Kai-Nan An

Mayo Clinic - Rochester, Рочестер, Minnesota, United States

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Publications (507)1119.32 Total impact

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    ABSTRACT: Low back pain (LBP) is a costly and widely prevalent health disorder in the U.S. One of the most common causes of LBP is degenerative disc disease (DDD). There are many imaging techniques to characterize disc degeneration; however, there is no way to directly assess the material properties of the intervertebral disc (IVD) within the intact spine. Magnetic resonance elastography (MRE) is a MRI-based technique for non-invasively mapping the mechanical properties of tissues in vivo. The purpose of this study was to investigate the feasibility of using MRE to detect shear wave propagation in and determine the shear stiffness of an axial cross-section of an ex vivo baboon IVD, and compare with shear displacements from a finite element model of a IVD motion segment in response to harmonic shear vibration. MRE was performed on two baboon lumbar spine motion segments (L3-L4) with the posterior elements removed at a range of frequencies (1000-1500Hz) using a standard clinical 1.5T MR scanner. Propagating waves were visualized in an axial cross-section of the baboon IVDs in all three motion-encoding directions, which resembled wave patterns predicted using finite element modeling. The baboon nucleus pulposus showed an average shear stiffness of 79±15 kPa at 1000Hz. These results suggest that MRE is capable of visualizing shear wave propagation in the IVD, assessing the stiffness of the nucleus of the IVD, and can differentiate the nucleus and annulus regions.
    No preview · Article · Dec 2015 · Magnetic Resonance Imaging
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    ABSTRACT: Background Rates of shoulder pain in individuals who use manual wheelchairs (MWCs) as their primary means of mobility have been reported to be as high as 70% during activities of daily living. Current prevailing thought is that mechanical impingement of the soft tissues that reside within the subacromial space between the humeral head and coracoacromial arch is a major contributor to the shoulder pain in users of MWCs. The subacromial space size is directly related to the kinematics at the shoulder joint. Yet to be answered are questions about which common daily tasks are characterized by the most potentially detrimental kinematics. Objective The purpose of this analysis was to quantify and compare potentially detrimental kinematics in three common tasks performed by individuals with spinal cord injury and shoulder pain. These data will add to the body of knowledge and test common assumptions about relative risk of tasks. Design A cross-sectional study of 15 MWC users with shoulder pain. Methods Electromagnetic surface sensor measures of mean and peak scapulothoracic (ST) internal and downward rotation, anterior tilt, and glenohumeral (GH) internal rotation were compared across propulsion, weight relief, and scapular plane abduction tasks using one-way repeated-measure ANOVA. Results Statistical differences were observed between the tasks for all rotations. Mean ST anterior tilt was greater in weight relief and propulsion than during scapular plane abduction (24°, 23°, and 13° of anterior tilt, respectively). Mean GH axial rotation during weight relief was more internally rotated than during propulsion and scapular plane abduction (9°, 26°, and 51° of external rotation, respectively). Limitations Surface-based measures of kinematics are subject to skin motion artifact, especially in translation which was not addressed in this study. Conclusion Each task presented with specific variables that might contribute to risk of developing shoulder “impingement” and pain. These data may assist therapists in their assessment of movement contributions to shoulder pain in this population, as well as in subsequent treatment planning.
    Full-text · Article · Nov 2015 · Frontiers in Bioengineering and Biotechnology

  • No preview · Article · Nov 2015 · Revue de Chirurgie Orthopédique et Traumatologique

  • No preview · Article · Nov 2015 · Revue de Chirurgie Orthopédique et Traumatologique

  • No preview · Article · Nov 2015 · Revue de Chirurgie Orthopédique et Traumatologique
  • M. Rizzo · A. Hooke · K. An · W. Cooney

