MRI anatomy and injuries of the fingers.

Magnetic resonance imaging (MRI) diagnosis of underlying finger pathology can be intimidating due to the presence of unique anatomy. The small size of the fingers and the unique orientation of the thumb compared to the fingers also introduce unique demands on the MRI system and the technologists performing the study. This article will review the anatomy pertinent to injuries at the fingers, provide protocol guidance, and discuss pathology encountered at the fingers. Although much of the encountered pathology in the fingers overlaps with adults, unique pathology to children will be highlighted when applicable.

Impingement syndromes of the ankle and hindfoot.

Ankle impingement refers to a chronic painful mechanical limitation of ankle motion caused by soft-tissue or osseous abnormality affecting the tibiotalar joint or extraarticular soft tissues. Impingement can be associated with a prior single traumatic event or repetitive microtrauma, often in an adolescent with anatomical predisposition. Impingement syndromes at the tibiotalar joint can be subdivided into anterior, anterolateral, anteromedial, posterior or posteromedial. Extraarticular impingement can consist of talocalcaneal or subfibular impingement. Impingement syndromes are just one possible etiology of persistent ankle pain, and although the diagnosis is often made or suspected clinically, the radiologist might be the first person to raise the possibility of the diagnosis or be called upon to provide support for the clinically suspected diagnosis. In this article I review the etiology, imaging findings and current treatment associated with these conditions.

Lower patient-reported function at 2 years is associated with elevated knee cartilage T1rho and T2 relaxation times at 5 years in young athletes after ACL reconstruction.

PURPOSE: The purpose was to test the following hypotheses: (1) magnetic resonance imaging (MRI) markers of early knee cartilage degeneration would be present in the involved limb of young athletes after anterior cruciate ligament reconstruction (ACLR) and (2) poor knee function would be associated with MRI markers of cartilage degeneration. METHODS: Twenty-five young athletes after primary, unilateral ACLR (mean age, 16.7 years) were followed to 5-year post-return-to-sport (RTS) clearance, as a part of a larger, prospective cohort study in young athletes post-ACLR. At 2-year post-RTS, patient-reported knee function was evaluated using the Knee injury and Osteoarthritis Outcome Score (KOOS). At 5-year post-RTS, qualitative MRI sequences (3 T) and quantitative T1rho and T2 maps segmented into six regions at the femur and tibia were performed for the involved and uninvolved knee cartilages. Relaxation times were compared between knees using Holm-corrected paired t tests. Linear regression was used to examine the association between KOOS scores at 2 years and relaxation times at 5 years. RESULTS: Elevated T1rho and T2 relaxation times were observed in the involved knee at the anterior medial femoral condyle compared to the uninvolved knee (p = 0.006, p = 0.024, respectively). Lower KOOS-Pain, KOOS-Symptoms, KOOS-ADL, and KOOS-Sport scores at 2-year post-RTS were associated with higher T1rho or T2 relaxation times in various regions of the involved knee at 5-year post-RTS (all p < 0.05). CONCLUSIONS: MRI markers of early cartilage degeneration were identified in the medial compartment of the involved knee in young athletes 5-year post-RTS after ACLR. Lower KOOS scores at 2-year post-RTS were associated with elevated knee cartilage T1rho and T2 relaxation times at 5-year post-RTS. Evaluating patient-reported function over time after ACLR appears to provide insight into future degenerative changes in the knee cartilage matrix.

Anatomy and injuries of the pediatric wrist: beyond the basics.

Ligamentous injuries of the pediatric wrist, once thought to be relatively uncommon, are increasingly recognized in the context of acute high-energy mechanism trauma and chronic axial loading, including those encountered in both recreational and high-performance competitive sports. Recent advances in MR-based techniques for imaging the pediatric wrist allow for sensitive identification of these often radiographically occult injuries. Detailed knowledge of the intrinsic and supportive extrinsic ligamentous complexes, as well as normal developmental anatomy and congenital variation, are essential to accurately diagnose injuries to these structures. Early identification of ligamentous injury of the pediatric wrist is essential within the conservative treatment culture of modern pediatric orthopedics because treatment of these lesions often necessitates surgery, and outcomes often depend on early and sometimes aggressive intervention. In this article, we review MR arthrogram technique and pediatric wrist anatomy, and correlate appearances on MR and selected ligamentous pathologies of the pediatric wrist.

Imaging assessment of patellar instability and its treatment in children and adolescents.

