KNEE OSEOARTHRITIS
Brace treatment for osteoarthritis of the knee: a prospective randomized multi-centre trial
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Summary
Objective
To evaluate the effect of a brace intended to reduce load in patients with medial or lateral compartmental osteoarthritis (OA) and concurrent varus or valgus alignment, respectively.
Design
This multi-centre randomized controlled trial (performed 2001–2003) studies the additive effect of a brace intended to reduce load in conservative treatment of unicompartmental OA of the knee. Setting: Orthopedic department of a university medical centre and of one general hospital. The follow-up was 12 months. Patients: 117 patients with unicompartmental OA of the knee. Intervention group (n=60) comprising conservative treatment with additional brace treatment and a control group (n=57) comprising conservative treatment alone. Primary outcome measures: Pain severity and knee function score. Secondary outcome measures: Walking distance and quality of life. Analysis: Multiple linear regression models according to the intention-to-treat-principle were used to assess outcome differences for the entire group of patients. In addition, we performed explorative subgroup analyses on primary overall outcomes stratified for alignment, degree of OA, origin of OA, and age.
Results
Although the primary outcome measures were improved in the intervention group in comparison with the controls at each assessment point, the differences reached only borderline significance. The reported walking distances at 3 months, 12 months and overall were significantly longer in the brace group (P=0.03, P=0.04 and P=0.02, respectively). Subgroup analysis showed a better effect in the varus group, in patients with severe OA, in patients with secondary OA and in patients younger then 60 years. In total 25 patients in the brace group and 14 in the control group changed their initial treatment, mostly (74%) because of a lack of beneficial effect.
Conclusions
The results indicate that a brace intended to reduce load shows small effects in patients with unicompartmental OA. However, many patients do not adhere in the long run to this kind of conservative treatment.
Introduction
Osteoarthritis (OA) of the knee is a common medical condition that is often seen in general practice and causes considerable pain and immobility. In the United States approximately 6% of the population aged 30 years and older and 12% of the population aged 65 years and older suffer from knee OA1. In addition to the consequences for the patient, OA forms a considerable burden for society because of its chronic course and the high costs of interventions2.
OA of the entire knee is distinguished from that of one compartment, which is generally caused by a mechanical problem3,4. Patients with OA of the medial compartment often have a varus alignment and the mechanical axis and load bearing pass through the medial compartment. Patients with OA of the lateral compartment generally have a valgus alignment and the mechanical axis and load bearing pass through the lateral compartment.
Malalignment increases the risk for progression of knee OA and predicts decline in physical function5. Overall, more patients with OA have varus alignment (76–93%) than valgus alignment6.
The initial treatment for OA of the knee is conservative, consisting of patient education (adaptation of activities and/or weight loss), and if needed physical therapy and medication7, 8, 9, 10, 11, 12, 13. The general purpose of a brace is to decrease pain and improve function; valgisation and varisation braces are available for unloading the medial and lateral compartment, respectively14, 15, 16, 17, 18.
A recently published Cochrane review concluded that there is very limited evidence for the effectiveness of brace treatment for knee OA, mainly because of lack of studies on this issue19. Therefore, the present study investigated the additive effect of a brace intended to reduce load in conservative treatment of unicompartmental OA with varus alignment or valgus alignment.
Material and methods
Study design
A multi-centre randomized controlled trial was designed to study the additive effect of a brace intended to reduce load in the conservative treatment of unicompartmental knee OA (Fig. 1).
Fig. 1
Flowchart showing the patients on the waiting list for surgical treatment, or who were lost to follow-up during the trial.
The study was conducted at the orthopedic outpatient departments of a university medical centre and of a general hospital. The medico-ethical committees of both hospitals approved the study protocol.
Inclusion/exclusion criteria
The inclusion criteria were symptomatic unicompartmental knee OA and a malalignment in patients aged 18 years and over. We diagnosed the OA as unicompartmental when the symptoms (pain and tenderness of the joint margins) were located over the medial or the lateral tibiofemoral compartment of the knee in combination with osteoarthritic signs according to the Ahlbäck score (Ahlbäck>0) in the same medial or lateral tibiofemoral compartment of the knee as well as in combination with varus alignment (in combination with medial compartment OA) or valgus alignment (in combination with lateral compartment OA), respectively20. The degree of malalignment and mechanical axis was measured on a whole leg radiograph in standing position and determined according to one line (mechanical axis of the femur) from the centre of the femur head using Mose circles to the middle of the distance between the tibial spines, and a second line (mechanical axis of the tibia) from the centre of the ankle to the centre of the tibial spines.
