Walter Smith

Mapping amphibian contact zones and phylogeographical break hotspots across the United States

Identifying congruence in the geographical position of lineage breaks and species range limits across multiple taxa is a focus of the field of comparative phylogeography. These regions are biogeographical hotspots for investigations into the processes driving divergence at multiple phylogenetic levels. We used spatially explicit statistical methods to identify these regions for amphibians across the United States. Significant clustering occurred in the Appalachian Mountains and in the general area of Alabama – a region underappreciated as an important amphibian hotspot. When the orders Caudata and Anura were examined separately, spatial clustering was still found in Alabama for both. However, in Caudata the Appalachians and California were also important, and for Anura, the Great Lakes region was highlighted. When species richness was statistically controlled, cluster hotspots shifted out of Alabama and the Appalachians and moved to broader swaths of the Great Lakes region, southwestern United States and California. The exact location of particular suture zones is probably a result of complex interactions between historical and ecological factors including physiography, climate and distance from glacial refugia. These contact zone and phylogeographical break hotspots are ideal arenas in which to test alternative speciation hypotheses and examine the extent of reproductive isolation using novel, integrative approaches combining modern methods in statistical phylogeography, ecological niche modelling and genomics.

Influences of temperature and oxygen upon habitat selection by bullfrog tadpoles and three species of freshwater fishes in two Alabama strip mine ponds

We studied the annual distributions of dissolved oxygen, temperature, and four aquatic vertebrates in two relatively young ponds (Road Pond and Strip Mine Pond) formed by strip mining operations in Alabama. On the basis of the limnological data, Road Pond was classified as warm polymictic and Strip Mine Pond as warm monomictic. In Strip Mine Pond, the summertime distribution of fish (bluegills, Lepomis macrochirus) was clearly related to oxygen availability, with fish avoiding severely hypoxic or anoxic water found at depths >2 m. However, bullfrog tadpoles commonly occurred in water at depths ≥ 2 m, where the PO2 was at or below their critical O2 tension. Tadpoles occurring at these depths switched from facultative air-breathing to obligate air-breathing and may have been using these depths as a refugium. In Road Pond, fishes (fathead minnows, Pimephales promelas, and golden shiners, Notemigonus crysoleucas) congregated during summertime in shallower waters. Bullfrog (Rana catesbeiana) tadpoles preferred the deeper portions of Road Pond. The contrasting distributions of tadpoles in the two ponds are potentially explainable on the basis of predation pressure.

Percutaneous Posterior to Anterior Screw Fixation of the Talar Neck: Soft Tissue Structures at Risk

Category: Trauma Introduction/Purpose: Fractures of the talar neck and body can be fixed with percutaneously placed screws directed from anterior to posterior or posterior to anterior. The latter has been found to be biomechanically and anatomically superior. Percutaneous pin and screw placement poses anatomic risks for posterolateral and posteromedial neurovascular and tendinous structures. The objective of this study was to enumerate the number of trials for proper placement of two parallel screws and to determine the injury rate to neurovascular and tendinous structures. Methods: Eleven fresh frozen cadaver limbs were used. 2.0 mm guide wires from the Stryker (Selzach, Switzerland) 5.0-mm headless cannulated set were percutaneously placed (under fluoroscopic guidance) into the distal posterolateral aspect of the ankle. All surgical procedures were performed by a fellowship-trained foot and ankle surgeon. Malpositioned pins were left intact to allow later assessment of soft tissue injury. The number of guide wires needed to achieve an acceptable positioning of the implant was noted. Acceptable positioning was defined as in line with the talar neck axis in both AP and lateral fluoroscopic views. After a layered dissection from the skin to the tibia, we evaluated neurovascular and tendinous injuries, and measured the shortest distance between the closest guide pin and the soft tissue structures, using a precision digital caliper. Results: The mean number of guide wires needed to achieve acceptable positioning for 2 parallel screws was 2.91 ± 0.70 (range, 2 - 5). The mean distances between the closest guide pin and the soft tissue structures of interest were: Achilles tendon, 0.53 ± 0.94 mm; flexor hallucis longus tendon, 6.62 ± 3.24 mm; peroneal tendons, 7.51 ± 2.92 mm; and posteromedial neurovascular bundle, 11.73 ± 3.48 mm. The sural bundle was injured in all the specimens, with 8/11 (72.7%) in direct contact with the guide pin and 3/11 (17.3%) having been transected. The peroneal tendons were transected in 1/11 (9%) of the specimens. The Achilles tendon was in contact with the guide pin in 6/11 (54.5%) specimens and transected in 2/11 (18.2%) specimens. Conclusion: The placement of posterior to anterior percutaneous screws for talar neck fixation is technically demanding and multiple guide pins are needed. Our cadaveric study showed that important tendinous and neurovascular structures are in close proximity with the guide pins and that the sural bundle was injured in 100% of the cases. We advise performing a formal small posterolateral approach for proper visualization and retraction of structures at risk. Regardless, adequate patient education about the high risk of injury from this procedure is crucial.

