(Radiology. 2000;216:207-212.)
© RSNA, 2000
Natural Progression of Osteochondritis Dissecans of the Humeral Capitellum: Initial Observations1
Masatoshi Takahara, MD,
Toshihiko Ogino, MD,
Michiaki Takagi, MD,
Hiroyuki Tsuchida, MD,
Hiroshi Orui, MD and
Toshikazu Nambu, MD
1 From the Department of Orthopedic Surgery, Yamagata University School of Medicine, Iida-Nishi 2-2-2, Yamagata, Japan (M. Takahara, T.O., M. Takagi, H.T., H.O.), and the Department of Radiology, Hokkaido University School of Medicine, Sapporo, Japan (T.N.). Received March 31, 1999; revision requested May 10; final revision received September 27; accepted October 20. Address correspondence to M. Takahara (e-mail: mtakahar@med.id.yamagata-u.ac.jp).
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ABSTRACT
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PURPOSE: To determine the earliest findings, subsequent changes, and natural course of osteochondritis dissecans of the humeral capitellum.
MATERIALS AND METHODS: Among 95 patients with osteochondritis dissecans of the humeral capitellum, 16 (mean age, 12.5 years) were selected for this retrospective study because they seemed to have early osteochondritis dissecans and had been followed up without any surgical treatment for 6 months or more (mean, 3.5 years).
RESULTS: The initial imaging appearances of the 16 patients' lesions were divided into two types: localized subchondral bone flattening without fragments in seven, and nondisplaced fragments in nine. Patients with lesion flattening had younger ages and significantly shorter durations of symptoms, and most had open growth plates. In five of the seven with flattening, new bone formed over the flattened bone, and the fragments united after arm motion reduction. In contrast, patients with nondisplaced fragments at clinical presentation had longer durations of symptoms with continued arm motion, and their nondisplaced fragments failed to unite.
CONCLUSION: The earliest feature of osteochondritis dissecans is subchondral bone flattening, over which new bone subsequently forms. The new bone then can unite with the underlying bone. However, if subjected to repetitive forces over a given time, unstable fragments develop. These fragments, even if not yet displaced, are unable to unite.
Index terms: Athletic injuries, 422.442 • Elbow, injuries, 422.442 • Elbow, MR, 422.121411, 422.121412 • Joints, injuries, 422.442 • Joints, US, 422.12981 • Osteochondritis dissecans, 422.442 • Radiography, 422.11
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INTRODUCTION
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Recently, magnetic resonance (MR) imaging has been established as the most sensitive and reliable means for assessment of osteochondritis dissecans (1–10). MR images show that most osteochondritis dissecans lesions are unstable and reveal features such as a high-signal-intensity interface between the fragments and their beds, a high-signal-intensity line through the articular cartilage, and a focal articular defect (1–10). In contrast, a few recent reports have described stable osteochondritis dissecans lesions in which no MR imaging signs of instability are detected, although changes such as localized subchondral bone flattening on radiographs and low signal intensity on T1-weighted images are evident (6,10).
Many authors have advocated that repetitive forces applied to the capitellum during throwing are the main cause of osteochondritis dissecans in athletes who throw and make the lesions unstable (10–13). However, to our knowledge the early pathologic conditions of osteochondritis dissecans have not been determined (14–20), and the natural course of osteochondritis dissecans remains unclear. The purpose of this study was to determine the earliest findings and subsequent changes in capitellar osteochondritis dissecans and to demonstrate its natural course.
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MATERIALS AND METHODS
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Ninety-five patients were diagnosed as having osteochondritis dissecans of the capitellum at our institutions between 1977 and 1994. Radiographs were available in all patients. The appearance of the capitellar osteochondritis dissecans was assessed retrospectively by one observer (M. Takahara) and was classified at radiography (21). In brief, lesions having localized subchondral bone flattening (Fig 1a) or nondisplaced fragments (Fig 1b) were assessed as early, and lesions having displaced fragments (Fig 1c) or loose fragments in the joint (Fig 1d) were assessed as advanced. Advanced osteochondritis dissecans is unstable, whereas early osteochondritis dissecans can involve stable and unstable lesions.
