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Imaging of Osteochondritis Dissecans of the Knee
Imaging of Osteochondritis Dissecans of the Knee Margaret D. Phillips, MD, and Stephen J. Pomeranz, MD The imaging goals in patients with osteochondritis dissecans are lesion identification, characterization, staging, and follow-up. The macroscopic features visible by imaging reflect the microscopic histology of the abnormality. Osteochondritis dissecans involves subchondral bone with possible resultant effect on the overlying articular cartilage. Unresolved, degenerative arthritis, effusion, and loose bodies may occur. In this article, features of the disorder as they appear on plain film, bone scintigraphy, and magnetic resonance imaging are reviewed. Oper Tech Sports Med 16:52-64 © 2008 Published by Elsevier Inc. KEYWORDS osteochondritis dissecans, knee, MRI, imaging
T
he imaging goals in patients with osteochondritis dissecans (OCD) are lesion identification, characterization, staging, and follow-up. The macroscopic features visible by imaging reflect the microscopic histology of the abnormality. Osteochondritis dissecans involves subchondral bone with possible resultant effect on the overlying articular cartilage.1,2 Unresolved, degenerative arthritis, effusion, and loose bodies may occur. In this article, features of the disorder as they appear on plain film, bone scintigraphy, and magnetic resonance imaging are reviewed. Although initially named as an inflammatory disorder in 1887 by Konig, the definite cause of OCD is unknown. Current hypotheses favor repetitive microtrauma with microfracturing of subchondral bone, subsequent ischemia, and altered local growth.3 The microscopic features include osteonecrosis with variable amounts of healing, fracture, inflammation, and subchondral avascularity. Granulation tissue and pseudocysts develop between the necrotic region and the healing bone. The articular cartilage basilar growth is altered, and revascularization with creeping substitution occurs. Reossification and healing can occur; however, because the cartilage bears the support beneath the necrotic bone, cartilage disruption may result.4,5 With weakening of the subchondral bone, support of the overlying cartilage decreases and cartilage may soften, fissure, and separate. The osteochondral fragments can dislodge and release into the joint. A recent histological analysis of cartilage from ankle OCD lesions revealed findings supportive of an apoptotic ProScan Imaging Educational Foundation, ProScan Imaging, Cincinnati, OH. Address reprint requests to: Margaret D. Phillips, ProScan Imaging Educational Foundation, ProScan Imaging, LLC, 5400 Kennedy Avenue, Cincinnati, OH 45213. E-mail: [email protected]
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1060-1872/08/$-see front matter © 2008 Published by Elsevier Inc. doi:10.1053/j.otsm.2008.09.001
process as one of the mechanisms involved.6 Genetic factors and epiphyseal dysplasia may play roles. These histological features of OCD, their spectrum, progression, and evolution, translate into the macroscopic appearance captured by imaging.
Diagnosis Knowledge of common OCD locations and morphology aids in their discovery. Although the exact percentages vary by study, the site of greatest OCD frequency involves the medial femoral condyle, with additional locations in the lateral femoral condyle, patella, and femoral trochlear sulcus. The lateral aspect of the medial femora condyle is most common. An extended classic lesion involves the medial femoral trochlea. Uncommonly, OCD may involve the anterolateral femoral condyle of the lateral trochlear groove. However, this pattern is increasing in frequency because of the high incidence of patellofemoral abnormal friction biomechanics in contact athletes and the high frequency of participation in collision sports (Stephen J. Pomeranz, personal observation 2006). Bilateral OCD occurs in 20% to 25% (and lesions can involve both condyles in an ipsilateral knee).4 The lesions typically appear elliptical, extending subjacent to the overlying cartilage.
Plain Film Typical plain-film series include anteroposterior (AP), lateral, tunnel, and tangential patellar (skyline, sunrise) views. Plainfilm findings reflect the subchondral loss of osseous matrix, appearing as a lucent area or subarticular concavity that may have a sclerotic rim. Tunnel views may better depict posterior
Imaging of OCD of the knee
Figure 1 (A) Axial T2 fast spin echo (FSE), patellar OCD. (B) Sagittal T1, patellar OCD.
Figure 2 (A) Coronal short-time inversion recovery (STIR), lateral femoral condylar OCD. (B) Sagittal FSE T2, lateral femoral condylar OCD. (C) Sagittal 3D T1-appearing steady-state free procession (SARGE), lateral femoral condylar OCD.
Figure 3 (A) T1 fat-weighted sagittal, stage 1 OCD. (B) Coronal STIR (water-emphasized, fat-suppressed) shows subjacent tiny pseudocyst, stage 1 lesion.
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54 condylar OCD, and the tangential patellar views better depict the rare patellar lesions. Documentation of lesion location, size, border, and morphology is made, along with an evaluation for physeal maturity because of its impact on management and prognosis. Determining the presence of skeletal immaturity is essential, because stable OCD (OCD in children with open physes) is generally amenable to conservative management.7 Films are also assessed for effusion, loose body, and signs of secondary osteoarthritis. A1959 report of talar transcondylar fractures or osteochondritis dissecans by Berndt and Harty described 4 stages on plain films that have been transferred to describe OCD lesions in the knee. These are stage I, with a small subchondral compression; stage II, with a partially detached in situ fragment; stage III, with a completely detached fragment that remains in situ; and stage IV, with a fragment detached from its native site.1,8
The thickness of a sclerotic margin and larger lesion size can support presence of instability. In one study, Mesgarzadeh and coworkers9 reported that a sclerotic margin of 3 mm or greater resulted in an association with loosening (sensitivity 50% and specificity 100%). In the same study, smaller lesions were more likely stable; those greater than 0.8 cm2 were loose.9 The authors of the report noted that an ossific center visualized by plain film showed no statistically significant difference between stable and loose lesions.9 This study did not distinguish the patients’ skeletal maturity. The location of OCD lesions can be described for research purposes with a scheme devised by Cahill and Berg.1,10 This method divides the knee into regions based on AP and lateral radiographs. Four vertical lines are drawn on the AP film, with the center 2 lines about the femoral trochlear notch and the other 2 lines dividing the medial and lateral condyles. The
Figure 4 (A) Coronal STIR (water-emphasized, fat-suppressed) stage 1 lesion. (B) Sagittal T1 fat-weighted, stage 1 lesion. (C) Sagittal FSE (fast spin echo) proton density fat-suppressed, stage 1 lesion. (D) Sagittal GRE (gradient-echo, water-emphasized) T2*, stage 1 lesion.
