Abstract
Background:
Magnetic resonance imaging (MRI) is considered to be the gold standard for imaging of osteochondritis dissecans (OCD).
Purpose/Hypothesis:
The purpose was to determine the additional value of a preoperative computed tomography (CT) scan in adolescent patients with capitellar OCD of the elbow. Consistent with the fact that OCD is a lesion involving the subchondral bone, the hypothesis was that CT would be superior to MRI for imaging OCD of the capitellum.
Study Design:
Cohort study (diagnosis); Level of evidence, 3.
Methods:
All patients being treated surgically for an OCD of the capitellum between 2006 and 2016 at one institution were reviewed for preoperative imaging. A total of 28 patients met the inclusion criteria. Corresponding MRI and CT scans were compared retrospectively. Multiple parameters were recorded, with special emphasis on OCD lesion size, fragmentation, and tilt as well as joint surface integrity, loose bodies, and osteophytes.
Results:
The OCD lesions were best seen on CT scans, whereas MRI T1-weighted images overestimated and T2-weighted images underestimated the size of defects. A subchondral fracture nonunion was found on CT scans in 18 patients, whereas this was seen on MRI T1-weighted images in only 2 patients (P < .001) and MRI T2-weighted images in 4 patients (P < .001). Fragmentation of the OCD fragment was found on CT scans in 17 patients but on MRI scans in only 9 patients (P = .05). Osteophytes as a sign of secondary degenerative changes were seen on CT scans in 24 patients and were seen on MRI scans in 15 patients (P = .02). Altogether, only 51 of 89 secondary changes including loose bodies, effects on the radial head and ulnohumeral joint, and osteophytes that were seen on CT scans were also seen on MRI scans (P = .002).
Conclusion:
OCD fragmentation and secondary changes were more often diagnosed on CT. These factors indicate OCD instability or advanced OCD stages, which are indications for surgery. In an adolescent who is considered at risk for OCD (baseball, gymnastics, weightlifting, tennis) and who has lateral elbow joint pain with axial or valgus load bearing, CT is our imaging modality of choice for diagnosing and staging OCD of the capitellum.
The capitellum of the elbow is the second most common site for osteochondritis dissecans (OCD) after the knee.10,20 OCD is typically seen in adolescent gymnasts, weightlifters, and overhead athletes such as baseball and tennis players.6,20 Evidence shows that the OCD is a stress fracture in the subchondral bone that develops from repetitive microtrauma, although other etiological factors have been considered as well.6,8,10,19,29 Capitellar OCD usually goes undiagnosed for many months or even ≥1 year until the stress fracture has developed into an established nonunion, often with fragmentation and collapse of the subchondral bone fragment itself. One reason for delayed diagnoses is a low detection rate of capitellar OCD on plain radiographs of about 50%. 18 Therefore, a high index of suspicion is necessary in an adolescent patient with elbow pain. 11
Currently, magnetic resonance imaging (MRI) is considered by most physicians to be the imaging modality of choice for diagnosis and especially evaluation of capitellar OCD.3,6,12,21,29 Computed tomography (CT) has not had an apparent, important role in the literature for diagnosing OCD.21,26 Although CT has not been compared with MRI for staging OCD,7,15,27 CT is useful for detection of OCD fragmentation, loose bodies, and sclerosis.21,25,26
Considering that OCD is mainly a pathological entity of bone, rather than cartilage, CT would logically provide better detailed images of the subchondral bone than would MRI. Also, the much finer resolution (0.6-mm CT cuts vs 3-mm MRI cuts) means that CT offers more precise assessment of minor structural changes in the subchondral bone. For these reasons, we started to use CT for diagnosing OCD of the capitellum. The aim of this study was to compare preoperative MRI and CT scans in patients with capitellar OCD for correlation with preoperative planning. The hypothesis was that CT would be superior to MRI for imaging OCD of the capitellum.
Methods
Patients
After approval was granted by our institutional review board (IRB No. 11-001458), the institutional documentation system was searched for “OCD” or “osteochondritis dissecans” and “elbow” for all surgeries between 2006 and 2016. Clinical charts of 85 patients treated surgically for OCD in 102 elbows were reviewed. Cases were excluded if imaging was incomplete (plain radiographs, CT, and MRI within 6 months before surgery), as were those with previous fractures of the elbow other than the OCD. In total, 73 cases were excluded for 1 or more of the following reasons: The time period was >6 months between radiography and surgery in 18 cases, between CT and surgery in 1 case, and between MRI and surgery in 5 cases. A preoperative MRI scan was missing in 37 cases and a preoperative radiograph in 4 cases. In 12 elbows the OCD was in the trochlea, 2 elbows had a previous fracture, 1 case was a revision case, and 2 elbows did not have an OCD lesion. Thus, 29 elbows in 28 patients met the inclusion criteria. The clinical notes of those patients were reviewed by 2 board-certified orthopaedic surgeons (J.A.M-L., S.A.M.) to determine affected side, preoperative range of motion, and predominant sports. All imaging modalities were evaluated by the same orthopaedic surgeons and additionally by 2 board-certified radiologists (E.E.S., M.S.C.). Unclear findings were discussed with the senior orthopaedic surgeon (S.W.O.) for consensus.
