CHARACTERIZATION OF COMPRESSIVE BEHAVIOR OF DEVELOPING HUMAN TALUS

Mechanical characterization of human cartilage anlagen is required in order to effectively model congenital musculoskeletal deformities. Such modeling can effectively explore the effect of treatment procedures and potentially suggest enhanced treatment methods. We therefore determined the stress relaxation behavior of cartilage plugs obtained from third-trimester still-born fetuses in unconfined and confined compression geometries. The material parameters determined were the aggregate modulus adult articular cartilage, stiffness was an order of magnitude lower than the values reported in the literature, inferring the relative softness of the tissue; and the permeability was an order of magnitude higher indicating relative ease of flow in the tissue. Poisson's ratio also was close to the higher end of the range found in previous studies. Such material is expected to deform and relax to larger extents

The Accuracy of the Electrocardiogram during Exercise Stress Test Based on Heart Size

BACKGROUND: Multiple studies have shown that the exercise electrocardiogram (ECG) is less accurate for predicting ischemia, especially in women, and there is additional evidence to suggest that heart size may affect its diagnostic accuracy. HYPOTHESIS: The purpose of this investigation was to assess the diagnostic accuracy of the exercise ECG based on heart size. METHODS: We evaluated 1,011 consecutive patients who were referred for an exercise nuclear stress test. Patients were divided into two groups: small heart size defined as left ventricular end diastolic volume (LVEDV) <65 mL (Group A) and normal heart size defined as LVEDV ≥65 mL (Group B) and associations between ECG outcome (false positive vs. no false positive) and heart size (small vs. normal) were analyzed using the Chi square test for independence, with a Yates continuity correction. LVEDV calculations were performed via a computer-processing algorithm. SPECT myocardial perfusion imaging was used as the gold standard for the presence of coronary artery disease (CAD). RESULTS: Small heart size was found in 142 patients, 123 female and 19 male patients. There was a significant association between ECG outcome and heart size (χ(2) = 4.7, p = 0.03), where smaller hearts were associated with a significantly greater number of false positives. CONCLUSIONS: This study suggests a possible explanation for the poor diagnostic accuracy of exercise stress testing, especially in women, as the overwhelming majority of patients with small heart size were women

Weightbearing CT Assessment of Foot and Ankle Joints in Pes Planovalgus Using Distance Mapping

The goal of this study was to describe the abnormal joint surface interaction at the ankle, hindfoot and midfoot joints in patients presenting with Pes Planovalgus (PPV) using three-dimensional (3D) distance mapping on weightbearing computed tomography (WBCT) images by comparing a series of PPVs to a series of normally-aligned feet. We hypothesized that in PPVs joint interactions would reveal significantly increased spaces in the medial side of the ankle, hindfoot and midfoot joints

Distance Mapping of the Foot and Ankle Joints using Weight Bearing CT: The Cavovarus Configuration

CATEGORY: Ankle; Hindfoot; Midfoot/Forefoot INTRODUCTION/PURPOSE: The cavovarus configuration sets the grounds for various pathological conditions, often involving the arthritic degeneration of the medial column. The objective of this study was to analyze the joint surface interaction at the ankle, hindfoot and midfoot joints using distance mapping on WBCT images in a series of cavovarus feet and compare them to normally aligned feet. METHODS: In this case-control study, a database containing WBCT datasets from 370 feet (189 patients) obtained in a specialized foot and ankle unit from July 2016 to October 2018 was used. Ten feet (10 patients) with asymptomatic cavovarus shape were extracted (cases group; N= 10) and compared to 10 matched-paired (by age, gender and body mass index) normally aligned feet (10 patients) (controls group; N=10). Colored distance maps were generated for the ankle, hindfoot and midfoot joints and divided in zones, therefore differences were assessed between the two groups. RESULTS: In the cavovarus group there was a significant increase in surface-to-surface distance at the posterior tibiotalar joint and a reduced distance at the anterior part, together with a greater distance at the posterior half of the medial gutter. Also, a decrease in surface-to-surface distance on the anterior half of the anterior facet and an increased distance on the posterior quadrants of the posterior facet of the subtalar joint were found. At the sinus tarsi, the lateral aspect of the talonavicular joint, the naviculocuneiform and the tarsometatarsal joints there was a statistically significant increase in surface-to-surface distance in cavovarus patients as compared to controls. CONCLUSION: In this study, the use of distance mapping analysis on WBCT images enabled to identify significant differences in surface-to-surface interaction at the foot and ankle joints between cavovarus and normally-aligned feet

Headless Screw Fixation of Metacarpal Neck Fractures: A Mechanical Comparative Analysis

Background: The purpose of this study was to compare the mechanical properties of metacarpal neck fracture fixation by headless compression screw (HCS) with that of Kirschner wire (KW) cross-pinning and locking plate (LP) fixation. Methods: A metacarpal neck fracture was created in 30 fourth-generation composite Sawbones metacarpal models. A volar-based wedge was removed using a custom jig to simulate a typical apex dorsal fracture, unstable in flexion. The models were divided into 3 equal groups based on the method of fixation: retrograde cross-pinning with two 1.2-mm KWs, 2.0-mm dorsal T-plate with six 2.0-mm locking screws (LP), and a 3.0-mm retrograde HCS. Models were fixed at the proximal end, mounted in a material testing machine, and loaded through a cable tensioned over the metacarpal head, simulating grip loading. Cyclic loading from 0 to 40 N was performed, followed by loading to failure. Load, displacement, and failure mode were recorded. Results: Stiffness of the HCS (7.3 ± 0.7 N/m) was significantly greater than the KW (5.8 ± 0.5 N/m) but significantly less than the LP (9.5 ± 1.9 N/m). With cyclic loading to 40 N, the LP exhibited significantly less displacement (0.2 ± 1.3 mm) compared with the HCS (2.5 ± 2.3 mm) and KW (2.8 ± 1.0 mm). Load to failure for the HCS (215.5 ±3 9.0 N) was lower than that of the KW (279.7 ± 100.3 N) and of the LP (267.9 ± 44.1 N), but these differences were not statistically significant. Conclusions: The HCS provided mechanical fracture fixation properties comparable with KW fixation. The LP construct allowed significantly less displacement and had the highest strength of the 3 fixation methods