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Clinical Observations |
Department of Radiology, University of Wisconsin Hospital, Clinical Science Center, E3/311, 600 Highland Ave., Madison, WI 53792-3252.
Received October 7, 2004;
accepted after revision December 6, 2004.
Address correspondence to R. Kijowski
(rkijowski{at}mail.radiology.wisc.edu).
Abstract
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CONCLUSION. The MRI findings of unstable and stable osteochondritis dissecans of the capitellum are similar to the findings described for osteochondritis dissecans of the femoral condyles and talar dome. Unstable osteochondritis dissecans lesions are surrounded by a rim of high signal intensity or a fluid-filled cyst on T2-weighted images. Stable osteochondritis dissecans lesions show no surrounding signal abnormality on T2-weighted images.
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MRI is useful in evaluating patients with osteochondritis dissecans of the capitellum. MRI can detect the presence of osteochondritis dissecans in the early stages of the disease process when radiographs are normal or show only subtle changes in the appearance of the capitellum [8, 9]. MRI may also provide useful information about the size, location, and stability of the osteochondritis dissecans lesion. These factors are all important when determining the best treatment option in patients with osteochondritis dissecans of the capitellum [10-13].
The ability of MRI to evaluate patients with osteochondritis dissecans of the femoral condyles and talar dome has been well documented in the radiology literature [14-16]. However, there have been only four previous studies to date describing the MRI findings of patients with osteochondritis dissecans of the capitellum, and only a few published cases have had surgical correlation [8, 9, 17, 18]. This study was performed to describe the MRI findings of patients with osteochondritis dissecans of the capitellum and to correlate these MRI findings with surgical findings of stability and instability.
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There were eight male patients and two female patients in the study group. Patients' age ranged from 13 to 27 years (mean age, 18 years). Four patients were baseball pitchers, one patient was a soft-ball player, and two had a history of acute elbow trauma. Three patients had no history of elbow trauma and were not involved in organized sports activities. All patients presented to their physician with complaints of lateral elbow pain that was exacerbated by use of the elbow.
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All 10 patients had surgery performed on their symptomatic elbow by an experienced orthopedic surgeon specializing in sports medicine. The surgical procedures were performed at an average of 45 days after the MRI examination. The indications for elbow surgery were persistent pain and an inability to perform recreational or occupational activities in three patients and persistent mechanical symptoms in seven patients. All capitellar osteochondritis dissecans lesions were assessed for stability at the time of surgery. An osteochondritis dissecans lesion was considered to be unstable if the articular cartilage overlying the lesion was disrupted. An osteochondritis dissecans lesion was also considered to be unstable if the articular cartilage overlying the lesion was intact but was soft and compressible when direct pressure was applied during surgical probing of the capitellar articular surface. The same surgical criteria for stability of an osteochondritis dissecans lesion were used in previous studies on osteochondritis dissecans of the femoral condyles and talar dome [14-16].
The MRI examinations of all 10 patients were retrospectively reviewed in consensus by two fellowship-trained musculoskeletal radiologists to determine the T1 and T2 signal characteristics of the capitellar osteochondritis dissecans lesions. Signal intensity was defined as being low on T1-weighted images if it was the same intensity as cortical bone, intermediate if it was the same intensity as muscle, and high if it was the same intensity as adipose tissue. Signal intensity was defined as low on T2-weighted images if it was the same intensity as cortical bone, intermediate if it was the same intensity as muscle, and high if it was the same intensity as fluid. The thin articular cartilage of the capitellum was poorly visualized using the pulse sequences and imaging parameters chosen for the MRI examinations. For this reason, the integrity of the articular cartilage overlying the capitellar osteochondritis dissecans lesions was not assessed. The surgical reports of all 10 patients were reviewed to determine whether the capitellar osteochondritis dissecans lesions were found to be stable or unstable at surgery.
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On T2-weighted images, the central signal intensity of the osteochondritis dissecans lesions was also variable with low, intermediate, or heterogeneous low and high signal intensity in both stable and unstable lesions (Figs. 1C, 2C, 3C, and 3D). However, the stable and unstable osteochondritis dissecans lesions had different appearances in the periphery of the lesions on T2-weighted images. Three unstable osteochondritis dissecans lesions had a peripheral ring of high signal intensity and one unstable osteochondritis dissecans lesion had an underlying cyst (Figs. 1C and 2C). In contrast, the six stable osteochondritis dissecans lesions had low signal intensity peripherally (Figs. 3C and 3D). In fact, due to suppression of the signal intensity of the marrow, it was often difficult to visualize the osteochondritis dissecans lesions on T2-weighted images (Figs. 3C and 3D).
