Rehabilitation Psychology © 2000 by the Educational Publishing Foundation February 2000 Vol. 45, No. 1, 20-37 For personal use only--not for distribution.

Psychological Factors, Rehabilitation Adherence, and Rehabilitation Outcome After Anterior Cruciate Ligament Reconstruction

Britton W. BrewerCenter for Performance Enhancement and Applied Research , Department of

Psychology Springfield College Judy L. Van Raalte

Center for Performance Enhancement and Applied Research , Department of Psychology Springfield College

Allen E. CorneliusCenter for Performance Enhancement and Applied Research , Department of

Psychology Springfield College Albert J. Petitpas

Center for Performance Enhancement and Applied Research , Department of Psychology Springfield College

Joseph H. SklarNew England Orthopedic Surgeons

Mark H. PohlmanNew England Orthopedic Surgeons

Robert J. KrushellNew England Orthopedic Surgeons

Terry D. DitmarBaystate Outpatient Rehabilitation

ABSTRACT

Objective: To examine prospectively the relationships among psychological factors, rehabilitation adherence, and short-term rehabilitation outcome after knee surgery. Study Design and Participants: Individuals with acute anterior cruciate ligament (ACL) tears ( N = 95) completed measures of self-motivation, social support, athletic identity, and psychological distress before reconstructive surgery. After surgery, participants ( n = 93) reported on their completion of home rehabilitation exercises and cryotherapy, and their rehabilitation practitioners indicated the patients' attendance at, and adherence during, rehabilitation sessions. Rehabilitation outcome measures were taken from participants ( n = 69) approximately 6 months postsurgery. Main Outcome Measures: Knee laxity, functional ability, and subjective symptoms were the primary outcomes assessed. Results: Self-motivation was a significant predictor of home exercise completion; athletic identity and psychological distress were significant predictors of knee laxity; and attendance at rehabilitation sessions and home cryotherapy completion were significant predictors of functional ability. Rehabilitation adherence did not mediate the relationship between psychological factors and rehabilitation outcome. Conclusions: The prospective associations obtained among psychological factors, rehabilitation adherence, and short-term rehabilitation outcome after ACL reconstruction may inform the development of interventions designed to enhance the rehabilitation of individuals with sport-related orthopedic injuries.

Recent estimates indicate a high incidence of sport-related and recreation-related injuries in the United States, with 3—17 million injuries sustained annually by children and adults in sport and recreational activities ( Bijur et al., 1995 ; Booth, 1987 ; Kraus & Conroy, 1984 ). One of the more prevalent and debilitating sport injuries is an acute tear of the anterior cruciate ligament (ACL) of the knee ( Derscheid & Feiring, 1987 ; Roos, Ornell, Gardsell, Lohmander, & Lindstrand, 1995 ). The ACL is critical in providing stability to the knee joint ( Muller, 1983 ). There is evidence that the incidence of ACL tears may be increasing ( Natri et al., 1995 ).

For young, active individuals who sustain ACL tears, reconstructive surgery is considered the treatment of choice ( Marzo & Warren, 1991 ). After surgical reconstruction of the ACL, physical therapy is considered essential to promote optimal rehabilitation ( Blair & Wills, 1991 ; DeCarlo, Sell, Shelbourne, & Klootwyk, 1994 ; DeCarlo, Shelbourne, McCarroll, & Rettig, 1992 ; Shelbourne & Wilckens, 1990 ). Postoperative treatment typically involves clinic- and home-based cryotherapy (icing) and exercises designed to promote strength and flexibility ( Blair & Wills, 1991 ; DeCarlo et al., 1994 ; Shelbourne, Klootwyk, & DeCarlo, 1992 ). Depending on an individual's insurance coverage, it is not uncommon for the clinic-based component of rehabilitation to include two to three sessions per week for 2 to 4 months. In contrast to the 9- to 12-month recovery time associated with traditional postsurgical ACL rehabilitation programs, athletes may return to sport participation as soon as 3 to 6 months after ACL reconstruction under the accelerated rehabilitation protocols currently in use ( Blair & Wills, 1991 ; DeCarlo et al., 1994 ).

In contemporary models of psychological response to sport injury ( Brewer, 1994 ; Wiese-Bjornstal, Smith, Shaffer, & Morrey, 1998 ), psychological factors (e.g., personal characteristics, situational variables, cognitive responses, and emotional responses) are thought to influence both rehabilitation behavior (e.g., adherence) and rehabilitation outcome. Theoretically, as shown in Figure 1 , psychological factors can affect rehabilitation outcome both directly and indirectly, with the latter relationship mediated by rehabilitation adherence.

