Neuromuscular Electrical Stimulation for
`Quadriceps Muscle Strengthening After
`Bilateral Total Knee Arthroplasty: A Case
`Series
`
`Jennifer E. Stevens, PT, PhD 1
`Ryan L. Mizner, MPT 2
`Lynn Snyder-Mackler, PT, ScD, ATC, SCS, FAPTA 3
`
`R E S E A R C H R E P O R T
`
`Study Design: A case series.
`Objectives: The purpose of this case series was to assess the effect of high-intensity neuromuscular
`electrical stimulation (NMES) on quadriceps strength and voluntary activation following total knee
`arthroplasty (TKA).
`Background: Following TKA, patients exhibit
`the quadriceps and
`long-term weakness of
`diminished functional capacity compared to age-matched healthy controls. The pain and swelling
`that results from surgery may contribute to quadriceps weakness. The use of high-intensity NMES
`has previously been shown to be effective in quickly restoring quadriceps strength in patients with
`weakness after surgery.
`Methods and Measures: All patients were treated for 6 weeks, 2 to 3 visits per week, in outpatient
`rehabilitation. Five patients (NMES group) participated in a voluntary exercise program for both
`knees and NMES for the weaker knee. Three patients (exercise group) participated in a voluntary
`exercise program for both knees without NMES. For each treatment session, 10 isometric
`electrically elicited muscle contractions were administered at maximally tolerated doses to the
`initially weaker
`leg of
`the NMES group. Quadriceps strength and muscle activation were
`repeatedly assessed up to 6 months after surgery using burst superimposition techniques.
`Results: At 6 months, the weak NMES-treated legs of 4 of 5 patients in the NMES group had
`surpassed the strength of the contralateral leg. In contrast, none of the weak legs in the exercise
`group were stronger than the contralateral
`leg at 6 months. Changes in quadriceps muscle
`activation mirrored the changes exhibited in strength.
`Conclusion: When NMES was added to a voluntary exercise program, deficits in quadriceps
`muscle strength and activation resolved quickly after TKA. J Orthop Sports Phys Ther 2004;34:21-
`29.
`Key Words: geriatric, inhibition, rehabilitation, total knee replacement
`
`1 Postdoctoral Associate, Department of Physical Therapy, University of Florida, Gainesville, FL. Dr.
`Stevens was a doctoral student, Biomechanics and Movement Science Program, University of Delaware,
`Newark, DE at the time of this study.
`2 Doctoral student, Biomechanics and Movement Science Program, University of Delaware, Newark, DE.
`3 Professor, Department of Physical Therapy and Biomechanics and Movement Science Program,
`University of Delaware, Newark, DE.
`This study was supported by NIH grant 1R01HD041055-01A1, NIH training grant T32 HD07490, and
`APTA Foundation Scholarships to Jennifer Stevens and Ryan Mizner (PODS). Research protocol was
`approved by the Human Subjects Review Committee at the University of Delaware.
`Please address all correspondence to Lynn Snyder-Mackler, Department of Physical Therapy, 301 McKinly
`Laboratory, University of Delaware, Newark, DE 19716. E-mail: smack@udel.edu
`
`Simultaneous bilateral to-
`
`arthroplasty
`knee
`tal
`(TKA) has become an in-
`creasingly common surgi-
`cal procedure for pa-
`with
`bilateral
`knee
`tients
`osteoarthritis or rheumatoid arthri-
`tis.1,5,9,20,21,23 Typically, patients are
`only permitted to undergo simulta-
`neous bilateral TKA if they are in
`excellent health due to the in-
`creased risk for complications
`from 2 surgical procedures (eg,
`longer anesthesia times).1,20,23
`When patients are appropriately
`chosen for
`the procedure, out-
`comes are comparable to patients
`who undergo a staged bilateral
`knee replacement,23 yet the total
`rehabilitation time is less.20
`Patients after TKA are often
`plagued with quadriceps
`femoris
`weakness and functional deficits
`that continue for years after sur-
`gery.2,4,15,39 These limitations
`in
`strength and function are thought
`to result
`from a combination of
`preexisting weakness before sur-
`gery
`and pain and swelling
`postsurgery.18,22,26 After bilateral
`TKA, patients are doubly affected
`by this persistent quadriceps weak-
`ness, which may result in serious
`functional
`limitations. Quadriceps
`weakness has been correlated with
`
`Journal of Orthopaedic & Sports Physical Therapy
`
`21
