Aaron D. Gray

Evaluation of the Microsoft Kinect for screening ACL injury

A study was conducted to evaluate the use of the skeletal model generated by the Microsoft Kinect SDK in capturing four biomechanical measures during the Drop Vertical Jump test. These measures, which include: knee valgus motion from initial contact to peak flexion, frontal plane knee angle at initial contact, frontal plane knee angle at peak flexion, and knee-to-ankle separation ratio at peak flexion, have proven to be useful in screening for future knee anterior cruciate ligament (ACL) injuries among female athletes. A marker-based Vicon motion capture system was used for ground truth. Results indicate that the Kinect skeletal model likely has acceptable accuracy for use as part of a screening tool to identify elevated risk for ACL injury.

Epidemiology of 3825 injuries sustained in six seasons of National Collegiate Athletic Association men's and women's soccer (2009/2010-2014/2015)

Aim To describe the epidemiology of National Collegiate Athletic Association (NCAA) mens and womens soccer injuries during the 2009/2010–2014/2015 academic years. Methods This descriptive epidemiology study used NCAA Injury Surveillance Program (NCAA-ISP) data during the 2009/2010–2014/2015 academic years, from 44 mens and 64 womens soccer programmes (104 and 167 team seasons of data, respectively). Non-time-loss injuries were defined as resulting in <24 h lost from sport. Injury counts, percentages and rates were calculated. Injury rate ratios (RRs) and injury proportion ratios (IPRs) with 95% CIs compared rates and distributions by sex. Results There were 1554 mens soccer and 2271 womens soccer injuries with injury rates of 8.07/1000 athlete exposures (AE) and 8.44/1000AE, respectively. Injury rates for men and women did not differ in competitions (17.53 vs 17.04/1000AE; RR=1.03; 95% CI 0.94 to 1.13) or practices (5.47 vs 5.69/1000AE; RR=0.96; 95% CI 0.88 to 1.05). In total, 47.2% (n=733) of mens soccer injuries and 47.5% (n=1079) of womens were non-time loss. Most injuries occurred to the lower extremity and were diagnosed as sprains. Women had higher concussion rates (0.59 vs 0.34/1000AE; RR=1.76; 95% CI 1.32 to 2.35) than men. Conclusions Non-time-loss injuries accounted for nearly half of the injuries in mens and womens soccer. Sex differences were found in competition injuries, specifically for concussion. Further study into the incidence, treatment and outcome of non-time-loss injuries may identify a more accurate burden of these injuries.

Validation of the Microsoft Kinect as a Portable and Inexpensive Screening Tool for Identifying ACL Injury Risk.

Objectives: A widespread screening tool to assess anterior cruciate ligament (ACL) injury risk should ideally be portable, inexpensive, markerless and easy to use. We hypothesize that our software program - for use with the Microsoft Kinect Motion Sensor - fulfills the above requirements. This study compares the measurements of knee abduction during a drop vertical jump (DVJ) between the Microsoft Kinect and the “gold standard” marker-based Vicon motion analysis system. Methods: Thirteen participants (10 male: 3 female; age 20-31) took part in this IRB approved study. Each participant performed between 5 and 7 DVJs, yielding a total of 84 DVJs. We simultaneously measured knee valgus motion (KVM) as measured from initial contact (IC) to the point of peak flexion (PF), frontal plane knee angle (FPKA) at both IC and PF, and knee-to-ankle separation (KASR) ratio measured at PF with the Kinect and Vicon systems. The intra-class correlation coefficient (ICC) (two-way, single measure, absolute agreement) was used to assess the degree of agreement between the Kinect and Vicon for each measure. Results: KVM had the lowest ICC value; 0.81 and 0.85 for the left and right leg, respectively. The other measures had similar ICC values of approximately 0.89 for both legs. Standard interpretations of the ICC suggest values above 0.75 indicate excellent agreement between the measurements (Table 1). Conclusion: This study demonstrates good correlation between the Microsoft Kinect and the Vicon system for measuring frontal plane knee kinematics during the DVJ. The DVJ test has been established as an ideal task for evaluating the motions that put athletes at risk for ACL injuries. Screening and early detection of ACL injury risk factors may lead to a relative risk reduction between 30% to 80% with an appropriate ACL injury prevention program. As compared to the “gold standard” Vicon system, the Microsoft Kinect is a portable, inexpensive, marker-less, and expedient system that likely has acceptable accuracy to become a practical means of mass screening of athletes for ACL injury risk factors. Further study will focus on validating the system with a larger and varied sample size and over a variety of functional tasks.

