Movement variability during single leg jump landings in individuals with and without chronic ankle instability
Introduction
Lateral ankle sprains are one of the most common sports-related injuries (Fong et al., 2007, Hootman et al., 2007). It is estimated up to 73% of people who suffer lateral ankle sprains develop chronic ankle instability (Yeung et al., 1994), defined as subjective and repeated episodes of giving way at the ankle (Hertel, 2002). Some individuals with chronic ankle instability demonstrate physiologically lax lateral ligaments, and can be classified as mechanically unstable (Hertel, 2002). Alternately, some individuals are not ligamentously lax, but still complain of giving way, perhaps due to sensorimotor deficits. These individuals may be classified as functionally unstable (Hertel, 2002). History of ankle trauma, including lateral ankle sprains and chronic instability, is related to development of ankle osteoarthritis (Valderrabano et al., 2006). With a traumatic history, ankle osteoarthritis may be preventable if lateral ankle sprains and chronic ankle instability can be adequately treated (Valderrabano et al., 2006).
There is currently a lack of consensus on the criteria used to define those with chronic ankle instability, and what factors contribute to chronic instability (Delahunt et al., 2010). Factors contributing to functional instability, such as deficits in sensorimotor control, strength, or dynamic balance have been identified (Hertel, 2002, Hubbard et al., 2007, Wikstrom et al., 2007). Mechanical factors such as physiologic lateral ligament laxity, in combination with functional factors, have also been identified (Brown et al., 2008, Hubbard et al., 2007). Additionally, comparison groups with a history of sprain but no functional limitations have been identified as “copers,” and offer a relevant clinical model comparison (Brown et al., 2008, Hertel and Kaminski, 2005, Wikstrom et al., 2010a). We are attempting to separate individuals with chronic ankle instability into those with primarily functional deficits and those with primarily functional but also secondary mechanical deficits. We are attempting to tease out the contributions of primarily functional, but also secondary mechanical, deficiencies and compare performance on movement variability measures to copers without functional or mechanical deficits and an uninjured control group that has never been exposed to functional or mechanical contributing factors.
Movement variability has been suggested as a factor contributing to developing and perpetuating injury (James, 2004, Konradsen, 2002, Konradsen and Voigt, 2002). Increased variability has been linked to risk of other musculoskeletal injuries including anterior cruciate ligament rupture (McLean et al., 1999), lower extremity overuse injury (James et al., 2000), patellofemoral pain (Heiderscheit et al., 2002), and injuries from falls (Hausdorff et al., 2001). There are a number of methods to quantify variability. One traditional, commonly used method is the coefficient of variation, the standard deviation normalized to the mean of the score distribution, representing relative or normalized variability converted to a percentage of the mean value (James, 2004). For the purposes of this study, the following operational definition of movement variability was used: variability in a single plane motion of a joint or body segment during time periods corresponding to transition from an unloaded to a loaded state (250 ms pre-initial contact to initial contact) and in transition from landing to single limb standing (1 s post-initial contact). The dependent variable, coefficient of variation, was calculated for those joints/segments in those specific windows of time associated with specific events, across multiple trials for each participant. Strengths of the coefficient of variation include its historical use, ease of interpretation and ability to compare performances with very different mean scores (James, 2004). Limitations of the measure include the influence of outlying or extreme data points and its reliance on the mean and standard deviation, particularly when the mean is close to zero (James, 2004). Additionally, this operational definition and dependent variable encompass only a single joint/segment at a discrete point in time, and does not compare coupling relationships in joints as others have done (Drewes et al., 2009).
