MSGID: 1:317/3 6270b022   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Image-based mechanical simulations improve accuracy in gauging healing   
   progress of bone fractures    
      
     Date:   
         May 2, 2022   
     Source:   
         Lehigh University   
     Summary:   
         When you first break a bone, the body sends out an inflammatory   
         response, and cells begin to form a hematoma around the injured   
         area. Within a week or two, that blood clot is replaced with a soft   
         material called callus that forms a bridge of sorts that holds the   
         fragments together. Over months, the callus hardens into bone,   
         and the healing process is complete. But sometimes, that bridge   
         between the bones fails to form, creating a nonunion.   
      
      
      
   FULL STORY   
   ==========================================================================   
   When you first break a bone, the body sends out an inflammatory response,   
   and cells begin to form a hematoma around the injured area. Within a week   
   or two, that blood clot is replaced with a soft material called callus   
   that forms a bridge of sorts that holds the fragments together. Over   
   months, the callus hardens into bone, and the healing process is complete.   
      
      
   ==========================================================================   
   But sometimes, that bridge between the bones fails to form, creating a   
   nonunion. In patients with long-bone fractures (of the tibia, fibia, or   
   femur, for example), nonunions can be particularly debilitating, severely   
   affecting their quality of life and ability to work. For surgeons,   
   nonunions can be difficult to diagnose as they require subjective   
   assessments of X-rays taken over a period of six to nine months. The   
   difficulty lies in that the bone couldbe healing, just very slowly, in   
   which case additional intervention may not be necessary. But if it's not   
   healing, the patient has endured months of pain and limited activity,   
   only to face additional surgery.   
      
   In a perfect world, surgeons would have a tool that could identify   
   nonunions earlier.   
      
   "The end goal is to save patients time, money, and frustration," says   
   Brendan Inglis, a Lehigh University graduate student in the Department   
   of Mechanical Engineering and Mechanics. "Because if the surgeon comes   
   back to you and says you have a clinically diagnosed nonunion, and you   
   need further interventions, that's going to further delay your ability to   
   get back to your life."  Inglis is the lead author of a paper recently   
   published in Scientific Reports that shows how the dual nature of the   
   healing zone, as both a soft and hard material, determines the mechanical   
   rigidity of the whole bone. The work builds on research in the lab of   
   Hannah Dailey, an assistant professor of mechanical engineering and   
   mechanics in Lehigh's P.C. Rossin College of Engineering and Applied   
   Science. Previously, the team has shown the viability of using a non-   
   invasive, imaging-based virtual biomechanical test to assess the progress   
   of fracture healing. Additionally, the team has developed and validated   
   a material properties assignment method for intact ovine bones using   
   virtual biomechanical testing.   
      
   The problem, says Inglis, was that the virtual tests overpredicted the   
   mechanical properties of the bone early in the healing process because   
   parts of the callus are still too soft to be modeled as bone.   
      
      
      
   ==========================================================================   
   "When we applied that model to fractured ovine tibia, essentially a   
   sheep's lower leg, the mechanical properties didn't match," he says. "Our   
   hypothesis was that all the soft tissue and cartilage involved in the   
   healing of a fractured limb was being overpredicted, meaning the callus   
   was being assigned properties that were too stiff."  In other words,   
   the previous model didn't accurately differentiate between bone and   
   callus. If callus was treated as being stiffer than it actually was,   
   it could imply that the bone was further along in the healing process   
   than it actually was.   
      
   "Callus is a highly heterogeneous tissue, meaning it contains more than   
   one density and stiffness value," says Inglis. "So if you're going to   
   model an operated limb, you can't treat everything as dense bone. You   
   need to come up with some way to treat callus differently. But the   
   mechanical properties of callus still aren't well understood, and there   
   wasn't anything in the literature that set the cutoff point between   
   where you start treating the healing zone as soft tissue, and where   
   you start treating it as bone."  To determine that cutoff, Inglis and   
   his team worked with collaborators at the Musculoskeletal Research Unit   
   (MSRU) at the University of Zurich. The Swiss researchers used a torsion   
   tester to measure torsional rigidity in excised sheep tibia, and the   
   Lehigh team used the corresponding CT scans and data to replicate those   
   biomechanical tests virtually.   
      
   Inglis explains that the brightness of the pixels within the CT bone   
   scans correlate to density. The brighter the pixel, the stiffer that   
   area of bone.   
      
      
      
   ==========================================================================   
   "You can imagine that from a black pixel to the brightest white pixel,   
   there's a whole spectrum of values. So essentially what we did was   
   find the cutoff below which the pixels are getting darker and should be   
   treated as very soft.   
      
   We postulated that prior to this study, those darker pixels were   
   being calibrated too high, and assumed to be too stiff in the model."   
   Utilizing a piecewise material model, they optimized a cutoff point that   
   separates soft tissue from bone.   
      
   "When you get that density cutoff right, the virtual models can accurately   
   replicate the rigidity you get from a bench biomechanical test of that   
   same bone," he says. "Once you have a model that's validated to what was   
   done on a bench test, you can start to predict different things about   
   the behavior of healing bones. And the more we understand about why the   
   healing process fails, the better our chances of creating a tool that   
   could one day inform surgeons.   
      
   So this model gives us a foothold into one day translating this work   
   into the clinic."  To illustrate their findings, Inglis created an app   
   that allows others in the field to interact with the data.   
      
   "As researchers, we often read a great paper, and come across a value   
   we'll be curious about, and the citation just points us to another paper,   
   which points you to another paper, and so it becomes this whole rabbit   
   hole effect," he says. "This app is a nice way to visualize what we   
   did, and build it into your own research. I think in an ideal world,   
   there will be more sharing of information like this because in the end,   
   that's the purpose of doing research."  This research is based in part   
   upon work supported by the National Science Foundation (NSF) under a   
   CAREER Award to Hannah Dailey (Grant No. CMMI- 1943287.)   
      
   ==========================================================================   
   Story Source: Materials provided by Lehigh_University. Note: Content   
   may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Brendan Inglis, Peter Schwarzenberg, Karina Klein, Brigitte von   
         Rechenberg, Salim Darwiche, Hannah L. Dailey. Biomechanical duality   
         of fracture healing captured using virtual mechanical testing and   
         validated in ovine bones. Scientific Reports, 2022; 12 (1) DOI:   
         10.1038/s41598-022- 06267-8   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220502094804.htm   
      
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