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Figure 1a. Initial radiographic appearances of osteochondritis dissecans of the capitellum. These images were obtained in different patients. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening without fragments (arrows). (b) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows nondisplaced bone fragments (arrowheads). (c) Anteroposterior radiograph shows a displaced fragment (arrow). (d) Anteroposterior radiograph shows a loose fragment (arrowheads) and a bone defect (arrow).
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Figure 1b. Initial radiographic appearances of osteochondritis dissecans of the capitellum. These images were obtained in different patients. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening without fragments (arrows). (b) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows nondisplaced bone fragments (arrowheads). (c) Anteroposterior radiograph shows a displaced fragment (arrow). (d) Anteroposterior radiograph shows a loose fragment (arrowheads) and a bone defect (arrow).
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Figure 1c. Initial radiographic appearances of osteochondritis dissecans of the capitellum. These images were obtained in different patients. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening without fragments (arrows). (b) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows nondisplaced bone fragments (arrowheads). (c) Anteroposterior radiograph shows a displaced fragment (arrow). (d) Anteroposterior radiograph shows a loose fragment (arrowheads) and a bone defect (arrow).
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Figure 1d. Initial radiographic appearances of osteochondritis dissecans of the capitellum. These images were obtained in different patients. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening without fragments (arrows). (b) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows nondisplaced bone fragments (arrowheads). (c) Anteroposterior radiograph shows a displaced fragment (arrow). (d) Anteroposterior radiograph shows a loose fragment (arrowheads) and a bone defect (arrow).
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The 95 patients with osteochondritis dissecans lesions were divided into 26 with early lesions and 69 with advanced lesions. Of the 26 patients with seemingly early lesions, four were treated surgically because of elbow pain or locking. The remaining 22 patients were treated nonsurgically. These patients were advised against heavy use of the elbow such as throwing, arm wrestling, and weight bearing for at least 6 months. Although six of the 22 (27%) were lost to the study, 16 (73%) had 6 months or more of follow-up and were selected as study subjects.
All 16 patients were boys and had played on baseball teams. The mean age of the patients was 12.5 years (age range, 11–16 years) at initial examination. The mean duration of symptoms at initial examination was 1.4 years (range, 0.1–4.0 years). Within 2 weeks after initial examination, 15 of the 16 patients underwent radiography, the recent-most six underwent ultrasonography (US), and the recent-most three underwent MR imaging. In one patient, because of personal circumstances, initial radiographs were obtained 4 months after US and MR images. Informed consent was obtained after the natures of the procedures were explained, and the Declaration of Helsinki principles were observed.
US images were obtained by using a real-time scanner (SSD-650; Aloka, Tokyo, Japan) equipped with a 7.5-MHz transducer. US showed cartilaginous changes in addition to bone changes. The US appearances of the lesions were divided by one observer (M. Takahara) into four types: Type I lesions had localized subchondral bone flattening and cartilaginous thickening (Fig 2a), type II lesions had nondisplaced fragments and an intact articular surface (Fig 2b), type III lesions had displaced fragments, and type IV lesions had osteochondral defects (22). The US assessment was compared with the radiographic assessment.
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Figure 2a. Healing of the osteochondritis dissecans lesion. (a) Posterior longitudinal US image obtained at initial examination shows localized subchondral bone flattening (arrows), whereas the normal capitellum has a rounded contour. The overlying cartilage is thick (arrowheads). (b) Posterior longitudinal US image obtained 4 months after initial examination shows newly formed bone (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (c) Posterior longitudinal US image obtained 8 months after initial examination shows the newly formed bone united with the surrounding bone. In a-c, c = capitellum, r = radial head.
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Figure 2b. Healing of the osteochondritis dissecans lesion. (a) Posterior longitudinal US image obtained at initial examination shows localized subchondral bone flattening (arrows), whereas the normal capitellum has a rounded contour. The overlying cartilage is thick (arrowheads). (b) Posterior longitudinal US image obtained 4 months after initial examination shows newly formed bone (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (c) Posterior longitudinal US image obtained 8 months after initial examination shows the newly formed bone united with the surrounding bone. In a-c, c = capitellum, r = radial head.
