STANDING PET OF THE RACEHORSE FETLOCK
Matthieu Spriet, University of California-Davis
One Sentence Summary: Validation of a PET technology for early detection of fetlock lesions in standing horses to prevent catastrophic breakdowns in racehorses.
Catastrophic breakdowns of the lower limb are the most common cause of horse fatalities on the racetrack. The fetlock is the region most frequently involved in catastrophic breakdowns due to fractures. Imaging techniques such as bone scans, computed tomography (CT scans) and magnetic resonance imaging (MRI), have improved the ability to detect injuries that predispose to breakdown when compared with X-rays but many limitations remain. Currently it is still not possible to confidently identify horses at risk for breakdown. Improving the detection of signs that precede breakdown is extremely important in order to reduce the number of accidents on the race track.
Positron Emission Tomography (PET) is an imaging technique that has recently become available for horses. PET relies on the same concepts as a bone scan commonly performed on racehorses and people: a small amount of an injected radioactive tracer concentrates in abnormal areas in bones, leading to the identification of bone injuries. The main difference between PET and a regular bone scan is that PET provides 3-dimensional information with higher resolution, providing precise localization of abnormalities. This allows improved recognition of early injuries that precede breakdowns, as confirmed in a recent study in nine racehorses. The main limitation of the current PET scan technique is the need to anesthetize the horse to obtain images.
To avoid the risks associated with general anesthesia, we have designed a PET system to obtain images in standing horses using only a sedative or tranquilizer. The scanner model previously used is being modified to orient in a way to allow positioning around the limbs of a standing horse. The new scanner has been designed with a ring of detector that opens freely to allow easy positioning and safe release if the horse moves. This important safety concept has been validated with a mechanical prototype of the new scanner.
We believe that this new scanner will be safe and easy to use on horses and provide images that will detect more injuries when compared with regular bone scans. Study Part 1 will validate the new PET scanner by comparing image quality of PET scans obtained from standing and anesthetized research horses at UC Davis. Study Part 2 will be a clinical trial comparing findings from bone scan images and standing PET scan images of racehorses at Santa Anita Racetrack. We expect that more abnormalities
(injuries) will be detected using PET scan than bone scan. PET scans will be repeated at 6 and 12 weeks to assess changes after treatment or rest.
ROBOTIC CT FOR ASSESSING OF BONE MORPHOLOGY
Kyla Ortved, University of Pennsylvania
One Sentence Summary: Preventing catastrophic injuries in the Thoroughbred racehorse: screening fetlock joints using standing robotic CT and biomarker analysis.
Thoroughbred racehorses can be considered elite athletes with high demands placed on their joints and bones. Race training is associated with repetitive stress much like the human runner. The body is capable of adapting to such stress overtime by gradually increasing the thickness and stiffness of areas of bone undergoing the greatest amount of stress. However, this adaptive system can be overwhelmed such that microfractures begin to develop. This is often referred to as maladaptive stress remodeling. If the cycle of repetitive stress does not cease, microfractures can lead to stress fractures or collapse of the joint surface. Unfortunately, some stress fractures can be catastrophic in the racing Thoroughbred. Additionally, collapse of the joint surface can lead to irreversible joint disease or osteoarthritis.
Diagnosing horses early in the process of maladaptive stress remodeling is extremely challenging. Plain radiographs are not sensitive enough to identify subtle changes in bone that may be suggestive of microdamage. Computed tomography (CT) is the best tool for evaluating bone; however, CT imaging of the limbs needs to be performed with the horse under general anesthesia. Magnetic resonance imaging (MRI) is also more sensitive than plain radiography; however, many MRI machines require general anesthesia, while standing MRI scans are time consuming (60-90 minutes). Recently, a new technology has emerged that allows a CT scan to be performed in the standing, sedated horse in a matter of seconds. Robotic arms that navigate a 360o path around a particular site on the limb acquire the CT images. The images are then reconstructed using advanced motion correction software and reconstruction software.