Imaging of OCD of the knee zones are numbered 1 through 5, proceeding medial to lateral. On the lateral radiograph, 2 radially oriented lines divide the condyles into anterior (A), central (B), and posterior (C). False-positive plain films for OCD can arise from misinterpreting normal variant grooves in the distal femoral articular surface.11 These grooves can be seen in the distal articular surface of the femur on the tangential patellar and lateral views where the femur articulates with the patella anteriorly and with the tibia posteriorly and inferiorly. The lateral condylar groove extends laterally from the anterior aspect of the intracondylar fossa to form a triangular depression. This depression contains the anterior lateral meniscus in extension. The medial condylar groove exists on the medial portion of the condyle and accepts the anterior medial meniscus in extension.11
Nuclear Medicine Studies in which the authors analyzed nuclear medicine imaging of OCD report mixed results of bone scintigraphy’s ability to predict lesion stability and outcome. In the Cahill
55 and Berg classification of OCD, the lesions are delineated by nuclear medicine and radiographic findings. The 5 stages include: Stage 0, normal; Stage 1, radiographs abnormal and bone scan normal; Stage II, increased uptake in the lesion on bone scan but not in the surrounding femoral condyle; Stage III, increased bone scan uptake in the lesion and in the adjacent femoral condyle; and Stage IV, increased uptake in the lesion and in the adjacent tibial plateau.1,10 In follow-up, Cahill and coworkers12 used scintigraphy to prospectively assess 92 knees in 76 juvenile patients who received conservative treatment of femoral condylar OCD. Analysis of the predictive value of joint scintigraphy and various other radiographic and clinical parameters were analyzed and revealed no statistically significant predictive value of scan classification. In a small retrospective series, Paletta and coworkers13 evaluated 12 patients with knee OCD and found the quantitative bone scan predictive value varied with the physeal status. Of the 6 patients with open physes, 4 had increased bone scan activity, and all these OCD lesions healed with
Figure 5 (A) Sagittal 3D fat-suppressed gradient echo, stage 1 lesion left knee. (B) Coronal T2 SPIR (spectrally sensitive inversion recovery – fat-suppressed), stage 1 lesion left knee. (C) Sagittal PD SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 1 lesion left knee. (D) Sagittal T1 (fat-weighted), stage 1 lesion left knee.
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M.D. Phillips and S.J. Pomeranz without surgery. Bone scintigraphy therefore displayed a 100% predictive value in the skeletally immature but did not achieve such status after physeal closure. Mesgarzadeh and coworkers9 examined 3-phase bone scanning in the setting of OCD. The patients ranged in age from 11 to 25 years. Skeletal maturity was not noted. In this small cohort, which likely included patients of both skeletal immaturity and maturity, flow phase findings proved not significant. Blood-pool phase revealed all 8 of the loose and 1 of the 6 stable OCD lesions to show focal increased uptake in the region of involvement. The authors concluded that hyperemia in the blood-pool images was 100% sensitive and 83% specific in identifying OCD loosening. The late-phase imaging underwent grading from 0 to 4, with grade 0 being normal activity; grade 1 being mildly increased local activity; grade 2 being moderately increased local activity; grade 3 being intense local activity; and grade 4 being intense uptake involving at least the entire affected condyle. All grade 0 or 1 lesions were stable. All grade 3 or 4 lesions were loose. Grade 2 lesions proved equally stable or loose. Therefore, the latephase imaging showed the degree of uptake correlated with disease severity.
Magnetic Resonance Imaging With its superior soft-tissue, bone architectural, and threedimensional capabilities, MRI plays a dominant role in current OCD detection, characterization, and follow-up. In the optimal MRI technique for OCD detection and characteriza-
Figure 6 (A) Sagittal T1 (fat-weighted), stage 2 lesion right knee. (B) Sagittal PD SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 2 lesion right knee. (C) Coronal T2 SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed) shows small cartilage defect, stage 2 lesion right knee.
nonsurgical treatment. The two skeletally immature patients with decreased scintigraphic activity did not respond to conservative management and required surgery. However, of the 6 patients with closed physes, all had increased radiotracer activity by bone scans and only 2 patients healed the OCD
Figure 7 Coronal STIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed) taken on a 0.3-T open system showing a stage 3 lesion.
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Figure 8 (A) Coronal T2 SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 3 lesion. (B) Coronal T2 SPIR, stage 3 lesion. (C) Sagittal PD SPIR, stage 3 lesion. (D) Sagittal PD SPIR, stage 3 lesion. (E) Sagittal PD SPIR, stage 3 lesion. (F) Coronal T2 SPIR stage 3 lesion. (G) Coronal T2 SPIR, stage 3 lesion. (H) Coronal T2 SPIR, stage 3 lesion.
tion in the knee, one uses a dedicated phased-array extremity coil. Sample examination parameters might include an axial T2-weighted fast spin-echo, a coronal T1-weighted spinecho sequence, a coronal frequency-selective fat-suppressed
T2-weighted fast spin-echo, a sagittal frequency-selective fatsuppressed proton-weighted fast spin-echo sequence, and a sagittal T2-weighted gradient echo sequence. Lesion location, size, and morphology are assessed using the
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58 composite of sequences. A 3-dimensional GRE water-emphasized sequence is optional for enhanced cartilage visualization.
Detection of Lesions Anatomically With MRI MRI has been used to assess the extent to which the previously discussed normal femoral variants appear similar to Stage 1 OCD, as well as what distinguishing features might help separate them. The authors of a retrospective study in which MRI examinations of the knee in 38 children were reviewed described several features witnessed in developmental
variants rather than OCD. The features of variants include ossification defects in the posterior femoral condyles with intact cartilage, accessory condylar ossification centers, spiculation of existing ossification, lack of marrow edema,14 and deep vascular grooves. The normal variant ossification defects are noted especially in the posteromedial femoral condyle. Some of the rarer types of OCD benefit from the superior spatial resolution of MRI. OCD of the patella was shown to be located central-inferiorly in all 18 cases retrospectively analyzed in a study from Cornell; in the 5 patients from the study group who underwent surgery, the cartilage abnormality classified on
Figure 9 (A) Coronal STIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 4 lesion. (B) Axial T2, stage 4 lesion showing loose body. (C) Axial T2, stage 4 lesion showing loose body. (D) Sagittal PD SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed). The stage 4 lesion led to premature osteoarthritis.
