Dr. Harvey has received honoraria from Vindico Medical Education (less than $10,000).
Version of Record online: 26 JUN 2012
Copyright © 2012 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 64, Issue 7, pages 2252–2259, July 2012
How to Cite
Lo, G. H., Harvey, W. F. and McAlindon, T. E. (2012), Associations of varus thrust and alignment with pain in knee osteoarthritis. Arthritis & Rheumatism, 64: 2252–2259. doi: 10.1002/art.34422
ClinicalTrials.gov identifier: NCT00306774.
The views expressed herein are those of the authors and do not necessarily represent the views of the Department of Veterans Affairs.
- Issue online: 26 JUN 2012
- Version of Record online: 26 JUN 2012
- Accepted manuscript online: 3 FEB 2012 11:24AM EST
- Manuscript Accepted: 31 JAN 2012
- Manuscript Received: 4 JAN 2011
- Houston VA Health Services Research and Development Center of Excellence. Grant Number: HFP90-020
- Arthritis Investigator Award from the American College of Rheumatology Research and Education Foundation
- Arthritis Foundation
- NIH. Grant Number: M01-RR-00054
- National Institute of Arthritis and Musculoskeletal and Skin Diseases. Grant Number: R01-AR-051361
To investigate associations of varus thrust and varus static alignment with pain in patients with knee osteoarthritis (OA).
This was a cross-sectional study of participants from a randomized controlled trial of vitamin D treatment for knee OA. Participants were video recorded while walking and scored for presence of varus thrust. Static alignment was measured on standard posteroanterior knee radiographs. Pain questions from the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire were used to assess symptoms. We calculated means for total WOMAC pain in relation to varus thrust and static varus alignment (i.e., corrected anatomic alignment <178 degrees). Ordinal logistic regressions were performed, with responses on individual WOMAC pain questions as the outcomes and varus thrust and varus alignment as the predictors.
There were 82 participants, 60% of whom were female. The mean ± SD age was 65.1 ± 8.5 years, and the mean ± SD body mass index was 30.2 ± 5.4 kg/m2. The mean total WOMAC pain score was 6.3 versus 3.9, respectively, in those with versus without definite varus thrust (P = 0.007) and 5.0 versus 4.2 in those with versus without varus alignment (P = 0.36). Odds ratios for pain with walking and standing were 4.7 (95% confidence interval 1.8–11.9) and 5.5 (95% confidence interval 2.2–14.2), respectively, in those with and those without definite varus thrust. There were no significant associations between varus alignment and responses to individual WOMAC pain questions. Sensitivity analyses suggested that varus classified using a more stringent definition might have been associated with pain on walking and standing.
In patients with knee OA, varus thrust, and possibly varus static alignment, were associated with pain, specifically during weight-bearing activities. Treatment of varus thrust (e.g., via bracing or gait modification) may lead to improvement of symptoms.
Osteoarthritis (OA) is a major public health problem, being the most common form of arthritis. It occurs in 33% of people over the age of 60 years in the US (1) and is a leading cause of disability among the elderly (2). This is particularly problematic given that only limited therapies have proven effective in reducing symptoms, the mainstays of treatment being nonsteroidal antiinflammatory drugs, nonspecific physical therapy interventions, local corticosteroid injection, and ultimately, when these are ineffective, total joint replacement (3). The economic ramifications of OA are also substantial, with direct costs attributable to the disease in the US exceeding 185 billion dollars in 2007 (4).
In recent years, there has been a growing body of data supporting the notion that biomechanics are important in the pathophysiology of knee OA, with research showing that static and dynamic alignment are potent predictors of longitudinal progression (5–7). Static alignment, defined as the coronal plane assessment of the hip-knee-ankle angle, is an important determinant of load distribution within a knee (7). The load-bearing axis, a line drawn from the mid–femoral head to the mid-ankle, passes medial to the knee in a varus knee, which leads to increased forces across the medial compartment. Dynamic alignment is assessed during ambulation. Varus thrust is an easily assessed measure of dynamic alignment that has been defined as the first appearance of varus or abrupt worsening of existing varus while the limb is bearing weight during ambulation, with a return of the limb to a less varus alignment during the swing, or non–weight-bearing, phase of gait (5). This is a simple clinical assessment that does not require use of a sophisticated gait laboratory. Because knee pain in OA occurs predominantly with weight bearing, it is reasonable to expect that dynamic findings may be more predictive of knee pain than static measures.
