A preliminary multifactorial approach describing the relationships among lower extremity alignment,...

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APreliminaryMultifactorialApproachDescribingtheRelationshipsAmongLowerExtremityAlignmentHipMuscleActivationandLowerExtremityJointExcursion

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DungNguyen

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SandraJShultz

UniversityofNorthCarolinaatGreensboro


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RandySchmitz



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RichardMLuecht



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Journal of Athletic Training 201146(3)246-256copy by the National Athletic Trainers Association Incwwwnataorgjat

original researCh

A Preliminary Multifactorial Approach Describingthe Relationships Among Lower ExtremityAlignment Hip Muscle Activation and LowerExtremity Joint ExcursionAnh-Dung Nguyen PhD ATC Sandra J Shultz PhD ATC FNATAFACSMt Randy J Schmitz PhD ATCt Richard M Luecht PhDtDavid H Perrin PhD ATC FACSMtDepartment of Health and Human Performance College of Charleston SC tApplied NeuromechanicsResearch Laboratory University of North Carolina at Greensboro

Context Multiple factors have been suggested to increasethe risk of faulty dynamic alignments that predict noncontactanterior cruciate ligament injury Few researchers have exam-ined this relationship using an integrated multifactorial ap-proach

Objective To describe the relationship among static lowerextremity alignment (LEA) hip muscle activation and hip andknee motion during a single-leg squat

Design Descriptive laboratory studySetting Research laboratoryPatients or Other Participants Thirty men (age = 239 plusmn

36 years height = 1785 plusmn 99 cm mass = 820 plusmn 141 kg) and30 women (age = 222 plusmn 26 years height = 1624 plusmn 63 cmmass = 603 plusmn 81 kg)

Main Outcome Measure(s) Pelvic angle femoral antever-sion quadriceps angle tibiofemoral angle and genu recurva-tum were measured to the nearest degree navicular drop wasmeasured to the nearest millimeter The average root meansquare amplitude of the gluteus medius and maximus muscleswas assessed during the single-leg squat and normalized tothe peak root mean square value during maximal contractions

for each muscle Kinematic data of hip and knee were also as-sessed during the single-leg squat Structural equation model-ing was used to describe the relationships among static LEAhip muscle activation and joint kinematics while also account-ing for an individuals sex and hip strength

Results Smaller pelvic angle and greater femoral antever-sion tibiofemoral angle and navicular drop predicted greaterhip internal-rotation excursion and knee external-rotation excur-sion Decreased gluteus maximus activation predicted greaterhip internal-rotation excursion but decreased knee valgus ex-cursion No LEA characteristic predicted gluteus medius or glu-teus maximus muscle activation during the single-leg squat

Conclusions Static LEA characterized by a more internallyrotated hip and valgus knee alignment and less gluteus maxi-mus activation was related to commonly observed compo-nents of functional valgus collapse during the single-leg squatThis exploratory analysis suggests that LEA does not influencehip muscle activation in controlling joint motion during a single-leg squat

Key Words knee injuries anterior cruciate ligament riskfactors posture malalignment

Key Pointsbull Static lower extremity alignment characteristics and hip muscle activation were directly related to commonly observed

components of functional valgus collapse during the single-leg squatbull However relationships between static lower extremity alignment and hip muscle activation were not observedbull Static lower extremity alignment may not influence hip muscle activation in controlling joint motion during a single-leg

squat

Multiplefactors contribute to the increased risk of non-contact anterior cruciate ligament (ACL) injury Infact a recent consensus statementl has highlighted

the need for a more integrated approach across risk-factor cat-egories (eg anatomical neuromuscular and biomechanical) Amore comprehensive approach to risk-factor assessment mayallow clinicians to accurately identify and understand thoserelevant risk factors that may contribute to at-risk knee posi-tions during dynamic activity

246 Volume 46 bull Number 3 bull June 2011

Among the many risk factors suggested to contribute to ACLinjury neuromuscular function (strength and activation) of thehip musculature has received increased attention because it isessential to providing proximal stability for lower extremitymotion2bull3 Neuromuscular deficits may compromise the stabil-ity of the hip when it is loaded during weight bearing resultingin faulty dynamic alignment of the lower extremity and poten-tially increasing the risk of injury Authors4-l0 of retrospectivestudies have reported decreased strength and activation of the

hip abductors in those with low back pain and lower extremityinjuries however prospective investigations of the relationshipbetween hip muscle function and lower extremity injury are lim-ited Only one group11 prospectively examined the relationshipbetween hip strength and lower extremity injury in collegiatebasketball and track athletes those who were injured over thecourse of the season had less hip abduction and hip extensionstrength than the uninjured athletes The authorsll suggestedthat the decreased strength of the hip musculature reduced theability to stabilize the hip resulting in adduction and rotationof the lower extremity and thus faulty alignment which con-tributed to lower extremity injury This faulty dynamic align-ment commonly termed functional valgus collapse1213andcharacterized by adduction and internal rotation of the hipand knee valgus predicts ACL-injury risk14 Whether a rela-tionship exists between decreased neuromuscular hip musclefunction and increased functional valgus collapse is currentlyunknown

In addition static lower extremity alignment (LEA) hasbeen proposed as an independent intrinsic risk factor for ACLinjury1215-18Authors19-22of retrospective studies have reportedgreater pronation pelvic angle and genu recurvatum in ACL-injured individuals These and other LEA characteristics thatincrease static hip and knee angles may predispose individuals toincreased inward collapse of the knee during dynamic activities

The limitation of previous examinations of the relationshipbetween anatomical alignment and neuromuscular function ofthe hip musculature is that only one LEA characteristic or se-lect LEA characteristics were examined No published studieshave addressed the relationship among LEA neuromuscularfunction of the hip and dynamic hip and knee motion usinga collective set of anatomic alignment variables that are suf-ficiently descriptive of lower extremity posture This relation-ship may be important because one skeletal malalignment maycause compensatory alignment changes at other bony segmentsresulting in abnormal stress patterns or compensatory motionsalong the kinetic chain

