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Abstract

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

Objective

Lower extremity functional performance and perception of functional abilities influence clinical management in people diagnosed with unilateral or bilateral knee osteoarthritis (OA). The purpose of this study was to determine if there were differences in perception of function and performance during functional tasks between individuals with unilateral and bilateral knee OA.

Methods

The functional abilities of patients with symptomatic and radiographic diagnosed unilateral (n = 84) or bilateral (n = 68) knee OA were evaluated with self-report measures and performance-based tests. Self-report measures included the Knee Outcome Survey, the Global Rating Scale, and the physical component of the Short Form 36 health survey; functional tests included the Timed Up-and-Go Test, the Stair Climbing Test, and the 6-Minute Walk Test. Multivariate analyses of variance were performed separately for men and women to determine if perception (self-report measures) and performance (functional tests) were dependent on the number of involved knees.

Results

No significant main effects were observed in functional performance between groups for either sex. Similarly, the perception measures did not differ between groups. In general, individuals diagnosed with unilateral and bilateral knee OA both performed functional tasks and perceived their functional ability similarly.

Conclusion

Regardless of the number of involved knees, individuals with knee OA perform and perceive their functional ability similarly, which suggests that clinicians need to consider other factors, such as how long the disease has been progressing or how functional abilities have changed, when treating patients with knee OA.


INTRODUCTION

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

The knee is the most common joint to be diagnosed with osteoarthritis (OA), and progression of the disease in this load-bearing joint leads to substantial disability and reduced functional capacity in a large range of daily activities (1, 2). Although the magnitude of functional impairments associated with knee OA is dependent upon the severity of the disease (3), it is unclear if impairment levels are also dependent upon the number of involved knees.

In studies of patients with knee OA, a single leg is often used as the reference by which functional outcomes are measured (4, 5), despite the fact that knee OA frequently affects both legs (6); this bilaterality may amplify the magnitude of functional impairments (7). Despite previous reports of a relation between bilaterality and greater disability (7–9), only self-assessment surveys of functional ability were used as outcomes to assess functional ability. Self-assessment surveys are commonly used to evaluate functional capacity and are integral in quantifying patient satisfaction and quality of life during treatment for knee OA. These instruments are easy to administer, making them the primary outcome measure for many interventional studies or large cross-sectional normative samples (10–14). However, these instruments must be cautiously interpreted as they are generally driven by pain (15–18), with greater pain associated with worse perception of function (11). It is not known whether perception of disability is related to the condition of the worse leg, or whether bilateral involvement would increase the actual or perceived functional deficits that these tools are intended to measure.

Self-report instruments and performance-based tests are used to drive patient care, measure the effectiveness of treatment, and stratify patients in research studies. However, it is unclear if the outcomes from these tests differ for individuals with unilateral compared to bilateral disease, even if the severity of OA is similar. Therefore, the aims of this investigation were: 1) to determine if the presence of bilateral disease amplifies self-reported and performance-based functional deficits and 2) to determine if the number of involved knees affects scores on performance-based and perception-based assessments differently, as these tests measure different domains of impairment. We hypothesized that both performance and perception of performance would be worse in individuals diagnosed with bilateral disease compared to those diagnosed with unilateral disease.

Significance & Innovations

  • Self-report measures of function (perception) do not differ between individuals diagnosed with unilateral compared to those diagnosed with bilateral knee osteoarthritis (OA).

  • Functional ability (performance-based tests) does not differ significantly between individuals diagnosed with unilateral and bilateral knee OA.

  • Measures of perception of function and actual functional abilities between individuals diagnosed with unilateral or bilateral knee OA do not differ irrespective of sex.

  • Treatment and management of care should focus on differences in patient sex and severity of disease and not the number of involved knees.

PATIENTS AND METHODS

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

Patients.

