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1 Universitätsinstitut für Radiologie, Universitätsspital Basel,
Petersgraben 4, Basel 4031, Switzerland.
2 Thomas Jefferson University Hospital, 111 S 11th St., Philadelphia, PA
19107.
Received November 17, 2003;
accepted after revision January 16, 2004.
Address correspondence to F. Floemer.
Abstract
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MATERIALS AND METHODS. MRI contrast-enhanced examinations (n = 19) of 35 patients with olecranon bursitis (septic, n = 14; nonseptic, n = 21) were jointly reviewed by two musculoskeletal radiologists. We evaluated bursa size, extent of marginal lobulation, septation, concomitant elbow joint effusion, soft-tissue edema, rim enhancement, soft-tissue enhancement, degree of fluid complexity, definition of bursa margins, presence of edema, thickening of the triceps tendon, and bone marrow edema.
RESULTS. Comparison of septic and nonseptic bursitis yielded the following results: marginal lobulation, 79% (11/14) versus 48% (10/21), p = 0.14; bursa septation, 64% (9/14) versus 57% (12/21), p = 1.0; moderate or marked complexity of bursa fluid, 64% (9/14) versus 29% (6/21), p = 0.15; poorly defined margins, 64% (9/14) versus 67% (14/21), p = 1.0; elbow joint effusion, 86% (12/14) versus 52% (11/21), p = 0.12; moderate to marked soft-tissue edema, 64% (9/14) versus 33% (7/21), p = 0.1; edema of the triceps, 57% (8/14) versus 48% (10/21), p = 0.73; thickening of the triceps, 43% (6/14) versus 14% (3/21), p = 0.21; bone marrow edema, 29% (4/14) versus 5% (1/21), p = 0.13; rim enhancement, 100% (11/11) versus 75% (6/8), p = 0.31; soft-tissue enhancement, 100% (11/11) versus 63% (5/8), p = 0.1.
CONCLUSION. Septic and nonseptic olecranon bursitis present with a considerable overlap of MRI findings without statistically significant differences. Septic olecranon bursitis can be excluded in the absence of bursal and soft-tissue enhancement.
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Olecranon bursitis is a clinical diagnosis, and MRI is rarely performed in this context. In patients with advanced infection, MRI is sometimes requested to evaluate abscesses or osteomyelitis. In daily MRI, routine diagnosis of olecranon bursitis is, however, not rare because of concomitant inflammation and effusion in the olecranon bursa after trauma in patients with rheumatoid arthritis and other diseases that lead to swelling and inflammation of the soft tissue on the dorsal aspect of the elbow.
Our goal was to describe MRI signal alterations of septic and nonseptic olecranon bursitis and to determine whether MRI evaluation allows differentiation of the two.
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MRI
MRI investigations were performed using a 1.5-T magnet (Signa, GE
Healthcare) in 27 patients and a 0.3-T system (Airis II, Hitachi Medical
Systems America) in eight patients.
All patients were imaged with a surface coil using a field of view between 12 and 20 cm in the axial, sagittal, and coronal planes. In all studies, three orthogonal planes were imaged. All patients had T1- and T2-weighted images, and additional contrast-enhanced images were obtained in 19 patients.
T1-weighted spin-echo sequences were acquired averaging 1–3 signals (TR range/TE range, 400–700/10–20). A fast spin-echo technique (8 echo train) was used to obtain T2-weighted images in all patients (4,000–6,000/70–100; average, 2–4 signals). Fat suppression was used for T2-weighted fast spin-echo images in 21 patients using selective presaturation of lipid resonant frequency. In six studies, images were obtained using a STIR fat-suppressed sequence (2,000–5,000/20–40; inversion time, 80 msec).
