Abstract
Background The drop vertical jump (DVJ) task has previously been used to identify movement patterns associated with a number of injury types. However, no current research exists evaluating people with chronic ankle instability (CAI) compared with people coping with lateral ankle sprain (LAS) (referred to as “LAS copers”) during this task.
Objective The aim of this study was to identify the coping movement and motor control patterns of LAS copers in comparison with individuals with CAI during the DVJ task.
Design This was a case-control study.
Methods Seventy individuals were recruited at convenience within 2-weeks of sustaining a first-time acute LAS injury. One year following recruitment, these individuals were stratified into 2 groups: 28 with CAI and 42 LAS copers. They attended the testing laboratory to complete a DVJ task. Three-dimensional kinematic and sagittal-plane kinetic profiles were plotted for the lower extremity joints of both limbs for the drop jump phase (phase 1) and drop landing phase (phase 2) of the DVJ. The rate of impact modulation relative to body weight during both phases of the DVJ also was determined.
Results Compared with LAS copers, participants with CAI displayed significant increases in hip flexion on their “involved” limb during phase 1 of the DVJ (23° vs 18°) and bilaterally during phase 2 (15° vs 10°). These movement patterns coincided with altered moment-of-force patterns at the hip on the “uninvolved” limb.
Limitations It is unknown whether these movement and motor control patterns preceded or occurred as a result of the initial LAS injury.
Conclusions Participants with CAI displayed hip-centered changes in movement and motor control patterns during a DVJ task compared with LAS copers. The findings of this study may give an indication of the coping mechanism underlying outcome following initial LAS injury.
The drop vertical jump (DVJ) has been a popular movement task choice in multiple lower limb biomechanical investigations because it recreates the bounding mechanics typical of a large number of field and court sports.1–4 That it also is regularly incorporated into strength and conditioning programs and injury rehabilitation programs5,6 pays testament to the diversity of neuromuscular demands associated with this task. During performance of the DVJ, participants drop off of a platform, land on both feet simultaneously, and immediately execute a maximal vertical jump before landing and maintaining static bilateral stance. Recently, the DVJ has been deconstructed into 2 phases on the basis of these first and second landings, which are seen to elicit dichotomous neuromuscular demands.1,2,7 The first phase, which consists of the first landing and the subsequent initiation of a maximal vertical jump,1,2 is consummated by movement patterns and motor control strategies directed at conserving the potential energy of the start position and amplifying the subsequent kinetic energy of the drop using the lower extremity as a spring-mass model.8 The second phase requires the participant to attenuate the kinetic energy of landing from his or her maximum jump height and adopt a position of controlled bilateral stance.1,2,8
Particular attention has been given to the use of the DVJ as an assessment tool in populations that are considered to have increased risk of incurring a future anterior cruciate ligament (ACL) injury and those with a history of ACL injury.3,4 This research has revealed a number of key movement pattern and motor control predictors4 and consequences3 of ACL injury, thus advancing current understanding of the relationship between neuromuscular control, injury risk, and how prevention or rehabilitation programs can be designed with these relationships in mind.9,10 By contrast, use of the DVJ task to elicit an equivalent set of potentially anomalous injury-associated movement patterns has rarely been reported in the lateral ankle sprain (LAS) literature, despite the comparable risk that jumping- and rebounding-type sports have in causing injury to the ankle as they do the knee.11 In light of the potential for acute LAS to degrade into a cascade of mechanical and functional insufficiencies, with injury recurrence in the weeks and months following the initial injury,12 evaluating participants with a history of LAS during a DVJ task would advance current understanding as to why these injuries are so prevalent in the aforementioned activities.
