Commentary and Perspective   |    
Radiolucent Tissue and the Straight ChildCommentary on an article by Sanjeev Sabharwal, MD, et al.: “Intra-Articular Morphology of the Knee Joint in Children with Blount Disease: A Case-Control Study Using MRI”
David J. Zaleske, MD
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Copyright © 2012 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2012 May 16;94(10):e71 1-2. doi: 10.2106/JBJS.L.00199
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There are many fascinating aspects about treating disorders involving the immature skeleton. The physiology or pathophysiology of radiolucent tissues may make treatment relatively straightforward or quite complicated for both patient and surgeon. The activities of cells in the epiphysis or physis, in the periosteum, and within the joint space change as growth occurs. A diaphyseal fracture generally presents fewer problems if the patient is younger, whereas a physeal fracture that has injured proliferating cartilage early in growth may require multiple surgical interventions. Furthermore, these cell populations are markedly influenced by mechanical force. An otherwise normal epiphysis in a developmentally dysplastic hip will not function appropriately if the hip remains dislocated or subluxated, yet if the hip dysplasia is detected early and the femoral head is relocated for a period of growth, the hip can be restored to a normal developmental trajectory.
The ability to image radiolucent cell populations is a tremendous asset to the surgeon in guiding therapy. In the example of developmental hip dysplasia, ultrasonography is particularly valuable before the secondary center of ossification develops to the stage at which it occupies a large part of the proximal femoral epiphysis. When applicable, ultrasonography is extremely helpful in establishing a diagnosis and measuring response to treatment. Magnetic resonance imaging (MRI) gives the ability to image these cell populations throughout growth.
Blount disease is a prototypical condition in which growth inhibition and alteration of the local mechanical environment are associated. There clearly is abnormal growth at the proximal posteromedial aspect of the tibia, and (depending on severity of the condition) other sites of maladaptive growth may also exist, such as at the distal aspect of the femur. This can lead to images made with use of conventional radiography in which the ossified part of the medial proximal tibial epiphysis is inferior to the relatively unaffected lateral aspect—i.e., it appears “depressed.”
In their study, Sabharwal et al. made specific measurements of radiolucent tissues in the medial compartment of the knee. They were able to conclude that “compared with the control group, children with Blount disease had a thicker unossified proximal medial tibial epiphysis, a thicker and wider medial meniscus, and a greater frequency of abnormal MRI signals in the medial meniscus, especially affecting the posterior horn.” Such measurements are a welcome addition to the literature. As the authors note, there have been a variety of opinions about the nature of these tissues and about how best to address the abnormal mechanics in children with Blount disease. One particular controversy has involved the indication for an intra-epiphyseal osteotomy as well as a proximal tibial metaphyseal osteotomy. Further studies using MRI (as in this paper) to assess the effects of procedures on the medial compartment tissues and their relation to outcomes are needed to provide even better evidence to guide treatment. The authors are to be congratulated for adding data helpful to the pursuit of this goal. Extending MRI analysis in Blount disease to the physis, measuring the anatomical response to treatment, and correlating the response with clinical outcome would be further additions that would aid clinicians and their patients.
In any clinical entity, the quest for a better treatment that leads to an improved outcome for the patient is best fulfilled when the primary etiology is established and the pathophysiology is rectified. There are many conditions involving altered growth of the immature skeleton. We have come a long way in understanding the function of the various cell populations of the skeleton and ameliorating the effects of growth disturbances in many clinical conditions1. Before we can directly address the primary causes of most disturbances of growth, we will need to restore the affected stem cell populations to normal function. We have “miles to go before [we] sleep.”2 But, who wants to sleep in exciting times for scientific progress…such as now?
Blount  WP;  Clark  GR. Control of bone growth by epiphyseal stapling; a preliminary report. J Bone Joint Surg Am.  1949;31:464-78.
Frost  R.  Stopping by woods on a snowy evening. 1923.

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Blount  WP;  Clark  GR. Control of bone growth by epiphyseal stapling; a preliminary report. J Bone Joint Surg Am.  1949;31:464-78.
Frost  R.  Stopping by woods on a snowy evening. 1923.
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