Research Review: Deficits in Neuromuscular Control of the Trunk Predict Knee Injury Risk

By Jinny McGivern, PT, DPT, CFMT, Certified Yoga Instructor

Edited by Amy Martinez DPT, PT

and Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Zazulak, B. T., Hewett, T. E., Reeves, N. P., Goldberg, B., and Cholewicki, J. (2007). Deficits in neuromuscular control of the trunk predict knee injury risk. The American journal of sports medicine, 35(7), 1123-1130. ARTICLE

Introduction: 

The knee joint is the second most commonly injured body part, and knee surgeries account for as much as 60% of all sports-related surgeries (1-2). Research is starting to imply that dynamic stability of the knee depends on the ability to react to changes in trunk position during cutting, stopping and landing movements (3-4). This 2007 study by U.S. researchers demonstrated a correlation between the amount of trunk displacement after a significant isometric force was suddenly removed, and the risk of knee injury during a 3-year follow-up. Human movement professionals should consider screening for and addressing any noted impairments in core stability prior to the beginning of a season.

Dr. Brookbush instructs model, Melissa Ruiz, on proper form during a Kneeling Chop Kneeling Chop. (Image: Courtesy of www.BrentBrookbush.com)

Study Summary

Study DesignProspective cohort study
Level of EvidenceIII - Evidence from at least one other type of quasi-experimental study
Participant CharacteristicsDemographics

  • Age (years +/- standard deviation):

    • 19.4 +/- 1.0 (female)
    • 19.3 +/- 1.8 (male)

  • Gender: 140 female, 137 male
  • Number of participants: 227
  • Collegiate athletes participating in various sports

Inclusion Criteria:

  • No history of knee injury

Exclusion Criteria:

  • N/A

Methodology

  • Participants filled out a questionnaire with demographic data, athletic experience and a history of any injury that prompted a visit to a physician
  • Baseline trunk stability was tested
  • Knee injuries were tracked over a 3-year period
  • Knee injury was defined as "ligament, meniscal or patellofemoral injury to the knee joint"

    • All knee injuries were confirmed by magnetic resonance imaging (MRI)
    • Fractures and contusions were not classified as knee injuries.

  • Core stability was evaluated by observing the response of the trunk to the sudden removal of an isometric force
  • Testing was performed with the participant's pelvis and lower extremities stabilized in a wooden apparatus

    • Participants were semi-seated with their lumbar spine in a self determined "comfortable position"

      • The hips were in approximately 20º of flexion, knees in approximately 90º of flexion and the feet were free

    • Each participant wore a chest harness at the T5 spinal level that was connected via a pulley to an electromagnet and supplied the resistance for the isometric contraction for the trunk
    • Resistance was "30% of the maximal isometric trunk exertion for an average healthy man (108 N) or woman (72 N)" as determined by a pilot study

  • Resistance was provided from 3 different directions:

    • Flexion (cable directed posterior from harness)
    • Extension (cable anterior from harness)
    • Lateral bending (cable right from harness)

  • Each participant performed 5 trials in which:

    • The electromagnet gradually increased direction-specific resistance
    • Participants were instructed to maintain their position and were provided with a visual of the target resistance level
    • The electromagnet was abruptly disengaged at random

    • Trunk motion was recorded via sensor at T5 after the release of the isometric force

      • At 150 milliseconds (ms) after release
      • At maximal trunk displacement

Data Collection and Analysis

  • A 3-factor analysis of variance and Tukey post hoc test identified significantly different values (force release direction, gender and history of injury) between injured and uninjured participants
  • The variables were combined with demographic data to create a multiple logistic regression model that predicted knee injury in the sample as a whole, the type of knee injury and the difference between male and female participants

    • Data from a parallel study were also included, in which the Active Trunk Re-positioning (APR) test was used to assess trunk proprioception (2).

      • Each participant's trunk was slowly rotated from neutral to 20º then slowly back to neutral.
      • Participants pressed a switch to stop the return rotation when they believed they had returned to neutral.
      • APR error was determined as the difference in degrees between neutral and where the apparatus was stopped.