Recently published material from our laboratory was designed to address this gap in the literature, as individuals with a 2-week history of a first-time LAS injury were evaluated during the performance of a DVJ task.13 Further analysis of this cohort was completed during single-leg landing,14 gait,15 postural control,16,17 and dynamic balance18 tasks. These analyses were then repeated 6 months subsequently.19–22 In both instances (within 2 weeks of injury and 6 months following), participants were compared with a healthy control group. With regard to the DVJ task, injured participants demonstrated alterations in movement patterns at their hip and joint loading asymmetries during both evaluations. The issue with these analyses, however, is that the array of symptom sequelae that may develop following an initial LAS injury (collectively termed “chronic ankle instability” [CAI]12,23) can only be diagnosed at the 1-year time point following initial injury. Similarly, one full year must pass before complete recovery (or the determination of LAS “coper” status) can be determined.24 Therefore, despite the addition of the 2-week and 6-month data sets to the literature, the external validity of these investigations was limited by the fact that all injured participants were grouped together for analyses regardless of their final diagnosis (CAI versus LAS coper) and compared with a control group of people without injuries.13,19
Following these investigations, we sought to evaluate these participants at a 1-year time point after their initial LAS injury so that they could be divided and compared accordingly (CAI versus LAS coper). These analyses13,19–22 will inform the choice of dependent variables in a longitudinal investigation designed to identify the key task-specific movement pattern predictors of CAI or LAS coper status. Although a number of longitudinal investigations are available evaluating such movement pattern predictors in ACL populations,4 no such research, to our knowledge, is available in people with a history of LAS injury. In the current investigation, we combined the same kinematic (angular displacement) and kinetic (moment-of-force) measures of lower extremity joint movement and motor control as in the aforementioned study19 to conceptualize the first and second phases of the DVJ task performance. This study was performed with the aim of exploring the movement patterns during the DVJ that are characteristic of—and, therefore, may contribute to—CAI. The rate of impact modulation (RIM) also was calculated to conceptualize the energy management strategies utilized by CAI and LAS coper participants.25 On the basis of the findings from the 2-week and 6-month reports,13,19 we hypothesized that individuals with CAI would exhibit extensor-dominant patterns of motor control at their hip joint and a reduction in ankle joint plantar flexion over the course of the DVJ compared with LAS copers.
Method
Participants
An initial cohort of participants were recruited at convenience within 2 weeks of sustaining a first-time, acute LAS injury from a university-affiliated hospital emergency department as part of a larger longitudinal investigation being completed in our laboratory. Recruitment of all participants was completed between March 1, 2012, and September 29, 2013. Data pertaining to this cohort during the performance of the DVJ task are currently available and detail various measures of injury severity.13 Seventy-one participants from this original cohort attended our laboratory 1 year following recruitment to complete the protocol to which the current study pertains. The following exclusion criteria were used for all participants at the time of recruitment: (1) no previous history of ankle sprain injury in either limb (excluding the initial acute episode); (2) no other severe lower extremity injury in the last 6 months; (3) no history of ankle fracture; (4) no previous history of major lower limb surgery; and (5) no history of neurological disease, vestibular or visual disturbance, or any other pathology that would impair their motor performance.16 Stratification of the cohort into CAI and LAS coper groups was completed according to recently published guidelines.26,27
Self-reported ankle instability was confirmed with the Cumberland Ankle Instability Tool (CAIT).28 Individuals with a score of <24 were designated as having CAI, whereas LAS copers were designated with a score of ≥24.26 Furthermore, to be designated as a LAS coper, participants must have returned to preinjury levels of activity and function and to have reported no instances of “giving way” at their ankle joint.29 The Foot and Ankle Ability Measure (FAAM) activities of daily living and sports subscales (FAAMadl and FAAMsport) were utilized as a means to evaluate general self-reported foot and ankle function30 but were not used as an inclusion criterion for the CAI group.27 The CAIT and subscales of the FAAM were completed on arrival to the testing laboratory, prior to the commencement of the test protocol. All participants provided written informed consent.
Protocol
Collection methods for this study have been previously documented.13,19 Briefly, participants were first instrumented with 22 infrared markers as part of the Codamotion bilateral lower limb gait setup (Charnwood Dynamics Ltd, Leicestershire, United Kingdom) and then required to complete 3 repetitions of a DVJ task following a practice period. Participants began standing barefoot atop a 0.4-m platform with their hands on their hips and their feet approximately shoulder width apart. They were subsequently instructed to drop down from the raised platform without any vertical launch and land on both feet simultaneously (phase 1). They then immediately executed a maximal vertical jump upon contact with the forceplates (phase 2).
