Screw Diameter and Use of a Washer Affect Symptomatic Implant Removal Rates in Pediatric Medial Epicondyle Fractures.

OBJECTIVE: Medial epicondyle fractures are a common pediatric injury. When operative, cannulated partially threaded screws, with or without a washer, are commonly utilized. These implants may need to be removed after full healing if symptomatic. There is mixed evidence regarding the influence of a washer on rates of implant removal, and the influence of screw size has not been studied. We aim to determine the rate of symptomatic deep implant removal for each fixation type and identify factors associated with the need for removal. METHODS: This was an IRB-reviewed, retrospective, case-cohort study. Patients treated at our institution between January 1, 2004 and December 31, 2019, age 18 years old or younger, with a medial epicondyle fracture managed operatively with 4.0 or 4.5 mm cannulated screws with or without washers were included. Patients with multiple operative ipsilateral elbow fractures and those who underwent implant removal for reasons other than pain or irritation were excluded. Removal rates were compared between screw sizes (4.0 vs 4.5 mm), as well as with and without a washer using a Cox proportional hazards model. RESULTS: In total, 151 patients met the inclusion criteria, 54 with symptomatic hardware removed and 97 without symptomatic hardware removed. A significantly higher number of patients treated with 4.5 mm screws compared with 4.0 mm screws underwent removal of symptomatic deep implants (50% vs 30%, P = 0.033). In a multivariable Cox regression model adjusting for age and ulnar nerve status, when no washer was used, the hazard ratio (HR) for symptomatic hardware removal for 4.5 mm screws was 2.92 times the HR for 4.0 mm screws (95% CI: 1.35-6.29). When a 4.0 mm screw was used, the HR for symptomatic hardware removal for a washer was 3.24 times the HR without a washer (95% CI: 1.53-6.84). CONCLUSION: Implant removal rates are influenced by screw size and the use of a washer. These results may help guide implant choice and counsel families regarding the rate of symptomatic implant removal. LEVEL OF EVIDENCE: Level III-therapeutic level, case-control study.

Recovery Curves for Lisfranc ORIF Using PROMIS Physical Function and Pain Interference.

OBJECTIVES: To determine the postoperative trajectory and recovery of patients who undergo Lisfranc open reduction and internal fixation using Patient-Reported Outcomes Measurement Information System (PROMIS) physical function (PF) and pain interference (PI). DESIGN: Retrospective cohort study. SETTING: Level 1 trauma center. PATIENT SELECTION CRITERIA: Patients who underwent Lisfranc open reduction and internal fixation between January 2002 and December 2022 with documented PROMIS PF and/or PI scores after surgery. OUTCOME MEASURES AND COMPARISONS: PROMIS PF and PI were mapped over time up to 1 year after surgery. A subanalysis was performed to compare recovery trajectories between high-energy and low-energy injuries. RESULTS: A total of 182 patients were included with average age of 38.7 (SD 15.9) years (59 high-energy and 122 low-energy injuries). PROMIS PF scores at 0, 6, 12, 24, and 48 weeks were 30.2, 31.4, 39.2, 43.9, and 46.7, respectively. There was significant improvement in PROMIS PF between 6 and 12 weeks ( P < 0.001), 12-24 weeks ( P < 0.001), and 24-48 weeks ( P = 0.022). A significant difference in PROMIS PF between high and low-energy injuries was seen at 0 week (28.4 vs. 31.4, P = 0.010). PROMIS PI scores at 0, 6, 12, 24, and 48 weeks were 62.2, 58.5, 56.6, 55.7, and 55.6, respectively. There was significant improvement in PROMIS PI 0-6 weeks ( P = 0.016). A significant difference in PROMIS PI between high-energy and low-energy injuries was seen at 48 weeks with scores of (58.6 vs. 54.2, P = 0.044). CONCLUSIONS: After Lisfranc open reduction and internal fixation, patients can expect improvement in PF up to 1 year after surgery, with the biggest improvement in PROMIS PF scores between 6 and 12 weeks and PROMIS PI scores between 0 and 6 weeks after surgery. Regardless the energy type, Lisfranc injuries seem to regain comparable PF by 6-12 months after surgery. However, patients with higher energy Lisfranc injuries should be counseled that these injuries may lead to worse PI at 1 year after surgery as compared with lower energy injuries. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Physeal Bar Formation After Pediatric Medial Malleolus Fractures.

