A National Perspective of Patellar Instability in Children and Adolescents in the United States: MPFL Reconstruction Is Three Times Higher Than the Incidence of Isolated Lateral Release.

PURPOSE: The objective was to (1) evaluate any recent changes in the United States in the incidences of medial patellofemoral ligament (MPFL) reconstruction and isolated lateral release for patellar instability in children and adolescents, (2) identify concomitant procedures with MPFL, and (3) report national complication rates after MPFL reconstruction with and without concomitant procedures in children and adolescents. METHODS: A national database was queried for patients aged 5 to 18 years who underwent operative treatment for patellar instability from 2010 to 2018. Inclusion criteria were either an MPFL reconstruction or lateral release for a diagnosis of patellar instability. Concomitant procedures with MPFL reconstruction assessed were tibial tubercle osteotomy, associated arthroscopic procedures, and lateral release. Changes in incidence in MPFL reconstruction, lateral release and concomitant procedures were assessed. The following postoperative complications were assessed: knee stiffness, infection, patella fracture, and growth arrest or angular deformity. RESULTS: 2,161 patients who underwent MPFL reconstruction and 1,159 patients who underwent isolated lateral release for patellar instability were identified. The incidence of MPFL reconstruction in adolescents from 2010 to 2018 did not change significantly (2010: 7.11, 2018: 5.91, P = .137), while isolated lateral release decreased (2010: 6.06, 2018: 1.83, P < .0001). Concomitant procedures with MPFL reconstruction were common, with arthroscopy being the most frequent (58-67%). The most common complication within 90 days of surgery was patella fracture (0.4% to 2.0%). Infection (0.4% to 1.0%) and growth arrest (0.09% to 0.61%) were the least common. MPFL and arthroscopy had a decreased risk of growth arrest following surgery compared to MPFL alone (P = .038). CONCLUSIONS: The incidence of MPFL reconstruction remained high from 2010 to 2018, while isolated lateral release decreased during the same time period. Complications after MPFL reconstruction, isolated lateral release, and concomitant procedures were infrequent, with postoperative patella fracture the most common. LEVEL OF EVIDENCE: IV, case series.

Sulcus Deepening Trochleoplasty and Medial Patellofemoral Ligament Reconstruction for Patellofemoral Instability: A 2-Year Study.

PURPOSE: To evaluate outcome data of patients undergoing DeJour sulcus-deepening trochleoplasty with medial patellofemoral ligament reconstruction (MPFLR) for high-grade trochlear dysplasia at a single institution in the United States. METHODS: A total of 67 patients (76 knees) with severe trochlear dysplasia and recurrent patellar instability were prospectively enrolled and underwent DeJour sulcus-deepening trochleoplasty with MPFLR from 2011 to 2019. Inclusion criteria included recurrent lateral patellar instability following failure of conservative treatment with radiographic evidence of severe trochlear dysplasia (DeJour types B or D). Patients with less than 2-year follow-up were excluded. Radiographic analysis, physical examination, clinical follow-up, patient demographics, and patient-reported outcome measures were obtained for all patients at each visit. RESULTS: Forty patients (44 knees) had complete 2-year or longer follow-up and were included. The majority of patients were female (81.8%) with a mean age of 19.2 years (standard deviation [SD] 6.7; range 13.2-47.0). Follow-up ranged from 2.0 years to 6.8 years (mean 3.6 years, SD 1.35). In total, 45.5% had failed previous surgery for patellar instability. Eight knees developed arthrofibrosis and the overall reoperation rate was 27.3%. No patients had fixation failure and no further surgery was required for instability. The mean preoperative International Knee Documentation Committee score of 50.8 improved to 79.1 (P < .001), and the mean preoperative Kujala score of 56.4 improved to 86.5 (P < .001). Patients reported high satisfaction rates (mean 9.1 of 10). When applicable, 100% of patients returned to work, whereas 84.8% returned to sport. There was no significant radiographic progression of patellofemoral arthritis at a mean of 2.4 years after surgery (SD 1.7). CONCLUSIONS: DeJour sulcus-deepening trochleoplasty combined with MPFLR and used with tibial tubercle osteotomy and lateral release is a reliable and effective treatment for recurrent patellar instability due to severe trochlear dysplasia, even in this group with many revisions of previous procedures. LEVEL OF EVIDENCE: IV, case series.

