Analysis of subjective knee complaints using visual analog scales FRED FLANDRY,*† MD, JON P.
From the
HUNT,‡ PhD, GLENN C. TERRY,* MD, AND JACK C. HUGHSTON,* MD
*Hughston Orthopaedic Clinic and the ‡Hughston Sports Medicine Foundation, Columbus, Georgia
ABSTRACT
value of 10 points, and negative (no) responses were given no points. The sum of awarded points represented a knee score. Although numerous modifications of O’Donoghue’s survey have been made, the method of a system using a possible 100 point numerical score has continued to be used as an evaluation tool. Geens et al.9 proposed a scale that combined objective and functional measurements with subjective findings. Pain was the only subjective finding to be surveyed in this system and was awarded decreasing points on a graduated scale of pain intensity. The total value of the subjective section accounted for only 35% of the total score. In 1972, Larson 17 proposed a method that not only awarded points in subjective, objective, and functional categories, but also deducted points from the overall score for loss of motion. Many studies1-3, 14, 15, 19-21 have used variations of the previously mentioned earlier scoring systems to evaluate results. Although new criteria such as swelling, grinding, or giving way have been introduced, most systems allot about the same percentage of points to the subjective category. Two departures from this standard methodology have appeared. Turba et a1.32 proposed a different approach to the analysis of subjective data and applied it to a study of extensor mechanism problems. In their method, zero was the optimal outcome, and points were tallied for the presence of adverse symptoms. Hughston and Barrettll proposed a discontinuous verbal method that by-passed numbers entirely and assigned an outcome of excellent, good, fair, or failure based on descriptions of each category. The importance of the separation of subjective, objective, and functional findings into separate scales has been noted by several authors. 11,19,29-31 By separating them, findings in one category do not favorably or adversely affect the other
questionnaire using a system of visual analog scales developed for analyzing subjective knee complaints. This system was tested on 117 consecutive patients who had undergone knee surgery and 65 patients at their initial office evaluation of a knee disorder. The validity of and patient affinity for this type of questionnaire was compared with that of three other established subjective evaluation methods. The visual analog scale system was shown to be valid and comparable to other methods while offering several advantages. It brought greater sensitivity and greater statistical power to data collection and analysis by allowing a broader range of responses than did traditional categorical responses. It removed bias that was introduced by examiner questioning, and it allowed graphic temporal comparisons. Most importantly, patient affinity was higher for this type of subjective A
was
evaluation than for other methods.
The discussion of the results of any therapeutic intervention requires an objective and universally acceptable means of comparing pretreatment and posttreatment status. This comparison is facilitated when the data consist of measured quantities such as range of motion, thigh circumference, or a measured single plane instability. Subjective complaints such as pain or functional limitations, on the other hand, are
difficult to
measure
and, hence,
to
analyze.
The need for analysis of the subjective results in the treatment of knee problems was raised by O’Donoghue22 in 1955. He proposed a 10 question, 100 point numerical survey for scoring subjective outcomes. Each question required a yes or no response. Positive (yes) responses were given a
two
categories.
Several problems arise in any system using point ratings. These problems include investigator bias, sensitivity, patient compliance, and interpretation bias. The point value assigned to a given symptom is, to varying degrees, based on
t Address correspondence and repnnt requests to Fred Flandry, MD, Hughston Orthopaedic Clinic, 6262 Hamilton Road, Columbus, GA 31995. 112
113
the
investigator’s arbitrary decision regarding the relative importance of that symptom to the overall score. The descriptors for any given point value force the patient to think like the investigator, or to fit into a category that the investigator has created. Having only a limited number of responses robs a system of a significant degree of sensitivity of measurement. More complete descriptors lead to long, wordy forms that may exceed the patient’s ability to complete the form reliably. If the patient requires assistance to complete a form, interpretation bias may be introduced. A continuous method of magnitude expression removes many of these problems. The visual analog scale (VAS) is a graphic continuous method of expression by which the rater (or patient) may describe the magnitude of a subjective experience (or symptom). It consists of a line of specified length with polar descriptors of the two extremes of a given experience at each end of the line (Fig. 1). Raters read the description and place a mark on the line at the point that they feel best places their own experience relative to the two extremes. Their response may then be converted to a numerical value by simple measurement techniques. Visual analog scales have been validated by many investigators’,’,’, 10,13,16,26 and have been found to be superior to discontinuous verbal or numerical descriptions.5 Testretest reliability is high and effectiveness has been demonstrated in measurements of sensory stimulus intensity (such
pain) and evaluations of functional capacity. 4, 6, 8, 10, ~s, ~s, zs Moreover, they reduce the artificial distribution of positive and negative responses inherent in other methods that result from a patient’s bias for or against certain numbers or descriptors. Although introduced by Labib et ail. 16 to analyze pain and function after total joint arthroplasty, VAS systems have not come into common usage in orthopaedic research. We undertook this study to explore the utility and validity of a VAS system for analyzing subjective knee data, to determine its effectiveness when compared with other established systems, and by its use, to minimize bias in subjective data collection, to improve compliance in completion of forms,
as
and to facilitate the statistical review of such data.