Transient patellar dislocation is a common entity in children and adolescents, characterized by lateral dislocation of the patella, usually with spontaneous reduction. Many predisposing conditions have been described, including trochlear dysplasia, excessive lateral patellar tilt, patella alta and lateralization of the tibial tuberosity. Associated injuries are bone bruises of the patella and lateral femoral condyle, tears of the medial retinaculum that include the medial patellofemoral ligament (MPFL), tears of the vastus medialis obliquus muscle, injuries of articular cartilage, and intra-articular bodies. Children who are refractory to conservative management, have a large cartilage defect, or are at substantial risk for recurrent dislocations are candidates for surgical procedures to prevent future dislocations. Procedures can include MPFL repair or reconstruction, tibial tubercle repositioning and lateral retinacular release. The purpose of this review is to illustrate the imaging findings of transient patellar dislocation in the acute setting, the normal imaging appearance after surgical intervention, and post-surgical complications.

Post-operative imaging of anterior cruciate ligament reconstruction techniques across the spectrum of skeletal maturity.

Due to an increased frequency of anterior cruciate ligament (ACL) injuries in young patients and improved outcomes in athletic performance following ACL reconstruction, surgery is increasingly being performed across the spectrum of skeletal maturity. We present a review of the range of reconstruction techniques performed in skeletally immature patients (physeal sparing techniques, which may involve epiphyseal tunnels or the utilization of an iliotibial band autograft), those performed in patients nearing skeletal maturity (transphyseal techniques), and the more conventional ACL reconstruction techniques performed in skeletally mature adolescents. It is important that radiologists be aware of the range of techniques being performed throughout the spectrum of skeletal maturity in order to accurately characterize the expected post-operative appearance as well as to identify complications, including those unique to this younger population.

Prenatal Diagnosis of Infantile Myofibroma with Postnatal Imaging Correlation.

Infantile myofibroma is the most common fibrous tumor in infancy. A majority of these lesions are solitary and occur in the head and neck region. Unless visceral sites are involved, the clinical course is typically benign. However, the difficulty in these cases is the differentiation of a benign myofibroma from a solitary malignant neoplasm and determination of visceral involvement. Prenatal diagnosis of this condition is rarely described in the literature, but it does indeed have a role in perinatal management. Our patient was initially identified by prenatal ultrasound with fetal MRI for further characterization of the mass. We present the case of a prenatally diagnosed solitary infantile myofibroma of the lower extremity and highlight the role of prenatal imaging in the diagnosis and treatment of this condition.

Juvenile Osteochondritis Dissecans: Correlation Between Histopathology and MRI.

OBJECTIVE: The objective of our study was to correlate specimens of juvenile osteochondritis dissecans (OCD) lesions of the knee to MRI examinations to elucidate the histopathologic basis of characteristic imaging features. MATERIALS AND METHODS: Five children (three boys and two girls; age range, 12-13 years old) who underwent transarticular biopsy of juvenile OCD lesions of the knee were retrospectively included in this study. Two radiologists reviewed the MRI examinations and a pathologist reviewed the histopathologic specimens and recorded characteristic features. Digital specimen photographs were calibrated to the size of the respective MR image with the use of a reference scale. Photographs were rendered semitransparent and over-laid onto the MR image with the location chosen on the basis of the site of the prior biopsy. RESULTS: A total of seven biopsy specimens were included. On MRI, all lesions showed cystlike foci in the subchondral bone, bone marrow edema pattern on proton density-or T2-weighted images, and relatively thick unossified epiphyseal cartilage. In four patients, a laminar signal intensity pattern was seen, and two patients had multiple breaks in the subchondral bone plate. Fibrovascular tissue was found at histopathology in all patients. Cleft spaces near the cartilage-bone interface and were seen in all patients while chondrocyte cloning was present in most cases. Focal bone necrosis and inflammation were infrequent MRI findings. Precise correlation of the MRI appearance to the histopathologic overlays consistently was found. CONCLUSION: A direct correlation exists between the histopathologic findings and the MRI features in patients with juvenile OCD. Additional studies are needed to correlate these MRI features with juvenile OCD healing success rates.

US for diagnosis of musculoskeletal conditions in the young athlete: emphasis on dynamic assessment.