Preliminary research on psychological aspects of sport injury rehabilitation has provided support for each of the pathways proposed in Figure 1 . With regard to Path a, a number of psychological factors have been associated with adherence to sport injury rehabilitation programs (see Brewer, 1998 , for a review), including self-motivation ( Duda, Smart, & Tappe, 1989 ; Fields, Murphey, Horodyski, & Stopka, 1995 ; Fisher, Domm, & Wuest, 1988 ; Noyes, Matthews, Mooar, & Grood, 1983 ), social support ( Byerly, Worrell, Gahimer, & Domholdt, 1994 ; Duda et al., 1989 ; Fisher et al., 1988 ), and mood disturbance ( Brickner, 1997 ; Daly, Brewer, Van Raalte, Petitpas, & Sklar, 1995 ), a factor associated in previous research ( Brewer, 1993 ) with level of self-identification with the sport role among athletes sustaining injuries.

As in the general health psychology literature ( Dunbar-Jacob & Schlenk, 1996 ; Hays et al., 1994 ), findings with respect to Path b have been inconsistent. Case history data have documented a positive relationship between rehabilitation adherence and rehabilitation outcome ( Derscheid & Feiring, 1987 ; Hawkins, 1989 ; Meani, Migliorini, & Tinti, 1986 ; Satterfield, Dowden, & Yasamura, 1990 ). Other studies,

however, have revealed nonsignificant ( Noyes et al., 1983 ) and inverse ( Shelbourne & Wilckens, 1990 ) adherence—outcome relationships.

Although a number of studies have documented the role of psychological factors in outcome after joint replacement surgery (e.g., Chamberlain, Petrie, & Azariah, 1992 ; Orbell, Johnston, Rowley, Espley, & Davey, 1998 ; Sharma et al., 1996 ), Path c has been examined in only two published studies involving sport injury rehabilitation. The psychological factors that have been associated with sport injury rehabilitation outcome are scores on the Minnesota Multiphasic Personality Inventory (MMPI; Hathaway & McKinley, 1951 ) hypochondriasis and hysteria scales ( Wise, Jackson, & Rocchio, 1979 ) and the self-reported use of selected coping skills ( Ievleva & Orlick, 1991 ). Also relevant to Path c, psychological interventions (e.g., biofeedback, guided imagery, and stress inoculation training) have been shown to enhance sport injury rehabilitation outcome (see Cupal, 1998 , for a review).

No single sport injury rehabilitation study has examined Paths a, b, and c, and few studies have tested any of the paths using prospective research designs. Consequently, the purpose of the current study was to examine the relationships among psychological factors, rehabilitation adherence, and rehabilitation outcome after ACL reconstruction using a prospective research design. By collecting psychological, adherence, and outcome data, it was possible to test the paths hypothesized in Figure 1 and to investigate the extent to which rehabilitation adherence mediates the relationship between psychological factors and rehabilitation outcome.

METHOD

Participants

Consecutive patients scheduled for ACL reconstruction and subsequent physical therapy at the clinic where the research was conducted ( N = 113) were recruited for participation in the study over a 30-month period by their orthopedic surgeon and a research assistant. Eleven patients refused to participate, 3 were unable to participate (as a result of language difficulties or lack of parental consent), and 4 were eliminated from the sample because they either did not have ACL surgery ( n = 2) or had extensive missing data ( n = 2). The remaining 95 participants (28 female patients and 67 male patients) had a mean age of 26.92 ( SD = 8.23) years. The racial—ethnic breakdown of the sample was as follows: 84 (88%) White, not of Hispanic origin; 7 (7%) Hispanic; 3 (3%) Black, not of Hispanic origin; and 1 (1%) Asian—Pacific Islander.

In terms of sport involvement, 49 (52%) participants indicated that they were competitive athletes, 41 (43%) indicated that they were recreational athletes, 3 (3%) indicated that they were nonathletes, and 2 (2%) did not respond to the item requesting this information. The majority of participants indicated that they sustained their ACL injury while participating in sport ( n = 85; 90%) and that the ACL surgery was the first time that they had had orthopedic surgery ( n = 60; 63%). Because all participants had fully torn ACLs, severity of injury was constant across participants. Of the 95 participants, 26 dropped out of the study before the 6-month postsurgery assessment (2 participants did not complete any of the adherence measures, and 26 participants did not complete any of the outcome measures).