    No preview · Article · Oct 2015
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    ABSTRACT: Background: Short-segment pedicle screw instrumentation (SSPI) is used for unstable burst fractures to correct deformity and stabilize the spine for fusion. However, pedicle screw loosening, pullout, or breakage often occurs due to the large moment applied during spine motion, leading to poor outcomes. The purpose of this study was to test the ability of a newly designed device, the Trans-Endplate Pedicle Pillar System (TEPPS), to enhance SSPI rigidity and decrease the screw bending moment with a simple posterior approach. Methods: Six human cadaveric spines (T11-L3) were harvested. A burst fracture was created at L1, and the SSPI (Moss Miami System) was used for SSPI fixation. Strain gauge sensors were mounted on upper pedicle screws to measure screw load bearing. Segmental motion (T12-L2) was measured under pure moment of 7.5 Nm. The spine was tested sequentially under 4 conditions: intact; first SSPI alone (SSPI-1); SSPI+TEPPS; and second SSPI alone (SSPI-2). Results: SSPI+TEPPS increased fixation rigidity by 41% in flexion/extension, 28% in lateral bending, and 37% in axial rotation compared with SSPI-1 (P<0.001), and it performed even better compared to SSPI-2 (P<0.001 for all). Importantly, the bending moment on the pedicle screws for SSPI+TEPPS was significantly decreased 63% during spine flexion and 47% in lateral bending (p<0.001). Conclusion: TEPPS provided strong anterior support, enhanced SSPI fixation rigidity, and dramatically decreased the load on the pedicle screws. Its biomechanical benefits could potentially improve fusion rates and decrease SSPI instrumentation failure.
    Preview · Article · Oct 2015 · PLoS ONE
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    ABSTRACT: Carpal tunnel syndrome (CTS) is one of the most common disorders of the hand. Assessment of carpal tunnel tissue mechanical behavior, especially that of the subsynovial connective tissue (SSCT), is important to better understand the mechanisms of CTS. The aim of this study was to develop a hyperelastic material model of human SSCT using mechanical test data and finite element modeling (FEM). Experimental shear test data of SSCT from 7 normal subjects and 7 CTS patients collected in a prior study was used to define material response. Hyperelastic coefficients (μ and α) from the first-order Ogden material property definition were iteratively solved using specimen-specific FEM models simulating the mechanical test conditions. A typical Ogden hyperelastic response for the normal and CTS SSCT was characterized by doing the same with data from all samples averaged together. The mean Ogden coefficients (μ/α) for the normal cadaver and CTS patient SSCT were 1.25×10(-5)MPa/4.51 and 1.99×10(-6)MPa/10.6, respectively when evaluating coefficients for individual specimens. The Ogden coefficients for the typical (averaged data) model for normal cadaver and CTS patient SSCT were 1.63×10(-5)MPa/3.93 and 5.00×10(-7)MPa/9.55, respectively. Assessment of SSCT mechanical response with a hyperelastic material model demonstrated significant differences between patient and normal cadaver. The refined assessment of these differences with this model may be important for future model development and in understanding clinical presentation of CTS.
    No preview · Article · Oct 2015 · Journal of Biomechanics
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    ABSTRACT: Ultrasound imaging has been used to evaluate various shoulder pathologies, whereas, quantification of the rotator cuff muscle stiffness using shear wave elastography (SWE) has not been verified. The purpose of this study was to investigate the reliability and feasibility of SWE measurements for the quantification of supraspinatus (SSP) muscle elasticity. Thirty cadaveric shoulders (18 intact and 12 with torn rotator cuff) were used. Intra- and inter-observer reliability was evaluated on an established SWE technique for measuring the SSP muscle elasticity. To assess the effect of overlying soft tissues above the SSP muscle, SWE values were measured with the transducer placed on the skin, on the subcutaneous fat after removing the skin, on the trapezius muscle after removing the subcutaneous fat, and directly on the SSP muscle. In addition, SWE measurements on 4 shoulder positions (0°, 30°, 60°, and 90° abduction) were compared in those with/without rotator cuff tears. Intra- and inter-observer reliability of SWE measurements were excellent for all regions in SSP muscle. Also, removing the overlying soft tissue showed no significant difference on SWE values measured in the SSP muscle. The SSP muscle with 0° abduction showed large SWE values, whereas, shoulders with large-massive tear showed smaller variation throughout the adduction-abduction positions. SWE is a reliable and feasible tool for quantitatively assessing the SSP muscle elasticity. This study also presented SWE measurements on the SSP muscle under various shoulder abduction positions which might help characterize patterns in accordance to the size of rotator cuff tears.
