Effect of Rule Changes Occurring Between 2003 and 2016 on Head Impact Frequency and Brain Strain Magnitude In North American Professional Ice Hockey

Abstract

Head impacts can result in various levels of brain trauma, from mild to severe, and often result in long lasting effects on human brain function (McAllister & McCrea, 2017; Sollmann et al., 2018). Over the past two decades alone the National Hockey League (NHL) has made several rule changes to the game (Marek, 2015; National Hockey League Official Rules 2010–11, 2010; National Hockey League Official Rules 2011–12, 2011; National Hockey League Official Rules 2014-15, 2014). Frequency and magnitude are needed to examine brain trauma as examining brain trauma solely on magnitude does not capture a full brain trauma profile or the long-term consequences of repetitive brain strain; higher frequencies at lower magnitudes of strain may result in long-term neurologic complications. The purpose of this study was to compare frequency of head impacts and frequency-magnitude of brain strain between the 2003-04 and 2016-17 seasons of North American professional ice hockey. Videos of head impact events from twenty 2003-04 and twenty 2016-17 regular season NHL games were analyzed. Head impact conditions were characterized by events type, inbound velocity, location and elevation, and reconstructed using physical and finite element model methods. Overall frequency of head impacts was similar between the two seasons. Head-to-glass had the highest frequency for event type in both seasons. Mann-Whitney U tests found there was a significant decrease in glove-to-head impact events in the 2016-17 season compared to the 2003-04 (U=111, p=0.009). There was also a significant decrease in the frequency of fight events in 2003-04 during regulation time when compared to 2016-17 (U=86, p<0.001). A significant increase in the frequency of head impacts within the low MPS level was found in the 2016-17 season compared to 2003-04 (U=130, p=0.050). Given the popularity of ice hockey nationally, continentally, and globally, the results of this study provide a better understanding of frequency of head impacts and magnitude of brain strain, allowing stakeholders to make informed decisions involving repetitive brain strain during the game and give insight in the effectiveness of rules involving head contact. Future studies should consider including the effect of rule changes on overtime and pre- and post-season game play compared to in-season games.