Neuromuscular Intervention Targeted to Mechanisms of ACL Load in Female Athletes
Condition: ACL Injury
MeSH terms: Anterior Cruciate Ligament Injuries
Study type: Interventional

Summary: 
      Females who participate in cutting and landing sports suffer anterior cruciate ligament (ACL)
      injuries at a 2 to 10-fold greater rate than males participating in the same high-risk
      sports. Fifty to 100 percent of ACL injured females will suffer osteoarthritis of the injured
      knee within one to two decades of the injury. External knee abduction moment (LOAD) predicts
      ACL injury with high sensitivity and specificity in female athletes. Control of lateral trunk
      motion (LTM) also predicts ACL injury with similar levels of sensitivity and specificity in
      female athletes. These predictors may be linked, as lateral positioning of the trunk can
      create high knee abduction load via both biomechanical and neuromuscular mechanisms. The
      mechanism of ACL injury in females include high knee LOAD and high LTM, with the majority of
      body weight shifted over the injured limb and the foot positioned lateral to the body's
      center of mass. An unanticipated perturbation is also often a contributor to the injury
      mechanism. LTM may result in increased knee LOAD by increasing the lateral position and
      magnitude of the GRF vector (ΔGRFv) or by increasing reactive hip adductor torque (HAdT). Our
      long-term objectives are to determine the mechanisms that cause ACL injury in female athletes
      and to develop neuromuscular training (NMT) interventions that specifically target these
      mechanisms. If the objectives of this proposal are achieved, an evidence-based NMT
      intervention will be developed and made available nationally that will effectively and
      efficiently reduce ACL injury risk in high-risk female athletes. The major goal of this
      proposal is to determine if increased LTM increases coronal plane knee load in high-risk
      groups of female athletes.
    

Detailed description: 
      1. Specific Aim 1 Determine the mechanisms by which trunk motion increases knee load in
           females.

           Rationale Aim 1 Knee external abduction moment (LOAD) and lateral trunk motion (LTM) are
           known to be strong predictors of ACL injury risk in female athletes, but it is not known
           whether these predictors are linked and which athletes are at increased risk. In
           addition, we do not know the specific neuromuscular mechanisms that predispose these
           athletes to greater risk of injury. Neuromuscular control of the trunk will be examined
           relative to GRF position and magnitude, hip torque and knee LOAD. We will determine if
           increased ΔGRFv and increased relative hip adductor torque (HAdT) underlie increased
           knee LOAD in females.

           Central Hypothesis Aim 1 Lateral trunk motion will increase knee LOAD in female athletes
           by increased ΔGRFv, increased HAdT or by a combination of these two mechanisms during
           cutting and landing.

           Hypothesis 1.1. Increased LTM induced by unanticipated lateral cutting will increase
           knee LOAD by increasing ΔGRFv, adjusting for HAdT, in female athletes.

           Hypothesis 1.2. Increased LTM induced by single-leg medial drop landing will increase
           knee LOAD by increasing HAdT, adjusting for ΔGRFv, in female athletes.

           Hypothesis 1.3. Increased LTM induced by combined drop landing and unanticipated lateral
           cutting will result in combinatorial increases in knee LOAD by increasing ΔGRFv and HAdT
           in female athletes.

           Hypothesis 1.4 Females with low ΔGRFv, low HAdT, and low knee LOAD will form a distinct
           group or cluster of subjects, those with high ΔGRFv or HAdT and moderate LOAD will form
           another cluster, and those with high ΔGRFv, high HAdT and high LOAD will form the last
           distinct group using data collected during DLUC.

        2. Specific Aim 2 Determine if NMT that decreases coronal plane trunk motion will decrease
           knee abduction LOAD in a double-blind cluster (by school and team) randomized controlled
           trial (RCT).

      Rationale Aim 2 This aim will determine how NMT targeted to LTM and its two knee loading
      mechanisms, ΔGRFv and HAdT, will affect knee LOAD in low, moderate and high LOAD subgroups of
      female athletes.

      Central Hypotheses Aim 2 NMT will increase control of coronal plane trunk motion and decrease
      knee LOAD by either mechanical (ΔGRFv), neuromuscular (HAdT) or both mechanisms and pre-test
      low, moderate and high knee LOAD subgroups of female athletes will demonstrate differential
      effects of NMT.

      Hypothesis 2.1 Knee LOAD will be lower in trained than untrained females during landing and
      cutting.

      Hypothesis 2.2 Post-test knee LOAD will not differ in trained high, moderate and low knee
      LOAD subgroups. Hypothesis 2.3 Post-test ΔGRFv and HAdT will not differ in trained high,
      moderate and low LOAD subgroups.

      Hypothesis 2.3 Post-test knee LOAD, ΔGRFv and HAdT values will not differ from pre-test
      values in untrained high, moderate and low knee LOAD subgroups.