Ultrasonography (US) is increasingly recognized as an important tool for diagnosis and therapeutic management of a variety of musculoskeletal conditions. Advantages of US use in the young athlete include the ability to diagnose dynamic conditions that are occult with other modalities, provide additional diagnostic information, and aid in treatment. Uses of US in young patients include evaluation of acquired musculoskeletal conditions that manifest with symptoms and assessment of congenital variants that may manifest with pain or limitations in activity. Acquired conditions in the young athlete include tendon disorders, such as proximal tendinosis, and ligament disorders, such as anterior talofibular ligament or ulnar collateral ligament tears. While static images are frequently able to depict these disorders without difficulty, a dynamic examination that provides stress to the joint of interest may be able to uncover a ligament tear or insufficiency and concurrently provide the clinician with information regarding joint stability. Numerous congenital variants that occur throughout the musculoskeletal system can be associated with awkward sensations such as snapping, popping, and clunking and occasionally with pain. Pathologic processes associated with congenital variants in the upper extremities include slipping rib syndrome, atraumatic anterior subluxation of the sternoclavicular joint, and snapping triceps syndrome. Conditions that affect the lower extremities include internal and external snapping hip syndrome, snapping knee syndrome, and medial plica syndrome. The dynamic capability of US is ideal for diagnosis of many conditions that affect the musculoskeletal system of the young athlete, many of which would be difficult or impossible to identify with use of other imaging modalities.

Posttreatment imaging of pediatric musculoskeletal tumors.

Pediatric patients who are diagnosed with musculoskeletal tumors often require serial imaging both during and after treatment. Although many of the treatments used in adults overlap with those used in children and adolescents, the growing skeleton presents specific challenges that require a unique approach. Surgical treatment of benign osseous lesions typically requires only curettage and bone grafting, whereas that of osseous malignancies generally consists of wide excision and limb salvage, with either endoprosthetic or biologic reconstruction. Current conventional endoprostheses consist of modular components that allow intraoperative customization; however, if there is great potential for future growth, an expandable endoprosthesis may be required. Biologic reconstruction may consist of an allograft and/or autograft and, in some circumstances, can spare the growth plates in a child, thereby allowing normal growth. Expected posttreatment imaging findings in soft-tissue tumors may include muscle flaps and postoperative fluid collections. Medical treatment, including radiation therapy and chemotherapy, can have predictable imaging manifestations, including signal alterations in bone marrow, muscle, and subcutaneous fat. Finally, treatment complications may manifest with clinical symptoms and include infection or mechanical failure, although other complications such as local tumor recurrence may go clinically undetected until surveillance imaging. Familiarity with the expected posttreatment imaging findings in pediatric patients with musculoskeletal tumors can aid in the detection of complications.

Avulsion fractures of the pediatric knee.

Although avulsion fractures of the pediatric knee are uncommon, they are important injuries to recognize because they are frequently associated with adjacent soft-tissue and osteocartilaginous abnormalities. Related injuries, which include entrapment of soft-tissue structures, intra-articular fracture extension, and intra-articular loose bodies, can complicate or alter therapy. The most commonly affected soft-tissue structures include the cruciate ligaments, collateral ligaments and supporting tendons, and extensor mechanism and retinacula. The purpose of this pictorial essay is to review avulsion fractures of the pediatric knee and to highlight associated injuries.

Rotator cuff tears in children and adolescents: experience at a large pediatric hospital.

BACKGROUND: Prior literature, limited to small case series and case reports, suggests that rotator cuff tears are rare in adolescents. However, we have identified rotator cuff tears in numerous children and adolescents who have undergone shoulder MRI evaluation. OBJECTIVE: The purpose of this study is to describe the prevalence and characteristics of rotator cuff tears in children and adolescents referred for MRI evaluation of the shoulder at a large pediatric hospital and to correlate the presence of rotator cuff tears with concurrent labral pathology, skeletal maturity and patient activity and outcomes. MATERIALS AND METHODS: We reviewed reports from 455 consecutive non-contrast MRI and magnetic resonance arthrogram examinations of the shoulder performed during a 2-year period, and following exclusions we yielded 205 examinations in 201 patients (ages 8-18 years; 75 girls, 126 boys). Rotator cuff tears were classified by tendon involved, tear thickness (partial or full), surface and location of tear (when partial) and presence of delamination. We recorded concurrent labral pathology when present. Physeal patency of the proximal humerus was considered open, closing or closed. Statistical analysis was performed to evaluate for a relationship between rotator cuff tears and degree of physeal patency. We obtained patient activity at the time of injury, surgical reports and outcomes from clinical records when available. RESULTS: Twenty-five (12.2%) rotator cuff tears were identified in 17 boys and 7 girls (ages 10-18 years; one patient had bilateral tears). The supraspinatus tendon was most frequently involved (56%). There were 2 full-thickness and 23 partial-thickness tears with articular-side partial-thickness tears most frequent (78%). Insertional partial-thickness tears were more common (78%) than critical zone tears (22%) and 10 (43%) partial-thickness tears were delamination tears. Nine (36%) patients with rotator cuff tears had concurrent labral pathology. There was no statistically significant relationship between rotator cuff tears and physeal patency (P > 0.05). Most patients were athletes (76%). Five tears were confirmed at surgery. Poor clinical follow-up limited evaluation of patient outcomes. CONCLUSION: Rotator cuff tears can be identified during MRI examination of symptomatic child and adolescent shoulders and often consist of tear patterns associated with repetitive microtrauma in overhead athletic activities or with single traumatic events. Rotator cuff tears are seen throughout the range of skeletal maturity, often coexist with labral tears and typically are found in athletes.