Imaging of OCD of the knee
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Figure 10 (A) Coronal T2 SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed) Stage 3 OCD. (B) Sagittal PD SPIR Stage 3 OCD. (C) Sagittal PD SPIR Stage 3 led to premature osteoarthritis. (D) Coronal T2 SPIR Stage 3 led to premature osteoarthritis.
the MRI was confirmed operatively.15 The following examination of a 12-year-old boy shows an example of a patellar OCD on a high-field open system (Fig. 1). OCD of the femoral sulcus may be missed by plain radiography because of the orientation of the femoral sulcus, but becomes more apparent on MRI axial and sagittal images.16 Lateral femoral condylar OCD has been studied in relation to the lateral meniscal state and a relationship has been proved to be present. In a study of 38 knees with lateral condylar OCD, 19 had complete discoid menisci, 15 had incomplete discoid menisci, and four menisci were reported as normal.17 The following example (Fig. 2) demonstrates a lateral femoral OCD in a 14-year-old boy with open physes. The lesion involves the weight-bearing region. Healing is present, with subtle fibrovascular reaction or stress change subjacent to lesion. The overlying cartilage is intact. The lateral meniscus has normal morphology and is not discoid.
Assessment of Lesion Stability With MRI In 1987, Mesgarzadeh and coworkers described the use of MRI in 21 joints of 15 patients for the assessment of OCD lesion stability, heralding future imaging studies to come.9 Fragment displacement provided the most evident sign of loosening. This early report noted the presence of fluid at the
Table 1 Strengths of MRI in the Management of OCD Cartilage fissuring Cartilage flaps that may produce locking Loose bodies Physeal status Condylar remodeling of dysplasia Health status of surrounding bone for fixation Friction stress as an indicator of abnormal biomechanics and need for an interventional procedure
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Figure 11 (A) Sagittal proton density fat suppressed (PD SPIR) showing lateral trochlear OCD. (B) Axial T2 weighted FSE image of lateral trochlear OCD. (C) Axial proton density fat suppressed (PDSPIR) image showing lateral trochlear OCD.
interface between the fragment and the surrounding bone as a reliable sign of loosening. In this small series without correlation to skeletal maturity, MRI was 92% sensitive and 90% specific in distinguishing loose from stable lesions. Subsequent studies further refined this conclusion, and demonstrate the importance of skeletal maturity as a major influence on the accuracy of MRI lesion stability. The arthroscopic staging system for OCD can be translated from the MRI appearance5:
● ● ● ●
Stage 1: Lesion is 1 cm to 3 cm in size with intact articular cartilage; Stage 2: Articular cartilage defect without loose body; Stage 3: Partially detached osteochondral fragment; and Stage 4: Detached lesion with loose body
DeSmet and coworkers18 reported criteria used as an indication of lesion instability. These criteria included a high-signal interface between the lesion and the surrounding bone (al-
Figure 12 (A) Axial T1 showing lateral trochlear OCD. (B) Sagittal proton density SPIR (fat suppressed) showing edema in the medial patella.
Imaging of OCD of the knee though they considered it suggestive and not absolute as a false positive was noted and granulation can have such an appearance) and round cyst-like areas beneath the fragments. The authors of a recent study in which adult versus juvenile OCD was evaluated concluded that although MRI criteria of OCD lesion instability in the knee have high sensitivity and specificity in adults, in children, lesions that are thought to be unstable by imaging often are actually stable. To assess the sensitivity and specificity of accepted MRI criteria for lesion instability, researchers at the University of Wisconsin retrospectively reviewed 32 children and 33 adults with OCD who had undergone both MRI and arthroscopy. Criteria for OCD instability included high T2-signal lesion rim, adjacent cysts, cartilage fracture, and fluid-filled OCD. As reported in the journal Radiology, the instability criteria together were 100% sensitive and 100% specific in adults. However, in children they proved 100% sensitive but only 11% specific.19 Therefore, surgical intervention in this group should only be considered when a nondisplaced OCD has 12 to 24 months of failed conservative treatment. An earlier British study corroborated this note of caution when evaluating children and adolescents. The researchers concluded that a high signal line behind the OCD lesion does not always indicate instability. MRI accuracy as a predictor of instability increased from 45% to 85% in their study when the high-signal T2 line had concomitant cartilage breach.20 The case of a 12-year-old boy with bilateral medial femoral OCD illustrates stable stage 1 lesions. The left knee OCD (Fig. 3) involves the weight-bearing and nonweight-bearing posteromedial femoral condylar epiphysis. Osteoedema is present, with tiny subchondral pseudocysts. Intact overlying is cartilage. Open physes are present. The right knee in the same patient shows an in situ subchondral osseous lentiform abnormality with mild subjacent edema and intact overlying cartilage (Fig. 4). A 48-year-old woman with bilateral OCD illustrates a stage 1 lesion in the left knee (Fig. 5) and a stage 2 lesion in the right (Fig. 6). The left knee has a medial femoral condylar OCD in the lateral aspect. The lentiform lesion extends from the nonweight-bearing femoral condyle to the posterior weight-bearing area. Bone edema exists within the lesion and subtle irregularity involves the overlying cartilage, but there is no cartilage fracture. The right knee (Fig. 6) in the same 48-yearold female with bilateral OCD displays a type 2 lesion with a small cartilage defect. The case of a 17-year-old boy illustrates a stage 3 lesion (Fig. 7). The patient has fusing physes and an OCD involving the mid and lateral medial femoral condyle. The low-field study shows the osteochondral fragment to have mild lateral displacement or “gapping” and surrounding high T2 signal. A stage 3 lesion interrogated at 1.5T is shown (Fig. 8). This 26-year-old man has an in situ medial femoral OCD extending from the posterior nonweight-bearing to the weight-bearing area. The lesion is nondisplaced, with slightly irregular overlying cartilage. A band of subjacent increased T2 signal is present and there are pseudocysts caused by
61 microinstability anteriorly. The OCD fragment is at risk for displacement. A stage 4 lesion is depicted in a 21-year-old man with an anteromedial femoral condylar OCD (Fig. 9). Marked hemicondylar edema and osteoarthropathy are present. An in situ unstable fragment is accompanied by loose bodies (arrows) within the joint capsule. Premature osteoarthritis is developing, witnessed by an early osteophyte and tibial stress edema. A moderate effusion exists.
