Documentation:FIB book/Sex Differences In Rugby Concussion Injuries

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Introduction

Approximately 9.6 million people play rugby across 123 countries, with female players accounting for 30% of this population.[1] The number of female rugby players continues to grow on a global scale, with competition increasing as well.[2] Despite this, research surrounding injury mechanisms in women’s rugby league remains limited.[2] This is largely due to the use of androcentric data to study injury rates and mechanisms in rugby, which is then inaccurately extrapolated in the context of women's rugby.[3]

The risk of injury associated with rugby tackles is quite high, with concussions being of particular concern.[4] In fact, it is estimated that 50% of concussions in rugby are caused by tackles, with 70% of those being inflicted on the player initiating the tackle.[2] Even though the number of rugby tackles per match are very similar between men and women (4-41 tackles per player per match and 4-26 tackles per player per match, respectively) and both leagues follow the same rules, there are notable differences in the styles of play.[4][5][6] For example, women's rugby is reported to be more possession-driven, whereas men's rugby focuses more on kicking tactics.[6] Despite this, studies assessing mechanisms of injury and head-impact are almost exclusively androcentric; training strategies and injury identification frameworks that are designed around male players are thereby inaccurately generalized to female players and pose a detriment to their safety.[3]

There is a large discrepancy in concussion data available between men and women. For example, while assessing Sports Concussions Assessment Tool (SCAT) baselines, 6288 male assessments are available compared to only 1071 female assessments.[7] Women have greater and more severe symptoms than men according to the sports concussion assessment tool in a study conducted by Tucker et. al.[7] This study suggests an increased risk of adverse concussion outcomes for women.[7] This perceived increased severity is likely due to the fact that the neuronal morphology, size, and composition of the corpus callosum is different between the sexes, which is a region of the brain that experiences greater shear and strain during impacts that result in concussion.[8]

An example of a rugby tackle.

There have been efforts to design protective head equipment to be worn while playing rugby. For example, scrum caps, a form of soft-shelled headgear, and mouthguards are permitted.[9][10] Both scrum caps and mouth guards are popularly thought to protect against concussions, however, studies have found that neither piece of equipment actually reduces the rate of concussion. The use of hard-shelled helmets are not permitted as it may encourage players to use riskier techniques when tackling; a phenomenon known as risk compensation.[10]

We can also observe the long-term consequences of rugby-related concussions for players of different sexes. Firstly, there is an increase in subsequent injury risk in rugby players of both sexes who have previously experienced a concussion. Professional rugby athletes who return to play in the same season after sustaining a concussion had a 60% greater risk of subsequent injury occurring.[11] Neuromuscular control is decreased after a concussion, which can impact gait and increase the risk for subsequent musculoskeletal (MSK) injury to occur. There is a 1.6 to 3.39 times increase in risk of sustaining a MSK injury following concussion, and the association between concussion and MSK injury is most apparent in the 181- 365 day time period after sustaining a concussion. This is likely due to the increased evidence of atrophy and apoptosis in brain cells, which typically occurs approximately 6 - 12 months after a concussion. There is also a chance of neurocognitive impairments appearing months after concussion, indicating that concussion has the potential to create significant extended health concerns.[5] There is no significant difference of MSK injury incidence between male and female rugby players who have sustained a concussion. This general trend of increase in subsequent injury risk for rugby players who have previously sustained a concussion indicates severe long-term consequences that can affect players of both sexes.[5]

Work Done Previously

A number of papers were analysed to determine the common techniques used to investigate the subject of rugby injury. More specifically focussing on papers that had sex segregated data or a focus on women’s rugby. When investigating concussions in rugby there are three main categories that can be formed in the practiced methodologies: 1. video analysis, 2. load detection and 3. epidemiologic data.

Video Analysis

Video analysis is a useful tool for collecting injury information. Biomechanical analysts parse through video recordings from games. By slowing down this footage they can observe injury events and then compare their videographical findings to the clinical records from the rugby season.[4][12] This has led to the finding that tackle technique has strong implications on injury probability with high tackles being one of the greatest risk factors. These results show that education on tackle technique is the most feasible way of addressing risk in the sport. The player who tackles (rather than being tackled) is more likely to be injured according to this video analysis.[4] These results are consistent between both men and women’s rugby leagues. Contrarily, women are 50% more likely to be injured than men in a tackle.[12] In West et al. the comparison of data analyst expert opinions to medical records indicates that the injury incidence may be under represented, as the data analysts found more suspected concussion events than the records show.[12] West et al. did not use medical records to validate the expertise of 6 sports medicine physicians.[12] Rather, these experts came to an agreement of 70% likelihood when assessing a video clip for a suspected injury event. This was done by showing the team of experts the video clip in question, and having each specialist predict whether it was 70% or more likely to have caused a concussion. The panel then came to agreement on their predictions to determine if the injury was 70% likely or not. This methodology was repeated in West et al.'s study focusing on men’s rugby.[13] Comparing the men vs women's studies found that the suspected concussion rate for the women’s league was much higher than the suspected concussion rate seen in men's rugby. However the medical attention rates for women's rugby were seen to be lower by about 60% despite the suspected injury rates being higher. This may be indicative of women being under treated for concussion compared to men.

