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Test–retest reliability of knee rating scales and functional hop tests one year following anterior cruciate ligament reconstruction
Original Research
Test±retest reliability of knee rating scales and functional hop tests one year following anterior cruciate ligament reconstruction Diana M. Hopper, Suet C. Goh, Laurel A. Wentworth, Derek Y. K. Chan, Jay H. W. Chau, Gregory J. Wootton, Geoffrey R. Strauss and Jeffrey J. W. Boyle
Diana M. Hopper PhD Suet C. Goh PhD Laurel A. Wentworth MSportsPhty Derek Y. K. Chan MSportsPhyty Jay H. W. Chau MSportsPhyty
Objectives: The aim of this study was to examine the test±retest reliability of the Cincinnati Knee Rating System and analogue scale, and four hop tests in subjects following anterior cruciate ligament (ACL) reconstruction, and to describe knee function one year following surgery. Design: Within-subject quasi-experimental design for test±retest reliability. Setting: A university rehabilitation laboratory. Participants: Nineteen subjects presenting at 12 months post ACL reconstruction were recruited from two orthopaedic surgeons. Main outcome measures: Knee rating scores, raw performance scores for the 6 m timed hop, cross over hop, stair hop and vertical hop, and hop test limb symmetry indices (LSI) were compared on two testing occasions, performed one week apart. Results: Intraclass correlation coef®cients (ICC) indicated high test±retest reliability for all measured parameters (0.81±0.98). No signi®cant difference between test occasions was observed for the knee rating scales and vertical hop raw scores. Signi®cant differences were noted for raw scores in the remaining hop tests (P 5 0.01). The LSI scores for all hop tests were not signi®cantly different between the two occasions. Mean values ranged from 88.8% to 96.6%. Conclusions: The knee rating scales and functional hop tests showed high test±retest reliability in an ACL-reconstructed population, supporting their use for evaluating this speci®c patient group over different sessions. Reconstructed limb functional performances were within normal limb c 2002 Harcourt Publishers Ltd symmetry values one year following surgery. *
Geoffrey R. Strauss MPE
Introduction
Jeffrey J. W. Boyle GradDipManipTher School of Physiotherapy, Curtin University of Technology, Selby Street, Shenton Park, Western Australia 6008, Australia
In recent years, clinical evaluation of the anterior cruciate ligament (ACL) reconstructed knee has gradually evolved from traditional orthopaedic testing to incorporate more functional means of assessment. This has given rise to the popularity of numerous knee rating systems (Lysholm & Gillquist 1982; Noyes et al. 1984; Tegner & Lysholm 1985; Risberg et al. 1999a) and functional assessment tests (Tegner et al. 1986; Barber et al. 1990; Noyes et al. 1991; Lephart et al. 1992; Risberg & Ekeland 1994; Wilk et al. 1994; Risberg et al. 1999b), in the attempt to provide a clearer indication of the
Correspondence to: Diana M. Hopper, Tel: 61 8 9266 3631; Fax: 61 8 9266 3636; E-mail: D.Hopper@curtin. edu.au
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doi : 10.1054/ptsp.2001.0094, available online at http://www.idealibrary.com on
status of the reconstructed knee. Amongst the many subjective rating scales documented in the literature, the commonly utilized Cincinnati Knee Rating System (CKRS) is reported to most precisely de®ne functional outcome (Sgaglione et al. 1995), and is highly sensitive to changes in knee function over time (Risberg et al. 1999a). It is suggested that a CKRS score of 85% or greater is suf®cient for the knee to withstand regular participation in strenuous sports involving jumping, cutting and pivoting manoeuvres (Noyes et al. 1989). The importance of functional performance tests in the clinical setting relates to their value in identifying or con®rming functional limitations,
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Test±retest reliability of knee rating scales
assessing the progress of rehabilitation, and determining the individual's readiness to return to their pre-injury level of activity. While functional tests cannot detect speci®c abnormalities, they provide a general measure of lower extremity function which encompasses clinical attributes such as joint stability, pain, muscle strength and power, while incorporating elements of neuromuscular coordination and coactivation, proprioception, and agility (Noyes et al. 1991; Barber et al. 1992; Wilk et al. 1994). More importantly, they provide an objective quanti®cation of dynamic knee performance under simulated activity conditions, by attempting to replicate stresses imposed on the knee in the everyday environment or during sporting activities (Lephart et al. 1992; Rudolph et al. 2000). Whilst a myriad of functional tests have been reported, the popularity of singlelimb hop tests is clearly evident in ACL outcome studies. This is not surprising given their advantage over two-legged tests of function, as the use of the uninjured limb as a biological control eliminates the need to rely on population-speci®c normative data. Any functional de®cit in the reconstructed knee is commonly described by the limb symmetry index (LSI), which re¯ects the performance of the reconstructed knee compared to the uninjured knee. In single limb hop tests, a difference in limb performance greater than 15% is classi®ed as abnormal, and may indicate an increased risk for giving way of the knee during sporting activities (Barber et al. 1992). Despite the common application of subjective rating scales and functional hop tests for predicting dynamic knee function following ACL reconstruction, few have reported their test±retest reliability. The value of these assessment tools as valid measures of knee function relies on their ability to demonstrate a high reliability, or the degree of consistency with which an instrument or rater measures a variable (Portney & Watkins 2000). This attribute is critical if criteria-based return-toactivity decisions potentially result from the objective data obtained from functional assessment tests (Clark 2001). A noteworthy study conducted by Barber-Westin et al. (1999) demonstrated the test±retest reliability of the CKRS for evaluating knee status in 50 healthy volunteers and 50 subjects with a variety of
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knee injuries. No reliability data were provided for ACL-reconstructed subjects. The reliability of functional hop tests has generally been investigated in healthy, uninjured populations (Booher et al. 1993; Bandy et al. 1994; Paterno & Greenberger 1996; Bolgla & Keskula 1997; Goh & Boyle 1997; Petschnig et al. 1998), with few studies carried out on ACL-reconstructed populations (Kramer et al. 1992; Paterno & Greenberger 1996; Brosky et al. 1999). The increasing popularity of functional outcome measures in assessing knee status highlights the need to document their reliability in speci®c populations. This study examined the test±retest reliability of the CKRS, an analogue scale, and four single-limb hop tests, in individuals one year following ACL reconstruction using the semitendinosus graft procedure. Knee function was also described using limb symmetry indices, to provide an estimation of functional recovery one year following ACL reconstruction.