Figure 13 (A) Coronal FSE STIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed,) medial femoral OCD. (B) Sagittal proton density FSE fat-suppressed image showing small pseudocyst.
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Figure 14 (A) Sagittal proton density fast spin echo fat-suppressed image demonstrates interval sclerosis of the small subjacent pseudocyst. (B) Sagittal proton density FSE fat-suppressed image shows stable slight cartilage irregularity. (C) Sagittal T1 (fat-weighted) of the OCD showed no change in lesion size during the 1-year period. (D) Coronal STIR FSE of the OCD showed no change in lesion size during the 1-year period.
Imaging of OCD of the knee
OCD Complications on MRI The cartilage irregularity, altered biomechanics, and inflammation that may accompany OCD may result in premature osteoarthritis. MRI affords the depiction of early osteoarthritis by demonstrating its effect on the meniscus, cartilage, synovium, capsule, joint fluid, joint alignment, and cortical margins. The case of a 39-year-old woman with a stage 3 lesion exemplifies such findings (Fig. 10). The imaging shows a medial femoral OCD with surrounding hyperintense rim and adjacent premature posterior medial meniscal freeedge degeneration. An anterior small femoral spur is developing, along with mild subjacent tibial stress edema and early medial meniscal pseudoextrusion. The use of MRI is ideal in evaluating certain features important in OCD management (Table 1).
MRI for OCD Follow-up and Treatment MRI affords follow-up assessment of OCD by allowing direct comparison of lesion size, subjacent osseous morphology, and overlying cartilage appearance, as well as providing insight into the status of healing, persistent abnormal biomechanics, or possible complications. The following case illustrates a lateral condylar OCD in a 14-year-old boy, a talented and avid sports participant who developed a lateral trochlear OCD (Fig. 11). Follow-up studies when the boy was 15 years old showed stability of the OCD but development of medial patellar edema (Fig. 12). This MRI finding led to the hypothesis that repeated patellar rotation and lateral translation contributed to the OCD formation. The patient subsequently underwent lateral retinacular release with symptomatic improvement. A second case example is that of a 16-year-old boy with an open femoral physis and a tibial physis in the early stages of closing who has an elliptical subchondral OCD in the lateral aspect of the medial femoral condyle (Fig. 13). The initial study shows a small subjacent pseudocyst, which underwent signal decrease by the 1-year follow-up (Fig. 14). This decrease likely represents interval sclerosis. Intact overlying cartilage, slightly irregular, remained stable. The 1-year follow-up examination is shown in Fig 14. Surgical treatment options for stable OCD with normal cartilage include drilling subchondral bone to stimulate vascular ingrowth and subchondral bone healing. Unstable lesion management options include fixation and grafting, chondrocyte transplant, or osteochondral grafting.1 The appearances on MRI of such procedures, including imaging with cartilage-sensitive sequences, have been reported.21-28
Summary and Conclusion Imaging of osteochondritis dissecans of the knee renders the microscopic features of the disorder visible macroscopically. Plain-film radiography depicts OCD in many patients, although femoral normal variants and certain OCD locations (particularly patellar and trochlear) may pose difficulty, and cartilage evaluation is limited. Bone scintigraphy affords mixed results in assessing lesion stability. The superior spa-
63 tial and anatomic tissue resolution of MRI allows the most detailed assessment of OCD lesion presence, morphology, size, character, and stability. Importantly, complications such as softening of the surrounding bone, pseudocysts, loose bodies, cartilage fissures or flaps, bony remodeling, and meniscal degeneration are accurately depicted. Accurate physeal closure status is a key value-added strength of magnetic resonance imaging. Recent literature supports the high sensitivity and specificity of MRI in characterizing OCD lesion stability in adults, though many pediatric OCD lesions with these same imaging features are actually stable. Knee MRI affords an assessment for complications and secondary osteoarthritis, as well as for longitudinal follow-up.
References 1. Crawford DC, Safron MR: Osteochondritis dissecans of the knee. J Am Acad Orthop Surg 14:90-100, 2006 2. Detterline AJ, Goldstein JL, Rue JP, et al: Evaluation and treatment of osteochondritis dissecans of the knee. J Knee Surg 21:106-115, 2008 3. Gangley TJ, Gaugler RL, Kocher MS, et al: Osteochondritis dissecans of the knee. Op Tech Sports Med 14:147-158, 2006 4. Stoller DW, Tirman PFJ, Bredella MA, et al: Diagnostic Imaging Orthopaedics. Salt Lake City, UT, Amirsys, 2004, pp 578-581 5. Stoller DW: Magnetic Resonance Imaging in Orthopaedics and Sports Medicine. Vol. 1. Baltimore, MD, Lippincott, 2007, pp 693-708 6. Franceshi LD, Grigolo B, Roseti L, et al: Osteochondritis dissecans. Histopathology 51:133-134, 2007 7. Robertson W, Kelly BT, Green DW: Osteochondritis dissecans of the knee in children. Curr Opin Pediatr 15:38-44, 2003 8. Berndt AL, Harty M: Transcondylar fractures (osteochondritis dissecans) of the talus. J Bone Joint Surg B Am 41:988-1020, 1959 9. Mesgarzadeh M, Sapega AA, Bonakdarpour A, et al: Osteochondritis dissecans: Analysis of mechanical stability with radiography, scintigraphy, and MR imaging. Radiology 165:775-780, 1987 10. Cahill BR, Berg BC: 99m-Technetium phosphate compound joint scintigraphy in the management of juvenile osteochondritis dissecans of the femoral condyles. Am J Sports Med 11:329-335, 1983 11. Harrison RB, Wood MB, Keats TE: The grooves of the distal articular surface of the femur – a normal variant. AJR Am J Roentgenol 126:751754, 1976 12. Cahill BR, Phillips MR, Navarro R: The results of conservative management of juvenile osteochondritis dissecans using joint scintigraphy. Am J Sports Med 17:601-606, 1989 13. Paletta GA, Bednarz PA, Stanitski CL, et al: The prognostic value of quantitative bone scan in knee osteochondritis dissecans. Am J Sports Med 26:7-14, 1998 14. Gebarski K, Hernandez RJ: Stage-I osteochondritis dissecans versus normal variants of