METHODS from information contained in our current evaluation forms and other scoring systems,1-3, 9, 11,14-22,32 we developed a VAS to analyze subjective knee data (Fig. 2). Initially, patients were instructed in its use with a simple scale to introduce the concept. They were then allowed to complete the form independently. We have since adapted our original form by converting the continuous line to continuous boxes allowing it to be read by automated data entry
Drawing
equipment (Fig. 3). The validity of the VAS was determined by comparing data obtained from it with three established knee outcome forms, which were modified as necessary to allow them to be completed by the patient. 17, 19,21 To test our system in a hospital setting, 117 consecutive patients who had undergone knee surgery that varied from arthroscopy to total arthroplasty completed our VAS and three other scales on a randomized basis. Sixty-five patients received the Lysholm’9 scale; 31, the NoyeS2’ knee scale; and 21, the Larson 17 scale. The data for each sample were recorded and the degree of association between comparable variables on each rating scale were established using a Pearson Product-Moment Correlation procedure. We postulated that high correlations between our VAS and the other knee scales would indicate that the questions were interpreted similarly by patients. To determine patient compliance and the relative utility of the VAS when compared with the other three scales, the forms were then used in our clinic to evaluate 41 consecutive patients who presented for an initial evaluation of a knee disorder. All of the patients in this sample were given the VAS and one of the other knee scales. Fourteen patients received the VAS and Lysholm scale; 15, the VAS and Noyes scale; and 12, the VAS and Larson scale. Patients completed both questionnaires before being seen by a physician. The order in which patients completed the knee scales was randomized to ensure that no order bias occurred in answering the questionnaires. After completing the two forms, patients were given a questionnaire to complete that asked: 1. Which form was easiest to complete? 2. Which form was more confusing? 3. Which form required more explanation to understand? 4. Which form allowed you to best depict your symptoms? The data from each group were recorded and the percentage of responses made by patients on each form was compared for the three groups using separate dependent t-tests.
RESULTS
Figure 1. A, a VAS for recording the severity of pain. The question posed would read, &dquo;How bad is the pain at its worst?&dquo; B, the patient places a mark at what he feels is the appropriate point on the line. C, through simple measurement techniques, this graphic representation may be converted to a
numerical value.
The correlations on hospitalized patients are reported in Tables 1 through 3. Variables on the VAS on the ordinate axis represent our visual analog scale in all three tables. Correlations between our VAS and the Lysholm knee scale were significant but low. The highest correlation ( = -0.68), between the VAS locking and Lysholm locking variables, was significant, but the association could still only be termed as moderate. The inverse relationship between the variables
114
Figure 2.
A VAS for
collecting subjective
indicates the difference between the the two scales.
knee data.
scoring procedures
for
Similarly, correlations between our VAS and the Noyes ranged from low to moderate, with a few notable exceptions (e.g., running [VAS] and run [Noyes], r -0.89; -0.83). As with the up stairs [VAS] and stairs [Noyes], r Lysholm scale, the inverse relationship between the variables reflects the difference in scoring procedures used for knee scale
=
=
each knee scale. Of the patients who presented for initial office evaluation, the mean percentage of responses for the VAS (M 89.01, SE 7.78) and for the Lysholm knee scale (M 89.42, SE 0.97). 7.73) was not significant, (t [12] = -0.04, P Similarly, the paired sample t-test comparing the VAS (M 100, SE 0.0) with the Larson knee scale (M = 84.85, SE 23.22) was not significant (t [10] 2.16, P = 0.056). However, the comparison between the mean percentage of 0.81) and the 98.47, SE responses for the VAS (M scale SE was knee (M 52.38, 29.86) significant Noyes (t [13] 5.68, P 0.001). Overall, these results indicate that there were no significant differences in user understanding among the VAS, =
=
=
=
=
=
=
=
=
=
=
=
=
=
=
Lysholm, and Larson knee scales. However, there was a significant difference between the VAS and the Noyes knee scale, suggesting that patients were less able to respond satisfactorily to the questions posed by the Noyes scale. Fifteen patients compared the VAS with the Noyes knee scale. Eighty percent found the VAS easier to complete; 20% felt there was no difference between the scales. Forty-seven percent felt the Noyes scale required more explanation to complete, 40% found no difference, and 13% found they required more explanation to complete the VAS. Sixty percent thought the Noyes scale was more confusing, 33% found no difference, and 7% thought the VAS was more confusing. When asked which scale allowed the best characterization of symptoms, 67% preferred the VAS, 20% thought there was no difference, and 13% preferred the Noyes scale. Fourteen patients compared the VAS with the Lysholm knee scale. Forty-three percent found the VAS easier to complete, 43% felt there was no difference between the scales, and 14% thought the Lysholm scale was easier to complete. Forty-two percent felt that the Lysholm scale required more explanation to complete, 29% found no difference, and 29% found they required more explanation to
115
Figure 3. The VAS we currently use is an adaptation of the original form. The continuous line has been converted to continuous boxes, thus allowing it to be read by automated data entry equipment. TABLE 1 Correlations between VAS (ordinate axis) and Scale19 in hospitalized patients
Lysholm Knee
more explanation. Fifty-eight percent thought the Larson scale was more confusing, 34% found no difference, and 8% thought the VAS was more confusing. When asked which scale allowed the best characterization of symptoms, 58% preferred the VAS, 25% thought there was no difference, and only 17% preferred the Larson scale.
