Discovery, Characterization, and Structure–Activity Relationships of an Inhibitor of Inward Rectifier Potassium (Kir) Channels with Preference for Kir2.3, Kir3.X, and Kir7.1

The inward rectifier family of potassium (Kir) channels is comprised of at least 16 family members exhibiting broad and often overlapping cellular, tissue, or organ distributions. The discovery of disease-causing mutations in humans and experiments on knockout mice has underscored the importance of Kir channels in physiology and in some cases raised questions about their potential as drug targets. However, the paucity of potent and selective small-molecule modulators targeting specific family members has with few exceptions mired efforts to understand their physiology and assess their therapeutic potential. A growing body of evidence suggests that G protein-coupled inward rectifier K (GIRK) channels of the Kir3.X subfamily may represent novel targets for the treatment of atrial fibrillation. In an effort to expand the molecular pharmacology of GIRK, we performed a thallium (Tl+) flux-based high-throughput screen of a Kir1.1 inhibitor library for modulators of GIRK. One compound, termed VU573, exhibited 10-fold selectivity for GIRK over Kir1.1 (IC50 = 1.9 and 19 μM, respectively) and was therefore selected for further study. In electrophysiological experiments performed on Xenopus laevis oocytes and mammalian cells, VU573 inhibited Kir3.1/3.2 (neuronal GIRK) and Kir3.1/3.4 (cardiac GIRK) channels with equal potency and preferentially inhibited GIRK, Kir2.3, and Kir7.1 over Kir1.1 and Kir2.1.Tl+ flux assays were established for Kir2.3 and the M125R pore mutant of Kir7.1 to support medicinal chemistry efforts to develop more potent and selective analogs for these channels. The structure–activity relationships of VU573 revealed few analogs with improved potency, however two compounds retained most of their activity toward GIRK and Kir2.3 and lost activity toward Kir7.1. We anticipate that the VU573 series will be useful for exploring the physiology and structure–function relationships of these Kir channels

Tibiotalocalcaneal Arthodesis via a Nitinol Containing Intramedullary Nail

Category: Ankle, Ankle Arthritis, Hindfoot Introduction/Purpose: Tibiotalocalcaneal (TTC) arthrodesis is a common procedure used in the management of foot and ankle pathologies. TTC fusions are frequently performed in patients with limited bone stock and poor vascular status. Adequate compression at the arthrodesis site is vital to successful fusion as even small amounts of bone resorption greatly increase nonunion risk. A recently designed hindfoot nail contains a built in nickel titanium alloy (nitinol) that has psuedoelastic properties which maintains compression across joint surfaces in the setting of bone resorption. The authors present a case series of patients who were managed with this nitinol containing intramedullary hindfoot nail system. Methods: Patients treated by one board certified orthopaedic foot and ankle surgeon who were managed with the nitinol containing hindfoot nailing system were retrospectively reviewed over a two year span. Electronic medical records were reviewed to collect demographic information and details regarding the patient’s procedure. Operative specifics collected included the data of the procedure and the preoperative diagnosis. Records were reviewed postoperatively as well to document the incidence of postoperative complications and functional outcomes. Proximal migration of the distal interlocking screw on lateral radiographs were measured in a standardized fashion at two, six, and twelve weeks to objectively assess additional compression obtained through the nitinol nailing system. Results: Eight patients were included in the case series with an average follow up time of 7 months postoperative (minimum of 4 months for one patient). The most common preoperative diagnosis was posttraumatic arthritis (n = 4). One patient suffered from wound dehiscence postoperatively that required operative intervention within the first three months – this patient’s wound healed by six months with no further complications. All patients were cleared for full weight bearing and activities as tolerated by six months, except only had four months of follow up available. The compression obtained through this nailing system increased at each follow up for all patients. The average compression obtained was 2.9 mm at two weeks, 3.8 mm at six weeks, and 4.4 mm at twelve weeks. Conclusion: Tibiotalocalcaneal arthrodesis can be an excellent procedure that provides significant pain relief and restores function. The patients in this case series all had excellent results with only one postoperative complication that ultimately did not result in any functional deficits. Furthermore, patients all demonstrated increased compression at each follow up radiographs which demonstrates the sustained compression obtained at the arthrodesis site through this hindfoot nail system. Further prospective work with a larger patient cohort is warranted to determine if this nailing system is superior to other TTC hindfoot nails

Impact of Vancomycin Treatment on Human Mesenchymal Stromal Cells During Osteogenic Differentiation

