Does the articularis cubiti muscle really exist? Anatomical, histological, and magnetic resonance imaging study with a narrative review of literature

Abstract

Although the term articularis cubiti muscle is incorporated in the official anatomical nomenclature, only sparse data about its appearance are available. It is usually described as few fibres originating from the medial head of the triceps brachii muscle and inserting to the capsule of the elbow joint. However, the most recent observations regarding the morphological relations in the posterior elbow region point towards the absence of a well-defined muscle. Therefore, this study was designed to verify the existence of the articularis cubiti muscle in question and to compile more data on the topographical features of the subtricipital area near the posterior aspect of the elbow. To address these questions, 20 embalmed upper limbs were dissected, and seven samples were collected for histological analysis. The laboratory findings were then correlated with 20 magnetic resonance imaging (MRI) scans of the elbow. Consequently, a narrative review of literature was performed to gain more information on the discussed muscle in a historical context. Upon the anatomical dissection, muscular fibres running from the posterior aspect of the shaft of the humerus to the elbow joint capsule and olecranon were identified in 100% of cases. Histologically, the connection with the joint capsule was provided via winding bands of connective tissue. On MRIs, the muscular fibres resembled a well-demarcated thin muscle located underneath the medial head of the triceps brachii muscle. Combined with the review of literature, we concluded that the constant articularis cubiti muscle originates from the posterior shaft of the humerus and attaches indirectly to the posterior aspect of the elbow joint capsule and directly to the superior portion of the olecranon. The obtained results slightly differ from the modern description, but are in agreement with the original publication, which has become misinterpreted throughout time. Presumably, the misused description has led to questioning the existence of an independent muscle. Moreover, our findings attribute to the articularis cubiti muscle, a function in pulling on the posterior aspect of the elbow joint capsule to prevent its entrapment, and possibly also a minor role in extension of the forearm. The presented results should be taken into consideration when intervening with the posterior aspect of the elbow joint because the articularis cubiti muscle poses a consistently appearing landmark.

Keywords: Lecomte's pronator of ulna; anconeus muscle; articularis cubiti muscle; elbow joint capsule; subanconeus muscle; triceps brachii muscle.

FIGURE 1

Macroscopic findings showing the deeply located muscular fibres under the triceps brachii muscle inserting to the posterior aspect of the elbow joint capsule and on the olecranon (a–d) and additional slips from these deep muscular fibres attaching proximally to the posterior aspect of the elbow joint capsule (e, f). DMF = deep muscular fibres; DS = detached slips; H = humerus; JC = joint capsule; MH = medial head of triceps brachii muscle; TBM = triceps brachii muscle; UN = ulnar nerve.

FIGURE 2

Microscopic findings of the relations between the deeply located muscular fibres and the elbow joint capsule (a). The muscular fibres are attached to the joint capsule via winding bands of connective tissue (b, c). Scale bar equals 100 μm. DMF = deep muscular fibres; PIFP = posterior intra‐articular fat pad; JC = joint capsule; VB = vascular bundle; WBCT = winding bands of connective tissue.

FIGURE 3

Deeply located muscular fibres (arrows) shown in transversal PDw‐TSE image of a 23‐year‐old female (a) and in sagittal T1‐TSE image of a 19‐year‐old male (b).

FIGURE 4

Timeline depicting the evolution of the definitions for the articularis cubiti muscle.