quired
DISCUSSION
complete the VAS. Fifty percent thought the Lysholm scale was more confusing, 36% found no difference, and 14% thought the VAS was more confusing. When asked which scale allowed the best characterization of symptoms, 79% preferred the VAS, 21 % thought there was no difference, and no patient preferred the Lysholm scale. Twelve patients compared the VAS and Larson knee scales. Forty-two percent found the VAS easier to complete, 33% thought there was no difference between the scales, and 25% thought the Larson scale was easier. As far as ease of completion, patients were equally divided over which re-
Our goals in developing the VAS were to create a method that would effectively and objectively record subjective data by minimizing collection and interpretation bias, and would facilitate statistical analysis by providing a means of converting the magnitude of these subjective experiences to numeric values. We also attempted to prove the validity of the system and demonstrate that such a method would be met with a high degree of patient acceptance and, therefore,
compliance. Most existing systems of subjective data collection rely on physicians to collect and record the data. An internal audit, however, of the
current methods of data collection at our subjective data was not collected as
clinic revealed that
116
TABLE 2 Correlations between VAS (ordinate axis) and Noyes Knee Scale2’ in hospitalized patients
TABLE 3 Correlations between VAS (ordinate axis) and Larson Knee Scale&dquo; in hospitalized patients
consistently as objective or radiographic findings. Moreover, when a physician questions the patient, interprets the patient’s responses, and supplies a response expressing magnitude, bias is introduced. For these reasons, it appeared that the most effective method of recording subjective data would be the patient’s independent completion of the questionnaire.
Existing knee scoring systems categorize the possibility of responses to one of several selections. In many cases, yes or no responses do not describe the magnitude of the subjective experience, thereby handicapping attempts at statistical analysis of results. We were attracted to the VAS as a way of collecting subjective data because the open structure of responses does not force patients to interpret the definition of the terms mild, moderate, or severe, or to assign themselves to such categories. The ease by which responses can be converted to objective measures allows both the magnitude (severity) and temporal nature (how often) of a symptom to be
quantified. Thus, bias is minimized and statistical
power is boosted.
Graphic representation
of
subjective experiences
is not
a
concept. In 1923, Freyd’ discussed the graphic rating scale and outlined the advantages of such systems. He stated that they are 1) simple and easily understood, 2) interesting and require minimal motivation from the rater, 3) quickly filled out, 4) simply and easily scored, 5) able to free the rater from direct quantitative terms, and 6) able to allow new
fine discrimination of an experience. This form of subjective analysis did not become widely used, however, until the last
decades.4-8, 10, 13,16,23-28 The need to separate subjective, objective, and functional
two
data would seem obvious. Yet, this approach is rarely taken with current knee scoring systems. For example, an ankylosed knee would receive high marks in the many knee stability examinations. These high scores could override the impact of low scores from adverse symptoms if symptoms and physical findings are combined for a common score. Assigning points per symptom necessarily reflects the judgment of the scoring system’s designer regarding the relative importance of that symptom. In an analysis system where each symptom is related to the asymptomatic condition, this bias is eliminated. If the investigator desires it, our VAS has the capability of weighing symptom or symptoms, but the relative value of a given symptom is not preassigned to the data collection. Our set of symptoms was based on our clinic’s knee evaluation sheet, our past experience in obtaining detailed symptom histories, and a review of other published knee scoring systems. To validate our ability to obtain comparable histories, we compared our form with three commonly used forms. Although we believe that our system offered a greater sensitivity of response with less bias, we would expect a comparable answer for any given symptom in any selected
patient.
