PHYS THER 2012 Stevens Lapsley 210 26

7/21/2019 PHYS THER 2012 Stevens Lapsley 210 26

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doi: 10.2522/ptj.20110124

Originally published online November 17, 20112012; 92:210-226.PHYS THER.

Wolfe, Donald G. Eckhoff and Wendy M. KohrtJennifer E. Stevens-Lapsley, Jaclyn E. Balter, PamelaKnee Arthroplasty: A Randomized Controlled TrialImprove Quadriceps Muscle Strength After TotalEarly Neuromuscular Electrical Stimulation to

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Early Neuromuscular ElectricalStimulation to Improve Quadriceps

Muscle Strength After Total KneeArthroplasty: A RandomizedControlled TrialJennifer E. Stevens-Lapsley, Jaclyn E. Balter, Pamela Wolfe, Donald G. Eckhoff,

Wendy M. Kohrt

Background. The recovery of quadriceps muscle force and function after totalknee arthroplasty (TKA) is suboptimal, which predisposes patients to disability with

increasing age.

Objective. The purpose of this investigation was to evaluate the efficacy ofquadriceps muscle neuromuscular electrical stimulation (NMES), initiated 48 hoursafter TKA, as an adjunct to standard rehabilitation.

Design. This was a prospective, longitudinal randomized controlled trial.

Methods. Sixty-six patients, aged 50 to 85 years and planning a primary unilateralTKA, were randomly assigned to receive either standard rehabilitation (control) orstandard rehabilitation plus NMES applied to the quadriceps muscle (initiated 48hours after surgery). The NMES was applied twice per day at the maximum tolerableintensity for 15 contractions. Data for muscle strength, functional performance, and

self-report measures were obtained before surgery and 3.5, 6.5, 13, 26, and 52 weeksafter TKA.

Results. At 3.5 weeks after TKA, significant improvements with NMES were foundfor quadriceps and hamstring muscle strength, functional performance, and kneeextension active range of motion. At 52 weeks, the differences between groups wereattenuated, but improvements with NMES were still significant for quadriceps andhamstring muscle strength, functional performance, and some self-report measures.

Limitations. Treatment volume was not matched for both study arms; NMES wasadded to the standard of care treatment. Furthermore, testers were not blindedduring testing, but used standardized scripts to avoid bias. Finally, some patients

reached the maximum stimulator output during at least one treatment session andmay have tolerated more stimulation.

Conclusions. The early addition of NMES effectively attenuated loss of quadri-ceps muscle strength and improved functional performance following TKA. Theeffects were most pronounced and clinically meaningful within the first month aftersurgery, but persisted through 1 year after surgery.

J.E. Stevens-Lapsley, PT, PhD,Physical Therapy Program, Depart-ment of Physical Medicine andRehabilitation, University of Colo-

rado, Mail Stop C244, 13121 E17th Ave, Room 3116, Aurora,CO 80045 (USA). Address allcorrespondence to Dr. Stevens-Lapsleyat:[email protected].

J.E. Balter, MS, Physical TherapyProgram, Department of PhysicalMedicine and Rehabilitation, Uni-versity of Colorado.

P. Wolfe, MS, Department of Pre-ventive Medicine and Biometrics,University of Colorado.

D.G. Eckhoff, MD, Departmentof Orthopedics, University ofColorado.

W.M. Kohrt, PhD, Division ofGeriatric Medicine, University ofColorado.

[Stevens-Lapsley JE, Balter JE,Wolfe P, et al. Early neuromuscularelectrical stimulation to improvequadriceps muscle strength aftertotal knee arthroplasty: a random-ized controlled trial. Phys Ther.2012;92:210226.]

2012 American Physical TherapyAssociation

Published Ahead of Print:November 17, 2011

Accepted: September 30, 2011Submitted: April 19, 2011

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Osteoarthritis (OA) is a chronicdegenerative joint diseasethat compromises the quality

of life of more than 50 million Amer-icans.1 To alleviate pain and disabil-

ity associated with knee OA, morethan 687,000 total knee arthroplas-ties (TKAs) are performed each yearin the United States.2 Future projec-tions suggest that by the year 2030,3.48 million TKAs will be performed

yearly.3 Although TKA reliablyreduces pain and improves functionin older adults with knee OA, therecovery of quadriceps muscle force

and function is suboptimal and pre-disposes patients to disability withincreasing age.4 6

One month after TKA, quadricepsmuscle strength drops 50% to 60% ofpreoperative levels, despite the initi-ation of rehabilitation within 48hours after surgery.79 Even 6 to 13

years after surgery, quadriceps mus-cle weakness persists in people withTKA compared with people who arehealthy.10 Lower-extremity muscle

weakness, particularly in the quadri-ceps muscle, has profound func-

tional consequences, especially inolder individuals. Quadriceps muscle

weakness has been associated with

decreased gait speed, balance, stair-climbing ability, and ability to risefrom a seated position, as well as

with an increased risk for falls.1117

Effective rehabilitation strategies toaddress quadriceps muscle weaknessafter TKA should target the sourcesunderlying early quadriceps muscle

weakness. One month after TKA,impairments in quadriceps musclestrength are predominantly due todeficits in voluntary activation (alsoreferred to as reflex inhibition),but also are influenced, to a lesserdegree, by muscle atrophy.7 Althoughthe neurophysiologic mechanisms forquadriceps muscle voluntary activa-

tion deficits are not fully understood,spinal reflex activity from swelling orpain in the knee joint may alter affer-

ent input from the injured joint andresult in diminished efferent motordrive to the quadriceps muscle thatreduces muscle strength. Neuromus-cular electrical stimulation (NMES)

offers an innovative approach topotentially mitigate quadriceps musclevoluntary activation deficits and pre-vent muscle atrophy early after sur-gery to restore normal quadricepsmuscle function more effectively than

voluntary exercise alone.1821 Severevoluntary activation deficits may limitimprovements in muscle strength inresponse to rehabilitation that uti-

lizes voluntary exercise,22 possiblybecause of the inability to generatemuscle contractions of sufficient

intensity to promote strength gains.Neuromuscular electrical stimula-tion has the potential to override vol-untary activation deficits and mayeven help re-educate the quadricepsmuscle to contract normally. Yet,

previous investigations of NMESapplication in an outpatient setting(23 times per week) have resulted

in conflicting evidence in favorof2023 and against24,25 benefits oftreatment. Early intervention withintensive NMES may offer greaterbenefits than the initiation of NMES 1

month after TKA26

because it may beeasier to prevent the decline of mus-cle function after surgery than toreverse losses after they occur.