Measures

Demographic, injury-related, psychological, adherence, and rehabilitation outcome variables were measured in this study.

Measures of demographic and injury-related variables.

A questionnaire was used to obtain demographic and injury-related information from participants. The questionnaire included items requesting information on participants' age, gender, race—ethnicity, date of ACL injury, source of ACL injury (i.e., sport-related activity or non-sport-related activity), and level of sport involvement (i.e., nonathlete, recreational athlete, or competitive athlete).

Psychological measures.

The psychological variables assessed in this investigation were self-motivation, social support, athletic identity, and psychological distress. Self-motivation was assessed with the Self-Motivation Inventory (SMI; Dishman & Ickes, 1981 ). The SMI is a 40-item questionnaire designed to measure "a behavioral tendency to persevere independent of situational reinforcements" ( Dishman & Ickes, 1981 , p. 421). Respondents are asked to rate the degree to which statements such as "I'm not very good at committing myself to do things," "I can persist in spite of pain and discomfort," and "I'm not very reliable" are characteristic of themselves on 5-point Likert scales. Empirical support for the reliability, internal consistency, construct validity, and predictive validity of the SMI in exercise settings has been found ( Dishman & Ickes, 1981 ).

Social support was measured by the Social Support Inventory (SSI; Brown, Alpert, Lent, Hunt, & Brady, 1988 ; Brown, Brady, Lent, Wolfert, & Hall, 1987 ). The SSI is a 39-item questionnaire that assesses satisfaction with support and help received from others over the previous month. Ratings are made on 7-point Likert-type scales ranging from 1 ( not at all satisfied ) to 7 ( very satisfied ). Examples of items are "assurance that you are loved and cared about," "information and guidance about how to cope with your situation," and "information on sources of financial assistance." Brown et al. (1987 , 1988 ) have obtained evidence for the reliability, construct validity, and criterion-related validity of the SSI.

The Athletic Identity Measurement Scale (AIMS; Brewer, Van Raalte, & Linder, 1993 ) was used to assess athletic identity, which is the degree to which an individual identifies with the athlete role. The AIMS is a questionnaire consisting of 10 Likert-type scales ranging from 1 ( strongly disagree ) to 7 ( strongly agree ). Examples of items are "I am an athlete," "Sport is the most important part of my life," and "Most of my friends are athletes." AIMS scores have been found to be predictive of postinjury psychological distress in athletes ( Brewer, 1993 ). In the preliminary validation study for the AIMS ( Brewer et al., 1993 ), the measure demonstrated high test—retest reliability ( r = .89 over a 2-week period) and internal consistency (alpha coefficients ranging from .81 to .93). AIMS scores increased with self-reported involvement in sport and were positively correlated with perceived importance of sport but were not significantly correlated with social desirability, self-esteem, self-rated sports competence, and coach-rated sport skill ( Brewer et al., 1993 ).

Psychological distress was measured by the Brief Symptom Inventory (BSI; Derogatis, 1992 ). The BSI consists of 53 items in a 5-point Likert format. Respondents indicate the extent to which they have been distressed by psychological and somatic symptoms over the previous 7 days. Published norms for nonpatient adults, nonpatient adolescents, psychiatric inpatients, and psychiatric outpatients are available. The reliability and validity of the BSI are well established ( Derogatis, 1992 ).

Adherence measures.

Adherence to rehabilitation was measured in three ways. First, patient attendance at rehabilitation sessions was monitored. For each participant, a ratio of sessions attended to sessions scheduled was calculated. Attendance has been used as an adherence measure in previous sport injury research ( Byerly et al., 1994 ; Daly et al., 1995 ; Derscheid & Feiring, 1987 ; Duda et al., 1989 ; Fields et al., 1995 ; Fisher et al., 1988 ; Lampton, Lambert, & Yost, 1993 ; Laubach, Brewer, Van Raalte, & Petitpas, 1996 ; Udry, 1997 ).