Patients with concurrent symptomatic OA of medial and lateral compartments, symptomatic patellofemoral OA (scored on the lateral radiograph of the knee), no malalignment, rheumatoid arthritis, previous high tibial osteotomy, symptomatic hip or ankle pathology, and an insufficient command of the Dutch language were excluded.
Procedures
After reading the patient information form informed consent was given and baseline measurements were made, patients were randomized according to a computer-generated procedure in blocks of 24; the allocation of treatment was concealed until after the patient was included and baseline measurements were executed; sealed envelopes contained the group assignment.
The follow-up assessments that took place at 3, 6 and 12 months included standardized questionnaires and physical examination by one investigator.
Treatment groups
Patients were randomly assigned to either an intervention group comprising conservative treatment with additional brace treatment, or to a control group comprising conservative treatment alone.
The conservative treatment was identical in both groups and consisted of standard care: i.e., patient education (adaptation of activities and/or weight loss), and (if needed) physical therapy and analgesics.
In the intervention group patients were fitted with a knee brace (OAsys brace, Innovation Sports, Irvine, CA, USA); this brace is commercially available for right/left leg in four sizes (Fig. 2). The brace is accepted and refunded by all Dutch health insurance companies. The brace consists of a thigh shell and a calf shell (both of carbon fiber) connected by titanium hinges on the medial and lateral sides. The adjustable slide bar on the medial side of the brace provides valgisation (1–12.5 degrees) with medial unloading, or varisation (1–10 degrees) with lateral unloading. The degree of varisation or valgisation depends on the degree of malalignment and the acceptance of the patient (extensive correction will cause pressure ulcers). A specialized orthopedic technician applied the brace and gave instructions to the patients. During the follow-up this specialized orthopedic technician was present at the orthopedic outpatient department. If necessary the brace was adjusted during the follow-up visits.
Fig. 2
Photograph showing the fitted brace.
Baseline evaluation
Age, gender, Body Mass Index (BMI), duration of complaints, severity of OA, varus alignment, pain severity, hospital for special surgery score (HSS score), walking distance, quality of life, and analgesic use were scored at baseline.
Outcome assessments at 3, 6 and 12 months
Primary outcome measures were pain severity measured with a visual analogue scale (VAS; range 0–10), and a knee function score using the HSS (range 0–100). The HSS is divided into six categories (pain, function, range of motion, muscle strength, flexion deformity, and instability), is often used in orthopedic interventions in knee OA, and consists of a questionnaire and a physical examination21. In the present study physical examination for the HSS knee function score was determined by one un-blinded assessor.
Secondary outcome measures were walking distance (in kilometers) and quality of life (measured with the EuroQol-5D)22.
Sample size
The sample size calculation was based on the study of Magyar et al. who reported a standard deviation (SD) of 9 in the HSS knee score in their study population23. For the present study, with a difference between two groups of five points we would reach clinically relevant differences (effect size 0.55). To detect such a difference with two-sided testing (α=0.05 and a power of 80%) we needed to include 51 patients in each study group. Over sizing by 15% allowed us to reach this power also in the largest subgroup of patients with unicompartmental OA with varus alignment.
Statistical analyses
All data were analyzed according to an intention-to-treat principle, implying that all patients who were randomized were included in the analyses, and that they were analyzed according to the group to which they were allocated.
Outcome assessments at 3, 6 and 12 months (pain severity, HSS knee function score, walking distance and quality of life) were analyzed using multiple linear regression analysis. These analyses were adjusted for the baseline value of the outcome measure. Further, those variables which changed the relationship (slope) between the independent variable (treatment group) and one of the dependent variables (outcomes) by more than 10% were considered as confounders and were included in the models. For patients who were lost to follow-up or were placed on the waiting list for surgical intervention (e.g., high tibial osteotomy, hemi/total knee prosthesis) during follow-up, the last available measurement or the last preoperative measurement was entered.