The purpose of this investigationwas to evaluate the efficacy of quad-riceps muscle NMES, initiated 48hours after TKA, as an adjunct tostandard rehabilitation in a random-

ized controlled trial. We hypothe-sized that NMES would attenuatequadriceps muscle strength loss by

decreasing voluntary activation defi-cits and result in better functionalperformance outcomes when com-pared with standard rehabilitation.

MethodDesign OverviewThis was a randomized, controlled,parallel-group intervention trial to

The Bottom Line

What do we already know about this topic?

Quadriceps femoris muscle weakness after total knee arthroplasty is

profound and often persists years after surgery. Early quadriceps weak-

ness is largely attributed to deficits in muscle activation. This weakness

has major functional consequences, especially in older patients.

What new information does this study offer?

According to this randomized controlled trial, daily application of neuro-

muscular electrical stimulation can help override deficits in quadriceps

femoris muscle activation and attenuate loss of quadriceps strength wheninitiated within the first week after total knee arthroplasty.

If youre a patient or a caregiver, what might thesefindings mean for you?

Using neuromuscular electrical stimulation early after total knee arthro-

plasty surgery may improve your ability to perform activities such as

walking and stair climbing. Although you may require a few sessions to get

used to the stimulation, many people learn to tolerate the stimulation

well.

Quadriceps Muscle Strengthening After Total Knee Arthroplasty

February 2012 Volume 92 Number 2 Physical Therapy f 211

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evaluate the benefits of adding NMESto a postoperative rehabilitation pro-gram. Eligible patients were ran-domly assigned with concealedallocation to either an NMES inter-

vention arm or a control interven-tion. Randomization included strati-fication for sex and decade of age.Participants were assessed 1 to 2

weeks preoperatively and at 3.5, 6.5,13, 26, and 52 weeks postoperativelyat the Clinical Translational ResearchCenter of the University of Colorado.Informed consent was obtained fromall participants.

Setting and ParticipantsPatients who underwent a primary

unilateral TKA by 3 orthopedic sur-geons at the University of ColoradoHospital were consecutively recruitedbetween June 2006 and June 2010.

Volunteers were recruited by referralor advertisement at preoperative edu-

cational sessions. All patients under-went a tricompartmental, cementedTKA with a medial parapatellar surgi-cal approach.

Patients were included if they were

aged 50 to 85 years. Exclusion crite-ria were uncontrolled hypertension,uncontrolled diabetes, body mass

index (BMI) greater than 35 kg/m2,significant neurologic impairments,contralateral knee OA (as defined bypain greater than 4/10 with activity),or other unstable lower-extremityorthopedic conditions.

Randomization andInterventions

Blocked randomization was used toensure balanced assignment of par-ticipants to the 2 interventiongroups by sex and decade of age,

with random block sizes of 4, 6, or 8.Group assignment occurred afterenrollment criteria were met andprior to the preoperative testing ses-sion. Testers were not blinded to

group assignment because resourcesdid not permit the hiring of separatepersonnel for testing and subsequent

evaluation of NMES dose to ensureproper use of the NMES device. Stan-dardized scripts and methods wereused to eliminate bias with testing.

Following surgery, standard inpa-tient rehabilitation began on postop-erative day 1 (Fig. 1) and continuedtwice daily for 3 days. All patients

were provided the same standardrehabilitation protocol for TKA, con-sisting of a defined set of core exer-cises, as previously described.27

Following hospital discharge, par-

ticipants received 6 treatments athome over 2 weeks and thenreceived 10 to 12 outpatient physical

therapy visits (Fig. 1). All homehealth and outpatient physical ther-apists followed a standardized reha-bilitation protocol as previouslydescribed27 and were not aware ofgroup assignment (Appendix). Exer-

cises consisted of knee passive rangeof motion (PROM) stretching; patel-lofemoral mobilization (as needed);incision mobility; cycling for rangeof motion (ROM); lower-extremityflexibility exercises for the quadri-

ceps, calf, and hamstring muscles;modalities (ice or heat as needed);gait training; and functional training

for transfers and stair climbing. Forstrengthening, both weight-bearingand nonweight-bearing exercises

were initiated with 2 sets of 10 rep-etitions and progressed to 3 sets of10 repetitions. Weights for the resis-tive exercises described below wereincreased to maintain a 10-repetitionmaximum intensity level such that

participants felt maximally fatiguedafter each set. If participants couldcomplete 11 consecutive repeti-tions, therapists were instructed toincrease resistance with the exer-cise. Resistive exercises consistedof seated knee extensions, straightleg raises, side-lying hip abduction,and standing hamstring muscle curls.

Body-weight exercises consistedof step-ups, lateral step-ups, step-downs (5- to 15-cm step), terminal

knee extensions, single-limb stance,and wall slides.

All participants were given a homeexercise program to be performed

twice daily during the acute phase ofrecovery (first 30 days) and thendaily until discharge from therapy.The home exercise programincluded ROM exercises and weight-bearing and nonweight-bearingstrengthening exercises for the quad-riceps, hamstring, hip abductor, hipextensor, and plantar-flexor muscles.The intensity and type of exercises

for the home program were similarto those performed during the super-

vised home and outpatient physical

therapy sessions.

Physical therapists reported treat-ment session details via a detailedflow sheet that was reviewed by thestudy team to monitor consistency of

treatment. Participants also weregiven home exercise logs and wereasked to track their progress withhome exercises.

A portable Empi 300PV stimulator

(Empi Inc, a DJO Global company, StPaul, Minnesota) was used for theNMES intervention because this

device has been found to producelevels of average peak torque com-parable to those produced by the

VersaStim 380 clinical stimulator(Electro-Med Health Industries,Miami, Florida) at comparable levelsof discomfort in previous NMESinvestigations,21,2830 but the latterstimulator is not practical for home

use.

