The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 82, Issue 6

Articles | June 01, 2000

Challenges in Evaluating Patients Lost to Follow-up in Clinical Studies of Rotator Cuff Tears*

Barbara M. Norquist, B.S.†; Benjamin A. Goldberg, M.D.†; Frederick A. MatsenIII, M.D.†

Investigation performed at the Department of Orthopaedics, University of Washington, Seattle, Washington
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding sources were the Orthopaedic Research and Education Foundation, the Bristol-Myers Squibb/Zimmer Institutional Award for Excellence in Orthopaedics, and the E. A. Codman Research Fund at the University of Washington.
†Department of Orthopaedics, University of Washington, Box 356500, 1959 N.E. Pacific Street, Seattle, Washington 98195-6500. E-mail address for F. A. Matsen, III: matsen@u.washington.edu.

J Bone Joint Surg Am, 2000 Jun 01;82(6):838-838

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Abstract

Background: Long-term follow-up studies are necessary to critically evaluate the outcome of a treatment intervention for a specific disorder. However, patients may cease participating in a long-term study and become lost to follow-up; thus, their current condition is unknown. The underlying characteristics that predispose a patient to become lost to follow-up are difficult to identify and control. Patients who are lost to follow-up may be contacted by telephone; however, the effect of administering a functional assessment questionnaire by telephone compared with that of mailing a questionnaire is unknown. The purpose of this study was to compare patients who continued to respond to requests for follow-up with those who did not. A second purpose was to compare responses obtained by mail with those obtained by telephone interview.

Methods: Two hundred and twenty-four patients with a rotator cuff tear were enrolled in an ongoing study of shoulder function and general health. Self-assessment questionnaires were mailed to every patient at six-month intervals. Sixty-seven patients (30 percent) regularly responded to mailings (identified as responders in this study), fifty-five patients (25 percent) responded occasionally (these patients were not included in the analysis), and 102 patients (46 percent) ceased to respond and became lost to follow-up (identified as nonresponders in this study). This investigation was performed to determine: (1) the characteristics of nonresponders compared with those of responders, (2) the functional status of nonresponders as assessed with a questionnaire over the telephone, and (3) the effect of administering a self-assessment functional questionnaire by telephone compared with that of sending the same questionnaire by mail.

Results: Nonresponders tended to have lower initial scores for the mental health summary (p = 0.03) and for social function (p = 0.01), were less likely to have had surgery (p = 0.009), and were less likely to consume alcohol (p = 0.03). At the last known time when they completed the mailed questionnaire, nonresponders reported significantly worse shoulder function than responders (p = 0.0001). However, on telephone questioning the mean number of shoulder functions that the nonresponders indicated that they could perform was greater than the mean number documented on their last mailed questionnaire (p < 0.0001). In a random subgroup of responders, the mean number of functions that the patients indicated that they could perform when interviewed by telephone was significantly greater than the number indicated on their most recent mailed questionnaire (p < 0.01). The results obtained by telephone from this random subgroup of responders were similar to those obtained by telephone from the nonresponders.

Conclusions: There are differences between patients who continue to participate in a study and those who become lost to follow-up. Functional assessment questionnaires administered by telephone yield different results than the same questionnaires sent by mail. These considerations are relevant to the design, implementation, and interpretation of clinical studies in which functional questionnaires are used.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Clinical follow-up studies are necessary to evaluate the results of treatment of musculoskeletal diseases, including disorders of the shoulder^2,3,15,17,22. As is the case with other types of clinical research, patients may drop out of a study and become lost to follow-up. The loss of continued patient follow-up may influence the results and conclusions of the study as the current status of the patient is unknown^2,15,17,22. Factors that predispose a patient to become lost to follow-up are not well defined.

Clinical follow-up studies can be conducted by mailing self-assessment questionnaires^1,7,9-12. A patient's report of pain on a self-completed questionnaire may be more accurate than that provided in an interview with his or her surgeon^2,13. Self-assessment questionnaires are inexpensive to administer¹¹, can be administered without the time and expense of a physician visit, and demonstrate excellent responsiveness to clinical changes after treatment¹. In addition, self-assessment questionnaires can be either administered by telephone or sent by mail.