When is Trochleoplasty a Rational Addition?

Trochlear dysplasia has been recognized as a dominant anatomic risk factor in patients with recurrent patellar instability. Sulcus-deepening trochleoplasty is a very effective and powerful procedure for correcting trochlear dysplasia and, specifically, eliminating the supratrochlear spur. However, it must be emphasized that trochleoplasty is not appropriate for patients with mild trochlear dysplasia or those without a large supratrochlear spur or bump. We discuss the characteristics and classification of trochlear dysplasia and discuss specific indications for sulcusdeepening trochleoplasty.

Sport Participation and Specialization Characteristics Among Pediatric Soccer Athletes.

BACKGROUND: Soccer is an increasingly popular sport for children and adolescents in the United States. Little is known about participation patterns related to sport specialization. PURPOSE: To investigate soccer participation levels and sport specialization characteristics among youth soccer athletes. STUDY DESIGN: Cross-sectional study. METHODS: Adolescent athletes aged between 12 and 18 years completed an online survey addressing participant demographics, sports and soccer participation history, and level of specialization. Descriptive analyses characterized participation, while chi-square and Kruskal-Wallis tests assessed the influence of specialization, sex, and grade on survey variables. RESULTS: Overall, 83.7% of 746 respondents participated in an organized soccer league outside of school, and 37% played in multiple leagues concurrently. Nearly three-quarters of respondents trained in soccer more than 8 months of the year, with those who participated in club soccer being more likely to train more than 8 months of the year. More respondents were classified as high specialization (37.5%), followed by moderate (35.6%) and low (28.6%) specialization. No differences between sexes were noted for level of specialization or quitting other sports to specialize in soccer, but male athletes were more likely to train more than 8 months per year compared with female athletes. Respondents in older grades (9th-10th and 11th-12th grades) were more likely to be highly specialized and quit other sports to focus on soccer. No differences between grade levels were found among respondents training more than 8 months per year. CONCLUSION: The study findings suggest that many youth soccer athletes participated in multiple teams or leagues at the same time and trained more than 8 months of the year. Characteristics including participation on a club team, level of specialization, and male sex were associated with a greater likelihood of exceeding the 8-month training recommendation.

What's New in Pediatric and Adolescent Anterior Cruciate Ligament Injuries?

BACKGROUND: Anterior cruciate ligament (ACL) tears in children and adolescent patients are being diagnosed and treated at an ever-increasing rates. We performed a review of recent literature regarding care of children and adolescent athletes with an ACL injury. METHODS: PubMed database was searched for all papers related to treatment of children and adolescents with ACL injuries from October 1, 2012 to September 30, 2015, yielding 114 publications. RESULTS: A total of 59 papers were found to have contributed important new findings. Papers were selected based on new findings in the following categories: epidemiology, anatomy, risk factors, sex disparity, prevention, surgical outcomes, timing and associated pathologies, and rehabilitation and return to sport. CONCLUSIONS: Pediatric ACL injuries continue to rise and there are multiple surgical procedures that restore clinical function with good outcomes. Early surgical treatment is favored to prevent concomitant articular injuries. Early return to play can increase risk of reinjury and should be met with caution in this age group. Prevention strategies should be further studied and implemented in hopes of decreasing the incidence of this injury and the long-term potential damage. LEVEL OF EVIDENCE: Level 4-titerature review.

Reliability of Casting Indices Among Members of an Orthopaedic Surgery Residency.