Pediatric medial malleolus fractures are commonly Salter-Harris (SH) type III or IV fractures of the distal tibia and are associated with a risk of physeal bar formation and subsequent growth disturbance. The purpose of this study was to determine the incidence of physeal bar formation following pediatric medial malleolus fracture and evaluate for patient and fracture characteristics predictive of physeal bar formation. Seventy-eight consecutive pediatric patients during a 6-year period who had either an isolated medial malleolar or a bimalleolar ankle fracture were retrospectively reviewed. Forty-one of 78 patients had greater than 3 months of radiographic follow-up and comprised the study population. Medical records were reviewed for demographic information, mechanism of injury, treatment, and need for further surgery. Radiographs were reviewed to assess for initial fracture displacement, adequacy of fracture reduction, SH type, percentage of the physeal disruption from the fracture, and physeal bar formation. Twenty-two of 41 patients (53.7%) developed a physeal bar. The mean time to diagnosis of physeal bar was 4.9 months (range, 1.6-11.8 months). Twenty-seven percent (6 of 22) of bars were diagnosed at greater than 6 months from injury. Adequacy of reduction was predictive of physeal bar formation, although all patients were reduced to within 2 mm. The mean residual displacement of patients with a bar was 1.2 mm compared with 0.8 mm for those without a bar (P=.03). Because the bar formation rate is greater than 50% on radiographs, routine radiographic assessment of all pediatric medial malleolar fractures should continue for at least 12 months after injury. [Orthopedics. 2024;47(1):e33-e37.].

Evaluating Factors Associated With Patient-Perceived Applicability of the QuickDASH Survey in Reflecting Their Goals of Care Prior to Hand Surgery.

PURPOSE: Patient-reported outcome measures intend to capture patients' perspectives on their health status. However, the patient-perceived applicability of many of these patient-reported outcome measures is unknown. We hypothesized that patients experiencing greater upper extremity disability and greater pain interference would be more likely to report that the Quick Disabilities of the Arm, Shoulder, and Hand questionnaire (QuickDASH) survey content is responsive to their daily lives and goals in seeking surgical care. METHODS: Adult preoperative hand surgery patients at a single tertiary academic center were recruited prospectively. QuickDASH, Patient-Reported Outcomes Measurement Information System Pain Interference computerized-adaptive-testing, and the Godin Leisure-Time Exercise Questionnaire (GLTEQ)-a validated adult physical activity level metric-data were collected. The following two Likert response questions were also asked: question (1) "How applicable is the above questionnaire to your treatment goals for your upper extremity condition?" and question (2) "How applicable is the overall questionnaire to your daily life?" Multivariable binary logistic regression was performed to define the factors associated with patients reporting that the survey was "very applicable." RESULTS: Of the 133 included patients, the mean age was 49 ± 18 years, 40% were women, and the mean GLTEQ score was 54.1 ± 5.5 (consistent with a high level of activity). For questions 1 and 2, 32% and 29% of the patients reported that QuickDASH was "very applicable," respectively. The multivariable model demonstrated that for every 10-point increase in QuickDASH, there was a 45% to 49% greater odds of respondents reporting that the survey was "very applicable," and for every 5-point increase in pain interference computerized-adaptive-testing, the odds increased by 55% to 70%. No association with GLTEQ was observed. CONCLUSIONS: Patients with greater upper extremity disability and pain interference were more likely to find the QuickDASH content to be applicable to their daily lives and goals in seeking surgical care. CLINICAL RELEVANCE: These findings suggest that QuickDASH may not be an optimal instrument when evaluating upper extremity function in cohorts with mild disability and low pain interference.

Congenital Ankylosis of the Knee Treated with Van Nes Rotationplasty: A Case Report.