Given the potential link between decreased neuromuscularfunction of the hip musculature and increased functional valguscollapse injury-prevention programs have been developed totarget the hip musculature23 However the underlying causesfor this neuromuscular dysfunction of the hip musculaturehave received little attention Differences in LEA may alterneuromuscular function of the hip muscles and contribute tofunctional valgus collapse This premise is based on researchshowing that changes in the length tension and orientationof the hip musculature directly influence the internal-momentarms of the muscle resulting in changes in hip muscle func-tions24-26

Few authors have examined the direct influence of LEA onhip muscle function but differences in LEA may be relatedto changes in the force and activation of the hip musculatureUsing a simulated hip model an increase in gluteus medius(Grned) force was necessary to maintain a level pelvis when thefemur was positioned in a more internally rotated position (aposition associated with femoral anteversion) compared withneutral alignmentY Further decreased activation of the Grnedas measured by surface electromyography (sEMG) amplitudewas demonstrated in those with increased relative femoral an-teversion during isometric strength testing28 Collectively thesefindings indicate that individuals with increased femoral ante-version require increased force production to control the hipand pelvis yet they demonstrate decreased activation together

these factors may severely reduce frontal-plane and transverse-plane hip control during functional activities Whether otheralignment factors at the pelvis knee lower leg and foot thatpromote a more inwardly rotated or adducted hip posture fur-ther compromise hip muscle function is unknown

Although it is tenable that differences in LEA characteristicsmay change the position of the femur relative to the pelvis thuspotentially altering the length tension and orientation of themuscles and their ultimate torque-producing capabilities abouta joint these assumptions are based primarily on findings froma static model Whether these relationships would hold in a dy-namic and constantly changing joint during functional activi-ties is unclear

Therefore we examined whether static LEA characteristicsand hip muscle activation were related to hip and knee kinemat-ics during a single-leg squat while accounting for sex and hipstrength Based on retrospective evidence that ACL-injured in-dividuals had greater magnitudes of static LEN9-22 and the po-tential for alignment to influence the neuromuscular function ofthe lower extremity muscles2728we wanted to explore both thedirect relationships of LEA and hip muscle activation on lowerextremity kinematics and the potential for indirect relationshipsbetween LEA and lower extremity kinematics based on the as-sociation of LEA with hip muscle activation Specifically wehypothesized that (1) greater magnitudes of static alignment ofthe lower extremity and decreased hip muscle activation woulddirectly predict greater functional valgus collapse (increasedhip adduction and internal rotation knee external rotation andvalgus excursion) during a single-leg squat and (2) indirect re-lationships would also occur such that greater magnitudes ofstatic LEA would predict decreased Grned and gluteus maximus(G ) activation (abduction and extension) and collectivelypredict greater functional valgus collapse

METHODS

Thirty men (age = 239 plusmn 36 years height = 1785 plusmn 99 cmmass = 820 plusmn 141 kg) and 30 women (age = 222 plusmn 26 yearsheight = 1624 plusmn 63 cm mass = 603 plusmn 81 kg) were recruitedfrom the university and the surrounding community to partici-pate in the study Each volunteer provided informed consent asapproved by the universitys institutional review board Partici-pants had no history of surgery to either lower extremity and noprevious hip joint or knee joint injury within the last 6 monthsAll measurements were taken on the dominant-stance limb (iethe stance extremity when kicking a ball)

Alignment Measurements

We measured 6 alignment characteristics on the pelvis andlower extremity These alignment characteristics were based oncommonly identified variables suggested to influence dynamicmotion and the risk of lower extremity injuries All measure-ment procedures were performed by a single examiner who hadpreviously established good to excellent test-retest reliabilityon all measures (intraclass correlation coefficient [ICC] [23] ~087)2329using techniques that have been previously describedin detail 29-32All standing measures were taken in a standard-ized stance with the left and right feet spaced equal to the widthbetween the left and right acromial processes and toes facingforward The stance was achieved by instructing participants tomarch in place and then take a step forward They were advisedto look straight ahead during all standing measures with weight

Journal of Athletic Training 247

evenly distributed over both feet Pelvic angle was measured ina standing position using an inclinometer and represented theangle formed by a line from the anterior-superior iliac spineto the posterior-superior iliac spine relative to the horizontalplane33 Femoral anteversion was measured in a prone posi-tion using the Craig test34 Quadriceps angle was measured ina standing position and represented the angle formed by a linefrom the anterior-superior iliac spine to the patella center and aline from the patella center to the tibial tuberosity Tibiofemoralangle was measured in a standing position and represented theangle formed by the anatomical axis of the femur and tibia inthe frontal plane29 Genu recurvatum was measured in supineposition with a bolster positioned under the distal tibia and rep-resented the sagittal-plane alignment of the femur and tibia29

Navicular drop was measured in a standing position and rep-resented the difference between the height of the navicular insubtalar joint neutral and a relaxed stance29 Each measure wasrepeated 3 times

Electromyography Procedures

Surface electromyography signals of the Gmed and Gmax wereobtained using a 16-channel Myopac telemetric system (RunTechnologies Company Mission Viejo CA) with an amplifica-tion of 1 mVIV frequency bandwidth of 10 to 1000 Hz com-mon mode rejection ratio of 90 dB minimum at 60 Hz inputresistance of 1 MQ and an internal sampling rate of 8 KHzThe sEMG signals were detected with lO-mm bipolar Ag-AgClsurface electrodes (Blue Sensor N-OO-S Ambu Products 01-stykke Denmark diameter = 448 x 22 mm skin contact size =30 x 22 mm) with a center-to-center distance of 20 mm and theelectrodes were positioned according to procedures describedby Cram and Kasman35 Electrodes were placed on the Gmed ata position one-third the distance from the greater trochanter tothe iliac crest Electrode placement on the Gmax was midway be-tween the greater trochanter and the first sacral vertebrae ThesEMG electrodes were oriented perpendicular to the length ofthe muscle fibers and placed over the midbelly The referenceelectrode was secured to the medial aspect of the tibia Beforethe electrodes were attached we thoroughly cleaned all skinareas with isopropyl alcohol Myoelectric data were acquiredstored and analyzed using DataPac 2K2 laboratory applicationsoftware (version 313 Run Technologies Company) duringthe maximal voluntary isometric contractions (MVICs) and thesingle-leg squat