BACKGROUND: Multiple casting indices have been described to evaluate the adequacy of cast placement in pediatric distal forearm fractures. The aim of this study was to determine the intrarater and interrater reliability of the measurements of 5 common casting indices among members of an orthopaedic surgery residency program. The cast index, 3-point index, gap index, padding index, and Canterbury index were evaluated. METHODS: This was a single-center prospective cohort reliability study that included 12 members of an orthopaedic surgery residency. Participants were placed into 1 of 4 groups by level of training: physician assistants, junior residents, senior residents, and attending orthopaedic surgeons. Twelve radiographs of casted pediatric distal forearm fractures were measured by each participant on 2 separate occasions. Statistical analysis using the intraclass correlation coefficient was used to determine the intrarater and interrater reliability. RESULTS: The cast index was the only casting index to meet our criteria for good intrarater and interrater reliability. CONCLUSION: Continued use of the cast index as a tool to assess pediatric distal forearm cast application is supported by this study. LEVEL OF EVIDENCE: Level 2.

Complications of Pediatric Elbow Fractures.

Fractures about the elbow in children are common and varied. Both diagnosis and treatment can be challenging, and optimal treatment protocols continue to evolve with new research data. This article reviews common complications related to pediatric elbow fractures and presents recent literature to help guide treatment.

Gunshot-associated Fractures in Children and Adolescents Treated at Two Level 1 Pediatric Trauma Centers.

INTRODUCTION: Gunshot injuries are a potentially significant cause of morbidity and mortality in the pediatric population. The objective of this study was to evaluate the epidemiology, fracture locations, associated injuries, types of treatment, and complications of gunshot-associated fractures in children and adolescents treated at two level 1 trauma centers. METHODS: The clinical and radiographic records of all children and adolescents who had a gunshot-associated fracture treated at 1 of 2 level 1 pediatric trauma centers between January, 2005, and April, 2013, were reviewed. The following characteristics were recorded: patient age and sex, type of weapon, fracture location, presence of neurovascular injury or other associated injuries, antibiotic treatment, method of stabilization, duration of hospital stay, complications, and need for subsequent procedures. RESULTS: Forty-nine patients with 58 fractures were identified; 9 patients had multiple fractures. The 41 males and 8 females had an average age of 12.2 years (range, 1 to 18 y). The tibia and femur were the most common sites of fracture (19% each), followed by the small bones of foot (4%) and the fibula (4%). Most of the fractures (71%) were treated nonoperatively. Nearly half (47%) of the patients had additional injuries, including abdominal or genitourinary injuries, neuropraxia or nerve injuries, and vascular injuries. Two patients (4%) developed infections (1 superficial and 1 deep) that required multiple irrigation and debridement procedures. Three patients developed compartment syndrome, and 4 patients had vascular injuries requiring repair. Nearly a third of patients (35%) had fractures or complications that required additional operative procedures. CONCLUSIONS: This large retrospective study highlights the significant morbidity of fractures caused by gunshots. Although the overall infection rate was low and most of these fractures were successfully treated nonoperatively, many of the patients required an additional operative procedure and nearly half had additional nonorthopaedic injuries. This emphasizes the necessity of coordination among emergency, general surgeons, intensivist, and orthopaedic surgical teams. LEVEL OF EVIDENCE: Level IV­retrospective case series.

Use of magnetic resonance imaging in the evaluation of spondylolysis.

