TY - JOUR
AU - Metter, E, Jeffrey
AB - Abstract Introduction Knee injuries among active duty military are one of the most frequent musculoskeletal injuries and are often caused by exercise or intense physical activity or combat training. These injuries pose a threat to force readiness. Our objective was to assess feasibility (including recruitment and retention rates) of three self-managed strengthening strategies for knee injuries and determine if they resulted in improvements in lower extremity strength, function, pain, and activity compared to usual physical therapy (PT) in military members. Methods A pilot study using a randomized controlled trial was conducted at three outpatient military medical treatment facilities. After baseline testing, 78 active duty military members with a knee injury were randomized to 1–4 trial arms: (1) neuromuscular electrical stimulation (NMES) applied to the quadriceps muscle; (2) graduated strength walking using a weighted vest (WALK); (3) combined NMES with strength walking (COMBO); (4) usual PT alone. All groups received usual PT. The primary outcome was the rates of change in knee extensor and flexor strength over 18 weeks. Secondary outcomes explored the rates of change in functional performance, pain, and activities of daily living scale (ADLS). The primary analysis for the endpoints used repeated measures, linear mixed-effects models. This study was approved by Institutional Review Boards at all facilities. Results The randomized sample (N = 78) included 19 participants in the PT-only, 20 in the WALK, 19 in the NMES and 20 in the COMBO groups. At baseline, there were no group differences. Fifty of the participants completed the 18-week study. The completers and non-completers differed at baseline on injury mechanism, with more completers injured during sports (45% vs 29%), and more non-completers during military training (36% vs 18%). Also, they differed in uninjured knee extension (completers 28% weaker), and uninjured knee flexion (completers 22% weaker). Adherence for self-reported daily step logs showed that the WALK group was 15% below goal and COMBO group 6% below goal. The 300 PV muscle stimulator showed the NMES group completed 34% of recommended stimulation sessions and the COMBO group 30%. Knee extension strength in the injured knee found only the COMBO group having a statistically higher improvement compared to PT-only (Change over 18 weeks: 10.6 kg in COMBO; 2.1 kg in PT-only). For the injured knee flexion changes, only the COMBO showed significant difference from PT-only (Change over 18 weeks: 7.5 kg in COMBO; −0.2 kg in PT-only). Similarly, for the uninjured knee, only the COMBO showed significant difference from PT-only in knee extension (Change over 18 weeks: 14.7 Kg in COMBO; 2.7 kg in PT-only) and knee flexion (Change over 18 weeks: 6.5 kg in COMBO; −0.2 kg in PT-only). Overall pain improved during the study for all groups with no significant group differences. Similarly, function and ADLS significantly improved over 18 weeks, with no significant group differences. Conclusions Knee extensor strength improvements in the COMBO group were significantly higher compared to usual PT. Pain, functional measures, and ADLS all improved during the study with no group differences. Further research is required to confirm these findings. INTRODUCTION Musculoskeletal-related injuries pose a threat to force readiness in military populations.1 Among musculoskeletal injuries, knee injuries are the most frequent among active duty military, often caused by overload during exercise, intense physical activity or combat training.2–7 The most frequent causes are running (45%) and resistance training (8%).3 Knee injuries can be long term, recur, and limit training. Knee injury rehabilitation is integral to accelerate service members’ return to duty. Research suggests that muscle weakness,4 biomechanical dysfunction,5,6 heavy load carriage,7,8 and lower fitness,9,10 contribute to these injuries. Pain and guarding from an acute injury may lead to weakness and atrophy of the quadriceps femoris. Failing to regain quadriceps strength may contribute to worsening of an existing injury and progression to chronic joint disease.11 Research is conflicting regarding the effectiveness of muscle strengthening to reduce symptoms.4,12,13 One approach is to augment strength training with alternative techniques to maximize strength gains following injury. We previously showed that neuromuscular electrical stimulation strengthened quadriceps muscles and reduced pain in knee osteoarthritis14 and trans-tibial amputees.15,16 We also found that a National Guard walking program increased fitness similar to the traditional Army physical fitness program.17 In the present study, we combined a progressive walking program with a weighted vest to incrementally increase load carriage with a passive NMES intervention, which may have synergistic effects. The primary objective was to conduct a pilot study using a randomized trial design to assess the feasibility (recruitment and retention, adherence rates, intervention acceptance) of three self-management strategies for knee injuries and determine if they resulted in improvement in lower extremity muscle strength compared to usual physical therapy (PT) in military service members. Secondary outcomes of function, pain and activity limitations were explored. The groups were neuromuscular electrical stimulation strength training (NMES), graduated strength walking using a weighted vest (WALK), NMES combined with WALK (COMBO), and PT-only as control group. All groups received usual physical therapy. We hypothesized that combining NMES with graduated strength walking would produce greater improvements in lower extremity muscle strength compared to PT-only than either intervention alone. METHODS Participants Participants were recruited from physical therapy referrals at three military facilities between November 2011 and August 2016. All participants provided written consent, and the study was approved by Institutional Review Boards at all facilities. The study was registered in ClinicalTrials.gov (Electromyostimulation and Strength Walking for Knee Injuries, ID: NCT02065518). Eligibility criteria are presented in Table I. TABLE I. Participant Inclusion and Exclusion Criteria Inclusion Criteria Age 18–50 years Military Service member at the time of injury Diagnosed with knee injury, anterior knee pain, overuse pain, patella-femoral pain, and chronic pain for less than 6 months associated with overuse syndromes which impacts work performance and daily activities Able