ossification in the knee in children. Pediatr Radiol 35:880-886, 2005 15. Choi YS, Cohen NA, Potter HG, et al: Magnetic resonance imaging in the evaluation of osteochondritis dissecans of the patella. Skel Radiol 36:929-35, 2007 16. Boutin RD, Januario JA, Newberg AH, et al: MR imaging features of osteochondritis dissecans of the femoral sulcus. AJR Am J Roentgenol 180:641-645, 2003 17. Deie M, Ochi M, Sumen Y, et al: Relationship between osteochondritis dissecans of the lateral femoral condyle and lateral menisci types. J Pediatr Orthop 26:79-82, 2006 18. DeSmet AA, Fisher DR, Graf BK, et al: Osteochondritis dissecans of the knee: Value of MR imaging in determining lesion stability and the presence of articular cartilage defects. AJR Am J Roentgenol 155: 549-553, 1990 19. Kijowski R, Blankenbaker DG, Kazuhiko S, et al: Juvenile versus adult osteochondritis dissecans of the knee: Appropriate MR imaging criteria for instability. Radiology 248:571-578, 2008 20. O’Connor MA, Palaniappan M, Khan N, et al: Osteochondritis disse-
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cans of the knee in children. A comparison of MRI and arthroscopic findings. J Bone Joint Surg Br 84:258-262, 2002 Macarini L, Murrone M, Marini S, et al: Aspects of magnetic resonance in the surgical treatment of osteochondral lesions of the knee. Radiol Med 106:74-86, 2003 Tins BJ, McCall IW, Takahashi T, et al: Autologous chondrocyte implantation in knee joint: MR imaging and histologic features at one-year follow-up. Radiology 234:501-508, 2005 Link TM, Mischung J, Wortler K, et al: Normal and pathological MR findings in osteochondral autografts with longitudinal follow-up. Eur Radiol 16:88-96, 2006 Berna-Serna JD, Martinez F, Reus M, et al: Osteochondritis dissecans of the knee: Sonographically guided percutaneous drilling. J Ultrasound Med 27:255-9, 2008 Recht MP, Goodwin DW, Winalski CS, et al: MRI of articular cartilage:
Revisiting current status and future directions. Am J Roentgenol 185:899-914, 2005 26. Welsch GH, Mamisch TC, Domayer SE, et al: Cartilage T2 assessment at 3-T MR imaging: In vivo differentiation of normal hyaline cartilage from reparative tissue after two cartilage repair procedures—initial experience. Radiology 247:154-161, 2008 27. Watanabe A, Wada Y, Obata T, et al: Delayed gadolinium-enhanced MR to determine glycosaminoglycan concentration in reparative cartilage after autologous chondrocyte implantation: Preliminary results. Radiology 239:201-208, 2006 28. Makino A, Muscolo DL, Puigdevall M, et al: Arthroscopic fixation of osteochondritis dissecans of the knee: Clinical, magnetic resonance imaging, and arthroscopic follow-up. Am J Sports Med 33:1499-504, 2005
T
he imaging goals in patients with osteochondritis dissecans (OCD) are lesion identification, characterization, staging, and follow-up. The macroscopic features visible by imaging reflect the microscopic histology of the abnormality. Osteochondritis dissecans involves subchondral bone with possible resultant effect on the overlying articular cartilage.1,2 Unresolved, degenerative arthritis, effusion, and loose bodies may occur. In this article, features of the disorder as they appear on plain film, bone scintigraphy, and magnetic resonance imaging are reviewed. Although initially named as an inflammatory disorder in 1887 by Konig, the definite cause of OCD is unknown. Current hypotheses favor repetitive microtrauma with microfracturing of subchondral bone, subsequent ischemia, and altered local growth.3 The microscopic features include osteonecrosis with variable amounts of healing, fracture, inflammation, and subchondral avascularity. Granulation tissue and pseudocysts develop between the necrotic region and the healing bone. The articular cartilage basilar growth is altered, and revascularization with creeping substitution occurs. Reossification and healing can occur; however, because the cartilage bears the support beneath the necrotic bone, cartilage disruption may result.4,5 With weakening of the subchondral bone, support of the overlying cartilage decreases and cartilage may soften, fissure, and separate. The osteochondral fragments can dislodge and release into the joint. A recent histological analysis of cartilage from ankle OCD lesions revealed findings supportive of an apoptotic ProScan Imaging Educational Foundation, ProScan Imaging, Cincinnati, OH. Address reprint requests to: Margaret D. Phillips, ProScan Imaging Educational Foundation, ProScan Imaging, LLC, 5400 Kennedy Avenue, Cincinnati, OH 45213. E-mail: [email protected]
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1060-1872/08/$-see front matter © 2008 Published by Elsevier Inc. doi:10.1053/j.otsm.2008.09.001
process as one of the mechanisms involved.6 Genetic factors and epiphyseal dysplasia may play roles. These histological features of OCD, their spectrum, progression, and evolution, translate into the macroscopic appearance captured by imaging.
Diagnosis Knowledge of common OCD locations and morphology aids in their discovery. Although the exact percentages vary by study, the site of greatest OCD frequency involves the medial femoral condyle, with additional locations in the lateral femoral condyle, patella, and femoral trochlear sulcus. The lateral aspect of the medial femora condyle is most common. An extended classic lesion involves the medial femoral trochlea. Uncommonly, OCD may involve the anterolateral femoral condyle of the lateral trochlear groove. However, this pattern is increasing in frequency because of the high incidence of patellofemoral abnormal friction biomechanics in contact athletes and the high frequency of participation in collision sports (Stephen J. Pomeranz, personal observation 2006). Bilateral OCD occurs in 20% to 25% (and lesions can involve both condyles in an ipsilateral knee).4 The lesions typically appear elliptical, extending subjacent to the overlying cartilage.
Plain Film Typical plain-film series include anteroposterior (AP), lateral, tunnel, and tangential patellar (skyline, sunrise) views. Plainfilm findings reflect the subchondral loss of osseous matrix, appearing as a lucent area or subarticular concavity that may have a sclerotic rim. Tunnel views may better depict posterior
Imaging of OCD of the knee
Figure 1 (A) Axial T2 fast spin echo (FSE), patellar OCD. (B) Sagittal T1, patellar OCD.