  • The regression was performed multiple times with minimally contributing variables removed each time until only variables with P< 0.1 remained
  • A binary logistic regression analysis was used to determine if the specific direction of trunk displacement was predictive of knee injury type and if there were differences between male and female participants
  • A priori power analysis determined that 21 injuries over the 3-year period were needed to achieve a statistical power of 0.8

Outcome Measures

  • History of low back pain
  • Knee injuries and type over 3-year period
  • Trunk displacement at 150 milliseconds for flexion, extension and lateral displacement
  • Maximal trunk displacement for flexion, extension and lateral displacement
  • Active trunk re-positioning (APR) error

Results

  •  During the 3-year follow-up period, 25 knee injuries occurred

    • 11 female and 14 male participants reported injuries
    • 11 injuries were ligament injuries (5 female, 6 male)
    • 6 injuries were ACL ruptures (4 female, 2 male)

  • Trunk displacement at 150 milliseconds (ms) was greater in knee-injured than in uninjured athletes

    • Knee injury P

    • Ligament injury P

    • ACL injury P

  • Maximal trunk displacement was significantly greater in knee-injured than in uninjured athletes

    • Knee injury P

    • Ligament injury P

    • ACL injury P

    • Uninjured P

  • Knee ligament injured females demonstrated significantly greater  maximal trunk displacement than uninjured females (P=.005)

    • No significant differences in maximal trunk displacement were noted between injured and uninjured males

  • The multiple logistic regression model determined:

    • Trunk displacement in all 3 directions at 150 ms (maximal trunk displacement variable eliminated because it correlated with displacement at 150 ms), absolute error in the APR test and the history of low back pain predicted knee injury with 83% sensitivity and 63% specificity (P

    • Trunk displacement at 150 ms and a history of low back pain predicted ligament injury with 91% sensitivity and 68% specificity (P=.001)
    • Trunk displacement in all directions at 150 ms was the sole predictor of ACL injury with 83% sensitivity and 76% specificity (P=.002)
    • The strongest predictor of injuries in females were the trunk displacement variables (85% accurate for knee injuries, 91% for ligament, 89% for ACL)

      • Active Proprioceptive Re-positioning (APR) error and history of low back pain were also predictors

    • The strongest predictor of injuries in male participants was a history of low back pain (P=.015).

  • The binary logistic regression determined:

    • Excessive lateral displacement was the strongest predictor of knee, ligament and ACL injuries in all athletes

      • It was a significant predictor of ligament injury in female athletes (100% sensitivity, 72% specificity, P=.024)
      • It did not predict injury in male athletes

Our ConclusionsThe results of this study demonstrate that greater trunk displacement following the sudden removal of a significant isometric force is correlated with increased risk of knee injury. This may imply that descriptions of Lower Extremity Dysfunction (LED) should include re-activity as well as changes in alignment.
Researchers' ConclusionsAthletes with a history of low back pain, increased trunk displacement following release of an isometric force and errors in trunk APR demonstrated an increased risk of knee injury. Males and females exhibited different predisposing factors for injury. The implementation of interventions that incorporate core stability training, including proprioceptive exercise, perturbation and correction of body sway, has the potential to reduce knee, ligament and ACL injury risk in male and female athletes.

Single Leg Balance Reactive Drill (Kill the Trainer) Single Leg Balance Reactive Drill (Kill the Trainer). (Image: Courtesy of www.BrentBrookbush.com)

How this study contributes to the body of research:

The relationship between core stability and lower extremity (LE) injury highlights the interdependence of the trunk and LE (5-8). Previous research has shown a correlation between decreased neuromuscular control of the core, hamstrings and ankle injuries (9-11). Unique to this study, the researchers prospectively investigated an athlete's trunk displacement following the sudden removal of a significant isometric force and correlation with future knee injury. This study demonstrates that decreased core reactivity is correlated with future knee injury.

How the Findings Apply to Practice:

The findings of this study demonstrate a correlation between decreased core reactivity and increased risk of future knee injury in athletes. This may imply interdependence between the trunk and LE, and suggest that assessment of Lower Extremity Dysfunction (LED) should include assessments for hipknee and ankle impairments and trunk compensation patterns. Further, human movement professionals should have a repertoire of techniques for addressing decreased core reactivity, and potentially integrated techniques for addressing coordination between the trunk/pelvis and lower extremity.

This study had many methodological strengths, including:

  • Prospective studies are relatively rare in human movement science. This study followed athletes for 3 years after testing and provides evidence that impairment may be a cause, and/or predictive of injury.
  • The researchers tested the trunk from multiple directions, which mimicked the potential variability in postural perturbations during sport activities.
  • An athlete's ability to generate a trunk stabilizing motor response (sudden trunk unloading test) and his or her ability to accurately perceive the position of their trunk in space (Active Trunk Repositioning test) were included in the regression models in this study.  Both accurate sensory input and efficient motor output are needed for optimal dynamic stability. 
  • Statistical analysis was performed on male and female participants together and separately.  This allowed for observation of whether different variables predicted injury in different sexes.
  • The researchers performed an a priori power analysis based on pilot testing to achieve a statistical power of 0.80, and exceeded the number of needed injuries in the study.