Category: Basic Sciences/Biologics Introduction/Purpose: Vancomycin is often delivered locally for surgical site infection prophylaxis. Recent reports of possible osteotoxicity have led to uncertainty concerning vancomycin’s safety in the setting of arthrodesis and bone healing. Bone formation during arthrodesis takes place as recruited human mesenchymal stromal cells (hMSCs) proliferate and differentiate into mature osteoblasts. The purpose of this research was to determine the impact of vancomycin treatment on hMSCs during osteogenic differentiation. Methods: Human MSCs were cultured in MSC growth media to an appropriate confluence. Cells were cultured for 24 hours to facilitate adherence, after which the media was aspirated and replaced with osteogenic differentiation media (Lonza, Switzerland). Osteogenic differentiation media was supplemented with vancomycin powder to yield solutions with concentrations of 0, 50, 500 & 5000 µg/mL. Fresh vancomycin powder was added with every media change. MSCs viability and proliferation were assessed via live/dead staining with 1 µM calcein-AM and 0.5 µM ethidium homodimer-1 (EthD-1) after 1, 3, and 7 days of differentiation and vancomycin treatment. Mineralization of differentiated cells was assessed via staining with 40 mM alizarin red (ARS; pH 4.1) after 21 days. Semi-quantification of the degree of mineralization was performed by measuring absorbance values at 405 nm using a microplate reader. Microscopy was used for qualitative evaluation. Results: Cell viability decreased with increasing vancomycin concentrations. Impairment of hMSC proliferation was also observed with increasing concentrations of vancomycin. MSCs treated with 5000 µg/mL vancomycin demonstrated significantly less cell growth compared to all other treatment groups (P=0.0001). Absorbance measurements from each well stained with alizarin red was used for semi-quantification of the degree of mineralization. As vancomycin concentrations were increased, absorbance levels decreased (Figure). This reduction in mineralization was also demonstrated qualitatively; with alizarin red less apparent in the wells with increasing vancomycin concentrations (Figure). Conclusion: Local vancomycin is utilized for prevention of infection, often in procedures that necessitate the formation of new bone. Bone healing requires migration, proliferation and differentiation of hMSCs. This work demonstrates impaired viability and function of hMSCs following vancomycin as well as decreased osteoblastic mineralization. Future work will require in vivo studies aimed at determining relative nonunion rates in the setting of vancomycin prophylaxis. Still, the results of this study suggest that vancomycin may be toxic to hMSCs and caution should be exercised by providers when considering vancomycin in foot and ankle patients requiring bony healing following fracture or arthrodesis

Development of a Novel Small Animal Ankle Arthrodesis Model

Category: Basic Sciences/Biologics Introduction/Purpose: Ankle arthrodesis is performed for a variety of ankle joint pathology with the most common being post traumatic arthritis. It is estimated that there are nearly twenty-five thousand ankle fusions performed annually in the United States. Reported complication rates vary between studies and patient population characteristics and comorbidities. Our understanding of the biology of ankle arthrodesis is based largely upon spine fusion and long bone animal models. However, bony healing and infection is greatly influenced by local soft tissue and vascular anatomy, therefore the application of data from these models may not be entirely accurate. There is currently no small animal ankle fusion model. Accordingly, the purpose of this study is to develop a reliable small animal ankle arthrodesis model. Methods: A total of twenty Lewis rats were included in this study. Ankle arthrodesis was performed on one extremity of fourteen rats with the other ankle serving as an internal control. An anterior approach was used to expose the tibiotalar joint. Careful technique was utilized to protect neurovascular structures. After adequate joint exposure, a power burr and sharp curette was used to remove joint cartilage. A .042 kirschner wire was then passed through the calcaneus and through the subtalar and tibiotalar joint. Six rats served as controls and their procedures did not involve any joint cartilage removal. Radiographs were taken immediately postoperatively and at 8 weeks. Bony healing was assessed in a blinded fashion by a board certified foot and ankle orthopaedic surgeon using a grading system based upon assessment of cortical bridging and joint space. Results: Sixteen rats – eleven fusions and five controls - underwent the procedure without any perioperative complications and were included in analysis. Four rats were excluded due to a perioperative complication and/or death. The most common postoperative complication encountered was a wound complication (n=3). Of the eleven rats in the fusion group, six (55%) were determined to be fused radiographically. Two of the five controls were radiographically fused (40%). Conclusion: This study demonstrates preliminary data from a novel small animal ankle arthrodesis model. Fifty-five percent of the rats in the fusion group fused based on radiographic evaluation at eight weeks postoperatively. Further work involves improving upon the surgical technique for fusion in this small animal model to help increase fusion rates, and using CT scans and biomechanical testing to further assess fusion. The development of a small animal ankle fusion model will enhance our understanding of the biology of ankle arthrodesis and allow for development of novel therapies aimed at increasing fusion rates and decreasing complications