Second, at each physical therapy appointment, the practitioner (e.g., physical therapist or athletic trainer) responsible for the rehabilitation of each participant on that day completed the Sport Injury Rehabilitation Adherence Scale (SIRAS; Brewer, Van Raalte, Petitpas, Sklar, & Ditmar, 1995 ). The SIRAS is a three-item measure in which practitioners rate, on 5-point Likert-type scales, patients' intensity of completion of rehabilitation exercises, the frequency with which they follow the practitioner's instructions and advice, and their receptivity to changes in the physical therapy program during that day's appointment. Scale anchors for the three items are minimum effort/maximum effort, never/always, and very unreceptive/very receptive, respectively. The items, which were derived from the adherence literature ( Duda et al., 1989 ; Meichenbaum & Turk, 1987 ), have been shown to constitute a single factor accounting for approximately 74% of the variance in SIRAS scores ( Brewer et al., 1995 ).

Cronbach's alpha coefficients of .81 and .82 ( Brewer et al., 1995 ; Daly et al., 1995 ) have been found for the SIRAS. A test—retest reliability coefficient of .65 has been obtained for the SIRAS over a 1-week period ( Brewer, Daly, Van Raalte, Petitpas, & Sklar, 1994 ). In support of the criterion-related validity of the SIRAS, attendance at rehabilitation sessions has been positively correlated with SIRAS scores in two studies ( Brewer et al., 1995 ; Daly et al., 1995 ). There is evidence that repeated administrations of the SIRAS across physical therapy appointments provide an internally consistent ( = .86) index of adherence during rehabilitation sessions ( Brewer, Van Raalte, Petitpas, Sklar, & Ditmar, 1996 ).

Third, patient self-reports of home exercise and cryotherapy completion were obtained. At each rehabilitation session, patients reported their degree of completion of prescribed home exercises and cryotherapy since their last appointment on a scale ranging from 1 ( none ) to 10 ( all ). Mean SIRAS, home exercise completion, and home cryotherapy completion scores were calculated for participants across all rehabilitation sessions attended.

Rehabilitation outcome measures.

Consistent with previous investigations in which ACL rehabilitation outcome was evaluated (e.g., DeCarlo et al., 1992 ; Engebretsen, Benum, Fasting, Molster, & Strand, 1990 ; Marder, Raskind, & Carroll, 1991 ; Noyes et al., 1983 ; Shapiro, Richmond, Rockett, McGrath, & Donaldson, 1996 ; Shelbourne & Nitz, 1990 ; Shelbourne, Whitaker, McCarroll, Rettig, & Hirschman, 1990 ), multiple measures of ACL rehabilitation outcome were taken. Specifically, laxity, functional ability, and subjective symptoms were assessed.

An instrumented evaluation of anterior—posterior laxity of the knee joint was conducted with a KT1000 knee arthrometer (MEDmetric Corporation, San Diego, CA). Trials were conducted for both the involved and uninvolved knees, and values were recorded at 15 pounds (6.75 kg) of force. A mean difference in KT1000 scores between the involved and uninvolved knees was calculated for each participant. In vitro and in vivo data support the reliability and validity of the KT1000 as a measure of knee laxity ( Daniel, Malcom, et al., 1985 ; Daniel, Stone, Sachs, & Malcom, 1985 ; Malcom, Daniel, Stone, & Sachs, 1985 ).

The one-leg hop for distance ( Daniel, Stone, Riehl, & Moore, 1984 ) was used as a test of functional ability. In this test, patients hopped for distance on one leg, taking off and landing with the same leg. Hop distances were recorded in centimeters. Both the involved and uninvolved legs were tested three times in the one-leg hop. A mean hop index score was calculated by dividing the mean distance hopped on the involved leg across the three trials by the mean distance hopped on the uninvolved leg ( Kramer, Nusca, Fowler, & Webster-Bogaert, 1992 ). Kramer et al. have obtained support for the test—retest reliability of the hop index (intraclass correlation coefficient: .81). The index has been used effectively to evaluate the rehabilitation of ACL injuries ( Tegner, Lysholm, Lysholm, & Gillquist, 1986 ).

Subjective symptoms were assessed with the Lysholm Knee Scoring Scale ( Lysholm & Gillquist, 1982 ; Tegner & Lysholm, 1985 ), a patient self-report instrument. The questionnaire has items pertaining to limping, support, locking, instability, pain, swelling, stair climbing, and squatting. Responses to each of the eight items are assigned a point value, and a total score is obtained by summing across the items. Total scores can range from 0 to 100. Support for the test—retest reliability of the scale (coefficient of variation: ±2.8% over a 3-day period) has been documented ( Lysholm & Gillquist, 1982 ). Scores on the Lysholm Knee Scoring Scale have been shown to correlate positively with activity level after ACL injury ( Tegner & Lysholm, 1985 ) and have been used to evaluate knee functioning after ACL reconstruction ( Draper & Ladd, 1993 ).

