| | Assessing Hip Abduction and Adduction Strength: Can Greater Segmental Fixation Enhance the Reproducibility?Presented in part to the British Association of Sports and Exercise Medicine, October 2006, Oxford, U.K. Abstract Laheru D, Kerr JC, McGregor AH. Assessing hip abduction and adduction strength: can greater segmental fixation enhance the reproducibility? ObjectiveTo improve the reproducibility of testing hip abduction and adduction using an isokinetic dynamometer by a novel testing protocol. DesignTest-retest design. SettingBiodynamics laboratory. ParticipantsFifteen healthy subjects (9 men, 6 women; age, 22.4±0.5y) were recruited. InterventionsTwo setups were compared: the first according to manufacturer’s guidelines (setup A) and the second a novel setup incorporating pelvic fixation (setup B). Setups A and B were performed in a random order. Both setups included the same battery of isokinetic (30°/s, 60°/s) and isometric tests, and were repeated 1 week later. Main Outcome MeasuresThe peak torque for each abduction and adduction exercise was noted and pelvic motion during testing was recorded. ResultsSetup B significantly (P<.05) reduced transverse pelvic rotation by between 7.5° and 8.0° dependent on test speed. Mean differences for reproducibility of peak torque, ranged from 0.8 to 11.7Nm. The coefficients of repeatability of both setups were similar, ranging from 21.4 to 56.3Nm across isokinetic exercises. A similar observation was noted for isometric exercises, with the differences between the coefficients of repeatability ranging from 18.6 to 40.0Nm. ConclusionsReducing pelvic rotation does not enhance reproducibility of the system and is not related to torque production. Further research is required to determine the optimal test setup. MORBIDITY RELATED TO the hip abductor and adductor muscle groups can affect a wide cross-section of people, from athletes to inpatients alike. For this reason, strength testing of the muscle groups is of importance for screening, rehabilitation, and injury-prevention purposes. Consequently, it is of paramount importance that a reliable method is available for the assessment of hip abductors and adductors. Gluteus medius and minimus are the main abductor muscles. They are key stabilizers of the pelvis1 and are involved in medial rotation of the thigh. The adductor group of muscles (adductor magnus, brevis, longus, gracilis) form the medial thigh compartment. The adductors pull the thighs medially to stabilize during bipedal stance, allow kicking with the medial aspect of the foot (eg, soccer, swimming) and maintain hip stability during running. Ice hockey and soccer players are particularly susceptible to adductor muscle strains. Approximately 10% of all ice hockey players’ injuries are adductor strains.2 These injuries have been linked to hip muscle weakness and muscle imbalance3 and previous injury.4 For example, those with adductor strength 80% less than abductor strength were 17 times more at risk of sustaining an injury.3 Similarly, the repetitive adduction performed by breaststroke swimmers places them at risk of hip adductor strain. Injury rates have been shown to positively correlate with an increased magnitude of breaststroke training, with up to 42.7% of breaststroke swimmers being unable to participate in events in 1 year due to an adductor injury.5 Such injuries may be preventable if the risk factors can be addressed before each season. However, the success of such screening programs depends on the accuracy and reproducibility of the methods used. The hip abductors are also important, particularly to long distance runners who are vulnerable to iliotibial band friction syndrome.6 Improvement in hip abductor strength, with an appropriate rehabilitation program, parallels symptomatic improvement and a successful return to their usual training regimes, suggesting that weakness may be a causal factor of injury in these athletes. Furthermore, poor endurance and delayed firing, as assessed by electromyography, of the hip abductors and adductors has also been linked to chronic ankle instability7 and even falls in elderly women.8 Nadler et al9 proposed that screening of hip strength prior to competitions may be important in the prevention of lower-limb injury and even lower-back pain in athletes. Preseason hip-strengthening exercises have been shown to be effective in reducing the incidence of adductor strains in one closely followed professional ice hockey team4; however, such interventions rely on objective and repeatable test protocols. There are 3 main methods of muscle strength testing; manual muscle testing (MMT), hand-held dynamometry (HHD), and mechanical isokinetic and isometric dynamometry. The Cybex dynamometera has been found by several investigators to be a reliable device for strength measurements in the lower limb,10, 11, 12 but much of this work has focused on the knee. Strength testing of the hip abductors and adductors is usually carried out in the lateral position on most Cybex systems.a To test the maximal