Load Detection

Flexion vs Extension of the Neck/Cervical Spine.

Another tool for assessing concussion in a rugby setting is via head-impact telemetry. Williams et al. implemented a 9-axis inertial measurement unit (IMU) into rugby mouthguards to measure anthropometric data.[3] This allowed researchers to test neck strength by pushing load cell pads against live study participants heads in various directions. Neck strength results from forward flexion, extension, right lateral flexion and left lateral flexion. It was found that these maximum voluntary contraction scores were 50%, 43%, 47% and 50% lower respectively compared to men. This indicates a sex based anthropometric difference regarding neck strength. This may relate to the higher tackle injury rates we see in women.[12] Direct head to ground impacts account for 38.5% of head impacts of women compared to the 9.7% of impacts for men.[3] Williams et al. found that over 50% of female impact events resulted in whiplash whereas there was only one instance of this occurring in the male rugby player dataset during 7 competitive matches of 14 men. The use of head impact telemetry yields important gender specific information that aids to contextualize the results we are seeing in video analysis and epidemiological concussion data. These results can also be supported due to the differing stabilization mechanism seen between men and women.[14] in Alsalaheen et al, live participants were fitted with headgear connecting to a force transducer and pulley.[14] The participants head positions were then perturbed by dropping weights attached to the pulley. Kinematic data and EMG data were collected to determine any trends between sex segregated groups. The results of this study showed that women used greater muscle activation to account for their reduced neck girth when compared to men, while their head kinematics had no significant differences.[14] The reduced neck girth and increased muscle activation for proportional loading seen in this study is in accordance with William et al.’s finding that women have reduced neck strength.[3] This may relate to the higher incidence of whiplash and concussion seen in women.

Epidemiological Analysis

Epidemiological data allows large swaths of injury data to be processed for injury results. We see in Barden et al. that the most common injury for females are concussions, with the most common injury type for males being ligament sprain.[15] This relates to the results of West et al. seen earlier that anthropometric differences between men and women may have implications into the rugby injuries they experience.[12] Furthermore concussion was 5.5 times more common in women than men according to the epidemiological review seen in West et al.[16] This study also validates what we see in Spiegelhalter et al. as the epidemiology shows that the majority of concussion injuries seen in tackle events result in the tackler being injured rather than the person being tackled.[4] Epidemiological data also suggests that a sport related concussion will result in an increased risk in musculoskeletal injury for the year following the concussion. [5][11]

Discussion

The results of these studies speak to a controversy in the greater context of professional rugby. Load detection studies of injury mechanisms reveal anthropometric differences between males and females. Primarily, this includes neck strength; decreased MVC rates in females indicate reduced ability to tolerate heavy loading in the head and neck regions as shown in the accompanying figure.[3] Sex-based anthropometric differences offer context for elevated suspected injury rates in women’s rugby, because many of these injuries pertain to the head and neck region, which we know to be weaker in females.[12] Women are more likely to be affected by direct head-to-ground impacts, whiplash events, concussions, and tackle-related neck injuries.[3][4] The controversy here is in the causative factor of this discrepancy. Despite the inherent sex-based differences in anthropometry, injury prevention and training strategies are still generated using male-centered, or androcentric, data. Androcentric data, as we have discovered, is not an accurate reflection of injury occurrence patterns in women’s rugby and therefore cannot be reasonably generalized to women. This in turn leads to the development of training strategies and injury prevention strategies that are ineffective for women.

Tackle-based injury rates in women are exacerbated by how concussion events due to this type of injury are studied. Specifically, many studies overemphasize impact on the player being tackled, and neglect the injury occurrence in the player doing the tackling.[1] We can confirm from the results of the video analysis studies that the player who tackles is more likely to be injured than the player being tackled.[4] Epidemiological studies also highlight how concussions are frequently diagnosed in tacklers.[1] Focusing on only the player being tackled limits the scope of these results. Because women are more frequently impacted by tackle-based injuries, they are also likely more affected by extrapolation of findings from these studies for development of injury prevention and training strategies.[12]