The present study was undertaken in order to determine the characteristics of nonresponders (patients who stop completing mailed self-assessment questionnaires) compared with those of responders (patients who continue to complete questionnaires), the current functional status of nonresponders as assessed with a questionnaire over the telephone, and the effect of administering a self-assessment functional questionnaire by telephone compared with that of sending the same questionnaire by mail. It is hoped that this information will aid in the design and interpretation of other clinical follow-up studies.

View Larger

Table I: Summary of the Initial Differences Between Nonresponders and Responders

*n.s. = not significant.

	Nonresponders (N = 102)	Responders (N = 67)	P Value*
Demographic characteristics
Mean age and standard deviation (yrs.)	60.1 ± 11.0	64.2 ± 13.2	n.s.
No. of men	66 (65%)	43 (64%)	n.s.
No. treated surgically	40 (39%)	40 (60%)	0.009
No. consuming alcohol	20 (20%)	23 (34%)	0.03
Mean initial Simple Shoulder Test score and standard deviation	4.69 ± 3.08	5.09 ± 3.18	n.s.
Mean initial Short Form-36 scores
Physical function	57.5	65.3	n.s.
Social function	66.5	77.5	0.01
Physical role function	25.5	31.7	n.s.
Emotional role function	58.1	70.7	n.s.
Mental health	71.1	76.6	n.s.
Vitality	54.9	60.6	n.s.
Comfort	37.6	42.6	n.s.
General health	68.2	72.8	n.s.
Mental health summary	49.5	53.4	0.03
Physical summary	35.5	37.4	n.s.

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Table I: Summary of the Initial Differences Between Nonresponders and Responders

*n.s. = not significant.

	Nonresponders (N = 102)	Responders (N = 67)	P Value*
Demographic characteristics
Mean age and standard deviation (yrs.)	60.1 ± 11.0	64.2 ± 13.2	n.s.
No. of men	66 (65%)	43 (64%)	n.s.
No. treated surgically	40 (39%)	40 (60%)	0.009
No. consuming alcohol	20 (20%)	23 (34%)	0.03
Mean initial Simple Shoulder Test score and standard deviation	4.69 ± 3.08	5.09 ± 3.18	n.s.
Mean initial Short Form-36 scores
Physical function	57.5	65.3	n.s.
Social function	66.5	77.5	0.01
Physical role function	25.5	31.7	n.s.
Emotional role function	58.1	70.7	n.s.
Mental health	71.1	76.6	n.s.
Vitality	54.9	60.6	n.s.
Comfort	37.6	42.6	n.s.
General health	68.2	72.8	n.s.
Mental health summary	49.5	53.4	0.03
Physical summary	35.5	37.4	n.s.

View Larger

Table II: Summary of the Final Differences Between Nonresponders and Responders

*n.s. = not significant.

	Nonresponders (N = 102)	Responders (N = 67)	P Value*
Last known mean Simple Shoulder Test score and standard deviation	3.26 ± 4.07	7.85 ± 3.70	0.0001
Last known mean Short Form-36 score
Physical function	51.3	61.9	n.s.
Social function	65.4	83.6	<0.01
Physical role function	34.6	41.5	n.s.
Emotional role function	50.6	74.0	0.01
Mental health	68.8	78.7	0.02
Vitality	46.7	59.3	0.01
Comfort	49.6	63.3	0.02
General health	55.8	71.6	<0.01
Mental health summary	46.8	54.1	<0.01
Physical summary	35.9	39.9	n.s.

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Table II: Summary of the Final Differences Between Nonresponders and Responders

*n.s. = not significant.

