Histological examination of both specimens showed a subchondral crack, fibrous granulation, and osteoid formation, but no evidence of antecedent osteonecrosis ( Figure 5).
Osteotomy of the MFC and MTP resulted in complete excision of the lesions. Softening of the subchondral bone at the affected site was observed. Parts of the cartilage layers at the affected sites of both the MFC and the MTP obtained during macroscopic UKA had delaminated from the underlying subchondral bone and easily yielded to pressure. Intraoperative examination showed that the articular cartilage at the lesion site in the MFC was smooth but slightly depressed, whereas the cartilage at the lesion site in the MTP had no abrasions and slight fibrillation and was depressed about 1 mm ( Figure 4). UKA was chosen because the prosthesis would be stabilized. Because of the persistence of knee pain and the progressive course of his disease, as shown by imaging results, unicompartmental knee arthroplasty (UKA) was performed. (a) Coronal SPIR and (b) sagittal proton density-weighted images showed persistent focal SPONK lesions of both the MFC and the MTP, but the surrounding bone edema had decreased (arrow).ĭespite treatment injections of hyaluronan and oral administration of nonsteroidal anti-inflammatory drug, the patient's symptoms did not improve. Initial nonsurgical treatment included restricted weight bearing on the affected lower leg. The patient was diagnosed with SPONK on both sides of the medial compartment. T1-weighted images showed corresponding focal low intensity lesions ( Figure 2(b)), with a horizontal tear present in the medial meniscus at the posterior horn. Short inversion time inversion recovery (STIR) MRI showed characteristic focal high intensity with band-like low signal intensity portions in the subchondral areas of both the MFC and the MTP, surrounded by diffuse high signal intensity ( Figure 2(a)). Plain radiographs revealed slight subchondral bone sclerosis on the tibial medial condyle, but the lesion was not radiolucent and there was no evidence of joint space narrowing (Figures 1(a) and 1(b)).
Physical examination showed tenderness at the medial femoral condyle and medial tibial condyle and slight limitations in the range of motion of the knee.
He had no history of previous trauma, meniscus surgery, steroid treatment, or excessive alcohol use. Severe pain continued for 6 months and did not improve. He described a sudden onset of severe pain localized to the medial aspect of his left knee. His previous medical history included coronary artery bypass surgery (CABG) in 2004 after a myocardial infarction. This condition was diagnosed on MRI soon after symptom onset.Ī 72-year-old man presented for evaluation of left knee pain of one-month duration. This report describes a very rare case of SPONK simultaneously involving the MFC and the MTP and associated with subchondral insufficiency fractures. Magnetic resonance imaging (MRI) can detect early changes in the subchondral area and assist in the diagnosis of SPONK. Early diagnosis of SPONK is difficult because plain radiographs may be negative, especially if the symptoms are of short duration. Involvement of the MTP is observed in only 2% of knees with SPONK, whereas early concomitant involvement of the MFC and the adjacent MTP is very rare.Īlthough the etiology of SPONK remains unclear, it may be due to vascular injury and/or antecedent trauma, although a recent report suggested that SPONK may result from subchondral insufficiency fractures. SPONK may also occur in the lateral femoral condyle, medial tibial plateau (MTP), or patella. Secondary osteonecrosis is usually observed in younger patients and involves multiple condyles, whereas SPONK usually develops suddenly in the medial femoral condyle (MFC) of patients aged >55 years. Osteonecrosis of the knee can be categorized as primary spontaneous osteonecrosis of the knee (SPONK) or secondary osteonecrosis of the knee associated with a variety of risk factors including use of steroids or alcohol.
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