We can validate the results of these studies by comparing the complementary findings of all three methodologies discussed in the previous section. Alsalaheen et al. shows increased muscle activation in females to compensate for reduced neck girth which is in accordance with the findings in Williams et al. pertaining to decreased neck strength in females.[3] These findings provide basis for the results of West et al. which show high incidences of suspected whiplash events and concussions in women.[12] This is further in accordance with the increased frequency of whiplash from female impact events compared to males. These findings also lend themselves to qualify the increased likelihood of head and neck injuries resulting from direct head-to-ground impacts and tackle events for females.[12]

Our methods of validating this claim are not without their limitations, however. One such limitation lies in sample sizes. For epidemiological analysis in particular, many of the included studies do not reveal the sample size used in determining the rates of concussions.[16] This is also a limitation in the historical analysis of how head acceleration and cervical muscle activation relate to concussion injury.[2] This, in turn, limits how definitively we can claim that the difference in neck-stabilizing mechanisms of males and females contributes to the occurrence of concussion events. The fact that no rotational data was collected for males further limits our ability to use results to study sex-based differences. The results of this study also indicated that more research needed to be done to determine the “effect of concussion on muscle activation and reflect”.[2] Despite this, the results of our epidemiological analysis are consistent with the findings of studies by West et. al. and Spiegelhalter et. al., suggesting validity regardless of sample size.

Video analysis-based studies are also limited by their qualitative nature. In the case of Spiegelhalter et al., the study does not quantify “indirect head accelerations or head contact magnitudes”.[4] Not only is it difficult to quantify results, but depending on the footage being analyzed, some injuries may be easier to distinguish than others. For example, one cannot definitively identify a concussion event from a video of the impact. This may decrease the accuracy of assessment, whether this be through medical records or through consensus opinion of physicians.[4][12][13]

Future Research

The current techniques being used to measure the concussion injury mechanism are video analysis, load detection via IMU and EMG, and epidemiological data. While the information in this literature review has accurately modeled the fact that female rugby players are predisposed to higher injury rates than their male counterparts, there are still a variety of limitations that need to be addressed to further understand the relevance of sport related concussions in non-professional leagues.

One of the primary unanswered questions is: how can we validate which tackle caused a sport related concussion or whiplash? Previously, the use of IMU’s have been used on athlete models to create an accurate representation of the maximum voluntary contraction of the male neck in comparison to that of the female neck, to correlate tackle injury rates to whiplash or concussion rates. In previous studies, the neck contraction scores calculated from IMU’s have been compared to the video analysis to contextualize the analysis with epidemiological values.[12] While this is a good way to measure the concussion mechanism given the available data, it does not necessarily give quantitative results as to how the voluntary contraction negates the rotational acceleration of the head. To address this research gap, future steps need to include the implementation of the IMU mouth guard into gameplay. By doing so, the IMU mouth guard can measure the angular velocity of the player's head throughout the game. In the case that there is a concussion reported, the angular velocity can be calculated and compared to the mechanism of the contact via video analysis. This study can be repeated in numerous athletes at varying ages and sexes to help determine the correlation of the type of tackle to the angular velocities of the head, with the ultimate goal of creating a threshold for concussion injuries based on epidemiological data. A separate protocol would exist for both males and females.

As previously mentioned, the medical attention rates are proportionately lower for women’s rugby than men’s rugby, despite the suspected injury rates being much higher.[12] Future work should be done to examine the extent to which this inconsistency exists in identification of suspected injury events between men and women. Based on these findings, the epidemiological results can be further refined based on the amounts of missing identification of concussions and injuries in women’s rugby.

The World Rugby Union’s current model is to complete a Head Impact Assessment on all players suspected of having a concussion which is completed by comparing the sideline assessment to that of a baseline assessment that was completed at the start of the season.[17] While this model works, it relies on the correct identification of a potential concussion in a game scenario via sideline video review and the discretion of the doctor on the sideline. Future research to address this gap would be the implementation of mandatory assessments of all players after each game. While this would be rather labor intensive, it would further validate the efficacy of video analysis on tackle mechanisms that cause concussions.

