An adolescent female softball player presented with gradually worsening right anterior knee pain and knee stiffness of several months duration. She had focal tenderness in the right infrapatellar region on palpation and mild pain during knee flexion. Initial radiographs of the right knee (Figure 1) were interpreted as normal. The patient was treated with a presumed diagnosis of patellar tendinitis and instructed to undergo a brief period of rest followed by physical therapy with gradual return to normal activity.
She returned 9 months later with persistent anterior right knee pain and mild knee pain with deep knee flexion. At this time, mild medial joint line tenderness was also elicited on palpation. Due to the medial joint line tenderness, a right knee MRI was performed to assess for medial meniscal pathology. A 1.6 x 1.4 cm osteochondral lesion of the medial femoral condyle was identified on MRI with mild marrow edema and cystic change at the interface between the osteochondral lesion and femoral condyle (Figure 2). There was no defect in the overlying cartilage or fluid-like signal at the interface of the osteochondral lesion and femoral condyle. The remainder of the MRI exam was normal.
The patient's medial joint line pain improved, but she continued to have mild anterior knee pain. A repeated MRI of the right knee was performed 6 months after the initial MRI to assess for changes in the osteochondral lesion. MRI of the left knee was performed at the same time due to the patient complaining of vague anterior left knee pain similar to the presenting right knee pain, which raised clinical concern for an occult osteochondral lesion of the left knee. She was at chronologic age of 13 years and 3 months at the time of the bilateral knee MRI. The osteochondral lesion of the right medial femoral condyle was unchanged in appearance between the two MRI exams (Figure 3). However, in the interim, a 9 mm focal periphyseal edema (FOPE) zone developed in the anterolateral aspect of the central proximal right tibia (Figure 4). A similar appearing 13 mm FOPE zone was present in the anterior aspect of the central proximal left tibia on the left knee MRI (Figures 5 and 6). While the distribution of FOPE zone periphyseal edema was equal on the epiphyseal and metaphyseal sides of the proximal right tibia, the periphyseal edema was more exuberant on the epiphyseal side of the proximal left tibia. The remainder of the left knee MRI was normal. The proximal tibial physis was narrowed, but open, bilaterally.
It was uncertain whether the patient's bilateral anterior knee pain was due to the FOPE zones or another etiology not elucidated on the MRI. However, the patient pain resolved after a several-week period of rest. She was released to continue activity as tolerated with instruction to return if pain increased. She did not return for follow-up.