During treatment, the lower limbwas secured by Velcro straps (VelcroUSA Inc, Manchester, New Hamp-shire) to a stable chair to allow forapproximately 85 degrees of hipflexion and 60 degrees of knee flex-ion. Self-adherent, flexible rectangu-

lar electrodes (7.6 12.7 cm, Super-trodes, SME Inc, Wilmington, NorthCarolina) were placed on the distal





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medial and proximal lateral portionsof the anterior thigh and markedto ensure consistent reapplication bythe participant (Fig. 1). Electrodesize for NMES is important becauseit has a direct effect on the density ofthe current. Small electrodes resultin a high current density and can

cause painful stimulation beforereaching a sufficient muscle contrac-tion to allow for muscle strengthen-

ing.31 Selection of appropriate elec-trode size, therefore, is essential forcomfortable stimulation, and appli-cation of the electrode over themotor point of the muscle reducesthe current threshold required. Inthe present study, we used large,rectangular electrodes to maximize

tolerance to treatment.

Neuromuscular electrical stimula-tion from the portable electricalstimulator was applied to the restingmuscle, and the participant wasinstructed to relax during theinduced muscle contraction. Theintensity was set to the maximalintensity tolerated during each ses-

sion, and participants were repeat-edly encouraged to increase theintensity as tolerated. The stimulator

Figure 1.Study treatment and testing session timeline. All participants received a similar inpatient, home, and outpatient physical therapy (PT)regimen. The neuromuscular electrical stimulation (NMES) intervention group also received 6 weeks of NMES treatment at home,which started 2 days after total knee arthroplasty (TKA) surgery (NMES setup pictured). Participants completed 6 testing sessions(preoperatively [pre-op] and 3.5, 6.5, 13, 26, and 52 weeks postoperatively [post-op]). The week 3.5 and week 6.5 time pointsrepresent the midpoint and completion of the NMES intervention, respectively, for the NMES group.





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was set to deliver a biphasic cur-rent, using a symmetrical wave-form, at 50 pps for 15 seconds(including a 3-second ramp-uptime) and a 45-second off time

(250-microsecond pulse duration).

This intervention began 48 hoursafter surgery in patients assigned tothe NMES group. A total of 15 NMESrepetitions were performed duringeach session, twice a day for 6 weeksafter TKA (Fig. 1). Initial familiariza-tion with the NMES device (EMPI300PV stimulator) occurred during

preoperative testing to facilitateapplication of NMES early after sur-gery. Participants used the NMES

unit a few times at home prior tosurgery to become familiar with thedevice. An emphasis was placed onthe importance of using the stimula-tor at an intensity that was tolerable,but slightly uncomfortable, although

there was no minimum intensityrequired for the study protocol. Inaddition, participants were repeat-edly instructed to continue toincrease the intensity as much as tol-erated within and between sessions.

Most participants demonstrated safeand proper use of the stimulator inthe hospital. When there were con-

cerns about patient implementationor tolerance to NMES, a study phys-ical therapist paid a home visit

within the first week of discharge tomonitor a home treatment session.The EMPI 300PV stimulator has anadherence meter to verify the accu-racy of patient reporting. Partici-pants also were given paper logs to

track adherence.

Outcome Measures andFollow-upIsometric quadriceps muscletorque and activation testing.Isometric quadriceps muscle torque(primary outcome) and activationtesting was performed using a dou-

blet interpolation test, as describedpreviously.27,32,33 A HUMAC NORMelectromechanical dynamometer

(CSMi, Stoughton, Massachusetts)was utilized to measure torque. Datawere collected using a Biopac DataAcquisition System at a sampling fre-quency of 2,000 samples per second

(Biodex Medical Systems Inc, Shir-ley, New York) and analyzed usingAcqKnowledge software, version3.8.2 (Biodex Medical Systems Inc).

Participants were positioned in anelectromechanical dynamometer sta-bilized with 60 degrees of knee flex-ion. They were asked to perform amaximal voluntary isometric con-

traction (MVIC) of the quadricepsmuscles using visual and verbal feed-back. Testing was repeated up to 3

times, with 1 minute of rest betweentrials, until 2 attempts were within5% of each other. The trial with thelargest maximal volitional isometricforce output then was normalized toeach participants body weight (in

kilograms) and used for data analysis.A Grass S48 stimulator with a Grassmodel SIU8T stimulus isolation unit(Grass Instrument Co, West War-

wick, Rhode Island) was utilized fortesting voluntary muscle activation

via self-adherent, flexible electrodes(7.6 12.7 cm, Supertrodes). Withthe participant seated and the

muscle relaxed, the intensity of stim-ulation was set using a 2-pulse,600-microsecond pulse duration,100-pps electrical train by increasingthe output in 10-V increments untilthe electrically induced torquereached a plateau (supramaximaldoublet in resting muscle). Volun-tary activation of the quadriceps

muscle was assessed using the dou-blet interpolation technique, wherea supramaximal stimulus wasapplied during an MVIC and again,immediately afterward, while thequadriceps muscle was at rest.27,32,33

A value of 100% represents full vol-untary muscle activation, and any-thing less than 100% represents

incomplete motor unit recruitmentor decreased motor unit dischargerates.3234 Normalization of the

torque from the superimposed dou-blet to the resting doublet allows forcomparisons of quadriceps muscleactivation across individuals andlower extremities.

Isometric hamstring muscletorque. Isometric hamstring mus-cle torque was measured using thesame positioning described above,although no hamstring muscle acti-

vation testing was performed. Thetrial with the largest maximal voli-tional isometric force output wasused and was normalized to the par-

ticipants body weight (in kilograms)for analysis.

NMES dose assessment. TheNMES training intensity (dose) wasassessed at week 3.5 and week 6.5testing sessions for participants inthe NMES group. While seated in theelectromechanical dynamometer,

participants were asked to use theirNMES stimulator at the same inten-sity used at home. The average elec-trically elicited (rather than volun-tary) torque while the stimulator wason was recorded across 15 contrac-

tions. This average torque then wasexpressed as a percentage of thequadriceps muscles MVIC during

the preoperative session to minimizethe potential for activation deficits toconfound torque measurements.

