Do We Need Another Gold Standard to Assess Acute Legg-Calvé-Perthes Disease?

Commentary In their article, Kim et al. concluded that they could use perfusion magnetic resonance imaging (MRI) to identify the extent/location of the femoral head ischemic process at an earlier sclerotic stage of Legg-Calvé-Perthes disease than typically would be possible with conventional radiographs1. Their MRI scans showed both the location and the extent of head involvement. The authors suggest that, by utilizing perfusion MRI, they could perform their choice of containment osteotomy (proximal femoral osteotomy) earlier in the course of the disease on selected patients (lateral pillar groups B and B/C according to the classification of Herring et al.). They speculated that if surgeons did not have to “wait to classify” (as they seemingly find necessary with conventional radiography), there would be less risk of collapse (while waiting). Perfusion scans identify epiphyseal blood flow at a single point in time; thus, conceivably perfusion scans of the same epiphysis performed days earlier or later might not show the same blood flow patterns. In other words, different perfusion scans may show different blood flow patterns for the same femoral head if one scan was performed during the sclerosis stage and the other, during fragmentation. Kim et al. have not proven that an MRI perfusion scan at any one point in time is (or is not) a valid determinant of the eventual location/extent of the femoral head necrosis. Approximately 40% of their patients underwent the MRI perfusion scan when the disease was in Waldenström stage IIa. Certainly, by that time, the extent of femoral head involvement would be identifiable on radiographs, obviating the need for sedating a child and performing a perfusion MRI. For those utilizing containment methods other than osteotomy to treat acute Legg-Calvé-Perthes disease, knowing the extent of head involvement is helpful, but it is not essential. Rather, the biggest challenge is effecting optimal containment treatment for all patients, even those with extensive lateral ischemic changes (Herring group C). Nonperfusion (or perfusion) MRI can be helpful in assessing both femoral head pathomorphology and the extent of necrosis. However, MRI is not essential for the timing of containment treatment. Rather, regardless of the stage of disease with which the patient presents, obtaining and maintaining a functional range of motion is the most critical factor in optimizing outcome1. Kim et al. suggested that the use of perfusion MRI will be helpful to them in both early selection of patients and optimizing the outcome of those selected patients with containment treatment with a femoral osteotomy. There is no conclusive evidence in the literature that containment treatment by femoral (or pelvic) osteotomy is better than non-osteotomy containment methods. In fact, what comparative evidence there is suggests that a non-osteotomy containment method is more effective than femoral osteotomy in the treatment of both Herring group-B and C hips1. Perfusion MRI may have a place in a clinical research protocol. However, it should not be considered as standard protocol necessary for decision-making in the treatment of Legg-Calvé-Perthes disease. Rather, conventional radiography has been and still is the gold standard for assessing and monitoring the course of treatment of acute Legg-Calvé-Perthes disease.