CASE: This is a case of a female patient born with thrombocytopenia-absent radius syndrome, with bilateral upper extremity phocomelia, bilateral hip dislocations, and congenital fusion of the right knee with progressively worsening flexion contracture. At age 3 years and 5 months, the patient was treated with excision of the knee ankylosis and Van Nes rotationplasty. This proved durable at age 20 years (final follow-up) without any need for further surgery and without complication. CONCLUSION: This is the first known report of Van Nes rotationplasty as a durable treatment option in the management of congenital knee ankylosis, which may avoid reoperation and eliminate risk of recurrence.

Functional Implications of Flat-Topped Talus Following Treatment of Idiopathic Clubfoot Deformity.

BACKGROUND: Though flatness of the talar dome (TD) is a potential consequence of operative and nonoperative clubfoot management, the functional impact of this deformity is not well understood. This study analyzes the relationship between TD morphology and ankle function at skeletal maturity in patients treated for idiopathic clubfoot during infancy. METHODS: 33 skeletally mature patients (average age 17.9 years) with 48 idiopathic clubfeet were identified. Weightbearing radiographs, gait analysis, and patient-reported outcomes using the Pediatric Orthopaedic Data Collection Instrument (PODCI) were obtained. Radius of curvature (ROC) of the TD and tibial plafond were measured along with other parameters of talar and calcaneal morphology. All measurements were correlated to PODCI scores and gait analysis data. RESULTS: Patients demonstrated marked variability in ROC of the TD (mean 30.8 mm, SD 13.6 mm), TD radius to talar length (R/L) ratio (mean 0.56, SD 0.28), opening angle of the TD (alpha angle) (mean 89.6°, SD 28.4°), and tibiotalar incongruity index (mean 0.18, SD 0.16). Increased tibiotalar incongruity index correlated with decreased maximum plantar flexion (r = ‒0.325, P = .02). A less acute alpha angle of the talar dome correlated with increased maximum ankle power generation (r = 0.321, P = .03) as did increased length of the talar neck (r = 0.358, P = .013). Increased tibiotalar incongruity index correlated negatively with PODCI global function domain scores (r = ‒0.490, P = .04; r = ‒0.381, P = .03, respectively), whereas length of the talar body correlated with higher global function scores (r = 0.376, P = .03) and lower pain scores (r = 0.350, P = .046). CONCLUSION: At skeletal maturity, flattening of the talar dome and tibiotalar incongruity on plain radiographs correlate modestly with gait changes, whereas tibiotalar incongruity and length of the talar body, not flatness of the talar dome, correlate with decreased patient-reported outcome scores. LEVEL OF EVIDENCE: Level III, prognostic.

Sesamoid View Weightbearing Radiography vs Weightbearing Computed Tomography in the Measurement of Metatarsal Pronation Angle.

BACKGROUND: First metatarsal pronation angle (MPA) is increasingly relevant in the management of hallux valgus and is assessed on weightbearing computed tomography (WBCT) and sesamoid-view weightbearing radiography (WBR). The purpose of this study is to compare MPA measured by WBCT against WBR to determine if any systematic discrepancy in MPA measurement exists between the 2 modalities. METHODS: A total of 40 patients with 55 feet were included for study. MPA was measured in all patients by 2 independent readers on both WBCT and WBR with an appropriate washout period between measurement modalities. Mean MPA by WBCT and WBR were analyzed; interobserver reliability was calculated with an intraclass correlation coefficient (ICC) value. RESULTS: Mean MPA as measured by WBCT was 3.7 ± 7.9 degrees (95% CI, 1.6-5.9; range -11.7 to 20.5). Mean MPA measured on WBR was 3.6 ± 8.4 degrees, (95% CI, 1.4-5.8; range -12.6 to 21.4). There was no difference in MPA as measured by WBCT compared to WBR (P = .529). Interobserver reliability was excellent with an ICC of 0.994 for WBCT and 0.986 for WBR. CONCLUSION: Measurement of first MPA by WBCT and WBR was not significantly different. In our cohort of patients with and without forefoot pathology, we found that either sesamoid view weightbearing radiographs or weightbearing CT can be used reliably to measure first MPA and will generate similar values. LEVEL OF EVIDENCE: Level IV, case series.