117
Figure 4. The preoperative and postoperative responses have been superimposed on the same form to graphically depict the impact of treatment. Note how a sense of the influence of the intervention is obtained at a glance in this form of presentation. Preoperative responses are marked with dots, postoperative responses are marked in solid black. Correlations between the VAS and the Larson knee scale consistently higher than for the Lysholm and Noyes knee scales. Table 3 shows that the correlations ranged from moderate (r -0.60) to high (r -0.95). These findings show a general trend of a greater degree of association between the variables used in the VAS and the Larson knee scale than between the VAS and each of the other two knee scales. Overall, the correlations between the VAS and each of the other three knee scales were statistically significant and showed a degree of association between the knee scales that ranged from low to high depending on the variables being considered and the knee scales being compared. We believe that any inconsistencies were more reflective of the patient’s difficulty in completing the forms unassisted than a lack of our form’s ability to satisfactorily obtain the data. Because a degree of association was evident between the VAS and each of the other knee scales, it was of interest to the authors to establish the preference of the patients for this scale in terms of user friendliness. We consider this finding to be an important factor because forms that are easy for patients to interpret reduce the amount of investigator involvement and possible bias, facilitate ease of data collection, and should contribute to reproducibility of results. Several design characteristics should be considered in the construction of a V AS.5, 7,12,24,25,27,28 The experience to be rated should be defined as discretely and simply as possible so that it may not be interpreted as a combination of traits. This experience should be introduced by a statement or question to which the rating furnishes the answer. Two extremes of the experience are placed at opposite ends of the scale; they should not be so extreme, however, as to never be selected. It is not necessary to alternate favorable extremes in successive scales. The descriptors should be short, readily understood expressions in common usage. The line should be of a length that may be easily visualized as a unit with definite cut-off points. A 100 mm line has were
=
=
become standard and is easily converted to a percentage value. The line should be a graphic continuum between the two descriptors. Numbers should not be superimposed on the line, since personal bias for certain numbers can interfere with the distribution of results.&dquo; The lines may be vertical or horizontal but the two types should not be combined on the same form. 7,25 Highest completion rates are obtained if the rater fills out a trial response under supervision to familiarize himself with the form. If an outcome score is desired, each question can yield a numeric value (Fig. 1) expressed as a percentage of the asymptomatic state (which in our convention would be 100%). The questions can be averaged or subgrouped and averaged if more weight is to be given to one or a set of questions. An individual symptom may be pulled out and tracked independently as well. Having a response that ranges from 0 to 100 and is carried to as many decimals as measurement techniques allow boosts statistical power tremendously over question forms where only several categorical answers are possible. Another advantage offered by the visual analog scale is the graphic depiction of change in findings over time, such as after some form of intervention. For example, postoperative responses may be superimposed on the preoperative response form to illustrate the effect of the operative procedure on subjective complaints (Fig. 4). In this manner, the effect of the intervention can be seen at a glance. We do not advocate replacing the traditional medical history with the VAS, but rather using it to ensure that a complete set of data will be collected for each patient with minimal bias. Although the history of injury or illness and mechanism of injury are not covered by this method, these components of the history are not used in the analysis of outcome. As an added benefit, completing this form assists patients in organizing their thoughts concerning their disability before being questioned by a physician. Considering its validity, increased patient compliance, greater sensitivity of measurement, and reduced bias, along with the advantages of graphic representation and numeric analysis, we believe that the VAS offers an important advance in the analysis of subjective complaints. Our VAS has been validated by clinical trials in patients with knee disorders. We offer it for use in orthopaedic and sports medicine research as a standard method of analysis in this area. It is our hope that its use will bring a greater degree of objectivity to data collection. REFERENCES 1 Aichroth P, Freeman MAR, Smillie IS, et al. A knee function assessment chart J Bone Joint Surg 60B 308-309, 1978 2 Arnold JA. A lateral extra-articular tenodesis for anterior cruciate ligament deficiency of the knee. Orthop Clin North Am 16 213-222, 1985 3. Arnold JA, Coker TP, Heaton LM, et al Natural history of anterior cruciate tears Am J Sports Med 7 305-313, 1979 4 Bond A, Lader M. The use of analogue scales in rating subjective feelings.
Br J Med Psychol 47 211-218, 1974 5. Carlsson AM Assessment of chronic painI Aspects of the rehability and validity of the visual analogue scale Pain 16 87-101, 1983 6. Cella DF, Perry SW Reliability and concurrent validity of three visualanalogue mood scales. Psycholog Rep 59 827-833, 1986
118 7
8 9
10
11 12
13
14 15 16
17 18
19
Dixon JS. Agreement between horizontal and vertical visual analogue scales 25 Br J Rheumatol 415-416, 1986 J Educ Psychol 14 83-102, 1923 Freyd, M The graphic rating scale Geens S, Clayton ML, Leidholt JD, et al. Synovectomy and debridement of the knee in rheumatoid arthritis. Part II Clinical and roentgenographic study of thirty-one cases J Bone Joint Surg 51A 626-642, 1969 Harms-Ringdahl K, Carlsson AM, Ekholm J, et al Pain assessment with different intensity scales in response to loading of joint structures. Pain 27 401-411,1986 Hughston JC, Barrett GR. Acute anteromedial rotatory instability Longterm results of surgical repair. J Bone Joint Surg 65A. 145-153, 1983 Huskisson EC Measurement of pain Lancet 2 :1127-1131,1974 Huskisson EC, Jones J, Scott PJ Application of visual-analogue scales to the measurement of functional capacity Rheumatol Rehab 15: 185-187, 1976 Insall JN, Ranawat CS, Aglietti P, et al. A comparison of four models of total knee-replacement prostheses J Bone Joint Surg 58A 754-765, 1976 Kettelkamp DB, Thompson C: Development of a knee scoring scale Clin Orthop 107. 93-99, 1975 Labib S, Fisher W, Laurin CA. The use of visual analogue scales (VAS) in assessment of pain and function in arthroplasty patients (abstract) Orthop Trans 10. 598, 1986 Larson RL Rating sheet for knee function, cited by SmillieI Diseases of the Knee Joint. Edinburgh, Churchill Livingstone, 1974, p 29 Lukianov AV, Gillquist J, Grana WA, et al. An anterior cruciate ligament (ACL) evaluation format for assessment of artificial or autologous anterior cruciate reconstruction results Clin Orthop 218 167-180, 1987 Lysholm J, Gillquist J: Evaluation of knee ligament surgery results with
special emphasis
on use
of
a
scoring scale Am J
Sports
Med 10 150-
154, 1982 20 Marshall JL, Fetto JF, Botero PM Knee ligament injuries A standardized evaluation method Clin Orthop 123 115-129, 1977 21 Noyes FR, McGinniss, GH Controversy about treatment of the knee with anterior cruciate laxity Clin Orthop 198. 61-76, 1985 DH. An analysis of end results of surgical treatment of major injuries to the ligaments of the knee J Bone Joint Surg 37A. 1-13, 124, 1955 23 Price DD, McGrath PA, Rafii A, et al The validation of visual analogue scales as ratio scale measures for chronic and experimental pain. Pain 17 22.
