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Radiology in the Study of Bone Physiology

Posted Sep 30, 2016 Updated Apr 10, 2023
By Michael V. Kushdilian MS , Lauren M. Ladd MD , Richard B. Gunderman MD PhD
9 min read

Rationale and Objectives

In this article, we review the core principles of bone physiology alongside imaging examples that demonstrate such principles.

Materials and Methods

The core principles of bone physiology are reviewed and further solidified with a corresponding abnormal pathophysiologic example. The key principles of bone physiology to be reviewed include the following: (1) formation and growth, (2) maintenance and repair, (3) metabolism and regulation, and (4) neoplastic disease. Lastly, a collection of secondary bone diseases is presented to demonstrate the skeletal manifestations of numerous systemic diseases. With this integrative method, we hope to emphasize the value of using radiology to teach physiology within a clinical context. This is especially relevant now, as many US medical schools undergo curricular reform with more emphasis on integrative interdisciplinary learning. Ultimately, we intend to provide a paradigm for incorporating radiology into the pre-clinical medical curriculum through a review of basic science physiology that underlies key radiographic findings of the skeletal system.

Results

Radiology is known for its role in helping make diagnoses and clinical decisions. However, radiology is also well suited to enhance medical education by offering the ability to visualize physiology in action. This is especially true in skeletal radiology, where radiographic osseous changes represent a wide range of physiological processes. Therefore, skeletal radiology can be a useful tool for illustrating concepts of physiology that underlie the normal and abnormal radiologic appearances of bone.

Conclusion

Radiology is an important but underutilized tool for demonstrating concepts in bone physiology.

Introduction and Background

One of the greatest underappreciated opportunities in medical education is the use of radiologic images to teach the basic medical sciences. Too often, medical students learn such subjects as anatomy, physiology, and pathology from text, diagrams, cadavers, and animal models rather than from living human subjects. Radiology makes it possible to visualize living human structure, function, disease, and injury in ways that can help learners gain a much deeper understanding of the material, creating indelible images that they carry with them into practice for many years. Nonetheless, radiology is underutilized in this regard.

Despite the explosion of diagnostic imaging utilization in clinical practice, estimated to be nearly twice the rate of laboratory and pharmaceutical usage , the role of radiology in medical education has remained stagnant across allopathic and osteopathic medical schools for decades . If available, a formal radiology clerkship is typically offered to medical students as a fourth-year elective, long after the basic science coursework has ended. This approach isolates radiology fromits foundation in the basic sciences and may put students at a disadvantage in their future clinical practices.

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Bone Development and Growth

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Figure 1, X-rays from three different patients show progressive intramembranous ossification in the cranium. (a) Radiolucent fibrous tissue of the coronal ( solid arrows ) and lambdoid ( dashed arrows ) sutures from a 28-day-old. (b) At 6 months of age, sutures have narrowed via osseous replacement. (c) By 13 years of age, the sutures have been completely replaced with bone leaving only thin radiolucent lines.

Figure 2, A benign osteoma of an adult skull on axial computed tomography. Excessive focal osteoid deposition during intramembranous ossification results in a densely calcified osseous prominence in or extending from a membranous bone as shown here at the squamo-mastoid suture line ( arrows ).

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Figure 3, Endochondral ossification in a 4-year-old boy. (a) Normal knee radiograph demonstrates open, lucent physes ( arrowheads ) and secondary ossification centers of the physes ( asterisks ) and patella ( arrow ), which appear radiodense after ossification. (b) T1-weighted sagittal magnetic resonance imaging from the same patient depicts the ossified metaphyses, intermediate signal intensity physeal cartilage ( arrowheads ), and partially ossified epiphyseal ( asterisks ) and patellar ( arrow ) secondary ossification centers. A portion of the unossified secondary ossification center cartilage will remain as articular cartilage.

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Figure 4, Axial computed tomography of an enchondroma in the distal femur of an adult patient. This well-circumscribed lucent lesion in the medial metaphysis ( solid arrows ) displays the classic appearance of chondroid matrix: relatively hypodense with small internal ring-and-arc calcifications ( dashed arrow ). Although it is eccentrically located, there is no significant endosteal scalloping, cortical reaction, or soft tissue mass to suggest a more aggressive malignant cartilage lesion.

Figure 5, A 4-year-old child with Blount's disease. (a) Radiographic long-leg study demonstrates bilateral varus deformities ( dashed arc ). (b) Magnified view of the knee shows the classic “bird's beak” appearance of the proximal metaphysis ( arrow ) as a result of excessive medial compressive force.

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Figure 6, Myositis ossificans adjacent to the proximal femur of a 28-year-old man on axial computed tomography. The inflammatory response within damaged muscle causes deposition of reparative fibrous tissue ( asterisk ) and subsequent peripheral ossification ( arrows ) by a rim of fibroblast-derived osteoblasts.

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Bone Maintenance and Repair

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Figure 7, Osteoporosis in two patients. (a) Hand radiographs of a 65-year-old woman and (b) spine radiographs of a different elderly patient, both of which demonstrate abnormally lucent bones ( asterisks ) and thin cortices ( arrows ) due to demineralization of osteoporosis. Demineralization leads to weak bones that are susceptible to compression fractures (outlined ) as seen in (b) .

Figure 8, Axial computed tomography images of the proximal femora of two 22-year-old men, a professional football player (a) and a nonathlete (b) , demonstrate the chronic adaptation and cortical thickening of bone with anabolic bone remodeling in response to repeated stress (Wolff's law). The athlete's bone (a) demonstrates 50% increase in cortical thickness, which provides greater mechanical strength and injury protection.

