The purpose of the current study was to develop a “clinician friendly” landing assessment tool derived from the highly predictive laboratory-based measurements that would be easy to use and would facilitate the potential for widespread use in clinical and field settings. A nomogram was developed from the logistic regression analyses that can be used to predict high KAM (>21.74Nm KAM) based on clinically measured tibia length, knee valgus motion, knee flexion ROM, body mass and quadriceps to hamstrings ratio.
The outcome tool () developed from the regression analysis can be used to predict the probability to demonstrate high KAM landing mechanics based on the described clinically obtainable measures tibia length, knee valgus motion, knee flexion range of motion, body mass and quadriceps to hamstrings ratio. Clinic-based tibia length can be measured using a standard measuring tape to quantify the distance between the lateral knee joint line to the lateral malleous. Body mass can be measured on a calibrated physician scale. Two dimensional (clinic-based) frontal and sagittal plane knee kinematic data can be captured with standard video cameras. QuadHam ratio is traditionally captured on isokinetic dynamometers in a clinical setting. If an isokinetic testing device is not readily available, then a surrogate measure of the QuadHam ratio can be developed based on the athlete’s body mass. The surrogate QuadHam ratio measure is obtained when a female athlete’s mass (kg) is multiplied by 0 .01 and the resultant value added to 1.10. If further simplicity is desired the mean value of 1.53 can be input into the nomogram to represent QuadHam ratio for the athlete.
Landing sequence images used for knee valgus motion () and knee flexion ROM () clinic-based measurement can be captured via the “print screen” feature available on most personal computers or they can be captured with freeware software such as VirtualDub software (copyright 1998–2009 Avery Lee). Recommended software for kinematic coordinate data capture and calculation are suggested to be performed with ImageJ (Rasband, W.S., ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, http://rsb.info.nih.gov/ij/
, 1997–2009) software that is also available without surcharge ().(Myer et al., 2010
A. The coordinate position of knee joint center is digitized in the frontal view measured at the frame prior to initial contact is used as the knee valgus position X1.
provides a completed algorithm for the presented subject using following the clinically feasible measurements quantified on her left leg: Tibia length: 36 cm; Knee valgus motion: 3.3 cm; Knee flexion ROM: 63.4°; mass: 57.2 kg; QuadHam: 1.78. Based on her demonstrated measurements, the prediction nomogram would indicate that this subject would have a 45% percent chance to demonstrate high KAM during her measured drop vertical jump. presents the completed algorithm for the same subject with the following clinic-based measurement of knee valgus motion on her right leg. The red solid lines indicate the shift in her measured knee valgus motion from 3.3 cm on her left leg to 6.0 cm or her right. Accordingly, this change in knee valgus motion shifts her probability of high knee load on her right leg to be 66% during this trial of the drop vertical jump.
Figure 4 A. Completed nomogram for a representative subject with the following clinically feasible measurements quantified on her left leg: Tibia length: 36 cm; Knee valgus motion: 3.3 cm; Knee flexion ROM: 63.4°; mass: 57.2 kg; QuadHam: 1.78). Based on (more ...)
Recent studies demonstrate that neuromuscular training reduces the high KAM risk factor for ACL injury, increases performance and decreases knee and ACL injury incidence in female athletes.(Hewett et al., 2004
, Myer et al., 2004
, Hewett et al., 2006a
, Hewett et al., 1996
, Myer et al., 2007
, Myer et al., 2006a
, Myer et al., 2006b
, Myer et al., 2005
) However, re-evaluation of ACL injury rates in female athletes indicate that this important health issue has yet to be resolved, as increased knowledge and application of injury prevention techniques have not led to measureable reductions in ACL injury incidence in female athletes.(Agel et al., 2005
) A recent investigation by Grindstaff and colleagues indicated that standard, non-targeted neuromuscular training programs may require application to 89 female athletes to prevent a single ACL injury.(Grindstaff et al., 2006
) It is possible that the identification of female athletes who demonstrate risk factors for ACL injury such as high KAM could improve the efficiency of neuromuscular training by targeting these individuals.