Data Processing and Analysis
Kinematic data were acquired at 250 Hz and kinetic data were acquired at 1,000 Hz using 3 Codamotion cx1 units and 2 fully integrated AMTI (ATMI Inc, Watertown, Massachusetts) walkway embedded forceplates (one forceplate for each limb), respectively, during trials of the DVJ task. The Codamotion cx1 units were time synchronized with the forceplates. Kinetic and kinematic data were passed through a fourth-order zero-phase Butterworth low-pass digital filter with 20-Hz and 6-Hz cutoff frequencies, respectively.31 A neutral stance trial was recorded for each participant and served as a reference position for subsequent kinematic data analyses and to align the participant with the laboratory coordinate system.32 Kinematic and kinetic data were acquired for both limbs of the lower extremity and exported from the Codamotion software to Microsoft Excel (IBM Corp, Redmond, Washington) file format for further analysis.
Time-averaged profiles were calculated for the joints of the lower extremity. These profiles were averaged across the 3 trials completed by each participant, with subsequent calculation of group mean profiles (CAI and LAS coper). All time-averaged profiles were plotted during the period from 200 milliseconds before initial contact (IC) to 200 milliseconds after IC for phases 1 and 2 of the DVJ for each limb.
The kinematic variables of interest were 3-dimensional hip, knee, and ankle angular displacements. The temporal kinetic variables of interest were sagittal-plane hip, knee, and ankle moment-of-force profiles. All moments were expressed in a global orthogonal reference frame and calculated from the forceplate, lower extremity kinematic, and anthropometric data using a standard inverse dynamics approach.33
The discrete kinetic variable of interest was the RIM of the vertical ground reaction force (GRF) for each limb, which was calculated as the peak vertical GRF normalized to body weight (BW) divided by the time from IC to peak vertical GRF25 separately for phases 1 and 2 of the DVJ (BW/s).
A symmetry angle (SA) calculation34 was used to evaluate the interlimb RIM symmetry for each participant over each phase of the DVJ, with a subsequent calculation of group means (CAI versus LAS coper). An SA value of 0% between matched data points indicates perfect symmetry, and 100% indicates that the 2 values are equal and opposite in magnitude.34
Finally, the vertical jump height (in meters) achieved between phases 1 and 2 of the DVJ was calculated and averaged across the 3 trials as a measure of task performance using the flight time method35 for CAI and LAS coper groups. Group mean profiles were subsequently calculated.
Data Analysis
The average of each participant's 3 trials for all variables was processed to compare group mean profiles (ie, CAI versus LAS coper). For both the CAI and LAS coper groups, the limb to which the LAS was incurred at the time of recruitment was labeled as “involved,” and the noninjured limb was labeled as “uninvolved.” The principal investigator who completed the experimental protocol was not blinded as to group assignment during data collection and analysis.
To compare temporal movement and motor control patterns between CAI and LAS coper groups, a series of independent-samples t tests for each data point of the time-averaged group 3-dimensional angular displacement and sagittal-plane moment-of-force profiles was undertaken. The significance level for these analyses was set a priori at P<.05. This method of curve analysis has previously been undertaken in our research laboratory and others.13,19,36,37 In agreement with the recommendations of Hopkins et al,38 the statistical analysis of temporal waveform data was supplemented with a measure of variance (95% confidence intervals); it should be noted that only the t tests were used to determine statistically significant differences between the groups (CAI versus LAS coper) in these instances. We favored the analysis of waveform data in its entirety over discrete value analysis, as we considered the former to provide greater insight into the progression of a given movement across the duration of the task.39
Independent-samples t tests for group (CAI versus LAS coper) RIM mean profiles for each phase of the DVJ for each limb were then completed. The significance level for this analysis was set a priori at a Bonferonni-adjusted alpha level of P<.025 [.05/(2 × limb)].