Procedure

Patients were recruited as participants by the three orthopedic surgeons on the project before their ACL reconstructive surgery. A research assistant described the purpose and procedures of the study to the patients who expressed interest in participating. Patients who agreed to participate in the study (and their parents or guardians when appropriate) read and completed an informed-consent form at their preoperative physical therapy appointment approximately 10 days before reconstructive surgery. At this time, participants were administered a battery of psychological questionnaires

(including demographic and injury-related items, the SMI, the SSI, the AIMS, and the BSI).

After reconstructive surgery, measures of adherence to rehabilitation were taken at each scheduled physical therapy appointment. Attendance—nonattendance was documented, the SIRAS was administered to the physical therapist or athletic trainer most involved with the patient's rehabilitation, and patient ratings of home exercise and cryotherapy completion in the time since the previous appointment were obtained.

The accelerated rehabilitation protocol after ACL reconstruction developed by Shelbourne and his colleagues ( DeCarlo et al., 1992 ; Shelbourne et al., 1992 ; Shelbourne & Nitz, 1990 ; Shelbourne & Wilckens, 1990 ) and recently updated ( DeCarlo et al., 1994 ) was prescribed by the orthopedic surgeons and followed by the physical therapists affiliated with the proposed study. This physical therapy protocol, which has been found superior to traditional, more conservative approaches ( DeCarlo et al., 1992 ), emphasizes early attainment of range of motion (extension and flexion of the knee), quadriceps strength, and normal gait ( DeCarlo et al., 1994 ; Shelbourne et al., 1992 ; Shelbourne & Nitz, 1990 ).

Rehabilitation outcome measures were administered as a regular part of patients' rehabilitation program approximately 6 months after reconstructive surgery. A physician assistant and the physical therapist responsible for each patient's treatment conducted the rehabilitation assessments. The physician assistant, who performed the KT1000 tests, was unaware of participants' responses to the presurgical questionnaire battery and adherence data. The physical therapist was unaware of participants' responses to the presurgical questionnaire battery and the questionnaires requesting information on completion of home exercises and cryotherapy.

Data Screening

Independent t tests were conducted to determine whether the participants who dropped out differed from those who remained in the study in regard to variables measured before surgery (e.g., age, self-motivation, social support, athletic identity, and psychological distress). No significant differences were found, indicating the presurgical equivalence of the participants who dropped out and those who remained in the study on these variables. Although follow-up data are unavailable for most of the participants who did not complete the study, several participants indicated that they dropped out of the study for practical reasons, such as moving to another town or transferring to a clinic closer to home.

Cronbach alpha coefficients for the self-motivation, social support, athletic identity, and psychological distress measures used in the presurgical assessment were .92, .97, .87, and .96, respectively. Because of skewed distributions, transformations were applied to several variables. The distribution for the BSI was positively skewed, and a log transformation produced a more normal distribution. The distribution for the SIRAS was negatively skewed, and a reflection and an inverse transformation produced a more normal distribution. As a result of missing data on some variables for some participants, the number of participants available for each of the main analyses varied slightly.

RESULTS

Means, standard deviations, and intercorrelations of psychological, adherence, and outcome measures are presented in Table 1 . To examine the potential influence of demographic factors on the findings, we calculated Pearson correlations between age and the adherence and outcome measures and performed t tests on the adherence and outcome measures using gender, source of ACL injury, and prior orthopedic surgery experience as independent variables. Age was significantly correlated with one-leg hop scores ( r = .36, p < .05). Participants with prior orthopedic surgery experience had significantly lower KT1000 scores than participants without prior orthopedic surgery experience, t (55) = 2.57, p < .05. All other correlations and t tests involving demographic factors were not statistically significant. On the basis of these results, age was used as a covariate in all analyses in which one-leg hop scores were the criterion, and prior orthopedic surgery experience was used as a covariate in all analyses in which KT1000 scores were the criterion.

