Clinical history: A 23-year-old male baseball player presents with elbow snapping and locking while throwing. Fat-suppressed proton density-weighted sagittal (1A and 1B) and fat-suppressed T2-weighted axial images (1C and 1D) are provided. What are the findings? What is your diagnosis?
Findings
Figure 2: An irregular, thickened posterolateral synovial fold extends into the posterior radiocapitellar joint (arrows). Mild bone marrow edema is apparent in the posterior radial head on the sagittal fat-suppressed proton density-weighted image (arrowhead, 2B). The axial fat-suppressed T2-weighted images (2C and 2D) also demonstrate the thickened posterolateral synovial fold (arrow, 2C) and radial head marrow edema (arrowhead, 2D) suggesting overlying chondromalacia.
Diagnosis
Elbow Synovial Fold Syndrome
Introduction
Elbow synovial fold syndrome, also known as posterolateral impingement or snapping plicae, is a condition characterized by the irritation of synovial folds in the elbow joint, often resulting in pain and reduced range of motion. This syndrome is typically associated with impingement of synovial folds—extensions of the synovial membrane that can become hypertrophied or inflamed. The resultant irritation can lead to discomfort, particularly during activities that involve repetitive elbow flexion and extension. Radiological imaging, including MRI and ultrasound, plays a crucial role in diagnosing this condition by revealing characteristic features such as the presence of hypertrophied synovial folds, impingement signs and associated radiocapitellar chondromalacia.
The condition’s diagnosis can be challenging due to its symptom overlap with other elbow pathologies such as common extensor tendinosis or loose bodies. Recent advancements in imaging techniques have enhanced the ability to distinguish elbow synovial fold syndrome from other disorders. MRI, in particular, provides detailed images of the soft tissues in and around the elbow, allowing for accurate assessment of synovial fold involvement. Understanding the specific radiological features and clinical presentations associated with elbow synovial fold syndrome is vital for effective management and treatment, which often involves a combination of conservative approaches like physical therapy, rest, nonsteroidal anti-inflammatory medicines, and, in some cases, surgical intervention.
Anatomy
The synovial plica of the elbow are a distinctive anatomical feature within the elbow joint’s synovial membrane. These plicae are composed of a layer of synovial tissue, which is a thin, delicate structure lined with synovial cells responsible for producing and maintaining synovial fluid. They vary among individuals, with no consensus in the literature concerning size, shape or anatomic location1 Their anatomical variability can influence the joint’s overall mechanics and susceptibility to certain pathologies, although their function is ultimately unknown2
The radiohumeral synovial fold is a reliably present anatomical feature composed of capsular tissue, situated along the proximal margin of the annular ligament. Although it is separate from the annular ligament, it seamlessly integrates with the radiocapitellar joint capsule, which merges subtly with the common extensor tendon, creating a unified attachment at the lateral epicondyle3 The synovial plicae of the elbow are found at the radiocapitellar joint and encircle the outer edge of the radial head.
The synovial plicae of the elbow consist of several distinct folds within the synovial membrane. The primary plicae include the anterior, lateral, posterolateral, and lateral olecranon folds (Figure 3).4
Anterior fold— Appears in 67% cadaveric specimens. This fold is a thin segment of the radiohumeral synovial fold. In cadaveric elbow specimens, the average size of the anterior fold is 18 mm in length, 4 mm in width, and 2 mm in thickness(Figure 4A).5,6,7
Lateral fold— Observed in 5–20% of cases. The lateral fold is a horizontal, meniscoid structure that projects into the radiohumeral joint, lying between the capitellum and the outer rim of the radial dome. It has a crescent shape, with a free edge extending 2.5–4.0 mm between the articular surfaces. This edge is often irregular and moves freely over the articular cartilage. In cadaveric specimens, the lateral fold averages 13 mm in length, 4 mm in width, and 2 mm in thickness (Figure 4B).5,6,7
Posterolateral synovial fold— Present in 86–100% of cadaveric specimens. Located at the junction between the lower sigmoid cavity of the ulna, the transverse sulcus of the major sigmoid cavity, and the radial dome, the posterolateral synovial fold extends forward to merge with the lateral fold and upward to connect with the lateral olecranon fold. In cadaveric specimens, its average dimensions are 29 mm in length, 5 mm in width, and 3 mm in thickness (Figure 4C).5,6,7
Lateral olecranon synovial fold— Present in 28–33% of individuals. Originating from the posterolateral fold, this fold runs proximally along the lateral edge of the olecranon, with its rounded apex at the peak of the lateral non-articular portion of the trochlear notch. It is positioned in the posterolateral olecranon recess near the anconeus muscle. The median size of the lateral olecranon fold in cadaveric specimens is 4 mm in length, 4 mm in width, and 2 mm in thickness (Figures 4A and 4D). 5,6,7
Figure 3: An anterior view of the elbow with the humerus removed and the capsule partially removed depicts the radial head and ulnar trochlea. The synovial plicae of the elbow encircle the radial head and are variably present. They blend with the joint capsule at the level of the proximal margin of the annular ligament (AL). The primary folds are the anterior (AF), lateral (LF), posterolateral (PLF), and lateral olecranon (LOF) folds.
