SEARCH

SEARCH BY CITATION

Abstract

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

Objective

To compare the effects of neuromuscular exercise (NEXA) and quadriceps strengthening (QS) on the knee adduction moment (an indicator of mediolateral distribution of knee load), pain, and physical function in patients with medial knee joint osteoarthritis (OA) and varus malalignment.

Methods

One hundred patients with medial knee pain, mostly moderate-to-severe radiographic medial knee OA, and varus malalignment were randomly allocated to one of two 12-week exercise programs. Each program involved 14 individually supervised exercise sessions with a physiotherapist plus a home exercise component. Primary outcomes were peak external knee adduction moment (3-dimensional gait analysis), pain (visual analog scale), and self-reported physical function (Western Ontario and McMaster Universities Osteoarthritis Index).

Results

Eighty-two patients (38 [76%] of 50 in the NEXA group and 44 [88%] of 50 in the QS group) completed the trial. There was no significant between-group difference in the change in the peak knee adduction moment (mean difference 0.13 Nm/[body weight × height]% [95% confidence interval (95% CI) −0.08, 0.33]), pain (mean difference 2.4 mm [95% CI −6.0, 10.8]), or physical function (mean difference −0.8 units [95% CI −4.0, 2.4]). Neither group showed a change in knee moments following exercise, whereas both groups showed similar significant reductions in pain and improvement in physical function.

Conclusion

Although comparable improvements in clinical outcomes were observed with both neuromuscular and quadriceps strengthening exercise in patients with moderate varus malalignment and mostly moderate-to-severe medial knee OA, these forms of exercise did not affect the knee adduction moment, a key predictor of structural disease progression.

Knee osteoarthritis (OA), predominantly affecting the medial tibiofemoral compartment, is a common chronic condition leading to pain, loss of function, and reduced quality of life. Patients with medial knee OA and varus malalignment have greater functional ([1]) and structural ([2]) decline than those with more neutrally aligned knees. Interventions that not only reduce symptoms but also slow disease progression are particularly needed for this subgroup of patients with knee OA.

The poorer prognosis for such patients is likely facilitated by a greater compressive load on the diseased compartment ([3]). Three-dimensional gait analysis is typically used to estimate compressive joint loads. The most widely studied parameter in knee OA is the external knee adduction moment (KAM), which reflects mediolateral joint load distribution. The KAM is higher in patients with varus malalignment than in those without ([4-6]), and higher KAM indices are associated with increased risk of OA structural progression ([7, 8]). The KAM is therefore a relevant target for treatments to slow disease progression.

Quadriceps strengthening (QS) is effective for reducing pain and improving physical function in patients with knee OA ([9, 10]). However, QS may be ineffective for reducing pain in patients with varus malalignment ([11]), and it does not seem to reduce the KAM ([11, 12]). This may be because QS aims to increase muscle force production rather than more directly targeting biomechanical contributors to medial compartment load (such as KAM lever arm length), which may require more specific focus on using muscles to control limb and overall body position.

Neuromuscular exercise (NEXA) is typically performed in functional weight-bearing positions and emphasizes quality of movement and alignment of the trunk and lower limb ([13]). Studies show that NEXA can improve pain and function in patients with knee OA ([13-15]), but that its addition to a strengthening program does not confer additional benefits ([16, 17]). Because some features of NEXA could affect knee joint load (via limb and trunk alignment), this intervention may be beneficial for patients with varus malalignment. There are no direct comparisons of NEXA and QS exercise, only preliminary findings from 2 uncontrolled studies supporting the potential efficacy of NEXA for reducing the KAM ([14, 18]) and no studies of neuromuscular training for this specific knee OA subgroup.

The aim of this randomized controlled trial was to compare the effects of a 12-week NEXA program with those of a QS exercise program in patients with medial knee OA and varus malalignment. The primary hypotheses were that 1) the peak KAM during walking would be reduced by NEXA but not by QS, leading to a significant difference between groups; and 2) NEXA would improve self-reported physical function and pain to a greater extent than QS.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

Participants

One hundred community volunteers ages ≥50 years with medial knee OA were recruited from July 2010 to June 2012 via advertisements. The institutional ethics committee approved the study, and all participants provided written informed consent.

Subjects were eligible if they reported average knee pain over the past week of ≥25 on a 100-mm visual analog scale (VAS), had pain/tenderness predominantly over the medial knee region, and had radiographic medial tibiofemoral joint OA. Specific inclusion criteria based on a posteroanterior weight-bearing radiograph were 1) Kellgren/Lawrence grade ≥2 ([19]); 2) anatomic axis angle of <181° for females or <183° for males, indicating varus alignment based on mechanical axis values using the sex-specific regression equations described by Krauss et al ([20, 21]); 3) medial tibiofemoral joint narrowing grade greater than lateral tibiofemoral joint narrowing grade ([22]); and 4) medial compartment osteophyte grade greater than or equal to lateral compartment osteophyte grade ([22]). Major exclusion criteria included knee surgery or intraarticular corticosteroid injection within 6 months, current or past (within 4 weeks) oral corticosteroid treatment, systemic arthritic conditions, prior hip or knee joint replacement or tibial osteotomy surgery, other nonpharmacologic treatment within the past 6 months, and body mass index of >36 kg/m2.

