http://informahealthcare.com/dre ISSN 0963-8288 print/ISSN 1464-5165 online Disabil Rehabil, Early Online: 1–4 ! 2015 Informa UK Ltd. DOI: 10.3109/09638288.2015.1046565

RESEARCH PAPER

Reliability of measuring hip abductor strength following total knee arthroplasty using a hand-held dynamometer Margaret B. Schache1,2, Jodie A. McClelland1, and Kate E. Webster1 School of Allied Health, La Trobe University, Melbourne, Australia, and 2Donvale Rehabilitation Hospital, Ramsay Health Care, Melbourne, Australia

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Abstract

Keywords

Purpose: To investigate the test–retest reliability of measuring hip abductor strength in patients with total knee arthroplasty (TKA) using a hand-held dynamometer (HHD) with two different types of resistance: belt and manual resistance. Method: Test–retest reliability of 30 subjects (17 female, 13 male, 71.9 ± 7.4 years old), 9.2 ± 2.7 days post TKA was measured using belt and therapist resistance. Retest reliability was calculated with intra-class coefficients (ICC3,1) and 95% confidence intervals (CI) for both the group average and the individual scores. A paired t-test assessed whether a difference existed between the belt and therapist methods of resistance. Results: ICCs were 0.82 and 0.80 for the belt and therapist resisted methods, respectively. Hip abductor strength increases of 8 N (14%) for belt resisted and 14 N (17%) for therapist resisted measurements of the group average exceeded the 95% CI and may represent real change. For individuals, hip abductor strength increases of 33 N (72%) (belt resisted) and 57 N (79%) (therapist resisted) could be interpreted as real change. Conclusions: Hip abductor strength can be reliably measured using HHD in the clinical setting with the described protocol. Belt resistance demonstrated slightly higher test–retest reliability.

Hip abductor, knee replacement, muscle strength History Received 5 July 2014 Revised 30 December 2014 Accepted 27 April 2015 Published online 19 May 2015

ä Implications for Rehabilitation  

Reliable measurement of hip abductor muscle strength in patients with TKA is important to ensure deficiencies are addressed in rehabilitation programs and function is maximized. Hip abductor strength can be reliably measured with a hand-held dynamometer in the clinical setting using manual or belt resistance.

Introduction End-stage knee osteoarthritis (OA) is a significant health issue resulting in pain, disability and diminished quality of life [1,2]. The number of total knee arthroplasty (TKA) procedures performed in the management of OA continues to increase each year [3]. Outcome studies of patients following TKA have demonstrated persistent reduced muscle strength in multiple lower limb muscle groups [4]. Ongoing lower limb muscle weakness has detrimental effects on many functional activities such as walking, climbing stairs and rising from a chair [5,6]. Whilst the strength of the quadriceps has been emphasized in both post-operative rehabilitation programs [7–9] and lower limb

Address for correspondence: Margaret B. Schache, Donvale Rehabilitation Hospital, Ramsay Health Care, 1119 Doncaster Rd, Donvale, Melbourne 3111, Australia. Tel (work): +61 3 9841 1257. E-mail: [email protected]

strength evaluation [4], the importance of measuring hip abductor strength is becoming increasingly debated. Hip abductor weakness is present in people with knee OA [10] and is likely to persist following TKA. Post-operative knee pain, reduced demands on the operated limb in the early post-operative period and habitual gait patterns may also contribute to further reductions in hip abductor strength and activation [11]. Hip abductor weakness in TKA patients is associated with reduced ability to walk curved and straight paths, ascend and descend stairs, and rise from a chair [12]. Therefore, it is important to measure hip abductor strength reliably so that any deficiencies may be addressed in rehabilitation programs to further improve function post TKA. The hand-held dynamometer (HHD) is a clinically useful tool for measuring strength. The reliability of measuring hip abductor strength using HHD has, however, not been established in a knee joint replacement population. Previous studies investigating the test–retest reliability of measuring hip abductor strength in other populations such as healthy adults, or adults with knee and hip OA have reported high levels of reliability [10,13,14] but there has been some concern about the effect of the tester’s strength on the reliability [15]. Resistance provided by a belt has been recommended over therapist resistance by some authors to negate