Methods A total of 19 subjects comprising 13 males and six females (mean age 26.8 + SD 8.4 years, range 16±45) were recruited from the databases of two orthopaedic surgeons. These subjects represented consecutive patients who consented to participate in the study. All subjects had undergone unilateral ACL reconstruction using the semitendinosus graft, and presented at an average of 12 months (+ 6 weeks) post reconstruction. Exclusion criteria included concomitant collateral ligament damage, musculoskeletal conditions affecting the hip or ankle joints of either lower extremity, existing or previous injury to the contralateral knee, cardiorespiratory ailments or vestibular dysfunction. Subjects were evaluated by the same examiner on two occasions (Occasions One and Two) with an interval of 7 days between test occasions. This minimized the potential confounding effects on test±retest outcomes associated with true improvements in knee function over a longer interval, yet allowed adequate recovery between test occasions hence minimizing the effects of fatigue on test results. Testing was performed at approximately the same time of the day to ensure standardization
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Distance hopped
15 cm
Fig. 1 The cross over hop test.
1 metre
1 metre
Fig. 2 The stair hop test.
for the day of the week in terms of activities of daily living and function, and where possible, the tests were held in the same location under constant environmental conditions. Subjects were instructed to wear the same footwear on both testing occasions. Verbal instructions from the examiner were standardized. At the beginning of each testing occasion, subjects completed a CKRS scale, and provided an analogue score (1 to 100 points) which re¯ected their overall general perception and satisfaction with their current knee status. Prior to functional testing, subjects performed a 5 min warm up on a stationary bicycle ergometer, and static stretches for the hamstrings, quadriceps, gastrocnemius and soleus muscle groups (three 10-second stretches performed bilaterally). A practice trial of each hop test was then performed for each limb prior to actual testing, to allow subjects to familiarize themselves with the tests and to minimize possible learning effects. The limb to be tested ®rst and the order of testing of the functional hop tests were randomly determined. Three
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trials were performed for each hop test, with adequate rest periods between trials to minimize fatigue effects.
Description of hop tests Six metre timed hop (Barber et al. 1990): Subjects were required to hop as fast as possible between timing gates placed 6 m apart (Speedlight Sports Timing System). The time taken to hop 6 m was recorded in seconds. Cross over hop (Noyes et al. 1991): This test required subjects to perform three consecutive hops for maximum distance, while crossing a 15 cm wide line between each hop (Fig. 1). The subject stood on the leg to be tested on the respective side of the line. Testing was repeated if the subject touched the line or grounded the other leg. The distance from the start line to the toe of the test leg following the third hop was measured. Stair hop: Subjects were instructed to hop up, then down three steps on a three-step platform (Fig. 2). They then turned about a ®xed marker
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Test±retest reliability of knee rating scales
1 m from the platform, and hopped back over the steps through timing gates. The time taken to complete the test was recorded in seconds. Vertical hop: This consisted of a single hop for maximum height on a force plate (Advanced Metal Technologies Incorporated strain gauge based force plate, sensitivity [Fz 0.0872mv/vN]). Subjects were instructed to perform a deep squat and hop maximally landing on the same foot. The test was performed correctly when one foot landed on the plate with elbows clasped behind the back throughout. The time off the force plate was measured in milliseconds using the strain gauge based force plate. Flight times were obtained from stored data ®les using the PEAK Performance Technology Incorporated data acquisition hardware and software (Sampling Module Version 5.1.3), and reduced from analogue to digital format.
Data analysis For each hop test, the best score was utilized for data analysis, thus providing the best possible indication of maximal performance. Two factor repeated measures analysis of variance
(ANOVA) was applied to evaluate test occasion and limb main effects, and test occasion by limb interactions. Limb symmetry indices (LSI) were derived for each hop test on both testing occasions. For the 6 m timed hop and stair hop tests, the LSI was calculated by dividing uninjured limb data by reconstructed limb data, and the result multiplied by 100. For the cross over hop and vertical hop tests, the LSI was quanti®ed by dividing reconstructed limb data by uninjured limb data, and the result multiplied by 100. A one factor repeated measures ANOVA was applied to examine for testing occasion main effects for all LSI scores as well as the CKRS and analogue scores. Intraclass correlation coef®cients or ICCs (3,1) were calculated to examine the extent of agreement between testing occasions for raw hop scores, questionnaire scores, and LSI scores. For all analyses, statistical signi®cance was de®ned by a probability level of P 5 0.05.