O’Donoghue
45-56, 1983 24 Scott J, Huskisson EC. Accuracy of subjective measurements made with or without previous scores An important source of error in serial measurement of subjective states Ann Rheum Dis 38 558-559, 1979 25. Scott J, Huskisson EC. Vertical or horizontal visual analogue scales Ann Rheum Dis 38. 560, 1979 26. Scott PJ, Huskisson EC. Measurement of functional capacity with visual analogue scales. Rheumatol Rehab 16: 257-259, 1977 27 Scott J, Huskisson EC Graphic representation of pain Pain 2 : 175-184, 1976 28 Sitton NG, Dixon JS, Bird HA Use of visual analogue scales Ann Rheum Dis 41 555-556, 1982 29 Tegner Y Cruciate ligament injuries Evaluation and rehabilitation Dissertation Linkoping University, Sweden, 1985 30 Tegner Y, Lysholm J Rating systems in evaluation of knee ligament injuries Clin Orthop 198 43-49, 1985 31. Tegner Y, Lysholm J, Odensten M, et al Evaluation of cruciate ligament injuries A review Acta Orthop Scand 59 336-341, 1988 32 Turba JE, Walsh WM, McLeod WD. Long-term results of extensor mechanism reconstruction. Am J Sports Med 7. 91-94, 1979
From the
HUNT,‡ PhD, GLENN C. TERRY,* MD, AND JACK C. HUGHSTON,* MD
*Hughston Orthopaedic Clinic and the ‡Hughston Sports Medicine Foundation, Columbus, Georgia
ABSTRACT
value of 10 points, and negative (no) responses were given no points. The sum of awarded points represented a knee score. Although numerous modifications of O’Donoghue’s survey have been made, the method of a system using a possible 100 point numerical score has continued to be used as an evaluation tool. Geens et al.9 proposed a scale that combined objective and functional measurements with subjective findings. Pain was the only subjective finding to be surveyed in this system and was awarded decreasing points on a graduated scale of pain intensity. The total value of the subjective section accounted for only 35% of the total score. In 1972, Larson 17 proposed a method that not only awarded points in subjective, objective, and functional categories, but also deducted points from the overall score for loss of motion. Many studies1-3, 14, 15, 19-21 have used variations of the previously mentioned earlier scoring systems to evaluate results. Although new criteria such as swelling, grinding, or giving way have been introduced, most systems allot about the same percentage of points to the subjective category. Two departures from this standard methodology have appeared. Turba et a1.32 proposed a different approach to the analysis of subjective data and applied it to a study of extensor mechanism problems. In their method, zero was the optimal outcome, and points were tallied for the presence of adverse symptoms. Hughston and Barrettll proposed a discontinuous verbal method that by-passed numbers entirely and assigned an outcome of excellent, good, fair, or failure based on descriptions of each category. The importance of the separation of subjective, objective, and functional findings into separate scales has been noted by several authors. 11,19,29-31 By separating them, findings in one category do not favorably or adversely affect the other
questionnaire using a system of visual analog scales developed for analyzing subjective knee complaints. This system was tested on 117 consecutive patients who had undergone knee surgery and 65 patients at their initial office evaluation of a knee disorder. The validity of and patient affinity for this type of questionnaire was compared with that of three other established subjective evaluation methods. The visual analog scale system was shown to be valid and comparable to other methods while offering several advantages. It brought greater sensitivity and greater statistical power to data collection and analysis by allowing a broader range of responses than did traditional categorical responses. It removed bias that was introduced by examiner questioning, and it allowed graphic temporal comparisons. Most importantly, patient affinity was higher for this type of subjective A
was
evaluation than for other methods.
The discussion of the results of any therapeutic intervention requires an objective and universally acceptable means of comparing pretreatment and posttreatment status. This comparison is facilitated when the data consist of measured quantities such as range of motion, thigh circumference, or a measured single plane instability. Subjective complaints such as pain or functional limitations, on the other hand, are
difficult to
measure
and, hence,
to
analyze.
The need for analysis of the subjective results in the treatment of knee problems was raised by O’Donoghue22 in 1955. He proposed a 10 question, 100 point numerical survey for scoring subjective outcomes. Each question required a yes or no response. Positive (yes) responses were given a
two
categories.