Radiographs
Preoperative anteroposterior (AP) and lateral radiographs were studied for status of capitellar growth plates, discontinuity of subchondral bone line, size of OCD, erosions, involvement of lateral capitellar ridge, radiolucency, sclerosis, fragmentation, tilt of OCD out of the joint line, loose bodies, and involvement of other parts than the capitellum, such as the radial head and the ulnohumeral joint.
MRI Scans
Preoperative MRI scans were evaluated for irregularity of the articular surface, cleavage of subchondral bone, size of OCD, capitellar erosion, involvement of the capitellar ridge, capitellar edema, fragmentation, tilt of OCD out of the joint line as sign of instability, loose bodies, and involvement of other parts than the capitellum, such as the radial head and the ulnohumeral joint. All available sequences in all 3 planes were reviewed.
CT Scans
The CT scans were assessed for status of the capitellar growth plate, irregularity of the articular surface (assessed by integrity and regularity/fracture of the subchondral bone line), size of OCD lesion, capitellar erosions, involvement of lateral capitellar ridge, OCD fracture line, fragmentation, tilting of the OCD fragment (with respect to the adjacent joint lines) as a sign of instability, loose bodies, and secondary or degenerative changes elsewhere in the joint including the ulnohumeral joint.
Increasing joint contracture may indicate an advanced stage of capitellar OCD. Therefore, MRI and CT findings were specifically compared with respect to preoperative contracture of less than and more than 30° and less than and more than 10°.
Statistical Analysis
Before reviewing the images, the authors clarified imaging criteria (eg, what is considered to be an osteophyte). A 91% interrater reliability was documented. Areas of disagreement were discussed with the senior author (S.W.O.D.) until 100% agreement was reached. Normal distribution of data was confirmed using the Shapiro-Wilk test. Statistical significance (P≤ .05) was determined by 1-way analysis of variance with the Tukey honestly significance difference post hoc test using SPSS statistical software (Version 22; IBM).
Results
Patients
A total of 29 elbows in 28 otherwise healthy patients were included in this study. One male patient had bilateral elbow involvement. The average age at surgery was 14 ± 2.7 years, and more patients were male (18 male vs 10 female). In 20 cases, the dominant elbow was affected (21 right vs 8 left elbows). The mean preoperative extension deficit was 9°± 16° (contralateral, –3°± 6°), and the mean preoperative flexion was 138°± 8° (contralateral, 146°± 5°). The mean preoperative pronation was 84°± 9° (contralateral, 87°± 6°), and the mean supination was 85°± 10° (contralateral, 89°± 5°). The studied population was very heterogeneous regarding the predominant sport potentially causing OCD (Table 1).
Primary Sport Potentially Causing Osteochondritis Dissecans
Imaging
The average time between imaging and surgery was 48 ± 41 days (range, 1-131 days) for radiographs, 48 ± 44 days (range, 1-167 days) for MRI, and 20 ± 29 days (range, 0-111 days) for CT. The capitellar growth plate was open in 10 cases and closed in 19 cases, which was assessed on radiographs and CT scans with no difference between the 2 modalities.
No major differences between MRI and CT were found with respect to loss of joint surface integrity, capitellar erosions, and OCD size. However, both modalities showed many more details than plain radiography (Figure 1, Table 2). Statistically, all 3 imaging modalities were comparable for detecting involvement of the lateral capitellar ridge, erosions of the radial head or the ulnohumeral joint, and number of capitellar osteophytes (Figure 2, Table 2).
Results for computed tomography (CT), magnetic resonance imaging (MRI), and radiography in capitellar osteochondritis dissecans (OCD) regarding loss of joint surface integrity, capitellar erosions, and OCD size. Results for CT and MRI were comparable with each other but significantly superior to results for radiographs. Statistical significance between groups is indicated with black bars. cor, coronal plane; sag, sagittal plane. (Reprinted with permission of the Mayo Foundation for Medical Education and Research.)
Overall Findings for OCD Lesion Appearance and Secondary Changes Depending on Imaging Modality a
Values are expressed as n unless otherwise noted. CT, computed tomography; MRI, magnetic resonance imaging; OCD, osteochondritis dissecans.
Statistical significance between radiography and MRI.
