Keywords
elbow - MR-imaging - posterolateral rotatory instability - posteromedial rotatory
instability - symptomatic minor instability of the lateral elbow (SMILE)
Abbreviations
ALF:
anterolateral facet of the coronoid process
AMF:
anteromedial facet of the coronoid process
aUCL:
anterior bundle of the ulnar collateral ligament
CT:
computed tomography
FABS:
flexion, abduction, and supination
FOOSH:
fall on outstretched hand
LUCL:
lateral ulnar collateral ligament
MR:
magnetic resonance
MRI:
magnetic resonance imaging
PLRI:
posterolateral rotatory instability
PMRI:
posteromedial rotatory instability
pUCL:
posterior bundle of ulnar collateral ligament
RCL:
radial collateral ligament
SMILE:
symptomatic minor instability of the lateral elbow
UCL:
ulnar collateral ligament
Introduction
Elbow pain encountered in clinical practice can result, particularly in athletes,
in significant morbidity. Chronic degenerative damage and acute lesions of ligaments
and tendons are primarily assessed clinically. Magnetic resonance imaging (MRI) is
a frequent, supplementary diagnostic tool in unclear cases, for the detection of secondary
findings and for preoperative planning due to its excellent soft tissue contrast.
Anatomical knowledge of the supporting structures, which provide stability to the
elbow joint, is essential to assess different anatomical characteristics in terms
of morphology and signal behavior and to correctly diagnose pathological findings.
Medial Compartment
Medial ligaments
The ulnar collateral ligament (UCL) is the main stabilizer against valgus elbow stress
and posteromedial rotatory instability [1]. The ulnar collateral ligament complex ([Fig. 1]) consists of the anterior bundle (aUCL), the posterior bundle (pUCL), and the transverse
bundle (Cooper’s ligament) of the ulnar collateral ligament. The origin of the aUCL
and pUCL is the anteroinferior surface of the medial epicondyle. Due to an origin
posterior to the axis of the elbow, with increasing flexion the ligament tension increases.
The aUCL inserts distal to the coronoid tip, at the sublime tubercle along the medial
aspect of the coronoid tip [2]. The majority of the restraint to valgus and posteromedial rotatory instability
is provided by the aUCL, which is composed of two portions [1]. These components are typically not seen as separate structures on MRI. On MRI the
aUCL has a proximal hyperintense striped appearance which should not be misinterpreted
as a pathologic finding ([Fig. 1]
A) [3]. The pUCL inserts along the midportion of the medial margin of the semilunar notch
and forms the floor of the cubital canal, and is a fan-shaped thickening of the capsule
([Fig. 1]
B) [2]. The transverse ligament does not significantly contribute to joint stability, especially
since its origin and insertion are located on the ulna and it does not connect two
different bones like other ligaments. It runs from the olecranon to the posterior
portions of the anteromedial facet of the coronoid process [4]. The transverse ligament cannot always be seen on MRI [5].
Fig. 1 Proton density (PD) fat-saturated coronal A and axial B T1-weighted MR images. Medial elbow anatomy. A shows the anterior bundle (aUCL; arrows) of the ulnar collateral ligament complex
and the flexor tendon aponeurosis (arrowhead). B depicts the posterior bundle (pUCL; open arrow) of the ulnar collateral ligament
complex and the arcuate ligament of Osborne (dashed arrow).
Injuries of the medial ligaments
The UCL, especially its anterior bundle (aUCL), is the most important stabilizer against
valgus stress [6]. Athletes in overhead sports, e.g. baseball, commonly endure UCL injuries, which
can result in valgus instability [7]. Due to repetitive valgus stress to the elbow, increased laxity and medial instability
of the UCL can occur. The final tear can arise during a throwing motion when forces
exceed the tensile strength of the anterior bundle [8]. Valgus extension overload syndrome forms the basic pathophysiologic model behind
the most common elbow injuries in throwing athletes [9]. Ligament weakening or failure can occur when forces near the rupturing point of
the aUCL are applied during throwing [10]. Additionally, in severe cases of elbow dislocation alongside injuries of the lateral
stabilizers, the UCL can also be torn, leading to valgus instability [11].