Procedures

This was a randomized, assessor-blinded, controlled trial. A detailed protocol has been published previously ([23]). Potential participants underwent telephone screening, then radiographic examination. Following the baseline assessment, the participants were randomized in permuted blocks of 6 or 8, stratified by physiotherapist, to one of two 12-week exercise groups: NEXA or QS. The randomization schedule was prepared by the study biostatistician, using a computer-generated random number table. Allocations were sealed in opaque, consecutively numbered envelopes by a person not involved with the trial, and these were kept in a central locked location. The envelopes were opened in sequence by an independent administrator who then revealed the group allocation to the relevant physiotherapist by e-mail, before the participant presented for his or her first appointment.

Interventions

Nine physiotherapists in private practices delivered both interventions. They had an average of 12 years (range 2–30 years) of clinical experience with musculoskeletal disorders. Three (30%) of these physiotherapists had postgraduate masters degree–level qualifications. All of the physiotherapists attended a 3-hour training session and were given a treatment manual.

The exercise programs have been described in detail elsewhere ([23]). For both programs, only the study leg was specifically exercised. Patients visited their physiotherapist 14 times during the 12 weeks: twice in the first and second weeks and weekly thereafter. Each visit lasted 30–40 minutes. Patients were asked to perform exercises at home 4 times each week in addition to the supervised physiotherapy sessions.

Neuromuscular exercises

Patients in the NEXA group performed 6 exercises aimed at improving the position of the trunk and lower limb joints relative to one another while dynamically and functionally strengthening the lower limb (Table 1 and Figure 1; additional information is available in Supplementary Figure 1, available on the Arthritis & Rheumatology web site at http://onlinelibrary.wiley.com/doi/10.1002/art.38317/abstract). During all exercises, the level of effort was to be self-rated as at least 5 of 10 on a modified Borg rating of perceived exertion (RPE) CR-10 scale ([24]). Progression, as determined by the physiotherapist, was provided by varying the repetitions, direction, and velocity of the movements by increasing the load and/or changing the support surface.

Table 1. Summary of exercise programs
  1. a

    Using the modified Borg rating of perceived exertion CR-10 scale.

Neuromuscular exerciseQuality of movement emphasized, with aim to position knee over foot and to avoid a medial or lateral position of the knee in relation to the foot
Effort rating of 5–8 of 10a
1. Forward and backward sliding or steppingStanding on affected leg and sliding or stepping opposite leg forward and backward, with progression achieved by adding an elastic resistance band around the affected leg to apply a varus-directed force during the movement, which the patient had to counteract in order to maintain the knee in the neutrally aligned position
3 sets of 10 repetitions
2. Sideways exercisesStanding on affected leg and sliding or stepping opposite leg sideways, standing on foam and closing eyes during the movement
Progression was achieved by adding an elastic resistance band around the study leg to apply a varus-directed force throughout movement, which the patient had to counteract in order to maintain the knee in the neutrally aligned position
3 sets of 10 repetitions
3. Functional hip muscle strengtheningStanding isometric abduction (2 sets of 5 repetitions), with progression to elastic band–resisted abduction during side stepping (2 × 30 steps)
4. Functional knee muscle strengtheningSquatting against a wall, with progressing to rising from sitting with increased weight taken through the study leg
3 sets of 10 repetitions
5. Step-ups and downStepping onto a step, with progression to add 2-kg hand weights and then step down with forward touch-down of opposite leg
3 sets of 10 repetitions
6. BalanceStanding on affected leg, with progressions including adding arm movements and then stepping forward onto foam
2 minutes practice
Quadriceps strengthening exerciseEach exercise 2–3 sets of 10 repetitions with 5–10-second hold
Resistance equivalent to 10-repetition maximum and rating of 5–8 of 10a
1. Quads over a roll (inner range knee extension)Using resistance of ankle weights
2. Knee extension in sittingSitting with knee at 90° flexion, fully extend knee using resistance of ankle weights
3. Knee extension with hold at 30° knee flexionSitting with knee at 90° flexion, extend to 30° using resistance of ankle weights
4. Straight leg raiseSupine, raise leg to 30° hip flexion using resistance of ankle weights
5. Outer range knee extensionSitting with knee at 90° flexion, extend to 60° against resistance of elastic band
image

Figure 1. Two examples of exercises in the neuromuscular program. Note that the patients are required to maintain the knee in an aligned neutral position as they slide the leg forward/backward or sideways. An elastic resistance band applies a varus-directed force that requires the patient to counteract this by pulling in a valgus direction in order to maintain the knee position.