IV gadopentetate dimeglumine (Magnevist, Berlex Laboratories), at a dose of 0.1 mmol/kg of body weight, was administered in 19 patients. Fat-saturated T1-weighted images were acquired in 19 patients using these two sequences: in 10 patients, a spin-echo technique with spectral fat suppression and identical T1-weighted parameters (400–700/10–20) as described previously was performed, and in nine patients a fat-suppressed fast multiplanar spoiled-gradient echo technique was used (150–340/2–3.3; flip angle, 90°).
Evaluation of MRI Examinations
Two musculoskeletal radiologists reviewed the MRI examinations in consensus
on a PACS (picture archiving and communication system) workstation (Canon
Medical Systems). All sequences of one examination were reviewed together as
an entity. The reviewers were aware that it was the goal of the study to
describe MRI signal alterations of the olecranon bursa and the surrounding
soft tissues. They were, however, blinded to clinical diagnosis, laboratory
results, and patient outcome.
The olecranon bursa size was reported in centimeters in three planes from T2-weighted images. Marginal lobulation and internal septation were graded as absent, mild, or moderate to marked from T1- and T2-weighted images. Complexity of bursal fluid was reported as simple (homogeneously hyperintense signal in the bursa), mild (minimal hypointense signal), or moderate to marked (moderate to marked hypointensity in the bursal fluid) on T2-weighted images. The marginal definition of the olecranon bursa was graded as either well or poorly defined on T1- and T2-weighted images. Concomitant elbow joint effusion was graded as absent, minor, or moderate to marked on T1- and T2-weighted images. Surrounding soft-tissue edema was rated as absent, mild, or moderate to marked on T1- and T2-weighted images. Signal alterations of the triceps tendon were also reviewed, and it was noted whether edema of the triceps tendon was visible on T2-weighted images. Thickening of the triceps tendon was also recorded. Bone marrow edema (focally hypointense signal on T1-weighted images with hyperintensity on T2-weighted images) was described as present or absent. Rim enhancement of the bursa and surrounding soft-tissue enhancement was graded as absent, mild, or moderate to marked.
Review of Patients' Reports
We reviewed the charts and surgical reports for all patients. It was
especially noted if patients had aspiration of the bursal fluid or whether
surgery was performed. The microbiology results were reviewed, and it was also
noted if concomitant osteomyelitis was documented by microbiology or histology
reports. Diagnosis of septic olecranon bursitis required patients to have
positive culture results from percutaneous aspiration of the bursa. Nonseptic
olecranon bursitis required patients to have negative culture results or
clinical improvement without surgery and without antibiotic treatment. The
patients' charts were also reviewed to note the cause of olecranon
bursitis.
Statistical Analysis
Statistical comparison of marginal lobulation, bursa septation, complexity
of bursa fluid, definition of the bursa margins, degree of elbow joint
effusion, presence of concomitant soft-tissue edema, edema and swelling or
interruption of the triceps, presence of bone marrow edema, degree of rim
enhancement, and degree of surrounding soft-tissue enhancement was performed
using Fisher's exact test (alternative hypothesis: two-tailed). A p
value of less than 0.05 was considered statistically significant.
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Twenty-one patients had nonseptic olecranon bursitis, as defined by negative culture results (n = 11) or clinical improvement without surgery and without antibiotic treatment (n = 10). Associated conditions in the patients with nonseptic olecranon bursitis were trauma without fracture (n = 9), trauma with fracture (n = 1), triceps tear (n = 5), diabetes mellitus (n = 1), scleroderma (n = 1), phlegmon (n = 1), and no associated condition (n = 3).
MRI Characteristics
The size of the bursae ranged between 1 x 1 x 0.5 cm and 10.6
x 4.7 x 1.8 cm. The bursa volume varied between 0.5 and 89.7 mL,
but the difference between the septic and nonseptic patient groups (p
= 0.31) was not statistically significant.
Table 1 summarizes the observed MRI findings of the patient group with septic (n = 14) and nonseptic (n = 21) olecranon bursitis. Table 2 summarizes the enhancement patterns of patients with septic (n = 11) and nonseptic (n = 8) olecranon bursitis.