A total of 152 individuals diagnosed as having unilateral or bilateral knee OA by an orthopedic surgeon were referred to the University of Delaware Physical Therapy Clinic for evaluation of their functional ability. Data were collected from June 2009 through January 2011. All patients were classified as having knee OA based on radiographic evidence of one or both of their knees with a Kellgren/Lawrence (K/L) score of ≥3 (19) and pain during activities of daily living. All patients were assessed with the Delaware Osteoarthritis Profile, a comprehensive functional evaluation that includes standard clinical measures, performance-based functional tests, and self-report measures of function. These data were part of a database maintained by the University of Delaware Physical Therapy Clinic, and analysis of this de-identified data set was approved by the Human Subjects Review Board.

Self-reported measures.

The physical component summary score (PCS) of the Short Form 36 (SF-36) health survey was used to assess a patient's perception of physical limitations and physical health (20, 21). The Knee Outcome Survey (KOS) activities of daily living scale (ADLS) was used to assess an individual's perception of performance during activities of daily living (22). The Global Rating Scale (GRS), a single knee- and leg-specific question, was used to assess the patient's knee function during usual daily activities. The KOS-ADLS and GRS are joint- and leg-specific questionnaires where subjects provide answers for each leg separately. To compare KOS-ADLS and GRS scores for patients with unilateral and bilateral disease, a single score for the bilateral group was computed, both by averaging the 2 knees and by taking the worse score of the 2 knees. Significant correlations were observed between average and worse scores for both the KOS-ADLS (ρ = 0.832, P < 0.001) and GRS (ρ = 0.926, P < 0.001). Data used in subsequent analyses were from the worse leg score.

Functional tests.

For the purposes of this study, 3 functional tests from the Delaware Osteoarthritis Profile were used to assess functional ability: the Timed Up-and-Go (TUG) test, the Stair Climb Test (SCT), and the 6-Minute Walk (6MW) Test. The TUG requires subjects to rise from a chair, walk 3 meters, and return to the seated starting position as quickly as possible. The TUG is commonly used to assess outcomes for patients with knee OA and has good reliability (23). The average time of 2 timed trials was used for analysis. The SCT is commonly used to assess functional ability in people with knee OA (23, 24). During this test, subjects ascend and then descend a flight of 12 stairs as quickly and safely as possible. Patients were permitted to use the handrail if necessary. The 6MW involved patients walking at a quick, comfortable pace around a 157.3-meter square for 6 minutes, with the total distance covered taken as the outcome measure.

Statistical analysis.

Power analyses were performed to estimate the sample size needed to detect a clinically important difference, if a difference were to exist, between patients with unilateral and bilateral knee OA. Consideration was made for data stratified by sex in performance-based and self-reported measures of function. Published minimal detectable change scores for the following measures were used from the literature: TUG (25), 6MW (25), SCT (23), and KOS-ADLS (26); sample size estimates were assessed using G-Power (version 3.1.2) for moderate (0.5) and high (0.8) levels of power. The results of our power analyses indicate that our sample size was sufficiently powered (moderate to large power) to detect clinically meaningful differences between groups, if clinically meaningful differences existed (Table 1).

Table 1. Power analyses for sample size estimation to detect a difference between individuals with unilateral compared to bilateral knee OA, if one were to exist*
 Mean 1MDCMean 2 (mean 1 + MDC)SDSample/group powerES
  • *

    OA = osteoarthritis; MDC = minimum detectable change; ES = estimated size; TUG = Timed Up-and-Go Test; 6MW = 6-Minute Walk Test; SCT = Stair Climb Test; KOS = Knee Outcome Survey; ADLS = activities of daily living scale.

  • Estimates were assessed for moderate (0.5) to high (0.8) levels of power.

  • MDC scores for the TUG and the 6MW were taken from Mangione et al (25).

  • §

    MDC scores for the SCT were taken from Kennedy et al (23), where subjects climbed 9 stairs compared to the 12 stairs tested here.

  • MDC scores (shown here as a percentage) for the KOS-ADLS were taken from Collins et al (26).