Over the past two years, New Bolton Center has been performing CT scans on standing, sedated horses, with the majority of scans being performed on the fetlock joints of Thoroughbred racehorses. We have been able to produce high-quality images of the fetlock joints in clinical cases using the robotic CT. In this research proposal, we are aiming to perform standing CT scans on young Thoroughbred racehorses during their first year of training such that we can begin to identify early changes in bone that may lead to pathology. In addition, we propose to collect blood samples during the 12-month study period for the purpose of identifying blood markers that may be affected by training. We are very fortunate to have full funding provided by the Pennsylvania Racing Commission to collect blood samples during the 12-month study period for the purpose of identifying endogenous bone and inflammatory biomarkers.
The overarching goal of this research is to assess robotic CT and paired blood analysis as an early screening tool for the development of bone injury such that horses can be treated before irreversible damage or catastrophic injury occurs. In the first aim, we will use robotic CT, to evaluate changes in the bones of the fetlock joint during the first year of race training in young (2-year-old) Thoroughbred racehorses. Horses will be enrolled before they begin race training as 2-year-olds and will have CT scans performed at 0 months (pre-training), 6 months and 12 months. In the second aim, we will collect blood samples from the same group of Thoroughbred racehorses undergoing CTs throughout their first year of training. We will measure changes in blood levels of osteocalcin (a marker of bone growth) and CTX-I (a marker of bone breakdown), as well as blood markers of inflammation.
TRAINING PROGRAMS FOR PREVENTION OF FETLOCK INJURY
Sue Stover, University of California-Davis
One Sentence Summary: Predicting proximal sesamoid bone fracture in racehorses from a calibrated computational model that incorporates training programs, track surface properties, and bone’s reparative processes.
One horse dies from an injury during racing and training for every 24 Thoroughbreds and every 44 Quarter Horses that start in a race [1, 2]. Musculoskeletal injuries cause 80-83% of deaths in racing and training [1-4]. Bone fracture is the most common fatal injury; the proximal sesamoid bones (PSBs), located in the fetlock joint, fracture the most often, accounting for 50-60% of all fractures [4]. Due to the PSBs location, there is no reliable way for veterinarians to determine if an animal is at risk for fracture before an event. Therefore, methods to predict and prevent PSBs fracture are needed.
To prevent bone fractures, we must understand how bone fractures develop in racehorses. We know that bone fractures rarely occur from a single bad step in athletes. Instead, fractures are the result of multiple factors that affect the accumulation of bone damage over racehorses’ careers. These factors are related to the distances that racehorses train and race, the speed of the horse during training and racing, and the stiffness of the race surface that training and racing occur on. Horses with PSB fractures spend more time in active training and racing, complete more events, train and race longer since last layup, have higher exercise intensities 6 months prior to death, and have greater cumulative career distances than other racehorses [8, 9].
Damaged bone can heal if given enough time; therefore, the weekly timing of works and races plays a large role in racehorses’ susceptibility to injury and bone fracture. Further, these factors interact with, and affect, each other over time. In order to understand the impact of training schedules and race surface properties on racehorses’ susceptibility to injury over time, the complex interaction of gait, speed, distance, and timing of exercise; alterations of limb loading due to race surface properties; and the time course of removal of damaged bone and the inherent time lag in the replacement by healthy new bone – must be understood. The complexity of the relationships require computer modeling approaches that take into account the time sensitive nature and interaction of the events to understand the resultant risk for injury.
The goal of this research project is to enhance a finite-element computational model of Thoroughbred PSBs to predict fracture risk based on an animal’s training history. The program uses training history (number of races, distances, etc.), race surface information, and a mathematical model of bone’s innate repair processes to predict damage levels in PSBs. These damage levels can then be related to fracture risk. This research proposal’s focus is on exercise and race surface as risk factors since both can be modified for the prevention of injury.
This project has three main steps (aims). Aim 1 is to calibrate our existing finite element (FE) model that uses training and race history as input factors to predict PSB damage, healing, and porosity, with PSB porosity and microdamage data collected from 20 case and control TB racehorses. Aim 2 is to test the model’s ability to predict PSB fracture using existing exercise history data from 392 TB racehorses and make necessary modifications to the model for the general racehorse population. Aim 3 is to determine what constitutes a “high fracture-risk” exercise program by determining the relative contributions of training regimen and exercise surface to the predicted PSB fracture-risk.