The elbow: review of anatomy and common collateral ligament complex pathology using MRI
The elbow is a complex joint whose stability is imparted by osseous and soft-tissue constraints. Anatomical and biomechanical knowledge of the supporting structures that provide stability to the medial and lateral elbow is essential to correctly interpret the pathological findings. Conventional MRI and MR arthrography are the imaging modalities of choice in the evaluation of elbow ligament injuries. Elbow instability can be classified according to timing (acute, chronic, or recurrent), the direction of displacement, the degree of displacement, and the articulations involved. This article reviews the MR imaging protocols recommended for each diagnosis and the normal anatomy and biomechanical aspects of the medial and lateral collateral ligament complex. We also present multiple cases of typical and atypical patterns of injury.
KeywordsMR imaging of the elbow Elbow anatomy Elbow instability Imaging technique Ligament injuries
An accurate imaging diagnosis contributes to the management of acute and chronic injuries of the elbow.
The anterior band of the medial or ulnar collateral ligament complex is the main stabilizer against valgus and internal rotation stress.
The lateral collateral ligament complex resists excessive varus and external rotational stress. The lateral ulnar collateral ligament is the most important in terms of stability.
Conventional MRI and MR arthrography are the imaging modalities of choice in the evaluation of elbow ligament injuries.
Posterolateral rotatory instability is the most common pattern of recurrent elbow instability.
The elbow is a complex joint whose stability is imparted by osseous as well as soft-tissue constraints, and injuries often involve several of these structures. The anterior band of the ulnar or medial collateral ligament (MCL) complex is the main static stabilizer of the elbow against valgus and internal rotation stress. The lateral collateral ligament (LCL) complex resists excessive varus and external rotational stress. The lateral ulnar collateral ligament is the most important in terms of stability. The classification of elbow dislocations is based on the direction of dislocation: posterior, posterolateral, posteromedial, lateral, medial, or divergent. Elbow dislocation is also classified as simple, without associated fracture, or complex, with an associated fracture. The radial head is usually fractured in adults with a complex elbow dislocation . The superior soft-tissue contrast of the magnetic resonance imaging (MRI) provides simultaneous evaluation of bone, hyaline cartilage, and soft tissue, allowing for assessment of all the static and dynamic stabilizers thus making accurate diagnoses possible with a single examination. In this article, we review the MRI protocols recommended for each diagnosis and the normal anatomy and biomechanical aspects of the MCL complex, the LCL complex, and the joint capsule. A better understanding of their anatomy and their relationship with adjacent structures is necessary to improve the detection of abnormalities. We also present multiple cases of typical and atypical patterns of injury of the MCL and LCL complex.
MRI of the elbow is best performed on a high-field strength magnet. To obtain adequate images of the ligamentous structures in the elbow, it is essential to use surface coils . Circumferential and phased array coils improve signal to noise and are therefore preferable. A wrist coil can be used in small adults and children when a large field of view is not needed. Larger patients can be imaged with a flexible coil, anterior neck coil, shoulder coil, or knee coil. A larger coil is especially useful when the patient cannot fully extend the elbow or when the patient needs to be imaged in the prone position with the arm overhead .
Placing the elbow at the isocenter of the scanner, where magnetic field homogeneity and gradient uniformity are best, usually requires prone positioning with the arm of interest extended overhead (“superman” position). This position can be uncomfortable and therefore prone to motion artifact, although it can be improved by adding motion-insensitive sequences, such a propeller. Modern phased-array multichannel coils allow placement of the elbow by the side of the patient in a supine position, which is more comfortable and less prone to motion. Nevertheless, achieving high-quality imaging with fat suppression can be difficult. The use of manual shimming and manual prescan can often correct this problem. The use of short-tau inversion recovery for fat suppression or methods of fat/water separation can also be useful [4, 5].
Direct MR arthrography distends the joint compartment, allowing for better delineation and visualization between tissues. It also allows detection of abnormal communication between joint compartment and extra-articular soft tissues. Indirect MR arthrography is less invasive and may be useful in some cases when direct MR arthrography is not feasible .
