Faculty Bibliography

Purpose: The purpose of this study was to determine if a 5-minute knee magnetic resonance imaging (MRI) protocol is interchangeable with a standard knee MRI protocol for evaluation of internal derangement of the knee. Materials and Methods: 100 consecutive patients, in whom a knee MRI was performed for internal derangement between January 2015 and June 2015, were retrospectively reviewed. All patients were scanned on a single 3 T MRI system (Siemens Verio) with a 15- channel knee coil (Siemens). The standard clinical protocol consisting of 6 2-dimensional fast spin echo (2D FSE) sequences without parallel imaging was performed along with 5 additional fast 2D FSE sequences with parallel imaging (acceleration factor = 2). 3 readers (2 musculoskeletal (MSK) radiologists and 1 MSK radiology fellow) independently reviewed the fast and standard images which were anonymized and separated into 2 different reading sets. Readers evaluated for the presence of meniscal and ligament tears, cartilage defects, and bone abnormalities. Frequency of major findings was measured. Interchangeability of fast and standard MRI was tested by comparing the agreement when 1 reader was using fast MRI and the other reader was using standard MRI (interprotocol agreement) with the agreement when both readers were using the standard MRI (intraprotocol agreement). Fast MRI was considered interchangeable if the interprotocol agreement was not less < 5% of the intraprotocol agreement. Results: The study population consisted of 69 males and 31 females with a mean age of 38.8 years (range 18 - 65). The average time for the fast protocol was 4 minutes 8 seconds compared to 17 minutes 20 seconds for the standard protocol. The most common findings reported on MRI as an aggregate of all readers was as follows: medial meniscal tears (46.7%), high grade partial thickness or full thickness cartilage defects (21.9%), lateral meniscal tears (21.3%), and ACL tears (15.7%). The intraprotocol agreement was very similar to the interprotocol agreement for all structures. The intraprotocol and interprotocol agreement were as follows for individual structures, respectively: Medial Mensicus (89.3% vs. 90.0%); Lateral Meniscus (89.3% vs. 89.0%); ACL (96.0% vs. 95.7%); PCL (98.0% vs. 98.3%); MCL (98.0% vs. 98.3%); LCL (98.7% vs. 98.2%); Cartilage (86.3% vs. 86.2%); Fracture/Contusion (90.7% vs. 93.0%); and Marrow Disease (98.0% vs. 98.0%) . The upper bounds of the 95% CIs for the differences between these two proportions were always <5%, suggesting that fast knee MRI can be interchanged with standard MRI without a significant increase in disagreements between readers. Conclusion: A 5-minute knee MRI consisting of multiplanar 2D FSE sequences using parallel imaging is interchangeable with a standard knee MRI for evaluating internal derangement of the knee

OBJECTIVE: To describe the post-surgical imaging appearance and complications of high tibial osteotomy in patients with the iBalance implant system (iHTO; Arthrex, Naples, FL, USA). MATERIALS AND METHODS: Retrospective, institutional review board-approved, Health Insurance Portability and Accountability Act-compliant review of imaging after 24 iBalance procedures was performed with attention to: correction of varus malalignment, healing at the osteotomy site, resorption of the osteoinductive compound, and complications. RESULTS: Immediate correction of the varus deformity was present in all cases. Lobular radiolucency was present in all cases, more pronounced on the lateral knee radiograph, simulating infection or erosive disease. Four radiographic signs of healing were observed: blurring at the opposing osteotomy bony margins and at the osteoinductive compound and the adjacent bone interface, callus formation, and resorption of the osteoinductive compound. Complications were present in 33 % of cases, including fracture through the lateral tibial cortex (21 %), genu varum recurrence (8 %), painful exuberant bone formation (4 %), persistent pain, requiring total knee arthroplasty (4 %), and non-union (after >6 months' follow-up), with suspected infection (4 %). CONCLUSION: Radiologists should be aware of the normal radiographic appearance following iBalance high tibial osteotomy, which may be confused with infection. Radiologists should also be aware of potential post-operative complications and compare all post-operative radiographs with the immediate post-operative examination to detect collapse of the osteotomy site and recurrence of varus angulation.