BACKGROUND: In early studies, magnetic resonance imaging (MRI) had low sensitivity and positive predictive value in the evaluation of the pars interarticularis pathology; however, more recent reports have suggested an expanded role for MRI. The purpose of the present study was to evaluate the effectiveness of MRI in the diagnosis of pars injuries and compare it to computed tomography (CT), which was used as the reference "gold standard" for the detection of fractures. METHODS: The radiographic and clinic data of 93 adolescents and young adults with a presumptive diagnosis of spondylolysis based upon history and clinic examination were reviewed. Only 26 patients who had MRI and CT images obtained within 30 days of each other were included. All images were reviewed by a fellowship-trained musculoskeletal radiologist and fellowship-trained pediatric orthopaedist. RESULTS: Overall, 39 individual pars lesions (stress reaction or fracture) were identified. MRI was effective in identifying 36 pars lesions. MRI identified 11 lesions in 9 patients with negative CT. Seven of these lesions were stress reactions (grade 1), whereas 4 were frank fractures. Three pars injuries were noted on CT while the MRI was negative. CONCLUSIONS: MRI is an effective method (92% sensitivity) for detecting pars injuries. It can detect stress reactions when a fracture is not visible on CT scan, allowing early treatment of these prelysis lesions. The 92% sensitivity of MRI is comparable with that of other diagnostic modalities such as bone scan, with the advantage of no radiation exposure. MRI should be strongly considered as the advanced imaging modality of choice in the evaluation of patients with suspected spondylolysis. LEVEL OF EVIDENCE: Level III-diagnostic study.

Intraobserver and interobserver reliability and the role of fracture morphology in classifying femoral shaft fractures in young children.

BACKGROUND: Spiral fractures of long bones have long been cited as indications of non-accidental trauma (NAT) in children; however, fracture types are only loosely defined in the literature, and intraobserver and interobserver variability in defining femoral fracture patterns is rarely mentioned. We sought to determine reliability in classifying femoral fractures in young children using a standard series of radiographs shown to physicians with varied backgrounds and training and to determine if a quantitative approach based on objective measurements made on plain radiographs could improve definition of these fractures. METHODS: On 50 radiographs, the fracture ratio--fracture length divided by bone diameter--was determined and radiographs were reviewed by 14 observers, including pediatric orthopaedic surgeons, emergency room physicians, and musculoskeletal radiologists, who classified the fractures as transverse, oblique, or spiral. A second review of the images in a different order was carried out at least 10 days after the first. RESULTS: Overall, intraobserver agreement was strong, whereas interobserver reliability was moderate. Experience level did not correlate with either result. Complete agreement among all observers occurred for only 5 fractures: 3 transverse and 2 spiral. An average fracture ratio near 1.0 appeared to be predictive of a transverse fracture and a ratio of >3.0, a spiral fracture; ratios between these 2 values resulted in essentially random classification. CONCLUSIONS: The ability to reproducibly classify femoral fractures in young children is highly variable among physicians of different specialties. These results support the belief that fracture morphology has little predictive value in NAT because of the wide variability in what observers classify as a spiral fracture of the femur. Caution should be used in the use of descriptive terms such as spiral, oblique, or transverse when classifying femoral fractures, as well as when evaluating children for possible NAT, because of the variability in classification. LEVEL OF EVIDENCE: Level III-diagnostic study.

Autoinhibition and phosphorylation-induced activation of phospholipase C-γ isozymes.

Multiple extracellular stimuli, such as growth factors and antigens, initiate signaling cascades through tyrosine phosphorylation and activation of phospholipase C-γ (PLC-γ) isozymes. Like most other PLCs, PLC-γ1 is basally autoinhibited by its X-Y linker, which separates the X- and Y-boxes of the catalytic core. The C-terminal SH2 (cSH2) domain within the X-Y linker is the critical determinant for autoinhibition of phospholipase activity. Release of autoinhibition requires an intramolecular interaction between the cSH2 domain and a phosphorylated tyrosine, Tyr783, also located within the X-Y linker. The molecular mechanisms that mediate autoinhibition and phosphorylation-induced activation have not been defined. Here, we describe structures of the cSH2 domain both alone and bound to a PLC-γ1 peptide encompassing phosphorylated Tyr783. The cSH2 domain remains largely unaltered by peptide engagement. Point mutations in the cSH2 domain located at the interface with the peptide were sufficient to constitutively activate PLC-γ1, suggesting that peptide engagement directly interferes with the capacity of the cSH2 domain to block the lipase active site. This idea is supported by mutations in a complementary surface of the catalytic core that also enhanced phospholipase activity.