Functional performance mea-sures. Measures of functional per-formance included the Timed Up &Go Test (TUG), the Stair-ClimbingTest (SCT), and the Six-Minute Walk

Test (6MWT). The TUG measuresthe time to rise from an armchair,walk 3 m, turn around, and returnto sitting in the same chair withoutphysical assistance.35 The minimaldetectable change associated withthe 90% confidence interval (MDC90)for the TUG in patients 1.5 monthsafter TKA is 2.49 seconds.36 The SCT

measures the total time to ascend aflight of stairs, turn around, anddescend. Participants were tested on





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1 of 2 staircases during the study dueto a change in facilities. Nine par-ticipants in the control group and 8participants in the NMES group wereconsistently tested on a 10-step stair-

case with 17.14-cm (6.75-in) stepheight. All other participants weretested on a 12-step staircase with17.14-cm step height. This differ-ence did not affect analysis because

within-subject changes were mea-

sured over time. The MDC90for thismeasure has been estimated atbetween 2.6 and 5.5 seconds in

patients recovering from TKA,depending on the time pointassessed and number of stairs.36,37

The 6MWT measures the total dis-tance walked (in meters) over 6 min-utes. This test has been used exten-sively to measure endurance and hasbeen validated as a measure of func-tional mobility following knee

arthroplasty.38

The 6MWT has excel-lent test-retest reliability, with intra-class correlation coefficients rangingfrom .95 to .97, and a low coefficientof variation (10.4%).39 The MDC90for the 6MWT is 61.34 m in patients1.5 months after TKA.36 Participantsalso were asked to wear a pedometer(Accusplit AE120XL Pedometer,

Steps Only, Accusplit, Livermore,California) prior to TKA surgery toevaluate baseline levels of physical

activity (Tab. 1).40 The pedometerwas secured to the waist and wornfor 3 consecutive days, from whichthe average number of steps per day

was calculated.

Pain. Pain was measured utilizingan 11-point verbal numeric pain rat-ing scale. Participants were asked torate their pain on a scale of 0 to 10,

with 0 representing no pain and 10

representing worst pain imaginable.

ROM. Active range of motion(AROM) of the knee was measuredin the supine position using a long-arm goniometer as previouslydescribed.41 For active knee exten-sion, the heel was placed on a10.16-cm (4-in) block, and the partic-ipant was instructed to activelyextend the knee. For active knee flex-ion, the participant was instructed to

actively flex the knee as far as possi-ble while keeping the heel on thesupporting surface. Throughout thisreport, negative values of extensionrepresent hyperextension.

Health status questionnaires.Health status was assessed using thePhysical Component Score (PCS)

and Mental Component Score (MCS)of the 36-Item Short-Form HealthSurvey questionnaire (SF-36). The

SF-36 has been shown to captureimprovements in 7 of its 8 domainsin patients after TKA in the first 3months after surgery42 and continuesto indicate improvements in health-

related quality of life over the next6 to 12 months.43 The SF-36 is reli-able and internally consistent.4345

The Western Ontario and McMasterUniversities Osteoarthritis Index

(WOMAC) was used to evaluateself-report of knee-specific impair-ment.46 It assesses the pain, joint

stiffness, and physical, social, andemotional function of a person withOA to determine the overall level ofdisability. The WOMAC is a valid, reli-able, and responsive self-administeredinstrument that can be used for short-term and long-term follow-up of kneeinjury, including OA.46

Participants were asked to rate theirperception of knee functional abilityon a global rating scale (GRS) of 0 to100. A score of 0 represented com-plete disability, and a score of 100represented a level of knee functionbefore the individual had any OAsymptoms.47,48

Data AnalysisThe study was designed to achieve90% power to detect the effects of

Table 1.Baseline Characteristics of the Intervention and Control Groupsa

Variable

NMES Group Control Group

Pbn % n %

Women 20 57.1 16 51.6 .65

Men 15 42.9 15 48.4

n X (SD) n X (SD) Pb

Age (y) 35 66.2 (9.1) 31 64.8 (7.7) .49

Height (cm) 35 168.9 (9.3) 31 169.6 (9.6) .77

Weight (kg) 35 78.0 (17.4) 31 90.0 (17.0) .01

BMI (kg/m2) 35 27.1 (4.9) 31 31.2 (4.2) .001

Pedometer (steps/day) 25 5,133 (3,109) 18 4,842 (3,757) .79

a NMESneuromuscular electrical stimulation, BMIbody mass index.b Pvalues are based on chi-square test for independent proportions or a 2-sided, 2-group ttest for difference in group means. Baseline data include allpatients who were randomized preoperatively.





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the intervention 3.5 weeks after TKAwith 25 participants per group. Theprimary outcome measure, differ-ence in quadriceps muscle torquebetween intervention (NMES) andusual care (control) at 3.5 weeks,

was tested using an analysis of cova-riance model; the 3.5-week change

from baseline was regressed on sex,age, and baseline quadriceps muscletorque with 59 complete cases (28 inthe NMES group, 31 in the controlgroup). Confirmatory measures wereevaluated at 3.5 weeks after surgeryin the same way. Baseline character-istics of the treatment groups werecompared using 2-sample t tests for

continuous measures or a chi-squaretest for independent proportions forcategorical measures.

A secondary aim of the study was toevaluate the long-term sustainabilityof the effects of NMES. Differencesin all outcomes at 3.5, 6.5, 13, 26,and 52 weeks after TKA were evalu-ated using maximum likelihood esti-mation of a multivariate, repeated-measures, mixed-effects model using

all available data. This approach isconceptually identical to repeated-measures analysis of variance, butavoids the case-wise deletion of par-ticipants with missing assessments.The maximum likelihood methodprovides unbiased estimates underthe assumption that missing data aremissing at random.49

SAS version 9.2 (SAS Institute Inc,Cary, North Carolina) was used for

all statistical analyses. All analyseswere intention-to-treat and did notadjust for nonadherence or intoler-ance to NMES. A 2-sided alpha levelof .05 was designated for statisticalsignificance.

Role of the Funding Source

This study was supported by theNational Institute of Aging(K23AG029978), an American Col-lege of Rheumatology New Investi-gator Award, the Foundation forPhysical Therapy Marquette Chal-lenge Grant, and Clinical and Trans-lational Science Award Grant (UL1RR025780). A peer-reviewed research

grant from Empi Inc, a DJO Globalcompany, was used for the purchaseof 300PV electrical stimulators and

Assessed for eligibility (N=526)

Randomized (n=66)

Unable to contact (n=59)Declined participation (n=36)Did not meet inclusion criteria (n=365)

Lost to follow-up (n=2)- infection in the knee (n=1)- C-Diff infection (n=1)

Lost to follow-up (n=4)- post-op complication (n=1)- DVT (n=1)- severe sciatica (n=1)- declined participation (n=1)

Lost to follow-up (n=2)- unable to schedule (n=2)

Lost to follow-up (n=1)- patient moved away (n=1)

Lost to follow-up (n=2)- TKA revision (n=1)- patient moved away (n=1)

52 wk

26 wk

13 wk

6.5 wk

3.5 wk

Pre-OP Control Group (n=31)

Control Group (n=31)



NMES Group (n=31)

NMES Group (n=31)

NMES Group (n=31)

NMES Group (n=31)

NMES Group (n=35)

NMES Group (n=30)



Figure 2.Recruitment, enrollment, and adherence of study participants. Enrollment numbers and withdrawals or those lost to follow-up areindicated in the boxes between time points. Overall, the total number of participants lost to follow-up through 52 weeks were 5 inthe neuromuscular electrical stimulation (NMES) group and 6 in the control group. DVTdeep venous thrombosis, TKAtotal knee

arthroplasty, C-Diffclostridium difficile, pre-oppreoperatively, post-oppostoperatively.