Results Mean scores for the questionnaire scales, hop test performance and LSI are presented in
Table 1 Means, standard deviations (SD) and ranges for questionnaire scores, hop test raw scores and limb symmetry indices (LSI), for two occasions of testing performed on 19 subjects post anterior cruciate ligament reconstruction (CKRS: Cincinnati Knee Rating System) Testing occasion 1
Testing occasion 2
Mean (SD)
Range
Mean (SD)
Range
82.1 (9.9) 79.8 (11.7)
66.8±98.9 60±95
82.6 (10.4) 79.9 (10.7)
65.8±98.9 60±98
6 metre timed hop (s) Reconstructed Uninjured
2.3 (0.6) 2.2 (0.5)
1.7±3.6 1.6±3.2
2.2 (0.5) 2.1 (0.3)
1.7±3.1 1.6±2.7
Cross over hop (m) Reconstructed Uninjured
4.0 (1.0) 4.4 (0.9)
2.0±5.6 2.4±5.6
4.2 (1.2) 4.7 (1.0)
1.9±6.0 2.2±6.3
Stair hop (s) Reconstructed Uninjured
8.5 (2.8) 7.9 (1.9)
5.3±16.1 5.7±12.4
7.9 (2.3) 7.5 (1.9)
4.9±13.9 5.1±13.2
Vertical hop (s) Reconstructed Uninjured
0.34 (0.06) 0.38 (0.04)
0.23±0.44 0.31±0.44
0.35 (0.07) 0.39 (0.04)
0.21±0.44 0.31±0.47
CKRS score Analogue score
LSI (%) 6 metre timed hop Cross over hop Stair hop Vertical hop
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94.7 90.7 95.5 89.4
(10.6) (13.3) (9.9) (9.8)
65.8±107.1 52.7±106.7 76.8±108.8 69.8±100.0
95.4 88.8 96.6 89.6
(9.2) (13.5) (6.0) (13.8)
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69.8±106.6 43.2±101.9 81.6±107.5 60.1±108.8
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Table 2 Intraclass correlation coef®cients (ICC) illustrating the degree of agreement between testing occasions for questionnaire scores, hop test performance scores, and limb symmetry indices (LSI) ICC CKRS score Analogue score 6 m timed hop Reconstructed Uninjured Cross over hop Reconstructed Uninjured Stair hop Reconstructed Uninjured Vertical hop Reconstructed Uninjured LSI 6 m timed hop Cross over hop Stair hop Vertical hop
0.97 0.96 0.96 0.95 0.98 0.95 0.96 0.96 0.94 0.92 0.93 0.94 0.90 0.81
Table 1. Table 2 lists the ICC values for questionnaire scores, hop test raw scores and LSI. In general, ICCs ranged from 0.81 to 0.98, indicating very high reliability of scores between test occasions. There were no signi®cant differences between testing occasions for the CKRS and analogue scores (P 0.53 and 0.88 respectively). Signi®cant differences between testing occasions were noted for the 6 m timed hop, cross over hop, and stair hop tests (P 5 0.01), but not for the vertical hop (P 0.34). For all hop tests, both the uninjured and reconstructed limbs demonstrated improvements in raw scores on the second testing occasion (Fig. 3). Limb differences were signi®cant for all tests (P 5 0.05), with better scores demonstrated in the uninjured limb. All limb by test occasion interactions were non-signi®cant. There was no testing occasion main effect for the LSI in all the hop tests. Mean LSI scores for the hop tests ranged from 88.8 to 96.6%. Three subjects registered LSI scores of 585% in all four hop tests on both testing occasions. Additionally, there were eight other hop test performances where a LSI of 585% was recorded. These were noted in three subjects.
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Discussion Clinicians often rely on a myriad of outcome measures to assess the post-operative status of the ACL-reconstructed knee and to assist them in identifying de®cits in function. Rehabilitation progress and the individual's readiness to return to pre-injury activity levels must be measured reliably to ensure meaningful interpretation of assessment results. In the present study, the test±retest reliability of the CKRS, an analogue scale, and four single-limb functional hop tests were examined in an ACLreconstructed population. The 6 m timed hop, cross over hop, stair hop and vertical hop tests were chosen for the current study as there is little data describing their test±retest reliability for evaluating functional outcome following ACL reconstruction, yet they represent singlelimb performance tests which are commonly utilized in ACL-related studies. Intraclass corrrelation coef®cients (ICC) were used to quantify the consistency of questionnaire scores, hop test performance scores and LSI scores over two testing occasions performed one week apart. The ICC values ranged from 0.90 to 0.98 for all measured values, with the exception of the LSI for the vertical hop (ICC 0.81). These ®ndings demonstrate an excellent agreement between the two testing occasions for both questionnaire and functional test scores. It is generally advocated that ICC values should be greater than 0.90 to ensure reasonable validity of majority of clinical measurements (Portney & Watkins 2000). There are limited data in the literature for comparison purposes as the majority of investigations have been performed on uninjured populations. Similar results however were noted in ACLreconstructed subjects by Brosky et al. (1999), for the 6 m timed hop scores and an alternate version of the vertical hop (ICC 5 0.88). The test±retest reliability of the one-legged hop for distance was demonstrated in 13 ACLreconstructed subjects (ICC 0.89 for uninjured and reconstructed limbs; Paterno & Greenberger 1996). For the CKRS scale, consistently high ICC values were also reported by Barber-Westin et al. (1999), for normal subjects and subjects with injured knees (ICC 0.68 to 0.98), and suggest that subjects' overall perception of their
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Test±retest reliability of knee rating scales
Uninjured limb Reconstructed limb 5.2
6 metre timed hop
2.6
5.0
2.5
4.8
2.4
4.6
Distance (metres)
Time (seconds)
2.7
2.3 2.2 2.1
4.4 4.2 4.0
2.0
3.8
1.9
3.6
1.8
One
3.4
Two
Cross over hop
One
Two
Vertical Hop
0.39 Distance (metres)
Time (seconds)
0.41
0.37
0.35
0.33
0.31 One
Two Testing Occasion
Fig. 3 Mean uninjured and reconstructed limb performance scores (+ 95% con®dence intervals) for the 6 m timed hop, cross over hop, stair hop, and vertical hop tests, performed on two occasions of testing one week apart.