    Full-text · Article · Oct 2015 · Journal of Biomechanics
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    ABSTRACT: An increased bone mineral density (BMD) in the proximity to tendon insertion can improve rotator cuff repair and healing. However, how a decrease of BMD in the humeral head affects the biomechanical properties of the rotator cuff tendon is still unclear. Previous studies have demonstrated ovariectomy in animals to lead to osteoporosis and decreased BMD, and Teriparatide (PTH) administration to improve BMD and strength of bone. This study aimed to explore the correlation between humeral head BMD and infraspinatus (ISP) tendon insertion strength, and if an increase in bone quantity of the humeral head can improve the strength of the rotator cuff.
    Preview · Article · Oct 2015 · PLoS ONE
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    ABSTRACT: Objective: To assess the correlation of clinician identified myofascial taut bands with their presence and characteristics on Magnetic Resonance Elastography (MRE) imaging. Design: Cross-sectional study. Setting: An MRI research laboratory. Participants: A convenience sample of 65 adults (45 women, 20 men) identified by skilled musculoskeletal physicians as having upper trapezius myofascial pain associated taut bands. Interventions: Subjects had their taut bands outlined and were positioned within a 1.5T MRI machine. Shear waves were induced with a pneumatic transducer located over the belly of the involved muscle. Wave propagation was visualized with MRE images across a vibration-cycle. Imaging data was assessed independently by two skilled MRE interpreters. Main outcome measures: The primary outcome measure was the determination of the intra- and inter-rater reliabilities of MRE taut band identification and their correlation with clinician identification of band presence. Secondary outcomes consisted of the elucidation of the physical characteristics of taut bands and their surrounding muscle tissue. Results: MRE intra- and inter-rater reliability was excellent with Kappa's and 95% Confidence intervals (CI) of 0.86, [0.68, 1.00]; and 0.93, [0.79, 1.00], respectively. Stiffness in MRE identified taut bands was elevated at a mean of 11.5 KPa (±2.4 KPa) and fell to a mean of 5.8 KPa (± 0.9 KPa) in surrounding muscle tissue (p<0.001); muscular tone in trapezius muscles without a taut band was relatively uniform at a mean of 6.6 KPa (±2.1 KPa). Agreement between the physicians and the MRE raters, however, was relatively poor (63.1%, 95% CI [50.2%, 74.7%]). Conclusions: Our findings suggest that while clinicians may overestimate, and current MRE techniques may underestimate, the presence of taut bands, that these bands exist, can be assessed quantitatively, and do represent localized areas of increased muscle stiffness.
    No preview · Article · Oct 2015 · Archives of physical medicine and rehabilitation
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    ABSTRACT: Understanding spinal kinematics is essential for distinguishing between pathological conditions of spine disorders, which ultimately lead to low back pain. It is of high importance to understand how changes in mechanical properties affect the response of the lumbar spine, specifically in an effort to differentiate those associated with disc degeneration from ligamentous changes, allowing for more precise treatment strategies. To do this, the goals of this study were twofold: (1) develop and validate a finite element (FE) model of the lumbar spine and (2) systematically alter the properties of the intervertebral disc and ligaments to define respective roles in functional mechanics. A three-dimensional non-linear FE model of the lumbar spine (L3-sacrum) was developed and validated for pure moment bending. Disc degeneration and sequential ligament failure were modelled. Intersegmental range of motion (ROM) and bending stiffness were measured. The prediction of the FE model to moment loading in all three planes of bending showed very good agreement, where global and intersegmental ROM and bending stiffness of the model fell within one standard deviation of the in vitro results. Degeneration decreased ROM for all directions. Stiffness increased for all directions except axial rotation, where it initially increased then decreased for moderate and severe degeneration, respectively. Incremental ligament failure produced increased ROM and decreased stiffness. This effect was much more pronounced for all directions except lateral bending, which is minimally impacted by ligaments. These results indicate that lateral bending may be more apt to detect the subtle changes associated with degeneration, without being masked by associated changes of surrounding stabilizing structures.
    No preview · Article · Sep 2015 · Computer Methods in Biomechanics and Biomedical Engineering
