Archives of Physical Medicine and Rehabilitation
Volume 89, Issue 8 , Pages 1535-1541, August 2008

Functional Recovery After Anterior Cruciate Ligament Reconstruction: A Longitudinal Perspective

  • Diana M. Hopper, PhD

      Affiliations

    • School of Physiotherapy, Curtin University of Technology, Bentley, Western Australia, Australia
    • Corresponding Author InformationReprint requests to Diana M. Hopper, PhD, School of Physiotherapy, Curtin University of Technology, GPO Box U1987, Bentley, WA, Australia 6845.
    • ,
  • Geoff R. Strauss, MPE

      Affiliations

    • School of Physiotherapy, Curtin University of Technology, Bentley, Western Australia, Australia
    • ,
  • Jeff J. Boyle, PhD

      Affiliations

    • Fremantle Football Club, Fremantle, Australia.
    • ,
  • Jonathan Bell, MSc

      Affiliations

    • School of Physiotherapy, Curtin University of Technology, Bentley, Western Australia, Australia

published online 01 July 2008.

Article Outline

Abstract 

Hopper DM, Strauss GR, Boyle JJ, Bell J. Functional recovery after anterior cruciate ligament reconstruction: a longitudinal perspective.

Objective

To evaluate functional hop performance in subjects with an anterior cruciate ligament (ACL) reconstruction with a bone-patellar tendon-bone graft during 12, 18, 26, 39, and 52 weeks.

Design

A longitudinal comparative study.

Setting

University research laboratory.

Participants

Patients (N=19) were evaluated at 12, 18, 26, 39, and 52 weeks after ACL reconstruction surgery.

Intervention

Testing on 5 separate occasions.

Main Outcome Measures

The Cincinnati Knee Rating System and analog scales, the 6-meter timed hop, crossover hop, stair hop, and vertical hop, and limb symmetry indices.

Results

The uninjured and injured legs and test order were randomized. There was a significant test occasion main effect for both the Cincinnati and analog scores (P=.001). Subjective rating scores improved over the 5 testing occasions. For all 4 hop tests, test occasion and limb main effects were significant (P=.001). Paired t test comparisons at each testing occasion indicated a significant difference between the reconstructed and uninjured limb (P<.05). Furthermore, significant test occasion main effects were noted for limb symmetry indices for the 4 hop tests (P=.001). Using a score of greater than or equal to 85% as a criterion for normative limb symmetry, normative scores were recorded in the 6-m timed hop at the week 18 test occasion, the stair hop and vertical hop at the week 26 test occasion, and the crossover hop at the week 39 test occasion.

Conclusions

These hop tests showed different levels of imposed demands on the knee that could be used to assess functional recovery and readiness to resume sport.

Key Words: Anterior cruciate ligament, Knee, Rehabilitation

List of Abbreviations: ACL, anterior cruciate ligament, ANOVA, analysis of variance

 

THE IMPORTANCE OF a patient's perception of knee recovery, and self-confidence in performing physical tasks after ACL reconstruction, is reflected by the plethora of subjective rating scales reported in knee outcome studies.1, 2, 3, 4 Among the many rating systems, the Cincinnati Knee Rating System has been shown to be a reliable, sensitive, and valid measurement tool for defining functional knee status.5, 6, 7

The popularity of functional performance tests for assessing knee status is clearly evident in the literature, with each task seen to place different demands on the knee joint under controlled clinical conditions. Both double and single-limb performance tests have been reported, involving running, jumping, and hopping tasks in straight lines or requiring pivoting and cutting actions.8, 9, 10, 11, 12, 13, 14, 15 The clinical utility of functional tests relates to their ability in providing an objective indication of dynamic lower-extremity performance under simulated conditions, designed to mimic the greater demands imposed on the knee in the everyday environment.10, 14, 16, 17, 18 Single-limb tasks, such as hopping tests, offer considerable benefits compared with 2-legged tasks, because they provide between-limb, within-subject comparisons without the need to rely on population-specific normative data. The functional status of the knee is often defined by the limb symmetry index or ratio, with an index of less than 85% used as a guide for abnormal symmetry.8, 11 Furthermore, it is suggested that a score of less than 85% may indicate an increased risk of giving way of the knee during participation in sporting activities.16 Many single-limb tests, however, have been noted to have poor sensitivity rates, and hence should not be used to detect specific deficits, but rather used as a general measure of lower-extremity performance to confirm functional limitations.8, 11 Furthermore, a combination of 2 tests or more is recommended to enhance the sensitivity of functional testing.8, 11

