T D Brown

University of Iowa, Iowa City, Iowa, United States

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Publications (95)237.2 Total impact

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    ABSTRACT: For systematic laboratory studies of bone fractures in general and intra-articular fractures in particular, it is often necessary to control for injury severity. Quantitatively, a parameter of primary interest in that regard is the energy absorbed during the injury event. For this purpose, a novel technique has been developed to measure energy absorption in experimental impaction. The specific application is for fracture insult to porcine hock (tibiotalar) joints in vivo, for which illustrative intra-operative data are reported. The instrumentation allowed for the measurement of the delivered kinetic energy and of the energy passed through the specimen during impaction. The energy absorbed by the specimen was calculated as the difference between those two values. A foam specimen validation study was first performed to compare the energy absorption measurements from the pendulum instrumentation versus the work of indentation performed by an MTS machine. Following validation, the pendulum apparatus was used to measure the energy absorbed during intra-articular fractures created in 14 minipig hock joints in vivo. The foam validation study showed close correspondence between the pendulum-measured energy absorption and MTS-performed work of indentation. In the survival animal series, the energy delivered ranged from 31.5 to 48.3 Js (41.3 ± 4.0, mean ± s.d.) and the proportion of energy absorbed to energy delivered ranged from 44.2% to 64.7% (53.6% ±4.5%). The foam validation results support the reliability of the energy absorption measure provided by the instrumented pendulum system. Given that a very substantial proportion of delivered energy passed-unabsorbed-through the specimens, the energy absorption measure provided by this novel technique arguably provides better characterization of injury severity than is provided simply by energy delivery.
    Journal of Biomechanical Engineering 06/2014; 136(6). DOI:10.1115/1.4025113 · 1.75 Impact Factor
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    ABSTRACT: Various techniques exist for quantifying articular contact stress distributions, an important class of measurements in the field of orthopaedic biomechanics. In situations where the need for dynamic recording has been paramount, the approach of preference has involved thin-sheet multiplexed grid-array transducers. To date, these sensors have been used to study contact stresses in the knee, shoulder, ankle, wrist, and spinal facet joints. Until now, however, no such sensor had been available for the human hip joint due to difficulties posed by the deep, bi-curvilinear geometry of the acetabulum. We report here the design and development of a novel sensor capable of measuring dynamic contact stress in human cadaveric hip joints (maximum contact stress of 20 MPa and maximum sampling rate 100 readings/s). Particular emphasis is placed on issues concerning calibration, and on the effect of joint curvature on the sensor's performance. The active pressure-sensing regions of the sensors have the shape of a segment of an annulus with a 150-deg circumferential span, and employ a polar/circumferential "ring-and-spoke" sensel grid layout. There are two sensor sizes, having outside radii of 44 and 48 mm, respectively. The new design was evaluated in human cadaver hip joints using two methods. The stress magnitudes and spatial distribution measured by the sensor were compared to contact stresses measured by pressure sensitive film during static loading conditions that simulated heel strike during walking and stair climbing. Additionally, the forces obtained by spatial integration of the sensor contact stresses were compared to the forces measured by load cells during the static simulations and for loading applied by a dynamic hip simulator. Stress magnitudes and spatial distribution patterns obtained from the sensor versus from pressure sensitive film exhibited good agreement. The joint forces obtained during both static and dynamic loading were within ±10% and ±26%, respectively, of the forces measured by the load cells. These results provide confidence in the measurements obtained by the sensor. The new sensor's real-time output and dynamic measurement capabilities hold significant advantages over static measurements from pressure sensitive film.
    Journal of Biomechanical Engineering 03/2014; 136(3). DOI:10.1115/1.4026103 · 1.75 Impact Factor