to provide freely informed consent Exclusion criteria Fracture or injury to external knee structures where knee extension or flexion is impaired Evidence of unstable tendon tear/rupture Significant co-morbid medical condition making unsupervised exercise contraindicated Reduced sensory perception in the lower extremities Inability to walk on a treadmill without an assistive device Pregnancy Inability to speak and/or read English Score of 23 or greater on the Center for Epidemiological Studies-Depression scale Demand type implanted pacemaker or defibrillator Vision impairment where participant is classified as legally blind Unwillingness to accept random assignment Inclusion Criteria Age 18–50 years Military Service member at the time of injury Diagnosed with knee injury, anterior knee pain, overuse pain, patella-femoral pain, and chronic pain for less than 6 months associated with overuse syndromes which impacts work performance and daily activities Able to provide freely informed consent Exclusion criteria Fracture or injury to external knee structures where knee extension or flexion is impaired Evidence of unstable tendon tear/rupture Significant co-morbid medical condition making unsupervised exercise contraindicated Reduced sensory perception in the lower extremities Inability to walk on a treadmill without an assistive device Pregnancy Inability to speak and/or read English Score of 23 or greater on the Center for Epidemiological Studies-Depression scale Demand type implanted pacemaker or defibrillator Vision impairment where participant is classified as legally blind Unwillingness to accept random assignment TABLE I. Participant Inclusion and Exclusion Criteria Inclusion Criteria Age 18–50 years Military Service member at the time of injury Diagnosed with knee injury, anterior knee pain, overuse pain, patella-femoral pain, and chronic pain for less than 6 months associated with overuse syndromes which impacts work performance and daily activities Able to provide freely informed consent Exclusion criteria Fracture or injury to external knee structures where knee extension or flexion is impaired Evidence of unstable tendon tear/rupture Significant co-morbid medical condition making unsupervised exercise contraindicated Reduced sensory perception in the lower extremities Inability to walk on a treadmill without an assistive device Pregnancy Inability to speak and/or read English Score of 23 or greater on the Center for Epidemiological Studies-Depression scale Demand type implanted pacemaker or defibrillator Vision impairment where participant is classified as legally blind Unwillingness to accept random assignment Inclusion Criteria Age 18–50 years Military Service member at the time of injury Diagnosed with knee injury, anterior knee pain, overuse pain, patella-femoral pain, and chronic pain for less than 6 months associated with overuse syndromes which impacts work performance and daily activities Able to provide freely informed consent Exclusion criteria Fracture or injury to external knee structures where knee extension or flexion is impaired Evidence of unstable tendon tear/rupture Significant co-morbid medical condition making unsupervised exercise contraindicated Reduced sensory perception in the lower extremities Inability to walk on a treadmill without an assistive device Pregnancy Inability to speak and/or read English Score of 23 or greater on the Center for Epidemiological Studies-Depression scale Demand type implanted pacemaker or defibrillator Vision impairment where participant is classified as legally blind Unwillingness to accept random assignment Study Design This study was a randomized controlled pilot trial comparing three self-management strategies added to usual care PT with PT-only. After baseline testing, participants (N = 78) were randomized using blocked randomization with permuted blocks of eight. Participants assigned to PT-only received usual physical therapy for 18 weeks; participants in the other three groups received usual physical therapy plus an 18-week treatment program. Knee extensor and flexor muscle strength, function, and subjective outcome measures were assessed at baseline, 3, 6, 9, 12, and 18 weeks. Telephone calls, e-mails, and/or text messages reminded participants of study visits. Intervention Programs Usual Physical Therapy Rehabilitation All participants received usual care physical therapy, in which the physical therapy intervention and number and type of sessions were not controlled. Self-Managed Neuromuscular Electrical Stimulation (NMES) Program In addition to usual care physical therapy, NMES participants received an 18-week program of NMES strength training to knee extensors at a location of choice using the EMPI 300PV muscle stimulator, a portable battery-power unit that delivered pulsed current programmed for a symmetrical biphasic rectangular waveform (100 mA; duty cycle 10 s on/50 s off; pulse rate 50 pps.; ramp time 3:1.5 s; 300μs at 50% amplitude). The protocol was four 15-minute NMES sessions per week. Each session contained 15 muscle contractions (10 s contraction with 50 s rest) per leg alternating between legs in a semi-reclined position with knees placed in 0–30° knee flexion. Two 3×5-inch self-adhesive electrodes were placed over the quadriceps femoris: one 2 cm above patella over the distal vastus medialis muscle and one over the proximal rectus femoris muscle. For consistency, stimulation intensity was based on calculated percentages of maximal voluntary contraction (MVC). Participants were trained at 15–20% of MVC during weeks 1–3, 21–30% during weeks 4–6, 31–40% during weeks 7–9, 41–50% during weeks 10–12, and >50% during weeks 13–18. Stimulator intensity increases were made at study visits, adjusting for strength changes throughout the intervention. Study staff contacted participants each week with telephone calls, e-mails, or text messages to determine pain levels and compliance with treatment schedule. At each study visit, staff reviewed training logs reporting date, duration, amplitude achieved, and pain levels. Participants received a handout describing electrode placement, NMES device usage, and training goals. Graduated Strength Walking (WALK) Program The WALK group used a pedometer-driven walking program and, at week 7, a weighted exercise vest. As with the NMES group, the WALK participants maintained a daily log. Pedometer readings formed the basis for setting step goals. The Digi-walker SW-200 pedometer (New-Lifestyles Inc; Lees Summit, MO)18,19 counted steps walked. Initial step goals were 10% above average baseline 3-day pedometer