Strength Assessment

A dynamometer (model 3 Biodex Medical Systems IncShirley NY) was used to record hip abduction and hip extensionMVICs Participants performed 3 trials of a 3-second MVICfor each muscle with a 30-second rest period separating trialsWe modified a technique described by Carcia et ap6 to measurehip abduction torque in weight bearing Volunteers stood adja-cent to the dynamometer looking straight ahead with the trunkerect feet facing forward and arms crossed over the chest Thedynamometer axis was aligned with the head of the femur de-termined by the intersection of a medially directed horizontalline from the greater trochanter and a distally directed verticalline from the anterior-superior iliac spine37 The resistance armof the dynamometer was positioned on the lateral side of thenonstance leg with the distal edge of the pad approximately 5


cm proximal to the lateral joint line and the hip positioned inapproximately 5deg of abduction Each participant performed theMVIC by abducting the hip while supporting his or her bodyweight on the dominant-stance limb and maintaining an erectposture For assessment of hip extension torque each individ-ual performed hip extension in the supine position with the hipflexed to 90deg and the dynamometer axis aligned with the greatertrochanter The resistance arm was positioned on the posteriorthigh just proximal to the knee joint line Previous work in ourlaboratory using these identical MVIC measurement protocolsdemonstrated good to excellent day-to-day reliability of torqueproduction for standing hip abduction (ICC[2k] = 091 SEM =003 Nmiddotmkg) and hip extension (ICC[2k] = 080 SEM = 046Nmiddotmkg)

Kinematic Analysis

Kinematic data for the pelvis thigh shank and foot weresampled at 100 Hz using 6-degrees-of-freedom electromagneticsensors (Ascension Technology Corporation Burlington VT)and Motion Monitor Software (Innovative Sports Training IncChicago IL) during the single-leg squat Electromagnetic posi-tion sensors were attached with double-sided tape and elasticwrap over the anterior mid shaft of the third metatarsal the mid-shaft of the medial tibia and the lateral aspect of the mid shaftof the femur of the dominant-stance limb An additional sensorwas secured on the sacrum Digitization procedures were per-formed using the default selection with a segmental referencesystem defining body segments the positive x-axis was definedas the posterior-to-anterior axis the positive y-axis was definedas the distal-to-proximallongitudinal axis and the positive z-axis was defined as the medial-to-lateral axis An initial neu-tral position was established in a standardized stance with theleft and right feet spaced equal to the width between the leftand right acromion processes and the toes facing forward Theankle and knee joint centers were estimated using the centroidmethod whereby the ankle joint center was calculated as themidpoint between the digitized medial and lateral malleoli andthe knee joint center was calculated by the midpoint betweenthe digitized medial and lateral femoral epicondyles The hipjoint center was determined by the Leardini et ap8 method

The starting position for participants was feet shoulder-width apart hips and knees extended toes facing forward equalweight on both feet and thumbs lightly touching the iliac crests(Figure 1) A plywood board was positioned at a distance ante-rior to the knee while volunteers performed a double-leg squatto 60deg of knee flexion based on real-time goniometer valuesThe plywood board was positioned to provide individuals withfeedback indicating that they had reached 60deg of knee flexionduring each trial and while performing a double-leg squat toensure proper placement of the board They then performed asingle-leg squat with instructions to squat straight down untilthey touched the board with the knee while looking straightahead A string was positioned perpendicular to the first toe atthe level of the chest to monitor forward flexion of the trunk(Figure 2) Participants were instructed to maintain an uprightposition without flexing the trunk forward or to the side in or-der to limit the influence of trunk motion on the hip muscula-ture Although we recognize that this is a constrained task therationale for this standardized positioning was to account for apotential confounding factor that may have contributed to con-flicting results in previous studies of hip muscle activation dur-

Figure 1 Starting position for the kinematic data collection withfeet shoulder-width apart hips and knees extended toes facingforward equal weight on both feet and thumbs lightly touchingthe iliac crests

ing dynamic tasks394O Compared with men women had greaterGmax activation during a single-leg squat39 but less activationduring single-leg landings4O Small sample sizes and method-ologic considerations in performing the tasks may explain thesecontrasting findings Specifically trunk motion which has adirect influence on activation of the hip musculature did notappear to be controlled in these studies41

Each single-leg squat trial was initiated by a verbal com-mand from the examiner and performed at a speed of 5 secondsfrom the starting position to 60deg of knee flexion The rate ofthe task was controlled by a metronome set at a cadence of 60beats per minute Participants transitioned from bilateral stanceto single-leg stance during the first 2 beats with the nonstanceknee and hip flexed approximately 45deg and 0deg respectivelyThe squat then began on the third beat and ended at 60deg of kneeflexion on the fifth beat (total squat time = 2 seconds) A forceplate marked the transition from double-leg stance to single-legstance and 60deg of knee flexion marked the end of the trial Vol-unteers were allowed sufficient practice to ensure that the taskwas performed properly and data were then collected during 5acceptable trials A trial was deemed unacceptable if the indi-vidual (1) touched the string (indicating increased forward flex-ion of the trunk) (2) touched the non stance leg to the groundor the stance leg (3) lifted either hand off the iliac crest or (4)

Figure 2 The single-leg squat was performed to 60deg of knee flex-ion A string was positioned perpendicular to the first toe at thelevel of the chest to monitor forward flexion of the trunk during thesingle-leg squat

failed to reach 60deg of knee flexion as confirmed by real-timegoniometry

Data Reduction and Analyses

The average of 3 measurements for each LEA characteris-tic was used for analyses Dynamometer torque data were re-corded as the maximum peak torque obtained from 3 MVICtrials each for hip abduction and hip extension Peak torque wasthen normalized to the participants body mass and reported innewton-meters per kilogram of body mass Kinematic signalsfrom the position sensors were low-pass filtered at 12 Hz usinga fourth-order zero-lag Butterworth filter Hip and knee angleswere calculated using Euler angle definitions with a rotationalsequence of Z X Y42 Initial joint angles were calculated as theaverage joint positions during the first second after transitionfrom double-leg to single-leg stance Final joint angles weredetermined as the value when participants achieved 60deg of kneeflexion Single-leg squat joint excursions were calculated as thedifference (final minus initial) for each trial and the averageacross 5 trials was used for statistical analysis