To evaluate prospective relationships between psychological factors and adherence to rehabilitation after ACL reconstruction, we calculated a set of regression analyses in which the four psychological factors assessed before surgery (i.e., self-motivation, social support, athletic identity, and psychological distress) were used to predict the four adherence measures (i.e., attendance, SIRAS score, home exercise completion, and home cryotherapy completion) in four separate regression equations. Separate analyses were used for the four adherence measures because they were generally uncorrelated with each other, with the exception of the home exercises and home cryotherapy scores. The regression equation predicting home exercise completion was statistically significant, F (4, 51) = 4.55, p < .005, R 2 = .26. Self-motivation ( = .39, p < .05) was the sole significant predictor of home exercise completion from among the psychological measures. The regression equation predicting SIRAS scores approached statistical significance, F (4, 51) = 2.17, p < .10, R 2 = .15. Social support ( = .27, p < .10) approached statistical significance as a predictor of SIRAS scores. The regression equations predicting attendance and home cryotherapy completion were not statistically significant.

To examine the relation between psychological factors and short-term postsurgical rehabilitation outcome after ACL reconstruction, we calculated a set of regression analyses in which the four psychological factors assessed before surgery (i.e., self-motivation, social support, athletic identity, and psychological distress) were used to predict the three rehabilitation outcome measures (i.e., KT1000, one-leg hop, and subjective symptoms) in three separate regression equations. Separate analyses were used for the three rehabilitation outcome measures because they were uncorrelated with each other. The regression equation predicting KT1000 scores was statistically significant, F (5, 34) = 4.88, p < .005, R 2 = .42. Psychological factors accounted for a significant proportion of variance in KT1000 scores over and above prior orthopedic surgery experience, F (4, 34) = 4.75, p < .005. Athletic identity ( = .36, p < .05) and psychological distress ( = .46, p < .01) emerged as significant predictors of KT1000 scores. The regression equations predicting one-leg hop performance and subjective symptoms were not statistically significant.

To test the hypothesis that adherence to rehabilitation is positively associated with short-term rehabilitation outcome after ACL reconstruction we conducted a set of

regression analyses in which adherence measures (i.e., attendance, SIRAS score, home exercise completion, and home cryotherapy completion) were used to predict rehabilitation outcome measures (i.e., KT1000, one-leg hop, and subjective symptoms) in three separate regression equations. Only the regression equation predicting the one-leg hop index was statistically significant, F (5, 44) = 4.70, p < .05, R 2 = .35. Adherence measures accounted for a significant proportion of variance in the one-leg hop index over and above age, F (4, 44) = 3.89, p < .01. Attendance ( = .28, p < .05), SIRAS scores ( = .28, p < .05), and home cryotherapy completion ( = .36, p < .05) were significant predictors of the one-leg hop index. Because none of the adherence measures were significantly correlated with both psychological and outcome measures, the criteria for mediation were not satisfied ( Baron & Kenny, 1986 ), and further analyses were not carried out.

DISCUSSION

In this study, selected psychological factors were associated prospectively with rehabilitation adherence and rehabilitation outcome after ACL reconstruction. Consistent with previous research ( Duda et al., 1989 ; Fields et al., 1995 ; Fisher et al., 1988 ; Noyes et al., 1983 ), self-motivation emerged as a significant predictor of rehabilitation adherence (i.e., home exercise completion). Athletic identity and psychological distress were significant predictors of rehabilitation outcome (i.e., knee laxity) such that higher athletic identity and lower psychological distress were associated with a more favorable outcome. Adherence, in the form of attendance at rehabilitation sessions, and home cryotherapy completion were related to one of the three rehabilitation outcomes assessed (i.e., functional ability). Contrary to the hypothesized pattern of results, adherence did not mediate the relationship between psychological factors and rehabilitation outcome. Thus, with reference to Figure 1 , partial support was obtained for Paths a, b, and c but not the mediated path from psychological factors to rehabilitation outcome through rehabilitation adherence (by way of Paths a and b).

The positive correlation between attendance at rehabilitation sessions and functional ability augments similar findings by Derscheid and Feiring (1987) for ACL reconstruction and suggests that patients benefit from participating in clinic-based rehabilitation activities. A possible interpretation of the inverse relationship found between home cryotherapy completion and functional ability is that patients who are recovering better experience less pain and thereby initiate less direct treatment.

A logical explanation for the significant relationships of athletic identity and psychological distress to knee laxity involves greater adherence–and, therefore, better rehabilitation outcome (i.e., less laxity)–for patients more strongly self-identified as athletes and less distressed. Because neither athletic identity nor psychological distress was associated with rehabilitation adherence, however, this explanation is not tenable. It is possible that the more athletically self-identified patients were more fit before surgery and therefore responded more favorably to reconstructive surgery than the less athletically self-identified patients. It is also possible that presurgical psychological distress influenced immune functioning, which in turn affected postsurgical healing ( Herbert & Cohen, 1993 ; Roitt, 1997 ). These explanations are speculative, though, and warrant further exploration.