Several problems arise in any system using point ratings. These problems include investigator bias, sensitivity, patient compliance, and interpretation bias. The point value assigned to a given symptom is, to varying degrees, based on
t Address correspondence and repnnt requests to Fred Flandry, MD, Hughston Orthopaedic Clinic, 6262 Hamilton Road, Columbus, GA 31995. 112
113
the
investigator’s arbitrary decision regarding the relative importance of that symptom to the overall score. The descriptors for any given point value force the patient to think like the investigator, or to fit into a category that the investigator has created. Having only a limited number of responses robs a system of a significant degree of sensitivity of measurement. More complete descriptors lead to long, wordy forms that may exceed the patient’s ability to complete the form reliably. If the patient requires assistance to complete a form, interpretation bias may be introduced. A continuous method of magnitude expression removes many of these problems. The visual analog scale (VAS) is a graphic continuous method of expression by which the rater (or patient) may describe the magnitude of a subjective experience (or symptom). It consists of a line of specified length with polar descriptors of the two extremes of a given experience at each end of the line (Fig. 1). Raters read the description and place a mark on the line at the point that they feel best places their own experience relative to the two extremes. Their response may then be converted to a numerical value by simple measurement techniques. Visual analog scales have been validated by many investigators’,’,’, 10,13,16,26 and have been found to be superior to discontinuous verbal or numerical descriptions.5 Testretest reliability is high and effectiveness has been demonstrated in measurements of sensory stimulus intensity (such
pain) and evaluations of functional capacity. 4, 6, 8, 10, ~s, ~s, zs Moreover, they reduce the artificial distribution of positive and negative responses inherent in other methods that result from a patient’s bias for or against certain numbers or descriptors. Although introduced by Labib et ail. 16 to analyze pain and function after total joint arthroplasty, VAS systems have not come into common usage in orthopaedic research. We undertook this study to explore the utility and validity of a VAS system for analyzing subjective knee data, to determine its effectiveness when compared with other established systems, and by its use, to minimize bias in subjective data collection, to improve compliance in completion of forms,
as
and to facilitate the statistical review of such data.
METHODS from information contained in our current evaluation forms and other scoring systems,1-3, 9, 11,14-22,32 we developed a VAS to analyze subjective knee data (Fig. 2). Initially, patients were instructed in its use with a simple scale to introduce the concept. They were then allowed to complete the form independently. We have since adapted our original form by converting the continuous line to continuous boxes allowing it to be read by automated data entry
Drawing
equipment (Fig. 3). The validity of the VAS was determined by comparing data obtained from it with three established knee outcome forms, which were modified as necessary to allow them to be completed by the patient. 17, 19,21 To test our system in a hospital setting, 117 consecutive patients who had undergone knee surgery that varied from arthroscopy to total arthroplasty completed our VAS and three other scales on a randomized basis. Sixty-five patients received the Lysholm’9 scale; 31, the NoyeS2’ knee scale; and 21, the Larson 17 scale. The data for each sample were recorded and the degree of association between comparable variables on each rating scale were established using a Pearson Product-Moment Correlation procedure. We postulated that high correlations between our VAS and the other knee scales would indicate that the questions were interpreted similarly by patients. To determine patient compliance and the relative utility of the VAS when compared with the other three scales, the forms were then used in our clinic to evaluate 41 consecutive patients who presented for an initial evaluation of a knee disorder. All of the patients in this sample were given the VAS and one of the other knee scales. Fourteen patients received the VAS and Lysholm scale; 15, the VAS and Noyes scale; and 12, the VAS and Larson scale. Patients completed both questionnaires before being seen by a physician. The order in which patients completed the knee scales was randomized to ensure that no order bias occurred in answering the questionnaires. After completing the two forms, patients were given a questionnaire to complete that asked: 1. Which form was easiest to complete? 2. Which form was more confusing? 3. Which form required more explanation to understand? 4. Which form allowed you to best depict your symptoms? The data from each group were recorded and the percentage of responses made by patients on each form was compared for the three groups using separate dependent t-tests.
RESULTS
Figure 1. A, a VAS for recording the severity of pain. The question posed would read, &dquo;How bad is the pain at its worst?&dquo; B, the patient places a mark at what he feels is the appropriate point on the line. C, through simple measurement techniques, this graphic representation may be converted to a
numerical value.
The correlations on hospitalized patients are reported in Tables 1 through 3. Variables on the VAS on the ordinate axis represent our visual analog scale in all three tables. Correlations between our VAS and the Lysholm knee scale were significant but low. The highest correlation ( = -0.68), between the VAS locking and Lysholm locking variables, was significant, but the association could still only be termed as moderate. The inverse relationship between the variables
114
Figure 2.