Independent-samples t tests for group (CAI versus LAS coper) RIM SA profiles for each phase of the DVJ also were undertaken. The significance level for this analysis was set a priori at a Bonferonni-adjusted alpha level of P<.025.
Finally, an independent-samples t test comparing jump height achieved between phase 1 and phase 2 of the DVJ was undertaken to elucidate any task performance discrepancies between CAI and LAS coper groups. The significance level for this analysis was set a priori at P<.05. All data were analyzed using Predictive Analytics Software version 20 (SPSS Inc, Chicago, Illinois).
Role of the Funding Source
This study was supported by the Health Research Board (HRA_POR/2011/46) as follows: Eamonn Delahunt (Principal Investigator), Chris Bleakley and Jay Hertel (coinvestigators), and PhD student Cailbhe Doherty.
Results
Based on the aforementioned criteria, 28 individuals were designated as having CAI, and 42 individuals were designated as LAS copers. Ten LAS copers scored ≥24 but <28 on the CAIT but fulfilled the required inclusion criteria for this group. One participant was excluded from the original group of 71 participants because he scored ≥24 on the CAIT but reported that he did not return to preinjury levels of activity participation. Participant characteristics and questionnaire scores are presented for the 70 included individuals in Table 1.
Participant Anthropometrics and Self-Reported Disability and Function Questionnaire Scores for the Involved Limb of CAI and LAS Coper Groupsa
Kinematic and Kinetic Analyses
Approximate values for temporal data are detailed below. Please see the relevant figure for specific values.
Participants with CAI displayed increased hip flexion on their involved limb during phase 1 of the DVJ compared with LAS copers (23° versus 18°, P<.05). During phase 2, participants with CAI again displayed increased hip flexion compared with the LAS copers, this time bilaterally (15° versus 10°, P<.05). Lower extremity (hip, knee, and ankle) sagittal- and frontal-plane ankle kinematic profiles for phases 1 and 2 of the DVJ are detailed in Figure 1.
Hip flexion-extension angle (A-1=phase 1, A-2=phase 2), knee flexion-extension angle (B-1=phase 1, B-2=phase 2), ankle inversion-eversion angle (C-1=phase 1, C-2=phase 2), and dorsiflexion-plantar flexion angle (D-1=phase 1, D-2=phase 2) during performance of phase 1 and phase 2 of the drop vertical jump (DVJ) task from 200 milliseconds pre–initial contact (IC) to 200 milliseconds post-IC for the involved and uninvolved limbs of the chronic ankle instability (CAI) and lateral ankle sprain (LAS) coper groups. Flexion, inversion, and plantar flexion are positive; extension, eversion, and dorsiflexion are negative. Black line with arrow=IC, red lines=CAI group, blue lines=LAS coper group, darker-colored lines=involved limb, lighter-colored lines=uninvolved limb. Shaded area enclosed by black line=area of statistically significant between-groups difference for the involved limb. Shaded area enclosed by gray line=area of statistically significant between-groups difference for the uninvolved limb. Error bars=95% confidence intervals at the level of P=.05.
Time-averaged sagittal-plane moment-of-force profiles also revealed a number of between-group differences on the uninvolved limb only for both phase 1 and phase 2 of the DVJ. The CAI group displayed an increase in flexor moment of the hip on their uninvolved limb during phase 1 (−0.4 N·m/kg versus 0 N·m/kg, P<.05) and an increase in their extensor pattern on this limb during phase 2 (0.1 N·m/kg versus 0.5 N·m/Kg, P<.05) compared with LAS copers. Sagittal-plane moment-of-force profiles for phases 1 and 2 of the DVJ are detailed in Figure 2.
