Do Knee Braces Prevent Knee Injury in College and High School Football Players?
Daniel Blackmon
PHYT 754
University of North Carolina-Chapel Hill
I chose this topic to be my capstone project due to my own experience with a knee injury while playing football, and by observing the commonplace use of braces on the knees of collegiate offensive linemen. I began researching the subject in the Evidence-Based Practice II course in the Fall semester, and continued to compile data while completing my capstone. My purpose is to compile the data available on the effectiveness of knee braces to prevent knee injury in college and high school football players, and use this information to educate athletes, their parents, physical therapists, athletic trainers, coaches, athletic directors, and any other individual who works intimately with college and high school football players. I have completed a research paper, which can be read below, an educational handout and presentation which could be presented as a potential in-service. I would like to thank my capstone committee – Mike Gross, Jon Hacke and Bing Yu – for their guidance throughout the duration of this project. Without their contributions and expertise it would not have been possible, and I am always humbled by their knowledge.
Background
Football is a tremendously popular sport in the United States, with over 1 million males participating in high school football in the 2012-2013 academic year.1 This figure is nearly double the amount of males who participated in the 2nd and 3rd most popular sports (outdoor track and field and basketball).1 Unfortunately, football also has the highest injury rate (2.52 per 10,000 athlete exposures) of any high school sport.2 Between 2005-2010, the knee was the most frequent site of injury, accounting for 44.9% of all injuries among high school football players.2 Knee injuries are also a common ailment for college football players as well, with 54% of participants at the 2005 NFL Combine having experienced a prior knee injury.3 Offensive linemen, defensive linemen and tight ends are the most affected with knee injuries.3 The medial collateral ligament (MCL), which restricts laterally-directed (valgus) forces at the knee, is the most frequently injured knee ligament in high school and college football players.4,5
A common preventive measure to reduce knee injuries in this population is the advent of the prophylactic knee brace. In 1977, former Oakland Raiders athletic trainer George Anderson designed the first prophylactic knee brace to prevent re-injury to the MCL of quarterback Ken Stabler.6 Since that time, the use of preventative braces has become commonplace despite limited research on their effectiveness.7,8
Currently, a variety of knee braces are utilized by athletes. Functional knee braces are intended to provide stability to unstable knees that have been injured previously, prophylactic knee braces are intended to be worn by individuals without prior knee injury to prevent or reduce the severity of injury, and rehabilitative braces are designed to limit the range of motion in injured and/or post-operative knees.9 The purpose of this paper is twofold: 1.) summarize the available information from laboratory studies on the protective effects of prophylactic knee braces on ligamentous, capsular, meniscal, and cartilaginous structures of the knee, and 2) also summarize the data on the rates of knee injury in unbraced and braced high school and college football players to determine the efficacy of their use in this population.
Laboratory Studies of Prophylactic Braces
Six studies were included for review, all of which evaluated the possible protective benefits of prophylactic knee braces under laboratory conditions. Three studies assessed brace performance through testing on cadaveric knees.10,11,12 Of the remaining three studies, one study used only human subjects,14 one used a mechanical surrogate lower extremity, 13and one used both humans and a mechanical surrogate.15 Braces included for evaluation in these studies were manufactured by Omni Scientific, DonJoy, Tru-Fit, McDavid, Mueller, SMI and Stromgren. While there were various test conditions in which some braces outperformed others, there was no consensus benefit of one brace over any of the others.10,11,12,13,14,15 Overall, the evidence from these laboratory studies does not collectively support or discourage the use of prophylactic knee braces for ligamentous protection.