MRI has become the examination of choice in evaluating elbows with clinically suspected
UCL injury [11]. MRI has been reported to have a sensitivity for partial-thickness tears of 14%
only [8]
[12]. In throwing athletes, the addition of a recently described flexed elbow valgus
external rotation (FEVER) view resulted in increased diagnostic confidence and recognition
of abnormal or torn UCL lesions, which were classified as normal on standard MR views
[13]. Schwartz et al. showed in their study that intra-articular contrast agent can increase
sensitivity for partial-thickness tears to 86%, with a 100% specificity [14]. The “T sign” indicates distal partial aUCL tearing and is seen especially on direct
MR arthrography when injected contrast extends distally from the joint line along
the cortical margin of the sublime tubercle of the ulna on coronal images ([Fig. 2]) [15]. Of note, another indication for direct MR arthrography of the elbow is to assess
chondral and osteochondral abnormalities [16].
Fig. 2 MR arthrography with T1 fat-saturated coronal MR image of a 27-year-old female shows
a partial tear (arrows) of the anterior bundle of the ulnar collateral ligament with
fluid between the ligament and the sublime tubercle, indicating a T sign.
Additionally, continued microtrauma may produce olecranon tip osteophytes, intraarticular
loose bodies, and articular damage.
The concept of posteromedial rotatory instability will be discussed further below.
Medial muscles
The flexor-pronator muscle complex compresses the elbow joint, supports osseous stability,
and provides dynamic stability to valgus stress [1]
[2]
[17]. The medial muscle group is divided into three layers. All muscles except for the
flexor digitorum profundus muscle originate from the common flexor muscle origin with
some fibers connecting to the UCL. The common flexor muscle origin forms an aponeurosis
originating from the medial epicondyle ([Fig. 1]
A). The superficial layer consists of the pronator teres, flexor carpi radialis, palmaris
longus, and flexor carpi ulnaris muscles. The middle and deep layer consist of the
flexor digitorum superficialis and profundus muscles [18]. The roof of the cubital tunnel is formed by a band of fibrous tissue, which spans
between the humeral and ulnar heads of the flexor carpi ulnaris muscle, i.e., Osborne’s
ligament also referred to as arcuate ligament of Osborne ([Fig. 1]
B). The ulnar nerve traverses in the cubital tunnel between the two heads of the flexor
carpi ulnaris muscle [19].
Medial tendon pathologies
Abnormal morphology of the tendons, such as signal attenuation changes or thickening,
is seen in tendinosis or tears, which can be best evaluated on coronal and axial sequences
[5]
[20]. A tear is characterized by interruption of tendon fibers. These defects are usually
filled with fluid and thus are best visualized on fluid-sensitive sequences. Chronic
stress to the common flexor tendons can cause medial epicondylitis, which is also
known as golfer’s elbow. The term epicondylitis is actually a misnomer because the
underlying pathology is chronic degeneration with tendinosis and partial tendon tearing
and is not related to an acute inflammatory reaction. The most probable hypothesis
is that microscopic tears due to repetitive overload of the tendon cause an epicondylitis
[20]. The most commonly affected muscles are the flexor carpi radialis, pronator teres,
and palmaris longus muscles [18].
Lateral Compartment
Lateral ligaments
The lateral collateral ligament complex consists of three primary structures: the
radial collateral ligament (RCL), the lateral ulnar collateral ligament (LUCL), and
the annular ligament ([Fig. 3]). The RCL arises from the inferior surface of the lateral epicondyle and has a wide
insertion into the annular ligament [21]. The annular ligament surrounds the radial head, and thus maintains its contact
with the ulna in the proximal radioulnar joint. It consists of a strong band of tissue
originating and inserting at the anterior and posterior margins of the lesser sigmoid
notch of the ulna [22]. The LUCL forms a posterior sling to support the radial head and functions as the
primary stabilizer to varus stress. It arises from the lateral epicondyle, passes
posterior to the radial head, and inserts into the supinator crest of the ulna [21]. The small fibers of the accessory lateral collateral ligament originate on the
supinator crest of the ulna and blend with the inferior margin of the annular ligament.
An additional accessory lateral collateral ligament was described in one-third of
individuals [2]
[23]. The function of the accessory collateral ligament is to stabilize the annular ligament
during varus stress [24]. However, MR visibility of this accessory ligament has not been described in the
literature to our knowledge yet.
Fig. 3 PD fat-saturated coronal A, B and axial C MR images. Lateral elbow anatomy with the lateral collateral ligaments of the elbow.