A VAS for
collecting subjective
indicates the difference between the the two scales.
knee data.
scoring procedures
for
Similarly, correlations between our VAS and the Noyes ranged from low to moderate, with a few notable exceptions (e.g., running [VAS] and run [Noyes], r -0.89; -0.83). As with the up stairs [VAS] and stairs [Noyes], r Lysholm scale, the inverse relationship between the variables reflects the difference in scoring procedures used for knee scale
=
=
each knee scale. Of the patients who presented for initial office evaluation, the mean percentage of responses for the VAS (M 89.01, SE 7.78) and for the Lysholm knee scale (M 89.42, SE 0.97). 7.73) was not significant, (t [12] = -0.04, P Similarly, the paired sample t-test comparing the VAS (M 100, SE 0.0) with the Larson knee scale (M = 84.85, SE 23.22) was not significant (t [10] 2.16, P = 0.056). However, the comparison between the mean percentage of 0.81) and the 98.47, SE responses for the VAS (M scale SE was knee (M 52.38, 29.86) significant Noyes (t [13] 5.68, P 0.001). Overall, these results indicate that there were no significant differences in user understanding among the VAS, =
=
=
=
=
=
=
=
=
=
=
=
=
=
=
Lysholm, and Larson knee scales. However, there was a significant difference between the VAS and the Noyes knee scale, suggesting that patients were less able to respond satisfactorily to the questions posed by the Noyes scale. Fifteen patients compared the VAS with the Noyes knee scale. Eighty percent found the VAS easier to complete; 20% felt there was no difference between the scales. Forty-seven percent felt the Noyes scale required more explanation to complete, 40% found no difference, and 13% found they required more explanation to complete the VAS. Sixty percent thought the Noyes scale was more confusing, 33% found no difference, and 7% thought the VAS was more confusing. When asked which scale allowed the best characterization of symptoms, 67% preferred the VAS, 20% thought there was no difference, and 13% preferred the Noyes scale. Fourteen patients compared the VAS with the Lysholm knee scale. Forty-three percent found the VAS easier to complete, 43% felt there was no difference between the scales, and 14% thought the Lysholm scale was easier to complete. Forty-two percent felt that the Lysholm scale required more explanation to complete, 29% found no difference, and 29% found they required more explanation to
115
Figure 3. The VAS we currently use is an adaptation of the original form. The continuous line has been converted to continuous boxes, thus allowing it to be read by automated data entry equipment. TABLE 1 Correlations between VAS (ordinate axis) and Scale19 in hospitalized patients
Lysholm Knee
more explanation. Fifty-eight percent thought the Larson scale was more confusing, 34% found no difference, and 8% thought the VAS was more confusing. When asked which scale allowed the best characterization of symptoms, 58% preferred the VAS, 25% thought there was no difference, and only 17% preferred the Larson scale.
quired
DISCUSSION
complete the VAS. Fifty percent thought the Lysholm scale was more confusing, 36% found no difference, and 14% thought the VAS was more confusing. When asked which scale allowed the best characterization of symptoms, 79% preferred the VAS, 21 % thought there was no difference, and no patient preferred the Lysholm scale. Twelve patients compared the VAS and Larson knee scales. Forty-two percent found the VAS easier to complete, 33% thought there was no difference between the scales, and 25% thought the Larson scale was easier. As far as ease of completion, patients were equally divided over which re-
Our goals in developing the VAS were to create a method that would effectively and objectively record subjective data by minimizing collection and interpretation bias, and would facilitate statistical analysis by providing a means of converting the magnitude of these subjective experiences to numeric values. We also attempted to prove the validity of the system and demonstrate that such a method would be met with a high degree of patient acceptance and, therefore,
compliance. Most existing systems of subjective data collection rely on physicians to collect and record the data. An internal audit, however, of the
current methods of data collection at our subjective data was not collected as
clinic revealed that
116
TABLE 2 Correlations between VAS (ordinate axis) and Noyes Knee Scale2’ in hospitalized patients
TABLE 3 Correlations between VAS (ordinate axis) and Larson Knee Scale&dquo; in hospitalized patients
consistently as objective or radiographic findings. Moreover, when a physician questions the patient, interprets the patient’s responses, and supplies a response expressing magnitude, bias is introduced. For these reasons, it appeared that the most effective method of recording subjective data would be the patient’s independent completion of the questionnaire.
Existing knee scoring systems categorize the possibility of responses to one of several selections. In many cases, yes or no responses do not describe the magnitude of the subjective experience, thereby handicapping attempts at statistical analysis of results. We were attracted to the VAS as a way of collecting subjective data because the open structure of responses does not force patients to interpret the definition of the terms mild, moderate, or severe, or to assign themselves to such categories. The ease by which responses can be converted to objective measures allows both the magnitude (severity) and temporal nature (how often) of a symptom to be
quantified. Thus, bias is minimized and statistical
power is boosted.
