Biomedical subjects

Steven W Meier

Publications and source records attributed to Steven W Meier.

4 recordsLinked to original sources

PubMed2006

Capturing patterns and symmetries in chaotic granular flow.

Segregation patterns formed by time-periodic flow of polydisperse granular material (varying in particle size) in quasi-two-dimensional (quasi-2D) tumblers capture the symmetries of Poincaré sections, stroboscopic maps of the underlying flow, derived from a continuum model which contains no information about particle properties. We study this phenomenon experimentally by varying the concentration of small particles in a bidisperse mixture in quasi-2D tumblers with square and pentagonal cross sections. By coupling experiments with an analysis of periodic points, we explain the connection between the segregation patterns and the dynamics of the underlying flow. Analysis of the eigenvectors and unstable manifolds of hyperbolic points shows that lobes of segregated small particles stretch from hyperbolic points toward corners of the tumbler, demonstrating the connection between regions of chaotic flow and the shape of the segregation patterns. Furthermore, unstable manifolds map the shape of lobes of segregated particles. The techniques developed here can also be applied to nonpolygonal tumblers such as elliptical tumblers, as well as to circular tumblers with time-periodic forcing.

Journal Article↗

PubMed2006

The effect of double-row fixation on initial repair strength in rotator cuff repair: a biomechanical study.

PURPOSE: The purpose of this study was to compare the initial mechanical strength of 3 rotator cuff repair techniques. METHODS: A total of 30 fresh-frozen cadaveric shoulders were prepared, and full-thickness supraspinatus tears were created. Specimens were randomized and placed into 3 groups: (1) transosseous suture technique (group I: TOS, n = 10, 6F/4M), (2) single-row suture anchor fixation (group II: SRSA, n = 10, 6F/4M), and (3) double-row suture anchor fixation (group III: DRSA, n = 10, 6F/4M). Each specimen underwent cyclic load testing from 5 N to 180 N at a rate of 33 mm/sec. The test was stopped when complete failure (repair site gap of 10 mm) or a total of 5,000 cycles was attained. RESULTS: Group I (TOS) failed at an average of 75.3 +/- 22.49 cycles, and group II (SRSA) at an average of 798.3 +/- 73.28 cycles; group III (DRSA) had no failures because all samples were stopped when 5,000 cycles had been completed. Fixation strength of the DRSA technique proved to be significantly greater than that of SRSA (P < .001), and both suture anchor groups were significantly stronger than the TOS group (P < .001). CONCLUSIONS: Suture anchor repairs were significantly stronger than transosseous repairs. Furthermore, double-row suture anchor fixation was significantly stronger than was single-row repair. Therefore, double-row fixation may be superior to other techniques in that it provides a substantially stronger repair that could lead to improved biologic healing. CLINICAL RELEVANCE: A high incidence of incomplete healing occurs in rotator cuff repair. Use of double-row fixation may help the clinician to address some deficiencies in current methods by increasing the strength of the repair, potentially leading to improved healing rates.

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PubMed2003

Approach to cartilage injury in the anterior cruciate ligament-deficient knee.

The treatment of articular cartilage lesions remains one of the great challenges facing orthopedic surgeons today. The technique of chondrocyte transplantation has opened the door for the application of biologic solutions to difficult problems. These techniques will prove the keystone of further advances into biologic joint repair and replacement. Enthusiasm, however, must be tempered by the numerous gaps in cartilage science and the overwhelming need for further long-term data to demonstrate the efficacy of these techniques in thwarting the presumed eventual progression of these lesions toward osteoarthritis. The status of the articular cartilage is of paramount importance in ACL decision-making. Every effort must be made to protect the existing hyaline articular cartilage during ACL reconstruction. Though current cartilage repair techniques are in their infancy, they remain stepping-stones to future developments. It is hoped that we will one day be able to regenerate normal hyaline cartilage without great morbidity. At present, the ACL surgeon must accept techniques that diminish symptoms and do not burn bridges to future advances. The orthopedic surgeon must increase his knowledge of the basic science of articular cartilage in order to best choose from the various cartilage treatments that evolve.

Anterior Cruciate Ligament↗

PubMedDate not supplied

Rotator cuff repair: the effect of double-row fixation on three-dimensional repair site.

There is a high rate of recurrent and residual tears after rotator cuff repair surgery. Recent cadaveric studies have provided surgeons with new knowledge about the anatomy of the supraspinatus tendon insertion. Traditional repair techniques fail to reproduce the area of the supraspinatus insertion, or footprint, on the greater tuberosity anatomically. Double-row suture anchor (DRSA) fixation is a new technique that has been developed to restore the supraspinatus footprint better. In this study, 3-dimensional mapping was used to determine the area of the footprint recreated with 3 different repair methods: a transosseous simple suture technique, fixation with a single row of suture anchors, and DRSA fixation. The DRSA fixation technique consistently reproduced 100% of the original supraspinatus footprint, whereas the single-row suture anchor fixation and transosseous simple suture techniques reproduced only 46% and 71% of the insertion site, respectively. Therefore, the footprint area of the DRSA fixation technique was significantly larger (P < .05) than that of the other 2 techniques. Furthermore, double-row fixation may provide a tendon-bone interface better suited for biologic healing and restoring normal anatomy.

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