A shows the extensor tendon aponeurosis (dashed arrow) and the radial collateral ligament
(RCL; arrows). The lateral ulnar collateral ligament (LUCL; open arrows) is shown
in B. C depicts the insertion of the RCL (arrow) at the annular ligament (AL; arrowheads).
Injuries of the lateral ligaments, posterolateral and posteromedial rotatory instability,
symptomatic minor instability of the lateral elbow (SMILE)
Loss of integrity of the LUCL, as an important element of the capsuloligamentous complex,
contributes to posterolateral rotatory instability [25]. Posterolateral rotatory instability (PLRI) commonly occurs due to trauma ([Fig. 4]). Most often patients suffered an elbow dislocation or a fall on an outstretched
hand, i.e. “FOOSH injury”, with a forceful valgus moment while the forearm was in
supination [26]. This is the most common type of elbow dislocation and the most frequent cause of
recurrent elbow instability [11]. A supination force coupled with valgus stress can result in rupture of the LUCL
and the posterolateral parts of the capsule and thus in dislocation. The LUCL is considered
the primary stabilizer of the elbow, especially against PLRI [11]. In cases of severe instability, additional lateral stabilizers such as the RCL,
parts of the annular ligament, and common extensor tendons are often injured [27]. This disruption of some or all of the lateral-sided stabilizers is due to posterior
displacement of the radial head relative to the capitellum of the humerus [28]. These can result in fractures of the coronoid process and radial head [29]. “Horii circle” describes that injuries tend to occur from lateral to medial with
three stages of soft-tissue injuries according to O’Driscoll [30]:
Fig. 4 PD fat-saturated coronal A and axial B MR images of a 42 year-old female artist with posterolateral rotatory instability
after an injury performing a handstand on one arm. A The arrows point at a partially disrupted anterior bundle of the ulnar collateral
ligament proximally and distally (distally showing a T sign). The open arrow points
at a partially torn lateral ulnar collateral ligament. B The arrowhead points at a completely torn and retracted posterior insertion of the
annular ligament.
-
In stage one, the LUCL is torn.
-
In stage two, the other lateral ligamentous structures, and the anterior and posterior
capsule are disrupted.
-
In stage three, a disruption of the medial side, i.e. the ulnar collateral ligament
complex occurs.
PLRI is often a clinical diagnosis. However, to evaluate fractures, subluxation, or
dislocation, plain radiographs or computed tomography (CT) should be performed. A
distance > 3 mm between the humerus and ulna (the “drop sign”) can be a sign of PLRI
and can also be noticed on sagittal CT and MR imaging. MRI is an excellent tool to
diagnose ligament injuries due to PLRI. However, in chronic PLRI cases, injuries of
the LUCL are not always easily identifiable on MRI [11]
[31].
Posteromedial rotatory instability (PMRI) occurs after an axial and varus load with the forearm in pronation which causes a
rupture of the RCL and a fracture to the anteromedial facet of the coronoid process
([Fig. 5]). Additionally, the pUCL has to be disrupted for a gross subluxation of the elbow
to occur [32]
[33].
Fig. 5 PD fat-saturated coronal A and axial B MR images of a 64 year-old male with posteromedial rotatory instability. A The arrow points at a proximally ruptured and retracted LUCL. The open arrow shows
a fracture at the anteromedial facet of the coronoid process, where the anterior band
of the ulnar collateral ligament inserts. B The arrowhead points at a disrupted posterior bundle of the ulnar collateral ligament
complex.
Similarities and differences between the two instability types are summarized in [Table 1].
Table 1 Comparison of typical injuries in posteromedial and posterolateral rotatory instabilities.
|
Finding
|
PLRI
(posterolateral rotatory instability)
|
PMRI
(posteromedial rotatory instability)
|
|
Abbreviations: ALF (anterolateral facet of the coronoid process), AMF (anteromedial
facet of the coronoid process), LUCL (lateral ulnar collateral ligament), RCL (radial
collateral ligament), aUCL (anterior band of ulnar collateral ligament), pUCL (posterior
band of ulnar collateral ligament).
|
|
Radial head fracture
|
Commonly present
|
Commonly absent
|
|
Coronoid process fracture
|
Tip of the coronoid/ALF
|
AMF
|
|
Lateral ligamentous injury
|
LUCL most commonly
|
Disruption of the RCL and LUCL at the humeral origin
|
|
Medial ligamentous injury
|
aUCL is commonly involved in severe stages
|
pUCL is commonly involved in severe stages
|
Iatrogenic causes of LUCL injuries can be multiple corticosteroid injections (e.g.
for lateral epicondylitis), inadequate repair of the LUCL, or too extensive debridement
of epicondylitis [27].