Anterolateral Tibial Bowing and Congenital Pseudoarthrosis of the Tibia: Current Concept Review and Future Directions.

PURPOSE OF REVIEW: Congenital pseudarthrosis of the tibia (CPT) is a rare condition closely associated with neurofibromatosis type I. Affected children are born with anterolateral bowing of the tibia which progresses to pathologic fracture, pseudarthrosis, and high risk of refracture even after initial union has been attained. There is currently no consensus on the classification of this disease or consensus on its treatment. The purpose of this review is to (1) review the clinical presentation, etiology, epidemiology, classification, and natural history of congenital pseudarthrosis of the tibia and (2) review the existing trends in treatment of congenital pseudarthrosis of the tibia and its associated complications. RECENT FINDINGS: Current treatment protocols focus primarily on combining intramedullary fixation with external or internal fixation to achieve union rates between 74 and 100%. Intramedullary devices should be retained as long as possible to prevent refracture. Cross-union techniques, though technically difficult, have a reported union rate of 100% and no refractures at mid- to long-term follow-up. Vascularized fibular grafting and induced membrane technique can be successful, but at the cost of numerous surgical procedures. Growth modulation is a promising new approach to preventing fracture altogether, though further study with larger patient series is necessary. The primary consideration in treatment of CPT is expected union rate and refracture risk. Combined intramedullary and external or internal fixation, especially with cross-union techniques, show most promise. Perhaps most exciting is further research on preventing fracture through guided growth, which may reduce the morbidity of multiple surgical procedures which have been the mainstay of treatment for CPT thus far.

Do We Really Need to Worry About Calcaneocuboid Subluxation During Lateral Column Lengthening for Planovalgus Foot Deformity?

BACKGROUND: Although lengthening of the lateral column through an osteotomy of the anterior calcaneus is an integral component of flatfoot reconstruction in younger patients with flexible planovalgus deformities, the procedure has been implicated in iatrogenic calcaneocuboid (CC) subluxation and subsequent degenerative changes at the CC articulation. The purpose of this study is to characterize alterations at the CC joint after lateral column lengthening (LCL) and determine if Steinmann pin stabilization of the CC joint before distraction maintains a normal relationship. METHODS: Seven matched pairs of fresh-frozen cadaveric feet underwent preprocedure plain radiography and cross-sectional computed tomography (CT) imaging. LCL by osteotomy through the anterior calcaneus was then performed. One foot of each matched pair had a single smooth Steinmann pin placed centrally across the CC joint before osteotomy distraction. Distraction across each osteotomy was then performed and maintained with a 12-mm porous titanium wedge. Repeat imaging was obtained and compared with preprocedure studies to quantify sagittal and rotational differences at the CC articulation. RESULTS: Following LCL, plain radiography demonstrated statistically significant increases in the percentage of the calcaneal articular surface dorsal to the superior aspect of the cuboid in both the pinned (8.2% vs. 17.6%, P=0.02) and unpinned (12.5% vs. 16.3%, P=0.04) specimens. No difference in the percentage of subluxation was found between the 2 groups after LCL. CT imaging demonstrated statistically significant increases in rotation between the calcaneus and cuboid after LCL in both the pinned (7.6±5.6 degrees, P=0.01) and unpinned (17±12.3 degrees, P=0.01) specimens. The degree of rotation was greater in unpinned specimens after LCL (P=0.043). CONCLUSIONS: Both sagittal and rotatory subluxation seem to occur at the CC joint after LCL regardless of pin stabilization. As a single pin would be expected to limit pure translation while having little effect on rotation, it is possible that the rotational changes identified on 3-dimensional imaging are interpreted as dorsal translation when viewed 2 dimensionally using plain radiography. Consideration should therefore be given to CC stabilization with 2 pins during LCL to prevent this rotatory subluxation. LEVEL OF EVIDENCE: Level V-cadaver study.

Effect of Lateral Column Lengthening on Subtalar Motion in a Cadaveric Model.