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    ABSTRACT: As cartilage loss and bone marrow lesions (BMLs) are associated with knee joint pain and structural worsening, this study assessed whether non-invasive estimates of articular contact stress may longitudinally predict risk for worsening of knee cartilage morphology and BMLs. This was a longitudinal cohort study of adults aged 50-79 years with risk factors for knee osteoarthritis. Baseline and follow-up measures included whole-organ magnetic resonance imaging score (WORMS) classification of knee cartilage morphology and BMLs. Tibiofemoral geometry was manually segmented on baseline magnetic resonance imaging (MRI), and three-dimensional (3D) tibiofemoral point clouds were registered into subject-specific loaded apposition using fixed-flexion knee radiographs. Discrete element analysis (DEA) was used to estimate mean and peak contact stresses for the medial and lateral compartments. The association of baseline contact stress with worsening cartilage and BMLs in the same subregion over 30 months was assessed using conditional logistic regression. Subjects (N = 38, 60.5% female) had a mean ± standard deviation (SD) age and body mass index (BMI) of 63.5 ± 8.4 years and 30.5 ± 3.7 kg/m2 respectively. Elevated mean articular contact stress at baseline was associated with worsening cartilage morphology and worsening BMLs by 30 months, with odds ratio (OR) [95% confidence interval (CI)] of 4.0 (2.5, 6.4) and 6.6 (2.7, 16.5) respectively. Peak contact stress also was significantly associated with worsening cartilage morphology and BMLs {1.9 (1.5, 2.3) and 2.3 (1.5, 3.6)}(all P < 0.0001). Detection of higher contact stress 30 months prior to structural worsening suggests an etiological role for mechanical loading. Estimation of articular contact stress with DEA is an efficient and accurate means of predicting subregion-specific knee joint worsening and may be useful in guiding prognosis and treatment.
    Osteoarthritis and Cartilage 06/2012; 20(10):1120-6. DOI:10.1016/j.joca.2012.05.013 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2011; 19. DOI:10.1016/S1063-4584(11)60163-5 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2011; 19. DOI:10.1016/S1063-4584(11)60164-7 · 4.26 Impact Factor
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    ABSTRACT: OBJECTIVE: In osteoarthritis (OA), subchondral bone changes alter the joint's mechanical environment and potentially influence progression of cartilage degeneration. Joint distraction as a treatment for OA has been shown to provide pain relief and functional improvement through mechanisms that are not well understood. This study evaluated whether subchondral bone remodeling was associated with clinical improvement in OA patients treated with joint distraction. METHOD: Twenty-six patients with advanced post-traumatic ankle OA were treated with joint distraction for 3 months using an Ilizarov frame in a referral center. Primary outcome measure was bone density change analyzed on CT scans. Longitudinal, manually segmented CT datasets for a given patient were brought into a common spatial alignment. Changes in bone density (Hounsfield Units (HU), relative to baseline) were calculated at the weight-bearing region, extending subchondrally to a depth of 8mm. Clinical outcome was assessed using the ankle OA scale. RESULTS: Baseline scans demonstrated subchondral sclerosis with local cysts. At 1 and 2 years of follow-up, an overall decrease in bone density (-23% and -21%, respectively) was observed. Interestingly, density in originally low-density (cystic) areas increased. Joint distraction resulted in a decrease in pain (from 60 to 35, scale of 100) and functional deficit (from 67 to 36). Improvements in clinical outcomes were best correlated with disappearance of low-density (cystic) areas (r=0.69). CONCLUSIONS: Treatment of advanced post-traumatic ankle OA with 3 months of joint distraction resulted in bone density normalization that was associated with clinical improvement.
    Osteoarthritis and Cartilage 02/2011; 19(6):668-75. DOI:10.1016/j.joca.2011.02.005 · 4.26 Impact Factor
  • Y. Tochigi, N. A. Segal, T. D. Brown
    Osteoarthritis and Cartilage 10/2010; 18. DOI:10.1016/S1063-4584(10)60174-4 · 4.26 Impact Factor
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    ABSTRACT: Novel biomechanical methods have been developed to objectively measure acute fracture severity (from inter-fragmentary surface area) and chronic contact stress challenge (from patient-specific finite element analysis) in articular fractures. These new methods help clarify the pathomechanics of the development of post-traumatic osteoarthritis, and can contribute directly to the clinical care of patients. In this manuscript, the value of these two new measures is demonstrated in three illustrative tibial plafond fracture cases, in which both metrics are correlated with cartilage status and with patient outcomes at a minimum of two years after injury. These clinical cases demonstrate the utility of new biomechanical variables to advance clinical research and patient care, by providing a basis to predict outcome and select treatment.
    The Iowa orthopaedic journal 01/2010; 30:47-54.