To date, outcome studies involving ACL-reconstructed populations have largely reported knee functional status at specific postoperative periods. We have found few longitudinal reports evaluating functional recovery of the ACL-reconstructed knee during the first postoperative year. A systematic review19 and randomized controlled trials in rehabilitation after ACL knee reconstruction20, 21 provide some insight into the rate of changes in a number of outcome measures between 3 months and 2 years after patella tendon autograft reconstruction. However, the fundamental question of functional recovery and return to sport22 is still unresolved. Even with the latest research, there still appears to be a paucity of literature that has investigated the progression of ACL knee construction functional recovery at different time intervals during the first year of recovery. This is especially important when advising athletes on return to sport. Therefore the primary purpose of the study was to examine functional recovery during the performance of 4 single-limb hop tests at 12, 18, 26, 39, and 52 weeks after ACL reconstruction using a bone-patellar tendon-bone graft. The secondary purpose was to assess the subject-reported measures and functional performance across 5 testing occasions after ACL reconstruction.

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Methods 

Participants 

The study sample included 19 subjects (10 men, 9 women), whom we recruited by convenience sampling from the physiotherapy databases of Royal Perth Hospital, Western Australia. Their mean age was 25.9 years (range, 19–34y). Subjects were included if they had undergone ACL reconstructive surgery using the patella tendon autograft technique and had satisfactorily completed a standardized accelerated postoperative rehabilitation program at the outpatient physiotherapy department. Exclusion criteria included orthopedic or musculoskeletal conditions affecting the hip or ankle joints of either lower limb, existing or previous injury to the contralateral knee, collateral ligament damage at the time of initial injury, complications after ACL surgery, persistent abnormal pain, swelling or instability of the knee after reconstruction, cardiorespiratory ailments, or vestibular dysfunction. Ethical approval was obtained from the Human Research Ethics Committee of Curtin University of Technology and Royal Perth Hospital.

We performed testing on 5 separate occasions at 12, 18, 26, 39, and 52 weeks postoperatively. All tests were performed in the same location, and where possible, under constant environmental conditions. Subjects were requested to wear the same pair of shoes on each test occasion. Verbal instructions from the examiner were standardized. On each testing occasion, subjects completed a Cincinnati Knee Rating System, and provided an analog rating ranging from 1 to 100 points, which best reflected their perception of current knee status. Prior to functional testing, a 5-minute warm-up was performed on a stationary bicycle ergometer, followed by static stretches for the hamstrings, quadriceps, gastrocnemius, and soleus muscle groups. Three 10-second stretches were performed for each lower extremity.

Prior to data collection, subjects were allowed 1 practice trial of each hop test for each limb, to facilitate familiarization with the tests and to minimize possible learning effects. The order of testing of the functional hop tests, and the limb to be tested first, were randomly determined. Three trials were performed for each hop test, with adequate rest periods ensured between each trial.

Functional Hop Tests 

Detailed description and instrumentation for the 6-meter timed hop, crossover hop (fig 1), stair hop (fig 2), and vertical hop tests used in this study are outlined in Hopper et al.23

Data Analysis 

We used the best score from each hop test for all data analyses, thus providing the best possible indication of optimal performance for each subject. Two-factor repeated-measures ANOVA were applied to examine for testing occasion and limb main effects, and testing occasion by limb interactions. Limb symmetry indices were calculated for the hop tests on each test occasion. The limb index for the 6-m timed hop and stair hop tests was determined by dividing uninjured limb performance data by reconstructed limb data, and the result multiplied by 100. For the crossover hop and vertical hop tests, the index was calculated by dividing reconstructed limb data by uninjured limb data, and the result multiplied by 100. One-factor repeated-measures ANOVA was used to examine test occasion main effects for the knee rating scores and limb symmetry indices. For all analyses, statistical significance was defined by a probability level of P less than .05.

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Results 

Subjective Rating Scales 

There was a significant test occasion main effect for both the Cincinnati and analog scores (P=.001). Subjective rating scores improved over the 5 testing occasions (table 1). Correlation coefficients between the Cincinnati and analog scores were .82, .81, .82, .83, and .91, for 12, 18, 26, 39, and 52 weeks, respectively (P<.05).