Few studies have determined if differences in motion variability exist in individuals with chronic ankle instability, particularly in proximal joints and during challenging sports-related movements. Applying dynamical systems theory, sensorimotor organization and coordination of degrees of freedom depends on the interaction of a number of factors, including task complexity, predictability of the environment, and the health of the person (James, 2004). Individuals adapt to a particular task using movement variability to deal with the personal, task, or environmental constraints (Davids et al., 2003). If ankle instability is considered a constraint on the system (Brown et al., 2009, McKeon and Hertel, 2008), the entire kinetic chain system (ankle, knee, hip, and trunk) should be assessed for variability. Specifically, variability during transitions, such as from jump landing to stance, may prove important in degree of movement variability with regards to injury. These periods of transition from unloaded to loaded state have been associated with ankle injury (Konradsen and Voigt, 2002). Individuals may prepare for transitions by increasing variability in certain joints while decreasing in others. Too much variability in the kinetic chain during transitions may hinder the ability of an individual with chronic ankle instability (CAI) to develop effective solutions to adapt to demands of specific sports-related tasks and the environmental constraints, indicating inability to coordinate and execute movement goals. Too little variability during transitions may hinder the ability of an individual with CAI to include a variety of degrees of freedom into an effective movement solution, indicating inability to adapt to new situations or changing situations. Proximal differences in joint motion and electromyography have been noted in chronic ankle instability populations (Bullock-Saxton, 1994, Bullock-Saxton et al., 1994, Caulfield and Garrett, 2002, Gribble and Robinson, 2009), and variability of motion may influence those findings. Evidence from a previous study indicated increased variability in a single plane at the ankle joint during a double limb landing transitioning from a run to stop jump to vertical jump (Brown et al., 2009). However, it is currently unclear what effects chronic ankle instability has on single joint movement variability in single limb landing. This study seeks to improve and expand on previous work associating variability with the constraints of chronic instability by utilizing transitions from single leg jump landing to single leg stance in a task that includes 3 different jump directions that provide different demands and constraints. An uninjured control group to assess “typical” variability is added and all 3 planes of motion and trunk kinematics will be included.
Thus, the purpose of this study was to determine if differences in movement variability exist at the ankle, knee, hip, and trunk in 3 planes of motion between individuals with mechanical ankle instability, functional ankle instability, copers, and controls during a single leg jump landing movement in anterior, lateral, and medial directions. We hypothesized that individuals with mechanically and functionally unstable ankles would demonstrate greater variability compared to copers and controls at each joint during the 250 ms before and the 1 s time period after landing. We selected these time frames as important windows where transitions may be occurring between jumping and landing and between landing and single limb stance. We also hypothesized increased variability based on previous literature (Brown et al., 2009, Delahunt et al., 2006, Drewes et al., 2009, Konradsen and Voigt, 2002), though with this novel analysis, it was unclear how variability might change between joints and planes of motion.
Section snippets
Participants
A previous study using coefficient of variation to assess kinematic variability of mechanically unstable, functionally unstable, and coper groups during stop jump maneuvers indicated that 25–140+ participants were necessary to achieve a power of 80 on ankle and knee sagittal and frontal plane motion, and hip sagittal and transverse plane motion during a stop jump (Brown et al., 2009). Another study analyzing gender differences during sidestep kinematics utilized mean standard deviation across
Results
The preliminary analysis indicated the groups were not statistically significantly different in age, height, weight, active ankle range of motion, or in height jumped in any of the 3 directions (P > 0.05; ηp2 < 0.10). The CAIT scores were significantly different between groups, with both the mechanically and functionally unstable ankle groups scoring significantly lower than both the coper and control groups, indicating decreased function (Table 1) (P < 0.05; ηp2 = 0.67). All following means and
Discussion
The most notable result is that the mechanically and functionally unstable ankle groups, and occasionally copers, appear to have less variability in knee and hip joint motions during single leg jump landing compared to an uninjured control group. Proximal joint variability appears to be different between these groups, specifically knee internal–external rotation and hip flexion–extension and abduction–adduction during pre-initial contact and stance. We report no differences in ankle motion and
Conclusions
Previous ankle injury appears to be a constraint on the movement system and those with ankle instability demonstrate decreased variability at the knee and hip. This may indicate central motor programming differences that decrease landing efficiency.
Acknowledgements
This study was funded by the University of Georgia Research Foundation. The sponsors had no involvement in the study design, collection, analysis and interpretation of data, in the writing of the manuscript; or in the decision to submit the manuscript for publication.
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