Lateral epicondylitis is generally considered an extra-articular condition [34]. However, Arrigoni et al. recently described a high incidence of intra-articular
pathological findings due to an associated laxity of the RCL in patients with permanent
lateral elbow pain [35]. They introduced a new concept of symptomatic minor instability of the lateral elbow (SMILE) showing that over 85% of patients with lateral epicondylitis demonstrate at least
one intra-articular pathology on arthroscopy, postulating the following cascade [34]:
-
Elongation of the RCL and annular ligament with relative hypermobility of the radial
head.
-
Incongruence of the proximal radioulnar joint resulting in radial head impingement
and chondropathy as well as joint inflammation leading to intra-articular synovitis.
-
Abrasion or shear of the stretched RCL/anterolateral capsule over the lateral portion
of the capitellum in the elbow varus and pronation with a risk of capitellum lesion
or capsular tears.
To date, only one radiological CT-arthrography-based study has described possible
radiological findings [36], and there are no MR studies. The SMILE concept is still new in the orthopedic literature
and until now has only been addressed by one study group. Thus, this pathological
concept needs to be further validated in future studies. A possible MR case of SMILE
is shown in [Fig. 6].
Fig. 6 PD fat-saturated MR images (coronal view in A and B, axial view in C, and sagittal view in D) of a 61-year-old male with chronic lateral epicondylitis, possibly due to symptomatic
microinstability of the lateral elbow (SMILE). A The radial collateral ligament shows thickening and signal alterations (arrowhead).
B A partial tear is present at the extensor tendon aponeurosis (arrow), consistent
with lateral epicondylitis, and a cartilage fissure is present at the trochlear ridge
(dashed arrow). C The annular ligament is elongated with widening of the proximal radioulnar joint
(open arrowhead). D A deep cartilage fissure is present at the radial head (open arrow) and synovial
thickening posterior to the radial head (dashed arrowhead). Of note to compare with
normal anatomy see [Fig. 3].
In cases of pulled elbow (i.e., “nursemaid’s elbow”) and Monteggia fracture, which
are typically seen in children, the annular ligament injury is primarily characterized
as varying degrees of annular ligament displacement [37]. Usually, the clinical examination is sufficient for diagnosis and treatment of
annular ligament displacement and no additional imaging is needed. [Fig. 7] shows a case of a displaced annular ligament onto the radial head.
Fig. 7 T2-weighted fat-saturated MR image of an 11-year-old boy with valgus trauma shows
a luxation of the annular ligament into the humeroradial joint (arrows).
Lateral muscles
The muscles on the lateral aspect of the elbow are divided into three layers: the
superficial layer, the extensor aponeurosis, and the supinator muscle [21]. The brachioradialis and extensor carpi radialis longus muscles form the superficial
layer. The extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi,
and extensor carpi ulnaris muscles form the aponeurosis [18]
[38]. The brachioradialis and extensor carpi radialis longus muscles have their origin
at the supracondylar ridge. The extensor carpi radialis brevis muscle arises from
the common extensor tendon and radial collateral ligament. The origin of the common
extensor group is the lateral humeral epicondyle superficial to the lateral collateral
ligament complex ([Fig. 3]
A). The deepest of the lateral muscle group is the supinator muscle with its origin
at the lateral epicondyle, lateral ligaments and supinator crest of the ulna and insertion
into the lateral aspect of the proximal radial shaft [21].
Lateral tendon pathologies
The most common elbow disease in middle-aged patients is lateral epicondylitis, referred
to as tennis elbow with a prevalence rate of 1% to 3% [39]. It is primarily a clinical diagnosis. Due to excessive use of the extensor muscles,
microtrauma with small tears of the aponeurosis occur ([Fig. 8]). Thus, the term epicondylitis is a misnomer on the lateral side as well. Incomplete
healing can result in granulation tissue and mucoid degeneration. The most commonly
affected muscle is the extensor carpi radialis brevis muscle [5]
[40]. The role of MRI is to exclude tendon ruptures, bone stress reactions, and differential
diagnosis of lateral elbow pain. Furthermore, it can be used for preoperative planning,
especially if additional joint pathologies are present [5].
Fig. 8 PD fat-saturated MR image of a 56-year-old female with lateral epicondylitis. The
arrow points at a partial rupture of the origin of the common extensor aponeurosis.
