Subchondral magnetic resonance imaging changes in early osteoarthrosis associated with tibial osteonecrosis

The authors report on 41 patients with acute or subacute knee pain and earl y or midstage degenerative arthrosis with osteonecrotic lesions in the subc hondral and metaphyseal region of the medial proximal tibia. Each lesion wa s identified only on magnetic resonance images (MRI). These MRI changes are classified and the clinical course is defined during a follow-up period av eraging 4.5 years. Radiographically, 22 patients had minimal degenerative c hanges; 12 had moderate arthritis; and 7 were normal. With MRI, 3 distinct types of lesions were identified. Type A lesions had localized areas of dec reased signal in the subchondral area. Type B lesions had diffuse signal ch anges with extension into the metaphysis. Type C lesions had metaphyseal in volvement as well as a marginated serpentine subchondral rim usually associ ated with advanced osteonecrosis. There were 9 type A lesions, 23 type B, a nd 9 type C. At the end of 1 year, 33 patients (80%) had no or mild symptom s, and 8 (20%) had persistent moderate pain. At 4.5-year follow-up, most pa tients had symptoms consistent with progressive osteoarthrosis, 12 patients had severe symptoms (29%), 17 (41%) had mild or moderate symptoms, and onl y 12 (29%) were asymptomatic or had minimal symptoms. The type of MRI chang e seen initially was predictive of prognosis. Only 6 (19%) of the 32 patien ts with type A or B findings had severe symptoms at last follow-up. Six (66 %) of the 9 patients with a type C MRI lesion had severe symptoms or had an operation by last follow-up. Twelve patients had follow-up MRI at a mean 1 5 months (range, 12 to 18 months) after the initial evaluation. The type A and B changes were either absent or significantly reduced. The type C subch ondral marginated rim changes remained but metaphyseal involvement was redu ced. There appears to be a spectrum of tibial subchondral MRI changes assoc iated with sudden onset of medial knee pain in patients with early osteoart hritis of the knee. These changes may be indicative of osteonecrosis. The i nitial MRI classification is useful in predicting prognosis. Recognition of this problem may avoid unnecessary intra-articular surgery.