Skeletal dysplasia encompasses a heterogeneous group of over 400 genetic disorders. They are individually rare, but collectively rather common with an approximate incidence of 1/5000. Thus, radiologists occasionally encounter skeletal dysplasias in their daily practices, and the topic is commonly brought up in radiology board examinations across the world. However, many radiologists and trainees struggle with this issue because of the lack of proper resources. The radiological diagnosis of skeletal dysplasias primarily rests on pattern recognition—a method that is often called the “Aunt Minnie” approach. Most skeletal dysplasias have an identifiable pattern of skeletal changes composed of unique findings and even pathognomonic findings. Thus, skeletal dysplasias are the best example to which the Aunt Minnie approach is readily applicable.

Discitis/ Osteomyelitis is an inflammatory process involving an intervertebral disc and the adjacent vertebral bodies. Infection is the most common cause of discitis, which is often spontaneous and hematogenous in origin. However, many noninfectious processes affecting the spine such as pseudarthrosis in ankylosing spondylitis, amyloidosis, destructive spondyloarthropathy of hemodialysis, Modic changes type 1, neuropathic arthropathy, calcium pyrophosphate dehydrate (CPPD) spondyloarthropathy and gout can mimic infectious discitis/ osteomyelitis. To determine whether a particular patient's spinal process is due to an infectious versus non-infectious cause can be challenging. Although clinical findings and laboratory studies including erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) can be helpful in the diagnosis of bacterial discitis/osteomyelitis due to their high sensitivity; however, their specificity is low. Moreover, both the infectious and non-infectious discitis can appear quite similar on the imaging studies. We present two cases of thoracic discitis with adjacent vertebral osteomyelitis of probable non-infectious etiology. Both were managed with instrumented fusion for stabilization. We also discuss a range of noninfectious causes of discitis/spondylitis and their radiological features which can help differentiate from infectious processes.

Background Meniscal tears, specifically lateral meniscal tears, have a larger than expected un-derdiagnosis rate in the presence of an ACL tear. The purpose of our study was to search for an MRI bone contusion pattern associated with MRI occult meniscal tears in patients with an ACL tear, specifically a contusion of the rim of the medial femoral condyle (RMFC). Our hypothesis was that there would be a significant association between RMFC contusions and MRI occult meniscal tears in patients with an ACL tear. We also searched for a difference between sexes with respect to the presence of the RMFC contusion in the setting of an occult meniscal tear. We also categorized the type, size, and location of these occult meniscal tears in the setting of an ACL tear. Methods This was a retrospective study that examined characteristics of occult meniscal tears and their association with a RMFC bone contusion. IRB approval was obtained. The date range of the study was June 2009 through December 2015. 6392 consecutive knee MRI reports in patients with an ACL deficient knee were reviewed. The study group included 22 patients with MRI occult meniscal tears, the control group included 110 patients. Relevant statistical values were calculated. Results The most common type of occult meniscal tears were small radial and small longitudinal tears of the lateral meniscus. Occult meniscal tears were associated with an RMFC contusion in the study group (p=0.0457), particularly in males (p = 0.0003). In males with a torn ACL, the sensitivity of an RMFC contusion for an occult meniscal tear was 80%. Conclusion In males with an ACL tear, there was a significant association between a contusion of the RMFC and an occult meniscal tear (commonly small radial or small peripheral partial-thickness longitudinal tears). RMFC contusions were reliably identified by radiologists in this study.Level of Evidence: II.

OBJECTIVE. The purpose of this article is to summarize the nomenclature of nonneoplastic conditions affecting subchondral bone through a review of the medical literature and expert opinion of the Society of Skeletal Radiology Subchondral Bone Nomenclature Committee. CONCLUSION. This consensus statement summarizes current understanding of the pathophysiologic characteristics and imaging findings of subchondral nonneoplastic bone lesions and proposes nomenclature to improve effective communication across clinical specialties and help avoid diagnostic errors that could affect patient care.

Background Use of three-dimensional (3D) color volume-rendered (VR) images has been reported to be more time-efficient compared to that of cross-sectional computed tomography (CT) images for the diagnosis of peroneal tendon dislocation. However, the diagnostic performance of this technique has not been studied. Purpose To test diagnostic accuracy of 3D color VR CT images of ankle for peroneal tendon dislocation in patients with acute calcaneal fractures. Material and Methods The study consisted of 121 ankle CT studies from 105 consecutive patients (85 men, 20 women; mean age, 42 years; age range, 16–75 years) with acute calcaneal fractures. Peroneal tendon dislocation was diagnosed on multiplanar CT images by consensus of two experienced musculoskeletal radiologists, which served as the reference standard. Three other musculoskeletal radiologists independently reviewed 3D images alone on a workstation. The readers determined whether or not there was peroneal tendon dislocation using three degrees of certainty (definite, probable, and possible). Diagnostic performance of 3D images for peroneal tendon dislocation was evaluated by calculating the sensitivities, specificities, and area under the receiver-operating characteristic (ROC) curves. Results Forty-eight (40%) out of 121 studies showed peroneal tendon dislocation based on the expert readings using multiplanar reformatted images. Sensitivities/specificities of 3D images measured 0.92/0.81, 0.88/0.90, and 0.81/0.92 for three readers, respectively. The area under the proper binormal ROC curve based on all three readers (0.93, 0.94, and 0.92) measured 0.93 with a 95% confidence interval of 0.89–0.98. Conclusion Diagnostic accuracy of 3D images is comparable to, but not as good as that of MPR images for the diagnosis of peroneal tendon dislocation in patients with acute calcaneal fractures.

When visible on radiographs, transient osteoporosis and osteonecrosis are quite distinct. Transient osteoporosis of the hip demonstrates radiographically marked osteoporosis. The osteoporosis can be so profound that the subchondral cortex of the head becomes nearly invisible. In contradistinction, when osteonecrosis is visible radiographically, it will have patchy areas of sclerosis or increased density (Figure 48.1). As the osteonecrosis progresses, areas of subchondral collapse and eventual osteoarthritis will develop.

Calcific tendinitis (also known as hydroxyapatite deposition disease) is best recognized on radiographic images. It appears as an area of amorphous calcification in the gluteal tendons near the greater trochanter, the iliopsoas tendon near the lesser trochanter, or the gluteus maximus tendon near the gluteal tuberosity of the femur (Figure 52.1). On MRI, the surrounding soft tissues will be edematous as evidenced by hyperintense signal on T2-weighted or STIR sequences.

The trochlear groove is the large curved depression that articulates with the trochlea of the humerus. At the junction of the olecranon and coronoid process there is an osseous ridge without cartilage in this trochlear groove called the trochlear ridge (Figure 21.1). This cartilage-free ridge can project above the articular surface of the trochlear groove by approximately 2–5 mm in 68% of the population. When a trochlear ridge is present, it does not cause impediment to smooth motion at the elbow and it does not decrease the range of motion at the elbow. However, when it approaches 3–5 mm in size it can be mistakenly confused for a central osteophyte (Figure 21.2). It has signal and morphologic characteristics of an osteophyte with projection from the articular surface with both cortical and medullary bone signal characteristics.