step count and were increased 10% every other week. Trainers emphasized the importance of walking 30 minutes continuously at least 4 days a week by week 6. After week 6 testing, weight was introduced using a nylon vest with compartments for variable weights. Participants were instructed to wear the vest during their 30-minute walk, 3–4 days a week. The beginning weight load was calculated using 2% of baseline body weight and increased by that amount every week for 12 weeks. The modified Borg’s RPE Scale20 was used to decide when weights were added. If the subject rated the previous week’s exercises at ≥4 (“somewhat hard”), weight was not increased, but the daily step goal was increased. If rated at ≤3 (moderate), the weight was increased. Participants received a booklet about goal setting, pedometer and weighted vest usage, exercise safety, perceived exertion, pain status, and activity intensity. Self-reported pain status (described below) was monitored to assure safe weight progression. If pain rating increased by ≥2 points above the rating for un-weighted walking, the weight was decreased by 1% body weight for the following week. Training logs and weekly follow-up contacts were the same as for the NMES group. NMES Combined With Graduated Strength Walking (COMBO) Program The COMBO group received self-managed NMES training and graduated strength walking. The COMBO protocol used four 15-minute NMES sessions per week and graduated pedometer-driven walking with a weighted vest added at week 7. This group also used training logs and received follow-up contact from study staff. Outcome Assessments Lower extremity muscle strength and Activity of Daily Living Scale (ADLS) were measured at 0, 3, 6, 9, 12, and 18 weeks. The 6-minute walk test, self-paced step test, and chair rise test were measured every 6 weeks. Pain levels were measured after each performance test. Lower Extremity Muscle Strength Lower extremity muscle strength was measured for isometric knee extension and flexion using the hand-held Nicholas Manual Muscle Tester (NMMT) (kg-force) (Lafayette Instruments; Lafayette, Indiana)21–23 to record peak force and time to peak force. An adjustable strap attachment by Ergo-Kit MMT system stabilized the NMMT during testing. Participants sat on an adjustable isometric testing chair secured with Velcro straps. The seat was adjusted to maintain the femur in 90 degrees of hip flexion with knees positioned in 70° flexion and legs dangled vertically. Knee flexion and extension were tested at 60% of distance from tibial tuberosity to medial malleolus. Three maximal efforts were performed holding each contraction for 4 seconds, separated by 10-second rest intervals. The highest score was recorded. Adherence to Treatments Treatment adherence was measured by training logs and compliance monitors in the 300PV. Daily training logs assessed progress towards step goals. To verify NMES training, the 300PV unit recorded session time, number of sessions, and average session time. Functional Recovery and ADLS We used three functional performance tests and a pain scale at baseline, 6, 12, and 18 weeks. ADLS was given at every 3-week visit. 30-Second Chair Stand Test (30-SCST) The 30–SCST assessed lower-body strength.24 A standard chair, 18 inches in height, was positioned against the wall for stability. Starting in a seated position with feet flat on the floor and arms crossed over the chest, participants repeated standing and sitting cycles at a self-paced speed for 30 seconds. The number of complete rises was recorded. Validity and reliability of the 30-SCST have been demonstrated.25,26 2-Minute Self-Paced Step Test (2-MST) The 2-MST27,28 measured mobility and endurance. For familiarization, participants stepped up and down slowly for 1 minute. Following a brief rest period, participants repeated the step cycle (up and down) for 2 minutes at their self-selected pace, as described by Petrela et al.29 The number of steps taken in 2 minutes and ending heart rate were recorded. Six-Minute Timed Walk Test (6-MWT) The 6-MWT,30,31 measured distance walked at a fast pace over 6-minutes. Participants were instructed to “walk as quickly as you can.” Distance was determined using a measuring wheel and recorded in inches. This test is a valid and reliable submaximal functional walking test.32,33 Knee Pain Following Performance Testing The Visual Analog Scale, an 11-point numerical rating scale,34–36 assessed knee pain intensity after performance testing. Participants verbally rated current knee pain intensity on a scale of 0 (no pain) to 10 (worst pain imaginable). Overall Pain Overall pain was assessed using item 3 from the IDKC Subjective Knee evaluation,37 “If you have knee pain, how severe it is?” Participants responded using the same 0 to 10 pain definitions. Activities of Daily Living Scale (ADLS) The ADLS measured self-perceived knee symptoms and limitations performing typical activities. The knee symptom subscale ranged from 0 to 35; the functional limitation subscale from 0–45. Higher scores are associated with higher function and diminished symptoms. The ADLS has been shown to be valid, reliable, and responsive to change in adults with knee injuries.38 Sample Size Estimation and Statistical Analyses Based on the simulation of a mixed effects model, 132 participants (33 per group) would detect an effect size difference of 0.5 with a 45% dropout rate for an alpha of 0.05 and power of 0.8, assuming the intra-subject correlation is 0.7. The sample size estimation was based on the primary outcome knee extensor strength. We re-adjusted the estimation based on actual subject recruitment of 78 at the end of the funded pilot study. For the same simulation model, 19 subjects per group with 40% dropout have a power of 0.8 for an effect size difference of 0.7. From our previous work, expected effect size differences range from approximately 0.4 to 0.9. Demographic and baseline characteristics were compared between groups using linear regression for continuous and Fisher’s exact test (FET) for categorical variables. The primary analyses for endpoints used repeated measures, linear mixed-effects models to test for change differences over time between the PT-only and the NMES, WALK, and COMBO. Two sets of models were examined. The first model tested the relationships between the outcome measures to change over time with the regression models including time, group and a time-by-group interaction with PT-only as reference. Each term was tested using likelihood ratio tests with effect size for the time-by-group interaction assessed by f2. A second