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Marginal lobulation was absent in more than half of the patients with noninfectious olecranon bursitis (Fig. 1A, 1B, 1C), but it was observed in 79% of patients with proven infection. Although moderate or marked marginal lobulation could be observed in some (14%) of the patients without infection, it was seen in more than a third (36%) of the patients with septic bursitis. The frequency of bursa septation and the degree of septation were almost equally distributed in both groups.
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Complexity of the bursal fluid, with hypointense signal in T2-weighted images (Fig. 2A), was classified as moderate to marked twice as frequently in the septic group. However, in both groups, absence of complexity was nearly equally distributed, and findings overlapped considerably.
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Elbow joint effusions (Fig. 2C) were present in 86% of patients with septic olecranon bursitis, and nearly half of the patients without bursa infection did not have concomitant joint effusion.
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Soft-tissue edema was present in all patients with septic olecranon bursitis and in 81% of the patients without bursa infection. Thickening of the triceps tendon (Fig. 2C) was observed three times more frequently in the septic group. In the nonseptic group, thickening of the triceps tendon (Fig. 2C) was seen after trauma to the dorsal aspect of the elbow.
Bone marrow edema of the olecranon (Fig. 2B) was seen in only one patient without bursa infection but in nearly one third of the patients with septic bursitis. Concomitant osteomyelitis was diagnosed at bone biopsy in three of these four patients. One patient with septic bursitis and bone marrow edema had negative bone biopsy results. The patient with bone marrow edema and nonseptic bursitis did not undergo bone biopsy, and the bone marrow edema was thought to be reactive due to repetitive traumatization during work. The patient did not receive antibiotics and did not develop symptoms of osteomyelitis during a follow-up time of 1 year.
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Rim enhancement of the bursa (Fig.
2D) was seen in all patients with septic bursitis, and most of
them had moderate to marked rim enhancement. One fourth of patients without
infection did not have rim enhancement, and most of this group also showed
moderate to marked
enhancement.
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Nonseptic olecranon bursitis has also been reported in football players who play on artificial turf [3]; can be due to overuse, repetitive trauma, inflammatory arthropathy, or obesity [4]; and in uremic patients may result from prolonged sustained pressure against the elbow [5]. Other causes of nonseptic olecranon bursitis include rheumatoid diseases and gout [6].
Approximately one third of the cases of olecranon bursitis are septic [6]. Trauma, breaks in the skin, or foci of infection in the surrounding soft tissues provide a portal of entry from which bacteria appear to enter the bursa [1]. Many patients with septic olecranon bursitis lack a history of trauma or a visible injury over the olecranon [1, 6]. Penetration through minute breaks in the skin must therefore occasionally happen.
Ninety percent of bursa aspirate cultures grow Staphylococcus aureus, and most of the remainder are infected with beta-hemolytic streptococci [1, 7, 8]. Impaired immunity is an important causative factor in up to half of all septic cases. The most common reason is alcohol abuse, but steroids, diabetes, renal impairment, and malignancy are also responsible [6, 9, 10]. Clinical differentiation of septic and nonseptic bursitis can be difficult because of the lack of specific clinical signs and symptoms [1, 6, 7]. The diagnosis of infection still requires the culture of freshly aspirated bursal fluid [11].
MRI characteristics of noninfected bursitis have previously been reported in bicipitoradial bursitis [12, 13], iliopsoas bursitis [14, 15], trochanteric bursitis [16], ischial bursitis [17], knee joint bursitis [18, 19], retrocalcaneal bursitis [16, 20], and forefoot bursitis involving the adventitial bursa adjacent to the head of the first metatarsal [21, 22] or the intermetatarsal bursa [22]. However, MRI characteristics of olecranon bursitis have, to our best knowledge, not been systematically analyzed.
All our patients had a hypointense collection on T1-weighted images with variable signal intensity in T2-weighted sequences over the olecranon. Concomitant surrounding soft-tissue edema with contrast enhancement was present in most of our patients, and most had enhancement of the bursa margins. The size of the olecranon bursa varied considerably, and no statistically significant difference in size was noted between the patients with infected and noninfected bursitis.