The sEMG of the Gmed and Gmax during the MVIC and sin-gle-leg squat trials was filtered from 10 Hz to 350 Hz using afourth-order zero-lag Butterworth filter and then processed us-


ing a centered root mean square (RMS) algorithm with 100-mil-lisecond time constant The peak RMS value obtained over 3MVIC trials for each muscle was used to normalize the sEMGdata during the single-leg squat The average RMS amplitudeof the 5 single-leg squat trials across the entire trial (after tran-sition to single-leg weight bearing to 60deg) was then normalizedto the individuals MVIC peak RMS value and reported as apercentage of the MVIC

Structural equation modeling was used to evaluate whetherincreased LEA and decreased hip muscle activation (Gmed andGmax considered separately) predicted greater functional valguscollapse (characterized by increased hip adduction and internalrotation knee external rotation and valgus excursion) during asingle-leg squat while accounting for the individuals sex andhip strength Our rationale in accounting for these additionalvariables was that LEA characteristics31 and hip strengthll43-45

are known to differ by sex and that muscle-activation ampli-tude of the primary hip abductor (Gmed) and hip extensor (Gma)

muscles may in part depend on their absolute force-producingcapabilities46 Hip abduction and hip extension strength wereincluded only in the specific path models that examined the re-lationships of Gmed and Gmax activation respectively as they arethe primary muscles that perform hip abduction and hip exten-sion The path diagram examining these relationships is illus-trated in Figure 3

Path analysis is an extension of multiple linear regressionswith the purpose of modeling explanatory chained relation-ships between observed variables It provides estimates of the

Naviculardrop

Pelvicangle

Femoralanteversion

Quadricepsangle

Tibiofemoralangle

Genurecurvatum

magnitude and significance of hypothesized causal connectionsamong sets of variables Path analysis provides a statistical ap-proach to understanding comparative strengths of direct and in-direct relationships among a set of variables47 Because the totalnumber of variables being estimated was greater than the totalsample size (resulting in the variable estimates being highly un-reliable) each full model was reduced to a more stable modelby first removing the dependent measures that had no statisti-cally significant paths (ie variables that had no significant pre-dictors) followed by removing the predictor variables that didnot approach significance or were nonsignificant in explainingany of the remaining outcome measures (dependent variables)Statistical significance was determined by the t-value statisticwhich reflects the ratio of the variable estimate to its standarderror A t value greater than +2 or less than -2 is considered sta-tistically significant47 All path analyses were performed usingLISREL (version 872 Scientific Software International IncLincolnwoodIL)

RESULTS

Measures of LEA hip muscle activation joint excursionduring the single-leg squat and hip torque are summarized inTable 1 The mean static alignment values are within the rangeof normal values reported in healthy adults using identical mea-surement methods29-31 Sex was related to LEA characteristicsand hip muscle activation (all P lt 05) women had greater pel-vic angle (t = 223) femoral anteversion (t = 460) quadriceps

Figure 3 Full path model for the dependent variables gluteal muscle activation and functional valgus collapse


Table 1 Descriptive Statistics for Dependent andPredictor Variables

Measure Mean plusmn SO Median Range

Lower extremity alignmentPelvic angle 0 111plusmn46 110 00 to 210Hip anteversion 0 107 plusmn 52 98 10 to 277Quadriceps angle 0 129 plusmn 56 120 10 to 290Tibiofemoral angle 0 107 plusmn 20 107 50 to 153Genu recurvatum 0 38 plusmn 38 30 -13 to 143Navicular drop mm 66 plusmn 60 63 -40 to 257

Muscle activation maximum voluntaryisometric contraction

Gluteus medius 027 plusmn 013 023 011 to 072Gluteus maximus 020 plusmn 019 014 003 to 104

Joint excursion 0

Hip adduction 114 plusmn 104 120 -153 to 355Hip internal rotation -23 plusmn 59 -16 -164 to 128Knee valgus -01 plusmn 80 -04 -235 to 170Knee external rotation 27 plusmn 61 22 -98 to 202

Hip strength NmiddotmkgHip-abduction torque 069 plusmn 019 066 037 to 133Hip-extension torque 346 plusmn 105 343 187 to 580

angle (t = 258) tibiofemoral angle (t = 309) genu recurvatum(t = 384) and G activation (t = 244) than men The inferen-tial goodness-of-fiat index indicated that both full models were aperfect fit (X2

0 = 000 P = 100 RMS error of approximation =

000) because the model was saturated with a degrees of free-dom

Relationship Among LEA Gmed Activation andJoint Excursion

The full model used to examine the extent to which LEAcharacteristics predicted Gmed activation and the variables col-lective influence on dynamic alignment during a single-legsquat while accounting for sex and hip abduction torque wasreduced to a more stable model (Figure 4) The variables thatremained in the model were the dependent variables of hipinternal-rotation and knee external-rotation excursions andthe predictor variables of pelvic angle femoral anteversiontibiofemoral angle and navicular drop The coefficients stan-dard errors of the coefficients and t statistics for paths Pj-PjSthat represent the relationships among the remaining variablesare shown in Table 2

The model explained 17 of the variance in hip internal-rotation excursion and 24 of the variance in knee external-rotation excursion during the single-leg squat Smaller pelvicangle (P6) and greater navicular drop (Ps) predicted greater hipinternal-rotation excursion whereas smaller pelvic angle (PIO)and greater femoral anteversion (Pn) and tibiofemoral angle(Pj2) predicted greater knee external-rotation excursion duringthe single-leg squat The model did not identify any indirect(ie sequential or chained) relationships between LEA andGmed activation in predicting joint excursion during the single-leg squat