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Figure 2c. Healing of the osteochondritis dissecans lesion. (a) Posterior longitudinal US image obtained at initial examination shows localized subchondral bone flattening (arrows), whereas the normal capitellum has a rounded contour. The overlying cartilage is thick (arrowheads). (b) Posterior longitudinal US image obtained 4 months after initial examination shows newly formed bone (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (c) Posterior longitudinal US image obtained 8 months after initial examination shows the newly formed bone united with the surrounding bone. In a-c, c = capitellum, r = radial head.
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MR images were obtained by using a 1.5-T magnet (Magnetom H15; Siemens Medical Systems, Erlangen, Germany). T1-weighted, spin-echo images (520/15-19 [repetition time msec/echo time msec]) and T2*-weighted, gradient-echo images (320/10, 10° flip angle) were obtained. MR images were assessed according to evidence of lesion instability (6,7). When T2*-weighted MR images showed a high-signal-intensity interface beneath the lesion, a high-signal-intensity line through the articular cartilage, or a focal articular defect, the lesion was assessed as unstable. However, a lesion was assessed as stable when the T2*-weighted images showed no MR imaging evidence of instability even though the T1-weighted images showed a low-signal-intensity area (Figs 3c, 4a). The MR imaging assessment of lesion stability was compared with the radiographic and US assessments by one observer (M. Takahara).
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Figure 3a. Stable capitellar osteochondritis dissecans and its healing process. (a-c) Images were obtained at initial examination. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening (arrows). There is a very small, faint bone fragment over the lateral part of the flattening, which suggests the start of new bone formation. The lesion is intermediate between flattening and fragments and was classified as flattening in this research study. (b) Anteroposterior longitudinal US image shows subchondral flattening (arrows) and overlying cartilaginous thickening, with an intact surface outline (arrowheads). c = capitellum, r = radial head. (c) Coronal, T1-weighted, spin-echo image (520/15) shows a focal, low-signal-intensity area (arrowheads) in the capitellum, although the sagittal T2*-weighted, gradient-echo image (not shown) showed no instability. (d-g) Healing of the osteochondritis dissecans lesion. (d) Anteroposterior radiograph obtained with the elbow at 45° of flexion 1 month after initial examination shows new bone formation (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (e) Anteroposterior radiograph obtained with the elbow at 45° of flexion 4 months after initial examination shows the union of the newly formed bone (arrows) and a decrease in the subchondral bone (arrowhead) of the central capitellum. (f) Anteroposterior radiograph obtained with the elbow at 45° of flexion 13 months after initial examination shows the newly formed bone (arrowhead) with an appearance similar to that of a nondisplaced fragment. (g) Anteroposterior radiograph obtained with the elbow at 45° of flexion 3 years 6 months after initial examination shows the union of the newly formed bone with the underlying capitellar bone and shows a normal capitellar appearance.
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Figure 3b. Stable capitellar osteochondritis dissecans and its healing process. (a-c) Images were obtained at initial examination. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening (arrows). There is a very small, faint bone fragment over the lateral part of the flattening, which suggests the start of new bone formation. The lesion is intermediate between flattening and fragments and was classified as flattening in this research study. (b) Anteroposterior longitudinal US image shows subchondral flattening (arrows) and overlying cartilaginous thickening, with an intact surface outline (arrowheads). c = capitellum, r = radial head. (c) Coronal, T1-weighted, spin-echo image (520/15) shows a focal, low-signal-intensity area (arrowheads) in the capitellum, although the sagittal T2*-weighted, gradient-echo image (not shown) showed no instability. (d-g) Healing of the osteochondritis dissecans lesion. (d) Anteroposterior radiograph obtained with the elbow at 45° of flexion 1 month after initial examination shows new bone formation (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (e) Anteroposterior radiograph obtained with the elbow at 45° of flexion 4 months after initial examination shows the union of the newly formed bone (arrows) and a decrease in the subchondral bone (arrowhead) of the central capitellum. (f) Anteroposterior radiograph obtained with the elbow at 45° of flexion 13 months after initial examination shows the newly formed bone (arrowhead) with an appearance similar to that of a nondisplaced fragment. (g) Anteroposterior radiograph obtained with the elbow at 45° of flexion 3 years 6 months after initial examination shows the union of the newly formed bone with the underlying capitellar bone and shows a normal capitellar appearance.