Table 1. Cincinnati Knee Rating System and Analog Scores at 12, 18, 26, 39, and 52 Weeks After ACL Reconstruction (N=19)
Cincinnati ScoreAnalog Score
WeekMean ± SDRangeMean ± SDRange
Week 1260.5±11.540.2–84.863.1±13.840–85
Week 1869.1±8.154.4–87.068.8±15.540–90
Week 2675.9±8.756.5–87.572.6±9.845–90
Week 3979.8±12.645.7–92.477.6±12.150–90
Week 5285.9±9.063.0–96.783.3±10.260–95

Hop Test Raw Scores 

Significant test occasion and limb main effects were noted for all 4 hop tests (P=.001). Limb by test occasion interactions were also significant (P=.001). Paired t test comparisons at each testing occasion indicated a significant difference between the reconstructed and uninjured limb (P<.05). Poorer scores were noted in the reconstructed limb on all testing occasions (fig 3).

  • View full-size image.
  • Fig 3. 

    Hop test performance scores for the uninjured and reconstructed limbs at 12, 18, 26, 39, and 52 weeks after ACL reconstruction (N=19). (A) 6-m timed hop, (B) crossover hop, (C) stair hop, and (D) vertical hop. Error bars represent 95% confidence intervals.

Limb Symmetry Indices 

Significant test occasion main effects were noted for limb symmetry indices for the 4 hop tests (P=.001). Mean values increased over the 5 testing occasions (table 2, fig 4). Using a score of greater than or equal to 85% as a criterion for normative limb symmetry, normative scores were recorded in the 6-m timed hop at the week 18 test occasion, the stair hop and vertical hop at the week 26 test occasion, and the crossover hop at the week 39 test occasion.

Table 2. Limb Symmetry Indices (in percent) for 4 Functional Hop Tests, Performed at 12, 18, 26, 39, and 52 Weeks After ACL Reconstruction (N=19)
Week6m Timed HopCrossover HopStair HopVertical Hop
Week 12
Mean ± SD79.1±14.276.8±13.568.7±19.474.1±13.0
Range49.2–99.245.2–91.134.6–95.053.3–97.7
Week 18
Mean ± SD85.7±8.581.1±9.984.2±9.583.2±10.7
Range62.6–97.158.0–96.864.8–98.766.9–100.0
Week 26
Mean ± SD89.6±7.484.8±10.292.7±4.986.4±7.5
Range66.8–98.463.2–100.084.8–98.873.0–97.5
Week 39
Mean ± SD93.9±8.788.5±8.895.2±4.888.8±6.2
Range63.4–100.068.4–100.083.7–100.073.5–100.0
Week 52
Mean ± SD94.7±8.591.9±8.795.9±7.290.4±7.8
Range65.0–100.073.6–100.176.4–100.173.0–100.0

The distribution of normative (≥85%) and abnormal limb symmetry indices (<85%) is shown in figure 5. At the week 12 test occasion, the highest number of abnormal scores was noted in the vertical hop (n=16) and stair hop (n=14). Eleven subjects scored abnormally in the 6-m timed hop and crossover hop. The number of subjects showing abnormal limb symmetry decreased over the 5 test occasions. By week 26, the lowest number of abnormal scores was noted in the stair hop and 6-m timed hop (n=1, n=3, respectively), whereas 8 and 9 subjects, respectively, recorded abnormal scores in the vertical hop and crossover hop. At the week 52 testing occasion, the highest number of abnormal limb indices was noted in the crossover hop (3 subjects).

  • View full-size image.
  • Fig 5. 

    Distribution of normative (≥85%) and abnormal limb symmetry indices (<85%) for 4 hop tests performed at 12, 18, 26, 39, and 52 weeks after ACL reconstruction. (A) 6-m timed hop, (B) crossover hop, (C) stair hop, and (D) vertical hop. Values are recorded as a cumulative number of subjects (N=19 for all hop tests).

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Discussion 

This study provides longitudinal data on functional recovery in 19 subjects during the first postoperative year after patella tendon autograft ACL reconstruction. Improvements in subject-reported measures and functional performance were evident across 5 testing occasions, performed at the 12-, 18-, 26-, 39-, and 52-week postreconstruction stages.