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recruitment/transportation costs forpatient visits. None of the sponsorshad any influence on the study design,

implementation, or data analysis andinterpretation.

ResultsFive hundred twenty-six patientsscheduled for TKA at the Universityof Colorado Hospital were assessedfor eligibility. Fifty-nine patients

were unable to be contacted, 365

did not meet the inclusion criteria,and 36 declined to participate. Ofthose who were ineligible, 11% werenot between the ages of 50 to 85

years, 13% had a BMI of greater than35 kg/m2, 31% had moderate tosevere contralateral pain or stagedTKAs within 6 months of each other,7% had other orthopedic conditions

that limited their function, 8% weresmokers, 7% had uncontrolled diabe-tes or neuropathy, and 23% had

other health conditions (eg, neuro-logical, cardiovascular). Therefore,66 patients (30 male, 36 female)

were enrolled in the study (Fig. 2).There were no differences betweengroups in sex, age, or height, butdifferences in weight and BMI werepresent (Tab. 1). There were nogroup differences in baseline self-reported and performance measures

with the exception of SF-36 PCS(Tab. 2). There were no adverse

events resulting from participationin the study in either group.

Raw data for strength and functionalperformance outcome measuresat all time points are presented inTable 3. At the 3.5-week visit, theNMES group had significantly greaterimprovements than the control group

in quadriceps and hamstring musclestrength; TUG, SCT, 6MWT, and GRSscores; and extension AROM (Tab. 2,

Fig. 3). Quadriceps muscle activationtended to be greater with NMES(P.09). No differences between

groups were noted for changes inthe SF-36 (MCS and PCS) and

WOMAC scores.

At 52 weeks after TKA, between-group differences were attenuated,but remained significant (ie, favoringNMES) for quadriceps and hamstringmuscle strength and TUG, SCT,

6MWT, GRS, SF-36 MCS, andWOMAC scores; improvement inactive extension ROM tended to bebetter in NMES (P.08). There wereno differences in SF-36 PCS scoresbetween groups.

The NMES dose ranged from 1.6% to76.7% of the preoperative MVIC

(mean [SD]: 16.1% [14.8%] at 3.5weeks; 17.7% [11.3%] at 6.5 weeks).Adherence to NMES treatment is rep-

Table 2.Mean Changes and 95% Confidence Intervals for the Primary and Secondary Outcome Measures at 3.5 Weeks(Primary Endpoint)a

Variable

Change From Baseline to

3.5 Weeks X (SE)bBetween-Group Difference in the

Change From Baseline

NMES Group Control Group Mean (95% CI) Pc

Normalized quadriceps muscle

strengthd (N-m/kg)

0.40 (0.05) 0.67 (0.06) 0.27 (0.12, 0.41) .001

Normalized hamstring muscle

strengthd (N-m/kg)

0.25 (0.03) 0.35 (0.04) 0.10 (0.01, 0.19) .04

Six-Minute Walk Test (m) 34.7 (15.5) 137 (18.3) 102.4 (58.1, 146.8) .001

Stair-Climbing Test (s) 8.9 (2.8) 22.2 (3.0) 13.3 (5.7, 21.0) .001

Timed Up & Go Test (s) 1.5 (0.6) 4.2 (0.7) 2.7 (1.0, 4.5) .003

Quadriceps muscle act ivation (%) 5.2 (3.3) 2.9 (3.7) 8.1 (1.2, 17.4) .09

Extension active range of motion () 2.2 (0.8) 5.2 (0.9) 3.0 (0.8, 5.2) .01

Flexion active range of motion () 26.4 (2.1) 25.5 (2.2) 0.9 (4.9, 6.8) .75

Global rating scale (points) 3.9 (3.3) 7.9 (3.8) 11.8 (2.0, 21.5) .02

SF-36 PCS (points) 0.0 (1.6) 1.1 (1.8) 1.1 (5.8, 3.6) .65

SF-36 MCS (points) 0.3 (1.6) 3.9 (1.8) 3.6 (0.9, 8.1) .12

WOMAC (points) 11.9 (2.7) 6.9 (2.9) 5.0 (12.4, 2.4) .18

Resting pain (points) 1.0 (0.4) 0.6 (0.4) 0.4 (1.4, 0.7) .50

a NMESneuromuscular electrical stimulation, CIconfidence interval, SF-3636-Item Short-Form Health Survey questionnaire, PCSPhysical ComponentScore, MCSMental Component Score, WOMACWestern Ontario and McMaster Universities Osteoarthritis Index.bValues are means standard error of the estimate. Negative values reflect a deficit from baseline; positive values reflect an improvement from baseline.c Pvalues are from the estimated between-group difference in change from baseline, conditioned on baseline. The model is change from baseline regressedon baseline and treatment assignment.d Normalized to weight.





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Time PointTime Point

Time Point Time Point

Time PointTime Point

Pre-op

3.5wk

6.5wk

13wk

26wk

52wk

Pre

-op

3.5wk

6.5wk

1

3wk

2

6wk

52wk

Pre-op

3.5wk

6.5wk

13wk

26wk

52wk

Pre-op

3.5wk

6.5wk

13wk

26wk

52wk

Pre

-op

3.5wk

6.5wk

13wk

2

6wk

52wk

Pre-op

3.5wk

6.5wk

13wk

26wk

52wk

* * * * * * * * *

*****

45

40

35

30

25

20

15

10

5

Time(s)

Time(s)

D

NMES

Control

A

NormalizedTorque(N-m/kg)

NormalizedTorque(N-m/kg)

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

B

* * *1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

E

16

14

12

10

8

6

4

95

90

Activation(%)

85

80

70

75

65

C F

* * * *

Distance(m)

600

550

500

450

400

350

300

250

Figure 3.Changes in strength and functional performance over time (mean standard error of the mean) in the neuromuscular electricalstimulation (NMES) group (black circles) and the control group (white circles): (A) quadriceps femoris muscle maximum voluntaryisometric contraction (MVIC) normalized to body weight, (B) hamstring muscle MVIC normalized to body weight, (C) quadricepsmuscle central activation, (D) Stair-Climbing Test, (E) Timed Up & Go Test, (F) Six-Minute Walk Test. Significant differencesbetween groups are indicated by asterisks (P.05). Pre-oppreoperatively.