Sagittal-plane joint moment-of-force profiles for the hip (A-1=phase 1, A-2=phase 2), knee (B-1=phase 1, B-2=phase 2), and ankle (C-1=phase 1, C-2=phase 2) during performance of phase 1 and phase 2 of the drop vertical jump (DVJ) task from 200 milliseconds pre–initial contact (IC) to 200 milliseconds post-IC for the involved and uninvolved limbs of the chronic ankle instability (CAI) and lateral ankle sprain (LAS) coper groups. Extension and plantar-flexion moments are positive; flexion and dorsiflexion moments are negative. Black line with arrow=initial contact, red lines=CAI group, blue lines=LAS coper group, darker-colored lines=involved limb, lighter-colored lines=uninvolved limb. Shaded area enclosed by black line=area of statistically significant between-groups difference for the involved limb. Shaded area enclosed by gray line=area of statistically significant between-groups difference for the uninvolved limb. Error bars=95% confidence intervals at the level of P=.05.
There was no significant difference in RIM between CAI and LAS coper groups for phase 1 or phase 2 of the DVJ for either limb. The RIM values obtained during both phases of the DVJ for CAI and LAS coper groups are detailed in Table 2.
Rate of Impact Modulation, With Corresponding Interlimb Symmetry Values, for Phases 1 and 2 of the DVJ for the Involved and Uninvolved Limbs of the CAI and LAS Coper Groupsa
Symmetry Analyses
There was also no significant difference in interlimb RIM symmetry between CAI and LAS coper groups (Tab. 2).
Performance Analysis
There was no significant difference in jump height scores between the LAS coper group (X̅=0.16 m, SD=0.6) and the CAI group (X̅=0.18 m, SD=0.5) (t56=−1.757, P=.08). The results of the analysis including LAS copers who scored ≥24 but <28 on the CAIT was consistent with the results when these individuals were excluded.
Discussion
To our knowledge, this is the first biomechanical analysis to detect movement and motor control pattern disparities between a group with CAI and LAS copers during a DVJ task. We analyzed the DVJ in separate phases in recognition of the dissimilar constraints imposed by the drop jump (phase 1) and drop landing (phase 2) components of this task.
During phase 1, the CAI group displayed increased preparatory or pre-IC hip flexion on their involved limb and a greater flexion moment pattern at this joint on their uninvolved limb ≃90 milliseconds post-IC compared with LAS copers. During phase 2, CAI participants again displayed an increase in hip flexion prior to and during IC. However, this increase was evident bilaterally in contrast to phase 1. Furthermore, they displayed greater extensor dominance at the hip ≃60 milliseconds post-IC on their uninvolved limb compared with the matched limb of LAS copers. These results are largely in agreement with our hypotheses, which were based on previously documented observations made on these groups earlier in the pathological process.13,19 Finally, because there was no difference in the jump height achieved by the CAI group compared with the LAS coper group, we believe the comparison of the underlying energetics and kinematics in a process-oriented analysis between these groups to be appropriate.40
An important consideration in the interpretation of these results is that the best method of analyzing temporal data is a continued source of controversy in the movement sciences.41 Time series data have natural temporal ordering, and this temporal dependence has previously been considered a primary challenge in movement analysis.42 Outside of nonlinear dynamic analyses (which are ideally suited to cyclical movement patterns)43 to evaluate human movement, researchers can: (1) analyze discrete values (which are assumed to be representative of entire waveforms) with univariate statistics; (2) convert temporal data into discrete values via a principal components analysis, with subsequent utilization of univariate statistics; (3) adopt a multivariate statistical approach, such as parametric mapping or functional analysis of variance, using a differential equation to represent the curve; and (4) use multiple discrete statistical comparisons for multiple (temporal) data points. In the current study, we did not undertake a multivariate approach (option 3 above) due to the inaccuracy that a differential equation may have in characterizing an irregularly shaped curve. Our chosen method analysis (option 4 above) is potentially prone to an increasing risk of family-wise error due to the number of comparisons that have been made (each data point for the waveform was subjected to a t test). Therefore, our findings need to be considered in the context of the methods of analysis that produced them and those of other studies.