TUG, seconds      
 Maly et al (18)7411315/101.333
 Goncalves et al (27)14.5418.5637/190.667
6MW, meters      
 Maly et al (18)4406550512358/290.528
 Goncalves et al (27)349.465414.496.136/180.676
SCT, seconds      
 Christiansen and Stevens-Lapsley (28)18.55.49§23.998.539/200.646
KOS-ADLS      
 Goncalves et al (27)55.511.466.920.954/270.545

Comparison of the dependent measures (age, body mass index [BMI], SCT, TUG, 6MW, SF-36, KOS-ADLS, and GRS) between men and women was examined, and if the majority of dependent variables differed between the sexes then separate analyses were performed. Chi-square analyses were performed to determine if the number of comorbidities was different for patients with unilateral compared to bilateral disease. Multiple analysis of variance (MANOVA) tests were performed to determine if significant differences between subjects with unilateral and bilateral disease existed for performance-based measures and self-report surveys. Separate MANOVAs were conducted for the functional performance tasks (SCT, TUG, and 6MW) and self-report surveys (SF-36 PCS, KOS-ADLS, and GRS).

We were also interested in the ability of each survey to differentiate between individuals with unilateral and bilateral disease, because each survey assessed different aspects of a patient's perception of function. Specifically, the KOS-ADLS questionnaire pertains to a patient's perception of how the knee influences activities of daily living, the GRS is a report of a patient's perception of their global functioning level, and the SF-36 PCS accounts for a patient's perception of overall physical health. Therefore, independent t-tests were used to determine differences between groups (unilateral versus bilateral disease) for each self-report questionnaire. To protect against Type I error, we set a familywise error rate of alphaFW = 0.01 for all comparisons (29).

RESULTS

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

Descriptive statistics of the sample are provided in Table 2. Neither age (P = 0.255) nor BMI (P = 0.098) was significantly different between unilateral and bilateral groups (Table 2). Similarly, age (P = 0.267) and BMI (P = 0.567) were not significantly different between patients with unilateral compared to bilateral disease for men (Table 3). Additionally, age (P = 0.845) and BMI (P = 0.049) were not significantly different for women, after adjusting the significance level for multiple comparisons (Table 3). The quantity of comorbidities was not different for patients with unilateral compared to bilateral disease (Table 4). Therefore, these variables were not adjusted in the final analyses.

Table 2. Descriptive statistics of the sample with comparisons between women and men, and between individuals with unilateral and bilateral disease*
 Patients, no.Mean ± SDSEMP
  • *

    SF-36 = Short Form 36 health survey; PCS = physical component summary; KOS = Knee Outcome Survey; GRS = Global Rating Scale; TUG = Timed Up-and-Go Test; SCT = Stair Climbing Test; 6MW = 6-Minute Walk Test.

Comparison by sex    
 Age, years    
  Female7460.0 ± 8.31.0 
  Male7858.6 ± 10.21.20.369
 Body mass index, kg/m2    
  Female6933.0 ± 8.01.0 
  Male7331.5 ± 4.80.60.188
 SF-36 PCS    
  Female6532.9 ± 9.71.2 
  Male7037.4 ± 8.91.10.006
 KOS, %    
  Female7346.9 ± 27.03.2 
  Male7760.9 ± 22.82.60.001
 GRS    
  Female7055.5 ± 24.22.9 
  Male7763.2 ± 23.12.60.050
 TUG, seconds    
  Female729.67 ± 2.460.29 
  Male777.72 ± 1.720.20< 0.001
 SCT, seconds    
  Female7219.5 ± 9.31.1 
  Male7511.9 ± 4.80.5< 0.001
 6MW, meters    
  Female73456.3 ± 99.011.6 
  Male77554.5 ± 113.112.9< 0.001
Comparison by disease    
 Age, years    
  Unilateral8458.5 ± 9.31.0 
  Bilateral6860.2 ± 9.31.10.255
 Body mass index, kg/m2    
  Unilateral7931.4 ± 5.80.7 
  Bilateral6333.3 ± 7.40.90.098
 SF-36 PCS    
  Unilateral7736.8 ± 9.61.1 
  Bilateral5833.1 ± 9.11.20.021
 KOS    
  Unilateral8259.1 ± 20.72.3 
  Bilateral6848.1 ± 29.93.60.009
 GRS    
  Unilateral8261.8 ± 25.12.8 
  Bilateral6556.7 ± 22.12.70.197
 TUG, seconds    
  Unilateral828.3 ± 2.30.3 
  Bilateral679.1 ± 2.40.30.036
 SCT, seconds    
  Unilateral8114.1 ± 7.30.8 
  Bilateral6617.6 ± 8.91.10.010
 6MW, meters    
  Unilateral83526.8 ± 118.513.0 
  Bilateral67481.8 ± 110.913.50.019
Table 3. Descriptive statistics of the sample separated for women and men, with comparisons between those with unilateral and bilateral disease*
 Patients, no.Mean ± SDSEMP
  • *