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Our study has shown that MRI can be used in patients with osteochondritis dissecans of the capitellum to determine the stability of the osteochondritis dissecans lesion. The MRI findings of unstable and stable osteochondritis dissecans of the capitellum are similar to the MRI findings described for osteochondritis dissecans of the femoral condyles and talar dome. The four findings of an unstable osteochondritis dissecans lesion of the femoral condyles and talar dome have been described on T2-weighted MR images as a thin line of high signal intensity at the interface between the osteochondritis dissecans lesion and the underlying bone, a discrete round area of high-signal-intensity beneath the osteochondritis dissecans lesion indicating a cyst, a high-signal-intensity line traversing the articular cartilage and subchondral bone plate into the osteochondritis dissecans lesion, and a focal defect in the articular surface of the osteochondritis dissecans lesion [14-16]. We noted the first two findings in our four patients with unstable capitellar osteochondritis dissecans lesions. We did not identify these findings in our six patients with stable capitellar osteochondritis dissecans lesions.
In one previous study, the most common MRI finding noted in 36 patients with unstable osteochondritis dissecans of the femoral condyles or talar dome was a peripheral high-signal-intensity line on T2-weighted images that was seen in 72% of the patients [15]. In our study, the most common finding noted in patients with unstable osteochondritis dissecans of the capitellum was also a peripheral high-signal-intensity line seen in three of four patients with unstable osteochondritis dissecans lesions. The only peripheral abnormality on T2-weighted imaging in one patient with an unstable capitellar osteochondritis dissecans lesion was an underlying cyst.
All of our patients with osteochondritis dissecans of the capitellum showed a focal area of signal abnormality on MRI within the anterolateral aspect of the capitellum. When evaluating the elbow on MRI, it is important not to mistake the normal pseudodefect of the capitellum for an osteochondritis dissecans lesion. The pseudodefect of the capitellum is caused by the abrupt transition between the smooth articular surface of the posterior-inferior aspect of the capitellum and the rough nonarticular surface of the adjacent lateral epicondyle [25]. This pseudodefect should be recognized as a normal anatomic variant and should not be confused with an osteochondritis dissecans lesion located more anteriorly within the capitellum.
There are few previous studies describing MRI findings in patients with osteochondritis dissecans of the capitellum. Takahara et al. [8] described the MRI findings in three young baseball pitchers with early capitellar osteochondritis dissecans. The osteochondritis dissecans lesions were of uniform low signal intensity on T1-weighted images but appeared normal on T2*-weighted gradient-echo images. These osteochondritis dissecans lesions, which eventually healed, were interpreted as stable on the basis of their MRI characteristics. However, surgical correlation was not available in any of the patients.
In another study, Bowen et al. [17] described two distinct MR signal intensity patterns in eight patients with osteochondritis dissecans of the capitellum. None of the eight patients had surgical correlation. The type 1 pattern consisted of a focal area of intermediate intensity signal surrounded by a low-signal-intensity ring on T1-weighted images. The peripheral portion of the low-signal-intensity ring became high signal intensity on T2-weighted images. The type 2 pattern consisted of a focal area of homogeneous low signal intensity on T1-weighted images and homogeneously high signal intensity on T2-weighted images. Three of the four patients in our study with surgically proven unstable osteochondritis dissecans of the capitellum showed the type 1 MRI signal intensity pattern described by Bowen et al. In the same study, Bowen et al. described the MRI findings in three patients with capitellar osteochondritis dissecans who did have surgical correlation. MRI depicted intraarticular loose bodies in all three patients. The MRI appearance of the remaining capitellar crater in these patients showed a segmental low-signal-intensity pattern on both T1- and T2-weighted images [17].
Janarv et al. [9] used MRI to preoperatively evaluate 13 patients with surgically confirmed osteochondritis dissecans of the capitellum. The authors described the size and location of the osteochondritis dissecans lesions on the MRI examinations. However, they did not describe the MRI signal characteristics of the osteochondritis dissecans lesions and did not correlate the MRI findings with surgical findings of stability and instability.