We sought to assess the potential use of an application allowing real-time ultrasound spatial registration with previously acquired magnetic resonance imaging in musculoskeletal procedures. The ultrasound fusion application was used to perform a range of outpatient procedures including piriformis, sacroiliac joint, pudendal and intercostal nerve perineurial injections, hamstring-origin calcific tendonopathy barbotage, and 2 soft tissue biopsies at our institution in 2015. The application was used in a total of 7 procedures in 7 patients, all of which were technically successful. The ages of patients ranged from 19 to 86 years. Particular use of the fusion application compared to sonography alone was noted in the biopsy of certain soft tissue lesions and in perineurial therapeutic injections.

Adaptation facilitates neural representation of a wide range of diverse inputs, including reward values. Adaptive value coding typically relies on contextual information either obtained from the environment or retrieved from and maintained in memory. However, it is unknown whether having to retrieve and maintain context information modulates the brain's capacity for value adaptation. To address this issue, we measured hemodynamic responses of the prefrontal cortex (PFC) in two studies on risky decision-making. In each trial, healthy human subjects chose between a risky and a safe alternative; half of the participants had to remember the risky alternatives, whereas for the other half they were presented visually. The value of safe alternatives varied across trials. PFC responses adapted to contextual risk information, with steeper coding of safe alternative value in lower-risk contexts. Importantly, this adaptation depended on working memory load, such that response functions relating PFC activity to safe values were steeper with presented versus remembered risk. An independent second study replicated the findings of the first study and showed that similar slope reductions also arose when memory maintenance demands were increased with a secondary working memory task. Formal model comparison showed that a divisive normalization model fitted effects of both risk context and working memory demands on PFC activity better than alternative models of value adaptation, and revealed that reduced suppression of background activity was the critical parameter impairing normalization with increased memory maintenance demand. Our findings suggest that mnemonic processes can constrain normalization of neural value representations.

OBJECTIVE: Subchondroplasty is a novel minimally invasive procedure that is used to treat painful bone marrow lesions in patients with knee osteoarthritis or insufficiency fractures. The objective of this article is to describe the surgical technique and the pre- and postoperative imaging findings of a small case series acquired at a single center. CONCLUSION: The radiologist should be familiar with the anticipated postoperative imaging appearances after subchondroplasty and the potential complications.

UNLABELLED:Given that the range of rewarding and punishing outcomes of actions is large but neural coding capacity is limited, efficient processing of outcomes by the brain is necessary. One mechanism to increase efficiency is to rescale neural output to the range of outcomes expected in the current context, and process only experienced deviations from this expectation. However, this mechanism comes at the cost of not being able to discriminate between unexpectedly low losses when times are bad versus unexpectedly high gains when times are good. Thus, too much adaptation would result in disregarding information about the nature and absolute magnitude of outcomes, preventing learning about the longer-term value structure of the environment. Here we investigate the degree of adaptation in outcome coding brain regions in humans, for directly experienced outcomes and observed outcomes. We scanned participants while they performed a social learning task in gain and loss blocks. Multivariate pattern analysis showed two distinct networks of brain regions adapt to the most likely outcomes within a block. Frontostriatal areas adapted to directly experienced outcomes, whereas lateral frontal and temporoparietal regions adapted to observed social outcomes. Critically, in both cases, adaptation was incomplete and information about whether the outcomes arose in a gain block or a loss block was retained. Univariate analysis confirmed incomplete adaptive coding in these regions but also detected nonadapting outcome signals. Thus, although neural areas rescale their responses to outcomes for efficient coding, they adapt incompletely and keep track of the longer-term incentives available in the environment. SIGNIFICANCE STATEMENT:Optimal value-based choice requires that the brain precisely and efficiently represents positive and negative outcomes. One way to increase efficiency is to adapt responding to the most likely outcomes in a given context. However, too strong adaptation would result in loss of precise representation (e.g., when the avoidance of a loss in a loss-context is coded the same as receipt of a gain in a gain-context). We investigated an intermediate form of adaptation that is efficient while maintaining information about received gains and avoided losses. We found that frontostriatal areas adapted to directly experienced outcomes, whereas lateral frontal and temporoparietal regions adapted to observed social outcomes. Importantly, adaptation was intermediate, in line with influential models of reference dependence in behavioral economics.

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.