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    ABSTRACT: Hypothesis: A composite of multilayer tendon slices (COMTS) seeded with bone marrow stromal cells (BMSCs) may impart mechanical and biologic augmentation effects on supraspinatus tendon repair under tension, thereby improving the healing process after surgery in rats. Methods: Adult female Lewis rats (n = 39) underwent transection of the supraspinatus tendon and a 2-mm tendon resection at the distal end, followed by immediate repair to its bony insertion site under tension. Animals received 1 of 3 treatments at the repair site: (1) no augmentation, (2) COMTS augmentation alone, or (3) BMSC-seeded COMTS augmentation. BMSCs were labeled with a fluorescent cell marker. Animals were euthanized 6 weeks after surgery, and the extent of healing of the repaired supraspinatus tendon was evaluated with biomechanical testing and histologic analysis. Results: Histologic analysis showed gap formation between the repaired tendon and bone in all specimens, regardless of treatment. Robust fibrous tissue was observed in rats with BMSC-seeded COMTS augmentation; however, fibrous tissue was scarce within the gap in rats with no augmentation or COMTS-only augmentation. Labeled transplanted BMSCs were observed throughout the repair site. Biomechanical analysis showed that the repairs augmented with BMSC-seeded COMTS had significantly greater ultimate load to failure and stiffness compared with other treatments. However, baseline (time 0) data showed that COMTS-only augmentation did not increase mechanical strength of the repair site. Conclusion: Although the COMTS scaffold did not increase the initial repair strength, the BMSC-seeded scaffold increased healing strength and stiffness 6 weeks after rotator cuff repair in a rat model.
    No preview · Article · Sep 2015 · Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.]
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    ABSTRACT: Osteoporosis is characterized by bony material loss and decreased bone strength leading to a significant increase in fracture risk. Patient-specific quantitative computed tomography (QCT) finite element (FE) models may be used to predict fracture under physiological loading. Material properties for the FE models used to predict fracture are obtained by converting grayscale values from the CT into volumetric bone mineral density (vBMD) using calibration phantoms. If there are any variations arising from the CT acquisition protocol, vBMD estimation and material property assignment could be affected, thus, affecting fracture risk prediction. We hypothesized that material property assignments may be dependent on scanning and postprocessing settings including voltage, current and reconstruction kernel, thus, potentially having an effect in fracture risk prediction. A rabbit femur and a standard calibration phantom were imaged by QCT using different protocols. Cortical and cancellous regions were segmented, their average HU values obtained and converted to vBMD. Estimated vBMD for the cortical and cancellous regions were affected by voltage and kernel but not by current. Our study demonstrated that there exists a significant variation in the estimated vBMD values obtained with different scanning acquisitions. In addition, the large noise differences observed utilizing different scanning parameters could have an important negative effect on small subregions containing fewer voxels.
    No preview · Article · Sep 2015 · Journal of Biomechanical Engineering
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    ABSTRACT: A new wireless sensor was designed, fabricated and applied for in situ monitoring of tensile force at a wound site. The sensor was comprised of a thin strip of magnetoelastic material with its two ends connected to suture threads for securing the sensor across a wound repair site. Since the sensor was remotely interrogated by applying an AC magnetic field and capturing the resulting magnetic field, it did not require direct wire connections to an external device or internal battery for long-term use. Due to its magnetoelastic property, the application of a tensile force changed the magnetic permeability of the sensor, altering the amplitude of the measured magnetic field. This work presents two sensor designs: one for high and one for low force ranges. A sensor was fabricated by directly adhering the magnetoelastic strip to the suture. This sensor showed good sensitivity at low force, but its response saturated at about 1.5 N. To monitor high tensile force, the magnetoelastic strip was attached to a metal strip for load sharing. The suture thread was attached to both ends of the metal strip so only a fraction of the applied force was directed to the sensor, allowing it to exhibit good sensitivity even at 44.5 N. The sensor was applied to two ex vivo models: a sutured section of porcine skin and a whitetail deer Achilles tendon. The results demonstrate the potential for in vivo force monitoring at a wound repair site.