Two groups of investigators reported that prophylactic braces reduced the impact momentum experienced from a blow to the knee, when compared to an unbraced knee, suggesting a potential cushioning benefit. 11,13 This may have a beneficial effect on the ligamentous structures of the knee, although this is unclear. Erickson et al. found that despite reduced impact momentum, wearing a brace did not reduce elongation of the ACL, but did contribute to a non-significant reduction in peak MCL strain.11 Another study reported a decreased onset of time for both ACL and ACL-MCL tension when compared to unbraced knees.13
Braces may contribute to a very slight reduction in the abduction angle in both extension and flexion from either a direct lateral, anterior oblique, or posterior oblique impact.10 These percentage reductions were small however, ranging from 2-13%, and prophylactic braces offered no protection against tibial external rotation. 10
Three studies applied lateral impact forces to braced and unbraced cadaveric knees. Each of these concluded that prophylactic braces offered no protective benefit to ligamentous structures10,11and one reported that they may have negative consequences.12 Paulos et al. identified four negative consequences on braced cadaveric knees during valgus stress testing.12 First, prophylactic braces may preload the MCL by increasing ligamentous tension prior to external impact, thereby reducing the time required for rupture and predisposing the ligament to risk.12 Another negative finding was “center axis shift”, which refers to a laterally-directed shift in the axis of valgus rotation away from the center of the knee towards the brace.12,15 . The authors cited this as a possible explanation for two occurrences in the braced knees: 1) increased ACL loading, and 2) cruciate ligament damage occurring at 2 mm less medial joint line opening than in the unbraced knees. Two additional negative consequences, brace slippage and premature joint line contact, were also noted. Premature joint line contact refers to the impact of the brace hinge with the joint line, generating three-point bending and concentrated energy at the tibiofemoral joint.12
However, a follow-up study France et al., which utilized 13 Division I college football players and a mechanical, surrogate lower extremity, concluded that MCL preload was negated by dynamic muscle support and joint compression during weightbearing.15 They also proposed that the previously observed center axis shift was likely not a significant enough factor to predispose an individual to knee injury. In accordance with the previous study, France et al. did observe that each of the braces made contact with the joint line during testing. Despite making contact, some of the braces were able to continue to provide resistance to valgus impact, while others deformed prior to making contact and were unable to offer any resistance to valgus loading.15
A second study by Paulos et al. concluded that braces reduced peak forces at both the ACL and MCL with a greater reduction in ACL peak force.13 The mean reduction in MCL peak load was 21.95% +/- 6.92% and ACL peak load was 38.9% +/- 15.32%. 13Paulos and France also assessed the ligamentous protection with the Impact Safety Factor (ISF).13,15 An ISF > 1.50 indicates the minimal beneficial value, and represents a 30% reduction in force transferred to a ligament.13 Paulos et al. reported a mean ISF for all braces tested for the MCL of 1.29 +/- 0.12 and 1.78 +/- 0.60 for the ACL. 13
France et al. determined that of the six braces studied, only the mean ISF of 1.51 for the DonJoy brace suggested protective benefit.15 Subjects in this study included 13 Division 1 college football players who volunteered to participate, and a surrogate, mechanical limb for potentially damaging lateral impact testing.15 This study tested knees in both an open chain position, as well as a closed chain position.15 France et al. concluded that despite the ineffectiveness of prophylactic braces to protect knee ligaments, evidence was not convincing enough to encourage or discourage their use.15
The final laboratory study utilized 10 randomly selected intramural flag football participants from Penn State University.14These subjects had a minimum of 2 years varsity high school football experience, no prior knee injuries, and no previous experience with a knee brace.14 The braces were tested with the subject long-sitting with a submaximal valgus force (117.7 Newtons) applied to the knee at 10 degrees of knee flexion. There were no significant differences in the amount of medial joint line opening between the braced or unbraced knees. The authors concluded that prophylactic bracing did not offer adequate protection to prevent damage to knee ligaments.14
Injuries in Braced and Unbraced Football Players
The majority of evidence on the preventative effect of prophylactic knee bracing in college and high school football players are low-level observational studies, with only one RCT. 16 Of the ten studies reviewed, one included information on multiple high school sports (including football), two were specific to high school football players, and seven focused on college football players. Despite the low level evidence, studies restricted to football players were strengthened by large sample sizes, ranging from 450 to 11,697 subjects.17,18 The outcomes of interest were total knee injuries between braced and unbraced players, knee injury rates between braced and unbraced players, and additional information regarding knee injuries (i.e. knee joint structures affected, injuries by position, etiology, etc.).