When direct arthrography is performed, the joint capsule can be injected with a mixture of gadolinium, saline or ropivacaine, and iodinated contrast material. With fluoroscopic guidance, the joint can be entered laterally over the radial head. Alternatively, a posterior approach has been suggested to avoid the radial collateral ligament complex or a posterolateral approach to also avoid the triceps tendon [5, 8, 10]. Then, 6–10 mL is normally sufficient to adequately distend the joint. The imaging protocol consists of fat suppressed T1-w fast spin-echo sequences in the axial, coronal, and sagittal planes. It should also include fat suppressed T2-w fast spin-echo images or STIR images in at least one plane in order to detect osseous and other extra-articular pathologies. Gradient-echo sequences or 3D volumetric sequences are also very useful. Some authors have proposed using saline solution when there is a documented allergy to gadolinium-based compounds. When performing MR arthrography with intra-articular saline solution, fat-suppressed T2-w sequences are essential and should replace the fat-suppressed T1-w sequences in the standard direct MR arthrographic protocol .
The elbow joint consists of three different articulations within a single synovial capsule: the ulnohumeral, the radiocapitellar, and the radioulnar joints. The first two joints function as a hinge, permitting flexion and extension; the last two joints accomplish the pivot motion of pronation and supination, and are functionally linked to the distal radioulnar joint and the wrist. The physiologic range of motion is 0 to 140° for flexion-extension movements and 0 to 180° for supination-pronation movements [5, 11].
The stability of the elbow joint depends on the integrity of several osseous and soft-tissue structures. The elbow has both static and dynamic constraints. The three primary static stabilizing structures are the ulnohumeral joint, which provides about 33% of valgus stability; the anterior bundle of the medial or ulnar collateral ligament complex, which provides about 54% of valgus stability; and the lateral ulnar collateral ligament component of the radial or lateral collateral ligament complex. The secondary static stabilizing structures include the radiocapitellar joint, the common flexor and extensor origins, and the joint capsule [1, 12]. The most important static soft-tissue constraints are the lateral ulnar collateral ligament and the anterior bundle of the medial collateral ligament [5, 7, 13]. The ulnohumeral joint is the most important osseous stabilizer of the elbow, providing primary stability below 20° or above 120° of flexion [5, 14].
The capsule of the elbow is reinforced by the collateral ligaments on the lateral and the medial side of the joint, but it is relatively weak anteriorly and posteriorly.
Medial or ulnar collateral ligament complex
Lateral collateral ligament complex
Ligament injuries can be classified into three grades. Grade I sprain: MR imaging shows increased signal intensity within the ligament on T1- and T2-w images. Partial-thickness tear or grade II sprain: MR imaging demonstrates focal partial discontinuity of ligament fibers with hyperintense fluid signal extending partially through the ligament, often associated with swelling of the ligament. Full-thickness tear or grade III sprain: MR imaging shows complete disruption of the ligament with a fluid gap between the torn ligament fibers, and extra-capsular extravasation of joint fluid .
Medial collateral ligament complex injury
The main function of the MCL complex is to maintain medial joint stability to valgus stress. The A-MCL is the most important component of the ligamentous complex acting as the primary medial stabilizer of the elbow from 30° to 120° of flexion . The P-MCL becomes a secondary stabilizer of the elbow when the joint is flexed beyond 90° .
Lateral collateral ligament complex injury
The LCL complex resists excessive varus and external rotational stress. Varus stress applied to the elbow may be due to an acute injury, but rarely to repetitive stress, as encountered on the medial side. Tears can involve one or more of the three bundles, but the LUCL is the most important in terms of stability . However, kinematic studies refer to both the LUCL and RCL working in concert to resist valgus stress. If both are injured, it can secondarily lead to subluxation or dislocation of the radiocapitellar joint even with an intact annular ligament, usually in the setting of chronic or repeated injury. LUCL tears usually involve the humeral origin [2, 5]. Failure to recognize LCL complex tears prior to surgical treatment of tennis elbow, particularly the LUCL, will lead to persistent postoperative symptoms.
Injuries of the LCL complex can occur in patients with advanced cases of tennis elbow, who also have tears of the common extensor tendon, and after a fall on the outstretched hand. Among iatrogenic causes of LCL complex disruption, we find overaggressive extensor tendon release for lateral epicondylitis, and radial head excision for comminuted fractures of the radial head [33, 34]. Repeated corticosteroid injections into the common extensor tendon and LCL complex origins might contribute to the weakening and ultimate failure of these structures .
In stage 1, there is posterolateral subluxation of the ulna on the humerus, which results in insufficiency or tearing of the LUCL (Fig. 23).
