Imaging Around the Ends of Bones

Radiology, probably more than most other disciplines, depends on interfacing with clinical patient care, basic science, and technical developments. To make a sustained valuable contribution, radiologists must understand and consider the needs as well as integrate the perspectives of their related disciplines.

These aspects are certainly molded by our working environment, be it a specialized center with a rigid frame of referrals, a higher share of pre-diagnosed diseases, or the need for very specific in-depth analysis and follow-up. Or perhaps it is a situation that has to cover a broad disease spectrum and rather must focus on identifying or separating classes of pathologies from normal and hence influence the orientation of the subsequent work-up and care for a particular patient.

The theme of this issue, imaging around the ends of bones, makes a contribution in the background of our daily routine work. In a considerable number of patients, we come across imaging findings where we are not certain about their clinical significance, pathophysiology, or etiology. Sometimes we are simply not sure about the extent of our knowledge and whether we can derive answers to clinical questions from our images.

This situation may also relate to findings we see so often (e.g., the alignment of physes or the configuration of vertebral end plates or plicae). We may automatically, almost subconsciously, check these as “grossly normal,” that is, without major pathology, but where we would probably have a hard time to specify or exclude those (sometimes subtle) variations related to the patient's symptoms and relevant to the treating physician.

Conversely, findings that are obviously pathologic, such as bone marrow edema syndrome (BMES) or suspected osteonecrosis, may also leave us wanting more clues about their precise etiology, further work-up, prognosis, and treatment options.

This issue of Seminars also brings in the perspectives of some of the related disciplines: anatomy, pediatric orthopaedic surgery, and pediatric radiology, as well as the approaches of colleagues from various radiologic working environments: university and teaching hospitals, specialized orthopaedic hospitals, and private practice.

Putz and colleagues offer their perspective from life experience and scientific discourse in macroscopic and microscopic anatomy and biomechanics. They illustrate how, literally bones, their ends and growth plates, evolve, and how this evolution is modulated by the local biomechanical environment—why they look they way they do. Some anatomical details easily explain day-to-day questions, such as vascular ingrowth into the cartilage model as a prerequisite for ossification. Or how the location of the proliferative stem cell reservoir at the epiphyseal end of the growth plate relates to the prognosis of physeal fractures in the pediatric patient. Of great help for day-to-day practical work is the list of appearances and fusions of the various ossification centers.

Form follows function. The locally acting forces determine skeletal development, that is, shape, alignment, and internal structure of bones, and hence are reflected by imaging. This concept is at the core of the approach of the pediatric orthopaedic surgeon too. It is both fascinating and logical to see Heimkes et al identify epiphyseal growth plate overuse as a risk factor for developing a cam deformity or to see varus/valgus hip alignment creating a deep/shallow acetabular groove with eccentric loading and wear patterns.

Vertebral end plates are not fundamentally different from epiphyses in other locations of the skeleton. Gersing and colleagues review the framework into which the various abnormalities can be classified according to age of manifestation and etiology. For example, they illustrate how a limbus vertebra comes about as a small remnant of local failure of ossification and that in itself, as a single entity, it should not be considered symptomatic. But when several such limbus vertebrae are seen together with multiple Schmorl's nodes, other end-plate irregularities, and a change in vertebral body shape, they are indicative of Scheuermann's disease.

Marc Steinborn, a pediatric radiologist, and Christian Glaser emphasize the development of the skeleton as a sequence over time, serving as a guide through the typical manifestations and time points of bone development and its disturbances. These include chondrification, segmentation, enchondral ossification, and, lastly, the appearance of secondary ossification centers with all the apophyses, accessory ossicles, and sesamoids.

In their article on the hand and wrist, Mespreuve et al describe their concise systematic approach from the topographic distribution and location of variants, pathologies, and potentially associated symptoms. They recommend bone marrow edema as a valuable finding indicative of altered mechanics and alerting the radiologist to likely clinically relevant abnormalities.

Osteonecroses are dreaded for their often detrimental consequences, not only for the affected bone but also for the joint as a whole. Schmitt et al delve deep into the pathophysiology and explain the three-layer concept of osteonecrosis, its imaging manifestation in the most commonly affected bones, and the combined use of magnetic resonance (MR) imaging and computed tomography in their work-up. It is often just a tiny piece of background knowledge, such as the relatively high susceptibility of osteoclasts to ischemia explaining sclerosis in necrotic bone, that helps us internalize the expected imaging evolution of a disease and establish our search pattern.

Conversely, in (idiopathic) BMES, although common in the lower extremity, our approach is still mostly descriptive and based on excluding other entities. As Wolfgang Fischer in his take on BMES and other (sub)chondral abnormalities points out, our understanding of etiology and pathophysiology is limited, and we should know and respect these limitations in our knowledge.

Wong and Lalam discuss the relevant image-related and clinical information on plicae, providing a base to integrate these into our personal frame of knowledge for routine clinical work. This is all the more relevant because plicae, similar to osteoid osteoma, for example, are an entity a bit off the mainstream, and we have to think of them actively to be able to suggest their diagnosis in the appropriate setting.

Cartilage as a major player in the pathogenesis of osteoarthritis, and its imaging has received much attention in this and the past decade. The contribution from Alizai and colleagues reaches out from clinical MR imaging of cartilage to select semiquantitative scores in osteoarthritis trials and discusses some potential risk factors identified for the presence, severity, and progression of cartilage damage. The authors end with an outlook on the current results of quantitative parametric imaging of cartilage and complete the circle of articles in this issue.

I would like to express my sincere thanks to all authors for taking the time and effort to create this issue. I also want to thank the editors in chief, Laura Bancroft and Phil Robinson, and the board for inviting me to contribute and, together with all the people from Thieme, for supporting me during the preparation of this issue.

This issue cannot and certainly should not claim to be comprehensive in view of the topic but rather contribute to creating our own individual framework for image interpretation and a red line guiding through image analysis.

I sincerely hope that whether you are an interested young colleague, an experienced musculoskeletal radiologist, or belong to one of radiology's close disciplines, that you will find it a pleasure to read through this issue's articles and maybe find some interesting piece of information, imaging pearl, or reference for further reading.