Treatment of pediatric femur fractures with the Pavlik harness: multiyear clinical and radiographic outcomes.

BACKGROUND: Femur fractures account for 1.4% to 1.7% of all pediatric fractures. The use of the Pavlik harness has been described for infants; however, previous reports have included only short-term follow-up. This study describes the multiyear clinical and radiographic results from patients younger than 6 months of age treated with a Pavlik harness. METHODS: The clinical and radiographic records were reviewed for all children under the age of 6 months who were treated with a Pavlik harness for an isolated femoral shaft fracture at a level 1 pediatric trauma center. Radiographs were obtained at final follow-up, as well as a standing full-length anteroposterior scanogram. Clinical examination was completed and inquiry regarding patient activity limitations, complications of treatment, and overall parent/provider satisfaction was made. RESULTS: Ten patients with 10 fractures met inclusion criteria. The average age of the patients at the time of injury was 2.2 months. The average duration of Pavlik harness treatment was 43 days (range, 31 to 54 d). The average age at final follow-up was 5.2 years (range, 2.6 to 7.3 y). At final follow-up, average angulation was 3 degrees valgus (range, 0 to 8 degrees) and 5 degrees procurvatum (range, 0 to 24 degrees). Only 1 patient had a measurable leg-length discrepancy of 7 mm at final follow-up. There were no complications noted. CONCLUSIONS: It is felt that pediatric patients have a significant potential for bone remodeling and that any angulation at the time of fracture union will remodel. Our study supports this notion as the final angulation at follow-up averaged 3 degrees valgus and 5 degrees procurvatum. In the patient group presenting with >20 degrees of angulation at the time of injury, final angulation averaged 5 degrees valgus and 11 degrees procurvatum. Treatment with the Pavlik harness provides for excellent clinical outcomes with a minimal complication rate. However, some patients, especially those presenting with a high degree of angulation, may have some degree of persistent radiographic angulation.

Associated injuries in children and adolescents with spinal trauma.

BACKGROUND: Over half of children and adolescents with spinal trauma have associated injuries, most commonly involving the appendicular skeleton, head and neck, and thorax. The incidence and characteristics of these associated injuries have been well described, but to our knowledge there has been no evaluation of the relationship between the injury characteristics and the patient age. METHODS: Data were obtained from the trauma registries of the local pediatric and adult level 1 trauma centers, and patients aged 0 to 19 years with spinal trauma were identified. For analysis, patients were divided into 3 age groups: 0 to 3, 4 to 12, and 13 to 19 years. Associated injuries were divided into 5 groups: head, thoracic, abdominal, appendicular skeletal fracture, and neurological. RESULTS: Overall, 25 patients had isolated dislocations and 307 patients had 366 spinal fractures or fracture-dislocations: 36% cervical, 31% thoracic, and 51% lumbar. Most (84%) of the injuries occurred in the 13- to 19-year-old group. Sixty-two percent of patients had associated injuries, most commonly thoracic injuries (pulmonary contusion, pneumothorax, rib fracture); 45% had multilevel spinal fractures, 39% of which were noncontiguous. Nearly three fourths of the noncontiguous fractures occurred in a different spinal region; cervical fracture with concomitant thoracic fracture was the most frequent pattern. CONCLUSIONS: This large series of consecutive patients highlights several important concepts concerning pediatric spinal fractures, including age-related patterns of injury, frequent associated injuries, and a high rate of multiple spinal injuries, especially noncontiguous injuries. It also emphasizes the importance of careful full-body examination and imaging of the entire spine in children and adolescents with a known spinal injury. LEVEL OF EVIDENCE: Level IV-case series.

The effect of immobilization devices and left-foot adapter on brake-response time.