Anterior Compartment
Anterior tendons, muscles, and pathologies
The anterior compartment contains two main flexors of the elbow, the biceps brachii
and the brachialis muscle. The long and short heads of the biceps muscle arise proximally
from the supraglenoid tubercle of the scapula and coracoid process. The biceps tendon
passes distally through the antecubital fossa to insert at the radial tuberosity ([Fig. 9]). The lacertus fibrosus or bicipital aponeurosis is formed by superficial tendon
fibers running across the antecubital fossa and blending with the fascia of the flexor-pronator
muscles ([Fig. 9]
A). This fibrous band prevents retraction of a torn biceps tendon to the upper arm
[21]. By positioning the arm in flexion, abduction, and supination (FABS position) ([Fig. 10]), the oblique biceps tendon can be visualized on one plane, and tendon retraction
may be quantified easier compared to standard MR positioning [41]. MRI can differentiate complete tears from partial tears, and tendinopathies ([Fig. 11]), as well as accompanying muscular injuries and hematomas [18]. Festa et al. showed that the sensitivity and specificity of MRI for complete tears
were 100% and 82.8%, respectively. In cases of partial tears, the sensitivity and
specificity of MRI were 59.1% and 100%, respectively [42]. It is crucial to know that the distal biceps insertion has a specific anatomical
feature. Although in most cases the two heads of the biceps tendon blend together
to insert as a common tendon at the radial tuberosity, tendon fibers remain separated.
Thus, the long head of the distal biceps tendon inserts at the proximal portion of
the radial tuberosity and the short head at the distal portion [43]. Therefore, scrutiny needs to be given to the diagnosis of a distal biceps tendon
tear, because only one portion/head of the tendon may be torn, while the other remains
intact ([Fig. 12]). In 25% of cases, the distal biceps tendon remains bifurcated due to persistent
division of the short and long head [44]. The distal biceps tendon does not have a tendon sheath. Fluid around the distal
biceps tendon is usually located within the adjacent bicipitoradial bursa. The bursa
has a U-shaped form surrounding the tendon. An abnormally distended bursa can mimic
a soft-tissue tumor, but knowledge of the distinct anatomy of the bursa helps to correctly
diagnose bursitis.
Fig. 9 T1-weighted axial A, B MR images. The biceps tendon courses distally through the antecubital fossa (arrows
in A and B), is attached to the lacertus fibrosus (dashed arrow in A), and inserts at the radial tuberosity B.
Fig. 10 PD-weighted A and PD fat-saturated B MR image of an intact biceps tendon examined with the arm in flexion, abduction,
and supination (FABS), enabling the visualization of the biceps tendon in one plane
(arrows).
Fig. 11 59-year-old man with elbow pain. Tendinopathy at the biceps tendon insertion with
signal alteration of the tendon (arrows), perifocal edema, and bone marrow edema at
the insertion site (arrowheads) is visible on axial A and coronal B PD fat-saturated MR images.
Fig. 12 59-year-old man with partial biceps tendon rupture on axial PD fat-saturated MR images.
Proximally at the radial tuberosity A the long head of the biceps tendon is intact, while distally the short head is torn
and retracted from the insertion B. Note the perifocal soft tissue edema.
The brachialis muscle arises from the distal humerus and inserts into the ulnar tuberosity
[21]. For assessing the musculotendinous junction, axial MRI sequences are suitable.
Injuries to the brachialis muscle are referred to as “climber’s elbow”, because the
muscle develops its greatest strength in 90° flexion and pronation. The brachialis
muscle is a predilection site for the development of heterotopic ossifications after
trauma [45].
Posterior Compartment
Posterior tendons, muscles, and pathologies
The posterior compartment consists of the triceps brachii muscle and the anconeus
muscle. The triceps tendon consists of three heads arising from the infraglenoid tubercle
of the scapula and proximal humerus [21]. The long and lateral head insert with a common tendon superficially at the tip
of the olecranon, while the medial head inserts with mostly muscular fibers at the deep portion of the olecranon tip ([Fig. 13]
A). Thus, clinical evaluation might be harder, if some triceps function is still preserved
due to just one of the triceps portions being torn. The triceps tendon may demonstrate
a striated appearance on T2-weighted/proton density-weighted MRI sequences due to
fibrovascular deposits. Similar to the biceps tendon, the most common location of
a triceps tendon rupture is at the base [5]
[21]
[46]. The tendon can rupture with both deep and superficial portions or just one of those.