set of models compared outcomes for groups at each observation using linear mixed effects regression with time as a factor and p-values calculated based on Satterthwate’s approximations. Data were analyzed using intent-to-treat analyses with all randomized participants included. Two-sided p-values of <0.05 were used to define statistical significance. Statistical analyses were completed using R, version 3.4.139 with mixed effects models using the lme440 and lmerTest41 packages. RESULTS Enrollment and Study Attrition The study assessed 523 military personnel, with 220 (42%) screened, and 79 meeting inclusion criteria and enrolled (Fig. 1). One withdrew during baseline testing, was not randomized, and is not included in analyses. The randomized sample (N = 78) included 19 participants in the PT-only, 20 in the WALK, 19 in the NMES and 20 in the COMBO groups (Fig. 1). FIGURE 1. View largeDownload slide Trial flow diagram of the study participants. FIGURE 1. View largeDownload slide Trial flow diagram of the study participants. Characterization of Completers Completers did not differ from non-completers on age (31.7 vs 35.5 yrs., p = 0.08), male gender (42% vs 54%, p = 0.35), race (32% vs 34% African-American, p = 0.99), rank (30% vs 11% officers, p = 0.09), overall pain (5.0 vs 5.8, p = 0.07), pain after functional performance (chair stand: 2.7 vs 2.8, p = 0.83, walk: 2.2 vs 2.6, p = 0.50, step: 3.5 vs 3.6, p = 0.85), injured knee extension strength (26.0 vs 31.2 kg., p = 0.11), or injured knee flexion strength (19.3 vs 22.3 kg., p = 0.17) at baseline (50 completers vs 28 non-completers). They differed on mechanism of injury (p = 0.05), with more completers injured during sports (45% vs 29%), and more non-completers injured during military training (36% vs 18%). Also, they differed in uninjured knee extension (completers 28% weaker 28.1 vs 39.8 kg., p = 0.004), and uninjured knee flexion (completers 22% weaker 19.2 vs 24.5 kg., p = 0.003). Adherence Adherence for self-reported daily step logs showed WALK group averaged 8,497 ± 5,269 daily steps and COMBO group 9,031 ± 3,775 daily steps (p = 0.83). The WALK group was 15% below goal (10,026 ± 4,409 steps) and COMBO group was 6% below goal (9,599 ± 3,334 steps) (p = 0.77). The 300 PV muscle stimulator showed the NMES group completed 34% of recommended stimulation sessions and the COMBO group 30%. Baseline Participant Characteristics All groups were similar at baseline in terms of age, sex, race, rank, and distribution of mechanism of injury (Table II). Baseline strength levels for injured and uninjured legs were similar for both knee extension and flexion, overall pain and functional measures. After completing the functional measures, pain was in the mid-moderate range for all groups and not significantly different. TABLE II. Participant Characteristics by Study Group (n = 78) NMESPlus PT (n = 19) WalkPlus PT (n = 20) COMBOPlus PT (n = 20) PT Only (n = 19) p-Value Age (mean yesrs) 35 (7.9) 35 (11.3) 33 (6.1) 33 (8.4) 0.72a Male (%) 9 (47.4) 9 (45.0) 9 (47.4) 9 (45.0) 1.0b Race (%)  Caucasian 11 (57.9) 8 (40.0) 13 (65.0) 8 (42.1) 0.71b  African-American 6 (31.6) 7 (35.0) 5 (25.0) 8 (42.1)  Asian/Pacific 0 (0.0) 2 (10.0) 1 (5.0) 0 (0.0)  Multi-racial 1 (5.3) 2 (10.0) 1 (5.0) 3 (15.8)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) Mechanism of injury (%)  Sports 7 (36.8) 5 (26.3) 10 (50.0) 8 (42.1) 0.39b  Work 2 (10.5) 0 (0.0) 1 (5.0) 3 (15.8)  Military training 6 (31.6) 5 (26.3) 3 (15.0) 5 (26.3)  Motor vehicle accident 0 (0.0) 0 (0.0) 1 (5.0) 0 (0.0)  Other 4 (21.1) 9 (47.4) 5 (25.0) 3 (15.8) Rank (%)  Enlisted 13 (68.4) 14 (70.0) 16 (80.0) 16 (84.2) 0.88b  Officer 4 (21.1) 5 (25.0) 4 (20.0) 3 (15.8)  Warrant officer 1 (5.0) 0 (0.0) 0 (0.0) 0 (0.0)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) NMESPlus PT (n = 19) WalkPlus PT (n = 20) COMBOPlus PT (n = 20) PT Only (n = 19) p-Value Age (mean yesrs) 35 (7.9) 35 (11.3) 33 (6.1) 33 (8.4) 0.72a Male (%) 9 (47.4) 9 (45.0) 9 (47.4) 9 (45.0) 1.0b Race (%)  Caucasian 11 (57.9) 8 (40.0) 13 (65.0) 8 (42.1) 0.71b  African-American 6 (31.6) 7 (35.0) 5 (25.0) 8 (42.1)  Asian/Pacific 0 (0.0) 2 (10.0) 1 (5.0) 0 (0.0)  Multi-racial 1 (5.3) 2 (10.0) 1 (5.0) 3 (15.8)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) Mechanism of injury (%)  Sports 7 (36.8) 5 (26.3) 10 (50.0) 8 (42.1) 0.39b  Work 2 (10.5) 0 (0.0) 1 (5.0) 3 (15.8)  Military training 6 (31.6) 5 (26.3) 3 (15.0) 5 (26.3)  Motor vehicle accident 0 (0.0) 0 (0.0) 1 (5.0) 0 (0.0)  Other 4 (21.1) 9 (47.4) 5 (25.0) 3 (15.8) Rank (%)  Enlisted 13 (68.4) 14 (70.0) 16 (80.0) 16 (84.2) 0.88b  Officer 4 (21.1) 5 (25.0) 4 (20.0) 3 (15.8)  Warrant officer 1 (5.0) 0 (0.0) 0 (0.0) 0 (0.0)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) Values are mean ± SD except where indicated; percentages may not add to 100% due to rounding. aLinear regression. bFisher’s exact test. TABLE II. Participant Characteristics by Study Group (n = 78) NMESPlus PT (n = 19) WalkPlus PT (n = 20) COMBOPlus PT (n = 20) PT Only (n = 19) p-Value Age (mean yesrs) 35 (7.9) 35 (11.3) 33 (6.1) 33 (8.4) 0.72a Male (%) 9 (47.4) 9 (45.0) 9 (47.4) 9 (45.0) 1.0b Race (%)  Caucasian 11 (57.9) 8 (40.0) 13 (65.0) 8 (42.1) 0.71b  African-American 6 (31.6) 7 (35.0) 5 (25.0) 8 (42.1)  Asian/Pacific 0 (0.0) 2 (10.0) 1 (5.0) 0 (0.0)  Multi-racial 1 (5.3) 2 (10.0) 1 (5.0) 3 (15.8)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) Mechanism of injury (%)  Sports 7 (36.8) 5 (26.3) 10 (50.0) 8 (42.1) 0.39b  Work 2 (10.5) 0 (0.0) 1 (5.0) 3 (15.8)  Military training 6 (31.6) 5 (26.3) 3 (15.0) 5 (26.3)  Motor vehicle accident 0 (0.0) 0 (0.0) 1 (5.0) 0 (0.0)  Other 4 (21.1) 9 (47.4) 5 (25.0) 3 (15.8) Rank (%)  Enlisted 13 (68.4) 14 (70.0) 16 (80.0) 16 (84.2) 0.88b  Officer 4 (21.1) 5 (25.0) 4 (20.0) 3 (15.8)  Warrant officer 1 (5.0) 0 (0.0) 0 (0.0) 0 (0.0)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) NMESPlus PT (n = 19) WalkPlus PT (n = 20) COMBOPlus PT (n = 20) PT Only (n = 19) p-Value Age (mean yesrs) 35 (7.9) 35 (11.3) 33 (6.1) 33 (8.4) 0.72a Male (%) 9 (47.4) 9 (45.0) 9 (47.4) 9 (45.0) 1.0b Race (%)  Caucasian 11 (57.9) 8 (40.0) 13 (65.0) 8 (42.1) 0.71b  African-American 6 (31.6) 7 (35.0) 5 (25.0) 8 (42.1)  Asian/Pacific 0 (0.0) 2 (10.0) 1 (5.0) 0 (0.0)  Multi-racial 1 (5.3) 2 (10.0) 1 (5.0) 3 (15.8)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) Mechanism of injury (%)  Sports 7 (36.8) 5 (26.3) 10 (50.0) 8 (42.1) 0.39b  Work 2 (10.5) 0 (0.0) 1 (5.0) 3 (15.8)  Military training 6 (31.6) 5 (26.3) 3 (15.0) 5 (26.3)  Motor vehicle accident 0 (0.0) 0 (0.0) 1 (5.0) 0 (0.0)  Other 4 (21.1) 9 (47.4) 