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Figure 3c. Stable capitellar osteochondritis dissecans and its healing process. (a-c) Images were obtained at initial examination. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening (arrows). There is a very small, faint bone fragment over the lateral part of the flattening, which suggests the start of new bone formation. The lesion is intermediate between flattening and fragments and was classified as flattening in this research study. (b) Anteroposterior longitudinal US image shows subchondral flattening (arrows) and overlying cartilaginous thickening, with an intact surface outline (arrowheads). c = capitellum, r = radial head. (c) Coronal, T1-weighted, spin-echo image (520/15) shows a focal, low-signal-intensity area (arrowheads) in the capitellum, although the sagittal T2*-weighted, gradient-echo image (not shown) showed no instability. (d-g) Healing of the osteochondritis dissecans lesion. (d) Anteroposterior radiograph obtained with the elbow at 45° of flexion 1 month after initial examination shows new bone formation (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (e) Anteroposterior radiograph obtained with the elbow at 45° of flexion 4 months after initial examination shows the union of the newly formed bone (arrows) and a decrease in the subchondral bone (arrowhead) of the central capitellum. (f) Anteroposterior radiograph obtained with the elbow at 45° of flexion 13 months after initial examination shows the newly formed bone (arrowhead) with an appearance similar to that of a nondisplaced fragment. (g) Anteroposterior radiograph obtained with the elbow at 45° of flexion 3 years 6 months after initial examination shows the union of the newly formed bone with the underlying capitellar bone and shows a normal capitellar appearance.
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Figure 3d. Stable capitellar osteochondritis dissecans and its healing process. (a-c) Images were obtained at initial examination. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening (arrows). There is a very small, faint bone fragment over the lateral part of the flattening, which suggests the start of new bone formation. The lesion is intermediate between flattening and fragments and was classified as flattening in this research study. (b) Anteroposterior longitudinal US image shows subchondral flattening (arrows) and overlying cartilaginous thickening, with an intact surface outline (arrowheads). c = capitellum, r = radial head. (c) Coronal, T1-weighted, spin-echo image (520/15) shows a focal, low-signal-intensity area (arrowheads) in the capitellum, although the sagittal T2*-weighted, gradient-echo image (not shown) showed no instability. (d-g) Healing of the osteochondritis dissecans lesion. (d) Anteroposterior radiograph obtained with the elbow at 45° of flexion 1 month after initial examination shows new bone formation (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (e) Anteroposterior radiograph obtained with the elbow at 45° of flexion 4 months after initial examination shows the union of the newly formed bone (arrows) and a decrease in the subchondral bone (arrowhead) of the central capitellum. (f) Anteroposterior radiograph obtained with the elbow at 45° of flexion 13 months after initial examination shows the newly formed bone (arrowhead) with an appearance similar to that of a nondisplaced fragment. (g) Anteroposterior radiograph obtained with the elbow at 45° of flexion 3 years 6 months after initial examination shows the union of the newly formed bone with the underlying capitellar bone and shows a normal capitellar appearance.