	Nonresponders (N = 102)	Responders (N = 67)	P Value*
Last known mean Simple Shoulder Test score and standard deviation	3.26 ± 4.07	7.85 ± 3.70	0.0001
Last known mean Short Form-36 score
Physical function	51.3	61.9	n.s.
Social function	65.4	83.6	<0.01
Physical role function	34.6	41.5	n.s.
Emotional role function	50.6	74.0	0.01
Mental health	68.8	78.7	0.02
Vitality	46.7	59.3	0.01
Comfort	49.6	63.3	0.02
General health	55.8	71.6	<0.01
Mental health summary	46.8	54.1	<0.01
Physical summary	35.9	39.9	n.s.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Since 1994, we have been performing a longitudinal study of the outcomes of surgical and nonsurgical treatment of rotator cuff tears. We record age, gender, alcohol use ("How many alcoholic drinks do you take per week?"), and smoking habits ("How many packs of cigarettes do you smoke per week?") when the patient enters the study. Both the Simple Shoulder Test and the Short Form-36 are administered to the patients at their initial visit. Patients are mailed both follow-up questionnaires at six-month intervals.

The Simple Shoulder Test is a standardized self-assessment of shoulder function that has been shown to be responsive to changes in function of the shoulder from the time of treatment^7,9-12. The Simple Shoulder Test has high test-retest reliability, can be completed by the patient in a short time, is easy to score, and has satisfactory responsiveness compared with other questionnaires for self-assessment of the shoulder¹. The Short Form-36 is a standardized self-assessment of general health status that measures eight parameters: physical function, social function, physical role function, emotional role function, mental health, vitality, comfort, and general health perception^18,19. The Short Form-36 is the most common measurement of health status in the United States⁸. In addition, the Short Form-36 has been used to evaluate shoulder disorders, often in conjunction with the Simple Shoulder Test^4,5,7,10,11. In this study, the Short Form-36 scores were age and gender-matched with those of controls from a large population sample¹⁶. Physical and mental health summaries were also calculated and standardized by norm-based scoring with a mean (and standard deviation) of 50 ± 10^5,18,19.

Two hundred and twenty-four patients were enrolled in the ongoing study on shoulder function and general health in patients with a rotator cuff tear. Sixty-seven patients (30 percent) regularly responded to mailings (identified as responders in this study), fifty-five patients (25 percent) responded occasionally (these patients were not included in the analysis), and 102 patients (46 percent) ceased to respond and became lost to follow-up (identified as nonresponders in this study). The 169 patients (75 percent) who were either responders or nonresponders were included in the study population for this investigation.

These patients had a mean age of sixty-two years. One hundred and nine patients (64 percent) were male. All had a full-thickness rotator cuff tear. After discussion of the options and risks, eighty patients (47 percent) elected to have surgery; forty of these patients became nonresponders, and forty became responders. The sixty-seven responders had continued to respond for a mean of 2.8 ± s the 102 nonresponders had stopped responding after a mean of 1.2 ± 1.4 years.

Telephone directories and clinic billing records were used to attempt to locate all nonresponders. Since these patients had not been responding to mailings and had not returned for office visits, it was decided to administer the Simple Shoulder Test by telephone in order to determine the current shoulder function of the patients who were located. In order to determine whether patients answer the Simple Shoulder Test similarly regardless of whether it is administered by telephone or mailed, the test was administered by telephone and sent by mail to thirty random responders. The telephone and mail assessments took place within one month of each other.

A two-tailed t test assuming unequal variances was used to compare the means of continuous data²⁰. The chi-square test for independence was used to compare noncontinuous, categorical data (for example, smoker compared with nonsmoker, a yes answer compared with a no answer on the Simple Shoulder Test, and male compared with female)²¹.

Results

Introduction | Materials and Methods | Results | Discussion | References

Initial Differences Between Nonresponders and Responders

The sixty-seven responders and 102 nonresponders were compared according to their initial self-assessed functional and general health status as well as demographic information (Table I). There were no significant differences in age, male-female distribution, the initial functional score on the Simple Shoulder Test, or the initial physical summary on the Short Form-36. Nonresponders had significantly lower initial scores for social function (p = 0.01) and for the mental health summary of the Short Form-36 (p = 0.03). Nonresponders had a lower prevalence of alcohol consumption than responders (p = 0.03). In addition, compared with nonresponders, responders were significantly more likely to have had a surgical procedure as a part of our treatment program for the rotator cuff tear (p = 0.009).