    Significance adjusted when Levene's test of equality of variance was not assumed. SF-36 = Short Form 36; PCS = physical component summary; KOS = Knee Outcome Survey; GRS = Global Rating Scale; TUG = Timed Up-and-Go test; SCT = Stair Climbing Test; 6MW = 6-Minute Walk Test.

Women    
 Age, years    
  Unilateral3359.8 ± 9.01.6 
  Bilateral4160.2 ± 7.71.20.845
 Body mass index, kg/m2    
  Unilateral3130.9 ± 7.11.3 
  Bilateral3834.7 ± 8.41.40.049
 SF-36 PCS    
  Unilateral3033.7 ± 9.51.7 
  Bilateral3532.2 ± 9.91.60.525
 KOS, %    
  Unilateral3251.7 ± 21.13.7 
  Bilateral4143.2 ± 30.64.80.166
 GRS    
  Unilateral3260.6 ± 25.44.5 
  Bilateral3851.2 ± 22.73.70.107
 TUG, seconds    
  Unilateral319.4 ± 3.00.5 
  Bilateral419.9 ± 2.00.30.346
 SCT, seconds    
  Unilateral3217.5 ± 8.81.6 
  Bilateral4021.0 ± 9.51.50.115
 6MW, meters    
  Unilateral32468.7 ± 107.819.0 
  Bilateral41446.6 ± 91.714.30.348
Men    
 Age, years    
  Unilateral5157.6 ± 9.51.3 
  Bilateral2760.3 ± 11.42.20.267
 Body mass index, kg/m2    
  Unilateral4831.7 ± 4.80.7 
  Bilateral2531.1 ± 4.91.00.567
 SF-36 PCS    
  Unilateral4738.8 ± 9.21.3 
  Bilateral2334.4 ± 7.61.60.049
 KOS, %50   
  Unilateral2763.8 ± 19.22.7 
  Bilateral 55.5 ± 27.85.40.124
 GRS50   
  Unilateral2762.6 ± 25.13.6 
  Bilateral 64.4 ± 19.23.70.748
 TUG, seconds    
  Unilateral517.7 ± 1.60.22 
  Bilateral267.8 ± 2.00.400.699
 SCT, seconds    
  Unilateral4911.8 ± 5.10.07 
  Bilateral2612.2 ± 4.10.80.729
 6MW, meters    
  Unilateral51563.3 ± 111.015.5 
  Bilateral26537.3 ± 117.423.00.343
Table 4. Comparison of the diagnosed comorbidities between patients with unilateral and bilateral disease, separated by sex and expressed as a percentage within group*
 Comorbidities, no.P
0123
  • *

    Comorbidities considered were heart disease, heart attack, high blood pressure, low blood pressure, and stroke. The significance levels indicated in the last column are for comparisons between individuals with unilateral compared to bilateral disease.

Females (n = 54)    
 Unilateral (n = 18)50.044.45.60
 Bilateral (n = 36)55.641.702.80.459
Males (n = 51)    
 Unilateral (n = 30)43.343.313.30
 Bilateral (n = 21)52.442.904.80.217

While age and BMI were not significantly different between the men and women, men performed significantly better than women in all 3 functional measures (TUG, SCT, and 6MW; P < 0.001) and perceived their function to be better in all 3 self-report measures (SF-36 PCS, KOS-ADLS, and GRS; P ≤ 0.05) (Table 2). Similar proportions of patients diagnosed with unilateral (58%) and bilateral (59%) disease utilized the handrail during the SCT; however, more women (68%) than men (50.1%) utilized the handrail. There were also significant differences in the distribution of sexes in the unilateral (33 women: 51 men) and bilateral (41 women: 26 men) disease groups (P = 0.01). Therefore, separate analyses (MANOVA and independent t-tests) were performed for each sex.