strength of a group of muscles, it is necessary to limit segmental body movement. Based on observations in our laboratory, this is very difficult to achieve voluntarily when lying laterally. It is likely that during abduction and adduction, rotation of the pelvis away from the anatomic position may facilitate the recruitment of different muscle groups for the same action, which may contribute toward inaccurate readings. The primary aim of this study was to develop a suitable methodology to decrease pelvic rotational movement during abduction and adduction testing on the isokinetic dynamometer. The secondary aim was to see whether the setup that reduced pelvic rotation enhanced the reproducibility and thus reliability of this form of testing. This would be done by comparisons with the setup suggested in the manufacturer’s instructions. Methods  Study Population We recruited 15 volunteers into the study and obtained written informed consent. The age, height, weight, and sex of each subject was noted. Exclusion criteria included previous or current history of hip pain or injury or current engagement in a weight altering diet. All subjects were instructed not to undertake vigorous exercise in the hour preceding their testing, in an attempt to prevent any confounding of the data as a result of fatigue. Apparatus Setup We used the Cybex Norm Isokinetic Dynamometer Systema for all testing. It was driven by Human Assessment Computer (HUMAC)b for Windows. Each subject was asked to wear loose fitting clothing. A belt was secured at the level of the anterior superior iliac spine (ASIS). In the midline, at the back of the belt, a plastic ruler was attached which projected vertically upward when the subject was lying on their side (adjusted when lying on their left or right side) (fig 1). During testing, once the subject was in place, a video camera was positioned at the level of their head, approximately 1m away, in line with the subject’s spine. The surface location of the head of the femur was found at the halfway point of a line joining the greater trochanter and the pubic tubercle.13 The height of the dynamometer, the length of the hip knee adapter, and the chair fore-aft distances were adjusted accordingly to ensure that the rotation of the head of the femur was at the same level as the dynamometer pivot and thus standardization was maintained. The full range of motion (ROM) of each limb was recorded. These dimensions were maintained for each side and each setup for both sessions. Setup A: Cybex Subjects were positioned in accordance with the manufacturer’s instructions. A hip and knee adapter was applied at the level of the quadriceps tendon, immediately superior to the patella on the testing side. A self-adhesive (Velcro) strap was applied over the resting thigh at the same level. This was fastened to the handle bars on each side of the Cybex seat (fig 2A). Testing was performed in this position with all subjects holding the handrail as shown. Setup B: Modified Cybex We developed this setup to minimize transverse pelvic rotation. A total of 4 straps were attached to the subject: ankle, thigh, abdomen, and chest (fig 2B). The hip and knee adapter was applied as detailed in setup A. The thigh strap was looped around the thigh and back onto the handle bar. A backboard of wood with sponge cushioning was attached to the backrest of the Cybex seat by the means of vises clamped to the side rails. The chest strap was looped around the subject, under the axillae and through slots in the wood piece, securing them to the backboard. The strap around the abdomen was fastened superior to the level of the ASIS, clear of the belt used for measuring pelvic rotation. This was looped around the subject and secured ventrally through the side rail. We found by visual observation that this setup reduced the range of transverse pelvic motion during testing. Exercise Protocol The exercises undertaken were identical for both setups (protocol details summarized in fig 3). Subjects were randomized to the setup they would undertake first. Both sides were tested sequentially with 1 setup and subjects were then allowed a 10-minute rest period while preparations were made for the other setup. We chose arbitrarily to test the right side first for each setup. The exercises involved both concentric isokinetic and isometric contractions. Isometric exercises were performed in the anatomic neutral position of the hip. Subjects were instructed to perform practice contractions at the start to familiarize themselves with what to expect. They were also given appropriate rest periods (up to 5min) after each set of contractions. The video recordings were made during the isokinetic exercises only. All subjects were given the same level of encouragement by the examiner. Each subject was instructed prior to the start that their maximal effort was required for each set of exercises, excluding the pretest contractions. Subjects returned 1 week later for repeat testing. The sequence of exercises and setups was identical to