Association of a Modified Frailty Index with Postoperative Outcomes after Ankle Fractures in Patients Aged 50 Years and Older

Category: Ankle, Trauma Introduction/Purpose: Frailty, a multifaceted syndrome resulting from a decrease in physiologic reserves, has been previously shown to play a significant role in elderly morbidity and mortality. The literature on frailty within orthopaedic surgery is limited currently. No study to date has assessed frailty as a predictor of postoperative outcomes in elderly patients with ankle fractures. We hypothesized that increasing frailty would be associated with increased 30-day reoperation rates and increased postoperative complications. Methods: The National Surgical Quality Improvement Project (NSQIP) was queried using the appropriate CPT codes to identify inpatients from 2005-2014 who were aged 50 years and older that sustained an ankle fracture and underwent operative fixation. Frailty was assessed using a modified frailty index (MFI), abbreviated with 11 variables from the Canadian Study of Health and Aging Frailty Index. The primary outcome was 30-day reoperation rate and secondary outcomes were postoperative surgical and medical complications, readmission rates, and length of stay. Bivariate and multivariate analysis was used to determine association between outcomes and MFI. Results: 6,749 patients were identified, and the mean age of these patients was 64.4 years. Patients with increased MFI scores had significantly higher rates of postoperative complications. In addition, increased MFI scores was also associated with increased 30 day readmissions and reoperations. Multivariate analysis also demonstrated that MFI was a stronger predictor of 30 day reoperation rates (odds ratio of 17.7, P < 0.001) than age, wound class, and ASA class. Conclusion: Frailty has the potential to be an important predictive variable of postoperative outcomes in patients aged 50 years and older who sustain ankle fractures. The modified frailty index can be a valuable preoperative risk assessment tool for the orthopaedic surgeon. Further study is necessary to examine the effect of the MFI in a larger prospective setting

External Fixation versus Primary Open Reduction and Internal Fixation (ORIF) of Intra-articular Calcaneus Fractures

Category: Hindfoot, Trauma Introduction/Purpose: Calcaneus fractures are common injuries of the foot and account for approximately sixty percent of all tarsal bone fractures. Anatomic reduction of the articular surface is associated with good long-term outcomes. Unfortunately, there is a high rate of complications following surgical fixation due to the fragile soft tissue envelope surrounding these injuries. External fixation of joint depression calcaneus fractures allows for restoration of morphology and preservation of soft tissues. The purpose of this work is to determine if acute external fixation in the management of joint depression calcaneus fractures leads to decreased postoperative complications and better outcomes. Methods: Patients were identified using the appropriate procedure codes over a ten year span at a level one trauma center. Those under the age of eighteen and underwent nonoperative treatment were excluded. Electronic medical records were reviewed to obtain, basic demographic data, comorbidities, and injury specifics. Calcaneus fractures were classified as open or closed and using the Essex-Lopresti classification system. Operative reports were reviewed to determine which patients initially underwent external fixation versus open reduction internal fixation (ORIF), furthermore any staged operative interventions were also noted. Electronic records were also reviewed to determine the length of follow up and incidence of postoperative complications. Bivariate analysis was used to identify an association between collected variables and postoperative complications (wound dehiscence, hardware failure, infection, nonunion). Multivariate logistic regression analysis was used to determine if patients treated with acute external fixation were associated with lower postoperative complication rates. Results: 152 calcaneus fractures were identified and included for analysis. The average age was thirty-eight and the majority of patients were male (111/152 = 73%). Average follow up was approximately five months. Seventeen percent (26/152) were open fractures. Twenty-six (17%) were treated initially with external fixation and eleven of these were a staged ORIF. The overall complication rate was 11% (17/152) with the most common complication being wound dehiscence. Only one complication occurred in the group initially managed with external fixation. Statistical analysis revealed that open fractures were associated with increased postoperative complication rates in a bivariate and multivariate model. Conclusion: External fixation of joint depression calcaneus fractures restores height and preserves the soft tissue envelope. Although there was only one complication in the external fixation group, the difference in complication rates was not statistically significant based on initial treatment. The low number of patients treated with external fixation initially and the short follow up are limitations of this study. Further work is needed with a larger patient cohort in a prospective setting. Acute external fixation may prove to be a useful tool to help prevent postoperative complications following joint depression calcaneus fractures

Racial Disparities in the Utilization of Lateral Ankle Ligament Reconstruction for Chronic Ankle Instability in the United States

