Prophylactic Knee Bracing in College Football Players Is Associated With a Low Rate of Anterior Cruciate Ligament Tears

Purpose

To analyze the annual incidence of anterior cruciate ligament (ACL) injuries in National Collegiate Athletic Association (NCAA) college football offensive linemen utilizing prophylactic knee bracing at a single institution from 2002 to 2023.

Methods

This was a retrospective cohort study on prospectively collected data from an institutional NCAA football injury database. We retrospectively analyzed data between 2002 and 2023 to assess the incidence of ACL injury in NCAA football players, comparing offensive linemen wearing bilateral prophylactic knee braces (PKBs) to the overall injury rates of all positions on the team. Injury rate per 1,000 athlete-exposures was calculated for each group with 95% confidence intervals (CIs), and the difference between groups was calculated with a significance level set at P <.05.

Results

There was an estimated total of 52,844 offensive linemen athlete-exposures and 298,320 all-position athlete-exposures in the cohort. There were 8 total ACL injuries in offensive linemen wearing bilateral PKBs over a period of 22 years, compared to 58 in all other positions, with an offensive linemen ACL injury rate of 0.151 per 1,000 athlete-exposures (95% CI, 0.030-0.273) versus an overall ACL injury rate of 0.194 per 1,000 athlete-exposures (95% CI, 0.145-0.243). There was a difference of 0.043 ACL tears per 1,000 athlete-exposures in favor of the offensive linemen, which did not reach significance ( P =.501).

Conclusions

In this study over a 22-year span, we found a low overall incidence of ACL tears among NCAA football offensive linemen wearing bilateral PKBs, with a lower, although not statistically significant, rate of ACL injury compared to players at all positions.

Level of Evidence

Level III, retrospective comparative study of prospectively collected data.

Lower extremity injuries make up the majority of athletic injuries across all National Collegiate Athletic Association (NCAA) sports, significantly contributing to missed playing time, injury burden, and overall health care costs. More specifically, knee ligamentous injuries are common NCAA football injuries both during the season and in the off-season, with the anterior cruciate ligament (ACL) being one of the most commonly injured articular structures. ^,^, NCAA football had the highest annual incidence of ACL injury across 15 major collegiate sports from 1988 to 2004 and again from 2004 to 2013, with data from the NCAA Injury Surveillance Program showing an overall rate of ACL injury of 0.17 per 1,000 athlete-exposures, with an exposure defined as participation in a practice or game. ^, National Football League (NFL) data from 2015 to 2018 revealed that ACL tears not only are common but also result in a much higher number of player-days lost per season than any other lower extremity injury. Furthermore, college ACL injury rates are not decreasing, despite the increased focus on injury prevention in recent years. The total number of annual college football players has increased by nearly 20,000 since the year 2000, per the NCAA sports participation database. As this participation continues to increase, ACL injuries can be expected to follow without improved injury prevention strategies.

Rigid knee braces have been in use since the 1960s for the prevention and mitigation of knee ligamentous injuries in football and other sports. Prophylactic knee bracing, defined by the American Association of Orthopaedic Surgeons in 1985, utilizes “off-the-shelf” braces for use in sport prior to injury with a stable knee. Braces typically consist of lightweight, hinged lateral and medial bars, secured with a sleeve or elastic straps. The braces theoretically resist varus, valgus, and rotational forces on the knee joint, supplementing the knee’s natural stiffness for contact and noncontact stresses. Currently, prophylactic knee bracing within American football remains controversial, with conflicting and inconclusive evidence of its utility for preventing ACL and other knee injuries. ^,^, For example, 1 historic study commonly cited from Hewson et al. in 1986 showed no change in injury rates between braced and nonbraced college football players. However, a more recent 2023 study on NFL players found a significantly reduced rate of major knee injury in players wearing prophylactic knee braces (PKBs). This study also found that the overall utilization of prophylactic bracing decreased from 16.3% to 5.6% by the end of the study period, further highlighting the confusion surrounding whether these braces prevent injury and should be worn by players. There is a paucity of updated literature to guide young players and training staff, and given the prevalence of ACL and other knee injuries, there is a continued need for research into the prophylactic potential of these knee braces.

We sought to contribute to the growing fund of literature on PKB usage and knee injury prevention potential, providing data to guide athletes and sports departments on appropriate use of these braces. The purpose of the present study was to analyze the annual incidence of ACL injuries in NCAA college football offensive linemen utilizing prophylactic knee bracing at a single institution from 2002 to 2023. We hypothesized that NCAA college football offensive linemen utilizing bilateral PKBs would have a low overall ACL injury rate compared to all positions on the team.