Last Known Responses to Mailed Questionnaires (Nonresponders Compared with Responders)

The last mailed questionnaires received from nonresponders were reviewed to determine the status of these patients at the final time that they responded (Table II). The initial mean Simple Shoulder Test score of nonresponders had dropped from 4.69 ± 3.08 to 3.26 ± 4.07 on the last mailed questionnaire before the patients ceased to respond. This follow-up score for nonresponders was significantly worse than the most recent follow-up score for responders (p = 0.0001), who had an improvement from an initial score of 5.09 ± 3.18 to 7.85 ± 3.70. On their last mailed questionnaires, nonresponders gave lower scores for social function (p < 0.01), emotional role function (p = 0.01), mental health (p = 0.02), vitality (p = 0.01), comfort (p = 0.02), general health (p < 0.01), and mental health summary (p < 0.01) in comparison with responders.

Recent Telephone Assessment of Nonresponders

Forty-eight nonresponders (47 percent) were contacted and given the Simple Shoulder Test by telephone in order to assess their current functional status. These patients had not returned a survey by mail for a mean of three years. On the last mailed assessments, this group of forty-eight patients had a mean Simple Shoulder Test score of 3.40 ± 4.28, which was not significantly different from that of the fifty-four nonresponders who were not located. The mean Simple Shoulder Test score (8.94 ± 3.11) obtained with the telephone assessment at the time of the present study was significantly higher than that documented on the last mailed assessment (p < 0.0001).

Effect of Method of Administration of Questionnaire (Telephone Compared with Mail)

To determine whether the method of administration of the questionnaire had an effect on the results, the Simple Shoulder Test scores obtained by telephoning thirty responders were compared with the Simple Shoulder Test scores obtained by mailing the questionnaires to these responders. The thirty responders were chosen at random from the pool of responders and were not significantly different from the responders who were not called. The scores based on the telephone responses were significantly higher than those based on the mailed responses. The mean score on the Simple Shoulder Tests sent by mail was 7.47 ± 3.68 compared with a mean score of 9.03 ± 3.23 when the Simple Shoulder Tests had been administered by telephone (p < 0.01). There was no significant difference between responders and nonresponders with regard to the Simple Shoulder Test scores obtained by telephone.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

There were three initial differences between responders and nonresponders. The nonresponders had lower scores for social function and for the mental health summary on the Short Form-36, were less likely to have had surgery, and had a lower prevalence of alcohol consumption. These differences may offer some insight into why patients become lost to follow-up. Patients with lower scores for mental health may have less energy and desire to answer questionnaires regularly. Surgical treatment may cause patients to feel as if more has been invested in their care, increasing their desire to continue to respond to follow-up questionnaires. We are unsure why less reported alcohol consumption would be associated with becoming lost to follow-up. Although this relationship may seem counterintuitive, it is of note that none of the patients in this series consumed more than three drinks per day; thus, there were no patients manifesting major alcohol abuse in this study group. The initial functional status of the shoulder was not predictive of a patient becoming lost to follow-up.

The loss of patients to follow-up can affect the final conclusions of an outcome study^6,14,15,17. In this study, when the patients stopped responding to mailed questionnaires the functional status of the shoulder had become significantly worse than the most recently documented status of the responders (p = 0.0001). Nonresponders also had lower scores, compared with those of responders, for social function, emotional role function, mental health, vitality, comfort, general health, and mental health summary on the last assessment before they became lost to follow-up. Poor shoulder function or poor general health may have contributed to patients becoming nonresponders. Murray et al. reported that patients with total hip replacement who became lost to follow-up had significantly worse pain, range of motion, opinion of their progress, and radiographic features at the last known assessment¹⁵. However, the status of those patients at the time of the report was not determined.