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Figure 3e. Stable capitellar osteochondritis dissecans and its healing process. (a-c) Images were obtained at initial examination. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening (arrows). There is a very small, faint bone fragment over the lateral part of the flattening, which suggests the start of new bone formation. The lesion is intermediate between flattening and fragments and was classified as flattening in this research study. (b) Anteroposterior longitudinal US image shows subchondral flattening (arrows) and overlying cartilaginous thickening, with an intact surface outline (arrowheads). c = capitellum, r = radial head. (c) Coronal, T1-weighted, spin-echo image (520/15) shows a focal, low-signal-intensity area (arrowheads) in the capitellum, although the sagittal T2*-weighted, gradient-echo image (not shown) showed no instability. (d-g) Healing of the osteochondritis dissecans lesion. (d) Anteroposterior radiograph obtained with the elbow at 45° of flexion 1 month after initial examination shows new bone formation (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (e) Anteroposterior radiograph obtained with the elbow at 45° of flexion 4 months after initial examination shows the union of the newly formed bone (arrows) and a decrease in the subchondral bone (arrowhead) of the central capitellum. (f) Anteroposterior radiograph obtained with the elbow at 45° of flexion 13 months after initial examination shows the newly formed bone (arrowhead) with an appearance similar to that of a nondisplaced fragment. (g) Anteroposterior radiograph obtained with the elbow at 45° of flexion 3 years 6 months after initial examination shows the union of the newly formed bone with the underlying capitellar bone and shows a normal capitellar appearance.
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Figure 3f. Stable capitellar osteochondritis dissecans and its healing process. (a-c) Images were obtained at initial examination. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening (arrows). There is a very small, faint bone fragment over the lateral part of the flattening, which suggests the start of new bone formation. The lesion is intermediate between flattening and fragments and was classified as flattening in this research study. (b) Anteroposterior longitudinal US image shows subchondral flattening (arrows) and overlying cartilaginous thickening, with an intact surface outline (arrowheads). c = capitellum, r = radial head. (c) Coronal, T1-weighted, spin-echo image (520/15) shows a focal, low-signal-intensity area (arrowheads) in the capitellum, although the sagittal T2*-weighted, gradient-echo image (not shown) showed no instability. (d-g) Healing of the osteochondritis dissecans lesion. (d) Anteroposterior radiograph obtained with the elbow at 45° of flexion 1 month after initial examination shows new bone formation (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (e) Anteroposterior radiograph obtained with the elbow at 45° of flexion 4 months after initial examination shows the union of the newly formed bone (arrows) and a decrease in the subchondral bone (arrowhead) of the central capitellum. (f) Anteroposterior radiograph obtained with the elbow at 45° of flexion 13 months after initial examination shows the newly formed bone (arrowhead) with an appearance similar to that of a nondisplaced fragment. (g) Anteroposterior radiograph obtained with the elbow at 45° of flexion 3 years 6 months after initial examination shows the union of the newly formed bone with the underlying capitellar bone and shows a normal capitellar appearance.
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Figure 3g. Stable capitellar osteochondritis dissecans and its healing process. (a-c) Images were obtained at initial examination. (a) Anteroposterior radiograph obtained with the elbow at 45° of flexion shows localized subchondral bone flattening (arrows). There is a very small, faint bone fragment over the lateral part of the flattening, which suggests the start of new bone formation. The lesion is intermediate between flattening and fragments and was classified as flattening in this research study. (b) Anteroposterior longitudinal US image shows subchondral flattening (arrows) and overlying cartilaginous thickening, with an intact surface outline (arrowheads). c = capitellum, r = radial head. (c) Coronal, T1-weighted, spin-echo image (520/15) shows a focal, low-signal-intensity area (arrowheads) in the capitellum, although the sagittal T2*-weighted, gradient-echo image (not shown) showed no instability. (d-g) Healing of the osteochondritis dissecans lesion. (d) Anteroposterior radiograph obtained with the elbow at 45° of flexion 1 month after initial examination shows new bone formation (arrow) over the flattened bone, with an appearance similar to that of a nondisplaced fragment. (e) Anteroposterior radiograph obtained with the elbow at 45° of flexion 4 months after initial examination shows the union of the newly formed bone (arrows) and a decrease in the subchondral bone (arrowhead) of the central capitellum. (f) Anteroposterior radiograph obtained with the elbow at 45° of flexion 13 months after initial examination shows the newly formed bone (arrowhead) with an appearance similar to that of a nondisplaced fragment. (g) Anteroposterior radiograph obtained with the elbow at 45° of flexion 3 years 6 months after initial examination shows the union of the newly formed bone with the underlying capitellar bone and shows a normal capitellar appearance.