Naviculardrop

Pelvicangle

Femoralanteversion

Tibiofemoralangle

Figure 4 Final model for the dependent variables gluteus medius activation and dynamic valgus alignment a Indicates significant pathcoefficient See Table 2 for path coefficient values


Relationship Among LEA Gmax Activation andJoint Excursion

The full model used to examine the extent to which staticLEA predicted G activation and the variables collective in-fluence on dynari~ alignment during a single-leg squat whileaccounting for sex and hip extension torque was also reducedto a more stable model (Figure 5) The variables that remainedin the model were the dependent variables of hip internal-ro-tation knee valgus and knee external-rotation excursion andthe predictor variables of pelvic angle femoral anteversiontibiofemoral angle and navicular drop The coefficients stan-dard errors of the coefficients and t statistics for paths PI-P20that represent the relationships among the remaining variablesare shown in Table 3

The model explained 27 of the variance in hip internal-rotation excursion 17 of the variance in knee valgus ex-cursion and 20 of the variance in knee external-rotationexcursion during the single-leg squat Smaller pelvic angle(P6) and greater femoral anteversion (P7) and navicular drop(Ps) predicted greater hip internal-rotation excursion whereassmaller pelvic angle (PI4) and greater femoral anteversion (PIS)and tibiofemoral angle (PI6) predicted greater knee external-rotation excursion during the single-leg squat Decreased Gmaxactivation predicted greater hip internal-rotation (PIS) and de-creased knee valgus (PI9) excursion Similar to the previousmodel we did not identify any indirect relationships betweenLEA and Gmax activation in predicting joint excursion duringthe single-leg squat

Naviculardrop

Pelvicangle

Femoralanteversion

Tibiofemoralangle

DISCUSSION

The primary findings were that LEA characteristics were di-rectly related to dynamic alignment during a single-leg squatwith greater femoral anteversion tibiofemoral angle andnavicular drop predicting greater hip internal-rotation excur-sion and knee external-rotation excursion Interestingly greaterpelvic angle predicted decreased hip and knee rotation Directrelationships were also noted between gluteal activation anddynamic alignment with decreased Gmax activation predictinggreater hip internal-rotation excursion but decreased knee val-gus excursion These results provide empirical support for pre-vious theories that differences in static LEA and gluteal muscleactivation contribute to greater hip joint and knee joint excur-sions during functional activities However no indirect (ie se-quential or chained) relationships were noted between LEA andgluteal activation in predicting dynamic motion no LEA char-acteristic predicted G d or G muscle activation during thesingle-leg squat once nindividuals sex and muscle strengthwere accounted for

Effects of LEA and Hip Muscle Activation on LowerExtremity Joint Excursion

Based on prevailing theories greater static hip and kneealignment and decreased hip activation were hypothesizedto predict greater frontal- and transverse-plane joint excur-sion during the single-leg squat Specifically individuals withmore femoral anteversion and navicular drop went into more

Figure 5 Final model for the dependent variables gluteus maximus activation and dynamic valgus alignment a Indicates significant pathcoefficient See Table 3 for path coefficient values


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hip internal-rotation excursion and individuals with greatertibiofemoral angle and femoral anteversion went into greaterknee external-rotation excursion with both motions consid-ered important components of functional valgus collapse 12The direct relationship between greater femoral anteversionand greater rotation of both the hip and knee during dynamicmotion seems logical given that more femoral anteversion haspreviously been associated with hip internal rotation and con-tributes to a compensatory increase in knee external rotation48These observed relationships suggest that static LEA charac-teristics may directly influence dynamic hip and knee anglesduring functional activities and may offer a potential mecha-nism by which greater navicular drop and static knee valgusangles were associated with ACL injury 19-22An explanation forgreater pelvic angle predicting decreased hip internal-rotationand knee external-rotation excursion is unclear Based on retro-spective evidence21that suggests a relationship between greateranterior pelvic angle and ACL injury our expectation was thatmore anterior pelvic tilt would be related to more dynamic jointexcursion Additional work is needed to better understand theinteraction between the pelvis and the femur and its influenceon dynamic alignment and ACL injury

The hypothesized relationship between hip muscle activa-tion and functional valgus collapse was partially supportedDecreased Gmax activation predicted greater hip internal-rotation excursion Although we found no studies that directlyexamined the relationship between hip muscle activation andjoint motion in healthy individuals this observed relation-ship does support current theories that decreased hip muscleactivation may affect dynamic stability of the hip resulting inan inability to maintain neutral alignment during single-limbweight-bearing activities3949-51However the positive relation-ship of greater Gmax activation predicting greater knee valgusexcursion is the opposite of what we expected An explanationof this positive relationship is unclear but it may be that hip ac-tivation strategies are different when controlling motions at thehip compared with motions at the knee Dynamic knee valgusobserved during functional tasks may reflect a combined mo-tion of knee valgus and hip internal rotation which would fur-ther suggest a positive relationship between G activation andthese motions However further examination m~four data indi-cated that hip internal rotation was negatively correlated withknee valgus excursion (r = -0370 P = 004) This observedrelationship between hip joint and knee joint motion may bespecific to a single-leg squat task and therefore further stud-ies are needed to determine whether the observed relationshipsbetween hip muscle activation and lower extremity kinematicsare consistent across functional tasks

Although we observed direct relationships between LEA andjoint excursion it is unclear from these data alone if static LEAdirectly predisposes individuals to the rotational hip and kneecomponents of functional valgus collapse or whether these pos-tural effects act through resulting biomechanical changes (iedecreased hip muscle activation) to increase dynamic hip andknee malalignments The use of a path analysis model was anovel approach toward examining multiple risk factors whichallowed us to examine the indirect relationships between LEAand functional valgus collapse by way of their effects on hipmuscle activation We hypothesized that static malalignmentswould directly predict decreased hip muscle activation whichwould further predict increased joint excursion

However this sequential or chained relationship was not ob-


served no static LEA characteristic was related to dynamic hipmuscle activation Relationships between LEA and hip musclefunction have been observed using static models but our re-sults do not support this relationship during dynamic activitieswhen joint position is constantly changing These findings sug-gest that static LEA alone may predispose individuals to greaterhip and knee rotations during dynamic activity independent ofGmax or Gmed activation during dynamic tasks

