks temporary median or ulnar nerve block — confine the injection to the localised TrP region

Satellite Trigger Points

References

  • Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1: The Upper Half of Body. 2nd ed. Baltimore: Williams & Wilkins; 1999. Chapter 32.
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