The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale is the sum of scores from 5 questions assessing knee symptoms (8). The WOMAC is a validated instrument that is widely used in studies of knee OA. However, there is growing evidence that the use of this summed score may not be appropriate. Findings of a study of the measurement properties of the WOMAC pain subscale suggested that the 5 WOMAC pain questions represent 2 separate domains, with the questions about pain when walking on a flat surface and on stairs representing one domain and the questions on nighttime and sitting activities representing a second domain (9); the question on standing loaded on both factors. Therefore, summation of the 5 questions may not be the optimal method for evaluating knee OA symptoms. It has been proposed that perhaps only the items that display homogeneity should be summed or that each question be evaluated individually. Because varus thrust is a measure of dynamic alignment that becomes evident with ambulation, the WOMAC questions that assess pain during weight-bearing activities were of particular interest to us.
The objective of this study was to evaluate the relationship of static alignment and varus thrust with pain in individuals with established knee OA. We hypothesized that there would be a relationship between varus thrust and pain, particularly with weight-bearing activities, but not between varus static alignment and pain.
PATIENTS AND METHODS
This was a cross-sectional study of a convenience sample selected from among participants in a randomized controlled trial (RCT) of vitamin D treatment for symptomatic radiographic knee OA. The trial was performed at Tufts Medical Center and took place from June 1, 2005 through September 30, 2010. All study activities were approved by the Tufts Medical Center Institutional Review Board. To be enrolled in the parent RCT, individuals had to have symptomatic radiographic tibiofemoral knee OA (Kellgren/Lawrence [K/L] grade  of ≥2) and had to have experienced pain in the same knee on most days of the month for at least 1 month in the last year. The study was not restricted to participants with medial tibiofemoral OA.
For enrollment in the present study, participants were recruited at the 2-year followup visit from the parent RCT and were required to consent to the additional assessment of varus thrust using a video recording as described below. Investigators were blinded with regard to the treatment allocation as well as to the pain assessment results at the time of enrollment into this study. We excluded participants who used any assistive device for ambulation. There was a period of a few months during which time was limited during the parent study clinic visits, and no participants were recruited into this ancillary study during that period.
Varus thrust assessments.
At the parent study 2-year followup visit, participants were video recorded walking 20 meters away from and toward a stationary camera at a self-selected speed. All evaluations were performed with the participants walking barefooted on the same walking course within the clinic. A standard digital video camera (60 Hz) was used.
The presence of varus thrust as described above, i.e., first appearance of varus or abrupt worsening of existing varus while the limb is bearing weight during ambulation, with a return of the limb to a less varus alignment during the swing, or non–weight-bearing, phase of gait, was assessed subjectively by 2 rheumatologists (GHL and WFH) trained to evaluate varus thrust. These individuals viewed the gait videos at separate reading sessions and were blinded with regard to the patients' pain assessments. Varus thrust was classified as being definitely present, possibly present, or definitely absent. On average, these assessments were based on the patients' first 5–6 strides taken while walking away from the camera and the last 5–6 strides taken while walking toward the camera that could be easily viewed on each video recording. Any disagreements were adjudicated by consensus of both evaluators. The varus thrust score subsequently was dichotomized into 2 groups, referred to below as “with definite varus thrust” (including only those with the designation of varus thrust being definitely present) and “without definite varus thrust” (those scored as having varus thrust possibly present and those scored as varus thrust being definitely absent).
Posteroanterior radiographs of the study knee in semiflexed position were obtained at the parent study screening visit and at the 2-year followup visit, on the same day the gait video recordings were obtained. Participants were asked to stand upright facing the anterior wall with their body weight distributed equally between the 2 legs. The great toes of both feet were verified to be in contact with the anterior wall. Both feet were fixed in 10 degrees external rotation by positioning on a foot map. Subsequently, the cassette holder was lowered so that the center of the film was located at the level of the participant's tibiofemoral joint line. The center line of the positioning frame was verified to be in the center of the cassette holder. Then the participant was asked to flex both knees until they touched the anterior wall of the frame, standardizing the extent of tibial flexion. With the great toes and knees still touching the anterior wall, both thighs were pressed directly against the wall, standardizing the extent of femoral flexion. The field of view was 14 × 17 inches for all radiographs. This was standardized by using a uniform cassette size for all knee radiographs, with all radiographs taken at a distance of 72 inches away from the joint of interest.