BACKGROUND: Although lengthening of the lateral column through a calcaneal neck osteotomy is an integral component of flatfoot reconstruction in younger patients with flexible planovalgus deformities, concern exists as to the effect of this intra-articular osteotomy on subtalar motion. The purpose of this study was to quantify the alterations in subtalar motion following lateral column lengthening (LCL). METHODS: The subtalar motion of 14 fresh-frozen cadaveric feet was assessed using a 3-dimensional motion capture system and materials testing system (MTS). Following potting of the tibia and calcaneus, optic markers were placed into the tibia, calcaneus, and talus. The MTS was used to apply a rotational force across the subtalar joint to a torque of 5 Nm. Abduction/adduction, supination/pronation, and plantarflexion/dorsiflexion about the talus were recorded. Specimens then underwent LCL via a calcaneal neck osteotomy, which was maintained with a 12-mm porous titanium wedge. Repeat subtalar motion analysis was performed and compared to pre-LCL motion using a paired t test. RESULTS: No statistically significant differences in subtalar abduction/adduction (10.9 vs 11.8 degrees, P = .48), supination/pronation (3.5 vs 2.7 degrees, P = .31), or plantarflexion/dorsiflexion (1.6 vs 1.0 degrees, P = .10) were identified following LCL. CONCLUSION: No significant changes in subtalar motion were observed following lateral column lengthening in this biomechanical cadaveric study. CLINICAL RELEVANCE: Although these findings do not obviate concerns of clinical subtalar stiffness following lateral column lengthening for planovalgus deformity correction, they suggest that diminished postoperative subtalar motion, when it occurs, may be due to soft tissue scarring rather than alterations of joint anatomy.

How to Measure Glenoid Bone Stock and Version and Why It Is Important: A Practical Guide.

Shoulder osteoarthritis (OA) is a common and debilitating condition and a source of high morbidity and medical expenditures across the world among individuals older than 60 years. Shoulder OA results in the gradual destruction of articular cartilage of the humeral head and glenoid component, causing inflammation, pain, and a restricted range of motion. Most patients are diagnosed with shoulder OA after experiencing shoulder pain and stiffness, and the diagnosis is often made after medical and physical histories are obtained and physical and imaging examinations are performed. Use of various surgical techniques such as total anatomic or reverse shoulder arthroplasty and hemiarthroplasty has increased in recent years, resulting in reduced morbidity and improved functional status of patients. However, the rate of surgical complications such as premature loosening of components is significant, reducing the effectiveness of such procedures. Data in the literature indicate that high-grade fatty infiltration of the rotator cuff muscle before surgery is associated with postoperative glenoid component loosening. High-grade rotator cuff fatty infiltration and atrophy have been found to be associated with more severe Walch classification-based glenoid morphology subtypes, increased joint line medialization, glenoid bone loss, and increased pathologic glenoid version. The authors describe how advanced imaging techniques are used for preoperative evaluation of the shoulder and discuss how to measure glenoid version and bone stock and classify glenoid morphology types on the basis of Walch classification, as these parameters are commonly used in surgical planning. Methods involving the use of Friedman and paleoglenoid lines for respective measurements are illustrated by using three-dimensional CT and MRI case examples. ©RSNA, 2020.

Successful Ponseti-treated Clubfeet at Age 2 Years: What Is the Rate of Surgical Intervention After This?

