Research Review by Dr. Kent Stuber©

Date:

Nov. 2007

Study Title:

The effectiveness of a balance training intervention in reducing the incidence of non-contact ankle sprains in high school football players

Authors:

McHugh MP, Tyler TF, Mirabella MR, Mullaney MJ, Nicholas SJ.

Publication Information:

American Journal of Sports Medicine 2007; 35(8): 1289-1294.

Summary:

Ankle sprains are a common athletic injury. Previous ankle sprains and a high body mass index (BMI) have been identified as risk factors for non-contact inversion ankle sprains (NCIAS) in football players, regardless of position. Commonly, ankle braces or tape are used in an attempt to reduce the risk of sprain, but the effectiveness of these strategies has recently been called into question. However, there is increasing support for the use of single limb balance training (SLBT) to reduce ankle injury risk.

The authors of this study hypothesized that having previous ankle injury and a high BMI increase NCIAS risk due to impaired ankle stability, and a lack of control of upper body mass during the dynamic movements required in football. As such, SLBT could counteract these deficits and lower risk. Therefore, this study aimed to determine if SLBT on a foam stability pad can reduce NCIAS incidence in high school football players who were at increased risk.

During the intervention period, 125 different players from 2 high school football teams were observed over 3 seasons. A previous history of ankle sprains, height, body mass, and use of ankle braces or tape were noted. 175 player seasons were followed in total. Players were assigned risk levels (minimal, low, moderate, or high) for NCIAS based on their BMI and previous ankle injury history. Players in the low, moderate, or high risk categories were assigned to perform the stability pad intervention.

Subjects in the intervention group performed SLBT on a foam stability pad for 5 minutes per leg (both legs were trained), five times per week for 4 weeks in the preseason. Subjects completed the same type of training twice weekly for nine weeks during football season. The SLBT was incorporated into the subjects’ regular weight room routines as part of a balance training station. Compliance was monitored by the team Athletic Therapist, and subjects had to make up for missed sessions.

The main outcome measure was incidence of NCIAS, which was defined as a sprain that required the player to miss at least one game or practice, and it had to be non-contact (i.e. did not occur while tackling or blocking, etc). The team Athletic Therapist collected data on NCIAS injuries and the number of missed games and practices due to such an injury. Injury incidence was calculated in units of per 1000 player exposures (an exposure being participation in a game or practice, and the analysis included the use of 95% confidence intervals).

Statistical analysis included chi square and Fisher exact tests to compare NCIAS incidence before and after the introduction of the intervention. 107 player seasons (for 84 players) were followed prior to the introduction of the intervention as a comparison.

Pertinent Results:

  • 128 out of the 175 players seasons were classified as low, moderate, or high risk and were thus assigned to the intervention analysis
  • 12 players were non-compliant, the rest of the players completed at least 34 out of 38 training sessions (20 preseason and 18 in-season)
  • pre-intervention period: the prevalence of NCIAS was 3% in the minimal risk group and 18% in the low-moderate-high risk group; 21 of the 84 players sustained an inversion ankle sprain, 13 of which were NCIAS; nine of those were by players with a previous history of ankle sprain
  • post-intervention period: the prevalence of NCIAS was 7% prevalence in the minimal risk group and 5% prevalence in the low-moderate-high risk group (actually 4% as one of the players in this group did not complete the intervention/was non-compliant); 20 out of 125 players had inversion ankle injuries, 9 of which were NCIAS and five of those were by players with a previous history of ankle sprain
  • overall, the prevalence of NCIAS was significantly reduced for those at risk - a 77% reduction in injury incidence for those in similar risk groups (2.2/1000 exposures to 0.5/1000 in the groups when combined) – p < 0.01
  • use of tape and/or ankle braces did not lower ankle injury incidence in the pre-intervention or post-intervention periods
  • player position similarly did not affect ankle injury incidence
The following summarizes the results based on players’ levels of risk:

Before the intervention the incidence for NCIAS was:
  • 0.4 injuries/1000 exposures for minimal risk players
  • 1.2 injuries/1000 exposures for low risk players
  • 1.9 injuries/1000 exposures for moderate risk players
  • 5.7 injuries/1000 exposures for high risk players
After the intervention the incidence for NCIAS was:
  • 0.8 injuries/1000 exposures for minimal risk players
  • 0.4 injuries/1000 exposures for low risk players
  • 0.6 injuries/1000 exposures for moderate risk players
  • 1.4 injuries/1000 exposures for high risk players

Conclusions & Practical Application:

The authors conclude that stability pad training was easily implemented and very effective in reducing the incidence of NCIAS in high school football players, as there was a 77% decrease in sprains, helping to eliminate the increased risk from having a previous ankle sprain and elevated BMI. The authors reasoned that the stability pad training improved proprioception and/or proximal control of the body mass helping players avoid inversion ankle injuries.

The results of this study should be interpreted with some methodological limitations in mind. There was no randomization to treatment versus control groups, and the analysis did not account for a number of potential confounding factors (ex. playing surface, shoe type, exact method of taping or ankle bracing).

That being said, this article is useful as it helps the clinician identify patients who are potentially at risk for NCIAS (those with previous ankle sprains and high BMI) and gives an intervention and an easy set of instructions as to how they can effectively reduce their risk of these injuries. The findings of this study can likely be applied to other sports where ankle injuries are common such as volleyball, basketball, tennis (and other racquet sports), soccer, rugby, etc.

The authors quite correctly chose to only evaluate the ability of the intervention to reduce NCIAS (from pivoting, changing directions, running, etc) as opposed to contact ankle inversion sprains as it is inherently difficult to prevent contact injuries in a collision based sport such as football.

It is interesting to note that the authors chose to use a foam stability pad as opposed to a balance disc/wobble board as they reasoned the stability pads were less expensive, lighter and more portable, and their previous clinical experience indicated that teenage athletes were more compliant in using the pads and generally preferred them. The 91% compliance rate of the subjects on the intervention in this study would point to this being correct.

This could provide an impetus for clinicians to consider foam stability pads more frequently in their recommendations to patients. Unfortunately, as with many studies like this, the specific exercises were not fully described.