reconstructed knee status can be reliably quanti®ed using the CKRS. The high ICC values noted in the present study were supported by non-signi®cant
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differences between testing occasions for questionnaire scores, vertical hop raw scores, and LSI scores. Although statistically signi®cant differences in raw scores were noted between
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testing occasions for the 6 m timed hop, cross over hop, and stair hop tests, the clinical relevance of these differences may be questioned. From Table 1, mean differences between testing occasions were 0.1 seconds for both limbs for the 6 m timed hop, 0.2 m and 0.3 m for the reconstructed limb and uninjured limb respectively for the cross over hop, and 0.6 seconds and 0.4 seconds respectively for the stair hop test. The magnitude of these differences may be considered minimal when interpreted in relation to actual performance scores. It is likely that improvements in performance scores noted bilaterally re¯ect a learning effect over the one week, or are indicative of an improvement in the subjects' con®dence in performing the tests. Limb symmetry indices however were not statistically different between testing occasions for all the hop tests. Therefore, despite the signi®cant improvement in raw performance scores for both limbs in three of the hop tests, the ratio of reconstructed limb performance, as a function of uninjured limb performance, essentially remained consistent over the two testing occasions. These ®ndings lend further support to the utilization of single limb hop tests for within-subject between-limb comparisons. More importantly, LSI scores may be considered reliable indicators of functional outcome following reconstructive knee surgery, supporting their clinical utility as valid outcome measurement tools for evaluating patients over different sessions. Findings from the current study bear signi®cant implications for clinicians when administering functional performance tests in their evaluation of ACL-reconstructed patients. Careful consideration should be given to potential learning effects, with measures taken to minimize their in¯uence such as ensuring an appropriate warm-up prior to testing, and administration of an adequate number of trials. From studies on uninjured populations, there is general consensus that learning effects can occur when performing functional hop tests (Booher et al. 1993; Bolgla & Keskula 1997; Goh & Boyle 1997). In the present study, improvements in performance were noted bilaterally over a oneweek period, despite the utilization of the best performance score from three trials on each testing occasion. There is little agreement in the literature regarding the optimum number of
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practice and test trials for prediction of trends and achievement of maximal performance results. Protocols used have included single, two, or three test trials, with or without practice trials (Noyes et al. 1991; Booher et al. 1993; Risberg & Ekeland 1994; Bolgla & Keskula 1997; Brosky et al. 1999). Bolgla and Keskula (1997) suggest that learning effects are best stabilized by allowing an adequate number of practices and test trials, even to the extent of subjects being exposed to and practising the functional tasks the day prior to testing. Statistical ®ndings should also be interpreted cautiously, with consideration given to the clinical relevance of any changes in performance. These measures are critical in ensuring that the clinician can con®dently apply functional hop tests as timeef®cient, cost-ef®cient, and more importantly, accurate and reliable measures of rehabilitation progress and knee functional ability. Any differences in performance noted during repeated testing occasions may then be interpreted in relation to actual changes in functional outcome, rather than attributed to measurement variability. The uninjured limb generally performed better in all the four functional hop tests, as re¯ected in the raw performance scores and LSI scores (Table 1). Mean LSI scores ranged from 88.8 to 96.6%, which are generally consistent with those noted in studies of ACLreconstructed subjects one or more years following surgery (Bach et al. 1998; Petschnig et al. 1998; Risberg et al. 1999b; Sernert et al. 1999). Bach et al. (1998) reported LSI scores ranging from 94 to 96%, 24 months post reconstruction, while a mean index of 91% was noted for the one-leg hop test in 527 patients 21 to 68 months following reconstruction (Sernert et al. 1999). At the one-year post-reconstruction stage, mean LSI scores of 96% and 91.4% were reported for the triple jump test and 22-step stair hop test respectively (Risberg et al. 1999b). Slightly lower values however were noted for the vertical jump, single hop, and triple hop, in an evaluation of 25 subjects 54 weeks following surgery (74.9%, 88.4%, and 89.5% respectively) (Petschnig et al. 1998). While performance de®cits may be attributed to various factors such as deconditioning of the limb musculature post injury and post surgery, strength de®cits, pain and psychological attributes, a limb difference of
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Test±retest reliability of knee rating scales
15% or less is shown to represent normal variation, regardless of limb dominance or sporting levels (Barber et al. 1990; Barber et al. 1992). In the study by Barber et al. (1990), 93 and 92% of the normal population tested demonstrated LSI scores of 85% or greater for the one-legged hop for distance and timed hop respectively. The range of LSI scores demonstrated in the current study is therefore generally comparable with healthy uninjured populations, suggesting that reconstructed limb function had returned to within normal limits in the majority of subjects. An analysis of individual performances however indicated persistent limb asymmetry in a small percentage of subjects. In particular, abnormal LSI scores were noted in all hop tests in three subjects, while three others registered performance de®ciencies in a number of the tests. Despite the relatively small number of subjects involved in the current study, these ®ndings re¯ect the varied nature of functional recovery one year following ACL reconstructive surgery. It is acknowledged however that the variance in time elapsed since surgery may account for intersubject differences in functional performance, given a potential 3 month variation between subjects at the point of testing.
Conclusion This study has demonstrated the test±retest reliability of the CKRS, an analogue scale, and four single limb functional tests in an ACLreconstructed population, supporting their application in the assessment of this speci®c patient group over different sessions. At the one-year post ACL reconstruction phase, LSI scores for four hop tests were within normal variation in the majority of subjects.
Acknowledgements The authors wish to thank orthopaedic surgeons Mr Graham Forward and Mr Keith Holt for providing access to their patient databases. This study was supported by a grant from the Physiotherapy Research Foundation (Australian Physiotherapy Association) and the New South Wales Sports Physiotherapy Group.