The current study has some limitations that should be addressed in future research. First, although it was reasonable to select a 6-month period after ACL reconstruction for the assessment of rehabilitation outcome based on the physical therapy protocol used for participants ( DeCarlo et al., 1992 ; Shelbourne et al., 1992 ; Shelbourne & Nitz, 1990 ), the study may have been of insufficient duration for the influences of psychological factors and rehabilitation adherence on rehabilitation outcome to fully emerge. In the Wise et al. (1979) study, associations between presurgical psychological variables and rehabilitation outcome were evident 1 to 3 years after knee surgery. Consequently, rehabilitation outcome should be assessed at regular intervals over a longer time period in subsequent investigations.

Second, given the difficulties associated with having volunteer participants engaged in research over a long period of time, it may be important to offer research participation incentives. Such incentives, which would help curb participant attrition (26% in this study) and the accompanying loss of statistical power, would be especially critical for studies of longer duration than the present study.

Third, prospective assessment of rehabilitation outcome variables (e.g., knee laxity and subjective symptoms) would allow participants to serve as their own controls and would account for a large portion of error variance in the rehabilitation outcome measures, thereby increasing the likelihood of obtaining significant relationships with the outcome variables. Even without this preoperative assessment, however, significant relationships were found with functional ability and knee laxity in the current study.

Fourth, although the assessment of adherence to home rehabilitation regimens in the current study represented an improvement over previous investigations of home-based sport injury rehabilitation adherence ( Almekinders & Almekinders, 1994 ; Noyes et al., 1983 ; Taylor & May, 1996 ), retrospective self-reports of adherence can be subject to biased, distorted, or inaccurate recall ( Dunbar-Jacob, Dunning, & Dwyer, 1993 ; Meichenbaum & Turk, 1987 ). Further improvements are possible by obtaining daily self-reports (cf. Stone, Kessler, & Haythornthwaite, 1991 ) and objective measurements (e.g., Levitt, Deisinger, Wall, Ford, & Cassisi, 1996 ) of adherence to home rehabilitation activities.

The preliminary results obtained in this study suggest the possibility that psychological interventions designed to reduce psychological distress and enhance rehabilitation adherence could enhance the rehabilitation of sport-related orthopedic injuries in general and ACL tears in particular. Before such interventions are developed, implemented, and evaluated (e.g., Fisher, Scriber, Matheny, Alderman, & Bitting, 1993 ; Worrell, 1992 ), however, it is necessary to determine that improving adherence also improves rehabilitation outcome. Research is needed to assess more thoroughly the relationship between adherence to rehabilitation protocols and outcome after ACL reconstruction. Further inquiry in this area has the potential to provide an empirical basis for psychologists to better serve people undergoing rehabilitation of sport- and recreation-related injuries.

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This article was supported in part by Grant R15 AR42087-01 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Its contents are solely the responsibility of the authors and do not represent the official views of the National Institute of Arthritis and Musculoskeletal and Skin Diseases. We thank Mark Andersen for his helpful comments on an earlier version and Marc Aconcio, Michael Astilla, Matt Bitsko, John Brickner, Chris Buntrock, Wally Bzdell, Catherine D'Agostino, Doug Harvey, Ron Hokanson, Miriam Holmes, Chris Izzo, Kelly Kane, Greg Kelleter, Dave LaLiberty, Jeff Laubach, Tara Nichols, Julie O'Brien, Jeff Rice, Eric Rienecker, Trina Runge, Corinne Smith, Ken Tubilleja, Faye Weiner, Jere Weinstock, Heidi Wolcott, Kathy Wurster, and Mark Yunger for their assistance in data collection. Correspondence may be addressed to Britton W. Brewer, Department of Psychology, Springfield College, Springfield, Massachusetts , 01109. Electronic mail may be sent to bbrewer@spfldcol.edu Received: March 1, 1999 Revised: June 7, 1999 Accepted: August 13, 1999

Table 1. Means, Standard Deviations, and Intercorrelations of Psychological, Adherence, and Outcome Measures

Figure 1. Schematic Representation of Hypothesized Relationships Among Psychological Factors, Rehabilitation Adherence, and Rehabilitation Outcome.