Subjective outcome, as reflected by Cincinnati and analog scores, improved significantly across the testing occasions. Cincinnati scores were generally comparable with those reported by Risberg et al,21 for 60 patients after patella tendon autograft reconstruction (67.4, 76.8, and 84.2, at 3, 6, and 12 months, respectively, postsurgery). Similarly, a mean Cincinnati score of 85.9 was noted for subjects in the current study at the 1-year postoperative stage. As suggested by Noyes et al,2 a score of 85% provides some indication that the knee is capable of withstanding the demands of strenuous sports requiring jumping and cutting maneuvers on a regular basis. The Cincinnati score also correlated highly with the analog score, suggesting that the subject's general perception of their knee status compared favorably with outcomes determined through questionnaire assessment. Given its sensitivity to changes in knee function over time,6 this rating system is ideally suited for longitudinal evaluation of the recovery rate of the reconstructed knee, as reported by the patient. The demonstrated validity and reliability of the Cincinnati Knee Rating System further strengthens its clinical utility as an accurate indicator of knee status.5, 7

Functional recovery was similarly reflected by improvements in hop test performance, in terms of raw performance scores and limb symmetry indices. In comparing the 4 hop tests, the 6-m timed hop appeared to be the easiest for subjects to perform, particularly during the early stages of recovery. Using a limb index of 85% or more as a criterion for normative symmetry,11 subjects in the current study had attained normative performance scores by week 18. By week 26, the majority had registered less than 15% between limbs, with 16 (84% of subjects) scoring 85% or higher. Similarly, Wilk et al15 reported that 37 (74%) of 50 subjects showed normative symmetry scores 6 months after reconstruction. Although these findings may provide some optimism regarding knee functional recovery at the 6-month postreconstruction stage, the clinician is reminded of the documented poor sensitivity of the timed hop test as a tool for identifying limb deficits.11 In their assessment of 67 subjects with ACL-deficient knees, Noyes et al11 noted that 51% had performed normally, despite self-reported symptoms of giving way. It may be hypothesized that the straight-line nature of the test does not place sufficient demands on the knee to elicit functional limitations that may become apparent during performance of tasks requiring pivoting or cutting-type maneuvers.

Although the stair hop limb index was lowest among the 4 hopping tasks at week 12, performance trends were generally similar to the timed hop test during the mid and late stages of recovery. Improvements in performance were most pronounced between weeks 12 and 26 (see fig 4), such that by week 26, the mean index was 92.7%, with only 1 subject showing abnormal limb symmetry (limb index, 84.8%). The poor score noted during the week 12 test occasion, coupled with the large intersubject variability (SD=19.4), perhaps reflects the novelty of the task and a lack of subject confidence in performing a vertical hop task during the early rehabilitation phase. This test represents a modification of the 22-stair hop test described by Risberg and Ekeland,13 which has been shown to be too difficult for some subjects to perform, even at the 2 to 4 year postreconstruction stage.24 Compared with the timed hop test, the present stair hop test provides an additional measure of dynamic limb performance in the vertical direction, yet may appear more manageable for apprehensive subjects compared to the 22-stair hop test. The current findings suggest its utility as a suitable functional outcome measure during the early and mid stages of recovery after ACL reconstruction.

The crossover hop consistently produced the highest number of abnormal symmetry scores during the mid and later stages of testing. Although the mean limb index approximated a normative value at week 26 (mean, 84.8%), abnormal performances were evident in 9 subjects (47%). This finding was also noted by Wilk et al,15 where 22 (44%) of 50 subjects showed abnormal limb symmetry at 6 months postreconstruction. Although the poor sensitivity of the crossover hop has been documented,11 one might suggest that the nature of the test, requiring a change in limb direction, potentially places greater demands on the knee joint. Its ability to confirm lower-limb deficits may therefore surpass that of the 6-m timed hop or stair hop test, particularly during the mid and later stages of recovery, as was evident in the current study. In the study by Goh and Boyle,24 subjects who had reported mild limitations 2 to 4 years after ACL reconstruction showed normative limb symmetry in the 6-m timed hop, yet lower-limb asymmetry was noted with the crossover hop test. Eastlack et al25 further proposed that the crossover hop is more discriminate of copers versus noncopers in ACL-deficient athletes, compared with the 6-m timed hop. Furthermore, Anderson and Foreman26 acknowledged this lack of sensitivity and recommended that the crossover hop test be increased to 4 hops and the width of the course be expanded.27 This adapted crossover hop may be more sensitive for confirming subtle limitations in knee function during the mid and later stages of rehabilitation. This test also represents an appropriate outcome measure in the assessment of the athlete wishing to return to sports requiring directional changes of the lower limb.