Triceps tendon ruptures can be best assessed on sagittal MRI. Entesophytes at the
triceps tendon can easily be seen on radiographs [46]. A retracted entesophyte should raise the suspicion of a tear of the triceps tendon
([Fig. 13]
B, C) [47].
Fig. 13 Anatomy of the triceps tendon insertion on a sagittal PD fat-saturated MR image A. The arrows point at the conjoint insertion of the long and lateral head of the triceps
tendon. The wavy contour and magic angle artifact are due to the examination in a
relaxed extended position, and should not be mistaken for a pathology. The deep portion
represents the muscular insertion of the medial head (open arrow) of the triceps muscle.
Radiograph B and MR image C of a different patient: B Lateral radiograph of the elbow shows an avulsed entesophyte of the triceps tendon
insertion (arrowhead). The correlating sagittal PD fat-saturated MR image C shows a partial rupture with retracted tendon portions (dashed arrow) of the common
long and lateral head of the triceps tendon, while other portions of the common tendon
(arrow) and the medial head (open arrow) insertion remain intact.
Usually the elbow is examined in a relaxed extended position, giving the tendon a
wavy contour on sagittal MR imaging, which should not be mistaken for a pathology
([Fig. 13]
A) [21]. Tendinopathies or ruptures of the triceps tendon are rare and often the result
of overloading from throwing sports [48]. An uncommon cause of pain in the posterior elbow, sometimes complicated by injury
of the ulnar nerve, is the “skipping/snapping elbow syndrome”. One of the reasons
is luxation/snapping of the ulnar nerve over the medial epicondyle during flexion
and extension movements. Additionally, an abnormal insertion of the medial triceps
head with equivalent dislocation can cause the symptoms [49]. Recurrent subluxation of the nerve at the elbow can result in neuritis. Neuropathy
of the ulnar nerve is the second most common peripheral nerve neuropathy after median
nerve neuropathy [50]. However, the diagnosis of an ulnar nerve neuropathy on MRI needs to be correlated
with symptoms ([Fig. 14]
A), especially with the knowledge that 60% of asymptomatic volunteers show increased
signal intensity of the ulnar nerve in the ulnar sulcus [51].
Fig. 14 Axial PD fat-saturated image A of a 33-year-old female with acute ulnar paresis and claw hand for three weeks shows
a hyperintense signal of the ulnar nerve (arrowhead) with surrounding soft-tissue
edema (dashed arrow). Axial T1-weighted MR image B and axial PD fat-saturated image C of a 58-year-old male shows an anconeus epitrochlearis muscle (arrows). The anconeus
epitrochlearis muscle originates from the medial epicondyle of the humerus, arches
over the ulnar nerve (arrowheads), and inserts at the medial olecranon. This was an
incidental finding in the examination, since the patient did not have any ulnar neuropathy
symptoms, and did not show any thickening or signal alterations of the nerve (arrowheads).
Of note: compare the unremarkable signal intensity of the ulnar nerve in C to the pathologic hyperintense signal in A.
The anconeus muscle arises from the posterior aspect of the lateral humeral epicondyle,
passing medially to insert along the lateral margin of the olecranon. The muscle tightens
the joint capsule and plays a minor role in extension of the elbow [21]. Due to compensatory overload in the context of lateral epicondylitis, signal changes
can occur in the anconeus muscle [18].
The anconeus epitrochlearis muscle is an anatomical variant that originates from the
medial epicondyle of the humerus, arches over the ulnar nerve, and inserts at the
medial olecranon ([Fig. 14]
B, C). Husarik et al. evaluated asymptomatic patients with MRI of their dominant elbow
and found an anconeus epitrochlearis muscle to be present in 23% of cases [51]. However, an anconeus epitrochlearis muscle can be associated with cubital tunnel
syndrome. Depending on the volume, this muscle can cause compression of the ulnar
nerve in the cubital tunnel [52].
Conclusion
Conventional MRI is an excellent imaging modality for the evaluation of elbow ligament
and tendon injuries. Knowledge of normal MR anatomy of ligaments and tendons of the
elbow is important to recognize pathologies. The most common elbow instability is
posterolateral rotatory instability with the LUCL being the most important stabilizer.
Recognition of injured ligaments is crucial to ensure appropriate therapy and restoration
of elbow stability.