No main effects were observed for the MANOVAs examining group differences (unilateral versus bilateral disease) in the functional performance measures for either women (P = 0.450) (Figure 1A) or men (P = 0.489) (Figure 1B). Similarly, no main effects were observed for the MANOVAs examining group differences (unilateral versus bilateral disease) in self-report measures for either women (P = 0.819) (Figure 2A) or men (P = 0.149) (Figure 2B). The findings are consistent when controlling for age and BMI for both the functional performance measures (P = 0.606 for women and P = 0.482 for men) and for self-report measures (P = 0.968 for women and P = 0.163 for men).

thumbnail image

Figure 1. Group differences (unilateral versus bilateral disease) in the functional performance measures for women (A) and men (B). Error bars show ±SDs. TUG = Timed Up-and-Go Test; SCT = Stair Climb Test; 6MW = 6-Minute Walk Test.

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thumbnail image

Figure 2. Group differences (unilateral versus bilateral disease) in self-report measures for women (A) and men (B). Error bars show ±SDs. PCS = physical component summary; KOS = Knee Outcome Survey; GRS = Global Rating Scale.

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The analyses of the individual self-report surveys between subjects with unilateral and bilateral disease revealed a small difference for the mean ± SD SF-36 PCS score between the men with unilateral disease (38.8 ± 9.2) compared with bilateral disease (34.4 ± 7.6; P = 0.049), which is smaller than the mean ± SD minimum clinically important difference of 0.5 ± 4.46, and not significant after adjusted for multiple comparisons. There were no significant differences in the KOS-ADLS or GRS scores between groups for men, or in any self-report survey for women diagnosed with unilateral versus bilateral disease (P ≥ 0.107).

DISCUSSION

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

Functional performance measures and self-report measures of function are commonly used to assess individuals diagnosed with knee OA. We hypothesized that patients diagnosed with bilateral disease would perform worse in functional tests and perceive their functional ability to be worse than individuals with unilateral disease. Contrary to our hypotheses, neither the performance-based functional tests nor the self-report questionnaires differed between individuals with unilateral and bilateral disease. Our results challenge the conventional clinical perspective that patients with unilateral disease compensate for impairments using the noninvolved leg, which has implications for the management of the disease and for categorization of subjects participating in interventional or clinical research.

One would intuitively presume that patients with unilateral disease rely on their noninvolved leg during functional tasks and demonstrate functional performance that surpasses patients with bilateral disease. This presumption was not supported by our findings, although others have reported functional differences between individuals with unilateral and bilateral disease. The incongruous findings may be explained by several critical methodologic differences between studies. Two studies indicate greater self-reported measures of pain and functional impairments in individuals with unilateral compared to bilateral pain (8, 9). However, neither of these studies required any diagnoses of knee OA, but surveyed all individuals ages >50 years registered with a group of general medical practices (8) or by surveying a large, random sampling of individuals ages >55 years, living within a given community (9). A third study (7) acquired data from a sample of community-dwelling individuals deemed at risk for developing knee OA based on age, female sex, previous knee injury, and high body weight. Additionally, the findings from all 3 studies were based on self-report measures of function (7–9), compared to the present study that compared both performance-based measures of functional ability between groups along with self-report measures. Self-report measures of function are driven by pain (17). Therefore, compared to self-report questionnaires, performance-based metrics of functional performance may provide a more accurate indication of functional ability and may more precisely capture advantageous compensatory movement strategies that improve functional performance in patients with unilateral knee OA. As our sample consisted only of individuals with severe symptoms who sought medical treatment and were diagnosed with knee OA, it is plausible that the relation between unilateral or bilateral involvement with functional limitations is not as strong as has been observed in individuals with mild symptoms.