5 (25.0) 3 (15.8) Rank (%)  Enlisted 13 (68.4) 14 (70.0) 16 (80.0) 16 (84.2) 0.88b  Officer 4 (21.1) 5 (25.0) 4 (20.0) 3 (15.8)  Warrant officer 1 (5.0) 0 (0.0) 0 (0.0) 0 (0.0)  Missing 1 (5.3) 1 (5.0) 0 (0.0) 0 (0.0) Values are mean ± SD except where indicated; percentages may not add to 100% due to rounding. aLinear regression. bFisher’s exact test. Knee Extension and Flexion Strength Levels (Primary Outcome) For knee extension strength over 18 weeks in the injured knee (Fig. 2), the COMBO group had a statistically higher improvement compared to PT-only (Change over 18 weeks: 10.6 kg in COMBO; 2.1 kg in PT-only). For the injured knee flexion strength changes, only the COMBO showed significant difference from PT-only (Change over 18 weeks: 7.5 kg in COMBO; −0.2 kg in PT-only). FIGURE 2. View largeDownload slide Change in the injured leg for knee extensor (p = 0.04) (Fig. 2A) and flexor strength (p = 0.002) (Fig. 2B) at baseline, 3, 6, 9, 12, and 18 weeks for the four treatment groups. Change in the uninjured leg for knee extensor (p = 0.002) (Fig. 2C) and knee flexor strength (p = 0.02) (Fig. 2D) at baseline, 3, 6, 9, 12, and 18 weeks for the four treatment groups. FIGURE 2. View largeDownload slide Change in the injured leg for knee extensor (p = 0.04) (Fig. 2A) and flexor strength (p = 0.002) (Fig. 2B) at baseline, 3, 6, 9, 12, and 18 weeks for the four treatment groups. Change in the uninjured leg for knee extensor (p = 0.002) (Fig. 2C) and knee flexor strength (p = 0.02) (Fig. 2D) at baseline, 3, 6, 9, 12, and 18 weeks for the four treatment groups. Similarly, for the uninjured knee, only the COMBO showed significant difference from PT-only in knee extension (Change over 18 weeks: 14.7 kg in COMBO; 2.7 kg in PT-only) and knee flexion strength (Change over 18 weeks: 6.5 kg in COMBO; −0.2 kg in PT-only). When comparing the three treatment groups to PT-only at each time point (Table III), the COMBO group showed differences from the PT-only group at weeks 6–18 in at least one strength measure and consistent differences across the strength measures at 12 and 18 weeks. The WALK group and NMES group did not show similar differences compared to the PT-only group. TABLE III. Strength and Pain Outcomes by Study Groups (N = 78) Week Injured Knee Extensor (kg-force) Injured Knee Flexor (kg-force) Uninjured Knee Extensor (kg-force) Uninjured Knee Flexor (kg-force) Pain Severity PT only 0 27.5 (12.4) 16.2 (9.4) 28.2 (13.0) 20.0 (06.7) 5.4 (1.9) 3 25.4 (15.9) 15.3 (8.3) 26.0 (15.5) 20.1 (7.9) 5.9 (2.3) 6 23.3 (11.5) 15.4 (9.9) 25.4 (11.2) 16.9 (7.2) 6.2 (2.5) 9 26.0 (15.1) 15.6 (12.6) 27.2 (14.0) 17.5 (12.6) 5.8 (2.4) 12 27.8 (16.0) 14.5 (7.3) 25.8 (14.2) 17.3 (8.4) 5.3 (2.6) 18 28.5 (17.3) 14.7 (7.8) 27.6 (12.0) 18.1 (6.8) 4.7 (3.1) NMESplus PT 0 32.6 (14.7) 16.6 (7.0) 37.2 (16.4) 22.5 (8.4) 4.9 (2.1) 3 32.0 (10.4) 16.9 (4.8) 38.3 (18.8) 23.5 (8.2) 5.0 (2.3) 6 33.7 (11.5) 21.3 (12.1)* 35.9 (13.9) 22.9 (6.6) 3.8 (1.6)* 9 33.9 (13.6) 15.3 (4.9) 35.9 (15.1) 20.8 (5.2) 4.1 (1.9) 12 33.0 (10.6) 16.5 (4.5) 35.8 (12.6) 22.7 (6.4) 4.2 (2.1) 18 36.2 (10.2) 17.4 (4.0) 32.3 (9.1) 23.1 (8.2) 3.6 (2.4) WALK plus PT 0 32.1 (15.5) 16.2 (8.6) 36.2 (21.2) 22.6 (8.0) 5.7 (1.7) 3 30.4 (10.3) 17.8 (5.5) 34.5 (14.9) 22.7 (7.4) 5.4 (1.9) 6 29.8 (10.0) 15.0 (4.5) 34.2 (15.1) 19.8 (6.4) 5.3 (2.5) 9 29.2 (13.7) 15.9 (5.6) 29.8 (19.9) 23.0 (10.4) 4.4 (1.7) 12 32.7 (16.6) 18.4 (5.7) 33.8 (15.9) 25.9 (12.2) 5.1 (2.7) 18 31.0 (16.6) 15.4 (5.5) 33.2 (20.3) 24.1 (12.0) 4.3 (2.4) Combo plus PT 0 24.3 (11.4) 13.7 (6.9) 27.6 (14.0) 19.8 (8.6) 5.1 (1.9) 3 27.8 (13.7) 14.9 (7.4) 28.0 (13.8) 20.2 (7.5) 5.0 (1.8) 6 27.1 (13.4)* 14.8 (5.9) 33.5 (19.4)* 19.9 (10.3) 5.0 (2.3) 9 34.0 (16.8)* 16.6 (7.2) 36.2 (18.3)* 27.4 (15.7)* 4.3 (2.4) 12 30.8 (14.8) 17.3 (7.4)* 38.7 (22.6)* 23.0 (11.1) 4.5 (2.0) 18 33.5 (15.8)* 19.3 (10.4)* 38.6 (22.1)* 24.2 (11.3)* 3.9 (2.3) Mixed effects regression models likelihood ratio testa t×g χ2(3) = 9.9, (p = 0.019) χ2(3) = 14.6 (p = 0.002) χ2(3) = 22.0 (p < 0.0001) χ2(3) = 8.4 (p = 0.038) χ2(3) = 0.3 (p = 0.95) f2 (t×g) 0.06 (0 0.00, 0.11) 0.07 (0.01, 0.10) 0.10 (0.02, 0.18) 0.05 (0.01, 0.10) 0.03 (0.00, 0.05) Week Injured Knee Extensor (kg-force) Injured Knee Flexor (kg-force) Uninjured Knee Extensor (kg-force) Uninjured Knee Flexor (kg-force) Pain Severity PT only 0 27.5 (12.4) 16.2 (9.4) 28.2 (13.0) 20.0 (06.7) 5.4 (1.9) 3 25.4 (15.9) 15.3 (8.3) 26.0 (15.5) 20.1 (7.9) 5.9 (2.3) 6 23.3 (11.5) 15.4 (9.9) 25.4 (11.2) 16.9 (7.2) 6.2 (2.5) 9 26.0 (15.1) 15.6 (12.6) 27.2 (14.0) 17.5 (12.6) 5.8 (2.4) 12 27.8 (16.0) 14.5 (7.3) 25.8 (14.2) 17.3 (8.4) 5.3 (2.6) 18 28.5 (17.3) 14.7 (7.8) 27.6 (12.0) 18.1 (6.8) 4.7 (3.1) NMESplus PT 0 32.6 (14.7) 16.6 (7.0) 37.2 (16.4) 22.5 (8.4) 4.9 (2.1) 3 32.0 (10.4) 16.9 (4.8) 38.3 (18.8) 23.5 (8.2) 5.0 (2.3) 6 33.7 (11.5) 21.3 (12.1)* 35.9 (13.9) 22.9 (6.6) 3.8 (1.6)* 9 33.9 (13.6) 15.3 (4.9) 35.9 (15.1) 20.8 (5.2) 4.1 (1.9) 12 33.0 (10.6) 16.5 (4.5) 35.8 (12.6) 22.7 (6.4) 4.2 (2.1) 18 36.2 (10.2) 17.4 (4.0) 32.3 (9.1) 23.1 (8.2) 3.6 (2.4) WALK plus PT 0 32.1 (15.5) 16.2 (8.6) 36.2 (21.2) 22.6 (8.0) 5.7 (1.7) 3 30.4 (10.3) 17.8 (5.5) 34.5 (14.9) 22.7 (7.4) 5.4 (1.9) 6 29.8 (10.0) 15.0 (4.5) 34.2 (15.1) 19.8 (6.4) 5.3 (2.5) 9 29.2 (13.7) 15.9 (5.6) 29.8 (19.9) 23.0 (10.4) 4.4 (1.7) 12 32.7 (16.6) 18.4 (5.7) 33.8 (15.9) 25.9 (12.2) 5.1 (2.7) 18 31.0 (16.6) 15.4 (5.5) 33.2 (20.3) 24.1 (12.0) 4.3 (2.4) Combo plus PT 0 24.3 (11.4) 13.7 (6.9) 27.6 (14.0) 19.8 (8.6) 5.1 (1.9) 3 27.8 (13.7) 14.9 (7.4) 28.0 (13.8) 20.2 (7.5) 5.0 (1.8) 6 27.1 (13.4)* 14.8 (5.9) 33.5 (19.4)* 19.9 (10.3) 5.0 (2.3) 9 34.0 (16.8)* 16.6 (7.2) 36.2 (18.3)* 27.4 (15.7)* 4.3 (2.4) 12 30.8 (14.8) 17.3 (7.4)* 38.7 (22.6)* 23.0 (11.1) 4.5 (2.0) 18 33.5 (15.8)* 19.3 (10.4)* 38.6 (22.1)* 24.2 (11.3)* 3.9 (2.3) Mixed effects regression models likelihood ratio testa t×g χ2(3) = 9.9, (p = 0.019) χ2(3) = 14.6 (p = 0.002) χ2(3) = 22.0 (p < 0.0001) χ2(3) = 8.4 (p = 0.038) χ2(3) = 0.3 (p = 0.95) f2 (t×g) 0.06 (0 0.00, 0.11) 0.07 (0.01, 0.10) 0.10 (0.02, 0.18) 0.05 (0.01, 0.10) 0.03 (0.00, 0.05) Values are mean ± SD except where indicated. *p < 0.05; comparing treatment group to PT control at each time point from a mixed effects model with time as a factor. aMixed effects models with time as continuous using the likelihood ratio test. The Chi-squared and corresponding p-values are present (df for time and group=1 and for t×g is 3). T×g tests whether change over time differs between at least one of the treatment groups and PT. f2 is the effect size for the t×g interaction with mean and (95% CI). TABLE III. Strength and Pain Outcomes by Study Groups (N = 78) Week Injured Knee Extensor (kg-force) Injured Knee Flexor (kg-force) Uninjured Knee Extensor (kg-force) Uninjured Knee Flexor (kg-force) Pain Severity PT only 0 27.5 (12.4) 16.2 (9.4) 28.2 (13.0) 20.0 (06.7) 5.4 (1.9) 3 25.4 (15.9) 15.3 (8.3) 26.0 (15.5) 20.1 (7.9) 5.9 (2.3) 6 23.3 (11.5) 15.4 (9.9) 25.4 (11.2) 16.9 (7.2) 6.2 (2.5) 9 26.0 (15.1) 15.6 (12.6) 27.2 (14.0) 17.5 (12.6) 5.8 (2.4) 12 27.8 (16.0) 14.5 (7.3) 25.8 (14.2) 17.3 (8.4) 5.3 (2.6) 18 28.5 (17.3) 14.7 (7.8) 27.6 (12.0) 18.1 (6.8) 4.7 (3.1) NMESplus PT 0 32.6 (14.7) 16.6 (7.0) 37.2 (16.4) 22.5 (8.4) 4.9 (2.1) 3 32.0 (10.4) 16.9 (4.8) 38.3 (18.8) 23.5 (8.2) 5.0 (2.3) 6 33.7 (11.5) 21.3 (12.1)* 35.9 (13.9) 22.9 (6.6) 3.8 (1.6)* 9 33.9 (13.6) 15.3 (4.9) 35.9 (15.1) 20.8 (5.2) 4.1 (1.9) 12 33.0 (10.6) 16.5 (4.5) 35.8 (12.6) 22.7 (6.4) 4.2 (2.1) 18 36.2 (10.2) 17.4 (4.0) 32.3 (9.1) 23.1 (8.2) 3.6 (2.4) WALK plus PT 0 32.1 (15.5) 16.2 (8.6) 36.2 (21.2) 22.6 (8.0) 5.7 (1.7) 3 30.4 (10.3) 17.8 (5.5) 34.5 (14.9) 22.7 (7.4) 5.4 (1.9) 6 29.8 (10.0) 15.0 (4.5) 34.2 (15.1) 19.8 (6.4) 5.3 (2.5) 9 29.2 (13.7) 15.9 (5.6) 29.8 (19.9) 23.0 (10.4) 4.4 (1.7) 12 32.7 (16.6) 18.4 (5.7) 33.8 (15.9) 25.9 (12.2) 5.1 (2.7) 18 31.0 (16.6) 15.4 (5.5) 33.2 (20.3) 24.1 (12.0) 4.3 (2.4) Combo plus PT 0 24.3 (11.4) 13.7 (6.9) 27.6 (14.0) 19.8 (8.6) 5.1 (1.9) 3 27.8 (13.7) 14.9 (7.4) 28.0 (13.8) 20.2 (7.5) 5.0 (1.8) 6 27.1 (13.4)* 14.8 (5.9) 33.5 (19.4)* 19.9 (10.3) 5.0 (2.3) 9 34.0 (16.8)* 16.6 (7.2) 36.2 (18.3)* 27.4 (15.7)* 4.3 (2.4) 12 30.8 (14.8) 17.3 (7.4)* 38.7 (22.6)* 23.0 (11.1) 4.5 (2.0) 18 33.5 (15.8)* 19.3 (10.4)* 38.6 (22.1)* 24.2 (11.3)* 3.9 (2.3) Mixed effects regression models likelihood ratio testa t×g χ2(3) = 9.9, (p = 0.019) χ2(3) = 14.6 (p = 0.002) χ2(3) = 22.0 (p < 0.0001) χ2(3) = 8.4 (p = 0.038) χ2(3) = 0.3 (p = 0.95) f2 (t×g) 0.06 (0 0.00, 0.11) 0.07 (0.01, 0.10) 0.10 (0.02, 0.18) 0.05 (0.01, 0.10) 0.03 (0.00, 0.05) Week Injured Knee Extensor (kg-force) Injured Knee Flexor (kg-force) Uninjured Knee Extensor (kg-force) Uninjured Knee Flexor (kg-force) Pain Severity PT only 0 27.5 (12.4) 16.2 (9.4) 28.2 (13.0) 20.0 (06.7) 5.4 (1.9) 3 25.4 (15.9) 15.3 (8.3) 26.0 (15.5) 20.1 (7.9) 5.9 (2.3) 6 23.3 (11.5) 15.4 (9.9) 25.4 (11.2) 16.9 (7.2) 6.2 (2.5) 9 26.0 (15.1) 15.6 (12.6) 27.2 (14.0) 17.5 (12.6) 5.8 (2.4) 12 27.8 (16.0) 14.5 (7.3) 25.8 (14.2) 17.3 (8.4) 5.3 (2.6) 18 28.5 (17.3) 14.7 (7.8) 27.6 (12.0) 18.1 (6.8) 4.7 (3.1) NMESplus PT 0 32.6 (14.7) 16.6 (7.0) 37.2 (16.4) 22.5 (8.4) 4.9 (2.1) 3 32.0 (10.4) 16.9 (4.8) 38.3 (18.8) 23.5 (8.2) 5.0 (2.3) 6 33.7 (11.5) 21.3 (12.1)* 35.9 (13.9) 22.9 (6.6) 3.8 (1.6)* 9 33.9 (13.6) 15.3 (4.9) 35.9 (15.1) 20.8 (5.2) 4.1 (1.9) 12 33.0 (10.6) 16.5 (4.5) 35.8 (12.6) 22.7 (6.4) 4.2 (2.1) 18 36.2 (10.2) 17.4 (4.0) 32.3 (9.1) 23.1 (8.2) 3.6 (2.4) WALK plus PT 0 32.1 (15.5) 16.2 (8.6) 36.2 (21.2) 22.6 (8.0) 5.7 (1.7) 3 30.4 (10.3) 17.8 (5.5) 34.5 (14.9) 22.7 (7.4) 5.4 (1.9) 6 29.8 (10.0) 15.0 (4.5) 34.2 (15.1) 19.8 (6.4) 5.3 (2.5) 9 29.2 (13.7) 15.9 (5.6) 29.8 (19.9) 23.0 (10.4) 4.4 (1.7) 12 32.7 (16.6) 18.4 (5.7) 33.8 (15.9) 25.9 (12.2) 5.1 (2.7) 18 31.0 (16.6) 15.4 (5.5) 33.2 (20.3) 24.1 (12.0) 4.3 (2.4) Combo plus PT 0 24.3 (11.4) 13.7 (6.9) 27.6 (14.0) 19.8 (8.6) 5.1 (1.9) 3 27.8 (13.7) 14.9 (7.4) 28.0 (13.8) 20.2 (7.5) 5.0 (1.8) 6 27.1 (13.4)* 14.8 (5.9) 33.5 (19.4)* 19.9 (10.3) 5.0 (2.3) 9 34.0 (16.8)* 16.6 (7.2) 36.2 (18.3)* 27.4 (15.7)* 4.3 (2.4) 12 30.8 (14.8) 17.3 (7.4)* 38.7 (22.6)* 23.0 (11.1) 4.5 (2.0) 18 33.5 (15.8)* 19.3 (10.4)* 38.6 (22.1)* 24.2 (11.3)* 3.9 (2.3) Mixed effects regression models likelihood ratio testa t×g χ2(3) = 9.9, (p = 0.019) χ2(3) = 14.6 (p = 0.002) χ2(3) = 22.0 (p < 0.0001) χ2(3) = 8.4 (p = 0.038) χ2(3) = 0.3 (p = 0.95) f2 (t×g) 0.06 (0 0.00, 0.11) 0.07 (0.01, 0.10) 0.10 (0.02, 0.18) 0.05 (0.01, 0.10) 0.03 (0.00, 0.05) Values are mean ± SD except where indicated. *p < 0.05; comparing treatment group to PT control at each time point from a mixed effects model with time as a factor. aMixed effects models with time as continuous using the likelihood ratio test. The Chi-squared and corresponding p-values are present (df for time and group=1 and for t×g is 3). T×g tests whether change over time differs between at least one of the treatment groups and PT. f2 is the effect size for the t×g interaction with mean and (95% CI). Pain, Functional Recovery and ADLS Overall pain improved across the course of the study for all groups with no significant difference between groups (Table III). Function and ADLS significantly improved in all groups over the 18 weeks (Table IV), with no significant differences between any groups. TABLE IV. Functional Outcomes by Study Groups (N = 78) Week 2-MST (steps) 30–SCST (no. rises) 6-MWT (inches) 2MST Pain 30-SCST Pain 6-MWT Pain ADLS Symptom ADLS Activity PT only 0 189 (67) 11.3 (3.7) 19,800 (3,398) 4.0 (2.4) 3.7 (2.3) 2.4 (2.2) 25.4 (4.7) 32.9 (6.1) 3 25.0 (5.5) 33.4 (6.8) 6 185 (76) 12.7 (3.8) 21,822 (4,346) 3.5 (2.8) 3.5 (2.6) 3.2 (2.5) 24.4 (6.5) 33.5 (8.1) 9 25.0 (6.1) 31.8 (6.9) 12 180 (82) 13.3 (4.8) 21,404 (2,534) 2.9 (2.6) 2.8 (2.2) 2.7 (2.1) 27.8 (6.3) 32.9 (7.7) 18 202 (92) 13.3 (3.7) 21,210 (3,718) 2.6 (2.4) 2.4 (2.0) 2.3 (2.1) 29.6 (5.2)* 36.4 (6.7) NMES plus PT 0 162 (62) 11.4 (1.8) 20,224 (5,162) 3.7 (2.7) 2.5 (2.4) 2.9 (2.4) 23.3 (6.3) 30.9 (4.9) 3 24.6 (6.9) 33.3 (5.2) 6 178 (78) 13.6 (2.6) 21,696 (3,905) 2.1 (2.5) 1.4 (1.8) 1.6 (1.9) 27.9 (6.4)* 35.5 (5.5) 9 29.3 (6.6) 39.8 (4.1)* 12 235 (46)* 13.9 (2.3) 22,210 (3,991) 3.0 (2.4) 2.0 (2.6) 1.9 (2.1) 26.5 (7.6) 35.7 (5.9)* 18 233 (75) 14.4 (1.5) 22,984 (3,390) 1.7 (2.4) 0.7 (0.9) 1.6 (2.2) 29.7 (4.7) 38.1 (4.9) WALK plus PT 0 199 (60) 12.7 (3.9) 19,728 (5,347) 3.0 (2.1) 2.1 (1.9) 1.8 (2.1) 25.1 (5.2) 30.9 (7.2) 3 26.2 (6.0) 34.8 (5.8)* 6 224 (64) 14.4 (4.0) 22,197 (3,242) 2.5 (2.5) 1.4 (2.0) 1.7 (2.8) 28.1 (4.7) 34.9 (6.1) 9 29.6 (4.1)* 35.3 (5.8)* 12 258 (42) 14.4 (2.3) 21,595 (3,092) 3.0 (2.4) 1.7 (2.5) 1.6 (2.0) 30.8 (3.0)* 36.7 (5.1)* 18 224 (56) 15.0 (2.7) 22,105 (3,718) 2.1 (2.7) 1.5 (2.2) 2.1 (2.9) 30.9 (4.3) 36.9 (6.0) Combo plus PT 0 172 (67) 10.7 (2.8) 18,974 (4,603) 3.7 (2.1) 2.7 (1.4) 2.5 (2.1) 22.9 (4.3) 31.5 (2.4) 3 26.0 (2.8) 33.0 (3.0) 6 205 (75)* 13.2 (1.9) 21,696 (3,905) 2.4 (1.4) 1.2 (1.4) 1.4 (1.2)* 27.4 (4.0)* 35.6 (4.4) 9 27.2 (4.7) 36.5 (4.4)* 12 202 (73) 14.5 (2.1) 20,824 (6,223) 1.9 (2.3) 1.2 (1.5) 1.6 (1.7) 27.6 (4.8) 36.6 (5.4)* 18 216 (73) 15.2 (2.2) 22,945 (2,883) 1.8 (2.6) 0.8 (1.5) 1.2 (2.1)* 29.8 (4.7) 38.6 (5.6) F2 for the mixed effects models F2 for interaction testa t×g χ2(3) = 4.0 (p = 0.26) χ2(3) = 3.3 (p = 0.35) χ2(3) = 0.3 (p = 0.96) χ2(3) = 5.5 (p = 