Accounting for Sex and Hip Muscle Strength

We chose to account for sex in the path-analysis modelsbecause many of the LEA characteristics31 and hip muscle-activation measures3940we examined are known to differ bysex By accounting for sex in the model we confirmed that sexwas related to LEA characteristics and hip muscle activationsuch that women had greater pelvic angle femoral antever-sion quadriceps angle tibiofemoral angle genu recurvatumand G activation than men These sex differences in LEAcharact~~istics and hip muscle activation may in part explainwhy females demonstrate greater dynamic knee angles and anincreased risk of ACL injury Future authors should examinemales and females separately because the relationships betweenmany of the postulated risk factors and ACL injury may not bethe same for each sex

The purpose of accounting for hip abduction and hip exten-sion strength in the path analyses was to better clarify the rela-tionship between hip muscle activation and functional valguscollapse by taking into consideration variations in the levels ofhip strength among participants which may itself explain dif-ferences in functional valgus collapse Although authors haveexamined activation of the hip musculature during functionalactivities such as single-leg landings and single-leg squats ei-ther kinematic data were not collected40or hip strength was notreported3940Based on these studies the relationship betweenposterior-lateral hip muscle function and dynamic joint mo-tion remains unclear In theory greater hip muscle activationwould be necessary to successfully perform a desired motionin the presence of reduced hip muscle strength The negativerelationships we observed between hip abduction torque andGmed activation (r = -0275 P = 034) and between hip exten-sion torque and G activation (r = -0612 P lt 001) confirmthat greater poster~~-lateral hip muscle activation was requiredin those individuals with decreased hip strength to success-fully perform the single-leg squat This inverse relationshipbetween hip muscle strength and activation suggests that rela-tive increases in gluteal muscle activation mayor may not bythemselves indicate better hip control depending on the actualtorque-producing capabilities of the muscles

Limitations

We acknowledge that measurement of femoral anteversionusing clinical methods has the potential for inconsistencieswith a range of reliabilities and validities of this measure re-ported in the literature The measurement technique we usedwas based on original work by Ruwe et al34who reported goodreliability between testers and high correlations with intraop-erative measurements Consistent with other authors who havereported high intratester2952and intertester reliability52 the tes-ter in this study had more than 10 years of clinical experienceand had established a high level of reliability on this measure

However a recent groupS3has since reported that clinical mea-surements of femoral anteversion were underestimates com-pared with values obtained via magnetic resonance imagingquestioning the validity of the Craig test in assessing femo-ral anteversion Our observed relationships between femoralanteversion and dynamic alignment which were consistentwith our hypotheses indicate that the clinical measurement offemoral anteversion represents some anatomical aspect of hiprotation and remains an important factor to consider when ex-amining risk of ACL injury Further work is needed to identifythe underlying characteristics being assessed using the clinicalmeasurement method

Aside from femoral anteversion all primary variables wereassessed while the participants were weight bearing in an effortto better represent a functional position However hip extensiontorque was measured nonweight bearing and more work is re-quired to confirm if relationships between strength and G

maxac-

tivation would remain consistent if both were assessed in a morefunctional position Our findings are limited to the dominant-stance limb of healthy college-aged adults and should not begeneralized to other populations Further these findings are lim-ited to a controlled functional single-leg squat task performed inan upright position Although we felt it was important to controlthe influence of various trunk positions on hip muscle activa-tion41that might have contributed to inconsistent findings fromprevious studies3940we acknowledge that this upright positionmay not be fully representative of more unconstrained dynamictasks potentially associated with ACL injury

CONCLUSIONS

A more integrated approach to risk-factor assessment isneeded to accurately identify and understand those relevant riskfactors that may contribute to at-risk knee positions during dy-namic activity The overall findings of this study revealed thatLEA characteristics clinically associated with static malalign-ment and hip muscle activation were directly related to com-monly observed components of functional valgus collapseduring the single-leg squat However this exploratory analy-sis did not identify any indirect relationships between LEAand Gmax activation in predicting joint excursion and suggeststhat LEA does not influence hip muscle activation in control-ling joint motion during a single-leg squat Future researchersshould continue to examine the other factors that influence hipmuscle activation and the mechanisms that explain the relation-ships between static and dynamic malalignments

Although the identified relationships were statistically sig-nificant the associated path coefficients were somewhat lowwhich indicates that other factors could combine with LEA andhip muscle activation to further affect dynamic motion Futureinvestigators should confirm whether the relationship amongLEA hip muscle activation and dynamic malalignment is con-sistent across a variety of functional tasks In addition contin-ued examination of differences in LEA characteristics amongboth older and younger individuals is needed to determinewhether these postures change with maturity This research willaid clinicians in determining the most appropriate time to initi-ate posterior-lateral hip strengthening programs with the goalof reducing injury Continued work in these areas will help cli-nicians more effectively identify those at greater risk for injuryand therefore help us to develop intervention strategies to re-duce the risk of noncontact ACL injury

ACKNOWLEDGMENTS

This study was funded in part by the NATA Research amp Ed-ucation Foundation

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8 Nadler SF Malanga GA DePrince M Stitik TP Feinberg JH The re-lationship between lower extremity injury low back pain and hip mus-cle strength in male and female collegiate athletes Clin J Sport Med2000 10(2) 89-97

9 Bullock-Saxton JE Local sensation changes and altered hip muscle func-tion following severe ankle sprain Phys Ther I99474(I)17-28

10 Jaramillo J Worrell TW Ingersoll CD Hip isometric strength followingknee surgery J Orthop Sports Phys Ther 199420(3)160-165

II Leetun DT Ireland ML Wilson JD Ballantyne BT Davis 1M Core stabil-ity measures as risk factors for lower extremity injury in athletes Med SciSports Exerc 200436(6)926-934

