Rates of anterior cruciate ligament (ACL) injuries continue to rise, especially in female athletes who play multidirectional sports. For example, in high school and collegiate athletes, the incidence of ACL injury is 2 - 6 times higher in females than males. Recent studies have demonstrated that the ACL can rupture due to overuse - specifically due to landing at high forces while pivoting the foot as typically occurs during sports where athletes quickly change direction. This project focuses on using wearable inertial measurement unit (IMU) sensors to identify these types of potentially injurious landings. IMUs, which consist of accelerometers, rate gyroscopes, and magnetic field sensors, can provide information about the acceleration, velocity and position of one body segment with respect to another and have been used to estimate various limb angles and GRFs (Ground Reaction Forces). The first phase or the project is to study soft tissue overuse injury using a wearable device in order to identify injurious loading cycles in a cadaver model. Findings obtained will then be validated in the field with female athletes. This project will produce new knowledge about the relationship between measurements taken by wearable devices and musculoskeletal fatigue loading. The results will lead to better methods for preventing ACL overuse injuries and will provide a framework for the monitoring and prevention of such injuries in athletic, military, firefighter and other populations at risk for injury. Graduate and undergraduate students from two universities (University of Michigan-Dearborn and University of Michigan-Ann Arbor) will work together on this project, increasing their exposure to research and helping to encourage enrollment in biomedical sciences graduate programs.
The goal of the project is to study soft tissue overuse injury mechanisms using a wearable inertial measurement unit (IMU) to identify injurious loading cycles and to validate this in the field with a view toward developing injury prevention strategies. Although it is known that fatigue failure of the ACL is possible, there is currently no way to identify loading conditions that cause this failure in the field, what types of activities athletes perform that put them at risk for this manner of loading or what mechanism underlie the apparently random failure of the ACL during athletic moves made hundreds of times before injury. To address these identification needs and achieve the project's goal, the Research Plan is organized under three objectives. The FIRST Objective is to identify injurious loading cycles using a wearable IMU based on kinematic inputs of impact force, knee moments, angles or anterior tibial translation in an in vitro model. Studies are designed to test the hypothesis that IMUs secured to the lower leg and thigh can accurately predict the occurrence of a loading cycle that is known to cause fatigue damage to the ACL. Female cadaver knee specimens will be placed in a tibial torsional device and instrumented with wearable IMUs on the tibia and thigh. Knees will be subjected to repeated loading (100 cycles total) at targeted landing forces, imposed by a drop weight to the end of the distal tibia, with a knee flexion moment and tibial torque designed to simulate a pivot landing. The SECOND Objective is to identify in vivo the athletic activities that correspond to injurious loading conditions, correlate various parameters such as GRF and knee moments to IMU measurements and examine error due to soft tissue motion. Studies are designed to test the hypothesis that there are specific physical activities that occur during multidirectional sports that correspond to known loading conditions that cause overuse ACL injury and linear acceleration and angular acceleration values measured by an IMU can be used to identify these movements in the laboratory. Volunteers from college soccer and basketball teams, instrumented with motion capture markers located on lower extremities and wearable IMUs above and below the knee, will be asked to complete possible injury related tasks, e.g. a jog with a pivot and sidestep and crossover cuts. A 6 degree-of-freedom kinematic model of the lower extremity will be created for each participant using Visual 3D software. The THIRD Objective is to validate the use of an IMU to detect and count potentially dangerous loading cycles in a real-world setting. Studies are designed to test the hypothesis that severe loading cycles can be identified using IMUs in a real-world setting and, unless restricted, these loading cycles can occur at a rate which could cause injury to the ACL because of inadequate time for healing. Adolescent female soccer players who participate in a highly competitive travel soccer program will be fitted with four wearable IMU devices during bi-weekly practices. Undergraduate and graduate students will attend each practice over a one-year period to collect data, video record the event, and provide technical support. The timing of severe loading cycles will be examined using the video recordings to determine whether this changes over time either due to activities in practice or fatigue, as it has been suggested that fatigue may increase the risk of ACL injury. Data will also be compared to determine whether there is a difference between the dominant and non-dominant sides and to examine the effects of age and BMI (Body Mass Index) on the number of severe loading cycles experienced.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