Figure 2 (A) Coronal short-time inversion recovery (STIR), lateral femoral condylar OCD. (B) Sagittal FSE T2, lateral femoral condylar OCD. (C) Sagittal 3D T1-appearing steady-state free procession (SARGE), lateral femoral condylar OCD.
Figure 3 (A) T1 fat-weighted sagittal, stage 1 OCD. (B) Coronal STIR (water-emphasized, fat-suppressed) shows subjacent tiny pseudocyst, stage 1 lesion.
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54 condylar OCD, and the tangential patellar views better depict the rare patellar lesions. Documentation of lesion location, size, border, and morphology is made, along with an evaluation for physeal maturity because of its impact on management and prognosis. Determining the presence of skeletal immaturity is essential, because stable OCD (OCD in children with open physes) is generally amenable to conservative management.7 Films are also assessed for effusion, loose body, and signs of secondary osteoarthritis. A1959 report of talar transcondylar fractures or osteochondritis dissecans by Berndt and Harty described 4 stages on plain films that have been transferred to describe OCD lesions in the knee. These are stage I, with a small subchondral compression; stage II, with a partially detached in situ fragment; stage III, with a completely detached fragment that remains in situ; and stage IV, with a fragment detached from its native site.1,8
The thickness of a sclerotic margin and larger lesion size can support presence of instability. In one study, Mesgarzadeh and coworkers9 reported that a sclerotic margin of 3 mm or greater resulted in an association with loosening (sensitivity 50% and specificity 100%). In the same study, smaller lesions were more likely stable; those greater than 0.8 cm2 were loose.9 The authors of the report noted that an ossific center visualized by plain film showed no statistically significant difference between stable and loose lesions.9 This study did not distinguish the patients’ skeletal maturity. The location of OCD lesions can be described for research purposes with a scheme devised by Cahill and Berg.1,10 This method divides the knee into regions based on AP and lateral radiographs. Four vertical lines are drawn on the AP film, with the center 2 lines about the femoral trochlear notch and the other 2 lines dividing the medial and lateral condyles. The
Figure 4 (A) Coronal STIR (water-emphasized, fat-suppressed) stage 1 lesion. (B) Sagittal T1 fat-weighted, stage 1 lesion. (C) Sagittal FSE (fast spin echo) proton density fat-suppressed, stage 1 lesion. (D) Sagittal GRE (gradient-echo, water-emphasized) T2*, stage 1 lesion.
Imaging of OCD of the knee zones are numbered 1 through 5, proceeding medial to lateral. On the lateral radiograph, 2 radially oriented lines divide the condyles into anterior (A), central (B), and posterior (C). False-positive plain films for OCD can arise from misinterpreting normal variant grooves in the distal femoral articular surface.11 These grooves can be seen in the distal articular surface of the femur on the tangential patellar and lateral views where the femur articulates with the patella anteriorly and with the tibia posteriorly and inferiorly. The lateral condylar groove extends laterally from the anterior aspect of the intracondylar fossa to form a triangular depression. This depression contains the anterior lateral meniscus in extension. The medial condylar groove exists on the medial portion of the condyle and accepts the anterior medial meniscus in extension.11
Nuclear Medicine Studies in which the authors analyzed nuclear medicine imaging of OCD report mixed results of bone scintigraphy’s ability to predict lesion stability and outcome. In the Cahill
55 and Berg classification of OCD, the lesions are delineated by nuclear medicine and radiographic findings. The 5 stages include: Stage 0, normal; Stage 1, radiographs abnormal and bone scan normal; Stage II, increased uptake in the lesion on bone scan but not in the surrounding femoral condyle; Stage III, increased bone scan uptake in the lesion and in the adjacent femoral condyle; and Stage IV, increased uptake in the lesion and in the adjacent tibial plateau.1,10 In follow-up, Cahill and coworkers12 used scintigraphy to prospectively assess 92 knees in 76 juvenile patients who received conservative treatment of femoral condylar OCD. Analysis of the predictive value of joint scintigraphy and various other radiographic and clinical parameters were analyzed and revealed no statistically significant predictive value of scan classification. In a small retrospective series, Paletta and coworkers13 evaluated 12 patients with knee OCD and found the quantitative bone scan predictive value varied with the physeal status. Of the 6 patients with open physes, 4 had increased bone scan activity, and all these OCD lesions healed with
Figure 5 (A) Sagittal 3D fat-suppressed gradient echo, stage 1 lesion left knee. (B) Coronal T2 SPIR (spectrally sensitive inversion recovery – fat-suppressed), stage 1 lesion left knee. (C) Sagittal PD SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 1 lesion left knee. (D) Sagittal T1 (fat-weighted), stage 1 lesion left knee.
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M.D. Phillips and S.J. Pomeranz without surgery. Bone scintigraphy therefore displayed a 100% predictive value in the skeletally immature but did not achieve such status after physeal closure. Mesgarzadeh and coworkers9 examined 3-phase bone scanning in the setting of OCD. The patients ranged in age from 11 to 25 years. Skeletal maturity was not noted. In this small cohort, which likely included patients of both skeletal immaturity and maturity, flow phase findings proved not significant. Blood-pool phase revealed all 8 of the loose and 1 of the 6 stable OCD lesions to show focal increased uptake in the region of involvement. The authors concluded that hyperemia in the blood-pool images was 100% sensitive and 83% specific in identifying OCD loosening. The late-phase imaging underwent grading from 0 to 4, with grade 0 being normal activity; grade 1 being mildly increased local activity; grade 2 being moderately increased local activity; grade 3 being intense local activity; and grade 4 being intense uptake involving at least the entire affected condyle. All grade 0 or 1 lesions were stable. All grade 3 or 4 lesions were loose. Grade 2 lesions proved equally stable or loose. Therefore, the latephase imaging showed the degree of uptake correlated with disease severity.
Magnetic Resonance Imaging With its superior soft-tissue, bone architectural, and threedimensional capabilities, MRI plays a dominant role in current OCD detection, characterization, and follow-up. In the optimal MRI technique for OCD detection and characteriza-
Figure 6 (A) Sagittal T1 (fat-weighted), stage 2 lesion right knee. (B) Sagittal PD SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 2 lesion right knee. (C) Coronal T2 SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed) shows small cartilage defect, stage 2 lesion right knee.
nonsurgical treatment. The two skeletally immature patients with decreased scintigraphic activity did not respond to conservative management and required surgery. However, of the 6 patients with closed physes, all had increased radiotracer activity by bone scans and only 2 patients healed the OCD
Figure 7 Coronal STIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed) taken on a 0.3-T open system showing a stage 3 lesion.