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    ABSTRACT: This paper presents a system for virtual reconstruction of comminuted bone fractures. The system takes as input a collection of bone fragment models represented as surface meshes, typically segmented from CT data. Users interact with fragment models in a virtual environment to reconstruct the fracture. In contrast to other approaches that are either completely automatic or completely interactive, the system attempts to strike a balance between interaction and automation. There are two key fracture reconstruction interactions: (1) specifying matching surface regions between fragment pairs and (2) initiating pairwise and global fragment alignment optimizations. Each match includes two fragment surface patches hypothesized to correspond in the reconstruction. Each alignment optimization initialized by the user triggers a 3D surface registration which takes as input: (1) the specified matches and (2) the current position of the fragments. The proposed system leverages domain knowledge via user interaction, and incorporates recent advancements in surface registration, to generate fragment reconstructions that are more accurate than manual methods and more reliable than completely automatic methods.
    Computer Vision Workshops (ICCV Workshops), 2009 IEEE 12th International Conference on; 11/2009
  • Osteoarthritis and Cartilage 09/2009; 17. DOI:10.1016/S1063-4584(09)60065-0 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2009; 17. DOI:10.1016/S1063-4584(09)60169-2 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2009; 17. DOI:10.1016/S1063-4584(09)60450-7 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2009; 17. DOI:10.1016/S1063-4584(09)60219-3 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2009; 17. DOI:10.1016/S1063-4584(09)60102-3 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2009; 17. DOI:10.1016/S1063-4584(09)60080-7 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2009; 17. DOI:10.1016/S1063-4584(09)60098-4 · 4.26 Impact Factor
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    ABSTRACT: We present a novel framework for the simultaneous segmentation of multiple interacting surfaces belonging to multiple mutually interacting objects. The method is a non-trivial extension of our previously reported optimal multi-surface segmentation. Considering an example application of knee-cartilage segmentation, the framework consists of the following main steps: 1) Shape model construction: Building a mean shape for each bone of the joint (femur, tibia, patella) from interactively segmented volumetric datasets. Using the resulting mean-shape model - identification of cartilage, non-cartilage, and transition areas on the mean-shape bone model surfaces. 2) Presegmentation: Employment of iterative optimal surface detection method to achieve approximate segmentation of individual bone surfaces. 3) Cross-object surface mapping: Detection of inter-bone equidistant separating sheets to help identify corresponding vertex pairs for all interacting surfaces. 4) Multi-object, multi-surface graph construction and final segmentation: Construction of a single multi-bone, multi-surface graph so that two surfaces (bone and cartilage) with zero and non-zero intervening distances can be detected for each bone of the joint, according to whether or not cartilage can be locally absent or present on the bone. To define inter-object relationships, corresponding vertex pairs identified using the separating sheets were interlinked in the graph. The graph optimization algorithm acted on the entire multiobject, multi-surface graph to yield a globally optimal solution. The segmentation framework was tested on 16 MR-DESS knee-joint datasets from the Osteoarthritis Initiative database. The average signed surface positioning error for the 6 detected surfaces ranged from 0.00 to 0.12 mm. When independently initialized, the signed reproducibility error of bone and cartilage segmentation ranged from 0.00 to 0.26 mm. The results showed that this framework provides robust, accurate, and reproducible segmentation of the knee joint bone and cartilage surfaces of the femur, tibia, and patella. As a general segmentation tool, the developed framework can be applied to a broad range of multi-object segmentation problems.
    Proceedings of SPIE - The International Society for Optical Engineering 02/2009; DOI:10.1117/12.812764 · 0.20 Impact Factor
  • Osteoarthritis and Cartilage 09/2008; 16. DOI:10.1016/S1063-4584(08)60600-7 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2008; 16. DOI:10.1016/S1063-4584(08)60314-3 · 4.26 Impact Factor
  • Osteoarthritis and Cartilage 09/2008; 16. DOI:10.1016/S1063-4584(08)60597-X · 4.26 Impact Factor

Publication Stats

1k Citations
237.20 Total Impact Points

Institutions

  • 1987–2012
    • University of Iowa
      • • Department of Orthopaedics and Rehabilitation
      • • Department of Biomedical Engineering
      Iowa City, Iowa, United States
  • 1990
    • University of Iowa Children's Hospital
      Iowa City, Iowa, United States