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`LUMENIS EX1015
`Page 1
`
`

`

`longer stair-climbing times,
`slower walking speeds,
`falls.8,40 One source of
`this
`and increased risk of
`weakness is voluntary activation deficits, which result
`from a failure of recruiting all available motor units
`or a reduction in the maximal motor unit discharge
`rate from those motor units which are recruited.19
`Voluntary activation deficit can be quantified by
`superimposing a supramaximal electrical stimulus on
`a maximally contracting muscle.10,19,34,36,37,41 Using
`this technique, voluntary activation deficits have been
`reported in patients with osteoarthritis or following
`including TKA.18,25,27,28,35 Voluntary
`knee surgery,
`activation deficits can result from pain,27 effusion,12
`and joint damage,16 all of which are potentially
`present
`in patients after TKA. Voluntary exercise
`programs have had limited success
`in restoring
`quadriceps
`strength when a substantial voluntary
`activation deficit is present.17
`Studies of various younger adult populations have
`demonstrated that neuromuscular electrical stimula-
`tion (NMES), at sufficient intensities, can be com-
`bined with volitional exercise to more effectively
`increase muscle strength and functional performance
`than volitional exercise alone.11,31,33 A recent case
`report
`suggested that
`incorporating high-intensity
`NMES into an outpatient rehabilitation program for
`muscle strengthening offers promise for restoring
`quadriceps strength.21 NMES has the potential
`to
`override muscle activation deficits
`resulting from
`impairments in central nervous system processing. In
`addition, NMES activates a greater proportion of type
`II (fast-twitch) muscle fibers when compared to
`volitional exercise at a comparable intensity.3,7,13,30,38
`Type II fibers are essential for higher levels of force
`production and their activation may translate to
`improved functional performance.
`stimulation to
`Applying high-intensity electrical
`only 1 limb following bilateral TKA provides an ideal
`opportunity for investigating the efficacy of NMES, as
`each patient provides a control limb for comparison.
`The purpose of this case series was to assess the effect
`of adding high-intensity NMES to a volitional
`strengthening program following TKA. The hypoth-
`esis was that adding NMES to a 6-week, voluntary
`exercise program would be more effective in improv-
`
`ing quadriceps activation and strength than voluntary
`exercise alone.
`
`METHODS
`
`Patients
`
`Eight patients with simultaneous, primary bilateral
`total knee replacements (Table 1) were recruited
`from
`local
`surgeons
`who
`performed
`tricompartmental cemented TKA with a medial
`parapatellar approach. Patients were excluded from
`the study if they were diagnosed with diabetes mel-
`litus, uncontrolled blood pressure, neurological disor-
`ders, neoplasms, or had a body mass index (BMI =
`weight [kg]/height [m2]) of greater than 40 (mor-
`bidly obese).
`Patients were assigned to 1 of 2 intervention
`groups: (1) ‘‘Ex legs’’ or (2) ‘‘NMES legs.’’ Patients
`in the Ex legs group received the same intervention
`for both legs, which consisted of voluntary exercises
`for strengthening of the lower extremity. Patients in
`the NMES legs group participated in a voluntary
`exercise program for the leg that was stronger at
`initial evaluation, and NMES was added to the
`voluntary exercise program for the leg that was
`weaker at initial evaluation (Table 2). The Human
`Subjects Review Committee at the University of Dela-
`ware approved the study and all subjects gave in-
`formed consent.
`
`Intervention
`
`Intervention began 3 to 4 weeks following TKA,
`after staples were removed. All patients were sched-
`uled for treatment at
`the University of Delaware
`Physical Therapy Clinic 3 times a week for 6 weeks
`(total of 18 visits) and were allowed to miss up to 4
`visits. All
`in-clinic and home exercise interventions
`were documented in patient data booklets to ensure
`consistency of care and patient compliance. Rehabili-
`tation for all patients included interventions to re-
`duce pain and inflammation, improve incision mobil-
`ity, restore knee flexion and extension range of
`motion,
`improve bilateral
`lower-extremity strength
`
`TABLE 1. Patient demographics for patients with bilateral total knee arthroplasty.