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Figure 4a. Failure of the stable osteochondritis dissecans lesion to heal. (a) Coronal, T1-weighted, spin-echo image (520/15) obtained at initial examination shows a focal, low-signal-intensity area (arrowheads) in the capitellum, but the sagittal, T2*-weighted, gradient-echo image (not shown) showed no instability. (b) Anteroposterior radiograph obtained 6 months after initial examination shows a nondisplaced fragment (arrow). The patient had continued baseball pitching, regardless of advice to stop. (c) Lateral radiograph obtained 4 years after initial examination shows loose fragments (arrows). (d) Sagittal T1-weighted, spin-echo MR image (520/15) obtained 4 years after initial examination shows an osteochondral defect (arrowheads) of the capitellum.
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Figure 4b. Failure of the stable osteochondritis dissecans lesion to heal. (a) Coronal, T1-weighted, spin-echo image (520/15) obtained at initial examination shows a focal, low-signal-intensity area (arrowheads) in the capitellum, but the sagittal, T2*-weighted, gradient-echo image (not shown) showed no instability. (b) Anteroposterior radiograph obtained 6 months after initial examination shows a nondisplaced fragment (arrow). The patient had continued baseball pitching, regardless of advice to stop. (c) Lateral radiograph obtained 4 years after initial examination shows loose fragments (arrows). (d) Sagittal T1-weighted, spin-echo MR image (520/15) obtained 4 years after initial examination shows an osteochondral defect (arrowheads) of the capitellum.
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Figure 4c. Failure of the stable osteochondritis dissecans lesion to heal. (a) Coronal, T1-weighted, spin-echo image (520/15) obtained at initial examination shows a focal, low-signal-intensity area (arrowheads) in the capitellum, but the sagittal, T2*-weighted, gradient-echo image (not shown) showed no instability. (b) Anteroposterior radiograph obtained 6 months after initial examination shows a nondisplaced fragment (arrow). The patient had continued baseball pitching, regardless of advice to stop. (c) Lateral radiograph obtained 4 years after initial examination shows loose fragments (arrows). (d) Sagittal T1-weighted, spin-echo MR image (520/15) obtained 4 years after initial examination shows an osteochondral defect (arrowheads) of the capitellum.
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Figure 4d. Failure of the stable osteochondritis dissecans lesion to heal. (a) Coronal, T1-weighted, spin-echo image (520/15) obtained at initial examination shows a focal, low-signal-intensity area (arrowheads) in the capitellum, but the sagittal, T2*-weighted, gradient-echo image (not shown) showed no instability. (b) Anteroposterior radiograph obtained 6 months after initial examination shows a nondisplaced fragment (arrow). The patient had continued baseball pitching, regardless of advice to stop. (c) Lateral radiograph obtained 4 years after initial examination shows loose fragments (arrows). (d) Sagittal T1-weighted, spin-echo MR image (520/15) obtained 4 years after initial examination shows an osteochondral defect (arrowheads) of the capitellum.
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By using the radiographs and US images obtained at initial examination, we divided the 16 lesions into two groups: those with localized subchondral flattening and those with nondisplaced fragments. For each group, we calculated the mean age of the patients, the mean duration of their symptoms, and the proportion of lesions with an open capitellar growth plate at initial examination. During the observation period, bone formation was investigated by using radiography. The mean period during which patients were observed nonsurgically was 3.5 years (range, 6 months to 12 years). The last radiographic results were assessed by one observer (M. Takahara) and were divided into three groups: healed, with no subchondral deformity; improved, with partial healing and some subchondral deformity; and not improved, with the lesion resulting in nonunion or in separation.
Statistical analysis was performed to investigate the differences between the patients with flattening and the patients with nondisplaced fragments. The Mann-Whitney U test was used to compare the mean ages of the patients and the mean lengths of symptoms at initial examination. The Fisher exact test was used to compare the proportions of lesions with an open growth plate and to compare the last radiographic results between the two groups. A P value of .05 was considered to indicate a significant difference.