Weaknesses that should be noted prior to clinical integration of the findings include:

  • The participants' baseline injury history was not reported. Such data would have provided more information about the sample prior to observation.
  • A significant amount of equipment was required to position participants and record perturbations.  Future research should consider the predictive value of core stability "field tests" that can be performed with minimal or no equipment.
  • A functional athletic position was not tested.  While the authors noted this was done to avoid compensation by any lower extremity muscles, this limits generalization of the findings to functional activity.
  • A young, athletic population was studied. Findings may not generalize to older or more sedentary populations.

How the study relates to Brookbush Institute Content

The Brookbush Institute (BI) has developed predictive models of postural dysfunction, such as the Lower Extremity Dysfunction (LED), to aid human movement professionals in selecting optimal assessments, manual interventions and exercise. This study demonstrates that decreased core reactivity is correlated with an increased risk of knee injury in athletes. The findings of this study were integrated with additional studies demonstrating a correlation between trunk muscle weakness, stability and Lower Extremity Dysfunction (LED). In a comprehensive treatment and/or training program, the BI recommends including core stability/reactivity exercises to ensure integration with the affected/addressed segment. The BI continues to pursue optimal practice by refining predictive models of postural dysfunction, and looks forward to the integration of more insightful studies like the one reviewed here.

The following videos illustrate core stability exercises used to build stability in multiple planes.

TVA and Gluteus Maximus Activation and Progressions

Quadruped Crawl

Quadruped Crawl 2

Resisted Quadruped Crawl

Kneeling Chop Pattern

Single Leg Standing Chop Pattern

Crunch and Catch

Bibliography:

  1. Ingram, J. G., Fields, S. K., Yard, E. E., and Comstock, R. D. (2008). Epidemiology of knee injuries among boys and girls in US high school athletics. The American journal of sports medicine, 36(6), 1116-1122.
  2. Powell, J. W., & Barber-Foss, K. D. (1999). Injury patterns in selected high school sports: a review of the 1995-1997 seasons. Journal of athletic training, 34(3), 277.
  3. Hewett, T. E., Paterno, M. V., & Myer, G. D. (2002). Strategies for enhancing proprioception and neuromuscular control of the knee. Clinical Orthopaedics and Related Research®, 402, 76-94.
  4. Hewett, T. E., Zazulak, B. T., Myer, G. D., & Ford, K. R. (2005). A review of electromyographic activation levels, timing differences, and increased anterior cruciate ligament injury incidence in female athletes. British journal of sports medicine, 39(6), 347-350.
  5. Zazulak, B. T., Hewett, T. E., Reeves, N. P., Goldberg, B., and Cholewicki, J. (2007). The effects of core proprioception on knee injury: a prospective biomechanical-epidemiological study. The American journal of sports medicine.
  6. Heiderscheit, B. C. (2010). Lower extremity injuries: is it just about hip strength? journal of orthopaedic & sports physical therapy, 40(2), 39-41.
  7. Leetun, D. T., Ireland, M. L., Willson, J. D., Ballantyne, B. T., & Davis, I. M. (2004). Core stability measures as risk factors for lower extremity injury in athletes. Medicine & Science in Sports & Exercise, 36(6), 926-934.
  8. Hodges, P. W., Butler, J. E., McKenzie, D. K., and Gandevia, S. C. (1997). Contraction of the human diaphragm during rapid postural adjustments. The Journal of physiology, 505(Pt 2), 539-548.
  9. Cholewicki, J., Silfies, S. P., Shah, R. A., Greene, H. S., Reeves, N. P., Alvi, K., & Goldberg, B. (2005). Delayed trunk muscle reflex responses increase the risk of low back injuries. Spine, 30(23), 2614-2620.
  10. Devlin, L. (2000). Recurrent posterior thigh symptoms detrimental to performance in rugby union. Sports Medicine, 29(4), 273-287.
  11. Beynnon, B., Vacek, P. M., Abate III, J. A., Murphy, D., & Paller, D. (2006, July). A prospective study of risk factors for first time ankle inversion ankle ligament trauma. In 32nd annual meeting of the American Orthopaedic Society for Sports Medicine

© 2018 Brent Brookbush

Questions, comments and criticisms are welcomed and encouraged.