Feasibility of ultrashort TE (UTE) imaging of children at 1.5 T.

Ultrashort TE (UTE) is a relatively new MRI technique that allows for the visualization of tissue structures with short T2 components that show little or no signal on all conventional MR imaging sequences. This technique, to the best of our knowledge, has been described only in adults and uses a half excitation pulse and radial k-space data acquisition to produce echo times of less than 100 microseconds with no need for additional hardware modifications. We describe the feasibility of using a 2-D UTE sequence in vivo on a routine 1.5 T clinical MR scanner to depict various musculoskeletal structures in children.

Juvenile osteochondritis dissecans: is it a growth disturbance of the secondary physis of the epiphysis?

OBJECTIVE: The primary physis is responsible for longitudinal bone growth. Similarly, epiphysial growth relies on endochondral ossification from the circumferential secondary physeal [corrected]. injury can result in disruption of normal ossification. The cause of juvenile osteochondritis dissecans (OCD) remains elusive. We hypothesized that juvenile OCD results from an insult affecting endochondral ossification from the secondary physis. The purpose of our study was to evaluate the MRI appearance of the distal femoral epiphysis-particularly the secondary physis-of children with juvenile OCD and to compare these findings with the MRI findings of unaffected children. MATERIALS AND METHODS: Knee MRI examinations of 30 children (age range, 8 years 8 months to 13 years 4 months) with OCD and 30 matched control patients were evaluated for skeletal maturity; location of the OCD lesion, if present; secondary physeal [corrected] continuity; overlying chondroepiphysial integrity, contour, and width; signal intensity of subchondral bone; and secondary physeal [corrected] conspicuity. Variables were compared using chi-square tests. RESULTS: All children were skeletally immature. Condylar lesions were medial in 24 knees and lateral in six knees. All were in the middle one third, posterior one third, or middle and posterior thirds in the sagittal plane. The majority of lesions spanned the intercondylar and middle one third of the femoral condyle in the coronal plane (73%). There was a significant difference between secondary physeal [corrected] disruption in juvenile OCD condyles compared with unaffected condyles (p < 0.001) and control condyles (p < 0.001). Compared with unaffected and control condyles, the OCD group showed chondroepiphysial widening (p < 0.001) and subchondral bone edema (p < 0.001) on MRI. Neither chondroepiphysial integrity nor chondroepiphysial contour was significantly different between groups (p = 0.21, p = 0.31, respectively). CONCLUSION: MRI of children with OCD consistently showed secondary physis disruption, overlying chondroepiphysial widening, and subchondral bone edema. We suggest that disruption of normal endochondral ossification may be associated with juvenile OCD.

MRI of displaced meniscal fragments.

A torn meniscus frequently requires surgical fixation or debridement as definitive treatment. Meniscal tears with associated fragment displacement, such as bucket handle and flap tears, can be difficult to recognize and accurately describe on MRI, and displaced fragments can be challenging to identify at surgery. A displaced meniscal fragment can be obscured by synovium or be in a location not usually evaluated at arthroscopy. We present a pictorial essay of meniscal tears with displaced fragments in patients referred to a pediatric hospital in order to increase recognition and accurate interpretation by the radiologist, who in turn can help assist the surgeon in planning appropriate therapy.

MRI of radiographically occult ischial apophyseal avulsions.