Figure 4: 4A - A sagittal fat-suppressed proton density-weighted image demonstrates the normal MRI appearance of the posterolateral (arrow) and anterior synovial folds (arrowhead). 4B - A coronal fat-suppressed T2-weighted MR image shows the normal MRI appearance of the lateral synovial fold (arrow). 4C - A fat-suppressed proton density-weighted axial MR image just proximal to the radiocapitellar joint shows the normal MRI appearance of the lateral olecranon synovial fold in the posterolateral olecranon recess (arrow). The olecranon (asterisk) and anconeus muscle (arrowhead) are also labeled. 4D - A fat-suppressed proton density-weighted axial image through the radiocapitellar joint demonstrates the appearance of the normal posterolateral (arrow) and lateral synovial folds (arrowhead) outlined by joint fluid.
MRI Findings of Elbow Synovial Fold Syndrome
MRI is the imaging method of choice in the evaluation of synovial plica. Normal synovial folds appear as smooth, hypointense bands surrounded by synovial fluid and are best assessed on fluid sensitive sequences8 Thick and fibrotic folds with abnormal signal intensity and irregular margins are typically seen in symptomatic cases on MRI1, often accompanied by signs of chronic synovitis and radiocapitellar chondromalacia. Chondromalacia is secondary to chronic mechanical snapping of the synovial folds over the articular surface.9 The posterolateral fold is the most commonly involved (Figures 5 and 6).
Choi and colleagues conducted an MRI comparison between symptomatic and asymptomatic elbow folds. Their findings revealed that the symptomatic folds were nearly twice as large, measuring 9 mm in the mediolateral dimension compared to 5 mm in asymptomatic folds, and 9 mm laterally versus 7.5 mm. Additionally, symptomatic folds tended to cover more than 30% of the radial head, whereas asymptomatic ones covered only 18%.10
Administration of IV contrast is not necessary for diagnosis but can improve detection of focal synovitis.11 However, synovitis may not be present in some cases, especially in patients with chronic symptoms.1
Figure 5: A fat-suppressed proton density-weighted sagittal image demonstrates an irregular and thickened posterolateral synovial fold (arrow) that extends into the posterior radiocapitellar articulation, covering 30-40% of the radial head in a patient with chronic posterolateral elbow pain. Adjacent full-thickness chondral fissuring of the posterior capitellum and subchondral marrow edema (arrowhead) are present.
Figure 6: A coronal fat-suppressed T2-weighted image from another patient with posterolateral elbow pain and snapping demonstrates irregular thickening of the posterolateral synovial fold (arrow), chondromalacia and mild subchondral marrow edema and cystic change on both sides of the joint (arrowheads), and posterolateral elbow synovitis.
Differential Diagnosis
The main differential diagnosis for elbow synovial fold syndrome is lateral epicondylitis/common extensor tendon tears (tennis elbow), which is one of the most common causes of posterolateral elbow pain (Figure 7). This is an overuse syndrome which predominantly affects the extensor carpi radialis brevis tendon.12 Repetitive stress results in micro-tearing and progressive degeneration due to an immature reparative response, which may progress to a full-thickness tendon tear.13 Elbow synovial fold syndrome should be considered in patients unresponsive to treatment for lateral epicondylitis. A more detailed discussion of lateral epicondylitis can be found here.
Figure 7: A coronal fat-suppressed T2-weighted image in a patient with chronic lateral elbow pain and swelling demonstrates abnormal thickening and increased signal intensity of the common extensor origin at the lateral epicondyle (arrow) with a fluid-intensity partial tear (arrowhead).