The overall outcomes during the 12 months were analyzed using linear regression for repeated measurements with the same adjustments as above. For these analyses, in case the patient was already lost to follow-up or underwent surgical intervention before the first 3-month follow-up, only baseline values were entered. Other measurements were not entered.
Standardized effect sizes (adjusted mean difference in outcome divided by the pooled SD) were calculated for all outcomes. Effect sizes between 0.2 and 0.5 represent small effects, between 0.5 and 0.8 moderate effects, and above 0.8 large effects24.
In addition, we performed explorative subgroup analyses on primary overall outcomes (using the methods stated above) stratified for alignment (varus vs valgus), degree of OA (mild: Ahlbäck 1 vs severe: Ahlbäck 2 and 3), and origin of OA (primary vs secondary: post-meniscectomy or cruciate lesion), and age (younger than 60 years vs 60 years and older).
The SPSS and SAS programs were used for the statistical analyses and a P-value of 0.05 was considered statistically significant.
Results
In the period January 2001 to January 2003, 118 patients were randomized. One patient withdrew immediately because of dissatisfaction with the randomization outcome (no brace) and refused any further participation; this patient was excluded from analysis, resulting in a total sample of 117 patients.
Table I shows that the mean age of the total group was 59.2 (SD 13.7) years, 50% was male and mean BMI was 28.5 (SD 4.8). There were 60 patients in the intervention group and 57 in the control group; four patients in the control group were lost to follow-up. In total 95 patients had varus alignment and 22 had valgus alignment. At baseline, compared with controls, scores on pain severity, HSS knee function and walking distance were worse in the brace group.
∗OA according to Ahlbäck.
†Hip–Knee–Ankle angle: an angle of more than 180° denoted a varus alignment.
Primary outcome measures
Compared with controls, pain severity (VAS) was less in the brace group at each of the three assessment points as well as overall during the 12 months follow-up; the largest difference was at 12 months (−0.81; 95% CI: −1.76; 0.14) (Table II). At 12 months and overall the difference in VAS score was borderline significant (P<0.1). Effect sizes at the three assessment points ranged from 0.3 to 0.4.
| Analysis in total group (N=117) | ||
|---|---|---|
| Mean difference (95% CI) | Effect size | |
| 3 months follow-up | ||
| Pain severity (VAS, 0–10) | −0.73 (−1.62;0.16) | 0.3 |
| Knee function (HSS, 0–100) | 3.5 (−0.24;7.24)* | 0.3 |
| Walking distance (km) | 1.21 (0.12;2.28)** | 0.3 |
| Quality of life (EQ-5D, 0–1) | 0.03 (−0.05;0.12) | 0.1 |
| 6 months follow-up | ||
| Pain severity (VAS, 0–10) | −0.58 (−1.48;0.32) | 0.3 |
| Knee function (HSS, 0–100) | 3.2 (−0.58;6,98)* | 0.3 |
| Walking distance (km) | 0.79 (−0.40;1.98) | 0.2 |
| Quality of life (EQ-5D, 0–1) | 0.01 (−0.08;0.10) | 0.0 |
| 12 months follow-up | ||
| Pain severity (VAS, 0–10) | −0.81 (−1.76;0.14)* | 0.4 |
| Knee function (HSS, 0–100) | 3.0 (−1.05;7.05) | 0.3 |
| Walking distance (km) | 1.34 (0.05;2.63)** | 0.4 |
| Quality of life (EQ-5D, 0–1) | 0.01 (−0.08;0.10) | 0.0 |
| Overall | ||
| Pain severity (VAS, 0–10) | −0.63 (−1.38;0.12)* | 0.3 |
| Knee function (HSS, 0–100) | 3.0 (−0.41;6.41)* | 0.3 |
| Walking distance (km) | 1.25 (0.15;2.35)** | 0.4 |
| Quality of life (EQ-5D, 0–1) | 0.02 (−0.05;0.09) | 0.1 |
*P<0.1, **P<0.05.
The mean difference is adjusted for baseline values for age, gender, BMI, duration of complaints, severity of knee OA, (alignment), baseline pain severity, knee function, walking distance, medication, and quality of life.