Statistical significance between radiography and CT.
Statistical significance between MRI and CT.
Results for computed tomography (CT), magnetic resonance imaging (MRI), and plain radiographs regarding involvement of the lateral capitellar ridge, erosions of the radial head and ulnohumeral joint, and number of capitellar osteophytes. Results for the imaging methods were statistically comparable. (Reprinted with permission of the Mayo Foundation for Medical Education and Research.)
CT scans detected subchondral fractures, fragmentation and/or tilting of the OCD fragment, loose bodies (including those in the ulnohumeral joint), and degenerative coronoid and olecranon osteophytes as well as osteophytes in the fossae (coronoid, radial and olecranon fossae) more often than did MRI and radiography (Figure 3, Table 2).
Detection rates of (A) primary and (B) secondary osteochondritis dissecans (OCD) changes. For both primary and secondary OCD changes, the detection rate for computed tomography (CT) was higher than detection rates for magnetic resonance imaging (MRI) and radiography. Statistical significance between groups is indicated with black bars. (Reprinted with permission of the Mayo Foundation for Medical Education and Research.).
Regarding secondary changes in the joint such as loose bodies, involvement of the radial head and the ulnohumeral joint, and osteophytes, 89 such changes were found in 27 patients on CT scans, 51 changes were found in 23 patients on MRI scans (P = .002), and 12 changes were found in 8 patients on plain radiographs only (P < .001) (Figure 4, Table 2).
Differences between imaging modalities in overall secondary changes due to osteochondritis dissecans (OCD) including loose bodies, changes on the radial head and the ulnohumeral joint, and osteophytes. The overall osteophytes are listed separately. Both categories are shown as number of patients with each condition. Statistical significance between groups is indicated with black bars. (Reprinted with permission of the Mayo Foundation for Medical Education and Research.) CT, computed tomography; MRI, magnetic resonance imaging.
CT and MRI findings were compared at early versus later stages of clinical disease progression, as indicated by elbow contracture. OCD fragmentation and tilt of the fragment out of the joint surface are considered unstable conditions, and the presence of either of these findings on preoperative imaging directly affected surgical decision making. Fragmentation was an indication for excision and debridement rather than internal fixation or retrograde drilling. Tilt of the fragment out of the joint surface was an indication for either excision and debridement or open reduction, bone grafting, and fixation rather than retrograde drilling. Absence of fragmentation or tilting was an indication for retrograde drilling, unless a lesion was found at the time of arthroscopy to be unstable. For this reason, fragmentation and tilt were analyzed in subgroups in the context of preoperative contractures of less than versus more than 10° and less than versus more than 30°. Interestingly, differences between imaging modalities were more significant for early stage OCD without relevant contracture (Figure 5; Table 2).
Differences in detection of (A) osteochondritis dissecans (OCD) fragmentation and (B) tilt of OCD fragment with different imaging modalities with respect to joint contracture of less than versus more than 10° and less than versus more than 30°. Statistical significance between groups is indicated with black bars. (Reprinted with permission of the Mayo Foundation for Medical Education and Research.) CT, computed tomography; MRI, magnetic resonance imaging.
Besides quantitative measurements, imaging was assessed qualitatively with special respect to the subchondral bone to determine whether there was a cleavage plane under the fragment indicating a nonunited shear fracture. When we studied the different modalities carefully, T1-weighted MRI and equivalent images appeared to overestimate the defects, whereas T2-weighted and equivalent images showed the defects more as edema thus underestimating the true defects. The actual condition of the subchondral bone was seen best on CT scans, with a clear cleavage plane between the OCD and the epiphyseal bone (Figure 6). This cleavage plane was found in 18 patients (62%) on CT scans but only in 2 patients (7%) on T1-weighted MRI scans (P < .001) and 4 patients (14%) on T2-weighted MRI scans (P < .001).
Corresponding sagittal images of the same patient. Images showed an edema-like appearance of osteochondritis dissecans on T2-weighted magnetic resonance imaging (MRI) and a large defect appearance on T1-weighted MRI. The computed tomography (CT) scan shows the cleavage plane with the actual bone status. (Reprinted with permission of the Mayo Foundation for Medical Education and Research.)
Discussion
To date, MRI is considered the gold standard for imaging OCD, especially in the early stage when radiographs are negative.3,6,11,12,21,29 Whereas OCD is most likely the result of a shear fracture in the subchondral bone,1,2,8-10,19 CT plays a minor role in the literature for diagnosis of OCD, although CT has been considered useful in advanced stages to detect fragmentation, loose bodies, and sclerosis.11,21,25 A higher overall detection rate for OCD of the capitellum has also recently been described for CT compared with MRI and radiography. 26 Additional information for exact localization is given by 3-dimensional CT imaging. 4 Recently, ultrasound has been used for early detection and screening of capitellar OCD in the form of loss of smooth articular surface.13,17,22,23 However, ultrasound is user-dependent and requires intensive training and experience.