    No preview · Article · Sep 2015 · IEEE transactions on bio-medical engineering
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    ABSTRACT: To determine if impregnating a suture with a cross-linking agent, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), improved suture pull-out strength and cell viability. Canine flexor digitorum profundus tendons were cut in canine zone D, and a single suture loop was placed in each end, with sutures soaked in either saline or an EDC solution with a concentration of 1%, 10%, or 50%. Suture pull-out strength, stiffness, and elongation to failure was determined by pulling the loop until failure. Cytotoxicity of the EDC treatment was evaluated by suspending treated sutures over cultured tenocytes. Mechanical properties for the EDC-treated side were improved over controls when treated with the 10% and 50% EDC solutions. The ratio of dead to live cells was significantly increased at all distances from the suture for the 50% EDC-treated group. Suture treated with a 10% EDC solution provided the best combination of mechanical reinforcement and limited toxicity. Sutures so treated may improve the ability of a tendon repair to sustain early mobilization. Copyright © 2015 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.
    No preview · Article · Aug 2015 · The Journal of hand surgery
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    ABSTRACT: Pregnancy-associated plasma protein-A (PAPP-A) serves to increase local insulin-like growth factor (IGF) stimulation of proliferation and differentiation in many tissues through proteolysis of inhibitory IGF-binding proteins. The purpose of this study was to investigate the effects of PAPP-A on tendon structure and mechanical properties. A total of 30 tails from 6-month-old mice were tested with 10 tails in each of following groups: PAPP-A knockout (KO), skeletal-specific PAPP-A overexpressing transgenic (Tg) and Wild type (WT). Morphologically, the total tail cross-sectional area (CSA), individual tissue CSAs of bone, muscle and tendon, and fascicle diameter were measured. A fascicle pullout test was performed to assess stiffness and strength of interfascicular structures. Fascicles were mechanically characterized through low and high displacement rate uniaxial tension tests providing modulus at each rate, hysteresis area and stress relaxation ratio. The KO mice had a smaller total tail CSA (p<0.05), fascicle diameter (p<0.05), absolute tendon CSA (p<0.05), fast and slow stiffness (p<0.05 for both) and larger hysteresis area (p<0.05) compared to WT and Tg mice. On the other hand, the Tg mice had a larger fascicle diameter (p<0.05), absolute tendon CSA (p<0.05), higher interfascicular strength and stiffness (p<0.05) and lower fascicular modulus at low displacement rates (p<0.05) compared to WT and KO mice. Tg mice also had larger total tail CSA area (p<0.05) and smaller hysteresis area (p<0.05) than KO mice, and larger normalized tendon CSA (p<0.05) than WT mice. Based on these data, we conclude that PAPP-A affects fascicle structure, thereby affecting tendon phenotype. Copyright © 2015. Published by Elsevier Inc.
    Full-text · Article · Aug 2015 · Journal of Structural Biology
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    ABSTRACT: Osteoporotic vertebral body fractures are an increasing clinical problem among the aging population. Specimen-specific finite element models, derived from quantitative computed tomography (QCT), have the potential to more accurately predict failure loads in the vertebra. Additionally, the use of extended finite element modeling (X-FEM) allows for a detailed analysis of crack initiation and propagation in various materials. Our aim was to study the feasibility of QCT/X-FEM analysis to predict fracture properties of vertebral bodies. Three cadaveric specimens were obtained, and the L3 vertebrae were excised. The vertebrae were CT scanned to develop computational models and mechanically tested in compression to measure failure load, stiffness and to observe crack location. One vertebra was used for calibration of the material properties from experimental results and CT gray-scale values. The two additional specimens were used to assess the model prediction. The resulting QCT/X-FEM model of the specimen used for calibration had 2 and 4 % errors in stiffness and failure load, respectively, compared with the experiment. The predicted failure loads of the additional two vertebrae were larger by about 41-44 % when compared to the measured values, while the stiffness differed by 129 and 40 %. The predicted fracture patterns matched fairly well with the visually observed experimental cracks. Our feasibility study indicated that the QCT/X-FEM method used to predict vertebral compression fractures is a promising tool to consider in future applications for improving vertebral fracture risk prediction in the elderly.
    No preview · Article · Aug 2015 · Medical & Biological Engineering