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RESULTS
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Initial radiographs showed that six lesions had localized subchondral flattening without fragments, and nine had nondisplaced fragments; US images showed three type I lesions and three type II lesions. The US assessment agreed with the radiographic assessment in five patients. In the remaining patient, US images showed a lesion with flattening at initial examination, whereas radiographs obtained 4 months later showed nondisplaced fragments. On the basis of the radiographic and US findings at initial examination, we divided the 16 early osteochondritis dissecans lesions into seven with flattening and nine with nondisplaced fragments. MR imaging showed that three lesions were stable, without evidence of instability. All three stable lesions had flattening (Table 1).
The mean age of the patients with flattening at clinical presentation was 11.7 years (age range, 11–14 years), and that of patients with nondisplaced fragments at clinical presentation was 13.1 years (age range, 11–16 years). The former tended to be younger than the latter (P = .05). Six (86%) of seven patients with flattening had an open capitellar growth plate at clinical presentation, whereas only one (11%) of nine patients with nondisplaced fragments had an open capitellar growth plate at clinical presentation. There was a significant difference in bone age between them (P < .01). The mean duration of symptoms was 0.7 year (range, 0.1–1.6 years) in the patients with flattening at clinical presentation and was 2.0 years (range, 1–4 years) in the patients with nondisplaced fragments. The patients with fragments at clinical presentation had symptoms for a significantly longer period than those with flattening (P < .05) (Table 2). The mean age at the onset of symptoms was 11.0 years (range, 10–13 years) in the patients with flattening and was 11.1 years (range, 10–13 years) in the patients with nondisplaced fragments.
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TABLE 2. Clinical and Radiographic Findings of Capitellar Osteochondritis Dissecans Lesions Treated Nonsurgically
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In all seven lesions with flattening at clinical presentation, new bone formed over the flattened bone during the observation period. The appearance of the lesions with flattening became similar to that of the lesions with nondisplaced fragments. In five of the seven lesions, the newly formed bone united with the underlying bone; the lesions healed without subchondral deformity (Figs 2, 3). In the remaining two lesions, the newly formed bone failed to unite and became separated from the underlying capitellar bone (Fig 4).
In six of the nine lesions with nondisplaced fragments at clinical presentation, the gaps between the fragments and their beds became narrowed or the areas of decreased subchondral bone became small during the observation period, which indicated bone formation. In three of these lesions, some fragments united with the surrounding capitellar bone, although partial subchondral deformity remained. These three were assessed as improved. The remaining six lesions were assessed as not improved; one had nonunited fragments, and five had grossly separated fragments.
The last radiographic results showed healing in five patients, improvement in three, and no improvement in eight. Five (71%) of the seven lesions with flattening at clinical presentation healed, with new bone formation over the flattened bone. In contrast, none of the nine lesions with nondisplaced fragments at clinical presentation healed (Table 2). The lesions with flattening had significantly better radiographic results than those with nondisplaced fragments at clinical presentation (P < .01).
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DISCUSSION
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Patients who had lesions with flattening at clinical presentation tended to be younger than those who had lesions with nondisplaced fragments, significantly more of them had an open growth plate, and the duration of their symptoms was significantly shorter. In addition, all lesions with flattening developed new bone over the flattened bone (Fig 5, A and B) and became similar to the lesions with nondisplaced fragments. All these results indicate that localized subchondral flattening without fragments represents an earlier stage of capitellar osteochondritis dissecans than bone fragmentation.
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Figure 5. The natural course of osteochondritis dissecans. A-C, Drawings show the healing process of the stable lesion with localized subchondral bone flattening. A, Localized subchondral bone flattening with thickening of the overlying cartilage is the earliest change in osteochondritis dissecans. The main causes can be repetitive forces to the epiphysis before maturation. B, New bone formation appears gradually over the flattened bone. C, Union of the newly formed bone with the underlying bone. D, E, Drawings show the progression of the lesion with nondisplaced fragments. D, Repetitive forces can make the fragments unstable. E, The unstable fragment fails to unite and is displaced from the underlying bone.
