A better understanding of the revascularization process during Legg-Calvé-Perthes disease has been desired for decades by many pediatric orthopaedic surgeons who have been seeking to improve on the natural history of the disease but have been limited in their ability to determine the prognosis of the disease on the basis of the initial radiographic appearance. Contrast-enhanced magnetic resonance imaging (MRI) in the initial stage of Legg-Calvé-Perthes disease has shown promise as a prognostic indicator of outcome. This interesting paper by Kim et al. focuses on the rate and patterns of revascularization of femoral heads in the active stage of Legg-Calvé-Perthes disease using serial perfusion MRI, shedding light on this important topic.
Serial perfusion MRI is a relatively new tool with which to better understand the process of revascularization after osteonecrosis in Legg-Calvé-Perthes disease. Building upon previous findings is the best way to arrive at a better understanding of any process. Although bone scintigraphy has been used previously to determine different revascularization patterns1,2, perfusion MRI is a better imaging modality for the visualization of the vascular events taking place during Legg-Calvé-Perthes disease.
In the study by Kim et al., 30 hips with Legg-Calvé-Perthes disease were evaluated using serial MRI. The first MRI was acquired during the initial fragmentation stage, and the subsequent MRIs were obtained at different time intervals. The primary reason for obtaining the MRIs was for the research for the study; they were not part of the clinical care. Although the MRIs provided very interesting information, it is likely that few health-care systems would allow serial MRI without a clinical reason for obtaining them; there is still some question as to the safety of the repeated sedation required for most children undergoing MRI. Also, there is not enough evidence to warrant obtaining serial MRIs as they do not change the decisions made about treatment.
Kim et al. did not evaluate the effect of treatment, although 15 of the hips were treated conservatively and 15 underwent a number of different surgical procedures. Regardless of the clinical outcomes, the main objective of this study was to evaluate the rate and pattern of revascularization of the femoral head. Revascularization was determined to occur in a similar fashion among all of the patients: it converged toward the anterocentral region of the epiphysis from the posterior, lateral, and medial aspects in a horseshoe-shaped pattern, and the anterocentral area of the epiphysis was the last region to show revascularization.
This is the key finding of this study, although many questions remain. Other authors have attempted to determine the source of vessel ingrowth, finding that the lateral epiphyseal arteries reliably insert on the posterior-superior aspect of the femoral neck from a superior-anterior to a superior-posterior position3. The pattern observed in this study supports the claim that the new vessels arise from the femoral neck and traverse through the margin of the articular epiphyseal cartilage to reach the periphery, and do not arise from metaphyseal vessels penetrating the proximal femoral physis. This will have important implications for surgical treatment as safe surgical dislocation is applied more frequently in this group of patients. It would also seem that physeal drilling is a less physiologic approach to trying to improve vascularization than somehow improving the peripheral vasculature.
An interesting finding of this study was that no hip showed a pattern consistent with repeated ischemia, which has been implicated as one of the reasons for being unable to determine prognosis on the basis of initial presentation. The finding of an MRI pattern that is predictive of the final outcome in Legg-Calvé-Perthes disease in this study has potential for improving our prognostic abilities. Indeed, it has been the “Holy Grail” for pediatric orthopaedic surgeons treating this condition, who have been very limited in their ability to accurately predict the course of the disease even when patients present at this initial stage; more often than not, patients present during a more advanced stage, at which point it becomes debatable whether treatment actually has a positive effect on the natural history. More studies like the present one will allow us to better understand when treatment may in fact improve the final result.
The authors note that serial MRI is not a part of their clinical routine practice, and they cannot make recommendations on weight-bearing or treatment decisions based on the changes seen on the serial MRI images. They simply are adding to the mounting volume of knowledge about the revascularization of the proximal femoral epiphysis after an ischemic event such as Legg-Calvé-Perthes disease.
All good research should generate more research questions, and this is the case with this study, which should encourage pediatric orthopaedic surgeons to continue to look for biologic solutions for this relatively common disease, instead of focusing on mechanical treatments that have not provided a long-term solution.
↵* The author indicated that no external funding was received for any aspect of this work. The Disclosure of Potential Conflicts of Interest form is provided with the online version of the article.
- Copyright © 2016 by The Journal of Bone and Joint Surgery, Incorporated