BACKGROUND: Acute avulsions of unossified ischial apophyses in children may go undetected on radiography. Therapy includes rest and rehabilitation; however, substantial displacement may require surgery. OBJECTIVE: Our purpose is to illustrate the utility of MRI in the detection of these radiographically occult injuries in skeletally immature children. MATERIALS AND METHODS: This retrospective study of more than 5 years included children with ischial avulsions who were evaluated with both radiography and MRI within 3 weeks of acute injury. Initially, radiographs were reviewed to identify those children with unossified ischial apophyses. Subsequently, their MRI examinations were assessed for physeal disruption, bone/soft tissue edema, periosteal/perichondrial elevation and disruption. Initial and follow-up radiographs (if available) were reviewed. Patient age, symptoms and offending activity were determined from clinical records. RESULTS: Five children met inclusion criteria. All initial radiographs were normal. MRI showed: edema (n = 5), periosteal elevation (n = 4), periosteal/perichondrial disruption (n = 4), >5.5 mm displacement (n = 0). Follow-up radiographs in two children (2 and 2.5 months from MRI) showed osseous ischial irregularity. The apophyses remained unossified. CONCLUSIONS: Acute unossified ischial apophyseal avulsions in children may be radiographically undetected. In the setting of correlative clinical symptoms, MRI can be used to identify these injuries and to help direct appropriate therapy.

The reliability to determine "healing" in osteochondritis dissecans from radiographic assessment.

BACKGROUND: Current literature supporting treatment strategies for osteochondritis dissecans (OCD) has limited prognostic utility. Presently, there is no gold standard for an OCD "healing" outcome. Accurate and reliable determination of the OCD healed status on the basis of radiographs would be valuable to provide a guide for evidence-based treatment of OCD. The purpose of this study was to determine interrater and intrarater reliability of radiographic assessment of OCD lesion healing in the knee. METHODS: A hospital database identified 39 consecutive patients with OCD in 42 knees, who were treated conservatively for at least 6 months. Patients were an average age of 11.9 years (±2.4 y). A total of 102 presentation slides were prepared, each containing 2 similar radiographic views from the same patient taken 6 months (±1 mo) apart. These slides were then categorized by 4 reviewers (1 orthopaedic surgeon, 1 orthopaedic fellow, and 2 musculoskeletal radiologists) blinded to patient data, as healed, not healed, or unable to evaluate the OCD lesion. Reviewers repeated their assessment at a minimum of 3 weeks after their first read. Intrarater and interrater reliability were measured with the Cohen κ coefficient and Randolph's free-marginal multirater κ, respectively, and with the percent agreement. RESULTS: OCD lesion categorization demonstrated insufficient interrater reliability with a κ of 0.44 and 63% agreement. The notch view had the highest interrater reliability with a κ of 0.63% and 76% agreement, and the lateral view had the lowest interrater reliability with a κ of 0.29% and 53% agreement. The OCD lesion categorization demonstrated substantial intrarater reliability with a κ of 0.68% and 81% agreement. CONCLUSIONS: Reviewers did not consistently agree on the "healing" status of the OCD lesions on the basis of radiographic assessments. Standard criteria to assess healing are needed to consistently evaluate OCD knee lesions in children. LEVEL OF EVIDENCE: Not applicable.

Return-to-sport quadriceps strength symmetry impacts 5-year cartilage integrity after anterior cruciate ligament reconstruction: A preliminary analysis.

Quadriceps femoris strength asymmetry at the time of return to sports participation after anterior cruciate ligament (ACL) reconstruction contributes to worse function and asymmetric landing patterns, but the impact on longitudinal outcomes is not known. This study determined if young athletes after ACL reconstruction with quadriceps femoris strength asymmetry at a return to sports clearance would demonstrate markers of knee cartilage degeneration 5 years later compared to those with symmetric quadriceps femoris strength at return to sports. Participants (n = 27) were enrolled at the time of medical clearance for sports participation (baseline testing) and followed for 5 years. At baseline, quadriceps femoris strength was measured bilaterally and a limb symmetry index was used to divide the cohort into two groups: return to sport clearance with high quadriceps femoris strength (RTS-HQ; limb symmetry index ≥ 90%) and return to sport clearance with low quadriceps femoris strength (RTS-LQ; limb symmetry index < 85%). At 5 years post-baseline, quantitative magnetic resonance imaging (T2 relaxation times (ms): involved knee medial/lateral femoral condyle and tibial plateau) data were collected. Group differences were evaluated with independent samples t tests. At 5 years post-return to sports, the RTS-LQ strength group (n = 14) demonstrated elevated T2 relaxation times at the anterior region of the lateral femoral condyle compared to the RTS-HQ strength group (n = 13). Clinical Significance: Just over 50% of this cohort was cleared for sports participation with involved limb quadriceps femoris strength deficits that may contribute to early markers of knee cartilage degeneration within the subsequent 5 years.