K/L scores (range 0–4) were obtained for the radiographs obtained at the screening visit. Static alignment measures were performed on the 2-year followup radiographs, using a previously validated method (11). Anatomic alignment measures were modified to better reflect mechanical alignment, subtracting a correction factor of 3.5 degrees for women and 6.4 degrees for men (11); knees with a corrected anatomic alignment of <178 degrees were categorized as being varus aligned, as similarly defined in other studies (12, 13).
The WOMAC pain questionnaire was administered to evaluate the study knee at the 2-year followup visit, on the same day as the gait video recordings. The questionnaire consists of 5 questions, each with a potential score of 0–4 (Likert scale), with 4 representing extreme pain. The questions related to weight bearing address pain on walking on a flat surface (question 1), pain on walking up and down stairs (question 2), and pain on standing upright (question 5). The questions related to non–weight bearing address pain at night while in bed (question 3) and pain on sitting or lying down (question 4). The scores from all 5 questions are summed to yield the total WOMAC pain score.
Age of the participants was ascertained based on self-reported date of birth at the time of study entry. Sex was self reported. Participants were weighed in kilograms wearing their street clothes without shoes, using a Seca 770 Alpha scale. Height in meters was measured using a Holtain Stadiometer. Walking speed was ascertained by asking the participant to ambulate 20 meters at a self-selected speed on the same date that the gait video, radiography, and WOMAC pain assessments were obtained. The faster result of 2 trials was recorded as the walking speed.
In the present analyses, we included only the study knee identified for the parent RCT that met the definition of symptomatic radiographic OA at baseline. To compare the baseline demographic characteristics and radiographic OA scores of the group with and the group without definite varus thrust, we used chi-square and t-tests. The mean total WOMAC pain score was calculated, initially without adjustment, for each of the 2 groups, and the significance of differences was determined by t-test. We then calculated least square means with adjustment for age, sex, height, weight, and 20-meter walking speed.
We also performed ordinal logistic regressions with responses to individual WOMAC pain questions as the outcomes and varus thrust as the predictor, subsequently adjusting for age, sex, height, weight, and 20-meter walking speed. Because few of the individual pain scores were very high, scores of 2, 3, and 4 were collapsed into one level for the ordinal logistic regression models. The proportional odds assumption was checked for all models. If the finding on the test of assumptions for proportional odds was statistically significant (e.g., meaning that the assumptions were not met) we did not present the results of those models; this is a conservative approach (14). We repeated the ordinal logistic regression using varus static alignment as the predictor. To address the possibility that the cutoff of 178 degrees may not be optimal in the definition of varus static alignment, we performed a sensitivity analysis evaluating alternative cutoff values of 171–180 degrees. All analyses were performed using SAS, version 9.2.
There were a total of 82 participants in the present study. Forty-nine (60%) were female. The mean ± SD age was 65.1 ±8.5 years, body mass index was 30.2 ± 5.4 kg/m2, height was 1.66 ± 0.09 meters, and weight was 83.6 ± 17.1 kg. Twenty-five (30.5%) of the participants were classified as having definite varus thrust, 15 (18.3%) as having possible varus thrust, and 42 (51.2%) as having absent varus thrust. Thirty-nine percent of the varus thrust readings required adjudication.
Characteristics of the group with and the group without definite varus thrust are shown in Table 1. Radiographic OA was more severe in the group with definite varus thrust (P = 0.016), and the percentage of subjects who were male was higher in this group (P = 0.003). The difference in mean weight between the 2 groups nearly reached statistical significance, with weight being higher in the group with definite varus thrust. In addition, 84% of those with definite varus thrust had static varus corrected anatomic alignment, compared with only 33% of those without varus thrust (P < 0.0001).
|With definite varus thrust (n = 25)||Without definite varus thrust (n = 57)||P|
|Age, years||65.2 ± 8.5||65.1 ± 8.6||0.95|
|Height, meters||1.68 ± 0.09||1.65 ± 0.09||0.20|
|Weight, kg||88.9 ± 17.2||81.2 ± 16.7||0.06|
|BMI, kg/m2||31.4 ± 5.7||29.7 ± 5.3||0.18|
|Sex, % female||36||70||0.003|
|K/L grade, no. (%)||0.016|
|2||9 (36)||38 (67)|
|3||7 (28)||12 (21)|
|4||9 (36)||7 (12)|
|Varus static alignment, no. (%)||21 (84)||19 (33)||<0.0001|
The mean total WOMAC pain score was 6.3 in the group with definite varus thrust, versus 3.9 in the group without (P = 0.007). After adjustment for age, sex, height, weight, and walking speed, the difference in means was less pronounced and no longer significant (5.7 versus 4.2, respectively; P = 0.09). The histogram of the distribution of total WOMAC pain scores in the 2 varus thrust subgroups shown in Figure 1 highlights the difference in total WOMAC pain score between the groups. The total WOMAC pain score did not differ significantly between subjects with and those without varus static alignment (mean 5.0 and 4.2, respectively; P = 0.36). After adjustment for the above-mentioned covariates, the difference in total WOMAC pain score according to varus static alignment status was further diminished (mean 4.8 and 4.5, respectively; P = 0.68).