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resented in Table 4. The average

(SD) intensity of stimulation was83.7 (3.1) mA at 3.5 weeks and 82.1(3.3) mA at 6.5 weeks). These find-

ings generally corresponded to amuscle contraction that was at leastequivalent to that achieved during astraight leg raise. Ten participants(32.3%) reached the limiting voltageof the stimulator (100 mA) during at

least 1 week of treatment; 3 partici-pants set the stimulator at 100 mAfor all 6 weeks of treatment.

DiscussionThe addition of NMES treatment to

the quadriceps muscles effectivelyattenuated loss of quadriceps musclestrength and improved functional

performance following TKA.Although the effects were most pro-nounced and clinically meaningful

within the first month after sur-gery,36,33 benefits persisted through1 year after surgery. Notably, 3.5

weeks after TKA, NMES applicationsubstantially attenuated loss of quad-riceps muscle strength (67% loss in

control group and 40% loss in NMESgroup). This finding translated intoeven greater attenuation of func-tional performance deficits, withchanges in the 6MWT distance at 3.5

weeks being the most notable (lossof 137 m in the control group andloss of 34.7 m in the NMES group).Self-report measures of physical

function (SF-36, WOMAC) did notdemonstrate early improvements

with NMES treatment, whereas

performance-based measures of

physical function (TUG, SCT,6MWT) did show improvements.These findings were expected

because patient perception fails tocapture the acute functional declinesafter TKA and may overstate thelong-term functional improvement

with surgery, largely becausepatient-reported outcomes typically

parallel pain relief after surgery.48,50

In 2003, a National Institutes ofHealth consensus statement on totalknee replacement stated that theuse of rehabilitation services is per-

haps the most understudied aspectof the perioperative management ofTKA patients.51(p15)Yet, since 2003,

few studies have provided additionalguidelines for evidence-based reha-bilitation following TKA.52 Onelarge-scale clinical trial with a pro-gressive exercise program involving6 weeks of outpatient physical ther-apy 2 to 3 times per week demon-strated a 38% faster SCT time, a 17%increase in 6MWT distance, and a

24% increase in quadriceps musclestrength 1 year after TKA comparedwith standard care.24 These findingswere despite the fact that the pro-gressive component of the interven-tion was initiated 3 to 4 weeks afterTKA, when large strength and func-tional losses had already occurred.Using rehabilitation strategies such

as NMES immediately after surgerymay be more effective because pre-

venting the decline of muscle func-

tion early after surgery is likely to be

more effective than working toreverse losses after they occur.Importantly, the aforementioned

investigation24 also used NMES forone treatment arm 2 times per week(10 contractions per session) andshowed no added benefits in quadri-ceps muscle strength or functionalperformance. Although the average

dose of NMES was greater than thatof the present study, it is possiblethat the frequency of NMES applica-tion (2 times per week) may nothave been sufficient to inducechanges or that the initiation of

NMES was too late to capitalize onthe early marked deficits in quadri-ceps muscle activation.

Other studies indicate that NMESholds promise for restoring musclefunction after TKA.23,53,54 Avramidiset al23 found a significant increase in

walking speed in response to 6weeks of daily NMES treatment (4hours per day) to the quadricepsmuscle compared with controls at 6

weeks after TKA. There was a carry-over in faster walking speed withNMES at 12 weeks postoperatively,

which is likely secondary to an ini-tially faster recovery of quadricepsmuscle strength and subsequentability to participate more fully inthe voluntary exercise program.

Although that investigation demon-

strated benefits of NMES application,the length of daily NMES treatment(4 hours per day) may be problem-

Table 4.Treatment Adherence During the 6-Week Interventiona

Treatment Adherence

No. of NMES Group Participants (% of Total Participants)

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Overall

Adherent (80%) 26 (83.9%) 26 (83.9%) 24 (77.4%) 19 (61.3%) 20 (64.5%) 18 (58.1%) 24 (77.4%)

Partially adherent (50%80%) 4 (12.9%) 3 (9.7%) 6 (19.4%) 7 (23%) 6 (19.4%) 6 (19.4%) 6 (19.4%)

Not adherent (50%) 0 (0.0%) 1 (3.2%) 0 (0.0%) 1 (3.2%) 1 (3.2%) 2 (6.5%) 0 (0.0%)

No records 1 (3.2%) 1 (3.2%) 1 (3.2%) 4 (12.9%) 4 (12.9%) 5 (16.1%) 1 (3.2%)

a Treatment adherence is reported as the number of participants, and the percentage of the total number of participants who received neuromuscularelectrical stimulation (NMES) is noted in parentheses. Treatment adherence was based on the percentage of expected home NMES treatment. Theexpectation was 15 contractions per session, 2 sessions per day, 67 days per week.





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atic in ensuring patient adherence tothe treatment. The present studysuggests that decreasing treatmenttime while encouraging a maximallytolerable intensity was even more

effective in attenuating loss of quad-riceps muscle strength and improv-ing functional performance than theaforementioned study. Gotlin et al55

studied the effects of NMES appliedwithin the first week after TKA andfound that NMES reduced kneeextensor lag from 7.5 to 5.7 degreescompared with controls, who had anincrease in extensor lag from 5.3 to

8.3 degrees in the same time frame.In addition, NMES decreased thelength of hospital stay from 7.4 to 6.4

days. Finally, when unilateral NMESwas initiated 3 to 4 weeks after bilat-eral TKA and continued for 6 weeks,quadriceps muscle activation andstrength increased 431% in the limbthat received NMES plus voluntary

exercise and only 182% in the con-tralateral limb with voluntary exer-cise alone.21 There is additional sup-port for the use of NMES in otherpatient populations with activationdeficits, such as anterior cruciate lig-

ament reconstruction, stroke, andcerebral palsy.20,5659

Although it has been difficult todetermine the underlying muscularand neural mechanisms responsiblefor improved muscle performance

with NMES, some theories haveemerged. The first is related to theintensity of the muscle contractionproduced during stimulation. Train-ing programs for people with mini-

mal activation deficits require train-ing intensities of at least 50% to 60% ofmaximal voluntary effort to overloadthe muscle sufficiently to inducehypertrophy, with higher intensitiesproducing greater hypertrophy.60,61