`
`Patient
`1
`2
`3
`4
`5
`6
`7
`8
`
`Height (m)
`1.75
`1.78
`1.85
`1.68
`1.85
`1.73
`1.73
`1.78
`
`Weight (kg)
`103.4
`97.1
`93.0
`88.9
`99.8
`118.8
`93.0
`87.5
`
`BMI
`33.8
`30.8
`27.1
`31.5
`29.2
`39.7
`31.1
`27.8
`
`Age (y)
`64
`67
`75
`64
`63
`76
`69
`61
`
`Gender
`M
`M
`M
`M
`M
`F
`M
`M
`
`Group
`NMES
`NMES
`NMES
`NMES
`NMES
`Exercise
`Exercise
`Exercise
`
`Abbreviations: BMI, body mass index (weight [kg]/height [m2]); F, female; M, male; NMES, neuromuscular electrical stimulation.
`
`22
`
`J Orthop Sports Phys Ther (cid:127) Volume 34 (cid:127) Number 1 (cid:127) January 2004
`
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`
`LUMENIS EX1015
`Page 2
`
`

`

`TABLE 2. Groups designations and corresponding interventions.
`
`Group Name/Leg
`NMES group
`Weak NMES legs
`Strong NMES legs
`Exercise group
`Weak Ex legs
`Strong Ex legs
`
`Intervention
`
`Volitional exercise, NMES
`Volitional exercise
`
`Volitional exercise
`Volitional exercise
`
`(midtraining), 9th (posttraining), 12th (3-month
`follow-up), and 24th (6-month follow-up) weeks after
`TKA. To minimize apprehension and discomfort
`during testing, patients were allowed to choose which
`leg was tested first during the initial evaluation. The
`order of testing remained the same for each subse-
`quent testing session.
`
`Abbreviation: NMES, neuromuscular electrical stimulation.
`
`Quadriceps Strength and Activation Testing
`
`R E S E A R C H R E P O R T
`
`Patients were seated on the electromechanical dy-
`namometer with their hips flexed to approximately
`85° and their knees flexed to 75°. The axis of the
`dynamometer was aligned with the axis of rotation of
`the knee joint and the bottom of the force trans-
`ducer pad was positioned against the anterior aspect
`of
`the leg proximal
`to the lateral malleolus. The
`lower leg,
`thigh, and pelvis were stabilized using
`inelastic straps with Velcro closures. Two 7.6×12.7-cm
`self-adhesive neuromuscular
`stimulation electrodes
`were secured to the thigh. The anode was placed
`over the motor point of the rectus femoris and the
`cathode was placed over the motor point of
`the
`vastus medialis.
`Strength testing began by instructing all patients to
`perform three 3-
`to 5-second voluntary isometric
`contractions at an intensity that they perceived as
`50% to 75% of their maximal effort. These contrac-
`tions served to familiarize the patient with the appa-
`ratus and to warm up the muscle. In addition, the
`quadriceps
`femoris muscle was
`stimulated several
`times at intensities that would elicit muscle contrac-
`tions to familiarize the patient with the sensation of
`electrical stimulation. After the patient was familiar
`with the procedure and the muscle warmed up,
`testing began by having the patient attempt a 3- to
`
`
`
`using high-intensity voluntary exercises, and improve
`functional performance (see Table 3). Each patient
`was evaluated and treated on the basis of individual
`impairments, as the guidelines for intervention in
`Table 3 permitted.
`NMES The weak NMES legs received identical
`intervention to all other legs except that 10 NMES-
`elicited quadriceps contractions were added to each
`treatment session. For the NMES intervention, pa-
`tients were seated on an electromechanical dyna-
`mometer (KinCom; Chattanooga Corporation, Chat-
`tanooga, TN), and a measuring arm, which restrained
`the movement of the leg, was secured to the lower
`leg (Figure 1). The knee was positioned at 60° of
`knee flexion and all contractions were isometric. The
`patient’s maximal voluntary isometric contraction
`(MVIC) was determined before the NMES interven-
`tion using the average peak force of two 5-second
`isometric contractions.