Download figure to PowerPoint

Quadriceps strengthening

Patients in the QS group completed 5 non–weight-bearing exercises based on those used in our previous clinical trial ([11]) (Table 1). The dose was 2–3 sets of 10 repetitions, with the starting weight matched to the participant's 10-repetition maximum weight if possible or to a weight needed to achieve a self-rating of 5–8 of 10 on the modified Borg RPE CR-10 scale ([24]). Progression was achieved by increasing the number of sets, the duration of the hold phase of the exercise, and the ankle weight or elastic band resistance, as guided by the physiotherapist.

Outcome measures

Measurements were performed in a blinded manner at baseline and followup, by the same assessor.

Gait analysis

Patients underwent 3-dimensional gait analysis during walking at their self-selected usual/comfortable speed. Movement was recorded using a 12-camera motion analysis system (Vicon MX) and AMTI force plates as the patients walked barefoot along a 10-meter walkway. Speed was determined using 2 photoelectric beams. Five successful trials (complete foot strike from one foot on one force plate) were achieved. The motion of 37 reflective markers (sample rate 120 Hz) and the ground reaction force (sample rate 1,200 Hz) were used to calculate the external KAM via inverse dynamics, using the University of Western Australia model programmed in Vicon BodyBuilder ([25]). Test–retest reliability (coefficient of multiple determination [R2]) of knee adduction/abduction moment curves has been reported as at least 0.75 ([25]). The primary variable was the overall peak KAM, normalized by dividing by body weight (N) times height (m) and expressed as a percentage (Nm/[body weight (BW) × height (Ht)]%), averaged over 5 trials. The normalized positive KAM angular impulse (positive area under the KAM-time curve) (Nm · second/[BW × Ht]%) was calculated as a secondary frontal plane knee moment variable. We also calculated the normalized peak knee flexion moment (KFM) during stance (Nm/[BW × Ht]%) to ensure that this sagittal plane moment did not concurrently increase and thus potentially counteract any beneficial effects of intervention on knee load ([26]).

Self-reported pain and physical function

The primary pain outcome was average overall knee pain during the past week. This, together with pain on walking during the past week, were assessed using a 100-mm VAS with terminal descriptors of “no pain” and “worst pain possible” ([27]). Such measurement has demonstrated reliability in OA ([27]). Pain was also assessed, along with stiffness and physical function, using the disease-specific valid and reliable Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) ([28]). The physical function subscale, which comprises 17 questions, was used as a primary outcome measure.

At the followup assessment, patients were asked to rate their overall change, change in pain, and change in physical function (compared with baseline) on a 7-point ordinal scale (1 = much worse and 7 = much better). All 3 ratings were dichotomized so that “improvement” was defined as a rating of “moderately better” or “much better.”

Muscle strength

Maximum, normalized, isometric strength (Nm/kg) was recorded for key muscle groups. Quadriceps and hamstring strength was measured with the patient in the sitting position at 60° knee flexion, using an isokinetic dynamometer (Kin-Com 125-AP; Chattecx), and the best of 3 maximal contractions was recorded. Isometric hip abductor strength and hip internal and external rotation muscle strength were measured using a hand-held dynamometer (Lafayette Manual Muscle Test System 01163) ([29]). For the hip strength measurements, the mean of 2 maximal trials was recorded ([29]).

Physical performance measures

The physical performance measures included a timed stair climb assessing the time to walk up and down six 17.5-cm–high steps as quickly as possible, using a hand rail if preferred ([30]); 30-second sit-to-stand test assessing the number of sit–stand–sits performed in 30 seconds ([31]); and balance tests, including timed single leg stance assessing the length of time single limb standing can be maintained up to 30 seconds, with the best attempt from 2 trials recorded ([32]), step test, whereby the patient stands on the study leg, and the number of steps by the nonstudy leg onto a 15-cm–high step and back to the floor in 15 seconds performed as quickly as possible is recorded ([33]), and the four square step test, which assesses the patient's ability to change direction while stepping ([34]).

Health-related quality of life

The Assessment of Quality of Life Version 2 instrument was used to measure health-related quality of life. This questionnaire has strong psychometric properties and is more responsive than other widely used scales ([35]).

Other measures

Radiographic disease severity was rated using the Kellgren/Lawrence system ([36]). Baseline de mographic information was collected. Co-interventions and adverse effects were determined from patient log books and physiotherapist treatment notes. Adherence was assessed by the number of physiotherapy sessions attended and by the number of home exercise sessions completed, as recorded by patients in a log book. The percent home exercise adherence was calculated by dividing the number of sessions completed by the maximum required number of 48.

The physical activity of the patients was self-reported, using the Physical Activity Scale for the Elderly (PASE) ([37]). This instrument records both the level and type of recreational and occupational physical activity undertaken by patients during the previous week.