Table 2 shows the proportional odds ratio for each individual pain question in the WOMAC calculated using definite varus thrust as the predictor. The proportional odds of having pain with walking and with standing upright among OA patients with definite varus thrust was ≥4 times that among those without definite varus thrust.
|Individual WOMAC pain question||Level of pain||Unadjusted proportional OR (95% CI) for pain with vs. without definite varus thrust||Adjusted proportional OR (95% CI) for pain with vs. without definite varus thrust†|
|Weight bearing–related questions|
|Pain on walking|
|With definite varus thrust||4||12||6||3||0||4.7 (1.8–11.9)‡||NA§|
|Without definite varus thrust||29||21||7||0||0|
|Pain on standing upright|
|With definite varus thrust||4||8||9||4||0||5.5 (2.2–14.2)‡||4.1 (1.5–11.6)‡|
|Without definite varus thrust||31||16||8||2||0|
|Pain on using stairs|
|With definite varus thrust||2||11||4||7||1||1.4 (0.6–3.4)||1.0 (0.4–3.0)|
|Without definite varus thrust||11||21||20||4||1|
|Non–weight bearing–related questions|
|Pain at night in bed|
|With definite varus thrust||11||6||7||1||0||2.1 (0.9–5.1)||2.3 (0.8–6.8)|
|Without definite varus thrust||35||12||8||1||1|
|Pain on sitting or lying|
|With definite varus thrust||11||10||3||1||0||1.5 (0.6–3.8)||1.3 (0.4–3.7)|
|Without definite varus thrust||34||13||8||1||1|
Table 3 presents the proportional odds ratio for each individual WOMAC pain question calculated using varus corrected anatomic alignment as the predictor. Pain was not more likely in the group with varus alignment compared to those without varus alignment, using any of the 5 individual questions in either unadjusted or adjusted analyses.
|Individual WOMAC pain question||Level of pain||Unadjusted proportional OR (95% CI) for pain with vs. without static varus corrected anatomic alignment||Adjusted proportional OR (95% CI) for pain with vs. without static varus corrected anatomic alignment†|
|Weight bearing–related questions|
|Pain on walking|
|Varus alignment||13||19||5||3||0||1.6 (0.7–3.5)||NA‡|
|No varus alignment||20||14||8||0||0|
|Pain on standing upright|
|Varus alignment||14||12||10||4||0||1.9 (0.8–4.3)||1.5 (0.6–3.8)|
|No varus alignment||21||12||7||2||0|
|Pain on using stairs|
|Varus alignment||5||18||9||6||2||1.0 (0.4–2.2)||0.8 (0.3–2.1)|
|No varus alignment||8||14||15||5||0|
|Non–weight bearing–related questions|
|Pain at night in bed|
|Varus alignment||23||7||7||2||1||1.0 (0.4–2.4)||1.2 (0.5–3.3)|
|No varus alignment||23||11||8||0||0|
|Pain on sitting or lying|
|Varus alignment||24||10||4||1||1||0.7 (0.3–1.6)||0.6 (0.2–1.6)|
|No varus alignment||21||13||7||1||0|
To address the possibility that the choice of 178 degrees as a cutoff to define varus static alignment was not the most appropriate, we performed a sensitivity analysis by modifying the cutoff used for the definition of varus alignment, using cutoffs between 171 degrees and 180 degrees (Table 4). Using any of these definitions, the mean of the total WOMAC score was not significantly different between those with and those without varus alignment. For the individual WOMAC questions, the only analyses in which the differences were intermittently significant were unadjusted analyses evaluating pain with walking and standing and adjusted analyses evaluating pain with sitting or lying down.