The current investigation provides the critical next step to merge the gap between laboratory identification of injury risk factors (Hewett et al., 2005
, Padua et al., 2009
) and clinical practice with this simplified algorithm that can be utilized with clinic-based assessment tools. The simplicity and lessened equipment and labor cost (relative to laboratory-based assessments that may exceed $1000 per athlete) associated with utilization of this tool may facilitate the identification of high ACL injury risk athletes on a more widespread basis in clinical and field settings. Prior work has utilized laboratory-based measures to determine the potential differing effects of neuromuscular training in female athletes who demonstrate high KAM landing strategies relative to those who do not.(Myer et al., 2007
) This prior study employed an abridged version of a comprehensive training protocol shown to alter biomechanical factors related to increased ACL injury risk in female athletes.(Myer et al., 2005
, Paterno et al., 2004
, Hewett et al., 2005
) The results of this study indicate that females who demonstrate increased high KAM may be able to reduce this risk factor via targeted neuromuscular training, while those athletes without this risk factor may not reap similar benefits from the training program.(Myer et al., 2007
) To further evaluate the potential effect of neuromuscular training on the high KAM risk factor, a linear regression analysis was performed to examine the potential association between the pre-test measures of high KAM and the change in this variable with neuromuscular training.(Myer et al., 2007
) In the trained group, the pre-test KAM predicted the potential to reduce KAM with training. In contrast, the control group showed no similar causal relationship of pre-test KAM measures to change in the post test measure. If this is the case, a logical extension of these findings would be that it is more important to identify and target athletes identified as high KAM for injury prevention training programs than those with low KAM.
Myer et al. evaluated a comprehensive neuromuscular training protocol that was developed to reduce ACL injury risk and improve sports related performance measures(Myer et al., 2005
). This comprehensive protocol successfully reduced knee abduction torques by 21%, but the females in the study who demonstrated low KAM may have masked the potentially larger training effects. This reported mean reduction in KAM may be masked by subjects who already demonstrated a low value of a measured risk factor that has been previously demonstrated (Knaus et al., 1993
), but is often ignored in clinical investigations (Harrell, 2001
). The current clinic-based tool can aid in the identification of female athletes with high KAM landing mechanics who will most likely obtain the greatest potential to significantly reduce dangerous knee loading profiles with targeted neuromuscular training. In addition, neuromuscular training targeted directly to reduce KAM in those who demonstrate high KAM landing mechanics may help athletes obtain landing mechanics that will take them out of “high-risk” category. These goals have not been previously achievable with non-targeted training protocols.(Myer et al., 2007
) In addition, based on the low risk of the treatment for high KAM (neuromuscular training), we chose to influence the algorithm for highly sensitive prediction for this outcome. While an increased number of false positives may be predicted with efforts to maximize sensitivity, female athletes predicted to demonstrate both low and high KAM will likely gain improved performance as a serendipitous effect of neuromuscular training targeted to prevent injury risk.
The risk for osteoarthritis in the female ACL injured population ranges from 50 to 100%,(Myklebust and Bahr, 2005
) with or without surgical reconstruction of the ligament. This high risk of long term osteoarthritis may be increased in those athletes who demonstrate excessive and repetitive high KAM during participation in sports and who are at increased risk of a knee valgus injury mechanism.(Meyer et al., 2009
, Hewett et al., 2005
) Accordingly, the prevention of ACL injury is currently the only effective intervention for these life-altering injuries. The high predictive sensitivity and specificity of this single factor points to the necessity to develop specific injury prevention protocols targeted to athletes who demonstrate high KAM, which increases their risk for ACL injury.
Theoretically, through identification of female athletes at greater risk for ACL injury, prevention strategies to reduce an ACL injury could be substantially improved. As mentioned previously, the current non-targeted neuromuscular training programs require application to 89 female athletes to prevent one ACL injury.(Grindstaff et al., 2006
) The current clinic-based assessment tool could increase the efficiency of neuromuscular training if it were to be targeted to high KAM female athletes. The results of the current investigation may aid in the dissemination of assessment techniques required for the application of targeted neuromuscular training intervention to high-risk populations. The authors acknowledge that the proposed algorithmic approach may have limited utility to predict injury risk during cutting, pivoting or maneuvers not associated with landing. Future efforts should aim to validate the proposed algorithm using clinic-based measurement techniques to determine the relationship to ACL injury prediction from both cutting and landing injury mechanisms. In addition, further research is warranted to delineate the most efficient training methods to target females who demonstrate high KAM landing mechanics to further improve the potential prophylactic effects.