Sample size

The primary end points were the peak KAM during the stance phase of walking, overall knee pain score on a VAS, and WOMAC physical function score. The minimum clinically important difference (MCID) to be detected for a change in the KAM is unknown. We powered the study to detect a between-group difference in change in the KAM of 7.5% (a decrease of ∼0.30 Nm/[BW × Ht]% in the NEXA group and no change in the QS group), because this may be associated with a significant decrease in the risk of disease progression ([7]). The MCID for OA trials is an 18-mm change in the pain score on a 100-mm VAS ([38]) and a change of 6 (of 68) physical function WOMAC units ([39]). Based on our previous data, we assumed a between-patient standard deviation of change in the KAM of 0.40 Nm/(BW × Ht)%, 30 mm for pain, and 12 units for WOMAC physical function, and a baseline-to–week 13 correlation in each outcome measure of 0.60. Thus, the required sample for a 2-tailed comparison of 2 groups using analysis of covariance (ANCOVA) with baseline values as covariates and assuming a baseline-to–week 13 correlation of 0.60, when the standardized effect size is 0.5 (WOMAC physical function), power is 0.8, and the Type I error is 0.05 was 41 patients per group ([40]). This was increased to 50 patients per group to allow for a 15% withdrawal rate. Due to the larger standardized effect size of the VAS and peak KAM end points, power for these measures was greater (92% and 99%, respectively).

Statistical analysis

The main comparative analyses between groups were performed by evaluators who were blinded with regard to the type of exercise, using an intent-to-treat approach. P values less than 0.05 were considered significant. To account for missing data, multiple imputations of missing followup measures were performed as a sensitivity analysis. Missing data were imputed for 12 patients in the NEXA group and 6 patients in the QS group, using multiple imputation assuming data were missing at random ([41]). For continuous outcome measures, differences in the mean change (followup minus baseline) was compared between groups using ANCOVA adjusted for baseline values of the outcome. In a subsequent analysis, walking speed was also included as a covariate for the KAM and peak KFM parameters. Model diagnostic checks utilized residual plots. Results are presented as estimated differences with 95% confidence intervals (95% CIs). The likelihood of overall improvement, as well as improvement in pain and function, was compared between groups using log-binomial regression. Results are presented as relative risks with 95% CIs.

RESULTS

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

Of the 999 volunteers, 899 (90%) were ineligible or chose not to participate. In total, 100 patients (50 in the NEXA group and 50 in the QS group) were randomized, and 82 patients (38 patients [76%] in the NEXA group and 44 patients [88%] in the QS group) completed the followup assessment (Figure 2). The baseline characteristics of the patients were similar between groups (Table 2). Patients in the cohort had mainly moderate-to-severe radiographic OA, were overweight, and had moderate varus malalignment (average 6° varus in males and 5° in females). More patients in the NEXA group withdrew due to increased pain or an unanticipated decision to undergo total joint replacement (n = 7) compared with patients in the QS group (n = 1). The baseline characteristics of the 18 participants lost to followup were similar to those of patients completing the study (data not shown).

image

Figure 2. Flow diagram of the study protocol. BMI = body mass index; K/L = Kellgren/Lawrence; NEXA = neuromuscular exercise; QS = quadriceps strengthening; IQR = interquartile range.

Download figure to PowerPoint

Table 2. Demographic and clinical characteristics of the NEXA and QS groups*
CharacteristicNEXA (n = 50)QS (n = 50)
  1. Except where indicated otherwise, values are the mean ± SD. NEXA = neuromuscular exercise; QS = quadriceps strengthening; IQR = interquartile range; COX-2 = cyclooxygenase 2.

  2. a

    Anatomic alignment, where neutral alignment is 181° for females and 183° for males and varus is <181° for females and <183° for males.

  3. b

    Using the Kellgren/Lawrence grading system.

  4. c

    Defined as at least once per week.

Age, years62.7 ± 7.362.2 ± 7.4
Symptom duration, median (IQR) months60.0 (96.0)84.0 (93.6)
Height, cm168.1 ± 9.2165.6 ± 10.1
Body mass, kg83.8 ± 13.581.6 ± 15.1
Body mass index, kg/m229.6 ± 3.929.7 ± 4.3
Male sex, no. (%)24 (48)24 (48)
Affected knee (right/left)30/2023/27
Unilateral symptoms, no. (%)20 (40)19 (38)
Dominant side affected, no. (%)28 (56)25 (50)
Knee alignment, degreesa177.3 ± 3.0176.4 ± 3.9
Males178.1 ± 2.7175.2 ± 4.5
Females176.5 ± 3.1177.1 ± 3.3
Radiographic disease severity, no. (%)b  
Grade 29 (18)13 (26)
Grade 321 (42)22 (44)
Grade 420 (40)15 (30)
Current drug treatment, no. (%)c  
Analgesics (acetaminophen combinations)17 (34)20 (40)
Nonsteroidal antiinflammatory drugs10 (20)10 (20)
COX-2 inhibitors3 (6)4 (8)
Opioids1 (2)1 (2)
Topical antiinflammatory agents3 (6)5 (10)
Glucosamine/chondroitin products24 (48)23 (46)
Topical liniment rubs9 (18)10 (20)
Fish oil3 (6)8 (16)