`Self-adherent,
`flexible electrodes (7.6×12.7 cm)
`were placed over the subject’s quadriceps to apply the
`electrical stimulation.29 A clinical neuromuscular elec-
`trical stimulator (Versastim 380; Electromed Health
`Industries, Miami Beach, FL) was set to deliver a
`2500-Hz alternating current, modulated at 50 bursts
`per second, with a ramp-up time of 2 to 3 seconds.29
`The intensity was
`set
`to the maximum intensity
`tolerated by the patient during each session. The
`patient was instructed to relax during stimulation and
`prevent cocontraction of the hamstrings as well as
`inadvertent voluntary quadriceps muscle contraction.
`The intensity was increased as tolerated throughout
`each session. Ten 10-second isometric contractions
`were elicited with an 80-second rest between each
`contraction.29 The electrically elicited knee extension
`peak force produced by each contraction of
`the
`quadriceps muscle was recorded by customized soft-
`ware (LabVIEW V 4.0.1; National Instruments, Austin,
`TX) on a personal computer.
`
`Testing Procedure
`
`Quadriceps strength and voluntary muscle activa-
`tion were tested. Testers were isolated from the
`subjects’ interventions and were not aware of which
`patients received the NMES intervention. Testing was
`performed in the 3rd (initial evaluation), 6th
`
`FIGURE 1. Experimental setup for neuromuscular electrical stimula-
`tion (NMES) treatment. Patients were seated and stabilized with the
`hip flexed to 85° and the knee flexed to 75°. Two 7.62×12.70-cm
`electrodes were placed over the vastus medialis and proximal rectus
`femoris of the quadriceps.
`
`J Orthop Sports Phys Ther (cid:127) Volume 34 (cid:127) Number 1 (cid:127) January 2004
`
`23
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`
`LUMENIS EX1015
`Page 3
`
`

`

`Range of motion (ROM)
`
`Strength
`
`TABLE 3. Rehabilitation program.
`• Exercise bike (10-15 min), started with forward and backward pedaling with no resistance until
`enough ROM for full revolution; progression: lower seat height to produce a stretch with each revolu-
`tion.
`• Active-assistive ROM for knee flexion, sitting or supine, using other leg to assist.
`• Knee extension stretch with manual pressure (in clinic) or weights (at home).
`• Patellar mobilizations: 3×30 superior/inferior; medial/lateral, as necessary.
`• Quad sets, straight leg raises (without quad lag), hip abduction (sidelying), standing hamstring curls,
`seated knee extension, standing terminal knee extensions from 45° to 0°, step-ups (5.08-15.24-cm
`block), wall slides to 45° knee flexion; 1 to 3 sets of 10 repetitions for all strengthening exercises.
`• Criteria for progression: exercises are to be progressed (eg, weights, step height, etc) once the patient
`can complete the exercise correctly and feels maximally fatigued at the end of each set.
`• Progression: 0.454-0.907-kg weights added to exercises, step-downs (5.08-15.24-cm block), front
`lunges, wall slides towards 90° knee flexion.
`• Ice and compression as needed.
`• Soft tissue mobilization until incision moves freely over subcutaneous tissue.
`• Ambulation training with assistive device as appropriate with emphasis on heel strike, push-off at toe-
`off and normal knee joint excursions.
`• Emphasis on heel strike, push-off at toe-off and normal knee joint excursions when able to walk with-
`out assistive device.
`• Stair ascending and descending step over step when patient has sufficient concentric/eccentric
`strength.
`• Blood pressure and heart rate are monitored at initial evaluation and as appropriate.
`
`Pain and swelling
`Incision mobility
`Functional activities
`
`Monitoring vital signs
`
`5-second MVIC while receiving verbal encouragement
`from the tester and visual feedback from the dyna-
`mometer’s real time force display. During the con-
`traction, a 135-V, 10-pulse, 100-pps
`train (1000-
`microsecond pulse duration) was delivered to the
`muscle to assess whether the subject was
`indeed
`maximally activating the quadriceps muscle (burst
`superimposition technique).19,24,34,37 A S8800 stimula-
`tor with a SIU8T stimulus
`isolation unit (Grass
`Instruments,
`Inc., Quincy, MA) was driven by a
`personal computer that uses customized software
`(LabVIEW V 4.0.1) to control the timing parameters
`of the stimulation protocol. Data were digitized at
`200 Hz and analyzed with customized software
`(LabVIEW V 4.0.1). With full voluntary muscle activa-
`tion, no increase in force was measured. If a subject
`was unable to activate the quadriceps muscle fully,
`MVIC testing was repeated up to 2 additional times
`and the maximal force noted during these 3 tests was
`used for analysis. Each attempt at achieving an MVIC
`was separated by 5 minutes to minimize the effects of
`muscle fatigue. The greatest maximal voluntary effort
`achieved during the testing session for each leg was
`used for analysis. The burst superimposition tech-
`nique has been shown to be highly reliable in
`subjects without pathology, with repeated testing that
`demonstrated an intraclass correlation coefficient of
`0.98 (mean age, 24.2 years; age range, 17-32 years).32
`
`Data Management and Analysis
`
`Because of the limited number of subjects included
`in this study, the data are presented individually and
`qualitatively to describe trends in outcomes.