BACKGROUND: In recent decades, nonoperative Ponseti casting has become the standard of care in the treatment of idiopathic clubfoot. However, the rate of recurrence, even after successful Ponseti treatment is not insignificant. The purpose of this study was to determine the future rate, timing, and type of surgery needed in patients whose idiopathic clubfeet treated by Ponseti casting were considered successful at the age of 2 years. METHODS: Inclusion criteria for this retrospective study were patients under 3 months with idiopathic clubfoot treated exclusively by Ponseti casting, who had successful outcomes at 2 years of age without surgery, and who had at least 5 years of follow-up. The total number of surgical interventions in the age range 2 to 5 and above 5 years, the number and type of procedures performed, and the timing of surgery were reviewed. RESULTS: Three hundred thirty-six patients with a total of 504 clubfeet fulfilled the inclusion criteria. One hundred twenty-two of these 336 patients (36.3%) eventually underwent surgical intervention. Between 2 and 5 years of age, 79 patients (23.5%) with 104 feet (20.6%) underwent surgery. The most common procedures performed between 2 and 5 years were limited (a la carte) in scope: tibialis anterior tendon transfer, posterior release, plantar fascia release, and repeat tendo-Achilles lengthening. At age above 5 years, 53 patients (20.1%) with 65 feet (16.9%) underwent surgery. Ten of these 53 patients had already undergone surgery between 2 and 5 years of age. The procedures most commonly performed were similar. CONCLUSIONS: In patients with idiopathic clubfoot who reached 2 years of age with successful outcomes from Ponseti cast treatment, ∼35% eventually underwent surgical intervention, mostly limited (a la carte), to regain or maintain a plantigrade foot. The most commonly performed procedures include tibialis anterior tendon transfer, posterior capsular release, plantar fascia release and repeat tendo-Achilles lengthening, either in isolation or in combination. However, before considering surgery, the need for these procedures can, and should, be minimized by recasting recurrent deformities using Ponseti method. LEVEL OF EVIDENCE: Level III.

Correction to: Qualitative and quantitative analysis of glenoid bone stock and glenoid version: inter-reader analysis and correlation with rotator cuff tendinopathy and atrophy in patients with shoulder osteoarthritis.

Purpose Glenoid bone stock and morphology and rotator cuff muscle quality and tendon integrity affect the outcome of total shoulder arthroplasty. We hypothesized that glenoid bone loss correlates with rotator cuff muscle fatty infiltration (FI), tendinopathy, and atrophy.Design Forty-three 3-D CT scans and MRIs of 43 patients (mean age 62 years; SD 13 years; range 22-77 years) referred for primary shoulder pain were evaluated. Measurements of glenoid bone stock, version, and posterior humeral subluxation index (HSI) were assessed on an axial CT image reconstructed in the true scapular plane. Measurements utilized the Friedman line to approximate the pre-pathologic surface. Glenoid morphology was assigned by modified Walch classification. Rotator cuff FI, atrophy, and tendon integrity were assessed on corresponding MRIs.Results There was a very strong negative correlation between increasing glenoid version and HSI (r = - 0.908; p < 0.0001). There was a moderately negative correlation between anterior bone loss and HSI (r = - 0.562; p < 0.0001) and a moderately positive correlation between posterior bone loss and HSI (r = 0.555; p < 0.0001). Subscapularis muscle FI correlated moderately with increased anterior and central bone loss and increased humeral head medialization (r = 0.512, p = 0.0294; r = 0.479, p = 0.033; r = 0.494, p = 0.0294, respectively). Inter-observer reliability (intra-class correlation coefficient [ICC] and kappa) was good to excellent for all measurements and grading.Conclusion Glenoid anteversion and anterior and posterior bone loss are associated with varying HSI. Subscapularis muscle FI, not tendon integrity, correlates to anterior and central glenoid erosion. The study adds evidence that neither rotator cuff tendinopathy nor muscle atrophy exhibits a significant relationship to HSI.

Qualitative and quantitative analysis of glenoid bone stock and glenoid version: inter-reader analysis and correlation with rotator cuff tendinopathy and atrophy in patients with shoulder osteoarthritis.