      Program Director/Principal Investigator (Last, First, Middle): Hewett, Timothy, Edwin PHS
      398/2590 (Rev. 11/07) Page Continuation Format Page

      A. Specific Aims The Specific Aims have not been modified from the original application. Our
      long-term goals are to determine the mechanisms by which female athletes become more
      susceptible to ACL injury and to develop interventions that address these mechanisms in order
      to reduce knee loads and ACL injury risk. The major goal of this proposal is to determine if
      decreased neuromuscular control of the trunk increases coronal plane knee load in high-risk
      groups of females. This overall objective of this application is to test the central
      hypotheses that lateral trunk motion increases knee load and that neuromuscular training that
      increases control of trunk motion will decrease knee abduction loading in females with
      moderate and high knee loads. Our rationale for this project is that its successful
      completion will provide a strong, evidence-based intervention that will effectively decrease
      ACL injury risk in high-risk female athletes.

      B. Studies and Results

      We continue to utilize a prospective randomized controlled design for Specific Aims 1 and 2
      as outlined in the original funded application. The Boone County Superintendent and the Boone
      County School Board approved the participation (testing, busing, randomized intervention,
      etc) of the school systems' girls' athletic programs (Basketball, Soccer and Volleyball) at
      their monthly school board meeting on Thursday, June 11, 2009 and pre-testing began on
      September 1, 2009. As outlined, school-sponsored basketball, soccer and volleyball teams from
      the Boone County, Kentucky school system have been and are almost completely recruited,
      tested and tracked. Testing will be completed by December 31, 2010. Female subjects from all
      the county high school and junior high schools are being screened prior to the start of their
      basketball and soccer and volleyball seasons.

      A total of 23 teams yielding 318 basketball players have been pre-screened and trained and
      post-screened September 1, 2009 through April 30, 2010. A total of 29 teams of approximately
      306 soccer and volleyball players (31 of which were not new athletes and were tested in prior
      basketball season) were pre-screened, trained and post-screened between May 2010 and December
      2010. We have faced challenges recruiting soccer players at the junior high school level in
      the county school system. Some of the junior high schools do not have organized soccer teams.
      We are addressing this challenge by recruiting volleyball teams within the county in order to
      fill in all of our randomized blocks. In addition, we will capture those athletes that will
      go on to play high school soccer, volleyball and basketball within the Fayette county school
      system (see supplement summary below). Thus far, we have enrolled and pretested (N=31 tested
      for both seasons) and tested a total of 593 athletes for our randomized controlled trial from
      9/1/09 through 12/31/10. The breakdown by sport and school level is summarized in the
      Enrollment Table. There were 558 athletes made the cuts on their respective teams who were
      randomized by cluster (team) into the intervention. This number includes all athletes who
      completed at least 1 intervention training session. 523 athletes had full data sets for
      analysis.

      For the initial biomechanical analyses, we have chosen to focus on Hypothesis 1.4 with the
      use Latent Profile Analysis (LPA). We will use LPA to examine whether we can cluster subjects
      with similar characteristics of the GRFv, HAdT, hip moments (minimum and maximum), lateral
      trunk motion and center of gravity displacement into distinct neuromuscular profiles. Our
      latent profile analyses will evaluate independent variables across the multiple tasks to form
      groups of girls with similar neuromuscular patterns for these variables where the
      heterogeneity of response pattern is minimized within each profile and maximized across
      profiles. Initially, two profiles are specified for the LPA model, then, in a stepwise
      fashion, the number of profiles specified is increased by one. At each step, changes in
      Bayesian information criteria (BIC), adjusted for sample size, is used to assess model fit
      and identify the number of profiles needed. The point at which the number of profiles is
      deemed adequate is when no significant drop in BIC is seen when the profile number is
      increased. In addition, the Lo-Mendell-Rubin adjusted likelihood ratio test is used to
      determine the optimal number of profiles.(Lo 2001) The analysis was implemented using Mplus
      5.(Muthen 2007) Validation of profile group includes examination as an independent predictor
      of LOAD.

      Analysis has begun and profiles have been created for the pre-test movements. Graphs
      depicting the standardized means along with the 2 generalized profiles are shown in Figure 1.
      For presentation purposes it is necessary to show the standardized values as the variables
      are on different scales, with hugely varying mean values. Due to the underlying normality
      assumption, it was necessary to transform the lateral trunk motion variable to the loge
      scale. In addition, it is necessary to account for the correlation between some of these
      variables; in particular maximum hip moment and GRFv and HAdT. We are continuing to examine
      the potential LPA models at this time and will be checking them against the post intervention
      data to determine any emergent profiles. Comparison of mean KAM, with and without adjustment
      for age and pubertal status by profile will also be the focus of future analyses.

      Figure 1. Profile analysis of Pre-Test Data Set (N=457) In addition, we have performed this
      initial assessment of the efficacy of the Randomized controlled intervention and will be
      presenting these initial results (The effect of Trunk focused Neuromuscular training on Hip
      Strength) at a national meeting this coming July.
    

Intervention name(s): Neuromuscular Training
Intervention type(s): Other
Intervention description(s): Combination of exercises and phases to initiate lateral trunk perturbations that force the athlete to decelerate and control the trunk in order to successfully perform the techniques.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Prevention
Keywords: Anterior Cruciate Ligament; Female Athlete; Sports Injuries; Injury Prevention