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A Comparison of Two Custom-Made and Two Off-the-Shelf Rigid Knee Orthoses in the Treatment of ACL-Deficient Knees

Renate P.M.J. Bos, MSc
Joke H. Grady, MSc
Pieter A.M. Vierhout, MD, DSc
Jaap de Vries, MD, DSc

ABSTRACT

The authors conducted a study of 45 patients with anterior cruciate ligament- (ACL-) deficient knees who had been fitted with rigid knee orthoses in the past three months. In addition to being diagnosed with knee pathologies, all patients had complained of pain and "giving way" (instability during physical activities).

The study was undertaken for two reasons: 1) to gain insight into the usability of two custom-made and two "off-the-shelf" rigid knee orthoses based on their actual use, usefulness and ease of use; and 2) to determine the influence of the type of orthosis on patient outcomes.

Almost all of the orthoses actually were used at home and in leisure time as well as at work and in sports. Usefulness of all types of rigid knee orthoses was the greatest in circumstances when the patients performed poorly before orthosis fitting. Ease of use played a secondary role. The four types of rigid knee orthoses did not significantly differ in respect to the research objectives.

Introduction

Despite an abundance of research, relatively little is known about the usability of rigid knee orthoses in cases of anterior cruciate ligament- (ACL-) deficient knees (1,2), which may be due to the type of research being carried out.

In general, current functional knee orthosis research is biomechanically oriented and is aimed at testing the restraint of the rigid knee orthosis in relation to tibial displacement, varus-valgus and axial rotation loads. Past researchers either used knee models (1,3,4) or tested the rigid knee orthosis in vivo (4-8). In each case, the braced knee generally is exposed to static clinical loads only. Sometimes, in vivo testing involves measuring the performance of the rigid knee orthosis in stabilizing the knee joint during certain well-defined and reproducible dynamic actions. The performance of the knee orthosis is assessed by measuring the strain on knee ligaments during the action or by assessing the changes in the joint moments of force or in muscle activity due to knee orthosis usage (8,9).

It is difficult to apply results of the above-mentioned biomechanical research in clinical practice because the research conditions do not or only partially correspond to the reality. In reality, the orthosis is worn in different circumstances in which actions are unpredictable, not well-defined.

Literature on user experiences with rigid knee orthoses is scarce. User experiences are either considered to be a matter of minor importance (6,10) or not important at all (1). The majority of these studies are limited to assessments of patient satisfaction about a rigid knee orthosis. This kind of research can be described as effect-oriented, meaning the clinician will be left ignorant concerning the causes of any (dis)satisfaction.

Neither the biomechanical approach nor the current effect-oriented research on user experiences gives clinicians adequate information about the usability of rigid knee orthoses, which is a disturbing problem in rigid knee orthosis prescription. To solve this problem, a new method of user research was used in this study. In this method, the actual use of a product depends on the usefulness and ease of use thereof.

The purpose of the present study was, first, to gain much-needed insight into the actual use of a rigid knee orthosis, the usefulness and the ease of use of the orthosis perceived and experienced by the patients, and the potential inter-relationship between these factors. This information was gathered by an extensive structured questionnaire. Second, the study was aimed at determining the influence of the type of rigid knee orthosis on the above-mentioned factors. It was therefore decided to perform the study with four types of current functional rigid knee orthoses for ACL insufficiency: two varieties of custom-made and two varieties of off-the-shelf rigid knee orthoses.

In this study, the authors distinguished "giving way" from reinjury. Giving way of the knee is the sensation of instability during physical activities, but reinjury implies a recurrent subluxation of the knee resulting in pain, swelling and limitation of activities for a number of days (11).

Subjects and Method

Subjects

The subjects who participated in this study had ACL lesions confirmed by arthroscopic examinations. Their ACLs had not yet been reconstructed or had ruptured again after a reconstruction a few years ago. Seventy-one percent of the patients had associated pathologies of other joint structures (see Table A) . Despite these varieties in diagnosis, all subjects complained about pain and giving way of the knee. The selection of the patients in this study was based on the latter common aspects. The patients were fitted with rigid knee orthoses because they were limited in their daily activities by pain and giving way of the knee. This is a routine procedure in the field of rehabilitation. The pretest group was comprised of 52 patients: 14 women ranging from 22 to 53 years old and 38 men ranging from 16 to 55 years old. They were referred to the rehabilitation center by a surgeon who specialized in knee pathology. None of the patients had ever worn a rigid knee orthosis before, and most were waiting for surgery.

