Medial elbow pain is a musculoskeletal issue that is frequently encountered in individuals engaged in repetitive activities, although it is less prevalent than lateral elbow pain [1,2]. Medial epicondylitis, a pathological condition involving the common flexor tendon, is recognized as the most common cause of medial elbow pain. However, other anatomical structures within the medial elbow region can also contribute to the pain, and these should be considered in the differential diagnosis. Such structures include the ulnar nerve, the medial head of the triceps, the ulnar collateral ligament (UCL), the medial antebrachial cutaneous nerve (MACN), and the elbow joint.

Ultrasonography (US) plays a key role in identifying the causes of medial elbow pain due to the superficial location of potential pain sources. Additionally, US represents a practical tool for screening other structures that may harbor coexisting pathologies or represent alternative diagnoses, even when positive findings are already apparent in one structure. Moreover, US offers the benefit of dynamic evaluation, which is essential for assessing the instability of a structure or joint laxity. Alongside US, incorporating the patient’s characteristic history, symptoms, and physical examination findings aids in refining potential diagnoses and conducting a more targeted US assessment. Table 1 presents common causes of medial elbow pain, their clinical features, and checklists for US evaluation.

This review article will discuss several etiologies of medial elbow pain, including medial epicondylitis, ulnar entrapment neuropathy, ulnar nerve instability, snapping triceps syndrome, UCL injury, MACN neuropathy, and elbow joint diseases, with a focus on US findings. Familiarity with potential diagnoses and their US features can assist radiologists in formulating a comprehensive diagnosis for medial elbow pain.

US examination of the medial elbow can be performed with the patient either seated or lying in the supine position on an examination table (Fig. 1). For a more expedient setup, the patient should sit facing the examiner and rest their arm on a table or pillow, with the elbow in external rotation and either extended or slightly flexed [3]. This seated arrangement also facilitates immediate comparison between sides. Alternatively, the supine position, with the arm extended, abducted, and externally rotated, provides greater comfort when assessing the medial elbow’s supporting structures, along with the ulnar nerve, the anterior band of the UCL, and their respective stabilities [4].

US examination of the medial elbow is typically initiated in the long axis. The cranial end of the transducer is positioned over the medial epicondyle, which is identifiable either by palpation or visual inspection. Subsequently, a coronal view can display the characteristic hyperechoic bony contour of the medial epicondyle and ulnotrochlear articulation [5]. In this longitudinal scan, the common flexor tendon and the anterior band of the UCL can be identified (Fig. 2). At its origin on the medial epicondyle, the common flexor tendon exhibits a hyperechoic and fibrillar pattern, which transitions to a hypoechoic musculature distally [6]. The anterior band of the UCL, located deep to the common flexor tendon, also displays a fibrillar structure but with more compact hyperechogenicity than the tendon. It extends from the medial epicondyle to the sublime tubercle of the ulna [6]. Additional assessment of these structures can be performed in the transverse plane, or short axis.

A slight external rotation of the arm facilitates the evaluation of the posteromedial elbow, including the ulnar nerve and cubital tunnel. The cubital tunnel is a fibro-osseous channel that lies between the medial epicondyle and the olecranon. This structure is covered by the cubital tunnel retinaculum, with the posterior band of the UCL forming its floor [7]. By positioning the transducer transversely at the posteromedial elbow to simultaneously visualize the medial epicondyle and the olecranon, the cubital tunnel and ulnar nerve can be assessed in the short axis (transverse view). The ulnar nerve typically exists within the cubital tunnel and is identifiable by its characteristic fascicular appearance, which includes hypoechoic neural bundles (Fig. 3) [6-8].

The dynamic evaluation of the medial elbow is described in the following sections.

Medial epicondylitis, commonly known as "golfer’s elbow," is a frequent source of medial elbow pain [2]. Patients may present with a history of repetitive actions that entail valgus stress and flexion of the elbow, involve wrist flexion and pronation, or are associated with activities such as golf, overhead throwing, and racket sports [2,9,10]. Chronic overuse and repetitive microtears to the common flexor tendon result in tendon degeneration and angiofibroblastic changes, which in turn can lead to tendinosis and tearing [10]. Typical symptoms include medial elbow pain, often with an insidious onset and sometimes accompanied by grip strength weakness [2]. The most tender point is usually found 5 to 10 mm distal and anterior to the medial epicondyle, and pain is elicited during resisted wrist flexion and forearm pronation [10].