Similar to higher-intensity voluntarymuscle contractions, electrically elic-ited muscle contractions at high

intensities produce muscle hypertro-phy and corresponding increases instrength.29,59,62,63 In the present

study, the training intensities werelower than those expected to pro-duce muscle hypertrophy. As such,altered motor unit recruitment mayexplain some of the improvements

in muscle function. Electrically elic-ited muscle contractions allow foractivation of a greater proportion oftype II muscle fibers than volitionalexercise at comparable intensi-ty.6466 Type II muscle fibers arelarger than type I fibers, so greateractivation of these fibers amplifiesforce production.67 Evidence alsosuggests that NMES influences func-

tional measures of motor perfor-mance via peripheral afferent inputsthat alter motor cortex excitabili-

ty.6871 Stimulation of peripheralafferent nerves can induce pro-longed changes in the excitability ofthe human motor cortex, which mayhelp explain the improvements inmuscle function with NMES.70,71

There are some methodologicalissues to consider when using NMES,including the length of treatment,safety considerations, and patienttolerance. The length of NMES treat-

ment (ie, 6 weeks) in this study waschosen to maximize the potential forphysiological changes in the quadri-

ceps muscle to translate intoimprovements in functional perfor-mance, but it remains uncertain

whether the full 6 weeks is neces-sary because of the robust earlyresponse to NMES treatment. After 3

weeks, the trajectory of improve-ment was similar for both treatmentgroups. Early application of NMES

attenuated the magnitude of declineseen with controls, but whether 3additional weeks of application wasneeded to sustain improvements isless clear.

Safety is an important considerationwith the use of NMES in a homesetting. All participants demon-

strated independence with theNMES unit within the first week athome, although some required an

additional training session at hometo ensure safety and encourage tol-erance. Marking the electrode loca-tions on the thigh was important toensure proper electrode placement.

Additionally, familiarization with theNMES unit before surgery increasedpatient comfort with its applicationafter surgery. Although preoperativefamiliarization may not always bepossible, oversight by physical ther-apists in any setting (inpatient, homehealth, or outpatient) and encour-agement to tolerate as much stimu-lation as possible may be important

for similar outcomes and safe imple-mentation of this treatment. Anothersafety consideration is the use of

NMES in patients with pacemakers.Although none of the patients in thepresent study had pacemakers, theuse of NMES with a pacemaker iscontroversial because potential elec-tromagnetic interference may result

in pacemaker malfunction. Some evi-dence suggests that electrical stimu-lation of the quadriceps muscleposes no risk to pacemakers,72

whereas other evidence suggestspotential electromagnetic interfer-

ence with pacemaker function.73

Finally, tolerance to NMES treatment

may be an important determinant ofeffectiveness, as suggested by thedose-response relationship betweenthe amount NMES applied and thestrength gains following anterior cru-ciate ligament reconstruction.29

Therefore, a major emphasis ofNMES treatment for the presentstudy was to encourage patients to

apply NMES to their maximum toler-ance. The study team provided sub-stantial verbal encouragement topatients to regularly turn up theintensity of stimulation both withinand between treatment sessions.Our clinical observations of NMESapplication in some clinical settingshave shown that therapists often are

reluctant to push patients to tolerateuncomfortable doses of stimulation.Patients likely sense this hesitation,





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which limits the potential to see ben-efits of NMES treatment. Therefore,

we repeatedly educated patients ateach testing session regarding theimportance of tolerating the maxi-

mal dose possible. Nevertheless, fora handful of patients, the NMES dosewas very low despite substantialefforts to encourage greater toler-ance, suggesting that some patientsmay be better candidates than othersfor NMES treatment. Further investi-gation of the present study will eval-uate whether there is a dose-responserelationship in this population to fur-

ther guide clinical decision makingregarding which patients are thebest candidates for this treatment.

There were several limitations to thepresent study that should be consid-ered. The lack of matching treatment

volume in the control and NMESgroups could have contributed to dif-

ferences in the responses to treat-ment. We considered adding isomet-ric contractions of the quadricepsmuscle for controls in the sameseated position used for NMES, but

we felt that this approach was not

used clinically. Rather, we chose tocompare 2 accepted clinicalapproaches to treatment. Another

limitation of this investigation wasthe lack of blinding, although stan-dardized scripts and testing methods

were used. Neuromuscular electricalstimulation treatment applicationduring testing was important forassessing safety and adherence,pushing patient tolerance, and mea-suring dose of NMES application.

Baseline differences in BMI werepresent, but BMI does not affect nor-malized quadriceps muscle strengthor functional performance capabili-ties if it is less than 40 kg/m2.74 In thepresent study, lower BMI in theNMES group may have facilitatedtreatment success because NMEStreatment may be more effective for

individuals who have less impedancefrom adipose tissue in their thighs.Finally, 10 patients reached the max-

imum output of the stimulator, sug-gesting that the benefits of NMESmight have been even greater withstimulation at higher intensities.

ConclusionThe addition of quadriceps muscleNMES initiated within 48 hours after

TKA attenuated loss of quadricepsmuscle strength 3.5 weeks after TKAand improved functional perfor-mance; benefits of NMES treatmentpersisted through 1 year. Functionalperformance for the NMES group at1 year began to approach outcomesfor older adults who were healthy,tested using identical methods,9 yet

they still lagged behind in clinicallymeaningful differences in TUG, SCT,and 6MWT performance.36 Even thecontrol group in this study exceededoutcomes previously reported inthe literature,52 yet they lagged evenfurther behind adults who werehealthy compared with the NMESgroup. Therefore, further research

focused on early intervention afterTKA is warranted to continue tooptimize patient outcomes.

Dr Stevens-Lapsley, Ms Balter, Dr Eckhoff,and Dr Kohrt provided concept/idea/research design. Dr Stevens-Lapsley, Ms Bal-ter, and Ms Wolfe provided writing and dataanalysis. Dr Stevens-Lapsley and Ms Balterprovided data collection and project man-agement. Dr Stevens-Lapsley and Dr Kohrtprovided fund procurement. Dr Eckhoff pro-vided participants. Dr Stevens-Lapsley pro-vided facilities/equipment. Dr Eckhoff andDr Kohrt provided consultation (includingreview of manuscript before submission).

