Do Preventative Knee Braces Prevent Knee Injuries in College and High School Football Players?

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 2^nd  and 3^rd 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 players^17,23,24 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 – Knee Brace Handout

Blackmon Capstone Presentation

Blackmon Feedback Form

 

References:

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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.

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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.

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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.

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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.