Percutaneous Tendon Achilles Lengthening: What Are We Really Doing?

Category: Hindfoot Introduction/Purpose: Percutaneous Achilles tendon lengthening (TAL) is a common procedure used to address equinus contracture of the foot. A triple hemisection technique has become popular due to its ease and efficiency. Several studies evaluate the surgical outcomes of this procedure, but currently, descriptive anatomical studies are lacking. The objective of the study was to evaluate the accuracy of performing Achilles tendon percutaneous hemisections, the amount of tendon excursion in the tensile gaps of the cuts after forced dorsiflexion and the improvement in the range of motion for dorsiflexion of the ankle joint. Methods: Ten fresh-frozen above-knee cadaveric specimens were used. A percutaneous triple hemisection of theAchilles tendon (proximal, intermediate, and distal) was performed. Maximum ankle dorsiflexion was evaluated pre- and postprocedure with a digital goniometer. After proper dissection, the relative width of the cuts was noted. Followingforced ankle dorsiflexion, displacement in the tensile gaps was measured in all 3 cuts with a precision digital caliper. Results: The overall relative width of the percutaneous cut was 51.3% ± 16.3% of the Achilles tendon diameter, 44.3%± 13.6% for the proximal cut, 50.3% ± 15.6% for the intermediate cut, and 59.3% ± 18.4% for the distal cut. Tendonexcursion averaged 13.0 ± 3.8 mm for the proximal cuts, 12.5 ± 4.7 mm for the intermediate cuts, and 8.2 ± 3.7 mm forthe distal cuts. One cadaver had a complete rupture of the Achilles tendon and was excluded from the excursion dataanalysis. The mean range of motion for ankle dorsiflexion was 8.1 ± 3.9 degrees preprocedure and 27.6 ± 5.3 degreespostprocedure. The dorsiflexion angle significantly increased (P < .0001) at an average of 19.5 ± 5.0 degrees following TAL. Conclusion: Our cadaveric study demonstrated that the percutaneous triple hemisection of the Achilles was an accuratetechnique that provided successful lengthening of the tendon and increased ankle dorsiflexion. Complete ruptures arepossible complications. Our cadaveric study showed that in a clinical situation, triple hemisections of the Achilles tendon can be performed reliably, with significant improvement of the ankle dorsiflexion, mainly through increased tendon excursion at the proximal and intermediate cuts, and with low risk of complete ruptures.

Intraoperative Syndesmotic Instability Test: A Novel Alternative Technique

Category: Ankle, Trauma Introduction/Purpose: Precise diagnosis of distal tibiofibular syndesmotic injury is challenging and a gold standard diagnostic test has still not been established. Tibiofibular clear space identified on radiographic imaging is considered the most reliable indicator of the injury. The Cotton test is the most widely used intraoperative technique to evaluate the syndesmotic integrity although it has its limitations. We advocate for a novel intra operative test using a 3.5 mm cortical tap. Methods: Tibiofibular clear space was assessed in nine cadaveric specimens using three sequential fluoroscopic images. The first image was taken prior to the application of the tap test representing the intact and non-stressed state. Then, a 2.5 mm hole was drilled distally on the lateral fibula, and a 3.5 mm cortical tap was then threaded in the hole. The tap test involved gradually advancing the blunt tip against the lateral tibia, providing a tibiofibular separation force (intact, stressed). This same stress was then applied after all syndesmotic ligaments were released (injured, stressed). Measurements were compared by one-way ANOVA and paired Student’s t-test. Intra and inter-observer agreements were evaluated by intraclass correlation coefficient (ICC). P-values <.05 were considered significant. Results: We found excellent intra-observer (0.97) and inter-observer (0.98) agreement following the imaging assessment. Significant differences were found in the paired comparison between the groups (p<.05). When using an absolute value for TFCS >6 mm as diagnostic for syndesmotic instability, the tap test demonstrated a 96.3% sensitivity and specificity, a 96.3% PPV and NPV and a 96.3% accuracy in diagnosing syndesmotic instability. Conclusion: Our cadaveric study showed that this novel syndesmotic instability test using a 3.5 mm blunt cortical tap is a simple, accurate and reliable technique able to demonstrate significant differences in the tibiofibular clear space when injury was present. It could represent a more controlled and stable low-cost alternative to the most used Cotton test.