Outcome measures in the NEXA and QS groups

Table 3 shows that there were no differences between the NEXA and QS groups for changes in the peak KAM (mean difference 0.13 Nm/[BW × Ht]% [95% CI −0.08, 0.33], P = 0.23), overall VAS pain score (mean difference 2.4 mm [95% CI −6.0, 10.8], P = 0.57), or WOMAC physical function score (mean difference −0.8 units [95% CI −4.0, 2.4], P = 0.63). Observed between-group differences were smaller than the MCID, and the 95% CIs indicated that the ranges of plausible between-group differences were unlikely to have included differences of any practical importance. Results were unchanged when the sensitivity analysis was performed. Neither group showed a significant change in the peak KAM from baseline, whereas significant improvements in pain and physical function were achieved in both groups (Table 3).

Table 3. Differences in outcome measures between groups*
OutcomeWeek 0Week 13Within-group difference, week 13 minus week 0, mean (95% CI)aBetween-group difference, NEXA minus QS, mean (95% CI)a
NEXA (n = 50)QS (n = 50)NEXA (n = 38)QS (n = 44)NEXA (n = 38)QS (n = 44)
  1. Except where indicated otherwise, values are the mean ± SD. 95% CI = 95% confidence interval; KAM = knee adduction moment; BW = body weight; Ht = height; VAS = visual analog scale; WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index; KFM = knee flexion moment; AQoL = Assessment of Quality of Life; PASE = Physical Activity Scale for the Elderly.

  2. a

    Adjusted for baseline values.

  3. b

    Number who maintained balance for the full 30 seconds. For neuromuscular exercise (NEXA) at week 0, n = 15 (30%); at week 13, n = 16 (42%). For quadriceps strengthening (QS) at week 0, n = 23 (46%); at week 13, n = 17 (39%).

  4. c

    P < 0.001.