`
`Quadriceps Strength The force (N) of the quadriceps
`MVIC was normalized to body mass index (N/BMI)
`for all comparisons to account for variations in force
`production that are a result of differences in body
`size. Three sets of comparisons were made for the 8
`individuals: (1) comparison within the NMES legs
`and Ex legs groups (strong versus weak legs); (2)
`comparison of weak legs between groups (weak
`NMES legs versus weak Ex legs); (3) comparison of
`strong legs between groups (strong NMES legs versus
`strong Ex legs).
`increase in normalized
`The average percent
`quadriceps muscle strength was also used to describe
`strength gains of
`the individuals. The percent
`in-
`crease was calculated using the following relationship:
`
`Percent increase in strength =
`6-month MVIC (N) – initial MVIC (N)
`initial MVIC (N)
`
`× 100
`
`Quadriceps Voluntary Muscle Activation Voluntary
`quadriceps muscle activation was calculated by mea-
`suring the peak volitional and electrically elicited
`forces during the MVIC test. The central activation
`ratio (CAR) was used to quantify voluntary muscle
`activation.19 The CAR is calculated by dividing the
`maximum voluntary force produced before the elec-
`trical
`stimulus by the maximum force produced
`during the superimposition of the electrical stimulus.
`A CAR of 1.0 signifies complete activation. In con-
`trast, a CAR of
`less than 1.0 suggests incomplete
`voluntary muscle activation. The same comparisons
`outlined earlier for quadriceps strength were made
`for voluntary activation.
`
`24
`
`J Orthop Sports Phys Ther (cid:127) Volume 34 (cid:127) Number 1 (cid:127) January 2004
`
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`LUMENIS EX1015
`Page 4
`
`

`

`R E S E A R C H R E P O R T
`
`The percent increase in quadriceps voluntary acti-
`vation was also used to describe improvements in
`activation of the individuals. The percent increase was
`calculated using the following relationship:
`
`Percent increase in CAR =
`6-month CAR – initial CAR
`initial CAR
`
`× 100
`
`NMES Dose The daily NMES dose was calculated as
`a ratio of the highest electrically elicited knee exten-
`sion force obtained in a session by the maximal
`MVIC achieved on that same day. The NMES doses
`are reported as average doses obtained over the 6
`weeks of treatment.
`
`RESULTS
`
`Compliance
`The average number of sessions was 17. No patient
`missed more than 3 sessions.
`
`Quadriceps Strength and Voluntary Muscle Activation
`Strong Versus Weak Legs The percent increases in
`quadriceps strength for the weak NMES legs ranged
`from 221% to 451% as compared to 50% to 152% for
`the strong NMES legs; whereas the percent increases
`in quadriceps strength for the weak Ex legs ranged
`from 41% to 148% as compared to 30% to 71% for
`the strong Ex legs (Table 4). Initially, the average
`quadriceps strength of almost all legs receiving NMES
`was less than that of
`the legs that received only
`voluntary exercise for strengthening (Table 5).
`the
`After 3 weeks of
`treatment (midtraining),
`quadriceps strength of the weak NMES legs showed a
`dramatic improvement in 4 out of 5 patients and was
`almost identical to, or had surpassed, the strength of
`the contralateral strong NMES legs. At 6 months, 4
`out of 5 patients with initially weak NMES legs
`remained stronger
`than their
`initially
`stronger
`
`leg (Table 5). Only 1 of the initially
`contralateral
`weak Ex legs
`showed a similar
`initial
`jump in
`quadriceps strength within the first 3 weeks of train-
`ing (patient 6), and none of the weak Ex legs were
`stronger as compared to their contralateral leg at 6
`months (Table 5).