Descriptive Epidemiology From the Research in Osteochondritis Dissecans of the Knee (ROCK) Prospective Cohort.

BACKGROUND: Osteochondritis dissecans (OCD) occurs most commonly in the knees of young individuals. This condition is known to cause pain and discomfort in the knee and can lead to disability and early knee osteoarthritis. The cause is not well understood, and treatment plans are not well delineated. The Research in Osteochondritis Dissecans of the Knee (ROCK) group established a multicenter, prospective cohort to better understand this disease. PURPOSE: To provide a baseline report of the ROCK multicenter prospective cohort and present a descriptive analysis of baseline data for patient characteristics, lesion characteristics, and clinical findings of the first 1000 cases enrolled into the prospective cohort. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Patients were recruited from centers throughout the United States. Baseline data were obtained for patient characteristics, sports participation, patient-reported measures of functional capabilities and limitations, physical examination, diagnostic imaging results, and initial treatment plan. Descriptive statistics were completed for all outcomes of interest. RESULTS: As of November 2020, a total of 27 orthopaedic surgeons from 17 institutions had enrolled 1004 knees with OCD, representing 903 patients (68.9% males; median age, 13.1 years; range, 6.3-25.4 years), into the prospective cohort. Lesions were located on the medial femoral condyle (66.2%), lateral femoral condyle (18.1%), trochlea (9.5%), patella (6.0%), and tibial plateau (0.2%). Most cases involved multisport athletes (68.1%), with the most common primary sport being basketball for males (27.3% of cases) and soccer for females (27.6% of cases). The median Pediatric International Knee Documentation Committee (Pedi-IKCD) score was 59.9 (IQR, 45.6-73.9), and the median Pediatric Functional Activity Brief Scale (Pedi-FABS) score was 21.0 (IQR, 5.0-28.0). Initial treatments were surgical intervention (55.4%) and activity restriction (44.0%). When surgery was performed, surgeons deemed the lesion to be stable at intraoperative assessment in 48.1% of cases. CONCLUSION: The multicenter ROCK group has been able to enroll the largest knee OCD cohort to date. This information is being used to further understand the pathology of OCD, including its cause, associated comorbidities, and initial presentation and symptoms. The cohort having been established is now being followed longitudinally to better define and elucidate the best treatment algorithms based on these presenting signs and symptoms.

Focal Periphyseal Edema (FOPE) zone on MRI of the adolescent knee: a potentially painful manifestation of physiologic physeal fusion?

OBJECTIVE: We have termed an MRI finding in the knees of adolescents characterized by a focal bone marrow edema pattern centered about the closing physis a "FOPE"-that is, focal periphyseal edema-zone. The cause of this appearance is unknown. Therefore, the purpose of this article is to review the MRI appearance of the FOPE zone and to postulate a causative mechanism. MATERIALS AND METHODS: FOPE zones were identified on knee MRI examinations performed for pain in 12 patients (seven girls, five boys; age range, 11 years 9 months-15 years 8 months); the examinations were collected over 5 years. Clinical history, skeletal maturity, size and location of FOPE zone, and concomitant ipsilateral knee abnormalities were recorded at presentation and on follow-up MRI examinations when available. Bone ages were estimated from knee radiographs using published standards. RESULTS: Fifteen FOPE zones measuring 2-27 mm were identified: eight were femoral; six, tibial; and one, fibular. All were centrally located. All physes were patent, albeit narrowed. The radiographic appearance of the physes was similar for both sexes. All patients with estimated bone ages of 11 and 12 years were girls. Two other girls had bone ages closer to 14 years, whereas all boys had estimated bone ages of 13 or 14 years. CONCLUSION: On knee MRI, a FOPE zone can be seen in adolescents and likely relates to the early stages of physiologic physeal closure. It may be associated with pain particularly when no other MRI abnormalities are present. When the characteristic appearance of a FOPE zone is observed on MRI, we suggest that it not be mistaken for an abnormality, requires no invasive diagnostic procedure, and does not need imaging follow-up.