We found no difference in functional performance measures between patients with unilateral and bilateral disease, suggesting that potential movement strategies that reduce the discomfort in the involved leg and take advantage of the integrity of the uninvolved leg do not translate into enhanced functional performance as measured by the TUG, the SCT, and the 6MW tests.

Significant sex differences existed in all measures of perception and performance of leg functional ability. While it is known that women are more likely to develop OA compared to men (1, 30–32), and a greater percentage of women exhibit symptomatic disease (6), our findings are still surprising in a sample where radiographic disease severity was similar. In general, healthy women are weaker and exhibit accelerated declines in performance of functional tests compared to men (33), but the women in the present study had significantly lower self-reported functional ability as well. These findings support previous work that determined that the functional abilities and perceptions of disability of women are affected by knee OA to a greater extent than men (34–36). The substantial differences between the rate of OA development, the etiology of the disease, and functional ability between men and women with knee OA combined with the sex differences in self-report measures observed here, support the separate analyses for men and women in future studies. The results of this study further support previously identified sex differences, in that, regardless of whether it is bilateral or unilateral disease, women were, on average, significantly more symptomatic with greater functional impairments (Table 2). Collectively, these findings suggest that clinicians should consider the treatment for individuals with OA to be similar for patients with unilateral or bilateral disease, while taking into account the patient's sex when determining treatment options and management of care. Women may require surgical or pharmacologic intervention earlier in the course of the disease.

Some limitations exist in our current study. Our cross-sectional sample, while initially of a large size (n = 152), was substantially reduced because of the necessary separation of sex. Because all data collection occurred at one time, we were not able to determine longitudinal differences between groups. Additionally, we did not control for severity of disease using the radiographic classification (K/L scores), although all subjects were classified as having K/L grades of ≥3. Controlling for radiographic severity within this study would have further reduced the sample size, as well as our ability to detect differences between groups. Symptomatic classification may be optimal to radiographic classification, as there is only weak correlation between clinical and radiographic severity of OA (37). Examination of the differences in movement strategies (e.g., the stepping pattern during the SCT) employed by the 2 groups was not performed. However, irrespective of the chosen movement strategies employed by the 2 groups, no group differences in performance outcomes were observed. The data presented here were from individuals with moderate symptomatic OA, who were diagnosed with K/L scores of ≥3, and our findings suggest that there are likely other factors that contribute to both the perception and performance in functional tasks. Duration of symptoms, joint effusion, bodily pain, and physical activity levels, which were not assessed in this study, may also contribute to functional performance and self-reported ability. Future studies should consider quantifying the physical activity levels of patients with unilateral and bilateral disease, to determine if the similarities in performance and perception of function are associated with general inactivity in both populations.

In conclusion, the similarity in performance of functional measures and responses on self-report instruments for individuals with unilateral and bilateral disease has implications for how clinicians treat patients diagnosed with knee OA and how subjects are classified in interventional research. Factors that should be considered when evaluating patients' functional limitations or perceptions of their functional ability may include how long the disease has been progressing or how functional abilities have changed that can be attributed to the disease; both will provide the clinician with a sense of the individual's functional capacity, as well as providing a sense of the individual's expected functional capabilities. Most importantly, clinicians need to understand that individuals with unilateral and bilateral disease perform and perceive their functional abilities similarly. When separate analyses were performed for men and women, the diagnosis of unilateral versus bilateral disease did not appear to affect performance or self-report differently, even though these tests capture different domains of disability. These results suggest that the worse leg dictates the outcome measures for both functional performance and self-report measures.

AUTHOR CONTRIBUTIONS

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

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 submitted for publication. Dr. Marmon 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. Marmon, Zeni, Snyder-Mackler.

Acquisition of data. Marmon.

Analysis and interpretation of data. Marmon, Zeni, Snyder-Mackler.

Acknowledgements

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

The authors would like to thank Dr. Michael J. Axe and First State Orthopedics for their assistance in patient recruitment, as well as the University of Delaware Physical Therapy Clinic for treating the subjects.

REFERENCES

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