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instances where the strength of the patient may exceed that of the tester [15,16]. There is a need to investigate the test–retest reliability of both methods of testing hip abductor strength in patients following TKA. The aim of this study was to examine the test–retest reliability of measuring hip abductor strength in patients with TKA using a HHD with two different types of resistance: belt and therapist resistance.

Method

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Subjects Thirty patients (17 females and 13 males) with a primary unilateral TKA were recruited from a metropolitan rehabilitation hospital between July and November 2013. Patients were eligible if they were over 50 years of age and underwent a primary unilateral TKA in the previous three weeks. Patients were excluded if they had unstable medical conditions preventing participation in the rehabilitation program, history of ipsilateral hip arthroplasty or fracture, neurological or any other conditions affecting strength or function of the lower limbs.

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Participants randomly allocated to Group A were tested under the belt resisted condition first followed by the therapist resisted condition after a 10-min rest. Testing order was reversed for participants in Group B. The test procedure was repeated on the following day to determine test–retest reliability of measuring hip abductor strength. All patients also attended their usual daily physiotherapy sessions in addition to the testing. Pain experienced during the testing was recorded on a visual analogue scale. A sample size of 30 was enrolled based on the desire for interrater reliability of at least 0.8 and accepting a minimum reliability of 0.5 (the calculations were based on two observations and required a minimum of 22 participants for a ¼ 0.05 and  ¼ 0.20) [20].

Procedure This research was approved by the institutions’ Human Ethics Research Committee (FHEC 13/114). All participants gave written informed consent prior to data collection. All tests were performed in a clinical examination room on an adjustable plinth at the rehabilitation hospital. Isometric muscle strength was measured in Newtons using the Power Track II Commander (J-TECH medical). A single physiotherapist (MS) performed all the testing. Hip abductor strength of the operated limb was measured under two different conditions: belt resistance and therapist resistance. Patients participated in a simulated testing procedure the day prior to the first test to allow for familiarization with the protocol and device. Patients were randomly assigned to either Group A or Group B which determined the order of belt and therapist resistances. This was to reduce any potential learning effects that a particular order of manual or belt resistance may have on hip abductor strength measurements. Patients were positioned supine with both hips in neutral abduction and rotation. Under both conditions, the HHD was placed 5 cm proximal to the lateral femoral condyle. Although resistance applied near the ankle to create a longer lever has demonstrated greater reliability in healthy subjects [17] a shorter lever where resistance is applied proximal to the knee joint was required to avoid stress on the recent knee replacement. Under the belt resisted condition, stabilization of the HHD was achieved by wrapping a seatbelt around the HHD and securing it to a rail on the adjacent wall at plinth height (Figure 1). Under the therapist resisted condition, the HHD was held in place and movement resisted by the therapist (Figure 2). Participants were asked to push against the HHD by abducting their limb. The participant practiced the test procedure by performing two to three submaximal isometric contractions until they were familiar with the correct action. The participant then performed a maximal voluntary isometric contraction (MVC) against the dynamometer and belt or therapist resistance, held for 5 s. The highest of three consecutive measures was recorded as the MVC. Taking three consecutive measures ensures the maximum isometric contraction was attained [18]. There was a 30-s rest between each trial and a standardized command of ‘‘go ahead, push, push, push, push and relax’’ [19]. After a 10-min rest, the three MVCs were repeated using the other condition. The 10-min rest was used to avoid fatigue and allow time to change the set-up.

Figure 1. Measurement of hip abductor strength using belt resistance.

Figure 2. Measurement of hip abductor strength using therapist resistance.