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References Bach B R, Levy M E, Bojchuk J, Tradonsky S, Bush-Joseph C A, Khan N H 1998 Single-incision endoscopic anterior cruciate ligament reconstruction using patellar tendon autograft: Minimum two-year follow-up evaluation. American Journal of Sports Medicine 26: 30±40 Bandy W, Rusche K, Tekulve F 1994 Reliability and limb symmetry for ®ve unilateral functional tests of the lower extremities. Isokinetics and Exercise Science 4: 108±111 Barber S D, Noyes F R, Mangine R, DeMaio M 1992 Rehabilitation after ACL reconstruction: Function testing. Orthopaedics 15: 969±974 Barber S D, Noyes F R, Mangine R E, McCloskey J W, Hartman W 1990 Quantitative assessment of functional limitations in normal and anterior cruciate ligamentde®cient knees. Clinical Orthopaedics and Related Research 255: 204±214 Barber-Westin S, Noyes F, McCloskey J 1999 Rigorous statistical reliability, validity, and responsiveness testing of the Cincinnati Knee Rating System in 350 subjects with uninjured, injured, or anterior cruciate ligamentreconstructed knees. American Journal of Sports Medicine 27: 402±416 Bolgla L A, Keskula D R 1997 Reliability of lower extremity functional performance tests. Journal of Orthopaedic and Sports Physical Therapy 26: 138±142 Booher L D, Hench K M, Worrell T W, Stikeleather J 1993 Reliability of three single leg hop tests. Journal of Sports Rehabilitation 2: 165±170 Brosky J, Nitz A, Malone T, Caborn D, Rayens M 1999 Intrarater reliability of selected clinical outcome measures following anterior cruciate ligament reconstruction. Journal of Orthopaedic and Sports Physical Therapy 29: 39±48 Clark N 2001 Functional performance testing following knee ligament injury. Physical Therapy in Sport 2: 91±105 Goh S, Boyle J J W 1997 Self evaluation and functional testing two to four years post ACL reconstruction. Australian Journal of Physiotherapy 43: 255±262 Kramer J, Nusca D, Fowler P, Webster-Bogaert S 1992 Test± retest reliability of the one leg hop test following ACL reconstruction. Clinical Journal of Sport Medicine 2: 240±243 Lephart S M, Perrin D H, Fu F H, Gieck J H, McCue F C III, Irrgang J J 1992 Relationship between selected physical characteristics and functional capacity in the anterior cruciate ligament-insuf®cient athlete. Journal of Orthopaedic and Sports Physical Therapy 16: 174±181 Lysholm J, Gillquist J 1982 Evaluation of knee ligament surgery results with special emphasis on use of a scoring scale. American Journal of Sports Medicine 10: 150±154 Noyes F R, Barber S D, Mangine R E 1981 Abnormal lower limb symmetry determined by functional hop tests after anterior cruciate ligament rupture. American Journal of Sports Medicine 19: 513±518 Noyes F R, Barber S D, Mooar L A 1989 A rationale for assessing sports activity levels and limitations in knee disorders. Clinical Orthopaedics and Related Research 246: 238±249
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Noyes F R, McGinniss G H, Mooar L A 1984 Functional disability in the anterior cruciate insuf®cient knee syndrome. Review of knee rating systems and projected risk factors in determining treatment. Sports Medicine 1: 278±302 Paterno M V, Greenberger H B 1996 The test±retest reliability of a one legged hop for distance in young adults with and without ACL reconstruction. Isokinetics and Exercise Science 6: 1±6 Petschnig R, Baron R, Albrecht M 1998 The relationship between isokinetic quadriceps strength test and hop tests for distance and one-legged vertical jump test following anterior cruciate ligament reconstruction. Journal of Orthopaedic and Sports Physical Therapy 28: 23±31 Portney L, Watkins M 2000 Foundations of Clinical Research. Applications to Practice, 2nd edn. New Jersey: Prentice Hall Risberg M, Holm I, Steen H, Beynnon B 1999a Sensitivity to changes over time for the IKDC form, the Lysholm score, and the Cincinnati knee score. Knee Surgery, Sports Traumatology, Arthroscopy 7: 152±159 Risberg M, Holm I, Tjomsland O, Ljunggren E, Ekeland A 1999b Prospective study of changes in impairments and disabilities after anterior cruciate ligament reconstruction. Journal of Orthopaedic and Sports Physical Therapy 29: 400±412
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Test±retest reliability of knee rating scales and functional hop tests one year following anterior cruciate ligament reconstruction Diana M. Hopper, Suet C. Goh, Laurel A. Wentworth, Derek Y. K. Chan, Jay H. W. Chau, Gregory J. Wootton, Geoffrey R. Strauss and Jeffrey J. W. Boyle
Diana M. Hopper PhD Suet C. Goh PhD Laurel A. Wentworth MSportsPhty Derek Y. K. Chan MSportsPhyty Jay H. W. Chau MSportsPhyty
Objectives: The aim of this study was to examine the test±retest reliability of the Cincinnati Knee Rating System and analogue scale, and four hop tests in subjects following anterior cruciate ligament (ACL) reconstruction, and to describe knee function one year following surgery. Design: Within-subject quasi-experimental design for test±retest reliability. Setting: A university rehabilitation laboratory. Participants: Nineteen subjects presenting at 12 months post ACL reconstruction were recruited from two orthopaedic surgeons. Main outcome measures: Knee rating scores, raw performance scores for the 6 m timed hop, cross over hop, stair hop and vertical hop, and hop test limb symmetry indices (LSI) were compared on two testing occasions, performed one week apart. Results: Intraclass correlation coef®cients (ICC) indicated high test±retest reliability for all measured parameters (0.81±0.98). No signi®cant difference between test occasions was observed for the knee rating scales and vertical hop raw scores. Signi®cant differences were noted for raw scores in the remaining hop tests (P 5 0.01). The LSI scores for all hop tests were not signi®cantly different between the two occasions. Mean values ranged from 88.8% to 96.6%. Conclusions: The knee rating scales and functional hop tests showed high test±retest reliability in an ACL-reconstructed population, supporting their use for evaluating this speci®c patient group over different sessions. Reconstructed limb functional performances were within normal limb c 2002 Harcourt Publishers Ltd symmetry values one year following surgery. *
Geoffrey R. Strauss MPE
Introduction
Jeffrey J. W. Boyle GradDipManipTher School of Physiotherapy, Curtin University of Technology, Selby Street, Shenton Park, Western Australia 6008, Australia
In recent years, clinical evaluation of the anterior cruciate ligament (ACL) reconstructed knee has gradually evolved from traditional orthopaedic testing to incorporate more functional means of assessment. This has given rise to the popularity of numerous knee rating systems (Lysholm & Gillquist 1982; Noyes et al. 1984; Tegner & Lysholm 1985; Risberg et al. 1999a) and functional assessment tests (Tegner et al. 1986; Barber et al. 1990; Noyes et al. 1991; Lephart et al. 1992; Risberg & Ekeland 1994; Wilk et al. 1994; Risberg et al. 1999b), in the attempt to provide a clearer indication of the
Correspondence to: Diana M. Hopper, Tel: 61 8 9266 3631; Fax: 61 8 9266 3636; E-mail: D.Hopper@curtin. edu.au
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doi : 10.1054/ptsp.2001.0094, available online at http://www.idealibrary.com on
status of the reconstructed knee. Amongst the many subjective rating scales documented in the literature, the commonly utilized Cincinnati Knee Rating System (CKRS) is reported to most precisely de®ne functional outcome (Sgaglione et al. 1995), and is highly sensitive to changes in knee function over time (Risberg et al. 1999a). It is suggested that a CKRS score of 85% or greater is suf®cient for the knee to withstand regular participation in strenuous sports involving jumping, cutting and pivoting manoeuvres (Noyes et al. 1989). The importance of functional performance tests in the clinical setting relates to their value in identifying or con®rming functional limitations,
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Test±retest reliability of knee rating scales