Peak KAM, Nm/(BW × Ht)%3.05 ± 0.903.21 ± 0.883.26 ± 0.953.30 ± 0.790.12 (−0.04, 0.29)−0.04 (−0.18, 0.10)0.13 (−0.08, 0.33)
Overall VAS score for pain, mm54.0 ±13.354.2 ± 16.834.1 ± 23.631.4 ± 19.3−19.9 (−26.9, −12.9)−22.0 (−27.9, −16.1)2.4 (−6.0, 10.8)
WOMAC physical function score (range 0–68)26.0 ± 9.128.2 ± 9.918.3 ± 9.620.1 ± 9.8−7.5 (−10.1, −4.9)−7.3 (−9.7, −4.9)−0.8 (−4.0, 2.4)
KAM impulse, Nm · sec/(BW × Ht)%1.15 ± 0.371.21 ± 0.361.20 ± 0.361.23 ± 0.370.02 (−0.05, 0.09)−0.02 (−0.08, 0.03)0.03 (−0.05, 0.12)
Peak KFM, Nm/(BW × Ht)%4.02 ± 1.383.96 ± 1.593.89 ± 1.644.05 ± 1.79−0.03 (−0.39, 0.32)0.07 (−0.18, 0.32)−0.11 (−0.54, 0.31)
Walking velocity, m/second1.21 ± 0.181.19 ± 0.221.25 ± 0.201.24 ± 0.210.04 (0.00, 0.09)0.03 (0.00, 0.07)0.01 (−0.04, 0.07)
VAS score for pain on walking, mm59.5 ± 15.055.3 ± 22.439.6 ± 25.940.0 ± 22.9−19.6 (−27.5, −11.8)−15.8 (−22.7, −8.9)−2.0 (−11.3, 7.4)
WOMAC pain score (range 0–20)8.1 ± 2.28.8 ± 3.36.4 ± 3.16.4 ± 2.9−1.7 (−2.6, −0.9)−2.4 (−3.1, −1.7)0.4 (−0.6, 1.4)
WOMAC stiffness score (range 0–8)4.3 ± 1.64.4 ± 1.63.6 ± 1.43.9 ± 1.8−0.7 (−1.1, −0.2)−0.5 (−1.0, 0.0)−0.2 (−0.8, 0.3)
AQoL version 2 (range −0.04–1.00)0.73 ± 0.140.73 ± 0.180.78 ± 0.140.78 ± 0.160.04 (0.00, 0.09)0.03 (0.00, 0.06)0.01 (−0.03, 0.05)
PASE score (range 0–>400)159.9 ± 82.7171.7 ± 89.81.75 ± 112.0196.2 ± 88.415.0 (−13.4, 43.5)19.2 (−2.8, 41.2)−9.1 (−42.9, 24.6)
Quadriceps strength, Nm/kg1.44 ± 0.421.47 ± 0.471.59 ± 0.471.62 ± 0.510.15 (0.08, 0.21)0.09 (0.02, 0.16)0.06 (−0.04, 0.16)
Hamstring strength, Nm/kg0.66 ± 0.200.71 ± 0.230.71 ± 0.230.79 ± 0.260.04 (0.00, 0.08)0.05 (0.01, 0.09)−0.02 (−0.07, 0.04)
Hip abduction strength, Nm/kg1.09 ± 0.381.19 ± 0.441.20 ± 0.451.23 ± 0.410.11 (0.02, 0.20)−0.01 (−0.08, 0.06)0.09 (−0.02, 0.21)
Hip extension strength, Nm/kg1.63 ± 0.561.78 ± 0.751.75 ± 0.541.86 ± 0.700.14 (0.02, 0.26)−0.03 (−0.14, 0.08)0.11 (−0.04, 0.26)
Hip internal rotation strength, Nm/kg0.47 ± 0.170.52 ± 0.180.50 ± 0.170.56 ± 0.170.05 (0.03, 0.08)0.03 (−0.01, 0.06)0.01 (−0.03, 0.05)
Hip external rotation strength, Nm/kg0.38 ± 0.140.39 ± 0.140.41 ± 0.120.45 ± 0.140.03 (0.01, 0.06)0.04 (0.01, 0.07)−0.02 (−0.05, 0.02)
Timed stair climb, seconds7.89 ± 2.458.08 ± 3.897.11 ± 2.236.84 ± 1.88−0.67 (−1.17, −0.18)−0.69 (−1.21, −0.16)0.11 (−0.46, 0.68)
30-second sit-to-stand, repetitions10.7 ± 2.310.6 ± 2.911.7 ± 2.112.0 ± 2.51.0 (0.4, 1.6)0.9 (0.4, 1.4)−0.03 (−0.72, 0.66)
Four square step test, seconds9.1 ± 2.18.6 ± 2.38.1 ± 1.87.9 ± 1.7−0.8 (−1.2, −0.5)−0.3 (−0.6, 0.0)−0.38 (−0.79, 0.03)
Step test, repetitions12.5 ± 3.113.1 ± 3.614.1 ± 3.214.4 ± 4.31.5 (0.8, 2.1)0.9 (0.2, 1.6)0.46 (−0.45, 1.37)
Single leg balance test, secondsb15.2 ± 11.920.1 ± 11.520.7 ± 9.918.9 ± 11.25.0 (2.7, 7.3)−1.8 (−3.7, 0.1)5.58 (3.04, 8.11)c

There were no between-group differences for changes in any of the secondary outcomes except the timed single leg stance test, where the NEXA group improved and the QS group showed a decrement (P < 0.001) (Table 3). Results were unchanged when a sensitivity analysis was performed. In the NEXA group, significant improvements were achieved in all secondary outcomes except the KAM impulse, peak KFM, and the PASE score. In the QS group, significant improvements were achieved in all outcomes except the KAM impulse, peak KFM, PASE score, strength of the hip abductors, extensors, and internal rotators, and timed single leg stance test.

The likelihood of patient-perceived improvement overall or improvement in pain and physical function was not different between groups. Improvement overall and improvement in pain was reported by 27 (59%) of 46 patients in the NEXA group and 27 (60%) of 45 patients in the QS group (relative risk 0.94 [95% CI 0.67, 1.33], P = 0.74). Improvement in physical function was reported by 28 (61%) of 46 patients in the NEXA group and 29 (64%) of 45 patients in the QS group (relative risk 0.91 [95% CI 0.66, 1.26], P = 0.57).

Adherence, adverse events, medication use, and co-interventions

The number of physiotherapy sessions attended ranged from 0 to 14 (median 12, interquartile range [IQR] 3.8) for the NEXA group, and from 1 to 14 (median 12, IQR 4.5) for the QS group (P = 0.98). The median percentage of home exercise sessions completed was 82% (IQR 31%) by the NEXA group and 91% (IQR 26%) by the QS group (P = 0.048). Among patients who completed the trial, adverse events were reported by 14 (30%) of 46 patients in the NEXA group and 10 (23%) of 44 patients in the QS group (P = 0.483), and those events were mostly related to increased knee pain (Table 4). Medication use and co-interventions during the trial were similar across groups.

Table 4. Adverse events, medication, and co-interventions in each group*
MeasureNEXAQS
  1. Adverse events were determined in 46 patients in the neuromuscular exercise (NEXA) group and 44 patients in the quadriceps strengthening (QS) group. Medication use and co-intervention were determined in 47 patients in the NEXA group and 44 patients in the QS group. Adverse events were defined as any treatment-related problem that lasted for >2 days and/or caused the patient to seek other treatment. Values are the number (%).