Results on the effectiveness of prophylactic bracing in high school and college football players are inconclusive. Findings from two studies suggest a decreased risk from knee braces.16,19 Sitler et al. performed the lone randomized controlled trial, utilizing participants on an intramural 8-man football team at the United States Naval Academy.16 Subjects in the intervention group received prophylactic braces that were worn bilaterally during practices and competitions; the control group did not wear knee braces. The braced group experienced a significant reduction in overall MCL injuries (p < 0.005), and nonsignificant reductions in ACL and contact-related MCL injuries.16 Albright et al. reported a nonsignificant trend of reduced knee injury rates for braced knees vs. unbraced knees.19 In this study, players wore braces at their own discretion and included players who wore braces both bilaterally and unilaterally.19
Results from four studies indicated an increased risk of injury from the use of prophylactic braces.18,20,21,25 Rovere et al. compared injury data from four Division 1 college football seasons at a single university.18 Prophylactic braces were worn bilaterally by all members of the team for two seasons, and were not worn by any in two other seasons. These researchers reported an increased rate of ligamentous knee injury during the braced seasons (7.5 per 100 players vs. 6.1 per 100 players), although there were no differences in injury statistics between brace manufacturers.18 Grace reported a significant increase in injury (p < 0.001) in high school football players when single-hinged knee braces were worn, and a non-significant increase when double-hinged braces were worn, when compared to unbraced knees.21
Hewson et al., Deppen et al. and Albright et al. determined that there were no differences in injury occurrence or severity between braced and unbraced players17,23,24 Yang et al. assessed the use of knee braces in multiple high school sports including football, and noted an increased risk of knee injury in braced players.22
The MCL was the most common site of injury in both braced and unbraced players. 16,17,18,19,20,23 Offensive linemen experienced the majority of knee injuries, along with defensive linemen, tight ends and linebackers.17, 18, 19, 20, 24 Injuries are more likely to occur during games than practices, and occur as a result of direct contact to the knee.17,18,19,20,23,24
Discussion
These results are consistent with the conclusions from two systematic reviews on prophylactic knee braces and football players.8,26 Pietrosimone et al. reviewed seven studies, and calculated the relative risk reduction (RRR), relative risk increase (RRI), Numbers Needed to Treat to Benefit (NNTB) and Numbers Needed to Treat to Harm (NNTH) related to the use of prophylactic knee braces .26 A relative risk reduction ranging from 10-56% was determined from three studies, while a relative risk increase of 17-114% was calculated from four others. NNTB was calculated from two studies (NNTB = 32 and 17), and a NNTH of 32 was determined from two others. The NNT analysis was complicated by the inclusion of infinity in the 95% confidence interval in three studies, indicating that the effectiveness of the brace could not be determined.26
Despite the inability to determine causation from the scarcity of randomized controlled trials, the reviewed literature does not support the use of prophylactic knee braces to reduce injuries in high school and college football players. This is in agreement with the position of the American Academy of Orthopaedic Surgeons, who do not recommend the use of prophylactic knee braces to prevent knee injuries in college football due to insufficient evidence.8
There are numerous limitations in the existing research. First, only one of the reviewed studies (Yang et al.) was published after 1994. The subjects and braces utilized in these studies may not accurately reflect the body dimensions of modern football players, current training regimens or current knee brace designs.28 Secondly, the high prevalence of observational studies does not allow for causation to be determined from the research conclusions. Pietrisimone et al. noted the low methodological quality of these studies, rating them a Level 4 per the Centre of Evidence-Based Medicine methodology, where Level 5 represents the lowest quality research.26 There is also a lack of uniformity in the outcomes across studies, as some investigated only ligamentous injuries while others reported on all knee injuries, and some authors reported statistical significance while others did not. Albright et al. commented on the difficulty of designing studies which can accurately delineate the true affect prophylactic bracing has on knee injuries in football due to the frequent, high-velocity collisions, various playing field surfaces and wide-ranging variability in weather conditions during competition.19
Conclusion
Physical therapists should educate individuals who play football, particularly those who play at-risk positions, about the risks of participation. While the evidence is limited, at the present time it does not support the use of knee braces to prevent knee injury. However, it also does not conclusively discourage their use. Physical therapists need to possess the knowledge from current research to provide information to athletes, athletes’ families, coaches, athletic directors and other stakeholders so that they can make decisions that fit their financial and physical needs most appropriately.
Blackmon Capstone Presentation
References:
1.) National Federation of State High School Associations (NFHS). 2012-2013 High School Athletics Participation Survey. http://www.nfhs.org/content.aspx?id=3282. Retrieved February 23, 2014.
2.) Rechel JA, Collins CL, Comstock RD. Epidemiology of Injuries Requiring Surgery Among High School Athletes in the United States, 2005-2010. The Journal of Trauma. 2011; 71: 982-989.
3.) Bradley J, Honkamp NJ, Jost P, et al. Incidence and Variance of Knee Injuries in Elite College Football Players. The American Journal of Orthopedics. 2008; 37: 310-314.
4.) McCullough KA, Phelps KD, Spindler KP, et al. Return to High School- and College-Level Football After Anterior Cruciate Ligament Reconstruction. The American Journal of Sports Medicine. 2012; 40: 2523-2529.
5.) Bradley J, Honkamp NJ, Jost P, et al. Incidence and Variance of Knee Injuries in Elite College Football Players. The American Journal of Orthopedics. 2008; 37: 310-314.