Reliability of hip strength measurement in TKA

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DOI: 10.3109/09638288.2015.1046565

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Statistical analysis

Results

Descriptive statistics were calculated for hip abductor strength obtained at the test sessions. Data were assessed for normality using the Shapiro–Wilk test. Relative reliability was calculated using intra-class coefficients (ICC3,1) with 95% confidence intervals (CI). ICCs were interpreted as excellent if values were greater than 0.75, moderate if values were 0.40–0.75 and poor if values were less than 0.40 [21]. Absolute reliability was calculated using 95% CI [22]. The 95% CI provides information about how much change would be required to be 95% confident that a real change had occurred. This was calculated for group and individual scores to illustrate the reliability of assessing hip abductor strength in an individual or in a group across two testing sessions. A 95% CI for the group mean score was derived from the difference between means of paired scores according to the formula:

The patients’ demographic data are summarized in Table 1. All patients had either stage 3 or stage 4 radiographic OA changes as measured on the Kellgren–Lawrence scale prior to TKA. Fifteen patients had their left limb operated and 15 had their right limb operated. All patients could walk a minimum of 20 m and used either crutches (76.7%) or a frame (23.3%) at the time of testing. The patients experienced negligible pain from the test procedure. When patients reported pain it was located around the knee as a result of the operative procedure and did not change during the testing. Test–retest reliability results are shown in Table 2. ICCs for measurement of hip abductor strength were excellent and slightly more reliable when a belt was used (ICC ¼ 0.82) compared with therapist resistance (ICC ¼ 0.80). The magnitudes of hip abductor strength were significantly higher when measured using the therapist resistance set-up than the seatbelt resistance set-up (p50.0001). To be 95% confident that a real change in an individual’s strength had occurred the difference in strength between the two measurements needs to be greater than 32.5 N (72%) in the belt resistance set-up, and greater than 57.1 N (79%) in the therapist resistance set-up. For groups of patients following TKA, the difference between the two measurements of strength needs to be greater than 7.5 N (14%) to be 95% confident that a real change had occurred under the belt resistance condition, and greater than 13.9 N (17%) under the therapist resistance condition.

95%CI ðmeanÞ ¼

Md  t0:975  SDdiff pffiffiffiffi ; N

ð1Þ

where Md is the difference of retest minus test scores; SDdiff is the standard deviation of the difference between retest and test scores; N is the number of subjects. For individual scores, 95% CIs were calculated by substituting N ¼ 1 into Equation (1) [23]. These CIs which have also been termed as ‘‘limits of agreement’’ inform the clinician as to how much an individual’s strength must improve to be 95% confident that a real change in muscle strength has occurred [22]. A paired t-test was used to assess the difference between the belt resisted and therapist resisted set-ups. Statistical analyses were performed using SPSS statistical software (Chicago, IL).

Table 1. Patient characteristics. Characteristics

Values

Age (years) Height (m) Mass (kg) BMI (kg m2)

71.93 ± 7.44 1.65 ± 0.10 87.33 ± 15.55 32.1 ± 5.9

Previous joint replacement: No Contralateral knee Contralateral hip Contralateral hip and knee Quadriceps lag ( ) Knee flexion ROM ( ) Time since surgery (days) Prosthesis type Cruciate retaining Posterior stabilized Patella resurfaced (%) Pain during testing (VAS) 0–10 scale

18 (60%) 8 (26.6%) 2 (6.7%) 2 (6.7%) 10.17 ± 7.60 82.00 ± 10.31 9.23 ± 2.66 24 6 20 3.85

(80%) (20%) (67%) (2.55)

Values are mean ± standard deviation (SD), n or as otherwise indicated; VAS, visual analogue scale.