Adverse events14 (30)10 (23)
Increased knee pain10 (22)8 (18)
Back pain1 (2)1 (2)
Pain in other area2 (4)1 (2)
Hip pain2 (4)1 (2)
Swelling/inflammation3 (7)1 (2)
Stiffness1 (2)0 (0)
Medication use  
Analgesia (acetaminophen combinations)15 (32)10 (23)
Nonsteroidal antiinflammatory drugs10 (21)6 (14)
Cyclooxygenase 2 inhibitors1 (2)3 (7)
Opioids2 (4)0 (0)
Topical antiinflammatory agents5 (11)1 (2)
Glucosamine/chondroitin products26 (55)23 (52)
Topical liniment rubs5 (11)5 (11)
Fish oil1 (2)4 (9)
Co-interventions4 (9)2 (5)
Other physiotherapy2 (4)1 (2)
Exercise3 (6)0 (0)
Osteopathy0 (0)1 (2)
Hydrotherapy1 (2)0 (0)
Elastic bandage1 (2)0 (0)

DISCUSSION

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

This study showed that neither 12 weeks of NEXA nor 12 weeks of QS significantly influenced the external KAM during walking in patients with mostly moderate-to-severe medial tibiofemoral OA and varus malalignment. However, both exercise programs provided similar improvement in clinical outcomes, including pain, function, and quality of life.

The finding of no difference in change in the KAM between exercise groups does not support our hypothesis. Three main considerations are related to this finding. The first is that NEXA did not influence the biomechanical contributors to the KAM as intended, most likely the length of the ground reaction force lever arm at the knee. Shortening the lever arm to reduce the KAM can be achieved through biomechanical alterations proximal or distal to the knee to bring the ground reaction force vector closer to the knee, and/or the knee closer to this vector ([42]). Although NEXAs were performed during weight-bearing and focused on lower limb and knee position control, they did not specifically target changes in the KAM during walking. Instead, it is possible that gait-retraining interventions are needed. For example, there is evidence suggesting that teaching patients to lean the trunk toward the affected limb, alter the foot progression angle, or adopt a medial thrust–type gait can reduce the KAM during walking ([42, 43]). It is also possible that training both limbs in a NEXA program is necessary to facilitate stabilization at the pelvis and hip, utilize the crossover effect of motor learning, and maintain ideal lower limb alignment. We chose to exercise only the affected limb, to reduce the patient burden; however, this may have attenuated any potential KAM-reducing benefits.

The second issue relates to our choice of task to measure the KAM. We selected walking because of the established link between the KAM during walking and OA structural disease progression ([7, 8]). It is possible that reductions in the KAM following exercise training might have been observed if a more demanding task had been used. This was observed in an uncontrolled pilot study ([14]) involving 13 middle-aged patients with early knee OA that evaluated a comparable NEXA and showed a 14% reduction in the peak KAM during a difficult one-legged rise task but not during walking. However, the clinical implications of a reduction in the KAM during a one-legged rise task in terms of disease progression are not clear.

The third consideration relates to the impact of the attributes of our medial knee OA sample. Our patients had a mean static varus alignment of ∼5°, representing moderate malalignment, with 10% having severe malalignment (>10°). It is possible that reducing the KAM with exercise (or other interventions) in the face of a seemingly fixed varus deformity and more severe disease may not be possible. However, although static varus malalignment is an important driver of the KAM ([44]), alignment is also a dynamic characteristic that can change during gait ([45]) and independently influence the KAM ([46]). Thus, there is at least the potential for neuromuscular changes resulting from exercise to influence this dynamic alignment and therefore the KAM, particularly when that exercise targets a more neutral dynamic alignment and muscular control of proximal and distal segments. In light of this, the subgroup of patients with medial knee OA and varus malalignment is relevant for investigating the effects of NEXA, given their generally higher KAMs ([44]). However, because we observed no effect, it is possible that any benefits of NEXA may be more evident in subjects at risk of knee OA (such as following joint injury) or patients with early OA, as has been observed in uncontrolled pilot studies ([14, 18]).

We also observed no significant effect of QS exercise on the KAM despite significant strength gains of 10%. This is not necessarily surprising, because single-plane, non–weight-bearing exercises are not specifically targeted at altering the magnitude or orientation of the ground reaction force or position of the knee—the primary determinants of the KAM during walking. This concurs with our prior randomized controlled trial in patients with medial knee OA with or without varus malalignment in which the same exercise program was used ([11]). Other clinical trials have demonstrated no change in the KAM following a hip strengthening program in patients with medial knee OA ([47, 48]) or following high-intensity lower limb–strengthening exercise in patients with knee OA involving any compartment ([12, 49]). Thus, there is currently little evidence to support a KAM-modifying effect of exercise in patients with medial or generalized moderate-to-severe knee OA.

