Faculty Bibliography

OBJECTIVE: The purpose of this article is to review currently available tendon treatments, especially those performed with sonographic guidance. CONCLUSION: Treatments of tendon disease have continued to develop and expand, and multiple therapeutic options have become available, all with varying levels of supportive clinical evidence of their efficacy. The use of ultrasound to direct these treatments improves accuracy and performance by facilitating visualization of the target and relevant adjacent structures.

Midbrain dopamine neurons encode reward prediction errors. In this issue of Neuron, Takahashi et al. (2016) show that the ventral striatum provides dopamine neurons with prediction information specific to the timing, but not the quantity, of reward, suggesting a surprisingly nuanced neural implementation of reward prediction errors.

OBJECTIVE: Detail the imaging findings in patients with proximal tibiofibular instability treated with surgical stabilization. METHODS: Retrospective analysis of preoperative imaging in patients with clinically confirmed tibiofibular instability. RESULTS: Operative fixation of the 16 patients was as follows: 11 using a fiberwire suture construct and 5 using screw fixation. Proximal tibiofibular ligamentous abnormalities were present in 100% of acute (< 6 months) and 85.7% of chronic (>6 months) instability cases who underwent MRI. CONCLUSION: MRI is sensitive in the evaluation of tibiofibular ligamentous integrity in proximal tibiofibular instability. Chronic instability should be considered in younger adults with isolated tibiofibular osteoarthritis.

Non-spherical emulsion droplets can be stabilized by densely packed colloidal particles adsorbed at their surface. In order to understand the microstructure of these surface packings, the ordering of hard spheres on ellipsoidal surfaces is determined through large scale computer simulations. Defects in the packing are shown generically to occur most often in regions of strong curvature; however, the relationship between defects and curvature is nontrivial, and the distribution of defects shows secondary maxima for ellipsoids of sufficiently high aspect ratio. As with packings on spherical surfaces, additional defects beyond those required by topology are observed as chains or "scars". The transition point, however, is found to be softened by the anisotropic curvature which also partially orients the scars. A rich library of symmetric commensurate packings are identified for low particle number. We verify experimentally that ellipsoidal droplets of varying aspect ratio can be arrested by surface-adsorbed colloids.

Purpose: iBalance high tibial osteotomy, (iHTO, Arthrex Inc, Naples, Florida), is a recently introduced surgical procedure for correction of knee varus malalignment. iHTO, utilizing a polyetheretherketone (PEEK) implant and osteoinductive compounds (OIC), presents challenging post operative radiographs which can easily be misinterpreted as infection. Our purpose is to report, based on review of 24 cases, the previously undescribed to the best of our knowledge, radiographic features of iHTO and its complications. Materials and Methods: Retrospective query of our digital database was performed to identify iHTO cases. The clinical and postsurgical images in all cases with > 1-month follow up imaging were reviewed with attention to 1. Correction of varus malalignment, 2. Healing at the osteotomy site, 3. Changes in the OIC, and 4. Complications. Results: There were 24 iHTOs in 23 patients (17 men, 6 women, ages 21-59, mean 44, median 46), imaged 1 to 29 months post-surgery, with angle of correction, when available, ranging from 5 to 14degree. Immediate post-surgical correction of varus malalignment was seen in 100 % of patients. 100 % depicted oval radiolucencies, at bone PEEK interface simulating erosions and infection. Four, often overlapping, signs of healing were noted: 1. Blurring of bony margins at the osteotomy site, noted within 2 weeks post surgery, 2. Blurring of sharp interface between OIC and host bone, 3. Anterior, posterior and less commonly medial bridging callus, 4. Resorption of OIC, noted as early as 4 months. Complications, seen in 7 cases (29 %), included genu varum recurrence (n = 2), painful exuberant bone formation, (n = 1), and propagation of the osteotomy through the lateral tibial cortex (n = 4). In patients with >6 months follow-up, nonunion and possible infection was seen in 1 patient. 2 patients required total knee arthroplasty due to iHTO failure. Conclusion: iBalance HTO typically depicts oval radiolucencies at the PEEK bone interface not to be mistaken for infection. Familiarity with this features, as well as with other signs of healing, should aid the radiologist in accurate interpretation of post operative films of iHTO patients

Surprise drives learning. Various neural "prediction error" signals are believed to underpin surprise-based reinforcement learning. Here, we report a surprise signal that reflects reinforcement learning but is neither un/signed reward prediction error (RPE) nor un/signed state prediction error (SPE). To exclude these alternatives, we measured surprise responses in the absence of RPE and accounted for a host of potential SPE confounds. This new surprise signal was evident in ventral striatum, primary sensory cortex, frontal poles, and amygdala. We interpret these findings via a normative model of surprise.

Dopaminergic neurons provide value signals in mammals and insects. During Drosophila olfactory learning, distinct subsets of dopaminergic neurons appear to assign either positive or negative value to odor representations in mushroom body neurons. However, it is not known how flies evaluate substances that have mixed valence. Here we show that flies form short-lived aversive olfactory memories when trained with odors and sugars that are contaminated with the common insect repellent DEET. This DEET-aversive learning required the MB-MP1 dopaminergic neurons that are also required for shock learning. Moreover, differential conditioning with DEET versus shock suggests that formation of these distinct aversive olfactory memories relies on a common negatively reinforcing dopaminergic mechanism. Surprisingly, as time passed after training, the behavior of DEET-sugar-trained flies reversed from conditioned odor avoidance into odor approach. In addition, flies that were compromised for reward learning exhibited a more robust and longer-lived aversive-DEET memory. These data demonstrate that flies independently process the DEET and sugar components to form parallel aversive and appetitive olfactory memories, with distinct kinetics, that compete to guide learned behavior.

This article reviews the technique, basic science principles and applications of integrated single photon emission CT (SPECT)-CT in musculoskeletal radiology. A review of the current evidence on the topic was undertaken, and selected clinical cases from the authors' institution have been used for illustration. SPECT-CT is a technology with emerging applications that offers technical advantages to image fusion of separately acquired SPECT and CT studies. The prevailing evidence indicates that there may be benefit in adding SPECT-CT to conventional imaging algorithms during the evaluation of some malignant and benign musculoskeletal conditions. SPECT-CT can improve both sensitivity and specificity by reducing equivocal interpretation in comparison to planar scintigraphy or SPECT alone. The evidence base for SPECT-CT in musculoskeletal radiology is still evolving. There is a lack of evidence comparing SPECT-CT with MRI in many key indications, and further research is required in these areas.