US is considered a practical and accurate modality for detecting medial epicondylitis, exhibiting good diagnostic performance with a sensitivity of 95.2%, specificity of 92%, and an accuracy of 93.5% [11]. On the long-axis view in the coronal plane, the normal tendon appears as a continuous band of longitudinal fibers with uniform high echogenicity, extending distally to the myotendinous junction and the hypoechoic musculature. US findings characteristic of medial epicondylitis include tendinosis features such as focal or diffuse hypoechoic changes, heterogeneous echotexture, and tendon swelling, as well as outward bowing, ill-defined margins, or subjacent fluid collection (Fig. 4) [4,10-12]. Intratendinous hyperechoic calcifications, adjacent entheseal irregularity, or traction spurs may also be present and can be confirmed on elbow radiographs, which supports the diagnosis [6,13,14]. The calcifications found in degenerated tendons are typically dystrophic, characterized by well-defined margins, a solid appearance, and strong posterior acoustic shadowing. This contrasts with the amorphous, nodular, punctate, and even cystic calcific deposits seen in calcific tendinitis, which exhibit variable posterior acoustic shadowing (Fig. 5) [15]. Neovascularization of the tendon, which can be detected using color or power Doppler US, varies and is more commonly observed in patients with a longer duration of symptoms [11]. When performing a Doppler examination, it is important not to apply excessive pressure with the probe, as the vessels in the pathological tendon are compressible and can be easily collapsed by probe pressure, which may result in missed detection of abnormal vascularity on Doppler US [16]. A partial-thickness tear is indicated by an anechoic cleft or incomplete fiber discontinuity. Although rare in medial epicondylitis, a full-thickness tear is characterized by complete discontinuity and retraction of the tendon, if present [6].

Medial epicondylitis often coexists with other pathologies, including ulnar neuropathy and UCL injury. Up to 60% of patients with medial epicondylitis experience concomitant ulnar neuropathy [17-20], which is associated with increased pain and worse surgical outcomes [18,21]. In these cases, the surgical approach for ulnar neuropathy may need to be adjusted, as anterior transposition of the nerve might be preferable to an isolated release of the cubital tunnel. This helps prevent the nerve from remaining in the inflammatory bed after surgery. Consequently, when medial epicondylitis is diagnosed using US, other medial elbow structures should also be examined.

Ulnar neuropathy at the elbow, also known as cubital tunnel syndrome, is the second most common compressive neuropathy affecting the upper extremity [2]. Although it was first introduced as ulnar entrapment neuropathy at the fibro-osseous passageway between the medial epicondyle and the olecranon, the term 'cubital tunnel syndrome' is now more commonly used to describe a wide range of conditions, encompassing ulnar nerve compression, neuropathy, or neuritis anywhere around the elbow [22,23].

Ulnar neuropathy typically results in paresthesia or numbness in the fourth and fifth digits, and patients may also experience elbow pain that radiates to the forearm and hand [24]. As the disease progresses to more severe stages, motor nerve impairment can develop, leading to weakness in the intrinsic hand muscles. This may manifest as an inability to adduct the fifth finger, known as the Wartenberg sign, or as a claw-hand deformity that primarily affects the fourth and fifth fingers [2,24-26].

Ulnar neuropathy or neuritis can develop due to compression or irritation of the nerve. This irritation may stem from nerve instability or the spread of local inflammation at the elbow, such as that seen with medial epicondylitis. Additionally, the superficial location of the ulnar nerve and its proximity to the bone make it particularly susceptible to traumatic injury [27]. Clinicians must be well-informed about these conditions, as the treatment approach for each can vary. This article will discuss the two main entities of ulnar nerve entrapment and instability, while also addressing snapping triceps syndrome, a similar pathology associated with ulnar nerve instability.

The UCL, also known as the medial collateral ligament of the elbow, is a critical stabilizer of the elbow joint, comprising anterior, posterior, and transverse bands. The anterior band of the UCL serves as the primary restraint against valgus stress on the elbow and is the focal point for assessing ligament injuries using US [54]. UCL injuries are particularly prevalent among overhead athletes, especially baseball pitchers, but they also affect participants in football, tennis, golf, and various other sports [55,56]. Overhead throwing activities subject the elbow to considerable valgus stress. This repetitive stress, combined with inadequate muscle stabilization, can result in ligament damage and subsequent valgus instability of the elbow [55,57,58]. Patients may experience chronic medial elbow pain during the late cocking and early acceleration phases of throwing. Alternatively, in the case of an acute injury, they may describe a sudden popping sensation followed by immediate pain and an inability to continue throwing [1,2].

The anterior band of the UCL originates from the inferior surface of the medial epicondyle, beneath the common flexor tendon, and extends to the sublime tubercle of the ulna. On US, it appears compact, hyperechoic, and fibrillar with a fan-like or cord-like structure. Applying valgus stress to the elbow can improve the visualization of the anterior band of the UCL, as the fibers tighten and become homogenously visible from the proximal to distal ends with the reduction of anisotropy. Partial tears of the anterior band of the UCL are characterized by hypoechoic changes, thickening, or focal anechoic defects involving discontinuity of the ligament. In cases of remote ligament injuries, intact fibers may appear lax. In skeletally immature adolescents, avulsion bone fragments from the medial epicondyle may be present. Complete tears of the ligament are indicated by the non-visualization or focal complete discontinuity of the fibers, accompanied by surrounding fluid or hemorrhage of variable echogenicity [4,6,59].