Snapping at the elbow can also be caused by ulnar nerve dislocation over the medial epicondyle of the humerus in elbow flexion or as the elbow is extended from a flexed position. A portion of the medial head of the triceps muscle or an accessory triceps tendon can also dislocate, causing one or more additional snaps.14
Conventional MRI with the elbow in an extended position frequently fails to detect the dynamic issues associated with ulnar nerve and triceps dislocations. Therefore, MRI scans in both flexed and extended positions are recommended for patients with suspected ulnar nerve dislocation, snapping, or those who have had previous ulnar nerve transposition surgery but continue to experience symptoms (Figure 8).15 A more detailed discussion of this syndrome can be found here.
Figure 8: 8A - An axial T1-weighted image with the elbow extended in a 15-year-old female with a long history of triceps pain shows the normal location of the ulnar nerve (arrowhead) and the medial triceps (arrow) posterior to the medial epicondyle (asterisk). 8B - The patient returned for additional imaging with the elbow in flexion. An axial T1-weighted image with the elbow fully flexed shows the ulnar nerve (arrowhead) and the medial triceps (arrow) anterior to the medial epicondyle (asterisk).
Intra-articular loose bodies are an additional differential consideration (Figure 9). Loose bodies can abruptly impair articular range of motion with associated crescendo pain, clicking and locking. Intra-articular bodies are composed of cartilage or cartilage and bone and result from any process that leads to disruption of the articular surface. They derive nutrition from synovial fluid and the surface cells form more cartilaginous layers, enlarging the body over time. The deeper cells receive less nutrition, resulting in cell death and calcification.16
Figure 9: 9A - A sagittal fat-suppressed proton-density weighted image in a patient with chronic elbow pain and locking. A moderate to large elbow joint effusion is present with a large, low signal intensity focus in the coronoid fossa compatible with a loose intra-articular body (arrow). Synovitis is noted in the olecranon fossa (arrowhead). 9B - An axial fat-suppressed T2-weighted image in the same patient demonstrates the large intra-articular body in the coronoid fossa (arrow) with adjacent synovitis and capsular thickening. 9C - A slightly more caudal axial image in the same patient shows additional small loose bodies anterior to the humerus (arrow) and in the posteromedial joint recess deep to the cubital tunnel (arrowhead). The adjacent ulnar nerve is mildly enlarged and increased in signal, suggesting mild ulnar neuritis (blue arrow).
Diffuse tenosynovial giant cell tumor, previously known as pigmented villonodular synovitis (PVNS), is also a differential consideration with patients presenting with joint swelling, pain and reduced range of motion. MRI may reveal mass-like synovial proliferation with lobulated or ill-defined margins, with low signal intensity due to hemosiderin deposition. Some areas of high signal intensity may be present on T2-weighted images due to joint fluid or inflamed synovium (Figure 10).17
Figure 10: 10A - A sagittal STIR image in a patient with posterolateral elbow pain and swelling demonstrates a large nodular hypointense focus anterior to the capitellum (asterisk), large effusion with diffuse, irregular synovial hypertrophy with innumerable irregular small nodular foci in both the anterior and posterior aspect of the joint (arrowheads), and regions of low signal intensity suspicious for hemosiderin, suggestive of PVNS. 10B - An axial STIR image in the same patient shows irregular, low signal synovial hypertrophy (arrowheads) in the posterolateral joint recess.