PURPOSE: Glenoid bone stock and morphology and rotator cuff muscle quality and tendon integrity affect the outcome of total shoulder arthroplasty. We hypothesized that glenoid bone loss correlates with rotator cuff muscle fatty infiltration (FI), tendinopathy, and atrophy. DESIGN: Forty-three 3D CT scans and MRIs of 43 patients (mean age 62 years; SD 13 years; range 22-77 years) referred for primary shoulder pain were evaluated. Measurements of glenoid bone stock, version, and posterior humeral subluxation index (HSI) were assessed on an axial CT image reconstructed in the true scapular plane. Measurements utilized the Friedman line to approximate the pre-pathologic surface. Glenoid morphology was assigned by modified Walch classification. Rotator cuff FI, atrophy, and tendon integrity were assessed on corresponding MRIs. RESULTS: There was a very strong negative correlation between increasing glenoid version and HSI (r = - 0.908; p < 0.0001). There was a moderately negative correlation between anterior bone loss and HSI (r = - 0.562; p < 0.0001) and a moderately positive correlation between posterior bone loss and HSI (r = 0.555; p < 0.0001). Subscapularis muscle FI correlated moderately with increased anterior and central bone loss and increased humeral head medialization (r = 0.512, p = 0.0294; r = 0.479, p = 0.033; r = 0.494, p = 0.0294; respectively). Inter-observer reliability (intra-class correlation coefficient [ICC] and kappa) was good to excellent for all measurements and grading. CONCLUSION: Glenoid anteversion and anterior and posterior bone loss are associated with varying HSI. Subscapularis muscle FI, not tendon integrity, correlates to anterior and central glenoid erosion. The study adds evidence that neither rotator cuff tendinopathy nor muscle atrophy exhibits a significant relationship to HSI.

Cations or Radicals? Inherent Reactivity of Biosynthetic Intermediates in the B-Ring Formation of Rotenoid Natural Products.

Compounds of the rotenoid class are naturally occurring in the Leguminosae and Nyctaginacae families. Rotenoids have found a myriad of uses, for example, in the agricultural industry as an insecticide and piscicide, and as an anticancer therapeutic. The scientific literature questions whether cyclization of the rotenoid B-ring occurs via a pathway containing either cationic or free-radical intermediates. In this work, both propositions are analyzed using DFT (B3LYP and M06-2X) and the G3 composite method in gas- and (implicit) solution-phase. The accuracy of these methods is compared to several experimental C-H bond dissociation energies (BDEs). We find that of the methods surveyed M06-2X provides the most accurate BDEs. Further, there is a clear thermodynamic preference for the free-radical pathway.

Conjugate Addition/[3,3] Sigmatropic Shift Processes for Formation of Medium-Ring Cyclic Amines - Do They Circumvent the Woodward-Hoffmann Rules?

Herein we describe our exploration, using density functional theory calculations, of a conjugate addition-rearrangement sequence that leads to medium-ring cyclic amines. On the basis of the results of our calculations, we conclude that the rearrangement step is rate determining. In addition, we analyze the role of a carbanion lone pair in the rearrangement step, concluding that it functions as a substituent on a [3,3] sigmatropic shift, rather than a nucleophile; thus, the Woodward-Hoffmann rules are not circumvented in this reaction via involvement of orthogonal orbitals on an atom involved in the rearrangement.

Potential energy surfaces for the HBr(+) + CO2 → Br + HOCO(+) reaction in the HBr(+) (2)Π3/2 and (2)Π1/2 spin-orbit states.

Quantum mechanical (QM) + molecular mechanics (MM) models are developed to represent potential energy surfaces (PESs) for the HBr(+) + CO2 → Br + HOCO(+) reaction with HBr(+) in the (2)Π3/2 and (2)Π1/2 spin-orbit states. The QM component is the spin-free PES and spin-orbit coupling for each state is represented by a MM-like analytic potential fit to spin-orbit electronic structure calculations. Coupled-cluster single double and perturbative triple excitation (CCSD(T)) calculations are performed to obtain "benchmark" reaction energies without spin-orbit coupling. With zero-point energies removed, the "experimental" reaction energy is 44 ± 5 meV for HBr(+)((2)Π3/2) + CO2 → Br((2)P3/2) + HOCO(+), while the CCSD(T) value with spin-orbit effects included is 87 meV. Electronic structure calculations were performed to determine properties of the BrHOCO(+) reaction intermediate and [HBr⋯OCO](+) van der Waals intermediate. The results of different electronic structure methods were compared with those obtained with CCSD(T), and UMP2/cc-pVTZ/PP was found to be a practical and accurate QM method to use in QM/MM direct dynamics simulations. The spin-orbit coupling calculations show that the spin-free QM PES gives a quite good representation of the shape of the PES originated by (2)Π3/2HBr(+). This is also the case for the reactant region of the PES for (2)Π1/2 HBr(+), but spin-orbit coupling effects are important for the exit-channel region of this PES. A MM model was developed to represent these effects, which were combined with the spin-free QM PES.

