MRI of Congenital and Developmental Abnormalities of the Knee Miller, Angie, M.D., Hernandez, Andrea, M.D., Pena, Andres, M.D., Jaramillo, Diego, M.D., M.P.H. Departments of Radiology, e Children’s Hospital of Philadelphia, Philadelphia, PA 19104

Congenital and developmental abnormalities of the knee are often initially identified on radiographs, but MRI can be utilized to Epiphyseal Meniscal detect physeal, epiphyseal, meniscal, ligamentous, and patellar abnormalities not suspected radiographically. Trevor’s Disease Discoid Meniscus Dysplasia Epiphysealis Hemimelica (Trevor’s disease) is characterized by localized overgrowth of an epiphysis of a long bone, most commonly Discoid meniscus is a variant in which the meniscus is more The various congenital and developmental abnormalities of the knee are best understood within the context of its normal development. The occurring medially and within the distal tibial or distal femoral epiphyses, and the talus. The lesions may be single or multiple, and ossify with disc-shaped than semicircular shaped, and in which a portion of the epiphyseal ossification center of the distal femur is present at birth, while the proximal tibial epiphysis forms a secondary ossification center during maturation. Premature closure of the physis with resultant deformity and occasional limb discrepancy may also be seen. Articular surface meniscus extends to the central portion of the tibial plateau. It occurs the first to third postnatal months. The normal secondary ossification center of the distal femoral epiphysis during childhood can have rough or irregularity may lead to early secondary osteoarthritis. more frequently laterally than medially. The incidence of a lateral serrated margins. The patella is completely cartilaginous at birth. Primary patellar ossification begins at 5 to 6 years, although small foci may be discoid meniscus is 1.5-3%, whereas that of a medial discoid meniscus evident at 2 to 3 years of age. The menisci obtain their characteristic shape before birth. Postnatally, the meniscal growth follows the distal femoral is 0.1-0.3%. It is associated with an abnormal attachment of the and proximal tibial enlargement, allowing for alteration in femorotibial contact and weight bearing with age. The cruciate ligaments blend into posterior lateral meniscus to the tibial plateau. A discoid meniscus can the epiphyseal cartilage of the distal femur and proximal tibia in early childhood. It is not until adolescence that the development of Sharpey’s be symptomatic, causing joint locking and joint line tenderness. The fibers occurs and the ligaments insert directly into the maturing ossification centers. abnormal biomechanics of the discoid meniscus makes it prone to Fig.11A Fig.11B Fig.11C Figure 11: Discoid meniscus, 9-year-old girl: Coronal proton density (Fig. 11A) and Sagittal T2 weighted tearing. images ( Fig.11B) demonstrate increased signal within a thickened lateral meniscus, with an intrameniscal The alignment of the knee varies during early childhood. Physiologic genu varum reaches a maximum degree at 6 months, and lasts until cyst within its anteromedial portion (arrow). Sagittal proton density image (Fig 11C) demonstrates markedly approximately 24 months. During the 3rd and 4th year, the knee becomes aligned in valgus, and the final alignment of slight genu valgus is irregular contour, thickening and increased signal within the lateral meniscus which also shows evidence of a reached at approximately 6 years of age. Patellar meniscal flounce(arrow). Fig.5A Fig.5B Fig.5C Fig.5D Fig.5E Fig.5F Nail Patella Syndrome Figure 5: Dysplasia Epiphysealis Hemimelica (Trevor’s disease), 1-year-old boy: AP and lateral view of the left knee (Fig.5A and B) demonstrates faint irregular ossification arising from the distal femoral condyle. Nail patella syndrome is an autosomal dominant Physeal Coronal T1 weighted (Fig.5C and D) and Sagittal T2 weighted (Fig.5E and F) images demonstrate overgrowth of the peripheral cartilage mass of the medial femoral epiphysis (arrow). Abnormal signal within the Blount Disease cartilage is suggestive of early ossification. condition characterized by nail dysplasia, patellar Blount disease (Infantile tibia vara) is due to a local growth disturbance of the medial aspect of the proximal tibial epiphysis, with failure of aplasia-hypoplasia, arthrodysplasia of the elbows, endochondral ossification of the medial growth plate. It primarily involves the physis, but ultimately affects the epiphyseal cartilage, the menisci, Tibial Hemimelia Epiphyseal Dysplasia posterior conical iliac horns, and nephropathy. Tibial hemimelia varies from mild Epiphyseal dysplasia is the secondary ossification centers, and the adjacent metaphyses. More than half of cases are bilateral. It is considered by some to be related to hypoplasia to complete absence of characterized by stippling of Figure 12: Nail patella syndrome, 22-year-old girl: AP view of the pelvis (Fig. 12A) stress on the medial compartment of the knee related to increased patient weight. demonstrates flaring of the iliac wings bilaterally. The characteristic iliac