Dynamic US with valgus stress applied to the elbow joint can be used to demonstrate joint space widening, indicative of ligamentous laxity. To apply valgus stress to the elbow, the examiner externally rotates the shoulder while the arm is abducted and the elbow is flexed. Normally, the medial elbow joint space opens less than 3 mm with a firm endpoint [2,60]. However, abnormal medial joint space widening can be observed under valgus stress in the presence of a UCL injury (Fig. 10). The recommended diagnostic criterion is a change in joint space exceeding 1 mm between unstressed and stressed conditions, with a sensitivity of 96% and specificity of 81% according to previous research [61,62]. Nonetheless, a caveat exists when diagnosing a UCL injury based solely on widened joint space; asymptomatic professional athletes may exhibit a joint space gap of up to 3-4 mm or display asymmetry between their throwing and non-throwing arms [63].

The MACN is a purely sensory nerve that provides cutaneous sensation to the medial forearm. It originates from the medial cord of the brachial plexus and runs medially and posteriorly to the axillary artery before piercing the deep fascia in conjunction with the basilic vein, with which it runs distally. The MACN typically divides into anterior and posterior branches at the mid-arm level [64,65]. Accordingly, the nerve can be identified on US by following the basilic vein and positioning the probe medial to the biceps brachii muscle in the subcutaneous tissue at the anteromedial elbow (Fig. 11) [66]. MACN injury is most commonly caused by iatrogenic events, including complications from venous puncture, injection for medial epicondylitis, and cubital tunnel release [66]. Patients generally present with pain and numbness over the medial elbow and forearm. While the nerve may not display overt changes on US, a positive Tinel sign elicited by compressing the probe over the nerve can aid in diagnosis [66]. Additionally, reports describe symptomatic snapping of the MACN over the medial epicondyle during elbow flexion and extension [66,67]. Consequently, dynamic US of the MACN should be considered in cases of suspected neuropathy.

Various etiologies of arthritis that affect the elbow joint can lead to medial elbow pain. Reviewing plain radiographs and the clinical history of patients prior to US examination can assist in forming an impression of the arthritic condition.

Primary osteoarthritis of the elbow joint is less common than post-traumatic arthritis and predominantly affects the ulnohumeral joint. The degenerative changes and osteophytes initially impact the tips of the olecranon and coronoid process, with the articular cartilage becoming involved in more advanced stages [68]. This leads to pain and a limited range of motion in elbow flexion and extension. Although it is challenging to directly identify narrowed joint spaces or cartilage lesions, US can detect the presence of osteophytes and intra-articular bodies, which can cause irritation and pain or may be accompanied by effusion [69]. A dynamic examination involving flexion and extension of the elbow may help to mobilize joint fluid and intra-articular bodies, thus differentiating loose bodies from fixed osteophytes [8]. Additionally, the examiner should assess for ulnar neuropathy, which can occur in patients with osteoarthritis due to nerve irritation or compression from osteophytes or ganglions near the cubital tunnel [70,71].

Inflammatory or crystal-induced arthritis can also involve the elbow joint, presenting with joint effusion, synovial hypertrophy, and destructive bone abnormalities. The posterior olecranon recess, when the elbow is flexed, is the most sensitive area for detecting small effusions. Here, US in the longitudinal plane can reveal the displacement of the hyperechoic fat pad due to joint distension [72]. A larger effusion can distend the coronoid and radial fossa in the anterior elbow. Unlike simple anechoic effusions, complex effusions may vary in echogenicity and are often challenging to differentiate from synovial hypertrophy. Compared to synovial hypertrophy, complex effusions exhibit compressibility of the recess, redistribution or movement of contents when pressure is applied, and an absence of blood flow on Doppler US [6]. Synovial hypertrophy associated with rheumatoid arthritis or other forms of inflammatory arthritis may display diffuse synovial proliferation, which is typically less echogenic than subcutaneous fat, as well as synovial hyperemia and joint distension (Fig. 12) [6]. Cortical irregularities and disruptions, often seen with synovitis, can indicate adjacent bone erosions due to inflammation [6,8]. In diseases characterized by crystal deposition, such as gout or pseudogout, hyperechoic foci of mineral deposition may be observed within the joint or periarticular soft tissue. Furthermore, olecranon bursitis, which is commonly associated with gout or rheumatoid arthritis, presents as a distended bursa with effusion and synovial proliferation.

Medial elbow pain has numerous potential causes beyond those previously discussed, such as lymphoproliferative disease (Fig. 13), occult tumors, and more. Without an active search for the underlying pathology, the true source of pain may be easily overlooked during US examination. Consequently, it is crucial for radiologists to scan the area of greatest pain to ensure that US is used for the efficient and thorough assessment of medial elbow pain.

In the evaluation of medial elbow pain, US provides an efficient and dynamic assessment of the medial elbow structures. Correlating characteristic clinical features can improve the accuracy of US by directing examiners to the suspected structures and aiding in the differentiation of the cause of pain. However, even when positive findings are identified in one structure, other structures should be screened for coexisting pathologies or alternative diagnoses. A thorough examination of the most painful site must be ensured. Adopting this comprehensive approach leads to a more accurate evaluation of medial elbow pain.