12 Ireland ML Anterior cruciate ligament injury in female athletes epidemi-ology J Athl Train 199934(2)150-154

13 Olsen 0 Myklebust G Engebretsen L Bahr R Injury mechanisms foranterior cruciate ligament injuries in team handball a systematic videoanalysis Am J Sports Med 200432(4)1002-1012

14 Hewett TE Myer GD Ford KR et al Biomechanical measures of neuro-muscular control and valgus loading of the knee predict anterior cruciateligament injury risk in female athletes a prospective study Am J SportsMed 200533(4)492-501

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16 Hutchinson MR Ireland ML Knee injuries in female athletes Sports Med199519(4)288-302

17 Ireland ML Gaudette M Crook S ACL injuries in the female athlete JSport Rehabil 19976(2)97-IIO

18 McClay Davis I Ireland ML ACL injuries the gender bias J OrthopSports Phys Ther 200333(8)A2-A8

19 Beckett ME Massie DL Bowers KD Stoll DA Incidence of hyper-pronation in the ACL injured knee a clinical perspective J Athl Train199227(I)58-62

20 Loudon JK Jenkins W Loudon KL The relationship between staticposture and ACL injury in female athletes J Orthop Sports Phys Ther199624(2)91-97

21 Hertel J Dorfman JH Braham RA Lower extremity malalignments andanterior cruciate ligament injury history J Sports Sci Med 20043(4)220-225

22 Woodford-Rogers B Cyphert L Denegar CR Risk factors for anteriorcruciate ligament injury in high school and college athletes J Athl Train199429(4)343-346


23 Hewett TE Lindenfeld TN Riccobene JV Noyes FR The effect of neu-romuscular training on the incidence of knee injury in female athletes aprospective study Am J Sports Med 199927(6)699-706

24 Dostal WF Andrews JG A three-dimensional biomechanical model of hipmusculature J Biomech 198114(11)803-812

25 Delp SL Hess WE Hungerford D Jones LC Variation of rotation momentarms with hip flexion J Biomech 199932(5)493-501

26 Dostal WF Soderberg GL Andrews JG Actions of hip muscles PhysTher 198666(3)351-361

27 Merchant AC Hip abductor muscle force an experimental study of theinfluence of hip position with particular reference to rotation J Bone JointSurg Am 196547462-476

28 Nyland J Kuzemchek S Parks M Caborn DN Femoral anteversion influ-ences vastus medialis and gluteus medius EMG amplitude composite hipabductor EMG amplitude ratios during isometric combined hip abduction-external rotation J Electromyogr Kinesiol 200414(2)255-261

29 Shultz SJ Nguyen A Windley TC Kulas AS Botic TL Beynnon BDIntratester and intertester reliability of clinical measures of lower extremityanatomic characteristics implications for multicenter studies Clin J SportMed 200616(2)155-161

30 Shultz SJ Nguyen AD Levine BJ The relationship between lower ex-tremity alignment characteristics and anterior knee joint laxity J SportsHealth 20091(1)54-60

31 Nguyen AD Shultz SJ Sex differences in clinical measures of lower ex-tremity alignment J Orthop Sports Phys Ther 200737(7)389-398

32 Shultz SJ Nguyen AD Schmitz RJ Differences in lower extremity ana-tomical and postural characteristics in males and females between matura-tion groups J Orthop Sports Phys Ther 200838(3)137-149

33 Gilliam J Brunt D MacMillan M Kinard RE Montgomery WJ Rela-tionship of the pelvic angle to the sacral angle measurement of clinicalreliability and validity J Orthop Sports Phys Ther 199420(4)193-199

34 Ruwe PA Gage JR Ozonoff MB De-Luca PA Clinical determination offemoral anterversion a comparison with established techniques J BoneJoint Surg Am 199274(6)820-830

35 Cram JR Kasman GS The Basics of Surface Electromyography Gaith-ersburg MD Aspen Publishers 1998

36 Carcia CR Eggen JM Shultz SJ Hip-abductor fatigue frontal-planelanding angle and excursion during a drop jump J Sport Rehabil200514(4)317-327

37 Nyland J Smith S Beickman K Armsey T Caborn DN Frontal planeknee angle affects dynamic postural control strategy during unilateralstance Med Sci Sports Exerc 200234(7)1150-1157

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for the estimation of hip joint centre location J Biomech 199932(1)99-103

39 Zeller BL McCrory JL Kibler WE Uhl TL Differences in kinematics andelectromyographic activity between men and women during the single-legged squat Am J Sports Med 200331(3)449-456

40 Zazulak BT Ponce PL Straub SJ Medvecky MJ Avedisian L HewettTE Gender comparison of hip muscle activity during single-leg landingJ Orthop Sports Phys Ther 200535(5)292-299

41 Schmitz RJ Riemann BL Thompson T Gluteus medius activity during iso-metric closed-chain hip rotation J Sport Rehabil 200211(3)179-188

42 Kadaba MP Ramakrishnan HK Wootten ME Gainey J Gorton G Co-chran GV Repeatability of kinematic kinetic and electromyographic datain normal adult gait J Orthop Res 19897(6)849-860

43 Murray MP Sepic SB Maximum isometric torque of hip abductor andadductor muscles Phys Ther 196848(12)1327-1335

44 Bohannon RW Reference values for extremity muscle strength obtainedby hand-held dynamometry from adults aged 20 to 79 years Arch PhysMed Rehabil 199778(1)26-32

45 Cahalan TD Johnson ME Liu S Chao EY Quantitative measurements ofhip strength in different age groups Clin Orthop Relat Res 1989246136-145

46 Shultz SJ Nguyen AD Leonard MD Schmitz RJ Thigh strength andactivation as predictors of knee biomechanics during a drop jump taskMed Sci Sports Exerc 200941(4)857-866

47 Raykov T Marcoulides GA A First Course in Structural Equation Model-ing Mahwah NJ Lawrence Erlbaum Associates 2000

48 Hvid I Andersen LI The quadriceps angle and its relation to femoral tor-sion Acta Orthop Scand 198253(4)577-579

49 Ferber R Davis 1M Williams DS 3rd Gender differences in lowerextremity mechanics during running Clin Biomech (Bristol Avon)200318(4)350-357