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Figure 8 (A) Coronal T2 SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 3 lesion. (B) Coronal T2 SPIR, stage 3 lesion. (C) Sagittal PD SPIR, stage 3 lesion. (D) Sagittal PD SPIR, stage 3 lesion. (E) Sagittal PD SPIR, stage 3 lesion. (F) Coronal T2 SPIR stage 3 lesion. (G) Coronal T2 SPIR, stage 3 lesion. (H) Coronal T2 SPIR, stage 3 lesion.
tion in the knee, one uses a dedicated phased-array extremity coil. Sample examination parameters might include an axial T2-weighted fast spin-echo, a coronal T1-weighted spinecho sequence, a coronal frequency-selective fat-suppressed
T2-weighted fast spin-echo, a sagittal frequency-selective fatsuppressed proton-weighted fast spin-echo sequence, and a sagittal T2-weighted gradient echo sequence. Lesion location, size, and morphology are assessed using the
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58 composite of sequences. A 3-dimensional GRE water-emphasized sequence is optional for enhanced cartilage visualization.
Detection of Lesions Anatomically With MRI MRI has been used to assess the extent to which the previously discussed normal femoral variants appear similar to Stage 1 OCD, as well as what distinguishing features might help separate them. The authors of a retrospective study in which MRI examinations of the knee in 38 children were reviewed described several features witnessed in developmental
variants rather than OCD. The features of variants include ossification defects in the posterior femoral condyles with intact cartilage, accessory condylar ossification centers, spiculation of existing ossification, lack of marrow edema,14 and deep vascular grooves. The normal variant ossification defects are noted especially in the posteromedial femoral condyle. Some of the rarer types of OCD benefit from the superior spatial resolution of MRI. OCD of the patella was shown to be located central-inferiorly in all 18 cases retrospectively analyzed in a study from Cornell; in the 5 patients from the study group who underwent surgery, the cartilage abnormality classified on
Figure 9 (A) Coronal STIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed), stage 4 lesion. (B) Axial T2, stage 4 lesion showing loose body. (C) Axial T2, stage 4 lesion showing loose body. (D) Sagittal PD SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed). The stage 4 lesion led to premature osteoarthritis.
Imaging of OCD of the knee
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Figure 10 (A) Coronal T2 SPIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed) Stage 3 OCD. (B) Sagittal PD SPIR Stage 3 OCD. (C) Sagittal PD SPIR Stage 3 led to premature osteoarthritis. (D) Coronal T2 SPIR Stage 3 led to premature osteoarthritis.
the MRI was confirmed operatively.15 The following examination of a 12-year-old boy shows an example of a patellar OCD on a high-field open system (Fig. 1). OCD of the femoral sulcus may be missed by plain radiography because of the orientation of the femoral sulcus, but becomes more apparent on MRI axial and sagittal images.16 Lateral femoral condylar OCD has been studied in relation to the lateral meniscal state and a relationship has been proved to be present. In a study of 38 knees with lateral condylar OCD, 19 had complete discoid menisci, 15 had incomplete discoid menisci, and four menisci were reported as normal.17 The following example (Fig. 2) demonstrates a lateral femoral OCD in a 14-year-old boy with open physes. The lesion involves the weight-bearing region. Healing is present, with subtle fibrovascular reaction or stress change subjacent to lesion. The overlying cartilage is intact. The lateral meniscus has normal morphology and is not discoid.
Assessment of Lesion Stability With MRI In 1987, Mesgarzadeh and coworkers described the use of MRI in 21 joints of 15 patients for the assessment of OCD lesion stability, heralding future imaging studies to come.9 Fragment displacement provided the most evident sign of loosening. This early report noted the presence of fluid at the
Table 1 Strengths of MRI in the Management of OCD Cartilage fissuring Cartilage flaps that may produce locking Loose bodies Physeal status Condylar remodeling of dysplasia Health status of surrounding bone for fixation Friction stress as an indicator of abnormal biomechanics and need for an interventional procedure
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Figure 11 (A) Sagittal proton density fat suppressed (PD SPIR) showing lateral trochlear OCD. (B) Axial T2 weighted FSE image of lateral trochlear OCD. (C) Axial proton density fat suppressed (PDSPIR) image showing lateral trochlear OCD.
interface between the fragment and the surrounding bone as a reliable sign of loosening. In this small series without correlation to skeletal maturity, MRI was 92% sensitive and 90% specific in distinguishing loose from stable lesions. Subsequent studies further refined this conclusion, and demonstrate the importance of skeletal maturity as a major influence on the accuracy of MRI lesion stability. The arthroscopic staging system for OCD can be translated from the MRI appearance5:
● ● ● ●
Stage 1: Lesion is 1 cm to 3 cm in size with intact articular cartilage; Stage 2: Articular cartilage defect without loose body; Stage 3: Partially detached osteochondral fragment; and Stage 4: Detached lesion with loose body
DeSmet and coworkers18 reported criteria used as an indication of lesion instability. These criteria included a high-signal interface between the lesion and the surrounding bone (al-
Figure 12 (A) Axial T1 showing lateral trochlear OCD. (B) Sagittal proton density SPIR (fat suppressed) showing edema in the medial patella.