Ankle Fusion Percutaneous Home Run Screw Fixation: technical aspects and soft tissue structures at risk

Category: Ankle Arthritis Introduction/Purpose: During internal fixation of ankle fusions, besides the standard crossed screw fixation pattern, the use of a percutaneously placed augmenting screw, directed from the posterolateral tibial metaphysis proximally across the ankle into the talar neck (“ankle fusion home run screw”), is a widely used technique. The placement of this screw is technically demanding and multiple attempts under fluoroscopy guidance are frequently needed to achieve a perfect positioning of the implant. Injuries to local neurovascular and tendinous structures might happen. The objective of this cadaver study was to identify the number of attempts necessary for a perfect positioning of the ankle fusion home run screw and the neurovascular and tendinous structures at risk. Methods: Eleven fresh frozen cadaver limbs were used. Guide wires (3.2 mm) from the Stryker (Selzach, Switzerland) 7.0-mm headless cannulated set were percutaneously placed into the distal posterolateral aspect of the leg, under fluoroscopic guidance, with the ankle held in neutral position. Mal positioned pins were not removed and served as guidance for the following pins. The number of guide wires needed to achieve an acceptable positioning of the implant was noted. After a layered dissection from the skin to the tibia, we evaluated neurovascular and tendinous injuries, and measured the shortest distance between the closest guide pin and the soft tissue structures, using a precision digital caliper. Results: The mean number of guide wires needed to achieve and acceptable positioning of the implant was 2.09 (SD 0.83, range 1- 4). The mean distances between the closest guide pin and the soft tissue structures of interest were: Achilles tendon 6.90 mm (SD 3.74 mm); peroneal tendons 9.65 mm (SD 3.99 mm); sural neurovascular bundle 0.97 mm (SD 1.93 mm); posteromedial neurovascular bundle 14.26 mm (SD 4.56 mm). Sural bundle was in contact with the guide pin in 5/11 specimens (45.5%) and transected in 3/11 specimens (27.3%). Conclusion: The placement of percutaneous ankle fusion home run screws is technically demanding and multiple guide pins are needed. Our cadaveric study showed that important tendinous and neurovascular structures are in close proximity with the guide pins and that the sural bundle is injured in approximately 73% of the cases. Caution should be taken during percutaneous placing of screws and an appropriate approach and surgical dissection to bone is advised.

Tendências no tratamento cirúrgico das fraturas do colo do fêmur em idosos

ABSTRACT Objective To analyze recent demographic and medical billing trends in treatment of femoral neck fracture of American elderly patients. Methods The American College of Surgeons National Surgical Quality Improvement Program database was analyzed from 2006 to 2015, for patients aged 65 years and older, using the Current Procedural Terminology codes 27130, 27125, 27235, and 27236. Patient demographics, postoperative complications, and frequency of codes were compared and analyzed over time. Our sample had 17,122 elderly patients, in that, 70% were female, mean age of 80.1 years (standard deviation±6.6 years). Results The number of cases increased, but age, gender, body mass index, rates of diabetes and smoking did not change over time. Open reduction internal fixation was the most commonly billed code, with 9,169 patients (53.6%), followed by hemiarthroplasty with 5,861 (34.2%) patients. Combined estimated probability of morbidity was 9.8% (standard deviation±5.2%), and did not change significantly over time. Postoperative complication rates were similar between treatments. Conclusion Demographics and morbidity rates in femoral neck fractures of elderly patients did not change significantly from 2006 to 2015. Open reduction internal fixation was the most common treatment followed by hemiarthroplasty.