The effects of neuromuscular training on the gait patterns of ACL-deficient men and women

https://doi.org/10.1016/j.clinbiomech.2011.10.008Get rights and content

Abstract

Background

Anterior cruciate ligament rupture is the most common knee ligament injury sustained by active individuals, and the relative injury risk is sex-specific. Women not only demonstrate an increased risk for injury, but also a poorer response following ligament rupture. Perturbation training has shown positive results in healthy females, but gender-specific responses to training after injury have not been evaluated. The purpose of this investigation was to describe the effects of perturbation training on the gait characteristics of male and female non-copers.

Methods

Biomechanical data were collected before and after training on 12 male and nine female non-copers using standard motion analysis techniques. Subjects walked at a consistent, self-selected speed over an embedded force plate. Data from both limbs were post-processed and analyzed using a mixed model analysis of variance and minimal clinically important differences to compare the limb behaviors of men and women.

Findings

Prior to training, only women demonstrated significant hip joint excursion asymmetry (ES = 1.03; P = 0.009). Minimal clinically important difference values showed that the involved limb of the women had reduced hip and knee flexion angles and moments, truncated knee excursions, and increased hip excursions when compared to their own uninvolved limb and the limbs of the male non-copers. Following training, only knee extensor moment values exceeded the minimal clinically important differences in women.

Interpretation

Female non-copers demonstrated unique movement strategies following injury and perturbation training. Women may be a meaningful subgroup of non-copers, and future investigations should consider the effects of gender in the outcomes of non-copers.

Introduction

Neuromuscular training is a type of physical therapy intervention advocated to mitigate movement pattern deficits and abnormalities in a variety of patient populations. In the world of sports orthopedics, the efficacy of neuromuscular treatment paradigms has been evaluated for purposes of injury prevention, performance enhancement, and rehabilitation following injury or surgery. Following anterior cruciate ligament (ACL) rupture, abnormal movement patterns and neuromuscular behaviors are commonly found in those athletes with recurrent knee instability, where there is a subluxation of the tibia on the femur (Rudolph et al., 1998, Rudolph et al., 2000, Rudolph et al., 2001). These individuals, classified as non-copers, demonstrate asymmetrical movement strategies, including reduced sagittal plane knee excursions (Rudolph et al., 1998) and knee moments (Alkjaer et al., 2003, Rudolph et al., 1998) and increased hip moments on the uninvolved side during gait (Rudolph et al., 2001). Surgical reconstruction alone does not fully abate these aberrant gait patterns (Hartigan et al., 2009) and non-copers also demonstrate a reduced ability to return to sport following ligament reconstruction (Hartigan et al., 2010). Current physical therapy practice guidelines for knee ligament sprains now advise supplementing traditional strength training with neuromuscular training as a means to improve function and mitigate abnormal movement (Logerstedt et al., 2010). Expectedly, researchers have begun to evaluate the efficacy of varied neuromuscular training regimens in promoting function and restoring normal, symmetrical movement patterns in these athletes.

Perturbation training is a form of neuromuscular training designed to improve the dynamic stability of the knee through the timely co-activations of surrounding musculature (Fitzgerald et al., 2000b, Fitzgerald et al., 2000c. This training is successful in improving the likelihood for high-functioning ACL-injured athletes, or potential copers, to return to sport in short-term without ligament reconstruction (Fitzgerald et al., 2000a, Hurd et al., 2008a). In non-copers, pre-operative perturbation training in combination with progressive quadriceps strengthening did not enhance their ability to return to sport when compared to strength training alone (Hartigan et al., 2010), but was effective in normalizing post-operative knee excursions during gait (Hartigan et al., 2009). In the U.S., prompt surgical intervention is typically advised for athletes with recurrent instability in an attempt to maximize return to sport abilities (Daniel and Fithian, 1994, Marx et al., 2003). In Norway, however, where delayed surgical intervention is the standard of care, researchers found that prolonged conservative management, including strength, agility, and other forms of neuromuscular training proved effective for 70% of non-copers (Moksnes et al., 2008). These investigations imply not only that a subgroup of non-copers exists, but that certain individuals may possess more adaptable neuromuscular systems than others.