Imaging of OCD of the knee though they considered it suggestive and not absolute as a false positive was noted and granulation can have such an appearance) and round cyst-like areas beneath the fragments. The authors of a recent study in which adult versus juvenile OCD was evaluated concluded that although MRI criteria of OCD lesion instability in the knee have high sensitivity and specificity in adults, in children, lesions that are thought to be unstable by imaging often are actually stable. To assess the sensitivity and specificity of accepted MRI criteria for lesion instability, researchers at the University of Wisconsin retrospectively reviewed 32 children and 33 adults with OCD who had undergone both MRI and arthroscopy. Criteria for OCD instability included high T2-signal lesion rim, adjacent cysts, cartilage fracture, and fluid-filled OCD. As reported in the journal Radiology, the instability criteria together were 100% sensitive and 100% specific in adults. However, in children they proved 100% sensitive but only 11% specific.19 Therefore, surgical intervention in this group should only be considered when a nondisplaced OCD has 12 to 24 months of failed conservative treatment. An earlier British study corroborated this note of caution when evaluating children and adolescents. The researchers concluded that a high signal line behind the OCD lesion does not always indicate instability. MRI accuracy as a predictor of instability increased from 45% to 85% in their study when the high-signal T2 line had concomitant cartilage breach.20 The case of a 12-year-old boy with bilateral medial femoral OCD illustrates stable stage 1 lesions. The left knee OCD (Fig. 3) involves the weight-bearing and nonweight-bearing posteromedial femoral condylar epiphysis. Osteoedema is present, with tiny subchondral pseudocysts. Intact overlying is cartilage. Open physes are present. The right knee in the same patient shows an in situ subchondral osseous lentiform abnormality with mild subjacent edema and intact overlying cartilage (Fig. 4). A 48-year-old woman with bilateral OCD illustrates a stage 1 lesion in the left knee (Fig. 5) and a stage 2 lesion in the right (Fig. 6). The left knee has a medial femoral condylar OCD in the lateral aspect. The lentiform lesion extends from the nonweight-bearing femoral condyle to the posterior weight-bearing area. Bone edema exists within the lesion and subtle irregularity involves the overlying cartilage, but there is no cartilage fracture. The right knee (Fig. 6) in the same 48-yearold female with bilateral OCD displays a type 2 lesion with a small cartilage defect. The case of a 17-year-old boy illustrates a stage 3 lesion (Fig. 7). The patient has fusing physes and an OCD involving the mid and lateral medial femoral condyle. The low-field study shows the osteochondral fragment to have mild lateral displacement or “gapping” and surrounding high T2 signal. A stage 3 lesion interrogated at 1.5T is shown (Fig. 8). This 26-year-old man has an in situ medial femoral OCD extending from the posterior nonweight-bearing to the weight-bearing area. The lesion is nondisplaced, with slightly irregular overlying cartilage. A band of subjacent increased T2 signal is present and there are pseudocysts caused by
61 microinstability anteriorly. The OCD fragment is at risk for displacement. A stage 4 lesion is depicted in a 21-year-old man with an anteromedial femoral condylar OCD (Fig. 9). Marked hemicondylar edema and osteoarthropathy are present. An in situ unstable fragment is accompanied by loose bodies (arrows) within the joint capsule. Premature osteoarthritis is developing, witnessed by an early osteophyte and tibial stress edema. A moderate effusion exists.
Figure 13 (A) Coronal FSE STIR (spectrally sensitive inversion recovery, water-emphasized and fat-suppressed,) medial femoral OCD. (B) Sagittal proton density FSE fat-suppressed image showing small pseudocyst.
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Figure 14 (A) Sagittal proton density fast spin echo fat-suppressed image demonstrates interval sclerosis of the small subjacent pseudocyst. (B) Sagittal proton density FSE fat-suppressed image shows stable slight cartilage irregularity. (C) Sagittal T1 (fat-weighted) of the OCD showed no change in lesion size during the 1-year period. (D) Coronal STIR FSE of the OCD showed no change in lesion size during the 1-year period.
Imaging of OCD of the knee
OCD Complications on MRI The cartilage irregularity, altered biomechanics, and inflammation that may accompany OCD may result in premature osteoarthritis. MRI affords the depiction of early osteoarthritis by demonstrating its effect on the meniscus, cartilage, synovium, capsule, joint fluid, joint alignment, and cortical margins. The case of a 39-year-old woman with a stage 3 lesion exemplifies such findings (Fig. 10). The imaging shows a medial femoral OCD with surrounding hyperintense rim and adjacent premature posterior medial meniscal freeedge degeneration. An anterior small femoral spur is developing, along with mild subjacent tibial stress edema and early medial meniscal pseudoextrusion. The use of MRI is ideal in evaluating certain features important in OCD management (Table 1).
MRI for OCD Follow-up and Treatment MRI affords follow-up assessment of OCD by allowing direct comparison of lesion size, subjacent osseous morphology, and overlying cartilage appearance, as well as providing insight into the status of healing, persistent abnormal biomechanics, or possible complications. The following case illustrates a lateral condylar OCD in a 14-year-old boy, a talented and avid sports participant who developed a lateral trochlear OCD (Fig. 11). Follow-up studies when the boy was 15 years old showed stability of the OCD but development of medial patellar edema (Fig. 12). This MRI finding led to the hypothesis that repeated patellar rotation and lateral translation contributed to the OCD formation. The patient subsequently underwent lateral retinacular release with symptomatic improvement. A second case example is that of a 16-year-old boy with an open femoral physis and a tibial physis in the early stages of closing who has an elliptical subchondral OCD in the lateral aspect of the medial femoral condyle (Fig. 13). The initial study shows a small subjacent pseudocyst, which underwent signal decrease by the 1-year follow-up (Fig. 14). This decrease likely represents interval sclerosis. Intact overlying cartilage, slightly irregular, remained stable. The 1-year follow-up examination is shown in Fig 14. Surgical treatment options for stable OCD with normal cartilage include drilling subchondral bone to stimulate vascular ingrowth and subchondral bone healing. Unstable lesion management options include fixation and grafting, chondrocyte transplant, or osteochondral grafting.1 The appearances on MRI of such procedures, including imaging with cartilage-sensitive sequences, have been reported.21-28
Summary and Conclusion Imaging of osteochondritis dissecans of the knee renders the microscopic features of the disorder visible macroscopically. Plain-film radiography depicts OCD in many patients, although femoral normal variants and certain OCD locations (particularly patellar and trochlear) may pose difficulty, and cartilage evaluation is limited. Bone scintigraphy affords mixed results in assessing lesion stability. The superior spa-
63 tial and anatomic tissue resolution of MRI allows the most detailed assessment of OCD lesion presence, morphology, size, character, and stability. Importantly, complications such as softening of the surrounding bone, pseudocysts, loose bodies, cartilage fissures or flaps, bony remodeling, and meniscal degeneration are accurately depicted. Accurate physeal closure status is a key value-added strength of magnetic resonance imaging. Recent literature supports the high sensitivity and specificity of MRI in characterizing OCD lesion stability in adults, though many pediatric OCD lesions with these same imaging features are actually stable. Knee MRI affords an assessment for complications and secondary osteoarthritis, as well as for longitudinal follow-up.
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