Materials

The following four types of rigid knee orthoses were chosen for the 45 subjects included in the first control group:

• Off-the-shelf:
    CTi²(Figure 1) : 10 patients
    Basko-KCO (Figure 2) : 12 patients
• Custom-made:
    MOS-genu (Figure 3) : 11 patients
    Bledsoe-ACL brace (Figure 4) : 12 patients

These rigid knee orthoses generally are used for treatment of an ACL-deficient knee in the authors' region. Although the materials and the constructions of the knee orthoses differ, their biomechanical principles are the same.

Measurement Instruments

Questionnaire

Many rating systems can be used to evaluate knee ligament injuries (12-16). The systems focus on evaluating disabilities during natural recovery or after knee ligament surgery. The possible treatment of an ACL-deficient knee by a rigid knee orthosis is not taken into account. In addition, the existing rating systems are effect-oriented, which means no information is provided on the factors leading to this result. Such information is of vital importance to optimize indication and design of aiding devices.

Since the existing rating systems were deemed inadequate, an extensive structured questionnaire was designed based on the framework of the Rehabilitation Technology Usability Model (RTUM), which has been especially developed for this purpose (17). Figure 5 shows RTUM with its components and various links.

According to Figure 5 , the actual use of a product (in this case, a rigid knee orthosis) depends on the attitude of the user based on his or her perception as well as experience with respect to the device's usefulness and ease of use. The characteristics of the product, the user and surroundings also are important. The term "experience" concerns the influence of the knee orthosis directly at orthosis/knee level-for example, the experienced inconvenience of the orthosis (transpiration, irritation of skin, orthosis slippage and pressure pain) or pain relief of the knee. "Perception" refers to the judgment of functioning with the knee orthosis, like an improvement in function in sports due to using a rigid knee orthosis. Finally, "ease of use" refers to the (in)convenience of orthosis usage and "usefulness" to the value of its usage.

Starting from the RTUM components, questions were composed in the fields of impairments and disabilities. Based on a pilot study with 10 patients, the definitive questionnaire was constructed. Results of this pilot study indicated the experience of pain and giving way were the most limiting factors in mobility and daily activities. Therefore, the level of disability initially was assessed by inquiring about the amount of pain and giving way of the knee during several mobilities: standing, walking, cycling, going up and down stairs, running, and making sudden movements (especially turning around). Furthermore, the questionnaire focused on the circumstantial use of the rigid knee orthosis in sports activities, at work and at home/in leisure time.

The research questionnaire was comprised of two parts. Part I (first contact/pretest) was designed to gain an insight into the history of the knee pathology, the impairments and disabilities of the patients when not wearing a rigid knee orthosis, and the patients' expectations concerning the orthosis. Part II (control contact/post-test) was designed to evaluate the experiences with and perceptions of the rigid knee orthosis. Nearly all of the questions were answered with the help of Visual Analog Scales (VAS) (18-22). VAS is a 100-mm line anchored by terms that represent the extreme answers (e.g., no pain to severe pain) on which patients can mark their answers. Scores range from 0.0 to 10.0.

Lysholm and Tegner Score

The patients also were judged by the Modified Lysholm Knee Scoring Scale and the activity score of Tegner and Lysholm (15). The activity score was subdivided into the "sports activity score" and the "work/daily living activity score" as used by Meins (23) and Sibbel et al. (21). The scales are especially applied to knee research in the field of surgery and sports medicine. Both the Modified Lysholm Knee Scoring Scale and the activity score are valid measurement instruments. According to Tegner and Lysholm (15), the intra-personal and interpersonal coefficients of variation of their scoring scale were 3 percent and 4 percent, respectively. The test-retest correlation coefficients were 0.97 and 0.90. A comparison with the valid Marshall Scoring Scale showed high correlations.

Experimental Sessions

During the first visit of the patients at the outpatient clinic of the Rehabilitation Centre "Het Roessingh," the type of rigid knee orthosis to be fitted was determined at random. The first part of the questionnaire was carried out before fitting the orthosis (first contact). Two, six and 12 weeks after orthosis fitting, the second part was carried out (first, second and third control).

Patients who had complaints concerning the rigid knee orthosis were immediately referred to the instrumentmaker for orthosis correction. When a patient underwent surgery, he or she was excluded from the remaining contacts. The patients were permitted to terminate their participation in the study at any time.

Data Analysis

Past research experience with the use of VAS led the authors to assume patients who scored 4 or less on questions about giving way and pain at the knee, inconvenience, and usefulness of the orthosis did not take much notice of the factor in question.

Statistical Analyses

Statistical analyses were made using two nonparametric tests suitable for small samples. The Wilcoxon signed rank test was used on individual questions to determine the effect of a rigid knee orthosis. The Kruskal-Wallis test is a test across the four rigid knee orthoses and determined the possible differences between them. The results are judged by an a of 5 percent (p <0.05).