Murphy [18] described the MRI findings of three patients with surgically confirmed displaced transchondral fractures of the capitellum associated with intraarticular loose bodies. All three patients had focal areas of low signal intensity extending into the subchondral bone marrow of the capitellum on T1-weighted images. In two patients, high-signal-intensity fluid was visualized within an osseous defect in the capitellum on T2-weighted images. It is unclear whether the patients described by Murphy were adolescents or young adults with displaced, unstable osteochondritis dissecans lesions or older individuals with osteochondral fractures after acute elbow trauma. However, this study did not describe the MRI findings in patients with stable osteochondritis dissecans lesions or in patients with unstable, nondisplaced osteochondritis dissecans lesions.
In our six patients with stable osteochondritis dissecans of the capitellum, the osteochondritis dissecans lesions were best visualized on T1-weighted images. In fact, it was often difficult to visualize these osteochondritis dissecans lesions on T2-weighted images. All stable osteochondritis dissecans lesions had peripheral low signal intensity on T2-weighted images that blended in with the low signal intensity of the normal adjacent bone marrow of the capitellum. It is important to identify a stable osteochondritis dissecans lesion of the capitellum on T1-weighted images. Although stable osteochondritis dissecans lesions are firmly attached at their interface with the cancellous bone, overlying chondromalacia is often present that can delaminate and produce loose bodies. When a stable osteochondritis dissecans lesion of the capitellum is identified on an MRI examination, the elbow joint should be carefully inspected for the presence of an associated intraarticular loose body. All six of our patients with stable osteochondritis dissecans lesions were found to have intraarticular loose bodies at surgery.
The main limitation of our study was the small number of patients in the study group. However, a small study population is not unexpected, as osteochondritis dissecans of the capitellum is an uncommon abnormality. Fewer than 5% of cases of osteochondritis dissecans involve the capitellum [26, 27]. The small number of previously published studies describing the MRI findings in patients with capitellar osteochondritis dissecans is further evidence of the low prevalence of the condition in the general population. In addition, despite a large sports medicine practice at our institution with referrals from three sports medicine orthopedic surgeons, two pediatric orthopedic surgeons, two pediatric sports medicine specialists, and two general sports medicine specialists, we identified only 10 patients over an 8-year period with osteochondritis dissecans of the capitellum who had MRI of the elbow and subsequent elbow surgery. It is possible that additional patients at our institution with capitellar osteochondritis dissecans had elbow surgery without a prior MRI examination. However, for the past 14 years, MRI has been routinely performed at our institution on all patients with osteochondritis dissecans of the femoral condyles and talar dome. It is also possible that additional patients with capitellar osteochondritis dissecans at our institution had MRI of the elbow and subsequent elbow surgery but were incorrectly diagnosed preoperatively or were not registered in our MRI database.
A second limitation of our study is that all of our patients with stable osteochondritis dissecans of the capitellum had surgery to remove intraarticular loose bodies from the elbow joint. It is uncertain whether the MRI findings of patients with stable osteochondritis dissecans lesions and no associated intraarticular loose bodies are identical to the MRI findings noted in our patients with stable osteochondritis dissecans lesions. Surgical correlation in patients with stable osteochondritis dissecans of the capitellum and no associated intraarticular loose bodies would be difficult to make because most of these individuals are treated with conservative therapy.
A final limitation of our study is the small number of patients with unstable osteochondritis dissecans of the capitellum. It is quite possible that not every unstable capitellar osteochondritis dissecans lesion has the MRI findings described in our study. However, our results are similar to those from larger previously published studies of patients with osteochondritis dissecans of the femoral condyles and talar dome. This suggests that the previously described MRI findings of instability for osteochondritis dissecans lesions of the femoral condyles and talar dome also apply to osteochondritis dissecans lesions of the capitellum.
In summary, our study has shown that the MRI findings of unstable and stable osteochondritis dissecans of the capitellum are similar to the findings described for osteochondritis dissecans of the femoral condyles and talar dome. Unstable osteochondritis dissecans lesions have a peripheral rim of high signal intensity or an underlying fluid filled cyst on T2-weighted images. Stable osteochondritis dissecans lesions show no peripheral signal abnormality on T2-weighted images.
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