assessing the progress of rehabilitation, and determining the individual's readiness to return to their pre-injury level of activity. While functional tests cannot detect speci®c abnormalities, they provide a general measure of lower extremity function which encompasses clinical attributes such as joint stability, pain, muscle strength and power, while incorporating elements of neuromuscular coordination and coactivation, proprioception, and agility (Noyes et al. 1991; Barber et al. 1992; Wilk et al. 1994). More importantly, they provide an objective quanti®cation of dynamic knee performance under simulated activity conditions, by attempting to replicate stresses imposed on the knee in the everyday environment or during sporting activities (Lephart et al. 1992; Rudolph et al. 2000). Whilst a myriad of functional tests have been reported, the popularity of singlelimb hop tests is clearly evident in ACL outcome studies. This is not surprising given their advantage over two-legged tests of function, as the use of the uninjured limb as a biological control eliminates the need to rely on population-speci®c normative data. Any functional de®cit in the reconstructed knee is commonly described by the limb symmetry index (LSI), which re¯ects the performance of the reconstructed knee compared to the uninjured knee. In single limb hop tests, a difference in limb performance greater than 15% is classi®ed as abnormal, and may indicate an increased risk for giving way of the knee during sporting activities (Barber et al. 1992). Despite the common application of subjective rating scales and functional hop tests for predicting dynamic knee function following ACL reconstruction, few have reported their test±retest reliability. The value of these assessment tools as valid measures of knee function relies on their ability to demonstrate a high reliability, or the degree of consistency with which an instrument or rater measures a variable (Portney & Watkins 2000). This attribute is critical if criteria-based return-toactivity decisions potentially result from the objective data obtained from functional assessment tests (Clark 2001). A noteworthy study conducted by Barber-Westin et al. (1999) demonstrated the test±retest reliability of the CKRS for evaluating knee status in 50 healthy volunteers and 50 subjects with a variety of
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knee injuries. No reliability data were provided for ACL-reconstructed subjects. The reliability of functional hop tests has generally been investigated in healthy, uninjured populations (Booher et al. 1993; Bandy et al. 1994; Paterno & Greenberger 1996; Bolgla & Keskula 1997; Goh & Boyle 1997; Petschnig et al. 1998), with few studies carried out on ACL-reconstructed populations (Kramer et al. 1992; Paterno & Greenberger 1996; Brosky et al. 1999). The increasing popularity of functional outcome measures in assessing knee status highlights the need to document their reliability in speci®c populations. This study examined the test±retest reliability of the CKRS, an analogue scale, and four single-limb hop tests, in individuals one year following ACL reconstruction using the semitendinosus graft procedure. Knee function was also described using limb symmetry indices, to provide an estimation of functional recovery one year following ACL reconstruction.
Methods A total of 19 subjects comprising 13 males and six females (mean age 26.8 + SD 8.4 years, range 16±45) were recruited from the databases of two orthopaedic surgeons. These subjects represented consecutive patients who consented to participate in the study. All subjects had undergone unilateral ACL reconstruction using the semitendinosus graft, and presented at an average of 12 months (+ 6 weeks) post reconstruction. Exclusion criteria included concomitant collateral ligament damage, musculoskeletal conditions affecting the hip or ankle joints of either lower extremity, existing or previous injury to the contralateral knee, cardiorespiratory ailments or vestibular dysfunction. Subjects were evaluated by the same examiner on two occasions (Occasions One and Two) with an interval of 7 days between test occasions. This minimized the potential confounding effects on test±retest outcomes associated with true improvements in knee function over a longer interval, yet allowed adequate recovery between test occasions hence minimizing the effects of fatigue on test results. Testing was performed at approximately the same time of the day to ensure standardization
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Distance hopped
15 cm
Fig. 1 The cross over hop test.
1 metre
1 metre
Fig. 2 The stair hop test.
for the day of the week in terms of activities of daily living and function, and where possible, the tests were held in the same location under constant environmental conditions. Subjects were instructed to wear the same footwear on both testing occasions. Verbal instructions from the examiner were standardized. At the beginning of each testing occasion, subjects completed a CKRS scale, and provided an analogue score (1 to 100 points) which re¯ected their overall general perception and satisfaction with their current knee status. Prior to functional testing, subjects performed a 5 min warm up on a stationary bicycle ergometer, and static stretches for the hamstrings, quadriceps, gastrocnemius and soleus muscle groups (three 10-second stretches performed bilaterally). A practice trial of each hop test was then performed for each limb prior to actual testing, to allow subjects to familiarize themselves with the tests and to minimize possible learning effects. The limb to be tested ®rst and the order of testing of the functional hop tests were randomly determined. Three
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trials were performed for each hop test, with adequate rest periods between trials to minimize fatigue effects.
Description of hop tests Six metre timed hop (Barber et al. 1990): Subjects were required to hop as fast as possible between timing gates placed 6 m apart (Speedlight Sports Timing System). The time taken to hop 6 m was recorded in seconds. Cross over hop (Noyes et al. 1991): This test required subjects to perform three consecutive hops for maximum distance, while crossing a 15 cm wide line between each hop (Fig. 1). The subject stood on the leg to be tested on the respective side of the line. Testing was repeated if the subject touched the line or grounded the other leg. The distance from the start line to the toe of the test leg following the third hop was measured. Stair hop: Subjects were instructed to hop up, then down three steps on a three-step platform (Fig. 2). They then turned about a ®xed marker
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Test±retest reliability of knee rating scales
1 m from the platform, and hopped back over the steps through timing gates. The time taken to complete the test was recorded in seconds. Vertical hop: This consisted of a single hop for maximum height on a force plate (Advanced Metal Technologies Incorporated strain gauge based force plate, sensitivity [Fz 0.0872mv/vN]). Subjects were instructed to perform a deep squat and hop maximally landing on the same foot. The test was performed correctly when one foot landed on the plate with elbows clasped behind the back throughout. The time off the force plate was measured in milliseconds using the strain gauge based force plate. Flight times were obtained from stored data ®les using the PEAK Performance Technology Incorporated data acquisition hardware and software (Sampling Module Version 5.1.3), and reduced from analogue to digital format.