Discussion The findings of this study suggest that HHD is a reliable tool to measure hip abductor strength in patients following TKA. Hip abductor strength measurements using either belt or therapist resistance of the HHD demonstrated ICCs of 0.82 and 0.80, respectively, which is considered an excellent level of retest reliability. These values are comparable to the ICC values obtained by a previous study using an isokinetic dynamometer [12]. However, clinicians should not rely on ICCs alone because they are influenced by the spread and distribution of the data as well as being difficult to interpret clinically. By calculating 95% CIs, the clinician can assess what represents a true change in muscle strength. To be 95% confident that a real change has occurred across groups, strength changes of at least 14% for belt resistance and 17% for therapist resistance methods would need to occur. The patients in the current study are in the very early postoperative stage and entering a phase in their recovery where there is rapid improvement in knee joint function and mobility. Therefore, improvements in strength of 72–79% may be expected in the first three months of surgery [5,24,25]. Both methods of resistance were reliable and there were minimal differences when interpreting the 95%CIs for both belt and therapist resistances. However, although reliable, the actual values of hip abductor strength when resisted by a therapist may be more susceptible to the individual strength of the therapist. The use of belt resistance involves a standard set-up with standardized

Table 2. Test–retest reliability of measuring hip abductor strength with belt or therapist-resistance of the dynamometer.

Dynamometer stabilization

Mean test score ± SD

Mean retest score (SD)

Belt Therapist

54.2 (25.0) 80.0 (32.0)

56.2 (24.6) 87.0 (29.4)

ICC3,1

95% CI of ICC3,1

Mean difference (SD)

95% CI of group mean

95% CI of individual

% Change 4 error group mean

% Change 4 error individual

0.82 0.80

0.66 to 0.91 0.61 to .90

1.9 (15.0) 6.9 (18.8)

3.66 to 7.52 0.08 to 13.93

28.69 to 32.54 19.61 to 57.13

13.6% 16.7%

71.9% 79.1%

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resistance and similar to the current study, belt resistance has been shown to be more reliable in other populations such as athletes [15]. Resistance from the therapist also produced significantly higher strength values than belt resistance, which should be taken into account when evaluating results of strength assessments and highlights the importance of using a consistent method. This difference is likely to be the result of the therapist adding an opposing force to the dynamometer, resulting in overestimation of the strength of the participant’s hip abductors. However, the use of the dynamometer by the therapist during exercise as immediate feedback would encourage the patient to perform a stronger contraction and improve the strength of the hip abductors during treatment. The most practical method of measuring hip abductor strength in the patient with TKA is to apply resistance proximal to the knee joint. Although resistance applied near the ankle and utilizing a longer leg lever has demonstrated greater reliability in healthy subjects [17], this study has shown that using the testing protocol described with a shorter lever and applying resistance proximal to the knee joint is reliable. This is particularly relevant in the early post-operative phase where the patient is more likely to experience higher levels of pain and apprehension and reliable strength measurements are important to document the efficacy of rehabilitation. Study limitations This study assessed the test–retest reliability of measuring hip abductor strength with one rater and therefore the results may not be generalized to inter-rater reliability. As the patients were 9.2 ± 2.7 days post TKA, the 95% CIs calculated for both groups and individual patients may be different for patients who are more advanced in their recovery from TKA, such as 6 or 12 months. This should be considered when assessing whether changes in muscle strength are true changes for these later stage patients.

Conclusion Hip abductor strength can be reliably measured using HHD in the early post-operative period for patients who have undergone TKA. The protocol described in this paper provides a reliable and simple method of measuring hip abductor strength in the clinical setting. Belt resistance demonstrated slightly higher test–retest reliability.

Declaration of interest The authors report no declaration of interest.