Development and Validation of a Portable and Inexpensive Tool to Measure the Drop Vertical Jump Using the Microsoft Kinect V2

Background: Noncontact anterior cruciate ligament (ACL) injury in adolescent female athletes is an increasing problem. The knee-ankle separation ratio (KASR), calculated at initial contact (IC) and peak flexion (PF) during the drop vertical jump (DVJ), is a measure of dynamic knee valgus. The Microsoft Kinect V2 has shown promise as a reliable and valid marker-less motion capture device. Hypothesis: The Kinect V2 will demonstrate good to excellent correlation between KASR results at IC and PF during the DVJ, as compared with a “gold standard” Vicon motion analysis system. Study Design: Descriptive laboratory study. Level of Evidence: Level 2. Methods: Thirty-eight healthy volunteer subjects (20 male, 18 female) performed 5 DVJ trials, simultaneously measured by a Vicon MX-T40S system, 2 AMTI force platforms, and a Kinect V2 with customized software. A total of 190 jumps were completed. The KASR was calculated at IC and PF during the DVJ. The intraclass correlation coefficient (ICC) assessed the degree of KASR agreement between the Kinect and Vicon systems. Results: The ICCs of the Kinect V2 and Vicon KASR at IC and PF were 0.84 and 0.95, respectively, showing excellent agreement between the 2 measures. The Kinect V2 successfully identified the KASR at PF and IC frames in 182 of 190 trials, demonstrating 95.8% reliability. Conclusion: The Kinect V2 demonstrated excellent ICC of the KASR at IC and PF during the DVJ when compared with the Vicon system. A customized Kinect V2 software program demonstrated good reliability in identifying the KASR at IC and PF during the DVJ. Clinical Relevance: Reliable, valid, inexpensive, and efficient screening tools may improve the accessibility of motion analysis assessment of adolescent female athletes.

Mass Screening of Youth Athletes for High Risk Landing Patterns using a Portable and Inexpensive Motion Sensor Device

Objectives: Biomechanical factors such as dynamic knee valgus predispose young athletes to lower extremity injury including tears of the anterior cruciate ligament (ACL). Identifying these risk factors may allow for targeted injury prevention strategies. Our prior work has validated the Microsoft Kinect vs. Vicon to detect knee-ankle separation ratio (KASR) during the drop vertical jump test (DVJ). Our hypothesis is that screening with the Microsoft Kinect will be safe, efficient, and provide information to help detect injury risk in youth athletes. Methods: A total of 180 healthy high school athletes, ages 14-18 (80 males and 100 females, age of 16.9 ± 1.31 and BMI of 22.8 ± 3.7) participated in this study. Each subject performed three successful DVJ (Fig. 1). We used an inexpensive, portable motion sensor device to measure the KASR, which captures the ratio of the horizontal distance between knees to the horizontal distance between ankles. From previous studies, a KASR value <1 indicates dynamic valgus, while being below 0.6 is considered severe risk. Demographic information and measurements for KASR on initial contact and peak flexion were analyzed statistically. Results: Using two motion sensor device stations, it took 1.5 minutes to screen and test each subject. There were no injuries that occurred during the screening process. Our results showed a statistically significant difference between male and female KASR for both initial contact (p<0.001) and peak flexion (p<0.001). Sixty out of the 100 female subjects (60%) tested positive for valgus (9 initial contact KASR, 1 peak flexion KASR, 50 both initial contact and peak flexion KASR) with two subjects screening for severe risk (KASR<0.6). The average KASR for females was 1.01 (peak flexion) and 0.967 (initial contact). Eighteen out of the 80 male subjects (22.5%) tested positive for valgus (6 initial contact KASR, 2 peak flexion KASR, 10 both initial contact and peak flexion KASR) with no male subjects screening positive for severe risk. The average KASR for males was 1.26 (peak flexion) and 1.13 (initial contact). Comparing males and females that screened positive for KASR, there was a significant gender difference between the KASR at initial contact with females exhibiting more valgus than males (p<0.001) (Table 1). Conclusion: Our findings suggest that a portable and inexpensive motion analysis device can detect dynamic valgus during the DVJ in youth athletes. Large scale screening for dynamic valgus was safe and efficient. Known gender disparities between male and females for neuromuscular imbalances were identified. Potential use of this information for targeted injury prevention is appealing and requires further investigation.

Examining the feasibility of a Microsoft Kinect ™ based game intervention for individuals with anterior cruciate ligament injury risk

We describe a feasibility study in which the Microsoft Kinect is used for a game-based exercise to strengthen posterior chain muscles which are often weak in those at high risk of anterior cruciate ligament (ACL) injury. In the game, subjects perform a single posterior chain strengthening exercise. The game uses a side-scrolling video display driven by a hip abduction exercise while a player lies down on the floor. Leg lifts beyond a predetermined angle trigger the jumping action of an animated tiger. We describe the scene and game control, which uses depth images from the Kinect. Although Kinect-based skeletal data are used for many games, the skeletal model does not yield good estimates for positions on the floor. Our proposed system uses multiple leg angle estimators for different angle regions to recognize the player lying down and capture the angle between two legs. We conducted an experiment that validates our system with marker-based Vicon ground truth data. We also present results of an end-to-end test using the game, showing feasibility.