Data analysis For each hop test, the best score was utilized for data analysis, thus providing the best possible indication of maximal performance. Two factor repeated measures analysis of variance
(ANOVA) was applied to evaluate test occasion and limb main effects, and test occasion by limb interactions. Limb symmetry indices (LSI) were derived for each hop test on both testing occasions. For the 6 m timed hop and stair hop tests, the LSI was calculated by dividing uninjured limb data by reconstructed limb data, and the result multiplied by 100. For the cross over hop and vertical hop tests, the LSI was quanti®ed by dividing reconstructed limb data by uninjured limb data, and the result multiplied by 100. A one factor repeated measures ANOVA was applied to examine for testing occasion main effects for all LSI scores as well as the CKRS and analogue scores. Intraclass correlation coef®cients or ICCs (3,1) were calculated to examine the extent of agreement between testing occasions for raw hop scores, questionnaire scores, and LSI scores. For all analyses, statistical signi®cance was de®ned by a probability level of P 5 0.05.
Results Mean scores for the questionnaire scales, hop test performance and LSI are presented in
Table 1 Means, standard deviations (SD) and ranges for questionnaire scores, hop test raw scores and limb symmetry indices (LSI), for two occasions of testing performed on 19 subjects post anterior cruciate ligament reconstruction (CKRS: Cincinnati Knee Rating System) Testing occasion 1
Testing occasion 2
Mean (SD)
Range
Mean (SD)
Range
82.1 (9.9) 79.8 (11.7)
66.8±98.9 60±95
82.6 (10.4) 79.9 (10.7)
65.8±98.9 60±98
6 metre timed hop (s) Reconstructed Uninjured
2.3 (0.6) 2.2 (0.5)
1.7±3.6 1.6±3.2
2.2 (0.5) 2.1 (0.3)
1.7±3.1 1.6±2.7
Cross over hop (m) Reconstructed Uninjured
4.0 (1.0) 4.4 (0.9)
2.0±5.6 2.4±5.6
4.2 (1.2) 4.7 (1.0)
1.9±6.0 2.2±6.3
Stair hop (s) Reconstructed Uninjured
8.5 (2.8) 7.9 (1.9)
5.3±16.1 5.7±12.4
7.9 (2.3) 7.5 (1.9)
4.9±13.9 5.1±13.2
Vertical hop (s) Reconstructed Uninjured
0.34 (0.06) 0.38 (0.04)
0.23±0.44 0.31±0.44
0.35 (0.07) 0.39 (0.04)
0.21±0.44 0.31±0.47
CKRS score Analogue score
LSI (%) 6 metre timed hop Cross over hop Stair hop Vertical hop
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94.7 90.7 95.5 89.4
(10.6) (13.3) (9.9) (9.8)
65.8±107.1 52.7±106.7 76.8±108.8 69.8±100.0
95.4 88.8 96.6 89.6
(9.2) (13.5) (6.0) (13.8)
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69.8±106.6 43.2±101.9 81.6±107.5 60.1±108.8
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Table 2 Intraclass correlation coef®cients (ICC) illustrating the degree of agreement between testing occasions for questionnaire scores, hop test performance scores, and limb symmetry indices (LSI) ICC CKRS score Analogue score 6 m timed hop Reconstructed Uninjured Cross over hop Reconstructed Uninjured Stair hop Reconstructed Uninjured Vertical hop Reconstructed Uninjured LSI 6 m timed hop Cross over hop Stair hop Vertical hop
0.97 0.96 0.96 0.95 0.98 0.95 0.96 0.96 0.94 0.92 0.93 0.94 0.90 0.81
Table 1. Table 2 lists the ICC values for questionnaire scores, hop test raw scores and LSI. In general, ICCs ranged from 0.81 to 0.98, indicating very high reliability of scores between test occasions. There were no signi®cant differences between testing occasions for the CKRS and analogue scores (P 0.53 and 0.88 respectively). Signi®cant differences between testing occasions were noted for the 6 m timed hop, cross over hop, and stair hop tests (P 5 0.01), but not for the vertical hop (P 0.34). For all hop tests, both the uninjured and reconstructed limbs demonstrated improvements in raw scores on the second testing occasion (Fig. 3). Limb differences were signi®cant for all tests (P 5 0.05), with better scores demonstrated in the uninjured limb. All limb by test occasion interactions were non-signi®cant. There was no testing occasion main effect for the LSI in all the hop tests. Mean LSI scores for the hop tests ranged from 88.8 to 96.6%. Three subjects registered LSI scores of 585% in all four hop tests on both testing occasions. Additionally, there were eight other hop test performances where a LSI of 585% was recorded. These were noted in three subjects.
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Discussion Clinicians often rely on a myriad of outcome measures to assess the post-operative status of the ACL-reconstructed knee and to assist them in identifying de®cits in function. Rehabilitation progress and the individual's readiness to return to pre-injury activity levels must be measured reliably to ensure meaningful interpretation of assessment results. In the present study, the test±retest reliability of the CKRS, an analogue scale, and four single-limb functional hop tests were examined in an ACLreconstructed population. The 6 m timed hop, cross over hop, stair hop and vertical hop tests were chosen for the current study as there is little data describing their test±retest reliability for evaluating functional outcome following ACL reconstruction, yet they represent singlelimb performance tests which are commonly utilized in ACL-related studies. Intraclass corrrelation coef®cients (ICC) were used to quantify the consistency of questionnaire scores, hop test performance scores and LSI scores over two testing occasions performed one week apart. The ICC values ranged from 0.90 to 0.98 for all measured values, with the exception of the LSI for the vertical hop (ICC 0.81). These ®ndings demonstrate an excellent agreement between the two testing occasions for both questionnaire and functional test scores. It is generally advocated that ICC values should be greater than 0.90 to ensure reasonable validity of majority of clinical measurements (Portney & Watkins 2000). There are limited data in the literature for comparison purposes as the majority of investigations have been performed on uninjured populations. Similar results however were noted in ACLreconstructed subjects by Brosky et al. (1999), for the 6 m timed hop scores and an alternate version of the vertical hop (ICC 5 0.88). The test±retest reliability of the one-legged hop for distance was demonstrated in 13 ACLreconstructed subjects (ICC 0.89 for uninjured and reconstructed limbs; Paterno & Greenberger 1996). For the CKRS scale, consistently high ICC values were also reported by Barber-Westin et al. (1999), for normal subjects and subjects with injured knees (ICC 0.68 to 0.98), and suggest that subjects' overall perception of their
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Test±retest reliability of knee rating scales
Uninjured limb Reconstructed limb 5.2
6 metre timed hop
2.6
5.0
2.5
4.8
2.4
4.6
Distance (metres)
Time (seconds)
2.7
2.3 2.2 2.1
4.4 4.2 4.0
2.0
3.8
1.9
3.6
1.8
One
3.4
Two
Cross over hop
One
Two
Vertical Hop
0.39 Distance (metres)
Time (seconds)
0.41
0.37
0.35
0.33
0.31 One
Two Testing Occasion
Fig. 3 Mean uninjured and reconstructed limb performance scores (+ 95% con®dence intervals) for the 6 m timed hop, cross over hop, stair hop, and vertical hop tests, performed on two occasions of testing one week apart.