|Cutoff for defining static varus corrected anatomic alignment, degrees||Unadjusted proportional OR (95% CI) for pain on walking with vs. without static varus corrected anatomic alignment||Unadjusted proportional OR (95% CI) for pain on standing with vs. without static varus corrected anatomic alignment||Adjusted proportional OR (95% CI) for pain on sitting or lying with vs. without static varus corrected anatomic alignment†|
|180||1.8 (0.8–4.2)||2.6 (1.1–6.2)‡||0.5 (0.2–1.4)|
|179||1.4 (0.6–3.1)||2.1 (0.9–4.7)||0.4 (0.1–1.1)|
|177||1.7 (0.7–3.8)||1.9 (0.8–4.2)||0.5 (0.2–1.5)|
|176||1.7 (0.7–3.8)||1.8 (0.8–4.2)||0.5 (0.2–1.5)|
|175||2.3 (1.0–5.4)‡||2.4 (1.0–5.7)‡||0.2 (0.1–0.7)‡|
|174||3.0 (1.2–7.3)‡||2.7 (1.1–6.6)‡||0.2 (0.1–0.8)‡|
|173||NA§||2.4 (1.0–5.9)‡||0.2 (0.1–0.8)‡|
|172||NA§||2.8 (1.1–7.2)‡||0.3 (0.1–1.0)‡|
|171||NA§||2.1 (0.7–6.0)||0.2 (0.04–1.0)‡|
This study is, to our knowledge, the first to show that in persons with symptomatic knee OA the presence of varus thrust, a measure of dynamic alignment known to be a predictor of structural progression (5, 15), is associated with greater overall knee pain, specifically during weight-bearing activities. We have also illustrated that varus static alignment, also a known predictor of structural progression (7), is possibly associated with pain on weight bearing, though with a much smaller effect estimate.
Of the study participants with definite varus thrust, 84% had varus static alignment, while only 33% of those without definite varus thrust had varus static alignment. Although definite varus thrust and varus static alignment are clearly closely related, they do not represent the exact same construct. Varus thrust is a measure of dynamic alignment visualized during gait, while varus static alignment is measured on a radiograph obtained while the patient is not moving. While both have been previously shown to be potent predictors of structural progression (5, 7, 15), highlighting the importance of biomechanics in knee OA pathophysiology, in this cross-sectional study we found that varus thrust was more convincingly associated with pain than was varus static alignment.
Understanding the differences between individuals with varus alignment who do have varus thrust and those with varus alignment who do not have varus thrust may provide important insights into sources of pain in knee OA. Intuitively, it is not surprising that a dynamic alignment measure would be predictive of symptoms in knee OA whereas the equivalent static alignment measure would be less so. Perhaps it is those who have greater laxity in the joint who have varus thrust, which can be best measured during gait. It could also be that varus thrust is a surrogate measure of the external adduction moment, another measure of dynamic alignment, which has been associated with excessive loading upon the medial compartment. In a study of 64 participants, Chang et al showed that those with varus thrust had a higher external adduction moment than those without varus thrust (5). Further, it was recently demonstrated that those with an elevated external adduction moment had a higher prevalence of medial compartment bone marrow lesions visualized on magnetic resonance imaging (16), a feature that has also been associated with knee pain (17–20).
Although the definition of varus static alignment used in this study was similar to those used in prior epidemiologic studies (12, 13), we addressed the possibility that other definitions could have been more appropriate by performing a sensitivity analysis in which the cutoff used for the definition of varus alignment was modified. Using any of the alternative definitions tested (171–180 degrees), the difference in the summed WOMAC between the 2 varus alignment groups was not statistically significant. For the individual WOMAC questions, the unadjusted analyses evaluating pain with walking and standing showed statistical significance in the direction we expected (Table 4). Surprisingly, the point estimates for the association of varus alignment with pain using the question on pain during non–weight bearing (sitting or lying down) were <1, suggesting that varus alignment was protective against pain with sitting or lying down. An interpretation of these findings could be that the cutoff of 178 is most appropriate, since this unexpected result was not evident with this definition. Alternatively, it could be that a lower cutoff definition is more appropriate and static alignment is associated with pain on standing but, for some as-yet-unexplained reason, participants are simultaneously less likely to develop pain with sitting or lying down. In any case, the relationship between varus static alignment and pain is substantially weaker than that between varus thrust and pain, as calculated using a variety of cutoff definitions for varus static alignment.