ACL-injured females represent an interesting subgroup of non-copers for several reasons. Research has well established that women are at higher risk for ACL injury (Agel et al., 2005, Arendt and Dick, 1995), and more likely to be classified as non-copers than men (Hurd et al., 2008b). Post-operative outcomes also appear to be gender-specific. Following ACL reconstruction, women reported lower function on self-report scores (Ageberg et al., 2010) and demonstrated a reduced likelihood to return to sport (Ardern et al., 2011). There is growing evidence that there are functional differences between men and women following injury and surgery, yet no studies have sought to compare the gait mechanics of men and women after ACL injury or after therapeutic intervention. Neuromuscular training focused on speed, agility, power, and form effectively address the biomechanical behaviors known to predict injury risk (Hewett et al., 1999, Hewett et al., 2006). Perturbation training, specifically, has been shown to enhance the muscular behaviors of healthy female athletes (Hurd et al., 2006). While perturbation training has produced varied results in non-copers as a group, and appears to have little effect on healthy male athletes (Hurd et al., 2006), comparing the movement strategies of male and female non-copers may clarify the effects of this training. Ultimately, understanding gender-specific movement behaviors before and after neuromuscular training could have significant implications on the rehabilitation of non-copers. Therefore, the purpose of this investigation was to describe the acute effects of pre-operative perturbation training on the movement behaviors of male and female non-copers. We hypothesized that prior to perturbation training women would demonstrate smaller peak angles, joint excursions and joint extensor moments in the involved knee when compared to their own uninjured limb and both limbs of men. We hypothesized female non-copers would demonstrate the characteristic non-coper compensatory hip strategy, including larger peak angles, joint excursions, and joint extensor moments at the involved hip compared to the uninjured limb and both limbs of male non-copers. Following perturbation training, it was hypothesized that only extensor moment asymmetries at the hip and knee would persist for both sexes.

Section snippets

Methods

Twenty-one ACL-deficient athletes (Table 1) were classified as non-copers within seven months of their index injury using an ACL-deficient functional screening examination (Fitzgerald et al., 2000a). All athletes participated in cutting, pivoting, or jumping activities for more than 50 hours/year prior to injury. Significant concomitant injuries (symptomatic meniscus tear, large osteochondral defects, or associated grade III ligament strains) excluded athletes from the potential subject pool.

Results

Of the six kinematic variables analyzed, a significant time × limb × gender interaction was found only for hip excursion during weight acceptance (P = 0.012) (Fig. 2). Prior to perturbation training, only female non-copers possessed significantly different hip joint excursions between limbs (Involved: 11.5° (4.7), Uninvolved: 6.9° (4.2), P = 0.009, ES: 1.03) (Fig. 2). No additional time × limb interactions or main effects were found with regard to joint kinematics for our female and male non-copers.

While

Discussion

The aim of this work was to characterize the movement behaviors of male and female non-copers before and after perturbation training. We hypothesized that women, when compared to men early after injury, would present with unique and asymmetrical limb behaviors. It was also hypothesized that women's gait abnormalities would resolve following pre-operative perturbation training. As expected, a gender-specific response to injury and perturbation training emerged.

During the weight acceptance phase

Conclusion

Differences in the gait characteristics of male and female non-copers have not been previously described. Our female non-copers not only presented with poorer performance following injury, but also seem to possess the abnormal gait behavior that is characteristic of non-copers as previously described. These data suggest that women may benefit the most from pre-operative perturbation training, as evidenced by the adoption of more symmetrical movement patterns. Our findings also underscore that

Acknowledgments

The authors acknowledge Drs. Wendy Hurd and Erin Hartigan for their contributions with subject recruitment, physical therapy services, and data collection and processing. We also acknowledge the outstanding clinical services provided to our patients by the University of Delaware Physical Therapy Clinic, and Dr. Michael J Axe for his patient referrals. This project was supported by funding awarded to Dr. Snyder-Mackler at the University of Delaware from the National Institutes of Health (

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