6.) Dermody KC. Oakland Raiders Lose Another Family Member with the Passing of George Anderson: Fan’s Look. Yahoo! Sports web site. http://sports.yahoo.com/nfl/news?slug=ycn-11180146. Retrieved February 23, 2013.
7.) Najibi S, Albright JP. The Use of Knee Braces, Part 1: Prophylactic Knee Braces in Contact Sports. The American Journal of Sports Medicine. 2005; 33: 602-611. doi: 10.1177/0363546505275128
8.) Salata M, Gibbs AE, Sekiya JK. The Effectiveness of Prophylactic Knee Bracing in American Football: A Systematic Review. Sports Health. 2010; 2: 375-379.
9.) BetterBraces.com. Prophylactic Bracing of the Collegiate Football Knee: A Review of Custom Fitted Functional vs. Lateral Braces in Offensive Linemen. http://www.betterbraces.com/prevent-football-injuries-in-offensive-linemen. Retrieved February 23, 2014.
10.) Baker BE, VanHanswyck E, Bogosian SP, et al. The effect of knee braces on lateral impact loading of the knee. The American Journal of Sports Medicine. 1989; 17(2): 182-186.
11.) Erickson AR, Yasuda K, Beynnon B, et al. An in vitro dynamic evaluation of prophylactic knee braces during lateral impact loading. The American Journal of Sports Medicine. 1993; 21(1): 26-35.
12.) Paulos LE, France EP, Rosenberg TD, et al. The biomechanics of lateral knee bracing. Part 1: Response to valgus restraints to loading. The American Journal of Sports Medicine. 1987; 15 (5): 419-429.
13.) Paulos LE, Cawley PW, France PE. Impact biomechanics of lateral knee bracing. The anterior cruciate ligament. The American Journal of Sports Medicine. 1991; 19 (4): 337-342.
14.) Salvaterra GF, Wang M, Morehouse CA, Buckley WE. An In Vitro Biomechanical Study of The Static Stabilizing Effect of Lateral Prophylactic Knee Bracing on Medial Stability. Journal of Athletic Training. 1993; 28(2): 113-119.
15.) France PE, Paulos LE, Jayarmann G, Rosenberg TD. The biomechanics of lateral knee bracing. Part II: Impact response of the braced knee. The American Journal of Sports Medicine. 1987; 15(5): 430-438.
16.) Sitler M, Ryan J, Hopkinson W, et al. The efficacy of a prophylactic knee brace to reduce knee injuries in football. The American Journal of Sports Medicine. 1990; 18: 310-315.
17.) Hewson GF, Mendini RA, Wang JB. Prophylactic knee bracing in college football. The American Journal of Sports Medicine. 1986; 14: 262-266.
18.) Rovere GD, Haupt HA, Yates SC. Prophylactic knee bracing in college football. The American Journal of Sports Medicine. 1987; 15: 111-116.
19.) Albright JP, Powell JW, Smith W, et al. Medial Collateral Ligament Sprains in College Football: Brace Wear Preferences and Injury Risk. The American Journal of Sports Medicine. 1994; 22: 2-11.
20.) Teitz CC, Hermanson BK, Kronmal RA, Diehr PH. Evaluation of the Use of Braces to Prevent Injury to the Knee in Collegiate Football Players. The Journal of Bone and Joint Surgery. 1987; 69: 2-9.
21.) Grace TG, Skipper BJ, Albuquerque JC, et al. Prophylactic Knee Braces and Injury to the Lower Extremity. The Journal of Bone and Joint Surgery. 1988; 70: 422-427.
22.) Yang J, Marshall SW, Bowling MJ, et al. Use of Discretionary Protective Equipment and Rate of Lower Extremity Injury in High School Athletes. American Journal of Epidemiology. 2005; 161: 511-519.
23.) Deppen RJ, Landfried MJ. Efficacy of Prophylactic Knee Bracing in High School Football Players. The Journal of Orthopaedic and Sports Physical Therapy. 1994; 20: 243-246.
24.) Albright JP, Powell JW, Smith W, et al. Medial Collateral Ligament Sprains in College Football. The American Journal of Sports Medicine. 1994; 22 (1): 12-18.
25.) Zemper E. A Two-Year Prospective Study of Prophylactic Knee Braces in a National Sample of College Football Players. Sports Training, Medicine and Rehabilitation. 1990; 1: 287-296.
26.) Pietrosimone BG, Grindstaff TL, Linens SW, et al. A Systematic Review of Prophylactic Braces in the Prevention of Knee Ligament Injuries in Collegiate Football Players. Journal of Athletic Training. 2008; 43: 409-415.
