Atraumatic osteonecrosis of the knee

Background: The purposes of this study were to define the clinical, demogra phic, and radiographic patterns of atraumatic osteonecrosis of the distal p art of the femur and the proximal part of the tibia at presentation and to report the outcome of treatment of this condition. Methods: Two hundred and forty-eight knees in 136 patients who were younger than the age of fifty-five years were treated at our institution between J uly 1, 1974, and September 15, 1998, for atraumatic osteonecrosis of the di stal part of the femur or the proximal part of the tibia, or both. Demograp hic and radiographic features were characterized. The results of nonoperati ve treatment, core decompression, arthroscopic debridement, and total knee arthroplasty were evaluated. Results: There were 106 female patients and thirty male patients, and their mean age was thirty-six years (range, fifteen to fifty-four years) at the time of diagnosis. One hundred and one patients (74 percent) had involvemen t of other large joints, with eighteen (13 percent) presenting initially wi th knee symptoms. One hundred and one patients (74 percent) had a disease t hat affected the immune system; sixty-seven of them had systemic lupus eryt hematosus. One hundred and twenty-three patients (90 percent) had a history of corticosteroid use. Technetium-99m bone-scanning missed lesions in sixt een (29 percent) of fifty-six knees. Eight (20 percent) of forty-one initia lly symptomatic knees treated nonoperatively had a successful clinical outc ome (a Knee Society score of at least 80 points and no additional surgery) at a mean of eight years. The knees that remained severely symptomatic for three months were treated with either core decompression (ninety-one knees) or total knee arthroplasty (seven knees). Seventy-two (79 percent) of the ninety-one knees treated with core decompression had a good or excellent cl inical outcome at a mean of seven years. Efforts to avoid total knee arthro plasty with repeat core decompression or arthroscopic debridement led to a successful outcome in fifteen (60 percent) of twenty-five knees. Thirty-fou r (71 percent) of forty-eight knees treated with total knee arthroplasty ha d a successful clinical outcome at a mean of nine years. Conclusions: Atraumatic osteonecrosis of the knee predominantly affects wom en, and in our study it was associated with corticosteroid use in 90 percen t of the patients. Evaluation should include standard radiographic and magn etic resonance imaging of all symptomatic joints. Prognosis was negatively related to large juxta-articular lesions. Nonoperative treatment should be reserved for asymptomatic knees only. Core decompression was successful (a Knee Society score of at least 80 points and no additional surgery) in 79 p ercent of the knees in which the disease was in an early stage. Total knee arthroplasty was successful in only 71 percent of the knees.