Treatment
Initially, non-surgical management of elbow synovial fold syndrome is recommended, which involves resting from all intense physical activities, undergoing physiotherapy, and using nonsteroidal anti-inflammatory drugs. If conservative treatment fails, arthroscopic removal of the problematic plica becomes the preferred option.1 Delaying arthroscopic intervention due to extended conservative treatment should be avoided, as early resection can prevent further damage to articular cartilage.19 Arthroscopic removal of the plica, along with addressing any focal fibrosis or synovitis and repairing chondral defects, typically results in excellent outcomes.18
Conclusion
Elbow synovial fold syndrome, also known as posterolateral impingement or snapping plica, is a condition marked by pain and mechanical issues in the joint. This syndrome is often overlooked or misdiagnosed. Recognizing this condition can help avoid misdiagnosis in patients who present with lateral elbow pain or a snapping sensation in the elbow. MRI is a valuable diagnostic tool to rule out other causes of lateral elbow pain and snapping. Prompt diagnosis and treatment are vital to prevent mechanical damage to the articular cartilage of the elbow.19
References
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- Isogai S, Murakami G, Wada T, Ishii S. Which morphologies of synovial folds result from degeneration and/or aging of the radiohumeral joint: an anatomic study with cadavers and embryos. J Shoulder Elbow Surg 2001; 10:169–181. ↩
- Tsuji H, Wada T, Oda T, et al. Arthroscopic, macroscopic, and microscopic anatomy of the synovial fold of the elbow joint in correlation with the common extensor origin. Arthroscopy 2008; 24:34–38. ↩
- Duparc F, Putz R, Michot C, et al. The synovial fold of the humeroradial joint: anatomical and histological features, and clinical relevance in lateral epicondylalgia of the elbow. Surg Radiol Anat 2002; 24:302–307. ↩
- Bonczar, M., Ostrowski, P., Bednarz, W. et al. Synovial plica of the elbow — detailed measurements and how to implicate its relevance in clinical practice. International Orthopaedics (SICOT) 47, 1031–1039 (2023). https://doi.org/10.1007/s00264-023-05726-9 ↩
- Koh S, Morris RP, Andersen CL, et al. Ultrasono-graphic examination of the synovial fold of the radiohumeral joint. J Shoulder Elbow Surg 2007; 16:609–615. ↩
- Isogai S, Murakami G, Wada T, Ishii S. Which morphologies of synovial folds result from degeneration and/or aging of the radiohumeral joint: an anatomic study with cadavers and embryos. J Shoulder Elbow Surg 2001; 10:169–181 ↩
- Awaya H, Schweitzer ME, Feng SA, et al. Elbow synovial fold syndrome: MR imaging findings. AJR 2001; 177:1377–1381. ↩
- Steinert AF, Goebel S, Rucker A, Barthel T. Snapping elbow caused by hypertrophic synovial plica in the radiohumeral joint: a report of three cases and review of literature. Arch Orthop Trauma Surg 2010; 130:347–351. ↩
- Choi SH, Ji SK, Lee SA, Park MJ, Chang MJ. Magnetic resonance imaging of posterolateral plica of the elbow joint: Asymptomatic vs. symptomatic subjects. PLoS One. 2017 Jun 16;12(6):e0174320. doi: 10.1371/journal.pone.0174320. PMID: 28622337; PMCID: PMC5473528. ↩
- Brunton LM, Anderson MW, Pannunzio ME, et al. Magnetic resonance imaging of the elbow: update on current techniques and indications. J Hand Surg Am 2006; 31:1001–1011. ↩
- Walz DM, Newman JS, Konin GP et-al. Epicondylitis: pathogenesis, imaging, and treatment. Radiographics. 2010;30 (1): 167-84. ↩
- Potter HG, Hannafin JA, Morwessel RM et-al. Lateral epicondylitis: correlation of MR imaging, surgical, and histopathologic findings. Radiology. 1995;196 (1): 43-6. ↩
- Childress HM. Recurrent ulnar-nerve dislocation at the elbow. J Bone Joint Surg Am 1956:38-A:978-984. ↩
- Spinner RJ, Hayden FR, Hipps CT, Goldner RD. Imaging the Snapping Triceps. AJR 1996;167:1550-1551. ↩
- Milgram J, Gilden J, Gilula L. Multiple Loose Bodies: Formation, Revascularization, and Resorption. A 29-Year Followup Study. Clin Orthop Relat Res. 1996;(322):152-7. ↩
- Narváez J, Narváez J, Ortega R, De Lama E, Roca Y, Vidal N. Hypointense Synovial Lesions on T2-Weighted Images: Differential Diagnosis with Pathologic Correlation. AJR Am J Roentgenol. 2003;181(3):761-9. ↩
- Kim DH, Gambardella RA, Elattrache NS, et al. Arthroscopic treatment of posterolateral elbow impingement from lateral synovial plicae in throwing athletes and golfers. Am J Sports Med 2006; 34:438–444. ↩
- Antuna SA, O’Driscoll SW. Snapping plicae associated with radiocapitellar chondromalacia. Arthroscopy 2001; 17:491–495. ↩