50 Malinzak RA Colby SM Kirkendall DT Yu B Garrett WE A comparisonof knee joint motion patterns between men and women in selected athletictasks Clin Biomech (Bristol Avon) 200116(5)438-445

51 Lephart SM Ferris CM Riemann BL Myers JB Fu FH Gender dif-ferences in strength and lower extremity kinematics during landing ClinOrthop Relat Res 2002401162-169

52 Jonson SR Gross MT Intraexaminer reliability interexaminer reliabilityand mean values for nine lower extremity skeletal measures in healthynaval midshipmen J Orthop Sports Phys Ther 199725(4)253-263

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Address correspondence to Anh-Dung Nguyen PhD ATC Department of Health and Human Performance College of Charles-ton 66 George Street 314 Silcox Center Charleston SC 29424 Address e-mail to NguyenYcofcedu


Journal of Athletic Training 201146(3)246-256copy by the National Athletic Trainers Association Incwwwnataorgjat

original researCh

A Preliminary Multifactorial Approach Describingthe Relationships Among Lower ExtremityAlignment Hip Muscle Activation and LowerExtremity Joint ExcursionAnh-Dung Nguyen PhD ATC Sandra J Shultz PhD ATC FNATAFACSMt Randy J Schmitz PhD ATCt Richard M Luecht PhDtDavid H Perrin PhD ATC FACSMtDepartment of Health and Human Performance College of Charleston SC tApplied NeuromechanicsResearch Laboratory University of North Carolina at Greensboro

Context Multiple factors have been suggested to increasethe risk of faulty dynamic alignments that predict noncontactanterior cruciate ligament injury Few researchers have exam-ined this relationship using an integrated multifactorial ap-proach

Objective To describe the relationship among static lowerextremity alignment (LEA) hip muscle activation and hip andknee motion during a single-leg squat

Design Descriptive laboratory studySetting Research laboratoryPatients or Other Participants Thirty men (age = 239 plusmn

36 years height = 1785 plusmn 99 cm mass = 820 plusmn 141 kg) and30 women (age = 222 plusmn 26 years height = 1624 plusmn 63 cmmass = 603 plusmn 81 kg)

Main Outcome Measure(s) Pelvic angle femoral antever-sion quadriceps angle tibiofemoral angle and genu recurva-tum were measured to the nearest degree navicular drop wasmeasured to the nearest millimeter The average root meansquare amplitude of the gluteus medius and maximus muscleswas assessed during the single-leg squat and normalized tothe peak root mean square value during maximal contractions

for each muscle Kinematic data of hip and knee were also as-sessed during the single-leg squat Structural equation model-ing was used to describe the relationships among static LEAhip muscle activation and joint kinematics while also account-ing for an individuals sex and hip strength

Results Smaller pelvic angle and greater femoral antever-sion tibiofemoral angle and navicular drop predicted greaterhip internal-rotation excursion and knee external-rotation excur-sion Decreased gluteus maximus activation predicted greaterhip internal-rotation excursion but decreased knee valgus ex-cursion No LEA characteristic predicted gluteus medius or glu-teus maximus muscle activation during the single-leg squat

Conclusions Static LEA characterized by a more internallyrotated hip and valgus knee alignment and less gluteus maxi-mus activation was related to commonly observed compo-nents of functional valgus collapse during the single-leg squatThis exploratory analysis suggests that LEA does not influencehip muscle activation in controlling joint motion during a single-leg squat

Key Words knee injuries anterior cruciate ligament riskfactors posture malalignment

Key Pointsbull Static lower extremity alignment characteristics and hip muscle activation were directly related to commonly observed

components of functional valgus collapse during the single-leg squatbull However relationships between static lower extremity alignment and hip muscle activation were not observedbull Static lower extremity alignment may not influence hip muscle activation in controlling joint motion during a single-leg

squat

Multiplefactors contribute to the increased risk of non-contact anterior cruciate ligament (ACL) injury Infact a recent consensus statementl has highlighted

the need for a more integrated approach across risk-factor cat-egories (eg anatomical neuromuscular and biomechanical) Amore comprehensive approach to risk-factor assessment mayallow clinicians to accurately identify and understand thoserelevant risk factors that may contribute to at-risk knee posi-tions during dynamic activity


Among the many risk factors suggested to contribute to ACLinjury neuromuscular function (strength and activation) of thehip musculature has received increased attention because it isessential to providing proximal stability for lower extremitymotion2bull3 Neuromuscular deficits may compromise the stabil-ity of the hip when it is loaded during weight bearing resultingin faulty dynamic alignment of the lower extremity and poten-tially increasing the risk of injury Authors4-l0 of retrospectivestudies have reported decreased strength and activation of the









METHODS









Strength Assessment




Kinematic Analysis

















Naviculardrop

Pelvicangle

Femoralanteversion

Quadricepsangle

Tibiofemoralangle

Genurecurvatum


RESULTS









Joint excursion 0









Naviculardrop

Pelvicangle

Femoralanteversion

Tibiofemoralangle






Naviculardrop

Pelvicangle

Femoralanteversion

Tibiofemoralangle

DISCUSSION






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ACKNOWLEDGMENTS


REFERENCES


































































METHODS









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Kinematic Analysis

















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Femoralanteversion

Quadricepsangle

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Genurecurvatum


RESULTS









Joint excursion 0









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REFERENCES






























































Strength Assessment




Kinematic Analysis

















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Pelvicangle

Femoralanteversion

Quadricepsangle

Tibiofemoralangle

Genurecurvatum


RESULTS









Joint excursion 0









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REFERENCES








































































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Pelvicangle

Femoralanteversion

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Genurecurvatum


RESULTS









Joint excursion 0









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RESULTS









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CONCLUSIONS



ACKNOWLEDGMENTS


REFERENCES




























































maxac-


CONCLUSIONS



ACKNOWLEDGMENTS


REFERENCES




























































































Date post:	15-Nov-2023
Category:	Documents
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A preliminary multifactorial approach describing the relationships among lower extremity alignment,...

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