BACKGROUND: The ability to perform an emergency stop is essential for safe driving and can be represented by total brake-response time, reaction time, and braking time. Immobilization of the lower extremities is routinely performed for a variety of musculoskeletal conditions. This study sought to investigate the effect of immobilization with a left-foot driving adapter, a controlled-ankle-motion device, and a short leg cast on braking times. Our hypothesis was that there would be a significant difference in braking-time values between individuals utilizing a left-foot driving adapter or immobilization device and control individuals wearing normal footwear. METHODS: A prospective, observational study was conducted to assess the effect of the immobilization devices on braking times. A driving simulator was used to assess total brake-response time, reaction time, and braking time in thirty-five volunteers. Volunteers were assessed while (1) wearing normal footwear (control group), (2) wearing a controlled-ankle-motion boot, (3) wearing a removable short leg cast, and (4) employing a left-foot driving adapter. RESULTS: The mean total brake-response time was significantly increased as compared with that of the control group in all three study groups. The mean reaction time was significantly increased for the short leg cast and controlled-ankle-motion groups as compared with reaction time in the control group. The mean braking time was significantly increased in the controlled-ankle-motion and left-foot driving-adapter groups as compared with braking time in the control group. CONCLUSIONS: Total brake-response time while wearing a controlled-ankle-motion boot or a short leg cast or while utilizing a left-foot driving adapter is significantly increased, or worsened, as compared with the response time while wearing normal footwear. This information may prove valuable to physicians when counseling patients on when it may be safe to return to driving.

Outcomes of internal fixation in a combat environment.

Due to the nature of the wounds and environment, internal fixation in battlefield treatment facilities is discouraged despite the lack of data. The purpose of this review is to describe the outcomes of fractures that were internally fixed in the combat environment. The records of patients who had internal fixation performed in the theater of combat operations were reviewed. Demographics, injury characteristics, procedure history, and outcomes were recorded and analyzed. Forty-seven patients had internal fixation performed on 50 fractures in a combat theater hospital. Hip, forearm, and ankle fractures made up the majority of cases with 14 (28%), 14 (28%), and 10 (20%), respectively. Sixteen (32%) fractures were open. The average Injury Severity Score was 11.4 +/- 1.1 (range, 4-34). Thirty-nine fractures (78%) healed without incidence. There was one (2%) infection and one (2%) acute surgical complication. Ten (20%) fractures, including the one infection, required additional procedures. Because internal fixation in the combat environment was used judiciously, complications were not higher than previously reported.

Lateral talar dome access utilizing temporary invasive distraction.

BACKGROUND: Autogenous osteochondral grafting is an operative option for the treatment of osteochondral lesions of the talus (OLT). Graft implantation often requires an osteotomy to gain perpendicular access to the recipient site. The purpose of this study was to determine the relative contributions of soft tissue releases, osteotomies, and invasive distraction on perpendicular access to the lateral talar dome. We hypothesized that temporary invasive distraction (TID) would provide greater perpendicular access than anterolateral arthrotomy alone and similar access compared to an anterolateral tibial osteotomy. MATERIALS AND METHODS: Eight fresh frozen cadaveric limb specimens were utilized. An anterolateral arthrotomy was performed and an osteochondral plug was harvested as far posterior as allowed. An additional two Kirschner wires were placed to mark the borders of the area of access. This process was then repeated utilizing: 1) an external fixator for distraction alone, 2) an anterolateral tibial osteotomy alone (with distraction released), and 3) an anterolateral tibial osteotomy (with distraction reapplied). The area accessible as well as the anterior to posterior (AP) access was measured and recorded for each approach. RESULTS: The approach utilizing TID provided greater access than arthrotomy with regard to AP access (p=0.0007) as well as area (p=0.003). The approach utilizing TID alone was equivalent to the anterolateral tibial osteotomy with regard to AP access as well as area. TID combined with osteotomy provided greater access than the TID or osteotomy approaches alone with regard to AP access (p=0.01 and p=0.02, respectively) and greater access than the external fixator alone with regard to area (p=0.02). CONCLUSION: Temporary distraction utilizing external fixation provides greater perpendicular access than anterolateral arthrotomy and access equivalent to anterolateral osteotomy alone. CLINICAL RELEVANCE: Utilizing TID may obviate the morbidity and possible complications associated with osteotomy and may prove to be a valuable tool in the treatment of osteochondral lesions of the talus.