`Quadriceps strength testing demonstrated consis-
`tent linear or curvilinear increases in strength for all
`legs over the course of 6 months, with the exception
`of patient 6 (Table 5). Patient 6 showed the greatest
`amount of variability in force production during
`consecutive testing sessions and had greater oscilla-
`tions in strength than the other patients.
`Quadriceps voluntary activation for the legs receiv-
`ing stimulation underwent a concurrent
`increase
`compared to the legs that did not undergo NMES
`during the first 3 weeks of
`treatment (Table 6).
`Quadriceps voluntary activation did not change as
`dramatically during the remaining testing sessions as
`it did during the first 3 weeks of training for patients
`in the NMES group.
`Weak NMES Legs Versus Weak Ex Legs
`Initial
`quadriceps strength of the weak NMES legs was less
`for patients 1 through 5 than that of the weak Ex legs
`of patients 7 and 8 (Table 5). Patient 6 was the
`exception to this observation and had quadriceps
`weakness that was comparable to that of the weak
`NMES legs. By midtraining, quadriceps strength of
`the weak NMES legs had almost equaled or surpassed
`that of the weak Ex legs in all patients except patient
`3. Quadriceps strength of the weak Ex legs improved
`by midtraining. Both the weak NMES legs and weak
`Ex legs continued to show improvements in strength
`through the 6-month follow-up, but the weak NMES
`legs demonstrated the greatest overall improvement
`(Table 5).
`Voluntary muscle activation of the quadriceps in-
`creased for all the weak NMES legs within the first 3
`weeks of treatment (Table 6). In comparison, the
`weak Ex legs only had 1 substantial change in
`quadriceps voluntary activation in patient 8, which
`
`TABLE 4. Percent change in quadriceps strength and voluntary activation from initial evaluation to 6-month follow-up.
`
`Patient
`1*
`2*
`3*
`4*
`5*
`6†
`7†
`8†
`
`Increase in Quadriceps
`Strength (%)
`
`Weak Legs
`451
`302
`233
`351
`221
`41
`80
`148
`
`Strong Legs
`76
`121
`152
`133
`50
`30
`67
`71
`
`Increase in CAR (%)
`Weak Legs
`Strong Legs
`39.0
`–1.6
`87.0
`11.0
`66.0
`52.0
`34.0
`5.0
`34.0
`–3.0
`–6.0
`–14.0
`–0.8
`–4.0
`54.0
`3.0
`
`Abbreviation: CAR, central activation ratio.
`*Neuromuscular electrical stimulation group.
`†Exercise group.
`
`J Orthop Sports Phys Ther (cid:127) Volume 34 (cid:127) Number 1 (cid:127) January 2004
`
`25
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`LUMENIS EX1015
`Page 5
`
`

`

`TABLE 5A. Force normalized to body mass index (N×[kg/m2]–1) for the initially weaker leg of all patients.
`
`Patient
`1*
`2*
`3*
`4*
`5*
`6†
`7†
`8†
`
`Initial
`Evaluation
`5.0
`3.8
`5.9
`7.8
`5.5
`5.2
`10.5
`9.5
`
`3 Weeks
`24.6
`12.3
`7.0
`19.8
`13.7
`9.8
`12.7
`10.3
`
`6 Weeks
`25.3
`12.6
`12.4
`21.4
`16.0
`5.4
`14.8
`14.5
`
`3 Months
`26.1
`13.7
`12.7
`26.0
`16.5
`9.3
`18.6
`20.9
`
`* Weak NMES legs, received neuromuscular electrical stimulation and voluntary exercise for strengthening.
`† Weak Ex legs, received only voluntary exercise for strengthening.
`
`TABLE 5B. Force normalized to body mass index (N×[kg/m2]–1) for the initially stronger leg of all patients.
`
`Patient
`
`1*
`2*
`3*
`4*
`5*
`6†
`7†
`8†
`
`Initial
`Evaluation
`12.9
`11.8
`7.1
`13.1
`9.8
`6.4
`11.3
`16.6
`
`3 Weeks
`20.3
`17.3
`10.4
`20.8
`11.2
`7.5
`12.8
`16.1
`
`6 Weeks
`21.1
`20.3
`13.5
`18.7
`17.8
`7.6
`15.0
`17.4
`
`3 Months
`22.3
`23.3
`16.9
`24.8
`15.5
`6.1
`14.9
`19.7
`
`* Strong NMES legs, contralateral leg received NMES and voluntary exercise for strengthening.