0.14) χ2(3) = 3.7 (p = 0.30) χ2(3) = 8.7 (p = 0.034) χ2(3) = 3.1 (p = 0.38) χ2(3) = 8.5 (p = 0.04) f2(t×g) 0.05 (0,0.11) 0.04 (0, 0.11) 0.03 (0, 0.08) 0.05 (0, 0.12) 0.05 (0, 0.11) 0.08 (0,0.16) 0.03 (0, 0.06) 0.04 (0, 0.09) Week 2-MST (steps) 30–SCST (no. rises) 6-MWT (inches) 2MST Pain 30-SCST Pain 6-MWT Pain ADLS Symptom ADLS Activity PT only 0 189 (67) 11.3 (3.7) 19,800 (3,398) 4.0 (2.4) 3.7 (2.3) 2.4 (2.2) 25.4 (4.7) 32.9 (6.1) 3 25.0 (5.5) 33.4 (6.8) 6 185 (76) 12.7 (3.8) 21,822 (4,346) 3.5 (2.8) 3.5 (2.6) 3.2 (2.5) 24.4 (6.5) 33.5 (8.1) 9 25.0 (6.1) 31.8 (6.9) 12 180 (82) 13.3 (4.8) 21,404 (2,534) 2.9 (2.6) 2.8 (2.2) 2.7 (2.1) 27.8 (6.3) 32.9 (7.7) 18 202 (92) 13.3 (3.7) 21,210 (3,718) 2.6 (2.4) 2.4 (2.0) 2.3 (2.1) 29.6 (5.2)* 36.4 (6.7) NMES plus PT 0 162 (62) 11.4 (1.8) 20,224 (5,162) 3.7 (2.7) 2.5 (2.4) 2.9 (2.4) 23.3 (6.3) 30.9 (4.9) 3 24.6 (6.9) 33.3 (5.2) 6 178 (78) 13.6 (2.6) 21,696 (3,905) 2.1 (2.5) 1.4 (1.8) 1.6 (1.9) 27.9 (6.4)* 35.5 (5.5) 9 29.3 (6.6) 39.8 (4.1)* 12 235 (46)* 13.9 (2.3) 22,210 (3,991) 3.0 (2.4) 2.0 (2.6) 1.9 (2.1) 26.5 (7.6) 35.7 (5.9)* 18 233 (75) 14.4 (1.5) 22,984 (3,390) 1.7 (2.4) 0.7 (0.9) 1.6 (2.2) 29.7 (4.7) 38.1 (4.9) WALK plus PT 0 199 (60) 12.7 (3.9) 19,728 (5,347) 3.0 (2.1) 2.1 (1.9) 1.8 (2.1) 25.1 (5.2) 30.9 (7.2) 3 26.2 (6.0) 34.8 (5.8)* 6 224 (64) 14.4 (4.0) 22,197 (3,242) 2.5 (2.5) 1.4 (2.0) 1.7 (2.8) 28.1 (4.7) 34.9 (6.1) 9 29.6 (4.1)* 35.3 (5.8)* 12 258 (42) 14.4 (2.3) 21,595 (3,092) 3.0 (2.4) 1.7 (2.5) 1.6 (2.0) 30.8 (3.0)* 36.7 (5.1)* 18 224 (56) 15.0 (2.7) 22,105 (3,718) 2.1 (2.7) 1.5 (2.2) 2.1 (2.9) 30.9 (4.3) 36.9 (6.0) Combo plus PT 0 172 (67) 10.7 (2.8) 18,974 (4,603) 3.7 (2.1) 2.7 (1.4) 2.5 (2.1) 22.9 (4.3) 31.5 (2.4) 3 26.0 (2.8) 33.0 (3.0) 6 205 (75)* 13.2 (1.9) 21,696 (3,905) 2.4 (1.4) 1.2 (1.4) 1.4 (1.2)* 27.4 (4.0)* 35.6 (4.4) 9 27.2 (4.7) 36.5 (4.4)* 12 202 (73) 14.5 (2.1) 20,824 (6,223) 1.9 (2.3) 1.2 (1.5) 1.6 (1.7) 27.6 (4.8) 36.6 (5.4)* 18 216 (73) 15.2 (2.2) 22,945 (2,883) 1.8 (2.6) 0.8 (1.5) 1.2 (2.1)* 29.8 (4.7) 38.6 (5.6) F2 for the mixed effects models F2 for interaction testa t×g χ2(3) = 4.0 (p = 0.26) χ2(3) = 3.3 (p = 0.35) χ2(3) = 0.3 (p = 0.96) χ2(3) = 5.5 (p = 0.14) χ2(3) = 3.7 (p = 0.30) χ2(3) = 8.7 (p = 0.034) χ2(3) = 3.1 (p = 0.38) χ2(3) = 8.5 (p = 0.04) f2(t×g) 0.05 (0,0.11) 0.04 (0, 0.11) 0.03 (0, 0.08) 0.05 (0, 0.12) 0.05 (0, 0.11) 0.08 (0,0.16) 0.03 (0, 0.06) 0.04 (0, 0.09) Values are mean ± SD except where indicated. *p < 0.05; Comparing treatment group to PT control at each time point from a mixed effects model with time as a factor. aMixed effects models with time as continuous using the likelihood ratio test. The Chi-squared and corresponding p-values are present (df for time and group=1 and for t×g is 3). t×g tests whether change over time differs between at least one of the treatment groups and PT. f2 is the effect size for the t×g interaction with mean and (95% CI). TABLE IV. Functional Outcomes by Study Groups (N = 78) Week 2-MST (steps) 30–SCST (no. rises) 6-MWT (inches) 2MST Pain 30-SCST Pain 6-MWT Pain ADLS Symptom ADLS Activity PT only 0 189 (67) 11.3 (3.7) 19,800 (3,398) 4.0 (2.4) 3.7 (2.3) 2.4 (2.2) 25.4 (4.7) 32.9 (6.1) 3 25.0 (5.5) 33.4 (6.8) 6 185 (76) 12.7 (3.8) 21,822 (4,346) 3.5 (2.8) 3.5 (2.6) 3.2 (2.5) 24.4 (6.5) 33.5 (8.1) 9 25.0 (6.1) 31.8 (6.9) 12 180 (82) 13.3 (4.8) 21,404 (2,534) 2.9 (2.6) 2.8 (2.2) 2.7 (2.1) 27.8 (6.3) 32.9 (7.7) 18 202 (92) 13.3 (3.7) 21,210 (3,718) 2.6 (2.4) 2.4 (2.0) 2.3 (2.1) 29.6 (5.2)* 36.4 (6.7) NMES plus PT 0 162 (62) 11.4 (1.8) 20,224 (5,162) 3.7 (2.7) 2.5 (2.4) 2.9 (2.4) 23.3 (6.3) 30.9 (4.9) 3 24.6 (6.9) 33.3 (5.2) 6 178 (78) 13.6 (2.6) 21,696 (3,905) 2.1 (2.5) 1.4 (1.8) 1.6 (1.9) 27.9 (6.4)* 35.5 (5.5) 9 29.3 (6.6) 39.8 (4.1)* 12 235 (46)* 13.9 (2.3) 22,210 (3,991) 3.0 (2.4) 2.0 (2.6) 1.9 (2.1) 26.5 (7.6) 35.7 (5.9)* 18 233 (75) 14.4 (1.5) 22,984 (3,390) 1.7 (2.4) 0.7 (0.9) 1.6 (2.2) 29.7 (4.7) 38.1 (4.9) WALK plus PT 0 199 (60) 12.7 (3.9) 19,728 (5,347) 3.0 (2.1) 2.1 (1.9) 1.8 (2.1) 25.1 (5.2) 30.9 (7.2) 3 26.2 (6.0) 34.8 (5.8)* 6 224 (64) 14.4 (4.0) 22,197 (3,242) 2.5 (2.5) 1.4 (2.0) 1.7 (2.8) 28.1 (4.7) 34.9 (6.1) 9 29.6 (4.1)* 35.3 (5.8)* 12 258 (42) 14.4 (2.3) 21,595 (3,092) 3.0 (2.4) 1.7 (2.5) 1.6 (2.0) 30.8 (3.0)* 36.7 (5.1)* 18 224 (56) 15.0 (2.7) 22,105 (3,718) 2.1 (2.7) 1.5 (2.2) 2.1 (2.9) 30.9 (4.3) 36.9 (6.0) Combo plus PT 0 172 (67) 10.7 (2.8) 18,974 (4,603) 3.7 (2.1) 2.7 (1.4) 2.5 (2.1) 22.9 (4.3) 31.5 (2.4) 3 26.0 (2.8) 33.0 (3.0) 6 205 (75)* 13.2 (1.9) 21,696 (3,905) 2.4 (1.4) 1.2 (1.4) 1.4 (1.2)* 27.4 (4.0)* 35.6 (4.4) 9 27.2 (4.7) 36.5 (4.4)* 12 202 (73) 14.5 (2.1) 20,824 (6,223) 1.9 (2.3) 1.2 (1.5) 1.6 (1.7) 27.6 (4.8) 36.6 (5.4)* 18 216 (73) 15.2 (2.2) 22,945 (2,883) 1.8 (2.6) 0.8 (1.5) 1.2 (2.1)* 29.8 (4.7) 38.6 (5.6) F2 for the mixed effects models F2 for interaction testa t×g χ2(3) = 4.0 (p = 0.26) χ2(3) = 3.3 (p = 0.35) χ2(3) = 0.3 (p = 0.96) χ2(3) = 5.5 (p = 0.14) χ2(3) = 3.7 (p = 0.30) χ2(3) = 8.7 (p = 0.034) χ2(3) = 3.1 (p = 0.38) χ2(3) = 8.5 (p = 0.04) f2(t×g) 0.05 (0,0.11) 0.04 (0, 0.11) 0.03 (0, 0.08) 0.05 (0, 0.12) 0.05 (0, 0.11) 0.08 (0,0.16) 0.03 (0, 0.06) 0.04 (0, 0.09) Week 2-MST (steps) 30–SCST (no. rises) 6-MWT (inches) 2MST Pain 30-SCST Pain 6-MWT Pain ADLS Symptom ADLS Activity PT only 0 189 (67) 11.3 (3.7) 19,800 (3,398) 4.0 (2.4) 3.7 (2.3) 2.4 (2.2) 25.4 (4.7) 32.9 (6.1) 3 25.0 (5.5) 33.4 (6.8) 6 185 (76) 12.7 (3.8) 21,822 (4,346) 3.5 (2.8) 3.5 (2.6) 3.2 (2.5) 24.4 (6.5) 33.5 (8.1) 9 25.0 (6.1) 31.8 (6.9) 12 180 (82) 13.3 (4.8) 21,404 (2,534) 2.9 (2.6) 2.8 (2.2) 2.7 (2.1) 27.8 (6.3) 32.9 (7.7) 18 202 (92) 13.3 (3.7) 21,210 (3,718) 2.6 (2.4) 2.4 (2.0) 2.3 (2.1) 29.6 (5.2)* 36.4 (6.7) NMES plus PT 0 162 (62) 11.4 (1.8) 20,224 (5,162) 3.7 (2.7) 2.5 (2.4) 2.9 (2.4) 23.3 (6.3) 30.9 (4.9) 3 24.6 (6.9) 33.3 (5.2) 6 178 (78) 13.6 (2.6) 21,696 (3,905) 2.1 (2.5) 1.4 (1.8) 1.6 (1.9) 27.9 (6.4)* 35.5 (5.5) 9 29.3 (6.6) 39.8 (4.1)* 12 235 (46)* 13.9 (2.3) 22,210 (3,991) 3.0 (2.4) 2.0 (2.6) 1.9 (2.1) 26.5 (7.6) 35.7 (5.9)* 18 233 (75) 14.4 (1.5) 22,984 (3,390) 1.7 (2.4) 0.7 (0.9) 1.6 (2.2) 29.7 (4.7) 38.1 (4.9) WALK plus PT 0 199 (60) 12.7 (3.9) 19,728 (5,347) 3.0 (2.1) 2.1 (1.9) 1.8 (2.1) 25.1 (5.2) 30.9 (7.2) 3 26.2 (6.0) 34.8 (5.8)* 6 224 (64) 14.4 (4.0) 22,197 (3,242) 2.5 (2.5) 1.4 (2.0) 1.7 (2.8) 28.1 (4.7) 34.9 (6.1) 9 29.6 (4.1)* 35.3 (5.8)* 12 258 (42) 14.4 (2.3) 21,595 (3,092) 3.0 (2.4) 1.7 (2.5) 1.6 (2.0) 30.8 (3.0)* 36.7 (5.1)* 18 224 (56) 15.0 (2.7) 22,105 (3,718) 2.1 (2.7) 1.5 (2.2) 2.1 (2.9) 30.9 (4.3) 36.9 (6.0) Combo plus PT 0 172 (67) 10.7 (2.8) 18,974 (4,603) 3.7 (2.1) 2.7 (1.4) 2.5 (2.1) 22.9 (4.3) 31.5 (2.4) 3 26.0 (2.8) 33.0 (3.0) 6 205 (75)* 13.2 (1.9) 21,696 (3,905) 2.4 (1.4) 1.2 (1.4) 1.4 (1.2)* 27.4 (4.0)* 35.6 (4.4) 9 27.2 (4.7) 36.5 (4.4)* 12 202 (73) 14.5 (2.1) 20,824 (6,223) 1.9 (2.3) 1.2 (1.5) 1.6 (1.7) 27.6 (4.8) 36.6 (5.4)* 18 216 (73) 15.2 (2.2) 22,945 (2,883) 1.8 (2.6) 0.8 (1.5) 1.2 (2.1)* 29.8 (4.7) 38.6 (5.6) F2 for the mixed effects models F2 for interaction testa t×g χ2(3) = 4.0 (p = 0.26) χ2(3) = 3.3 (p = 0.35) χ2(3) = 0.3 (p = 0.96) χ2(3) = 5.5 (p = 0.14) χ2(3) = 3.7 (p = 0.30) χ2(3) = 8.7 (p = 0.034) χ2(3) = 3.1 (p = 0.38) χ2(3) = 8.5 (p = 0.04) f2(t×g) 0.05 (0,0.11) 0.04 (0, 0.11) 0.03 (0, 0.08) 0.05 (0, 0.12) 0.05 (0, 0.11) 0.08 (0,0.16) 0.03 (0, 0.06) 0.04 (0, 0.09) Values are mean ± SD except where indicated. *p < 0.05; Comparing treatment group to PT control at each time point from a mixed effects model with time as a factor. aMixed effects models with time as continuous using the likelihood ratio test. The Chi-squared and corresponding p-values are present (df for time and group=1 and for t×g is 3). t×g tests whether change over time differs between at least one of the treatment groups and PT. f2 is the effect size for the t×g interaction with mean and (95% CI). DISCUSSION We compared three self-management treatments plus usual care PT to usual care PT alone. For strength, the COMBO group (NMES, graduated strength walking plus usual care PT) had a statistically significant greater increase in lower extremity strength compared to the PT-only group. The results for pain, function and ADLS showed improvement in all four groups over 18 weeks and no significant difference between groups. However, clinical significance is still to be determined. This pilot study also examined the feasibility of using these self-management interventions in an active duty population. Limited studies exist using NMES and strength walking combined with conventional rehabilitation for knee injuries. NMES therapy has been shown to be effective combined with conventional rehabilitation, after anterior cruciate ligament reconstruction, for increasing quadriceps strength but inconclusive for function performance.42–44 The use of a progressive walking program with a weighted vest simulates load of required gear worn during military operations.7 The progressive weight increase potentially minimizes re-injury and aids in re-acclimation to load carriage during military operations.45 NMES is light-weight and portable with rechargeable batteries. In field conditions recharging may be problematic.A Cochran review46 of eight randomized clinical trials (N = 345), examined NMES with or without exercise for knee pain and function in PFPS. They concluded there is insufficient and low-quality evidence for NMES achieving clinically important differences in knee pain patients. For future research, outcome measures that mimic soldier-related tasks, or components of the Army Combat Readiness Test might be considered. There were several limitations to this study. First, the functional measures do not reflect soldier-related required tasks. This may limit the external validity. As no significant differences were found for functional measures, other measures more aligned with military tasks may have identified performance differences. As a pilot/feasibility study, the generalizability is limited. As approximately only 15% of patients with musculoskeletal disorders are referred to physical therapy, the application to all military members with knee injuries is unknown. The completion rate was low (64.1%), questioning the reliability of the results. In addition, the knee injuries were heterogenous, and specific exercises may have greater impact on some injuries (e.g., tendinopathies, overuse injuries) compared to other injuries (e.g., joint sprain). It is possible that a more homogenous subset of injuries may have produced different results. Finally, compliance with self-management was difficult to confirm, especially with the NMES device. The 300PV compliance monitor did not record participant’s time usage if turned off prior to completing the training cycle. This may have reduced the recorded time, making it difficult to estimate true compliance. Prior studies have shown that self-reported compliance with independent exercise programs can be greatly over-estimated. CONCLUSIONS A combination of NMES and weighted vest walking in addition to usual care PT showed greater changes in muscle strength compared to usual care PT in a military population with knee injury. However, these interventions did not show any greater improvement in pain and function compared to physical therapy over 18 weeks. Given that the function results were the same as in usual care PT, these self-management interventions may have value for service members who cannot attend usual PT care. Further study is needed on the feasibility and implementation of these strategies within the military. ACKNOWLEDGMENTS We would like to thank the service members who volunteered to participate in this study. FUNDING This research was sponsored by the TriService Nursing Research Program, Uniformed Services University of the Health Sciences. The Uniformed Services University of the Health Sciences (USU), 4301 Jones Bridge Rd., Bethesda, MD 20814-4799, is the awarding and administering office. Award number: HU0001-10-1-TS04. RECRUITMENT INFORMATION AND ETHICAL APPROVAL Participants were recruited from Walter Reed National Military Medical Center (WRNMMC), Bethesda, MD; Malcolm Grow Medical Clinic (MGMC), Joint Base Andrews, Maryland; and Womack Army Medical Center (WAMC), Fort Bragg, NC. 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The information or content and conclusions do not necessarily represent the official position or policy of, nor should any official endorsement be inferred by, the TriService Nursing Research Program, the Uniformed Services University of the Health Sciences, the Department of Defense, or the U.S. Government (Award # HU0001-10-1-TS04; Project # N10-P01). The Uniformed Services University of the Health Sciences (USU), 4301 Jones Bridge Rd., Bethesda, MD 20814–4799 is the awarding and administering office. © Association of Military Surgeons of the United States 2018. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
TI - Self-Managed Strength Training for Active Duty Military With a Knee Injury: A Randomized Controlled Pilot Trial
JF - Military Medicine
DO - 10.1093/milmed/usy347
DA - 2019-07-01
UR - https://www.deepdyve.com/lp/oxford-university-press/self-managed-strength-training-for-active-duty-military-with-a-knee-MgGixvEIVx
SP - e174
VL - 184
IS - 7-8
DP - DeepDyve
ER -