Results

Premeasuring

Table A shows the majority of the research population suffered from other knee injuries in addition to their ACL lesions. However, they predominantly had symptoms of pain and giving way of the knee. Standing, walking at a comfortable speed, climbing stairs and home/leisure activities in general caused few complaints (VAS score <4). Activities at work resulted in moderate complaints (VAS score 54). At higher levels of activity, such as sports activities, sudden rotating movements and, to a lesser degree, running, more severe, function-disturbing symptoms of pain and giving way emerged (VAS score >4). Due to these experiences, 50 percent to 75 percent of the patients (depending on the kind of knee orthosis sample in question) did not participate in a sport.

In spite of an at-random distribution of the different types of knee orthoses among the participating patients, the Tegner and Lysholm "work/daily living activity score" was one level higher in the CTi2 sample than in the other samples. The Tegner and Lysholm "sports activity score" was one level higher in both the Basko-KCO sample and the CTi2 sample.

The patients had high expectations (VAS score 8) regarding the usefulness of the rigid knee orthosis during risk-bearing activities (especially in sports). However, they also intended to use the rigid knee orthosis at home/in leisure time and at work. They expected the potential inconvenience of the knee orthosis would be balanced by its usefulness.

Remeasuring

Dropouts

Table B shows a decline in the number of patients during the course of the study. Because of the limited time period of this study, a number of control contacts could not be carried out. Some patients dropped out because of a personal matter, natural recovery or surgery.

Only four patients dropped out due to striking problems with the knee orthosis. Two of them could not function as they would have liked while wearing the rigid knee orthosis (CTi2, MOS-genu). The other two (CTi2, Basko-KCO) suffered reinjury during peakloads of the knee in sports (basketball and soccer).

Actual Use

Actual use of the rigid knee orthosis, as shown in Table C , was determined by the patients themselves and was reflected in different circumstantial use. Most of the patients used their rigid knee orthoses either during sports activities only or during activities at home/in leisure time as well as at work and in sports.

In general, the four types of rigid knee orthoses were worn most hours a week at work (see Table D) , greatly exceeding the number of wearing hours during sports and at home/in leisure time (except for the MOS-genu orthosis at home).

It is striking that about 50 percent of the nonsporting patients resumed or started to play a sport due to wearing a rigid knee orthosis.

Reinjury of the Knee

Six patients reinjured their knees while wearing the rigid knee orthosis (four CTi2s and two Basko-KCOs). The major cause was an aggressive rotating movement during sports activities. Four of these six patients continued using the rigid knee orthosis until at least 12 weeks after initial fitting.

Experienced Usefulness

Table E represents the results of the Wilcoxon signed rank test, which indicate the influence of the rigid knee orthosis on pain and giving way depends on the type of activity. The level of significance is achieved in more than 50 percent of the cases. However, the effect of wearing a knee orthosis is more often significant during more strenuous activities such as running, sudden rotating movements and sports. The average pain and giving way scores show a significant reduction, with the exception of one. The Kruskal-Wallis test shows no differences between the types of orthoses with respect to their effect on pain and giving way.

Experienced Ease of Use

Even though the patients were not greatly inconvenienced by local discomfort (except for transpiration, which averages a VAS score of 5), they did not consider the rigid knee orthosis to be a user-friendly and comfortable technical aid. The average VAS score on these more global aspects of the orthosis was 6 or less (see Figures 6 and 7 ).

A common complaint concerned the proper donning and doffing of the rigid knee orthosis. Except for the MOS-genu sample, most of the patients complained about the knee hinges damaging their clothes and the volume (great dimensions) of the rigid knee orthosis (the orthosis, for example, often did not coordinate well with jeans). Again, the Kruskal-Wallis test showed no differences between the rigid knee orthoses concerning discomfort.

Perceived Usefulness and Ease of Use

After three months, the overall usefulness of the rigid knee orthosis was judged by an average VAS score of 8. In addition to the specific usefulness of the orthosis at home and during leisure time, its aid at work and in sports had to be judged. It appeared the improvement in the functioning of the patients wearing a rigid knee orthosis was directly related to the usefulness and ease of use of the orthosis and the practical (personal and social) relevance of these factors as perceived by the wearer. This applies to all three situations.

Figures 8 , 9 and 10 show the patients' judgments of their functioning (by VAS) within each of the three wearing conditions. The average VAS score on functioning hardly exceeded an 8 while the maximum is 10. If this score was achieved, most often it decreased in the next control.

The functioning of the patients at home/in leisure time showed little improvement after orthosis fitting (see Figure 8) . At work, the improvement was moderate (see Figure 9) . Table F shows that in both circumstances the rigid knee orthosis did not significantly contribute to the quality of function.