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5. Mizner RL, Petterson SC, Snyder-Mackler L. Quadriceps strength and the time course of functional recovery after total knee arthroplasty. J Orthop Sports Phys Ther 2005;35:424–36. 6. Reeves ND, Spanjaard M, Mohagheghi AA, et al. Older adults employ alternative strategies to operate within their maximum capabilities when ascending stairs. J Electromyogr Kinesiol 2009; 19:e57–68. 7. Lin CW, March L, Crosbie J, et al. Maximum recovery after knee replacement – the MARKER study rationale and protocol. BMC Musculoskelet Disord 2009;10:69. 8. Petterson SC, Mizner RL, Stevens JE, et al. Improved function from progressive strengthening interventions after total knee arthroplasty: a randomized clinical trial with an imbedded prospective cohort. Arthritis Rheum 2009;61:174–83. 9. Stevens-Lapsley JE, Balter JE, Kohrt WM, et al. Quadriceps and hamstrings muscle dysfunction after total knee arthroplasty. Clin Orthop 2010;468:2460–8. 10. Hinman RS, Hunt MA, Creaby MW, et al. Hip muscle weakness in individuals with medial knee osteoarthritis. Arthritis Care Res 2010; 62:1190–3. 11. Mizner RL, Snyder-Mackler L. Altered loading during walking and sit-to-stand is affected by quadriceps weakness after total knee arthroplasty. J Orthop Res 2005;23:1083–90. 12. Piva SR, Teixeira PE, Almeida GJ, et al. Contribution of hip abductor strength to physical function in patients with total knee arthroplasty. Phys Ther 2011;91:225–33. 13. Pua YH, Wrigley TV, Cowan SM, et al. Intrarater test–retest reliability of hip range of motion and hip muscle strength measurements in persons with hip osteoarthritis. Arch Phys Med Rehabil 2008;89:1146–54. 14. Thorborg K, Petersen J, Magnusson SP, et al. Clinical assessment of hip strength using a hand-held dynamometer is reliable. Scand J Med Sci Sports 2010;20:493–501. 15. Thorborg K, Bandholm T, Holmich P. Hip- and knee-strength assessments using a hand-held dynamometer with external beltfixation are inter-tester reliable. Knee Surg Sports Traumatol Arthrosc 2013;21:550–5. 16. Katoh M, Yamasaki H. Comparison of reliability of isometric leg muscle strength measurements made using a hand-held dynamometer with and without a restraining belt. J Phys Ther Sci 2009;21: 37–42. 17. Krause DA, Schlagel SJ, Stember BM, et al. Influence of lever arm and stabilization on measures of hip abduction and adduction torque obtained by hand-held dynamometry. Arch Phys Med Rehabil 2007; 88:37–42. 18. Brown LE, Weir JP. ASEP Precoedures recommendation I: accurate assessment of musclular strength and power. J Exerc Physiol Online 2001;4:1–21. 19. Sisto SA, Dyson-Hudson T. Dynamometry testing in spinal cord injury. J Rehabil Res Dev 2007;44:123–36. 20. Walter SD, Eliasziw M, Donner A. Sample size and optimal designs for reliability studies. Stat Med 1998;17:101–10. 21. Portney LG, Watkins MP. Foundations of clinical research. New Jersey: Prentice-Hall; 2000. 22. Altman D. Practical statistics for medical research. London: Chapman & Hall; 1991. 23. Taylor NF, Dodd KJ, Graham HK. Test–retest reliability of handheld dynamometric strength testing in young people with cerebral palsy. Arch Phys Med Rehabil 2004;85:77–80. 24. Bade MJ, Kohrt WM, Stevens-Lapsley JE. Outcomes before and after total knee arthroplasty compared to healthy adults. J Orthop Sports Phys Ther 2010;40:559–67. 25. Rahmann AE, Brauer SG, Nitz JC. A specific inpatient aquatic physiotherapy program improves strength after total hip or knee replacement surgery: a randomized controlled trial. Arch Phys Med Rehabil 2009;90:745–55.

Reliability of measuring hip abductor strength following total knee arthroplasty using a hand-held dynamometer.

To investigate the test-retest reliability of measuring hip abductor strength in patients with total knee arthroplasty (TKA) using a hand-held dynamom...
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