`† Strong Ex legs, contralateral leg received only voluntary exercise for strengthening.
`
`6 Months
`27.4
`15.1
`19.5
`35.4
`17.6
`7.4
`18.9
`23.4
`
`6 Months
`22.7
`26.0
`17.8
`30.6
`14.8
`8.3
`18.9
`28.3
`
`occurred later in training than for the weak NMES
`legs. It should be noted that the central activation of
`2 of the 3 weak Ex legs was initially higher than for
`the weak NMES legs, possibly offering a lesser oppor-
`tunity for improvement.
`
`Strong NMES Legs Versus Strong Ex Legs The strong
`legs of individuals in both groups had comparable
`initial quadriceps strength (Table 5). At 6 months,
`the strong NMES legs had average strength gains that
`were greater (range, 50%-152%) than the strong Ex
`legs (range, 30%-71%) (Table 4). The voluntary
`muscle activation in the strong legs did not change as
`much throughout the testing period as it did for the
`weak legs (Table 6).
`
`NMES Dose
`
`The NMES dose ranged from 29% to 53% (Table
`7). While the patient with the highest NMES dose
`(53%) had the greatest
`increase in quadriceps
`strength (451%), the small sample size of this case
`series does not afford the opportunity to make
`inferences regarding a dose-response relationship.
`
`DISCUSSION
`
`This case series suggests that adding NMES to a
`rehabilitation program after TKA may
`facilitate
`
`quadriceps strength gains more rapidly than volun-
`tary exercise alone. In addition, the results of this
`case series suggest
`that a full 6 weeks of NMES
`treatment may not be necessary to achieve the
`benefits of the treatment, given that the most dra-
`matic improvement took place in the first 3 weeks.
`The improvement in quadriceps activation in those
`legs that received NMES in the first 3 weeks was
`accompanied by
`a
`concomitant
`increase
`in
`quadriceps strength. NMES provoked a large and
`rapid increase in quadriceps force production in the
`weakest patients, who traditionally have modest re-
`sults with voluntary exercise programs.17
`The timing and the degree of change in voluntary
`muscle activation from the initial evaluation to the
`midtraining test corresponded to the initial rapid
`changes in quadriceps strength. This suggests that
`during the initial phases of NMES treatment, much
`of the initial change in quadriceps strength can be
`explained by a resolution of activation deficits. After
`midtraining, additional improvements in the strength
`between both subgroups were more likely a product
`of muscle hypertrophy because voluntary muscle
`activation remained fairly constant in many of the
`individuals from midtraining to the 6-month follow-
`up.
`A similar pattern of strength gains emerged when
`the weak NMES legs were compared to the weak Ex
`
`26
`
`J Orthop Sports Phys Ther (cid:127) Volume 34 (cid:127) Number 1 (cid:127) January 2004
`
` Journal of Orthopaedic & Sports Physical Therapy®
`
` Downloaded from www.jospt.org at on July 27, 2021. For personal use only. No other uses without permission.
`
` Copyright © 2004 Journal of Orthopaedic & Sports Physical Therapy®. All rights reserved.
`
`LUMENIS EX1015
`Page 6
`
`

`

`R E S E A R C H R E P O R T
`
`in quadriceps
`improvements
`legs, with greater
`strength and voluntary activation for the weak NMES
`legs than for the weak Ex legs. Strength gains for the
`weak Ex legs were modest and did not seem to
`correspond as well with changes in voluntary muscle
`activation, as was the case in the weak NMES legs. We
`believe that NMES may have initially contributed to
`improved quadriceps strength by facilitating muscle
`activation. Given the small sample size, we cannot
`rule out the possibility that the higher initial activa-
`tion levels for the weak Ex legs allowed less room for
`improvement than for the weak NMES legs.
`Muscle activation of both legs in patient 6 (Ex legs
`group) was high compared to expected values follow-
`ing surgery.25,35 Patient 6 reported no pain with
`muscle contraction or during functional activities at
`any point after surgery. The lack of pain may be
`partially responsible for the high muscle activation
`initially after surgery. It is also interesting to note the
`larger fluctuations in strength of the weak voluntary
`exercise leg for this patient and the minimal improve-
`ment in overall quadriceps strength over the course
`of 6 months. Patient 6 had a high self-report of knee
`function initially and a low expectation to improve
`her function. Low expectations with concomitant low
`motivation may explain some of the inconsistency in
`improvement.