The significance of increased fluid signal on magnetic resonance imaging in lumbar facets in relationship to degenerative spondylolisthesis.

STUDY DESIGN: Retrospective radiographic review of consecutive patients with universally applied standard. OBJECTIVES: To define MRI findings at the facet joints that may suggest abnormal sagittal plane translation seen on standing lateral flexion-extension (SLFE) radiographs. SUMMARY OF BACKGROUND DATA: MRI findings, including facet joint orientation, facet joint osteoarthritis, and the presence of synovial cysts, have all been linked with degenerative spondylolisthesis (DS). MRI can also detect facet joint effusion; however, there has not been a study specifically addressing the association of facet fluid signal to degenerative spondylolisthesis (DS). METHODS: MRI and SLFE films of all patients seen at a single institution for an orthopedic spine consultation over a 2-year period were analyzed. The presence of facet effusions, synovial cysts, increased intensity within the interspinous ligament, degenerative changes at the facets, and anterior sagittal plane translation were all recorded. The data were analyzed to determine if there was a significant association between the presence of DS and the following: facet effusion, degenerative changes of the facets, synovial cysts, increased signal in the interspinous ligament, age, and gender. RESULTS: There were 139 patients without DS at (NegDS) and 54 with DS (PosDS) on SLFE films at L4-L5 (n = 193). PosDS patients were more likely to be older (P < 0.0001), female (P = 0.0042), have synovial cysts (P < 0.0001), have higher osteoarthritis grade (P < 0.0001), and have larger facet effusion size (P < 0.0001). For both groups, facet joint effusions were also found to be significantly larger in patients with Grade 2 or less osteoarthritis, than in patients with Grade 3 osteoarthritis. Twenty-two percent of the listheses were not detectable on supine MRI. CONCLUSION: Large (> 1.5 mm) facet effusions are highly predictive of degenerative spondylolisthesis at L4-L5 in the absence of measurable anterolisthesis on supine MRI. A clinically measurable facet effusion (> or = 1 mm) suggests the need for SLFE films to diagnose degenerative spondylolisthesis that can be missed with supine positioning on MRI.

Intramolecular hydrogen bond strength and pK(a) determination of N,N'-disubstituted imidazole-4,5-dicarboxamides.

N,N'-Disubstituted imidazole-4,5-dicarboxamides (I45DCs) form an intramolecular hydrogen bond worth an estimated 14 +/- 1 kcal/mol, as measured with a model structure in DMSO-d6 at 3 mM, thereby predisposing the molecular conformation to a folded rather than extended form. The I45DCs also show evidence of aggregation in both CDCl3 (>1 mM) and DMSO-d6 (>10 mM) solutions. These compounds are uncharacteristically weak bases in comparison with imidazoles bearing similar electron-withdrawing groups.

Synthesis of symmetric bis(imidazole-4,5-dicarboxamides) substituted with amino acids.

A series of symmetric bis(imidazole-4,5-dicarboxamides) (bis-I45DCs) were prepared with amino acid esters and a variety of linker groups. The critical pyrazine intermediates, substituted with amino acid esters, were synthesized by stoichiometric control of the amino acid ester, even though primary alkanamines, in comparison, generally offer less selectivity for this reaction. Diamines are added to subsequently react with and open the remaining acyl imidazole bonds in the pyrazine intermediates and thereby yield the bis-I45DCs.