Although there was no influence of exercise on the KAM, which is an indicator of mediolateral knee load distribution, we cannot exclude an effect of exercise on the magnitude of compressive knee load. Although good correlations between the KAM and compressive joint load as calculated by complex musculoskeletal modeling have been reported ([50]), single-patient studies using instrumented knee replacements have shown that, under some circumstances, the 2 may not always correspond. This lack of concordance may be attributable to concomitant alterations in other knee joint moments, particularly the KFM ([26]), and to alterations in muscle activation patterns ([51, 52]) that are not accounted for in estimations of the KAM using inverse dynamics. Although the KFM was not different between groups and did not change, it is possible that muscle activation may have been affected by exercise and hence altered knee load.

Although the KAM itself is a predictor of disease progression ([7, 8]), we cannot determine the direct effects of NEXA on structural outcomes. A more intensive 16-week supervised NEXA program performed for 1 hour thrice weekly demonstrated improved cartilage quality, as assessed using delayed gadolinium-enhanced magnetic resonance imaging, in middle-aged patients ([53]). However, the only randomized controlled trial assessing the effects of exercise on structural disease progression as the primary outcome in patients with established knee OA demonstrated a nonsignificant tendency toward less frequent progression of joint space narrowing over 30 months ([54]). Further, longer-term studies are needed before definitive conclusions can be made regarding whether exercise can modify structural disease progression in individuals at risk of OA or patients with established OA.

Contrary to our hypothesis, both exercise groups showed similar improvement in pain (for NEXA, 37% improvement [effect size 1.04]; for QS, 41% improvement [effect size 1.20]) and physical function (for NEXA, 29% improvement [effect size 0.80]; for QS, 26% improvement [effect size 0.74]) with large effect sizes. The between-group differences were small, with CIs that fell well short of the MCIDs ([38, 39]). The benefits of exercise for clinical outcomes in knee OA are supported by meta-analyses ([9]), and although there are few direct comparisons of different types of exercise, the results of pooled analyses suggest similar improvement for all types ([9]). Our findings concur with this conclusion. Overall, our data indicate that practitioners should prescribe the type of exercise that most suits the patient's needs and/or preferences, based on individual assessment.

Our findings of improvements in pain and function with QS exercises in patients with medial knee OA and varus malalignment are not completely consistent with those of our previous clinical trial using the same strength exercise program ([11]). A potential explanation may be the greater number of therapist sessions in the current study (14 versus 7 in the previous study). This is supported by a database review showing significantly greater benefits for pain and function with exercise programs involving >12 contacts with a health professional compared with those involving ≤12 contacts ([9]).

The strengths of our study include the randomized controlled design with attention to key methodologic features. Limitations include an inability to prevent patients from knowing their treatment allocation, although the research hypotheses were not disclosed. We did not include a control group not receiving treatment, and as such, the symptomatic benefits observed may be related to the therapeutic environment and/or an expectation of benefit rather than exercise per se ([55]). Another limitation is the greater number of withdrawals from the NEXA group due to pain and joint replacement surgery. However, the results were unaltered when sensitivity analyses were performed. Nevertheless, the weight-bearing nature of NEXAs may be more symptom-provocative compared with non–weight-bearing QS. This might also partly explain the lower rates of adherence to home exercise in the NEXA group. Finally, because our sample comprised patients with mostly moderate-to-severe knee OA with moderate varus malalignment, our results cannot necessarily be generalized to patients with milder disease or differing amounts of malalignment. Although different effects may be seen in early-stage disease, we restricted our sample to patients with definitive OA, to achieve a more homogeneous sample.

In conclusion, our results showed similar improvement in pain and function following neuromuscular or quadriceps strengthening exercise in a cohort of patients with moderate varus malalignment and mostly moderate-to-severe medial knee OA. They do not support the premise that such forms of exercise can influence the KAM, a key predictor of structural disease progression.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Bennell had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Bennell, Wrigley, Hodges, Hunt, Roos, Forbes, Ageberg, Hinman.

Acquisition of data. Kyriakides, Metcalf.

Analysis and interpretation of data. Bennell, Kyriakides, Metcalf, Egerton, Wrigley, Hodges, Hunt, Roos, Forbes, Ageberg, Hinman.

Acknowledgments

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

Physiotherapy was provided by Katherine Edmonds, Frances Gray, Jonathan Harris, Susan Hong Labberton, Arthur Lee, Tim McCoy, Jack Mest, Gabrielle Molan, Michael Ranger, and Tim Simpson.

REFERENCES

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

Supporting Information

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. Acknowledgments
  8. REFERENCES
  9. Supporting Information

Additional Supporting Information may be found in the online version of this article.

FilenameFormatSizeDescription
ART_38317_sm_SupplData.doc4501KSupplementary Data

Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.