Degree of septation of the bursa, definition of bursa margins, amount of elbow effusion, and presence of triceps edema were nearly equally distributed in the septic and noninfected groups and will therefore not be of much help in recognition of potential infection. Other MRI criteria were more frequent or more severe in the septic group and may indicate potential infection: Marked lobulation, marked complexity, marked soft-tissue edema, and thickening of the triceps tendon were twice as common in the septic group. Marked bursa wall enhancement and marked soft-tissue enhancement were also more frequent in the septic group, but marked rim enhancement was also seen in most noninfected bursitis cases, and half of these noninfected bursae had marked soft-tissue enhancement. None of the criteria that were observed more frequently in the septic group reached statistical significance. However, lack of surrounding bursa wall enhancement and adjacent soft-tissue enhancement was not observed in the presence of septic olecranon bursitis. Similar results were found in a recent article comparing MRI signal alterations of infected and uninfected joints [23]. The authors concluded that no single MRI criterion such as degree of joint effusion, synovial thickening, synovial enhancement, or bone marrow edema was pathognomonic for an infected joint.
Previous reports of noninfected bursae in other parts of the body describe marked signal alterations similar to those in our study, including marked lobulation [4, 12, 13, 23], septation [4, 12, 17–19], complexity [14, 23–25], wall thickening [4, 14, 17, 23, 26], adjacent joint effusion [14, 27], soft-tissue edema [23], rim enhancement [4, 14, 17, 22, 23, 28], soft-tissue enhancement [29], and thickening of the adjacent tendon [12, 19, 27, 29, 30].
Diseases that lead to a complicated aspect of affected and noninfected bursae include chronic degenerative arthritis [14], repetitive trauma [2, 27, 31–33], acute trauma [33], rheumatoid arthritis [23, 27, 34], gout [1], chronic bursitis [25], and polymyalgia rheumatica [27].
Thickening of the triceps tendon was observed in nearly half of the patients with septic bursitis and a minority of patients without infection. Concomitant edema of the triceps was observed in nearly half of both patient groups. It is therefore important to realize that olecranon bursitis may lead to signal alterations compatible with triceps tendon tears [29].
Bone marrow edema was observed in four patients with septic bursitis, and three of these patients also had osteomyelitis. Only one patient with nonseptic bursitis had bone marrow edema, and clinical follow-up suggested a reactive cause due to repetitive traumatization. Bone marrow edema in patients with septic olecranon bursitis may therefore not be specific for the presence of concomitant osteomyelitis.
Some limitations apply to our study: We selected our patient group by a systematic review of MRI reports identified with the index term "olecranon bursitis," so a comparatively high number of patients may have been included who had relatively minor reaction and swelling of the olecranon bursa due to another abnormality of the elbow. Also, none of our patients had bursitis related to a rheumatoid disease such as rheumatoid arthritis or gout that might result in extensive swelling and inflammatory reaction. This finding may have led to an underestimation of signal alterations of noninfected olecranon bursitis.
We conclude that septic and nonseptic olecranon bursitis present with a considerable overlap of MRI findings: Bursa septation, definition of bursa margins, amount of elbow effusion, and presence of triceps edema were nearly equally distributed. MRI signal alterations that were more frequent or more severe in the septic group include marked lobulation, marked complexity of bursal fluid, marked soft-tissue edema, and thickening of the triceps tendon. Potential indications for MRI evaluation of patients with olecranon bursitis are the exclusion of concomitant osteomyelitis or abscess formation. The presence of bone marrow signal changes in the olecranon is, however, not specific for osteomyelitis. Bursal aspiration still remains the gold standard to differentiate septic and aseptic olecranon bursitis. Contrast-enhanced images allow exclusion of infection in one fourth of patients who have aseptic bursitis, because of the lack of bursa and soft-tissue enhancement.
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