Direct dynamics simulation of the activation and dissociation of 1,5-dinitrobiuret (HDNB).

Certain room-temperature ionic liquids exhibit hypergolic activity as liquid bipropellants. Understanding the chemical pathways and reaction mechanisms associated with hypergolic ignition is important for designing new fuels. It has been proposed (J. Phys. Chem. A 2008, 112, 7816) that an important ignition step for the hypergolic ionic liquid bipropellant system of dicyanamide/nitric acid is the activation and dissociation of the 1,5-dinitrobiuret anion DNB(-). For the work reported here, a quasiclassical direct dynamics simulation, at the DFT/M05-2X level of theory, was performed to model H(+) + DNB(-) association and the ensuing unimolecular decomposition of HDNB. This association step is 324 kcal/mol exothermic, and the most probable collision event is for H(+) to directly scatter off of DNB(-), without sufficient energy transfer to DNB(-) for H(+) to associate and form a highly vibrationally excited HDNB molecule. Approximately 1/3 of the trajectories do form HDNB, which decomposes by eight different reaction paths and whose unimolecular dynamics is highly nonstatistical. Some of these paths are the same as those found in a direct dynamics simulation of the high-temperature thermal decomposition of HDNB (J. Phys. Chem. A 2011, 115, 8064), for a similar total energy.

Direct dynamics simulations of the product channels and atomistic mechanisms for the OH(-) + CH3I reaction. Comparison with experiment.

Electronic structure and direct dynamics calculations were used to study the potential energy surface and atomic-level dynamics for the OH(-) + CH3I reactions. The results are compared with crossed molecular beam, ion imaging experiments. The DFT/B97-1/ECP/d level of theory gives reaction energetics in good agreement with experiment and higher level calculations, and it was used for the direct dynamics simulations that were performed for reactant collision energies of 2.0, 1.0, 0.5, and 0.05 eV. Five different pathways are observed in the simulations, forming CH3OH + I(-), CH2I(-) + H2O, CH2 + I(-) + H2O, IOH(-) + CH3, and [CH3--I--OH](-). The SN2 first pathway and the proton-transfer second pathway dominate the reaction dynamics. Though the reaction energetics favor the SN2 pathway, the proton-transfer pathway is more important except for the lowest collision energy. The relative ion yield determined from the simulations is in overall good agreement with experiment. Both the SN2 and proton-transfer pathways occur via direct rebound, direct stripping, and indirect mechanisms. Except for the highest collision energy, 70-90% of the indirect reaction for the SN2 pathway occurs via formation of the hydrogen-bonded OH(-)---HCH2I prereaction complex. For the proton-transfer pathway the indirect reaction is more complex with the roundabout mechanism and formation of the OH(-)---HCH2I and CH2I(-)---HOH complexes contributing to the reaction. The majority of the SN2 reaction is direct at 2.0, 1.0, and 0.5 eV, dominated by stripping. At 0.05 eV the two direct mechanisms and the indirect mechanisms have nearly equal contributions. The majority of the proton-transfer pathway is direct stripping at 2.0, 1.0, and 0.5 eV, but the majority of the reaction is indirect at 0.05 eV. The product relative translational energy distributions are in good agreement with experiment for both the SN2 and proton-transfer pathways. For both, direct reaction preferentially transfers the product energy to relative translation, whereas transfer to product vibration is more important for the indirect reactions. For the proton-transfer reactions the velocity scattering angle distribution is peaked in the forward direction and in quite good agreement with experiment. However, for the SN2 reaction, the experimental scattering is isotropic in nature whereas forward scattering dominates the simulation distributions. The implication is that the simulations give too much stripping, which leads to forward scattering. The dynamics for the OH(-) + CH3I SN2 pathway are similar to those found previously for the F(-) + CH3I SN2 reaction.