The improvement of function during sports activities was significant (see Figure 10) for all orthosis samples in most of the patient controls except for the CTi2 sample (see Table F) . The many significant increases of the Tegner and Lysholm sports activity score in Table G are in line with this. As can be seen from the sports activity score in (see Figure 11) , the custom-made rigid knee orthoses (CTi2 and Basko-KCO) were used in more strenuous situations.

Discussion

The results of this study provide insight into the usability of rigid knee orthoses-specifically, the actual use, usefulness and ease of use of the orthoses.

The patients had the highest expectations from the rigid knee orthosis in relation to its usability in sports situations. This is not very surprising since during the pretest the patients emphasized the experience of pain at and giving way of their knees, especially in knee-stressing situations. In other words, the chance of improvement was great. however, the patients intended to use the orthoses not only during sports activities but also at work, at home and in leisure time.

The patients wore their orthoses during sports activities to reduce pain and giving way, especially during sudden rotating movements. In addition, the patients' sports functioning improved considerably (from an average score of 2 to an average score of 7), and their average sports activity scores increased. The inconvenience of using an orthosis while participating in sports (even for a few hours a week) was far outweighed by the device's usefulness.

However, certain risks remained when playing a sport while wearing a rigid knee orthosis; six patients suffered one or more reinjuries of the knee. One injury occurred during activities at work, and the remaining five took place during sports activities. The research results impy that at the moment of injury the latter five patients scored 7 or higher on the sports activity score of Tegner and Lysholm. This means they played competitive sports like league matches of tennis, athletics (running), motorcross, speedway, handball, basketball or cross-country track and/or they played leisure sports like soccer, ice hockey, squash, athletics (jumping) or cross-country track. Altogether, 13 patients scored 7 or higher on the sports activity score. Since five of them had one or more reinjuries, the orthosis should not be indicated without reservations when patients plan to play one of the above-mentioned sports activities. This study shows people tend to expect too much from the orthosis. The orthoses apparently fail in stabilizing the knee joint in activities beyond a certain knee stressing level.

At home/in leisure time and at work, the orthosis had less effect on patient performances. After three months, the functioning had hardly improved (from an initial average VAS score of 6 to an average score of 7). One can therefore reason a rigid knee orthosis is less valuable in contributing to performance when somebody already is performing rather well. Nevertheless, the orthosis also was worn at home/in leisure time and at work (which corresponds to the expectations with regard to prospective use). This means something beyond sports participation motivated the patients to wear the orthoses. These patients indicated they wore their orthoses for reasons of precaution-mainly during knee stressing activities. After three months, the orthosis was even worn considerably more hours a week at work than during sports activities; but work is a long-lasting activity with fewer opportunities to take off the orthosis.

During the first 12 weeks after fitting the orthosis, only four patients stopped wearing the rigid knee orthosis due to insufficient usefulness and ease of use (two patients) and reinjury during sports activities (two patients). It is possible the small number of dropouts is due to the attention paid to the patients.

Concerning the second purpose of this study, the four rigid knee orthoses did not significantly differ in respect to usability. Yet a few nonconformities could be distinguished between the custom-made and the off-the-shelf rigid knee orthoses, which, however, could be explained by unpredicted circumstances. First, there was a relatively large number of reinjuries in the custom-made orthosis samples compared to the off-the-shelf samples. This difference was considered nonsignificant since the custom-made rigid knee orthoses in this study were used in more strenuous situations. Second, there were a few nonsignificant results (concerning the reduction of pain and giving way during sudden rotating movements and sports) in the custom-made samples as contrasted with the off-the-shelf samples, but these nonsignificant results coincided with the events of reinjuries.

Conclusion

This study shows wearing a rigid knee orthosis can be of value in all kinds of situations (at home/in leisure time, at work and during sports), provided the general functioning or the performance of activities before orthosis fitting is relatively poor. The orthosis is able to significantly relieve pain and giving way if the patient initially has a VAS score >4. Second, the orthosis can significantly improve function if the patient initially has a VAS score of <6 in the conditions in question.

The orthosis should not be indicated without reservations when patients score 7 or more on the sports activity score of Tegner and Lysholm or intend to play one of the sports of this level. In such situations, the prescriber should warn patients about the possibility of reinjury even while wearing an orthosis. Furthermore, prescribers should point out the various instances in which the rigid knee orthosis could be used and that this orthosis has value beyond sports applications.

The outcomes of this study indicate it is justified to provide an off-the-shelf instead of a custom-made rigid knee orthosis in patients who complain of pain and giving way of the knee due to an ACL-deficient knee. However, in cases of problems with the fitting of an off-the-shelf orthosis, it is preferable to provide a custom-made rigid knee orthosis.

Acknowledgements

The authors wish to thank the dealers/manufacturers of the Bledsoe-ACL, MOS-genu, CTi2 and Basko-KCO orthoses and Oostnederland healthcare insurance company for their cooperation and financial support of this study.

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