horns the tibia and is associated with other the epiphyses and are not present in this particular patient. Axial 3D gradient-echo (Fig.12B) and Figure 1: Bilateral Blount disease, abnormalities of the knee, including Axial T2 weighted images (Fig.12C) demonstrate a hypoplastic patella with 2-year-old girl abnormality of thinning of the patellar articular cartilage, particularly of the medial facet, with AP view of the knees (Fig.1A) patellar and cruciate ligament development of the areas of abnormal signal intensity consistent with chondromalacia. The patellar Fig.12A Fig.12B Fig.12C demonstrates the initial deformities, absent menisci, and secondary ossification retinaculum is poorly developed. radiographic changes of Bipartite Patella irregular metaphyseal abnormal collateral ligaments. centers. In the knee, there is Figure 13: Nail patella Bipartite patella occurs when the patella develops from two ossification with a medial and less distinct shaping of the syndrome, infant girl: Axial distal pointing metaphyseal gradient echo image of the separate ossification centers, resulting in a main and accessory spur, irregular metaphyseal Fig.6A Fig.6B Fig.7A Fig.7B secondary ossification left knee demonstrates bone. The main and accessory bones are connected by ossification along the medial hypoplasia of the patella, a Figure 6: Tibial hemimelia, newborn male: centers with relative flattening of the distal femoral condylar contours. tibial physis, fragmentation of shallow trochlea, and lateral fibrocartilaginous tissue. The findings are usually of no clinical AP view (Fig. 6A) demonstrates complete tibial hemimelia and inward turning of the foot. Sagittal the adjacent medial femoral patellar subluxation. oblique T2-weighted image (Fig.6B) demonstrates a hypertrophied proximal fibular epiphysis that Figure 7: Epiphyseal dysplasia, 10 year old girl: Sagittal T1 and T2 weighted images (Fig.7A and 7B) significance. epiphysis, and resultant tibia (Courtesy of Dr. Tal Laor). Fig.1A Fig.1B Fig.1C Fig.1D articulates with the distal femoral epiphysis. The patella is absent. (Image courtesy of Jaramillo D, Hoffer demonstrate abnormal flattening of the distal femoral condylar contours and irregularity of the developing vara deformity. Coronal 3D FA. Cartilaginous epiphysis and growth plate: normal and abnormal MR imaging findings. AJR Am J secondary ossification center. There is diffusely abnormal signal within the developing cartilage gradient-echo (Fig.1B and C) images demonstrate irregularity of metaphyseal ossification along the tibial physis, stippling of the secondary ossification centers, and overgrowth of the cartilage of the Figure 14: Bipartite patella, 2-year-old boy: Coronal T1 weighted image (Fig.14A) in a young Roentgenol. 1992 May;158(5):1105-10) medial compartment of the knee. Sagittal 3D gradient-echo (Fig. 1D) image demonstrates stippling of the medial femoral epiphysis and hypertrophy of the medial meniscus. patient demonstrates a nonossified cartilaginous patella. Coronal T1 weighted fat saturated post-contrast image (Fig. 14B) demonstrates a separate cartilaginous component of the Congenitally Short Femur superolateral patella, not yet ossified. Figure 2: Bilateral Blount’s disease, 5-year-old girl Congenitally short femur ranges from mild hypoplasia to complete absence of the femur. Fig.13 Fig.14A Fig.14B Coronal proton density (Fig.2A and B) images in an older child demonstrate bilateral medial tibial physeal depression with associated bony bridging between the tibial epiphysis and In childhood it is characterized by anterolateral bowing of the femur and medial cortical Congenital Dislocation of the Patella metaphysis (arrow). There is associated widening of the lateral tibial physis. Tibia vara deformity thickening. It results in an abnormality of the tibial and femoral condyles, which may be is present with irregularity of the medial epiphyseal and metaphyseal bone. Sagittal proton Congenital dislocation of the patella represents a spectrum of developmental dysplasia of the density (Fig.2C) image demonstrates hypertrophy and increased signal within the medial flattened. Unlike in proximal focal femoral deficiency, the hip joint is unaffected. patella and of the extensor mechanism. Flattening of the lateral femoral condyle occurs with an meniscus, irregularity of the cortex of the posteromedial femoral condyle, and irregularity of the medial proximal tibial physis, through the area of bony bridging. increasing degree of genu valgum and external tibial rotation. The patella Figure 8: Congenitally short femur, 28 week gestational age girl: is hypoplastic and the intercondylar sulcus is shallow. Echo planar images of the right (Fig.8A arrow) and left femur (Fig. 8 B arrow) demonstrate asymmetric femoral length, with the ossified segments of the right and left femora measuring 6.1 cm and 3.4 cm, respectively. Fig.8B Fig.8A Figure 15: Congenital patellar dislocation, 1-year-old boy: Axial PD (Fig.15A) image demonstrates lateral Fig.2A Fig.2B Fig.2C Proximal Focal Femoral Deficiency dislocation of the patella and a shallow intercondylar notch. The lateral