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Figure 9, Frontal radiograph of a 3-year-old with osteopetrosis demonstrates densely sclerotic pelvic and proximal femoral bones ( arrows ), replacing the marrow space, and undertubulation (Erlenmeyer flask deformity) of the distal metadiaphysis ( outlined ). As the marrow space is replaced with unopposed bone formation, pancytopenia and organomegaly from extramedullary hematopoiesis often occur.

Figure 10, Pelvis radiograph of a 56-year-old man with Paget's disease of the right hemipelvis. Patchy lucencies are sequelae of the initial osteoclastic activity, followed by a robust osteoblastic response causes coarsening and distortion of the trabeculae ( arrows ) and thickening of the cortex ( outline ).

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Figure 11, Radiographs of primary and secondary fracture repairs. (a–c) A 17-year-old man with a transverse scaphoid waist fracture ( solid arrows ) demonstrating primary fracture repair. The fragments are anatomically aligned (a) , and the fracture gap is bridged directly (b, c) with new woven bone ( dashed arrows ) and without callus formation. (d–f) Secondary fracture repair of a 4-year-old with transverse fractures of the radius and ulna ( solid arrows ). Progressive healing (e) demonstrates new bone formation via ossification of a fibrous callus ( dashed arrows ) to stabilize the fracture. Remodeling continues for months to years after reapproximation, and the medullary cavity and cortices are eventually restored (f) .

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Figure 12, A 66-year-old woman with nonunion of oblique distal tibial and fibular fractures. (a) Radiographs demonstrate a persistent fracture gap, displacement, and angulation with a large nonbridging callus ( arrow ) that has attempted to stabilize the fragments without success. (b) Computed tomography reveals the hypodense, nonossifying fibrous tissue within the fracture gap ( asterisks ).

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Bone Metabolism and Regulation

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Figure 13, Bone resorption and abnormal mineralization in hyperparathyroidism. (a) Radiograph of the index finger shows severe bone resorption of the tufts ( arrow ), or acroosteolysis, in this 32-year-old man. (b) Sagittal computed tomography of the lumbar spine of a 52-year-old man demonstrates linear bands of subchondral endplate sclerosis ( arrows ), known as a “rugger jersey spine,” with alternating bands of lucency ( asterisks ) in the central vertebral bodies due to osteopenia.

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Figure 14, Rickets and osteomalacia. (a) Frontal radiograph from a 3-year-old girl with rickets disease demonstrates diffusely demineralized, radiolucent bones ( asterisks ) with flared metaphyses ( arrows ) due to poorly mineralized osteoid at the periphery of the metaphyses. This also results in pliable bones with resultant lateral bowing (genu varum). (b) Lateral distal femoral radiograph of a 58-year-old demonstrates the radiolucent and bowed appearance of a long bone ( dashed arrows ) from osteomalacia and defective mineralization in a skeletally mature patient.

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Neoplastic Disease

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Figure 15, Frontal radiograph of a chondrosarcoma from an 81-year-old man. There is a large mixed lytic and sclerotic intramedullary lesion with characteristic “ring-and-arc” pattern ( solid arrows ) of chondroid matrix. Unlike the previously described benign chondroid lesion (enchondroma), this lesion is large, spanning the entire medullary space of the mid and distal femoral metadiaphysis. Other notable features include indistinct margins, endosteal scalloping ( dashed arrow ), and periosteal thickening ( arrowheads ).

Figure 16, Two adolescent patients with osteosarcomas. (a) Frontal radiograph of the distal femur with an aggressive periosteal reaction ( arrows ) and “cloudlike” mineralization of osteoid matrix. (b) Nuclear medicine bone scan from the same patient shows intense radiotracer uptake where the malignant cells are producing bone at an accelerated rate. (c) A second patient with another aggressive pattern of periosteal reaction, known as Codman triangle ( dashed arrow ). Note the tumor expansion into adjacent soft tissues ( asterisks ).

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Secondary Disorders of Bone

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Figure 17, A 55-year-old man with a large posterior heel soft tissue ulcer ( solid arrows ) and osteomyelitis of the posterior calcaneal tubercle ( asterisk ) on sagittal Short T1 Inversion Recovery (STIR) MRI. There are abnormal areas of edema appearing as high fluid signal, which is consistent with acute osteomyelitis. Small susceptibility foci are seen in the soft tissues and tracking cranially along the Achilles tendon ( dashed arrows ), which are gas foci indicating extensive spread of soft tissue infection.

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Figure 18, Metastatic bone disease in two patients. (a) Axial computed tomography image of the head in a 73-year-old man with metastatic renal cell cancer. Note that the metastasis has eroded the calvarium, leaving a lytic lesion and an associated soft tissue mass ( arrows ). (b) Sagittal computed tomography of the lumbar spine in a 73-year-old man with multifocal sclerotic lesions ( arrows ) due to the osteoblastic response of prostate cancer metastasizing to bone.

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Figure 19, Hand radiographs from different patients with arthritis. (a) Hand radiograph demonstrates features of osteoarthritis as irregular damage to articular cartilage, resulting in asymmetric joint space loss in the distal interphalangeal joints ( white arrows ), osteophyte formation, and subchondral sclerosis ( black arrows ). (b) Rheumatoid arthritis demonstrates symmetric joint space narrowing with a more proximal distribution ( white arrowheads ). Sequelae of synovial inflammation are seen as periarticular erosions ( arrow ) and osteopenia from hyperemia-stimulated accelerated bone resorption. Ulnar deviation of the phalanges results from subluxation of the metacarpophalangeal joints ( lines ).

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Conclusion

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Academic Radiology, Volume 23, Issue 10
Journals General Radiology
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