Two previously published studies are available that detail an evaluation of participants with chronicity following LAS injury in comparison with copers during a “stop-jump” task,44,45 although this analysis was completed on their involved limb only. The stop-jump task is comparable to the DVJ task because both tasks possess energy amplification (phase 1) and attenuation (phase 2) stages and require the participant to complete the task by landing from a maximal vertical jump in a controlled manner.8,44,45 Although temporal waveform data were not plotted for movement and motor control variables in these studies and only phase 1 of the stop-jump task was evaluated,44,45 one of the presented findings is comparable and consistent with those of the current study: CAI group participants adopted a position of increased hip flexion at IC.44 That they also displayed greater external rotation at the hip44 was in contrast to our findings, as no such pattern was evident. These 2 studies44,45 were among the first studies to use an LAS coper sample as a comparison group for the CAI group participants.
More recently, an International Ankle Consortium consensus statement has been published outlining the ideal experimental definition of CAI cohorts.12 Participants with CAI in the aforementioned studies were actually grouped according to whether they had predominantly mechanical or functional insufficiency components of the heterogeneous CAI condition,44,45 which is contrary to the subsequently published methodological guidelines.12 In contrast, because the current analysis is part of a larger longitudinal investigation, both LAS coper and CAI groups' outcomes were only recently defined and confirmed, whereas the participants in the studies by Brown and colleagues were long established as being chronically impaired.44,45 This duration of disability may have as yet unknown implications on the extent of their anomalous patterns of neuromuscular control. As such, and due to the differences in the nature of the prescribed task (and the methods of analysis used to quantitate this task), caution must be placed in the direct comparison of our findings with those of Brown and colleagues.44,45
The moment-of-force profiles presented as part of the present analysis give an important indication of the loading associated with the development of chronic injury.46,47 These profiles are of particular relevance because they identify the forces of amplification and attenuation required for the relevant phases of the DVJ. That between-group differences were only evident on the uninvolved limb highlights the potential capacity for people with CAI to exhibit bilateral deficits in neuromuscular control48,49 and the importance of performing a bilateral experimental analysis. Indeed, the label of “uninvolved limb” is a misnomer on the basis of the current findings and perhaps should be replaced with “contralateral limb.”
The reason predicating the increased flexor and extensor patterns during phases 1 and 2 of the DVJ, respectively, may have links with off-loading strategies identified in these individuals in the acute phase of injury.13,19 When these participants were evaluated in comparison with a noninjured control group within 2 weeks of sustaining their LAS, they exhibited greater extension dominance on their uninvolved limb joints compared with their involved limb during both phases of the DVJ. These motor patterns were coupled with RIM asymmetries when this cohort of participants were grouped together and compared with a noninjured control group. At both the 2-week and 6-month assessments that preceded the current report, participants with LAS exhibited significantly greater RIM asymmetry (approximately 13% compared with 5% in controls), with their uninvolved limb being subjected to significantly greater force per unit of time.13,19 This finding led us to theorize that people who are early in the recovery process re-weight dependence from the injured limb onto the contralateral limb to fulfill the energy demands of the task.14,15 On the basis of the current findings, this asymmetry persists (both groups displayed 10% asymmetry) but is not likely to predicate outcome (CAI or LAS coper) because no between-group differences were manifested.
As we previously alluded to, the increased flexor moment pattern on the contralateral hip during phase 1 of the present study may represent the persistence of a re-weighting strategy whereby this limb is “relied on” to produce the flexor pattern that precedes the extension required to initiate phase 2. However, because there was neither a between-group difference in the extensor pattern subsequent to this flexion moment nor any difference in the jump height achieved during the task, the product of this motor control process is not immediately evident. Similarly, during phase 2 of the DVJ, the increase in contralateral hip extensor pattern relative to that of LAS copers may represent an off-loading strategy to re-weight force attenuation on the limb not affected by the initial LAS and may have its roots in the motor control patterns that emerged immediately postinjury. The lack of a between-group difference in RIM or RIM symmetry makes it difficult to be conclusive regarding the value of this strategy.