  • No preview · Article · Aug 2015
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    ABSTRACT: The purpose of the study was to test a novel treatment that carbodiimide-derivatized-hyaluronic acid-lubricin (cd-HA-lubricin) combined cell-based therapy in an immobilized flexor tendon repair in a canine model. Seventy-eight flexor tendons from 39 dogs were transected. One tendon was treated with cd-HA-lubricin plus an interpositional graft of 8×10(5) BMSCs and GDF-5. The other tendon was repaired without treatment. After 21-day of immobilization, 19 dogs were sacrificed; the remaining 20 dogs underwent a 21-day rehabilitation protocol before euthanasia. The work of flexion, tendon gliding resistance, and adhesion score in treated tendons were significantly less than the untreated tendons (P<0.05). The failure strength of the untreated tendons was higher than the treated tendons at 21 and 42 days (P<0.05). However, there is no significant difference in stiffness between two groups at day-42. Histologic analysis of treated tendons showed a smooth surface and viable transplanted cells 42 days after the repair, whereas untreated tendons showed severe adhesion formation around the repair site. The combination of lubricant and cell treatment resulted in significantly improved digit function, reduced adhesion formation. This novel treatment can address the unmet needs of patients who are unable to commence an early mobilization protocol after flexor tendon repair. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    No preview · Article · Jul 2015 · Journal of Orthopaedic Research

Publication Stats

8k Citations
1,119.32 Total Impact Points


  • 1985-2015
    • Mayo Clinic - Rochester
      • • Division of Orthopaedic Surgery
      • • Department of Orthopedics
      Рочестер, Minnesota, United States
  • 2009-2012
    • Rochester College
      Rochester, New York, United States
    • University of Rhode Island
      Кингстон, Rhode Island, United States
  • 2011
    • Sapporo Medical University
      • Graduate School of Health Sciences
      Sapporo, Hokkaido, Japan
    • Osaka University
      • Division of Orthopaedic Surgery
      Suika, Ōsaka, Japan
  • 2010
    • University Medical Center Utrecht
      Utrecht, Utrecht, Netherlands
  • 2005
    • Mayo Foundation for Medical Education and Research
      Rochester, Michigan, United States
  • 2003
    • National Cheng Kung University
      • Institute of Biomedical Engineering (IBE)
      臺南市, Taiwan, Taiwan
  • 2001-2002
    • Brock University
      • Faculty of Applied Health Sciences
      St. Catharines, Ontario, Canada