The authors acknowledge Dana Judd, PT,DPT, for assistance with patient testing and

treatment;Roger Enoka, PhD, John Kittelson,PhD, Margaret Schenkman, PT, PhD, andRobert Schwartz, MD, for consultation andguidance on research design and implemen-tation; Ben Shulman, BS, for statistical anal-

yses; and Tami Struessel, PT, DPT, for con-sultation and guidance on physical therapyinterventions. They also thank the physicaltherapists at the University of ColoradoHospital.

The study was approved by the ColoradoMultiple Institutional Review Board.

A portion of these results were presented atthe Combined Sections Meeting of the

American Physical Therapy Association; Feb-ruary 69, 2009; Las Vegas, Nevada.

This study was supportedby the National Institute

of Aging (K23AG029978),an American College of

Rheumatology New Investigator Award, theFoundation for Physical Therapy MarquetteChallenge Grant, and a Clinical and Transla-tional Science Award Grant (UL1RR025780).

A peer-reviewed research grant from EmpiInc, a DJO Global company, was used tosupport the purchase of 300PV electricalstimulators and recruitment/transportationcosts for patient visits.

Trial registration: ClinicalTrials.gov Identifier:NCT00800254.

DOI: 10.2522/ptj.20110124

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Appendix.Standardized Rehabilitation Protocol for Inpatient (Early), Home Health (Middle), and Outpatient (Late) Physical Therapy in

Addition to Home Neuromuscular Electrical Stimulation Treatmenta

Early Inpatient Rehabilitation Exercise Program

Postoperative day 1

Bedside exercises: ankle pumps, quadriceps sets, gluteal sets, hip abduction (supine), short-arc quads, straight leg raise

(if able) Knee ROM: heel slides

Bed mobility and transfer training (bed to and from chair)

Postoperative day 2

Exercises for AROM, active-assisted ROM, and terminal knee extension

Strengthening exercises (eg, ankle pumps, quadriceps sets, gluteal sets, heel slides, short-arc quads, straight leg raises,

supine hip abduction) 13 sets of 10 repetitions for all strengthening exercises, twice/day

Gait training with assistive device on level surfaces and functional transfer training (eg, sit to and from stand, toilet transfers,

bed mobility)

Postoperative days 35 (or on discharge to rehabilitation unit)

Progression of ROM with active-assisted exercises and manual stretching, as necessary

Progression of strengthening exercises to the patients tolerance, 13 sets of 10 repetitions for all strengthening exercises,

twice/day

Progression of ambulation distance and stair training (if applicable) with the least restrictive device

Progression of activities-of-daily-living training for discharge to home

NMES Treatment (Weeks 16)

Begin on postoperative day 2 For NMES group:15 electrically elicited contractions 2/day

NMES parameters:biphasic current, symmetrical waveform, 250-microsecond pulse duration, 50 pps for 15 seconds

(including a 3-second ramp-up time) and a 45-second off time

Middle Home Health Rehabilitation Exercise Program (Weeks 23)

ROM

Active-assistive ROM for knee flexion, sitting or supine, using other leg to assist

Passive knee extension stretch with manual pressure by physical therapist or weights

Patellar and knee mobilizations

Strength

Quad sets

Short-arc quads*

Straight leg raises (without quad lag)*

Hip abduction (side lying)*

Hamstring curls (standing)*

Sitting knee extension (long-arc quad)*

13 sets of 10 repetitions for all strengthening exercises; *maximal fatigue should occur after each set

Progression:*weights can be added if patient can complete the exercise and maintain control through 3 sets of 10

repetitions without increased pain or swelling

Functional activities

Gait training with assistive device, as appropriate, with emphasis on heel-strike, proper toe-off, and normal knee joint

excursions

Emphasis on heel-strike, proper toe-off, and normal knee joint excursions when able to walk without assistive device

Step-ups (5.8-cm [2-in] block)

Mini squats (30 of knee flexion)

Progression: step-ups (10.16-cm [4-in] block), mini squats to 45 of knee flexion

Pain and swelling

Ice and compression as needed

Incision mobility

Soft tissue mobilization until incision moves freely over subcutaneous tissue

NMES Treatment

For NMES treatment:continue NMES 2/day

(Continued)





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Appendix.Continued

Late Outpatient Rehabilitation Exercise Program (Weeks 48)

ROM

Exercise bike (1015 min), initiate with forward and backward pedaling and no resistance until enough ROM for full

revolution;progression: lower seat height to produce a stretch with each revolution

Knee flexion stretch: sitting (planting foot and scooting to edge of chair); standing (surgical extremity on a stair with stretch

into knee flexion)

Knee extension stretch with manual pressure (in clinic) or weights (at home)

Strength

Straight leg raises (without quad lag)*

Hip abduction (side lying)*

Hamstring curls (standing)*

Sitting knee extension*

13 sets of 10 repetitions for all strengthening exercises; maximal fatigue should occur after each set

Progression:*weights are to be progressed only once the patient can complete the exercise and maintain control through

3 sets of 10 repetitions without increased pain or swelling

Functional activities

Terminal knee extensions from 45 to 0

Gait training with emphasis on heel-strike, proper toe-off, and normal knee joint excursions without assistive device

Step-ups and step-downs (5.8- to 10.16-cm) with good concentric and eccentric control

Wall slides to 45 of knee flexion

Stair ascending and descending, step over step, when patient has sufficient concentric and eccentric strength Sit-to-stand repetitions with emphasis on eccentric control

Progression: increase step height for step-ups and step-downs to 15.24 cm (6 in) if demonstrating good concentric and

eccentric control, increase wall slides to 60 and 90 knee flexion, lower chair height for sit-to-stand

Pain and swelling

Ice and compression as needed

NMES Treatment

For NMES treatment:continue NMES 2/day until week 6

a ROMrange of motion, AROMactive range of motion, NMESneuromuscular electrical stimulation.





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doi: 10.2522/ptj.20110124Originally published online November 17, 2011

2012; 92:210-226.PHYS THER.Wolfe, Donald G. Eckhoff and Wendy M. KohrtJennifer E. Stevens-Lapsley, Jaclyn E. Balter, PamelaKnee Arthroplasty: A Randomized Controlled TrialImprove Quadriceps Muscle Strength After TotalEarly Neuromuscular Electrical Stimulation to

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