Performance trends for the vertical hop paralleled that of the crossover hop. Despite a mean limb index of 86.4% at week 26, 8 subjects (42%) recorded abnormal limb symmetry scores. Comparison of the current findings with other studies is limited by the diversity of vertical hop test protocols, with numerous versions reported in the literature. Not surprisingly, the sensitivity of the vertical hop for assessing lower-limb function remains unclear. In the study by Barber et al,8 31% of normative subjects scored less than 85% on a modified version of the vertical hop, indicating its poor sensitivity. Conversely, Petschnig et al12 proposed that the vertical hop had the highest sensitivity rate in detecting lower-limb limitations. At 13 weeks postreconstruction, all subjects in their study (n=30) scored 85% or lower, whereas 72% showed abnormal symmetry at the 54 week postoperative stage.12 This contrasted with the lower sensitivity of the single and triple hop for distance, where 93% and 90% of subjects, respectively, scored abnormally at week 13, and only 28% and 16%, respectively, at week 54. In the current study, the similarly high number of subjects showing abnormal limb symmetry for the vertical hop at week 12 (84% of subjects) reflects the more challenging nature of the task, and perhaps the greater sensitivity of the vertical hop compared with the timed hop and stair hop tests. Based on the present findings, the vertical hop may therefore be more appropriate for lower-limb functional assessment during the mid and later stages of recovery.

With the exception of the crossover hop, the functional test limb indices indicate a return to normative limb symmetry at 26 weeks after ACL reconstruction. The mean index for the crossover hop at this stage was 84.8%. These findings concur with guidelines from established rehabilitation protocols, allowing a return to previous levels of sport 4 to 9 months after reconstruction.19, 28, 29 One is reminded, however, that the knee may still be at risk of giving way during sports despite a within-normal deficit of 15% or less in the reconstructed limb.2, 14

Study Limitations 

The benefits of functional hop tests have been well documented. Although they provide an objective within-subject, between-limb comparison, they are simple to administer, requiring minimal personnel, cost, equipment, and space.16 The clinician, however, should acknowledge a number of limitations prior to implementing these tests. Given their questionable sensitivity, hop tests should not be used to identify specific abnormalities, although their high specificity enables confirmation of lower-extremity functional limitations.11 A combination of at least 2 tests is recommended to increase the sensitivity rate, enabling the discrimination of subtle limb deficits.11 This is supported by Itoh et al,9 who reported a sensitivity rate of 82% when a combination of 4 hop tests was used to evaluate functional limitations in 50 ACL-deficient subjects. Furthermore, learning effects in performing these tasks have been documented in uninjured populations.24, 30

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Conclusions 

In the current study, there was a general trend for slight improvements in raw performance scores for the uninjured limb over the 5 test occasions, particularly between weeks 12 and 18 of testing. This trend may perhaps reflect a lack of confidence in performing a novel task, or a detraining effect of the uninjured limb secondary to reduced physical activity.27 Some attention should therefore be given to the method of task administration to minimize learning influences, such as ensuring an adequate warm-up prior to testing, and considering the optimum number of pretest practice trials and test trials. These measures will serve to ensure that the clinician can confidently attribute differences in performance scores to actual changes in limb function, rather than to inconsistencies or variability in measurement.

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Acknowledgments 

We thank the Department of Physiotherapy, Royal Perth Hospital (Shenton Park), for their assistance in compiling the subject database, and Jayne Sutcliffe, BSc, for assisting with data collection.

Special thanks also to Suet Goh, PhD, and Christina Neo, BSc, for their valuable contributions.

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References 

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 Published online June 30, 2008 at www.archives-pmr.org.Supported by the Physiotherapy Research Foundation and Australian Physiotherapy Association, New South Wales Sports Physiotherapy Group.No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.

PII: S0003-9993(08)00283-9

doi:10.1016/j.apmr.2007.11.057

Archives of Physical Medicine and Rehabilitation
Volume 89, Issue 8 , Pages 1535-1541, August 2008

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