dislocation of the extensor mechanism Rickets is seen on the coronal PD (Fig.15B) image. Coronal 3D (Fig.15 C) reconstructed image further demonstrates the Proximal Focal Femoral Deficiency (PFFD) describes a spectrum of disorders ranging from hypoplasia to aplasia of abnormal patellofemoral relationship. Rickets is a disorder of childhood caused by a deficiency of or resistance to vitamin D or its derivative 1,25-dihydroxycholecalciferol. Abnormal Fig.15A Fig.15B Fig.15C endochondral ossification results, with an imaging appearance of widened and irregularly shaped physes, and flaring or cupping of the the proximal femur. The acetabulum is dysplastic. At the knee, PFFD is associated with flattening of the distal metaphyses. There is widening of the physes of the secondary ossification centers, with delay in the appearance of femoral epiphysis and underdevelopment of the intercondylar notch. There is often absence of the cruciate ligaments. Global these centers, and absence of the zone of provisional calcification. Vascular Malformation Figure 3: Rickets, 13-month-old girl The most common congenital vascular lesions of the knee are vascular Sagittal STIR (Fig.3) image demonstrates widening of the distal femoral and proximal tibial physes as well as the physis of the secondary ossification center (arrow). A normal zone of provisional calcification is not visualized. malformations, resulting from abnormal vascular formation during Figure 9: PFFD, 6-year-old girl: Coronal proton density (Fig.9) image of the right hip demonstrates a hypoplastic acetabulum, fibrous connection between the femoral head and the shaft of the femur, and a small but spherical femoral head. The distal femur is also hypoplastic. embryonic life. The dilated blood vessels that build up these lesions Figure 4: Rickets, 7-year-old boy Fig.9 Coronal T1 weighted (Fig.4A) image demonstrates loss of the zone of provisional calcification with medial tibial physeal bridging of uncertain etiology. Coronal 3D gradually enlarge and can be classified based on their type of blood gradient-echo (Fig.4B and C), sagittal T1 weighted (Fig. 4D), and sagittal STIR (Fig. 4E) images demonstrate widening of the distal femoral and proximal tibial physes flow into slow-flow (capillary, venous, lymphatic) lesions, high-flow with abnormal intraphyseal signal. Pallisading longitudinal vertical hypodense areas within the physis are suggestive of mineralization along the metaphyseal side of the physis. (arterial) lesions, and combined slow/fast-flow lesions Clinically, these Fig.3 patients are subject to repeated bouts of hemarthrosis if the lesion is

Fig.16A Fig.16B Fig.16C located within a joint space. Figure 16: Venous malformation, 3-year-old boy: Sagittal PD image (Fig.16A) demonstrates a multilobulated mass in Hoffa’s fat pad. It contains areas of low T2 signal intensity, consistent with phleboliths (arrow). (Fig. 16B) Sagittal contrast enhanced T1 weighted image (Fig.16C) demonstrates heterogeneous enhancement of the multilobulated mass which may be due to a lymphatic component or to delayed filling with contrast. Conclusion: MRI is valuable in detecting and characterizing the physeal, epiphyseal, meniscal, ligamentous, and patellar abnormalities associated with congenital and developmental disorders of the knee. Fig.10A Fig.10B Fig.10C Fig.10D Fig.10E Figure 10: PFFD, 6-year-old boy: Lateral view (Fig.10A) of the femur demonstrates hypoplasia of the intertrochanteric portion of the right femur, with abnormal ossification. Coronal proton density image (Fig.10B) of References the pelvis demonstrates a hypoplastic acetabulum without uncovering of the femoral head. Coronal proton density (Fig. 10C) and T1-weighted (Fig. 10D) images of the knee demonstrate lateral dislocation of the 1. Craig JG, Holsbeeck M, Zaltz I (2002) The utility of MR in assessing Blount disease. Skeletal Radiology 31: 208-213 5. Anton CG, Applegate KE, Kuivila TE, Wilkes DC (1999) Proximal femoral focal deficiency (PFFD): more than an abnormal hip. Semin Musculoskelet Radiol 3:215-226 patella (Fig. 10D, arrow), and large medial and lateral discoid menisci with associated high signal consistent with degeneration. Sagittal proton density image (Fig.10E) demonstrates absence of the cruciate ligaments 2. Shapiro F. Pediatric orthopedic deformities: basic science, diagnosis, and treatment. Orlando (FL): Academic Press; 2002. 6. Laor T, Jaramillo D, Hoffer FA, Kasser JR (1996) MR imaging in congenital lower limb deformities. Pediatr Radiol 26:381-387 3. Strouse PJ, Koujok K (2002) Magnetic Resonance imaging of the pediatric knee. Top Magn Reson Imaging 13(4): 277-94 7. Resnick D. Diagnosis of bone and joint disorders, 3rd edition. Philadelphia: WB Saunders, 1995: 3589. and rounding of the femoral and tibial epiphyses. There is absence of a well formed intercondylar notch. 4. John A. Ogden. Skeletal injury in the child, 3rd edition. Berlin: Springer Verlag, 2000. 8. Jaramillo D, Hoffer FA (1992) Cartilaginous epiphysis and growth plate: normal and abnormal MR imaging findings. AJR Am J Roentgenol. May;158(5):1105-10 Fig.4A Fig.4B Fig.4C Fig.4D Fig.4E