Nonresponders who were assessed by telephone reported higher Simple Shoulder Test scores for shoulder function (mean, 8.94) than they had reported on their last known mailed questionnaire (mean, 3.40). Such a large difference in shoulder function demonstrates that the last known assessment of patients lost to follow-up may not represent their current status. Alternatively, the better results obtained with telephone follow-up may be a function of the mode of administration of the questionnaire. Previous studies have demonstrated that the Simple Shoulder Test has a test-retest reliability correlation coefficient of 0.99 when administered in an identical fashion¹. However, the current study demonstrates that the mode of administration may influence the response: in a random subgroup of responders, the scores of the Simple Shoulder Test were significantly better (p < 0.01) when the test had been administered by telephone than when it had been sent by mail. Since the telephone and mailed assessments were completed within one month of each other, it is unlikely that there had been any major change in function. Wildner noted that patients expressed a lower opinion of their final outcome when they were assessed by telephone compared with when they were evaluated with a consultant interview²². He speculated that the less personal nature of a telephone interaction could explain this result. A mailed questionnaire is less personal than a telephone questionnaire, which could have contributed to our findings. Both nonresponders and responders provided better scores when the Simple Shoulder Test had been administered by telephone than when it had been sent by mail. In fact, the responders' mean score on the Simple Shoulder Test administered by telephone was nearly identical to that of the nonresponders; this finding suggests that the so-called telephone effect may be sufficiently strong to overcome much of the difference between these groups.

Dorey and Amstutz studied patients with total hip replacement who had been lost to follow-up³. The patients were contacted by telephone, which increased the rate of follow-up from 55 to 90 percent. However, the survivorship curve did not change significantly. Dorey and Amstutz thus concluded that loss of patients to follow-up was not likely to affect results. However, they only analyzed the survival of the replacement; they did not assess the most recent functional result. Wildner noted that eighteen patients who had been lost to follow-up assigned a generally lower subjective grade to the outcome compared with twenty-one patients who had been followed with a consultant interview²². However, no statistical comparison was performed.

Patients who are lost to follow-up are different than those who continue to participate in a study. The data obtained from patients who continue to participate cannot be generalized to patients who are lost to follow-up. Furthermore, telephone interviews of patients who are lost to follow-up may generate results that cannot be commingled with results obtained from mailed self-assessments because the mode of administration may affect the responses. These observations have important implications with regard to the design and interpretation of the results of clinical research.

References

Introduction | Materials and Methods | Results | Discussion | References

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Britton, A. R.; Murray, D. W.; Bulstrode, C. J.; McPherson, K.; and Denham, R. A.: Pain levels after total hip replacement. Their use as end points for survival analysis. J. Bone and Joint Surg.,79-B(1): 93-98, 1997.79-B(1)93 1997

Dorey, F., and Amstutz, H. C.: The validity of survivorship analysis in total joint arthroplasty. J. Bone and Joint Surg.,71-A: 544-548, April 1989.71-A544 1989

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Lippitt, S. B.; Harryman, D. T., II; and Matsen, F. A., III: A practical tool for evaluating function: the Simple Shoulder Test. In The Shoulder: A Balance of Mobility and Stability, pp. 501-518. Edited by F. A. Matsen, III, F. H. Fu, and R. J. Hawkins. Rosemont, Illinois, American Academy of Orthopaedic Surgeons, 1993.

Martin, D. P.; Engelberg, R.; Agel, J.; and Swiontkowski, M. F.: Comparison of the Musculoskeletal Function Assessment questionnaire with the Short Form-36, the Western Ontario and McMaster Universities Osteoarthritis Index, and the Sickness Impact Profile health-status measures. J. Bone and Joint Surg.,79-A: 1323-1335, Sept 1997.79-A1323 1997

Matsen, F. A., III; Lippitt, S.; Sidles, J. A.; and Harryman, D. T., II: Practical Evaluation and Management of the Shoulder. Philadelphia, W. B. Saunders, 1994.

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Topics

mental health ; rotator cuff ; telephone ; shoulder region ; rotator cuff injury ; lost to follow-up

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Barbara M. Norquist, Benjamin A. Goldberg, Frederick A. MatsenIII; Challenges in Evaluating Patients Lost to Follow-up in Clinical Studies of Rotator Cuff Tears*. The Journal of Bone & Joint Surgery. 2000 Jun;82(6):838-838.

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