Head kinematics and concussion injuries in Rugby Union players
05 May 2015
Rugby is intrinsically an impact sport. Sometimes, concussions arise during collisions between players or collisions with the ground. Concussion is a form of mild traumatic brain injury and this has resulted in negative publicity for the high-impact nature of rugby.
Tackling is regarded as the phase of play that is the most likely event to cause a concussion for a player – for both the ball carrier and the tackler. However, the exact causes of concussion in rugby are not well understood. Studies of other impact sports may yield useful information for understanding head injuries in rugby. For example, in boxing, there is an increasing record of literature which links repeated concussion injuries to early-onset dementia and depression.
In the United States, a link between chronic traumatic encephalopathy and American football has been suggested. This is a progressive neurological deterioration arising from repetitive head impacts, and symptoms usually include memory and cognitive difficulties, depression, aggression and eventually dementia. It is also believed to affect around 20% of professional boxers and a boxing study found that the condition develops progressively over a long time period, usually 10-20 years after the boxer has retired. Repeated concussions and sub-concussive impacts are considered to be the cause of the condition.
To date, there is no evidence of this condition arising from rugby participation. However, the incidence of concussion during professional rugby appears to be rising and there is a demand for effective player-protection strategies.
Player kinematics and concussion
Collecting reliable evidence is a pre-requisite for injury prevention in any scenario and a greater understanding of the dynamics of head impacts in rugby is required. Accordingly, PhD student Gregory Tierney and associate professor Ciaran Simms from the Trinity Centre for Bioengineering have recently gained funding from the Irish Research Council to use a novel biomechanical tool known as model-based image matching (MBIM) to improve our understanding of player kinematics during impact events.
This method uses video evidence from games and training sessions to extract player kinematics during rugby collisions. This approach was pioneered by Prof Tron Krosshaug and Prof Roald Bahr of the Oslo Sports Trauma Research Centre and has been used to assess the mechanisms of injury for knee-ligament injuries in basketball and skiing, as well as ankle injuries in field hockey.
If a rugby player is suspected of having a concussion, they are removed from play and assessed by side-line medical staff using the Head Injury Assessment (HIA) form. The HIA is a standardised tool, based on cognitive-based scientific literature, for the side-line medical assessment of suspected concussion injuries in rugby. If the player’s score is positive, they are removed from play. Even with a negative score, it is at the team doctor’s discretion whether the player can return to play.
The first step of this project, along with physiotherapists Karl Denvir of Leinster Rugby and Garett Coughlan of the Irish Rugby Football Union, is to complete a detailed analysis of the events leading to a concussion to find certain kinematic trends which are causing concussion injuries to occur within the game. This will then improve the selection process of head impacts that will be analysed in detail using MBIM.
The real strength of model-based image matching is that it can provide an understanding of the motion patterns from real-world collision events if appropriate video sequences of sufficient quality are available. Specifically, MBIM fits a skeletal model of a player to the video data from several angles. This allows the measurement of three-dimensional temporal joint angle time histories from video data captured using un-calibrated cameras. These data can then be used to infer linear and rotational velocity and acceleration time histories.
How MBIM works
MBIM works on the basis of creating virtual surroundings which are based on the actual dimensions of the sports field. A skeleton model is then used to fit the player’s anthropometry into each video frame. The model has 21 body segments, resulting in 57 degrees of freedom. Once the matching is done, the kinematics can be extracted from the animation program. By reconstructing representative injury cases in this way, linear and rotational kinematic measurements of head kinematics during rugby-collision events are made available for the first time. These data may help establish tolerance thresholds for concussion injuries in rugby.
The kinematic data extracted from the MBIM can be inputted into multibody models of the player to predict the impact forces and finite element computer models of the brain to predict the brain strains during the event. These results can then be compared to player HIA scores to find a relationship between impact forces and strain locations in the brain and areas of failure within the HIA such as memory, balance and clinical signs.
In a parallel study, the research team are collaborating with Dr Fiona Wilson, a physiotherapist in the School of Medicine at Trinity College Dublin. Her research is focused on the potential for blood biomarkers from the players to provide evidence and prognosis of traumatic brain injury following a collision. Blood is taken at baseline (pre-season) and after an impact, and analysis of specific biomarkers can be used as a signal that the blood brain barrier has been compromised.
The goal of the collaboration is to try to derive a number of different assessment modalities which together can provide stronger specificity in assessing brain injuries arising from rugby collisions. It is hoped that these approaches can eventually lead to a method that assists side-line medical staff with the early detection of concussion.
Recently, Aviva Premiership club Saracens have been highlighted for wearing the X2 Biosystems patch. This is a small instrument attached to the back of players’ ears. It consists of very small accelerometers and gyroscopes that allow the acceleration during impacts to be measured. The device is regarded as more accurate than instrumented helmets and mouthguards due to the reduction in relative movement between the device and the head. Gregory Tierney and Dr Ciaran Simms are currently considering the use of this product in a future study, as it allows for a much greater sample size to be gained when assessing the kinematic thresholds of concussion.
Greg Tierney’s work has been awarded ‘The Best Early Stage PhD’ at the Bioengineering In Ireland Conference, 2015 (BINI 2015).http://www.engineersjournal.ie/2015/05/05/kinematics-concussion-rugby-ireland/http://www.engineersjournal.ie/wp-content/uploads/2015/04/Rugby-concussion-ireland-1024x682.jpghttp://www.engineersjournal.ie/wp-content/uploads/2015/04/Rugby-concussion-ireland-300x300.jpgBioresearch,Trinity College Dublin