Methods

Institutional review board approval was obtained for this study. From 2002 to 2023, our research group prospectively collected player injury data from the institution’s NCAA Division I football team for all positions year-round. It has been standard since the start of data collection for all offensive linemen to wear bilateral PKBs during practice and games. Injury data during this period were compiled into a database for research and analysis, updated continuously. All recorded instances of ACL tears, as diagnosed by the team physician based on physical examination and/or confirmatory imaging, in all players were identified and extracted. Other variables extracted from the data set for our analysis included year of injury and position type (offensive lineman vs other position). Activity was extracted using a string search for “game” or “practice.” Position was extracted using a string search for “off” and “line.” No demographic data were collected in the database as this was not part of the initial collection protocol. We excluded athletes with ACL injuries sustained outside of football, as well as athletes with incomplete data in the data set. There were no other exclusion criteria.

In our data analysis, each “practice” or “game” equated to 1 athlete exposure per player. As we did not have discrete data on exactly how many players from each position played in each practice and game in the 22-year study period, we estimated the number of offensive linemen and other-position players who participated in each event based on approximations from the team’s professional medical training staff. For each game, we estimated that, on average, 7 total offensive linemen played, so there were 7 offensive linemen exposures per game. We estimated that 28 other-position players participated, resulting in 28 other exposures, for a total of 35 athlete-exposures per game. For each practice, we estimated that 15 offensive linemen participated for 15 exposures and 70 other-position players participated for 70 exposures, for a total of 85 exposures per practice. Each year consisted of 11 games and 155 practices. We computed the mean proportion of ACL injuries per athlete-exposure per year and converted this to the rate per 1,000 athlete-exposures. Rates were calculated overall for all positions and for the subsample of offensive linemen, reported with 95% confidence intervals (CIs). The difference between these groups was then calculated with a 2-sample t test, with the significance level set to P <.05.

Results

From 2002 to 2023, there were an estimated 2,402 overall (practice and game) athlete-exposures per year for offensive linemen using the methodology outlined above, totaling 52,844 offensive linemen athlete-exposures. For all positions, there were an estimated 13,560 athlete-exposures per year, totaling 298,320 all-position athlete-exposures. One instance of ACL injury in a single athlete was excluded as it was due to a non-athletic-related injury. Four other injury events were missing injury type (i.e., it was unknown if these were ACL injuries or other injuries), so these were also excluded from the analysis. There were a total of 8 instances of ACL tears among offensive linemen wearing bilateral PKBs over the study period, compared to 58 total ACL tears for all positions. Yearly breakdowns of these exposures, events (i.e., ACL tears), and calculated injury rates per 1,000 exposures are shown in Table 1 . Over the entire study period, the offensive linemen ACL injury rate was 0.151 per 1,000 athlete-exposures (95% CI, 0.030-0.273), and the all-position ACL injury rate was 0.194 per 1,000 athlete-exposures (95% CI, 0.145-0.243), resulting in a difference between these groups of 0.043 injuries per 1,000 athlete-exposures ( P =.501). Figure 1 shows the comparison of yearly ACL injury rates per 1,000 exposures for offensive linemen versus all positions.

Table 1

Overall ACL Injuries and Injury Rate per 1,000 Athlete-Exposures Each Year for All Positions and the Subsample of Offensive Linemen Wearing Bilateral Prophylactic Knee Braces

Year	Event Type	Events	Exposures	ACL Injury Rate per 1,000 Exposures
All positions
2002	Overall	1	13,560	0.074
2003	Overall	3	13,560	0.221
2004	Overall	1	13,560	0.074
2005	Overall	6	13,560	0.442
2006	Overall	4	13,560	0.295
2007	Overall	1	13,560	0.074
2008	Overall	0	13,560	0.000
2009	Overall	3	13,560	0.221
2010	Overall	2	13,560	0.147
2011	Overall	1	13,560	0.074
2012	Overall	2	13,560	0.147
2013	Overall	5	13,560	0.369
2014	Overall	4	13,560	0.295
2015	Overall	3	13,560	0.221
2016	Overall	3	13,560	0.221
2017	Overall	2	13,560	0.147
2018	Overall	2	13,560	0.147
2019	Overall	4	13,560	0.295
2020	Overall	3	13,560	0.221
2021	Overall	3	13,560	0.221
2022	Overall	1	13,560	0.074
2023	Overall	4	13,560	0.295
Total	Overall	58	298,320	0.194
Offensive line
2002	Overall	0	2,402	0.000
2003	Overall	0	2,402	0.000
2004	Overall	0	2,402	0.000
2005	Overall	1	2,402	0.416
2006	Overall	0	2,402	0.000
2007	Overall	0	2,402	0.000
2008	Overall	0	2,402	0.000
2009	Overall	0	2,402	0.000
2010	Overall	0	2,402	0.000
2011	Overall	0	2,402	0.000
2012	Overall	0	2,402	0.000
2013	Overall	1	2,402	0.416
2014	Overall	1	2,402	0.416
2015	Overall	2	2,402	0.833
2016	Overall	2	2,402	0.833
2017	Overall	0	2,402	0.000
2018	Overall	0	2,402	0.000
2019	Overall	0	2,402	0.000
2020	Overall	0	2,402	0.000
2021	Overall	0	2,402	0.000
2022	Overall	0	2,402	0.000
2023	Overall	1	2,402	0.416
Total	Overall	8	52,844	0.151