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Possible causes of osteochondritis dissecans include trauma, ischemia, defects in ossification, and genetic factors (14–20). During the throwing motion, the capitellum is exposed to compression and to shear forces. These repetitive forces are suggested to be the main causes of capitellar osteochondritis dissecans (10–13). On the basis of this suggestion and our results, we conclude that repetitive forces on the capitellum can cause lesions with localized subchondral flattening. We found this mostly in capitella with open growth plates. Therefore, we propose that repetitive forces applied to the epiphysis before maturation can cause the localized subchondral flattening that represents the earliest stage of osteochondritis dissecans. The mean age at the onset of symptoms was 11 years (age range, 10–13 years) in the patients with subchondral flattening, the same as in those patients with nondisplaced fragments. This may suggest a critical age for the risk of developing osteochondritis dissecans.
In all lesions with flattening, new bone formed over the flattened bone, and their appearances (Fig 5, B) became indistinguishable from those of lesions with nondisplaced fragments (Fig 5, D). However, the lesions with flattening at clinical presentation showed a high healing rate (Fig 5, A-C), whereas most of those with fragments at clinical presentation failed to show fragment union (Fig 5, D and E). Our results indicate that lesions with flattening at clinical presentation are clinically stable, whereas lesions with nondisplaced fragments at clinical presentation are unstable. The patients with nondisplaced fragments at clinical presentation had had symptoms associated with physical activity for a significantly longer period before seeking medical care. We believe that patients with osteochondritis dissecans who do not seek help immediately and instead continue to be active and to impose repetitive trauma on their lesions produce fragments that eventually become nonunited. We consider the continued activity despite clinical symptoms to be a cause of worse outcome in the group with nondisplaced fragments at clinical presentation. Repetitive forces on the areas of new bone formation can cause unstable bone fragments.
Results of this study have shown that the earliest feature of osteochondritis dissecans is localized subchondral bone flattening over which new bone appears subsequently and that the newly formed bone either unites or fails to unite. Therefore, we now propose the following staging of osteochondritis dissecans: Stage I (earliest) represents subchondral bone flattening in the epiphysis before growth plate closure (Fig 5, A); stage IIA (stable), new bone formation over the flattened bone (Fig 5, B and C); stage IIB (possibly unstable), fragmentation due to repetitive trauma (Fig 5, D); stage III (obviously unstable), displacement of the fragment (Fig 5, E); and stage IV (terminal), complete separation of the fragments. We think that this staging represents the natural progression of osteochondritis dissecans and the various pathologic conditions that may be evident.
To our knowledge, lesions at stage I, the earliest stage of osteochondritis dissecans, rarely have been detected. This may be because the duration of stage I is only several months or less after the onset of symptoms. It is necessary to detect osteochondritis dissecans during this short period to prevent the lesions from becoming unstable. It has been suggested that the early finding of localized subchondral flattening is difficult to detect on anteroposterior or lateral radiographs (10). Therefore, we recommend anteroposterior radiography with the elbow at 45° of flexion, US, and MR imaging to detect early capitellar osteochondritis dissecans. Our results suggest that nondisplaced fragments should be divided into two types: stable (stage IIA) and unstable (stage IIB). Radiography alone may be insufficient for assessing lesion stability; therefore, MR imaging also should be used (1–10). In addition, we suggest the possible use of US (22,23). We think that our staging system can be used as a basis for discussing other study populations. To our knowledge, correlations between staging, arthroscopic assessment, and clinical outcome remain to be determined.
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ACKNOWLEDGMENTS
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We thank Kiyoshi Kaneda, MD, and many doctors in the Department of Orthopaedic Surgery, Hokkaido University School of Medicine, Sapporo, Japan, for providing the subjects and Hitoshi Ishikawa, MD, for support in this study.
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FOOTNOTES
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Author contributions: Guarantor of integrity of entire study, M. Takahara; study concepts and design, M. Takahara; definition of intellectual content, M. Takahara; literature research, M. Takahara, T.N.; clinical studies, M. Takahara, T.O., T.N.; data acquisition and analysis, M. Takahara, T.N.; statistical analysis, H.O.; manuscript preparation, M. Takahara; manuscript editing, T.O.; manuscript review, M. Takagi, H.T.
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TOP
ABSTRACT
INTRODUCTION