27.) Paluska SA, McKeag DB. Knee Braces: Current Evidence and Clinical Recommendations for Their Use. American Family Physician. 2000; 15: 411-418.
28.) Kraemer WJ, Torine JC, Silvestre R, et al. Body Size and Composition of National Football League Players. Journal of Strength and Conditioning Research. 2005; 19(3): 485-489.
4 Responses to “Do Preventative Knee Braces Prevent Knee Injuries in College and High School Football Players?”
Daniel Blackmon
Kenneth,
Thanks for commenting on my project. I thought that it would interest you given your athletic background and our previous discussions on your personal experience with knee braces.
In regards to ankle injuries, there are differing findings in the studies I used. Grace et al. found a significant increase in ankle injuries in college football players who wore knee braces, while Zemper et al. reported no association. In a large study on high school athletes, Yang et al. determined not only an association between knee braces and increased knee injury, but also increased ankle injury with ankle braces. They did not compare the use of ankle braces on knee injuries, however. I did not see any studies that specifically addressed limiting movement distally and its impact on knee injuries, but that is another possibility I had not considered.
While that doesn’t specifically address your question, there may be some relationship to restricting movement at the knee on subsequent ankle injuries.
Daniel
Kenneth Ngwu
Daniel,
I believe you have done an outstanding job with your CAPSTONE. I believe I communicated to you earlier through a previous DB post, about how I felt my performance as an offensive lineman (OL) was hindered by wearing a knee brace. It was probably due to the weird alignment of my knees, but I also remember other teammates feeling the same way since all OL were once required to wear knee braces. Those who traditionally wore knee braces typically had a history of knee injuries and were usually not as aggressive as needed for performance on the field. This led me to believe they were still somewhat apprehensive about certain movements with their knee, which may help explain the effectiveness of knee braces. However, this is not an ideal form of protection especially in contact sports such as American football.
Also, I’m curious to know if any of the studies accounted for any differences in injury rates or observed knee forces between those with ankle braces/straps and those without. I believe most players especially OL wear an ankle brace or either have some taping applied that provides a similar support. This support is intended to limit ankle movements mostly in inversion/eversion. Therefore, I wonder if ankle support can impact the probability of a knee ligament injury since ankle movement may help prevent harmful forces from occurring within the knee during sports performance.
Daniel Blackmon
Good comments, Susie. You are absolutely correct in that it is very difficult to really design a study that can truly delineate the role of knee bracing in knee injury. I think the nature of the sport, where a 250+ lbs. individual collides into the side of a person’s leg, makes it difficult to really say that any externally applied brace can “prevent” an injury in such an event.
The subjects in the Sitler RCT were significantly smaller than individuals in 11-on-11 college and high school football, with a mean bodyweight of 173 lbs. In addition, they were playing 8-on-8 football, which excludes three individuals from the playing surface as opposed to the traditional 11-on-11 game.
In the Rovere et al. study, 51 of the 54 knee injuries occurred during games on a dry, grass playing surface, however the vast majority of the games were played on dry, grass surfaces.
Regarding athletic performance and prophylactic bracing, some of the studies commented that skill players were much more resistant to wear braces in games than practices due to a belief that they would sacrifice agility.
Thanks for commenting! Hopefully I addressed your questions.
Daniel
Susie Williams
Daniel,
What an interesting topic! While reading through the evidence I kept going back and forth as to what I would tell a patient questioning whether or not to use a brace. It seems that the evidence both supporting and against bracing has a number of aspects in the research designs that could potentially limit the strength of their conclusions. For example, in Sitler’s RCT, were the two groups equal at baseline for not only playing position, but the side of the field, playing time, size and weight of the athlete, and strength and flexibility of the muscles surrounding the knee joint? In the Rovere study that looked at differences during different seasons, were the playing conditions similar (dry vs wet fields, opposing teams, etc)? For this second study there wasn’t a large difference (7.5% vs 6.1%) in the number of injuries between braced and unbraced (although significant) that question me to believe whether it’s the brace leading to injury versus some other aspect. I also think you could bring to question how the athlete performs when he is wearing a brace versus when he isn’t. Does he work harder, cut more across the field, play more aggressively when the brace is on because he believes it will protect him? Or does the brace limit his ability to perform?
Ultimately, I think as Physical Therapists all we can do is offer the evidence, and your handout does a great job of showing the inconclusiveness that is currently present along with a nice inclusion of images and wording to make it patient-friendly. Great work!
Susie