`Although the number of patients included in this
`case series is small,
`the varying degrees of
`initial
`
`weakness present with the burst superimposition test
`was consistent with that present
`in patients with
`unilateral TKA tested identically (n = 28).35 We have
`no reason to believe that the initial weakness mea-
`sured is not an accurate reflection of their quadriceps
`strength.
`The comparisons between the weak legs of indi-
`viduals in both groups was included in the analysis, as
`it discredits
`the argument
`that
`the remarkable
`strength gains in the weak NMES legs were simply a
`result of a bias for greater potential improvement due
`to selecting only the initially weak leg to receive
`NMES. In fact,
`it could be argued that those legs
`which are weak, with corresponding large voluntary
`activation deficits, represent more of a ‘‘worse case’’
`scenario for clinicians. This would bias against find-
`ing greater gains
`in strength and activation with
`voluntary strengthening protocols.
`When comparing the strong NMES legs to the
`strong Ex legs, cross-education from the NMES inter-
`vention may explain the greater strength gains in the
`strong legs of the NMES group. The only difference
`in the treatment protocol between each group of
`strong legs was that the strong legs in the NMES
`group had a contralateral weak leg that received
`NMES intervention. Research has shown that both
`unilateral voluntary and unilateral electrically elicited
`strength training carries over into strength gains in
`the untrained limb.6,14 For electrically elicited
`
`TABLE 6A. Central activation ratios for the initially weaker leg of all patients.
`
`Patient
`
`1*
`2*
`3*
`4*
`5*
`6†
`7†
`8†
`
`Initial
`Evaluation
`0.61
`0.34
`0.57
`0.74
`0.71
`1.00
`0.93
`0.57
`
`3 Weeks
`0.97
`0.69
`0.70
`0.95
`0.91
`1.00
`0.91
`0.53
`
`6 Weeks
`0.85
`0.60
`0.84
`0.90
`0.95
`0.93
`0.91
`0.87
`
`3 Months
`0.86
`0.74
`0.68
`0.97
`0.94
`0.99
`0.93
`0.78
`
`* Weak NMES legs, received neuromuscular electrical stimulation in addition to voluntary exercise program for strengthening.
`† Weak Ex legs, received only voluntary exercise for strengthening.
`
`TABLE 6B. Central activation ratios for the initially stronger leg of all patients.
`
`Patient
`
`1*
`2*
`3*
`4*
`5*
`6†
`7†
`8†
`
`Initial
`Evaluation
`0.86
`0.63
`0.60
`0.95
`0.88
`0.95
`0.95
`0.79
`
`3 Weeks
`0.96
`0.69
`0.71
`0.98
`0.80
`0.90
`0.91
`0.69
`
`6 Weeks
`0.84
`0.66
`0.82
`0.93
`0.96
`0.74
`0.93
`0.87
`
`3 Months
`0.87
`0.75
`0.86
`1.00
`0.85
`0.80
`0.87
`0.85
`
`6 Months
`0.84
`0.64
`0.95
`1.00
`0.96
`0.94
`0.92
`0.87
`
`6 Months
`0.84
`0.70
`0.91
`1.00
`0.85
`0.82
`0.92
`0.82
`
`* Strong NMES legs, contralateral leg received neuromuscular electrical stimulation in addition to voluntary exercise program for strengthening.
`† Strong Ex legs, contralateral leg received only voluntary exercise for strengthening.
`
`J Orthop Sports Phys Ther (cid:127) Volume 34 (cid:127) Number 1 (cid:127) January 2004
`
`27
`
` Journal of Orthopaedic & Sports Physical Therapy®
`
` Downloaded from www.jospt.org at on July 27, 2021. For personal use only. No other uses without permission.
`
` Copyright © 2004 Journal of Orthopaedic & Sports Physical Therapy®. All rights reserved.
`
`LUMENIS EX1015
`Page 7
`
`

`

`TABLE 7. Relationship between neuromuscular electrical stimu-
`lation (NMES) dose and increase in quadriceps strength for
`weak NMES legs. NMES dose is an average of