Graphic representation
of
subjective experiences
is not
a
concept. In 1923, Freyd’ discussed the graphic rating scale and outlined the advantages of such systems. He stated that they are 1) simple and easily understood, 2) interesting and require minimal motivation from the rater, 3) quickly filled out, 4) simply and easily scored, 5) able to free the rater from direct quantitative terms, and 6) able to allow new
fine discrimination of an experience. This form of subjective analysis did not become widely used, however, until the last
decades.4-8, 10, 13,16,23-28 The need to separate subjective, objective, and functional
two
data would seem obvious. Yet, this approach is rarely taken with current knee scoring systems. For example, an ankylosed knee would receive high marks in the many knee stability examinations. These high scores could override the impact of low scores from adverse symptoms if symptoms and physical findings are combined for a common score. Assigning points per symptom necessarily reflects the judgment of the scoring system’s designer regarding the relative importance of that symptom. In an analysis system where each symptom is related to the asymptomatic condition, this bias is eliminated. If the investigator desires it, our VAS has the capability of weighing symptom or symptoms, but the relative value of a given symptom is not preassigned to the data collection. Our set of symptoms was based on our clinic’s knee evaluation sheet, our past experience in obtaining detailed symptom histories, and a review of other published knee scoring systems. To validate our ability to obtain comparable histories, we compared our form with three commonly used forms. Although we believe that our system offered a greater sensitivity of response with less bias, we would expect a comparable answer for any given symptom in any selected
patient.
117
Figure 4. The preoperative and postoperative responses have been superimposed on the same form to graphically depict the impact of treatment. Note how a sense of the influence of the intervention is obtained at a glance in this form of presentation. Preoperative responses are marked with dots, postoperative responses are marked in solid black. Correlations between the VAS and the Larson knee scale consistently higher than for the Lysholm and Noyes knee scales. Table 3 shows that the correlations ranged from moderate (r -0.60) to high (r -0.95). These findings show a general trend of a greater degree of association between the variables used in the VAS and the Larson knee scale than between the VAS and each of the other two knee scales. Overall, the correlations between the VAS and each of the other three knee scales were statistically significant and showed a degree of association between the knee scales that ranged from low to high depending on the variables being considered and the knee scales being compared. We believe that any inconsistencies were more reflective of the patient’s difficulty in completing the forms unassisted than a lack of our form’s ability to satisfactorily obtain the data. Because a degree of association was evident between the VAS and each of the other knee scales, it was of interest to the authors to establish the preference of the patients for this scale in terms of user friendliness. We consider this finding to be an important factor because forms that are easy for patients to interpret reduce the amount of investigator involvement and possible bias, facilitate ease of data collection, and should contribute to reproducibility of results. Several design characteristics should be considered in the construction of a V AS.5, 7,12,24,25,27,28 The experience to be rated should be defined as discretely and simply as possible so that it may not be interpreted as a combination of traits. This experience should be introduced by a statement or question to which the rating furnishes the answer. Two extremes of the experience are placed at opposite ends of the scale; they should not be so extreme, however, as to never be selected. It is not necessary to alternate favorable extremes in successive scales. The descriptors should be short, readily understood expressions in common usage. The line should be of a length that may be easily visualized as a unit with definite cut-off points. A 100 mm line has were
=
=
become standard and is easily converted to a percentage value. The line should be a graphic continuum between the two descriptors. Numbers should not be superimposed on the line, since personal bias for certain numbers can interfere with the distribution of results.&dquo; The lines may be vertical or horizontal but the two types should not be combined on the same form. 7,25 Highest completion rates are obtained if the rater fills out a trial response under supervision to familiarize himself with the form. If an outcome score is desired, each question can yield a numeric value (Fig. 1) expressed as a percentage of the asymptomatic state (which in our convention would be 100%). The questions can be averaged or subgrouped and averaged if more weight is to be given to one or a set of questions. An individual symptom may be pulled out and tracked independently as well. Having a response that ranges from 0 to 100 and is carried to as many decimals as measurement techniques allow boosts statistical power tremendously over question forms where only several categorical answers are possible. Another advantage offered by the visual analog scale is the graphic depiction of change in findings over time, such as after some form of intervention. For example, postoperative responses may be superimposed on the preoperative response form to illustrate the effect of the operative procedure on subjective complaints (Fig. 4). In this manner, the effect of the intervention can be seen at a glance. We do not advocate replacing the traditional medical history with the VAS, but rather using it to ensure that a complete set of data will be collected for each patient with minimal bias. Although the history of injury or illness and mechanism of injury are not covered by this method, these components of the history are not used in the analysis of outcome. As an added benefit, completing this form assists patients in organizing their thoughts concerning their disability before being questioned by a physician. Considering its validity, increased patient compliance, greater sensitivity of measurement, and reduced bias, along with the advantages of graphic representation and numeric analysis, we believe that the VAS offers an important advance in the analysis of subjective complaints. Our VAS has been validated by clinical trials in patients with knee disorders. We offer it for use in orthopaedic and sports medicine research as a standard method of analysis in this area. It is our hope that its use will bring a greater degree of objectivity to data collection. REFERENCES 1 Aichroth P, Freeman MAR, Smillie IS, et al. A knee function assessment chart J Bone Joint Surg 60B 308-309, 1978 2 Arnold JA. A lateral extra-articular tenodesis for anterior cruciate ligament deficiency of the knee. Orthop Clin North Am 16 213-222, 1985 3. Arnold JA, Coker TP, Heaton LM, et al Natural history of anterior cruciate tears Am J Sports Med 7 305-313, 1979 4 Bond A, Lader M. The use of analogue scales in rating subjective feelings.
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10
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19
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