reconstructed knee status can be reliably quanti®ed using the CKRS. The high ICC values noted in the present study were supported by non-signi®cant
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differences between testing occasions for questionnaire scores, vertical hop raw scores, and LSI scores. Although statistically signi®cant differences in raw scores were noted between
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testing occasions for the 6 m timed hop, cross over hop, and stair hop tests, the clinical relevance of these differences may be questioned. From Table 1, mean differences between testing occasions were 0.1 seconds for both limbs for the 6 m timed hop, 0.2 m and 0.3 m for the reconstructed limb and uninjured limb respectively for the cross over hop, and 0.6 seconds and 0.4 seconds respectively for the stair hop test. The magnitude of these differences may be considered minimal when interpreted in relation to actual performance scores. It is likely that improvements in performance scores noted bilaterally re¯ect a learning effect over the one week, or are indicative of an improvement in the subjects' con®dence in performing the tests. Limb symmetry indices however were not statistically different between testing occasions for all the hop tests. Therefore, despite the signi®cant improvement in raw performance scores for both limbs in three of the hop tests, the ratio of reconstructed limb performance, as a function of uninjured limb performance, essentially remained consistent over the two testing occasions. These ®ndings lend further support to the utilization of single limb hop tests for within-subject between-limb comparisons. More importantly, LSI scores may be considered reliable indicators of functional outcome following reconstructive knee surgery, supporting their clinical utility as valid outcome measurement tools for evaluating patients over different sessions. Findings from the current study bear signi®cant implications for clinicians when administering functional performance tests in their evaluation of ACL-reconstructed patients. Careful consideration should be given to potential learning effects, with measures taken to minimize their in¯uence such as ensuring an appropriate warm-up prior to testing, and administration of an adequate number of trials. From studies on uninjured populations, there is general consensus that learning effects can occur when performing functional hop tests (Booher et al. 1993; Bolgla & Keskula 1997; Goh & Boyle 1997). In the present study, improvements in performance were noted bilaterally over a oneweek period, despite the utilization of the best performance score from three trials on each testing occasion. There is little agreement in the literature regarding the optimum number of
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practice and test trials for prediction of trends and achievement of maximal performance results. Protocols used have included single, two, or three test trials, with or without practice trials (Noyes et al. 1991; Booher et al. 1993; Risberg & Ekeland 1994; Bolgla & Keskula 1997; Brosky et al. 1999). Bolgla and Keskula (1997) suggest that learning effects are best stabilized by allowing an adequate number of practices and test trials, even to the extent of subjects being exposed to and practising the functional tasks the day prior to testing. Statistical ®ndings should also be interpreted cautiously, with consideration given to the clinical relevance of any changes in performance. These measures are critical in ensuring that the clinician can con®dently apply functional hop tests as timeef®cient, cost-ef®cient, and more importantly, accurate and reliable measures of rehabilitation progress and knee functional ability. Any differences in performance noted during repeated testing occasions may then be interpreted in relation to actual changes in functional outcome, rather than attributed to measurement variability. The uninjured limb generally performed better in all the four functional hop tests, as re¯ected in the raw performance scores and LSI scores (Table 1). Mean LSI scores ranged from 88.8 to 96.6%, which are generally consistent with those noted in studies of ACLreconstructed subjects one or more years following surgery (Bach et al. 1998; Petschnig et al. 1998; Risberg et al. 1999b; Sernert et al. 1999). Bach et al. (1998) reported LSI scores ranging from 94 to 96%, 24 months post reconstruction, while a mean index of 91% was noted for the one-leg hop test in 527 patients 21 to 68 months following reconstruction (Sernert et al. 1999). At the one-year post-reconstruction stage, mean LSI scores of 96% and 91.4% were reported for the triple jump test and 22-step stair hop test respectively (Risberg et al. 1999b). Slightly lower values however were noted for the vertical jump, single hop, and triple hop, in an evaluation of 25 subjects 54 weeks following surgery (74.9%, 88.4%, and 89.5% respectively) (Petschnig et al. 1998). While performance de®cits may be attributed to various factors such as deconditioning of the limb musculature post injury and post surgery, strength de®cits, pain and psychological attributes, a limb difference of
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Test±retest reliability of knee rating scales
15% or less is shown to represent normal variation, regardless of limb dominance or sporting levels (Barber et al. 1990; Barber et al. 1992). In the study by Barber et al. (1990), 93 and 92% of the normal population tested demonstrated LSI scores of 85% or greater for the one-legged hop for distance and timed hop respectively. The range of LSI scores demonstrated in the current study is therefore generally comparable with healthy uninjured populations, suggesting that reconstructed limb function had returned to within normal limits in the majority of subjects. An analysis of individual performances however indicated persistent limb asymmetry in a small percentage of subjects. In particular, abnormal LSI scores were noted in all hop tests in three subjects, while three others registered performance de®ciencies in a number of the tests. Despite the relatively small number of subjects involved in the current study, these ®ndings re¯ect the varied nature of functional recovery one year following ACL reconstructive surgery. It is acknowledged however that the variance in time elapsed since surgery may account for intersubject differences in functional performance, given a potential 3 month variation between subjects at the point of testing.
Conclusion This study has demonstrated the test±retest reliability of the CKRS, an analogue scale, and four single limb functional tests in an ACLreconstructed population, supporting their application in the assessment of this speci®c patient group over different sessions. At the one-year post ACL reconstruction phase, LSI scores for four hop tests were within normal variation in the majority of subjects.
Acknowledgements The authors wish to thank orthopaedic surgeons Mr Graham Forward and Mr Keith Holt for providing access to their patient databases. This study was supported by a grant from the Physiotherapy Research Foundation (Australian Physiotherapy Association) and the New South Wales Sports Physiotherapy Group.
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