Knee function (HSS) in the brace group was better at each assessment point; the largest difference was seen at 3 months follow-up (3.5 points; 95% CI: −0.24; 7.24). Borderline significance (P<0.1) was observed at 3 months (P=0.07), 6 months (P=0.10), and overall (P=0.09). The effect size at the three assessment points was 0.3.
Secondary outcome measures
The reported walking distances at 3 months (1.21 km; 95% CI: 0.12; 2.28), 12 months (1.34 km; 95% CI: 0.05; 2.63) and overall (1.25 km; 95% CI: 0.15; 2.35) were significantly longer in the brace group (P=0.03, P=0.04 and P=0.02, respectively) (Table II). Effect sizes at the three assessment points ranged from 0.2 to 0.4. No significant differences in quality of life evaluations were found between the intervention and control groups.
All our analyses were adjusted for baseline use of analgesics (none, when needed, and daily). Also during the follow-up we scored the analgesic use: there was increasingly lower medication use for each follow-up period in the brace group compared to the control group.
Subgroup analysis
Explorative subgroup analyses stratified for the alignment showed a better and significant effect of the brace in the varus group (n=95) for the knee function score (estimate HSS 4.15; P=0.03) compared to the effect of the brace in the valgus group (n=22) (estimate HSS 0.20; P=0.96). The effect for the pain severity showed a similar trend, but not as pronounced as for knee functions.
Explorative subgroup analyses stratified for degree of OA showed a better effect of the brace in patients with severe OA (n=43) for pain severity (estimate VAS −1.31; P=0.10) compared to the effect of the brace in patients with mild OA (n=74) (estimate VAS −0.21; P=0.65). The effect for the knee functions showed a similar trend, but not as pronounced as for pain severity.
Explorative subgroup analyses stratified for the origin of OA showed a better effect of the brace in patients with secondary OA (n=47) for knee function (estimate HSS 4.87; P=0.06) compared to the effect of the brace in patients with primary OA (n=70) (estimate HSS 1.59; P=0.51). The effect for pain severity showed a similar trend, but not as pronounced as for knee function.
Explorative subgroup analyses stratified for age showed a slightly better effect of the brace in patients younger than 60 years (n=60) for knee function (estimate HSS 3.38; P=0.13) compared to the effect of the brace in patients aged 60 years and older (n=57) (estimate HSS 2.48; P=0.38). The effect for pain severity showed a similar trend, but not as pronounced as for knee function.
Discontinuation of treatment during follow-up
During the 12-month follow-up period, 25 patients in the brace group and 14 patients in the control group changed their initial treatment, mostly at around 3 months; in both groups the main reason for this was no effect of treatment (74%) (Table III). Other reasons for stopping brace treatment were skin irritation and bad fit, and three patients stopped because the symptoms strongly reduced. Change in treatment during follow-up included surgery (e.g., high tibial osteotomy, n=8; knee arthroplasty, n=16). Thirteen patients changed brace treatment for standard conservative treatment (Fig. 1).
| Brace group N=60 | Control group N=57 | |
|---|---|---|
| Stopped with treatment (total) | 25 | 14 |
| Within 3 months | 16 | 6 |
| Between 3 and 6 months | 6 | 6 |
| Between 6 and 12 months | 3 | 2 |
| Alternative treatment | ||
| High tibial osteotomy | 5 | 3 |
| Unicompartment knee prosthesis | 3 | 0 |
| Total knee prosthesis | 3 | 10 |
| (Other) brace | 1 | 1 |
| Only usual conservative care | 13 | 0 |
| Reason for stopping treatment | ||
| No effect | 15 | 14 |
| Skin irritation | 2 | – |
| Bad fit | 2 | – |
| Minimal symptoms | 3 | – |
| Several reasons | 3 | – |
Discussion
The results of this study indicate that a brace intended to reduce load offers small additional beneficial effect in knee OA compared with conservative treatment alone.
Many of the measured outcomes showed only a borderline significant difference. We decided in advance to perform two-sided testing. However, looking at the comparison (standard care vs standard care in combination with brace treatment), one-sided testing would have been allowed because one expects an additional beneficial effect of the additional treatment. Had we used one-sided testing, almost all of our primary outcomes would have been statistically significant.