Despite the exploratory nature of this experiment and the large number of resultant dependent variables in the current analysis, it is interesting to note that only at the hip joint did between group differences emerge. The crucial role that the hip plays in the combined dissipation of impact forces while preventing collapse of the lower extremity during landing is well established.50–52 This role is illustrated in the present study by the sinusoidal trajectory of the hip's moment-of-force profile following ground contact during either phase of the DVJ; an initial extensor pattern is closely followed by a flexor pattern in the fulfillment of these combined roles. Similar to the findings of Brown et al44 during the stop-jump task, the CAI group participants displayed greater hip flexion during phase 1 of the DVJ on their previously injured limb. Analysis of phase 2 results revealed similar patterns of increased hip flexion for this limb, in addition to the contralateral limb. In both cases, the increase in hip flexion began prior to IC, which suggests that this movement pattern is part of a preparatory strategy adopted by CAI participants to fulfill task constraints.53,54 Hip muscle activation onset patterns and weakness of the hip musculature have previously been implicated in the presence of CAI.55,56 This finding, in combination with the findings of the current study, is of particular relevance to clinicians, who must avoid the development of rehabilitation programs without consideration of neuromuscular control as a global concept. Either weakness or a change in activation patterns in the hip musculature may produce deviations in joint motion, which have the capacity to manifest elsewhere in the kinetic chain,22 including the contralateral side.55 Should these deficits persist, the motor apparatus may enter a cycle of injury recurrence belied by anomalous neuromuscular control. On the basis of the current findings and those of Brown et al,44 it appears that the hip may play an important role in the development of CAI; therefore, clinicians must consider the potential value of designing rehabilitation programs with joints proximal to the injured ankle in mind. It is likely rehabilitative success would be potentiated by a program that includes the entire kinetic chain, which may drive patients toward a coper path rather than a CAI path.
The issue, however, is that the accuracy of such speculations cannot be confirmed on the basis of the present research alone due to its design. Although this study was part of a longitudinal analysis designed to identify the sensorimotor predictors of CAI, the importance of the observed deficits remains unclear. Despite the consistency of the current results compared with our previous findings of the same cohort in the acute phase of injury13 and 6 months following this phase,19 caution must be placed in declaring their relevance to the development of CAI. That all of the reported deficits were observed in a single cohort of participants also threatens the generalizability of our results; however, as we have noted, the observed deficits are consistent with other CAI cohorts completing similar tasks.44,45 A further limitation of the present study is that there was potential for statistical error, as the cohort was recruited at convenience with no a priori sample size calculation being undertaken. However, a post hoc power analysis of discretized kinematic and kinetic variables at the point of the greatest observed between-group difference revealed that we had strong observed power (values for observed power ranged from 0.8 to 0.9). In contrast, our nonsignificant findings were associated with low-to-moderate statistical power (values for observed power ranged from 0.15 to 0.5, with a mean value of 0.33 and a median value of 0.34). A post hoc sample size calculation based on the difference in mean and standard deviation values for the RIM variable revealed that we would have needed a minimum of 250 participants to achieve a level of power of 0.80. We believe that it would be difficult and unrealistic to recruit this number of participants. It is important to note, however, that the nonsignificant differences were associated with small effect sizes, indicating that these relationships are not likely to be clinically important.
Footnotes
Dr Doherty, Professor Hertel, Professor Caulfield, Professor Ryan, and Dr Delahunt provided concept/idea/research design. Dr Doherty, Dr Bleakley, Professor Hertel, Professor Caulfield, Dr Patterson, and Dr Delahunt provided writing. Dr Doherty provided data collection. Dr Doherty, Dr Bleakley, Dr Sweeney, and Dr Patterson provided data analysis. Dr Doherty, Dr Bleakley, Professor Hertel, and Dr Delahunt provided project management. Dr Delahunt, Dr Bleakley, and Professor Hertel provided fund procurement. Professor Ryan provided participants. Dr Delahunt provided facilities/equipment. Dr Doherty, Dr Bleakley, and Dr Delahunt provided consultation (including review of manuscript before submission).
The study was approved by the Institutional Review Board of University College Dublin.
This study was supported by the Health Research Board (HRA_POR/2011/46) as follows: Eamonn Delahunt (Principal Investigator), Chris Bleakley and Jay Hertel (coinvestigators), and PhD student Cailbhe Doherty.
- Received March 25, 2015.
- Accepted February 4, 2016.
- © 2016 American Physical Therapy Association