Examining methods to estimate static body sway from the Kinect V2.0 skeletal data: implications for clinical rehabilitation

Static body sway is a clinically relevant activity parameter, used to assess postural balance, across a wide spectrum of patient populations. We have examined static body sway using two different segmental total body center of mass (TBCM) estimation methods, the Generator of Body Data III (GEBOD) and Winters method, using Microsoft Kinect skeletal data. Twenty subjects were recruited through an IRB study and asked to perform three trials of single leg stance with their eyes closed, with positioning based on the Balance Error Scoring System. A force plate system was used to estimate the ground truth data for comparison. Results show that both GEBOD and Winters method performed similar in estimating anterior-posterior (AP) and medio-lateral (ML) body sway. The results also show highly correlated measurements by the two TBCM estimation methods when compared with the force plate system (mean RMSE value of 10.18 mm square in AP and 8.00 mm square in ML direction). Ordinary Least Square (OLS) linear regressions were performed to improve body sway results obtained from the two methods. Improved sway range values obtained from the simple regression method was able to reduce the estimation errors by 50% (~ 10 mm in both AP and ML body sway). The two static body sway estimation methods were found reliable for obtaining body sway. Thus, the inexpensive, portable Kinect V2.0 can be used for clinical measurements.

Not as Straight(forward) as an Arrow: Ultrasound Use to Detect a Carbon-Fiber Foreign Body

Case: A fifteen-year-old boy sustained an archery injury when a carbon-fiber arrow shaft embedded in the volar aspect of his left forearm. The shaft was removed, but at a follow-up visit he still felt the sensation of a retained foreign body in the tissue. Although radiographs were negative, ultrasound examination found three foreign bodies of various lengths still located in the soft tissue. Further surgery removed the objects without difficulty. Conclusion: Ultrasound examination can be a valuable diagnostic tool when radiographs yield inconclusive results after penetrating wounds due to radiolucent foreign bodies.

Do Ankle Sleeves And Lace-Up Braces Effect Neuromuscular Control And Athletic Performance?

Objectives: Athletes commonly wear fitted silicone ankle sleeves (SAS) and lace-up ankle braces (LAB). There is limited data about their effect on neuromuscular control or athletic performance. Our goal is to evaluate their efficacy in a young, active population during athletic tasks using motion analysis. Methods: Ten subjects (5 males, 5 females) without prior musculoskeletal injury were recruited. They were asked to perform the Drop Vertical Jump test (DVJ), 45 degree bound, and cutting maneuvers under three conditions: No brace, SAS, LAB. DVJ was used as a surrogate for neuromuscular control, and the 45 degree bound and cutting for athletic performance. Tasks were performed in separate sessions to minimize effects of fatigue. Markerless motion-capture technology was used for data collection. For the DVJ, knee flexion, hip internal rotation, and dynamic valgus were measured during both contact and loading phases of landing. Ankle torque and range of motion were also evaluated. For the 45 degree bound, ankle torque was measured during the initial movement to the dominant knee. Performance time for the cutting with the dominant pivot foot was recorded. Statistics were calculated using a two-tailed Students t-test with significance set at p=0.05. Results: When compared to controls for both the contact and loading phases of the DVJ, use of the SAS or LAB demonstrated significantly decreased hip internal rotation (67%, 15%, respectively), ankle torque (13%, 11% respectively), and ankle range of motion (p<0.01). Knee flexion was increased at initial contact in both the SAS and LAB groups compared to control (p<0.01). There was no significant effect of the braces on dynamic knee valgus, and no differences detected between the SAS and LAB on all parameters. When compared to controls for the 45 degree bound, ankle torque was significantly reduced for subjects wearing either SAS or LAB (24%, 13.5% respectively, p<0.01). The use of SAS or LAB had no significant effect on timed cutting maneuver vs. controls (p=0.1181, p=0.1124 respectively). There were no differences detected between the SAS and LAB for all parameters. See Figure 1 for results. Conclusion: Athletes wearing ankle sleeves and lace-up braces demonstrated improvements in neuromuscular control during the DVJ (decreased hip internal rotation, increased knee flexion at initial contact), decreased ankle torque during 45 degree bounding maneuvers, and no performance time deficit versus control during cutting maneuvers. There were no differences detected in either neuromuscular control or athletic performance between the brace types. The effect that these findings have on the incidence of lower extremity injury remains largely unknown and requires further investigation.