References

  1. ↑ 1.0 1.1 1.2 Yeomans, C., Kenny, I. C., Cahalan, R., Warrington, G. D., Harrison, A. J., Purtill, H., … Comyns, T. M. (2021). Injury Trends in Irish Amateur Rugby: An Epidemiological Comparison of Men and Women. Sports Health: A Multidisciplinary Approach, 13(6), 194173812199714. https://doi.org/10.1177/1941738121997145
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Scantlebury S, Ramirez C, Cummins C, Stokes K, Tee J, Minahan C, et al. Injury risk factors and barriers to their mitigation for women playing rugby league: a Delphi study. Journal of Sports Sciences. 2022 Jun 12;1–14.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Williams EMP, Petrie FJ, Pennington TN, Powell DRL, Arora H, Mackintosh KA, et al. Sex differences in neck strength and head impact kinematics in university rugby union players. European Journal of Sport Science. 2021 Oct 28;22(11):1–10.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 Spiegelhalter, M., Scantlebury, S., Heyward, O., Hendricks, S., Cummins, C., Gardner, A. J., … Jones, B. (2023). The propensity of non-concussive and concussive head contacts during elite-level women’s rugby league matches: a prospective analysis of over 14,000 tackle events. Journal of Science and Medicine in Sport, 26(3). https://doi.org/10.1016/j.jsams.2023.03.003
  5. ↑ 5.0 5.1 5.2 5.3 Yener, N., Glendon, K., & Pain, M. T. G. (2022). The association between sport-related concussion and musculoskeletal injury in university rugby athletes. Physical Therapy in Sport. https://doi.org/10.1016/j.ptsp.2022.05.001
  6. ↑ 6.0 6.1 Nolan D, Curran O, Brady AJ, Egan B. Physical match demands of International Women’s Rugby Union: A three-year longitudinal analysis of a team competing in the women’s six nations championship. Journal of Functional Morphology and Kinesiology. 2023;8(1):32. doi:10.3390/jfmk8010032
  7. ↑ 7.0 7.1 7.2 Tucker, R., Falvey, E., Fuller, G., Brown, J., & Raftery, M. (2020). Baseline SCAT Performance in Men and Women. Clinical Journal of Sport Medicine, Publish Ahead of Print(6). https://doi.org/10.1097/jsm.0000000000000847
  8. ↑ Stitt D, Draper N, Alexander K, Kabaliuk N. Laboratory Validation of Instrumented Mouthguard for Use in Sport. Sensors. 2021 Sep 9;21(18):6028.
  9. ↑ Marshall SW. Evaluation of protective equipment for prevention of injuries in Rugby Union. International Journal of Epidemiology. 2004;34(1):113–8. doi:10.1093/ije/dyh346
  10. ↑ 10.0 10.1 McIntosh AS, McCrory P, Finch CF, Best JP, Chalmers DJ, Wolfe R. Does Padded Headgear Prevent Head Injury in Rugby Union Football? Medicine & Science in Sports & Exercise. 2009;41(2):306–13. doi:10.1249/mss.0b013e3181864bee
  11. ↑ 11.0 11.1 Cross M, Kemp S, Smith A, Trewartha G, Stokes K. Professional rugby union players have a 60% greater risk of time loss injury after concussion: A 2-season prospective study of clinical outcomes. British Journal of Sports Medicine. 2015;50(15):926–31. doi:10.1136/bjsports-2015-094982
  12. ↑ 12.00 12.01 12.02 12.03 12.04 12.05 12.06 12.07 12.08 12.09 12.10 12.11 12.12 West, S. W., Shill, I. J., Sutter, B., George, J., Ainsworth, N., Wiley, J. P., … Emery, C. A. (2022). Caught on camera: a video assessment of suspected concussion and other injury events in women’s rugby union. Journal of Science and Medicine in Sport, 25(10), 805–809. https://doi.org/10.1016/j.jsams.2022.07.008
  13. ↑ 13.0 13.1 West SW, Cross M, Trewartha G, Taylor A, Brooks J, Kemp S, et al. Trends in match concussion incidence and return-to-play time in male professional Rugby Union: A 16-season prospective cohort study. Brain Injury. 2021 Sep 8;1–10.
  14. ↑ 14.0 14.1 14.2 Alsalaheen B, Johns K, Bean R, Almeida A, Eckner J, Lorincz M. Women and Men Use Different Strategies to Stabilize the Head in Response to Impulsive Loads: Implications for Concussion Injury Risk. Journal of Orthopaedic & Sports Physical Therapy. 2019 Nov;49(11):779–86.
  15. ↑ Barden C, et al. Employing Standardised Methods to Compare Injury Risk Across Seven Youth Team Sports. Int J Sports Med. 2021;42(11):1019–26.
  16. ↑ 16.0 16.1 West, S. W., Shill, I. J., Bailey, S., Syrydiuk, R. A., K. Alix Hayden, Palmer, D., … Emery, C. A. (2023). Injury Rates, Mechanisms, Risk Factors and Prevention Strategies in Youth Rugby Union: What’s All the Ruck-Us About? A Systematic Review and Meta-analysis. Sports Medicine. https://doi.org/10.1007/s40279-023-01826-z
  17. ↑ HIA protocol [Internet]. 2017 [cited 2023 Nov 6]. Available from: https://www.world.rugby/the-game/player-welfare/medical/concussion/hia-protocol


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