In stage 2, the elbow dislocates incompletely, so that the coronoid process is perched under the trochlea. The RCL, and the anterior and posterior articular capsule are disrupted, in addition to the LUCL (Fig. 24).
- In stage 3, the elbow dislocates completely with progressive disruption of the MCL and the coronoid process rests behind the humerus. The LUCL, the RCL, and the articular capsule are disrupted. Stage 3 is further subdivided into three categories:
◦ Stage 3A: disruption of the posterior bundle of the MCL while the anterior bundle of the MCL remains intact.
◦ Stage 3C: the entire distal humerus is stripped off soft tissues, rendering the elbow grossly unstable even when a splint or cast is applied with the elbow in a semi-flexion position (Fig. 28).
The classic clinical presentation of patients with PLRI includes pain as well as a sensation of locking, clicking, or snapping when the arm moves from a flexed to an extended elbow position. Ultimately, the diagnosis of PLRI is based on history and physical examination using provocative maneuvers. The pivot shift test of the elbow is designed to test for PLRI due to insufficiency of the LUCL and the RCL . Diagnosis is often difficult, as the clinical exam can be misleading unless performed under anesthesia. MR imaging can therefore be extremely useful in evaluating for tears of the LUCL in patients presenting with lateral elbow pain or instability. It is best evaluated in coronal oblique, coronal, and axial planes. Associated posterolateral subluxation of the radial head is best appreciated on sagittal images . LUCL tears may appear as an isolated finding in patients with PLRI in stage 1, or they can be detected in association with the rupture of the MCL in stage 3B. MR imaging is also useful in assessment of the cubital tunnel retinaculum, and the ulnar nerve in posterior dislocations.
The appearance of chronically torn and remodeled LUCL is similar to that described for the MCL, with thickening, abnormally increased signal, and discontinuity as possible findings (Figs. 26, 27, and 28).
Elbow fractures with ulnohumeral instability tend to occur in five general patterns: radial head fracture with ulnohumeral dislocation, terrible triad, varus posteromedial rotatory instability (VPMRI), olecranon fracture dislocation (OFD), and lateral column fracture of the distal humerus with ulnohumeral dislocation. VPMRI consists of a fracture of the anteromedial coronoid facet and a rupture of the LCL complex. OFD consists of a fracture of the olecranon with subluxation/dislocation of the intact forearm relative to the distal humerus. This is usually accompanied by a radial head fracture. A “terrible triad” consists of a posterior elbow dislocation, radial head fracture, coronoid process fracture, and a rupture of the LCL complex. These patients are at high risk for chronic instability .
Displaced radial head and neck (DRHN) fracture is always a complex fracture caused by the combination of a valgus force and pathologic forearm external rotation. They are accompanied by collateral ligament injuries and bony contusion. According to the Charalambous classification , type 3D and 4D DRHN fractures tended to have a higher association with MCL rupture compared with type 1D and 2D DRHN fractures, commonly associated with LUCL rupture, although this was not statistically significant .
Another important consideration with respect to elbow dislocation is that, as the ring of soft tissues is disrupted posterolaterally to medially, the articular capsule is torn and insufficient. Therefore, fluid in the elbow joint can escape through the capsular tear and a joint effusion, which is an indirect sign of elbow trauma, may not be present.
Conventional MRI and MR arthrography are the imaging modalities of choice in the evaluation of elbow ligament injuries. Proper coil selection, pulse sequence parameters, and patient positioning enhance the ability of MR imaging to demonstrate subtle injuries to the ligament and the regional osseous and soft-tissue structures. Anatomical and biomechanical knowledge of the support structures that provide stability to the medial and lateral elbow is essential to correctly interpret the pathological findings. Familiarity with the associated injuries that can be seen in MCL and LCL complex ruptures will therefore improve detection of ligament abnormalities. MR imaging is useful in the evaluation of children with elbow pain, as it can demonstrate physeal as well as ligamentous and osseous injury.
The authors gratefully thank Dr. F. Serrano, Dr. A. Luna, and Dr. M. Grande for their patience and support.