Notably, the severity of radiographic knee OA was greater in patients with definite varus thrust as compared to those without definite varus thrust. We did not enter K/L score as a potential covariate in our adjusted model, expecting that varus thrust could be a mediator of any association between higher K/L scores and knee pain. However, because there is a possibility that varus thrust may be associated with pain independently of K/L score, we did perform additional analyses adding K/L score to the unadjusted logistic regression models and found that varus thrust was still significantly associated with the total WOMAC pain score, in addition to scores on the individual standing and walking pain questions. These findings support the notion that varus thrust is associated with knee pain independent of the fact that varus thrust is associated with more severe radiographic OA.
Although there is some doubt regarding the measurement properties of the summed WOMAC pain subscale, it is still the outcome measure currently recommended by the Osteoarthritis Research Society International (21) and accepted by the Food and Drug Administration for assessment of symptoms in knee OA clinical trials. In this study, we evaluated pain by using the sum of the WOMAC pain questions as well as the individual WOMAC pain questions; use of both allowed for better characterization of the heterogeneous pain that occurs in knee OA.
Varus thrust is a clinical assessment of dynamic loading that can be performed inexpensively. We used a standard video camera to record participants ambulating, at a self-selected speed, 20 meters away from and then toward the camera. With the adjudication of the measure between 2 rheumatologists who were blinded with regard to pain assessments, we did find that this measure was strongly related to the summed WOMAC pain assessment and specifically, weight-bearing pain, i.e., pain with walking on a flat surface and pain with standing. Because the number of knees for which adjudication of this reading was required was substantial (39%), we performed a sensitivity analysis in which we restricted the analyses to only those knees for which adjudication was not required. In this analysis, the results were similar with the exception that the difference in total WOMAC pain score in participants with definite varus thrust versus those without definite varus thrust (mean 5.2 and 3.9, respectively) was no longer statistically significant (P = 0.20) (likely reflecting a loss of power with the lower number of observations), though the direction of the relationship was still similar. However, the unadjusted odds ratios for the individual pain questions remained unchanged, with the results of the analyses of pain on walking and standing being statistically significant, suggesting that the association between varus thrust and pain is real.
There are limitations to this study, an important one being the relatively small sample size. It will be important to replicate our findings in a larger cohort of OA patients. Also, this was a cross-sectional study, limiting our ability to draw conclusions regarding whether varus thrust causes pain; longitudinal studies will be needed to investigate this. Another important limitation is that for our measure of static alignment we used posteroanterior radiographs with the knee in semiflexion (available from the parent study) to assess a corrected anatomic alignment, as opposed to the accepted gold standard of using long-limb radiographs to measure mechanical alignment. Anatomic alignment is a valid and useful biomechanical parameter, but results could differ from those obtained using true mechanical alignment (11). Therefore, the possibility remains that static alignment assessed via mechanical alignment could be more strongly associated with knee OA pain.
Nonetheless, our study demonstrated a strong association between varus thrust and pain in individuals with knee OA, particularly with weight-bearing activities. This finding was not replicated with regard to an association of varus static alignment with pain, though there was a suggestion of this possibility from our sensitivity analyses using a more stringent definition of varus alignment. The potential clinical implications of the present findings include the notion that patients with varus thrust might represent a specific phenotype of OA, such that patients with this phenotype may selectively respond to customized biomechanical modifications. For instance, treatment of varus thrust with bracing or gait retraining may provide symptomatic relief for the patients with this particular finding. Because varus thrust has been demonstrated in other studies to be associated with structural progression (5, 16), biomechanical intervention to improve symptoms may also provide structural benefits. Identification of varus thrust in patients with knee OA may therefore bring us closer to finding an effective symptom- and structure-modifying treatment for this disease.
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. Lo 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. Lo, Harvey, McAlindon.
Acquisition of data. Lo, Harvey, McAlindon.
Analysis and interpretation of data. Lo, Harvey, McAlindon.
- 10Kellgren JH, Lawrence JS, editors. The epidemiology of chronic rheumatism: atlas of standard radiographs. Oxford: Blackwell Scientific; 1963.
- 142011 April 9–13; Philadelphia. URL: http://www2.sas.com/proceedings/sugi30/205-30.pdf.. Using the proportional odds model for health-related outcomes: why, when, and how with various SAS procedures. Presented at the SAS Users Group International Conference;
- 20Osteoarthritis Initiative Investigators Group. Bone marrow lesions and joint effusion are strongly and independently associated with weight-bearing pain in knee osteoarthritis: data from the Osteoarthritis Initiative. Osteoarthritis Cartilage 2009; 17: 1562–9., , , , , , et al, for the