The proposed cause of a shear-type fracture of the subchondral bone1,2,8-10,19 is supported by the current study. A cleavage plane as a result of a nonunited subchondral fracture was found on CT scans in 62% of patients, whereas this cleavage plane was found on MRI scans in only 14% of patients. Moreover, OCD fragmentation and tilt of subchondral bone out of the joint line were found more often on CT scans than on MRI scans. Importantly, these findings were more obvious before contracture of the affected elbows was present as a potential sign of an advanced OCD stage, indicating an early stage of unstable OCD in these cases. This fact contradicts previous studies considering MRI the preferred modality to detect early OCD and CT to detect advanced stages.11,21,25
Secondary changes in the joint such as loose bodies, involvement of the radial head and the ulnohumeral joint, and osteophytes are considered advanced stages of disease and are treated surgically to avoid further damage to the joint. Significantly, most such secondary changes were found on CT scans. MRI detected only 57% of overall secondary changes and 48% of osteophytes seen on CT. Thus, the OCD stage is likely to be more advanced than apparent on MRI.
A number of differences between CT and MRI were not statistically significant in this study, which may be due to the small number of patients. For example, only 57% of loose bodies in the ulnohumeral joint seen on CT were detected with MRI and only 66% of OCD fragments that were tilted out of the joint line on CT were detected on MRI. van Bergen et al 24 reported a higher sensitivity for CT than for MRI regarding OCD (100% vs 96%) and loose body detection (90% vs 65%) compared with intraoperative findings.
The higher detection rate for CT comes at the cost of a higher radiation exposure, about 0.21 mSv (CT with the arm above the head), 14 compared with 0.01 mSv for plain radiography of the elbow 28 and no radiation exposure for MRI. The radiation dose of an elbow CT is about 7% of the average background radiation exposure for an individual (3 mSv/y) and about 10 times more than one experiences during a 7-hour flight on an airplane (0.02 mSv).5,16,28 We believe that the advantages of CT in capitellar OCD justify the moderate radiation exposure with regard to the young age of the study population. Furthermore, the additional information obtained from CT plays an important role in surgical planning and preparation.
There are several limitations of this study. Unfortunately, no specific notes were made regarding whether the final decisions for surgery were based on one or the other imaging modality, which is a limitation of this study. However, in those patients referred for evaluation who had already obtained an MRI scan, a CT scan was also ordered if the information was not sufficient for a final treatment decision. This assumption is supported by the mean time period between each imaging modality and the time of surgery. Radiography and MRI were performed on average 48 days preoperatively, whereas CT was performed on average 20 days before surgery.
Another limitation of this study is its retrospective nature, whereby 67% of capitellar OCD cases had to be excluded due to incomplete preoperative imaging. Moreover, intraoperative findings were not documented in a standardized manner. Therefore, correlating the preoperative imaging with operative findings was not routinely possible. Interestingly, all 5 patients treated by retrograde drilling had fragmentation of the lesion apparent on CT but not on MRI, which showed only edema in the defect. Another interesting finding was that of the 20 cases of OCD that were debrided, 20% did not show OCD fragmentation or tilt on MRI, whereas CT showed either OCD fragmentation or tilt. This was important because it demonstrated instability of the lesion. In 3 patients, the only treatment needed was loose body removal. The loose bodies were seen preoperatively on CT scans in all 3 patients but on MRI scans in only 2 of the 3 patients.
In conclusion, this study showed that CT was superior to MRI for imaging of capitellar OCD because the results of CT directly affected surgical decision making in several ways that would not have happened if we had only radiographs and MRI scans. However, MRI did not directly change surgical decision making over what information was derived via CT. In an adolescent who is considered at risk for OCD (such as athletes involved in baseball, gymnastics, weightlifting, or tennis) and who has lateral elbow joint pain with axial or valgus load bearing, CT is our imaging modality of choice for diagnosing and staging OCD of the capitellum.
Footnotes
Acknowledgements
The authors gratefully acknowledge the editorial assistance of James S. Fitzsimmons, Grace K. Chaney, and Colin M. O’Driscoll.
Submitted July 30, 2021; accepted August 16, 2022.
One or more of the authors has declared the following potential conflict of interest or source of funding: This study was funded by the Mayo Foundation for Medical Education and Research. SOD has received royalties from Acumed LLC, Wright Medical, DJO (Aircast), and Stryker Corp and speaking honorarium from SIGN Fracture Conference. E.E.S. has received hospitality payments from Siemens Medical Solutions. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.