Category: Ankle; Other Introduction/Purpose: Chronic ankle instability (CAI) is a common diagnosis among people with previous ankle injuries. Once conservative treatment is exhausted, lateral ankle ligament reconstruction (LALR) is the gold standard surgical treatment for CAI. Previous studies have reported on the impact of race on access to orthopedic procedures in the United States. However, there are few studies evaluating racial disparities in elective foot and ankle surgeries, including LALR. Recognizing and addressing disparities in the access of health resources are imperative in combating systemic care rationing. Thus, our study aims to investigate racial disparities including utilization and perioperative metrics of lateral ankle ligament reconstruction. Methods: A retrospective study was performed using the National Surgical Quality Improvement Program (NSQIP) database. Patients that utilized the Current Procedural Terminology (CPT) code 27698 corresponding to LALR from 2011 to 2020 were included. 61% of these patients had available race/ethnicity data and were included. Designations of race and ethnicity were standardized as White non-Hispanic (WNH), Black non-Hispanic (BNH), Hispanic, Asian American and Pacific Islander (AAPI), and Other. Race/ethnicity stratifications of NSQIP patients were compared to 2010 and 2020 census data from the United States (US) Census Bureau. 30-day postoperative complications and length of hospital stay were also compared between WNH and all other patients combined. Independent T-tests, Chi-squared, and Fisher's exact tests were performed to compare differences including age, gender, and post-operative complications at an α = 0.05. Results: Overall, 1295 patients were included in the study. There were 3.3 times more WNH patients than all other groups who underwent LALR during the study period. This utilization exceeds what would be expected based on population statistics (1.9 times more WNH in the population in 2010 and 1.3 times more WNH in 2020). WNH patients were older with a mean age of 38 years, compared to 36 years for BNH patients (p < 0.05). Amongst the WNH patients, 17.4% smoked which was significantly more than other race/ethnicities. (p=0.012). There were no differences in overall 30-day complication rate or individual types of complications based on race and ethnicity. There were also no significant differences in total length of hospital stay. Conclusion: Our study found that there was increased utilization of LALR amongst White non-Hispanics compared to all other racial/ethnic groups. These numbers do not mimic the current population trends based on the national census data. Despite this discrepancy, no differences in postoperative complications and length of stay based on race and ethnicity were found. These results suggest that there may be systemic barriers for patients to undergo care for LALR and that further research needs to be conducted on racial disparities within orthopedics

Racial Disparities in the Utilization of Lateral Ankle Ligament Reconstruction for Chronic Ankle Instability in the United States

Background: Previous studies have reported on the impact of race and ethnicity on access to orthopaedic procedures in the United States. However, there are few studies evaluating racial disparities in elective foot and ankle surgeries. Recognizing and addressing disparities in the access of health resources are steps to improve care rationing. Our study specifically investigated potential racial disparities with utilization and perioperative metrics of lateral ankle ligament reconstruction. Methods: A retrospective study was performed using the National Surgical Quality Improvement Program (NSQIP) database. Current Procedural Terminology ( CPT ) code 27698 was used to identify patients who underwent LALR from 2011 to 2020. Sixty-one percent of these patients had available race/ethnicity data and were included in the study. Designations of race and ethnicity were standardized as White non-Hispanic, Black non-Hispanic, Hispanic, Asian American and Pacific Islander, and Other. Race/ethnicity stratifications of NSQIP patients were compared to 2010 and 2020 census data from the United States (US) Census Bureau. Thirty-day postoperative complications and total length of hospital stay, for all complications, were also compared between White patients and all other patients combined. Independent t tests, χ 2 , and Fisher exact tests were performed to compare differences including age, gender, and postoperative complications. Results: Overall, 1295 patients were included in the study. White non-Hispanic patients underwent 3.3 times more LALR than all other patients during the study period. This finding shows a higher prevalence of surgery on White non-Hispanic patients than all others reported in the US Census Bureau data for 2010 and 2020, where the ratio of White non-Hispanic vs all others were 1.9 and 1.5-fold, respectively. White patients were marginally older with a mean age of 38 years, compared with 36 years for Black patients ( P  < .05). There were no differences in 30-day complication rates or total length of hospital stay based on race and ethnicity. Conclusion: Our study found that there was increased utilization of LALR for White non-Hispanic patients compared with all other racial/ethnic groups. These numbers do not mimic the current population trends based on the national census data. Despite this discrepancy, no differences in postoperative complications and length of stay were found based on race and ethnicity. These results suggest that there may be barriers for patients who are not White non-Hispanic to undergo care for LALR. Level of Evidence: Level III, retrospective cohort study