JAB drafted the manuscript. LC, MDLP and BA assisted in selecting and acquiring the images. SR and JBS revised the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
- 2.Kaplan LJ, Potter HG (2006) MR imaging of ligament injuries to the elbow. Radiol Clin North Am 44:583–594Google Scholar
- 3.Kijowski R, Tuite M, Sandford M (2004) Magnetic resonance imaging of the elbow. Part I: normal anatomy, imaging technique, and osseous abnormalities. Skeletal Radiol 33:685–697Google Scholar
- 6.Cotten A, Jacobson J, Brossmann J et al. Collateral ligaments of the elbow: conventional MR imaging and MR arthrography with coronal oblique plane and elbow flexion. Radiology 204:806–812Google Scholar
- 10.Lohman M, Borrero C, Casagranda B, Rafiee B, Towers J (2009) The posterior transtriceps approach for elbow arthrography: a forgotten technique? Skeletal Radiol 38(5):513–516Google Scholar
- 12.O’Driscoll SW, Jupiter JB, King GJ, Hotchkiss RN, Morrey BF (2001) The unstable elbow. Instr Course Lect 50:89–102Google Scholar
- 13.Chung CB (2010) Elbow ligaments and instability. In: Chung CB, Steinbach LS (eds) MRI of the upper extremity. Wolters Kluwer Health/Lippincott Williams & Wilkins, Philadelphia, pp 402–428Google Scholar
- 14.Munshi M, Pretterklieber ML, Chung CB et al. (2004) Anterior bundle of ulnar collateral ligament: evaluation of anatomic relationships by using MR imaging, MR arthrography, and gross anatomic and histologic analisis. Radiology 231:797–803Google Scholar
- 15.Chung CB, Steimbach L (2010) MRI of the upper extremity: shoulder, elbow, wrist and hand. Lippincott Williams & Wilkins, PhiladelphiaGoogle Scholar
- 19.de Haan J, Schep NWL, Eygendaal D, Kleinrensink GJ, Tuinebreijer WE, den Hartog D (2011) Stability of the elbow joint: relevant anatomy an clinical implications of in vitro biomechanical studies. Open Orthop J 5:168–176Google Scholar
- 23.Seki A, Olsen BS, Jensen SL, Eygendaal D, Søjbjerg JO (2002) Functional anatomy of the lateral collateral ligament complex of the elbow: configuration of Y and its role. J Shoulder Elbow Surg 11(1):53–59Google Scholar
- 24.Sanal HT, Chen L, Haghighi P, Trudell DJ, Resnick DL (2009) Annular ligament of the elbow: MR arthrography appearance with anatomic and histologyc correlation. AJR Am J Roentgenol 193:122–126Google Scholar
- 27.Morrey BF, An KNK (1983) Articular and ligamentous contributions to the stability of the elbow joint. Am J Sports Med 11(5):315–319Google Scholar
- 28.O'Driscoll SW, Morrey BF, Korinek S, An KN (1992) Elbow subluxation and dislocation. A spectrum of instability. Clin Orthop Relat Res (280):186–197Google Scholar
- 29.Seiber K, Gupta R, McGarry MH, Safran MR, Lee TQ (2009) The role of the elbow musculature, forearm rotation, and flexion in elbow stability: an in vitro study. J Shoulder Elbow Surg 18(2):260–268Google Scholar
- 31.Kijowski RM, Tuited M, Stanford M (2005) Magnetic resonance imaging of the elbow. Part II: abnormalities of the ligaments, tendons, and nerves. Skeletal Radiol 34(1):1–18Google Scholar
- 38.Charalambous CP, Stanley JK, Mills SP et al (2013) Comminuted radial head fractures: aspects of current management. J Shoulder Elbow Surg 20:996–1007Google Scholar
- 39.Rhyou IH, Kim KC, Kim KW, Lee JH, Kim SY (2013) Collateral ligament injury in the displaced radial head and neck fracture: correlation with fracture morphology and management strategy to the torn ulnar collateral ligament. J Shoulder Elbow Surg 22:261–267Google Scholar
- 40.Cerezal L, Studer A, Carro LP, Villalba A (2018) Postoperative elbow imaging. In: Sutter R (ed) MRI of the elbow, 1st edn. Breitenseher Publisher, Horn, pp 95–116Google Scholar
- 42.Camp CL, Sanchez-Sotelo J, Shields MNS, O’Driscoll SW (2017) Lateral ulnar collateral ligament reconstruction for posterolateral rotatory instability of the elbow. Arthrosc Tech 6(4):e1101–e1105Google Scholar
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