Studies comparing the effectiveness of braces to treat OA of the knee are scarce: only one randomized controlled trial has evaluated the effectiveness of braces for patients with unicompartmental OA of the knee with varus alignment16. The results of the present study confirm those of the latter study, which included 119 patients who were followed for 6 months. In that study, a valgus brace was compared with a neoprene sleeve and with standard medical treatment (control group); the brace group showed greater improvement compared with the sleeve group, which showed greater improvement compared with the control group.
Also a cross-over study showed in 12 patients with OA of the medial compartment and a varus alignment significant improvements gait with a valgus corrective brace compared with a neutral brace25.
In our study valgisation bracing in medial compartment OA was more effective than varisation bracing in lateral compartment OA. This might indicate that the unloading theory does not apply in patients with lateral compartment and a valgus alignment.
Moreover, the knee adduction moment during the stance phase of walking causes mainly medial loading6, 26. Possibly, a simple sleeve will show the same or more effect in patients with lateral compartment OA due to increased proprioception27, 28. This was also discussed by Kirkley et al. who reported an effect of a neoprene sleeve in unicompartmental OA with varus alignment16. Therefore, in general OA of the knee where there is no specific compartment to unload, a sleeve or a neutral brace may also be beneficial due to possible increased proprioception and stability27.
Study limitations
First, the assessor was also the caregiver as well as the one who informed the patient about the aims of the study. Although the kind of intervention did not allow blinding of patients, methodological strength would have been gained by blinding the assessor for the functional outcome measurement (HSS knee score), e.g., by using an independent assessor. However, because the same effects were found for the self-evaluated functional outcome (i.e., walking distance), and because the caregiver had no definite opinion about the effectiveness of the brace, we assume that the assessments made by the caregiver had minimal or no bias.
Second, several patients stopped brace treatment during the 12-month follow-up, mainly due to noneffectiveness. Moreover, most of these patients stopped brace treatment before the first 3-month assessment point; this may be too short a period (in the absence of adverse side-effects) for a beneficial effect to emerge.
Third, although we used the HSS knee function score (frequently used in orthopedic research), the WOMAC-function seems to have become the function score of choice21, 29. Nevertheless, in view of the very high correlation between the WOMAC-pain and WOMAC-function, some have suggested that the WOMAC-function measures pain rather than function30.
Clinical implications
Although a brace intended to reduce load indicates a small additional beneficial effect in conservative treatment of knee OA during a 12-month follow-up, many patients do not adhere to the brace treatment in the long run, either because the positive effects are too small or because the adverse effects are too large.
Based on explorative subgroup analysis in the present study, a brace intended to reduce load seems to be a treatment option for younger patients with unicompartmental OA with varus alignment, because few conservative alternatives have proven effective31, 32. Correction osteotomy in relatively young patients with unicompartmental OA has good results, but this surgery can present complications33, 34. Knee arthroplasty for younger patients is not recommended because the degree of patient activity and life expectancy means that the arthroplasty may wear out and/or loosen35. For older (aged >60 years) less active patients, however, brace treatment seems less effective and therefore standard conservative treatment is recommended. If symptoms persist in this older group, a knee arthroplasty (nowadays a routine procedure with good long-term results) can be considered36, 37.
Future research
Besides the above-mentioned practical considerations, a larger study is needed to identify predictive factors for the success of brace treatment. Particularly for the valgus group a larger study population is needed to identify what type of brace will benefit this group. In addition, brace treatment should be compared with using a neoprene sleeve with possibly better treatment adherence.
Acknowledgment
We thank RMD Bernsen for the statistical analysis. Contributors: RWB, JANV, and LNJEMC had the idea of the study. RWB and SMABZ designed the study. RWB and TMR collected the data. SMABZ was responsible for the interpretations of the data. RWB wrote the manuscript. All authors critically commented on the paper and gave their final approval of the version to be published. RWB is the guarantor. Funding: This study was supported by the Revolving Fund (RF01-12) of the Erasmus University Medical Centre Rotterdam, The Netherlands. Competing interests: None declared. Ethical approval: Medical Ethics Committees of the Erasmus Medical Centre Rotterdam and Leyenburg Hospital, The Hague, The Netherlands.
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