their first session. This was in part due to time constraints resulting from the inflexibility of the isokinetic system’s software. Data Analysis The maximum torque produced for each part of the exercise protocol was determined from the raw data files exported by the HUMAC software. The measurements of pelvic rotation were determined from the videos of each exercise procedure using playback and snapshot features of Windows Movie Maker software. Measurements were made of the swing of the ruler in the transverse plane. The extremes of rotation on each side of the resting position were captured, collated, printed, and then measured manually to the nearest degree using a protractor. Data were compared using a Student t test (paired) to look for significant differences between the setups. Left and right sides were analyzed separately using the underlying assumption of independence of data points. We used statistical methods described by Bland and Altman14 for assessing repeatability between 2 sets of measurements to assess the reliability of each setup configuration. The maximum torque values from weeks 1 and 2 were noted and the differences between them used to assess repeatability. This allowed an appraisal of the setups’ repeatability in terms of the real units of newton-meters. Discussion The burden of hip abduction and adduction morbidity has been highlighted2, 5, 6, 8; however, isokinetic dynamometry testing of these muscle groups has been associated with low repeatability.11, 15 One causal factor that has been implicated with this low repeatability is excess pelvic mobility, although this has never been quantified or evaluated.16, 17, 18, 19 The novel setup described in this study was noted to reduce pelvic rotation in the transverse plane, particularly at the slower speed of 30°/s. Despite this, the results indicate that there is no great difference in repeatability between a conventional setup and one that minimizes pelvic rotation. Movement of other body segments may influence the repeatability; for example, the degree of femoral rotation may also be important. During ambulation, the abductors on the stance side cause medial femoral rotation moving the pelvis toward it. When testing in the lateral position, the situation is variable; based on our observations, there is a tendency to laterally rotate the femur when attempting to produce maximal force and this may lead to more inconsistent results between readings. However, there is mixed evidence on this topic.17, 20, 21, 22 It is not clear how this movement could be controlled during isokinetic testing. Figure 5 suggests that pelvic rotation has a weak relationship with peak torque production; this would indicate that the movement of the pelvis will have minimal if any impact on the maximum torque output. This is corroborated by the limited differences observed in mean group peak torque between each setup (2.8−15.1Nm during isokinetic testing; 6.7−7.8Nm during isometric testing). This factor is further supported when considering normal pelvic motions during gait. The pelvis does not move greatly (>10°) in gait.23 A reason may be that training of this muscle in the vast majority of the nonathletic population may only be limited to ambulation—and as such the peak torque produced would be within this narrow (anatomic position) range. The implications of the findings lie in the clinical significance of the absolute values and their respective coefficients of repeatability. The degree of accuracy and change that is sought in routine screening is the deciding factor. Data adapted from Fredericson et al6 show changes in abduction torque of approximately 119Nm, after 6 weeks of rehabilitation, among long-distance runners. Abduction torque values of 19.0Nm have been considered low18 after total hip arthroplasty and increases of 22.2Nm or more as significant after 8 weeks of rehabilitation.24 Subject groups with relatively large torque changes, outside the limits of repeatability, remain the key benefactors of this type of testing. Such increases would show trends that would be easily discernible from artifact. Rowing coaches have been known to increase training from 0- to 4-kg weights—a difference of 39N for the subject (P. Thompson, head coach, UK British women and lightweights, personal communication, May 18, 2006)—a value well within the coefficient of repeatability of the isometric contractions performed in this study. Real change would not then be distinguishable from repeatability error. Study Limitations Limitations of the study methodology might have contributed to reduced accuracy of the findings. In setup B, variances between sessions of the anchoring strap tension may have influenced the pelvic ROM. Subjects recruited were all university attendees, with a narrow age range, and had a mixed repertoire of sporting talent, exercise habits, and motivation.25 Further investigation is necessary on subjects of a more aged or diseased disposition to assess feasibility of the setup. Athletes might have been more motivated to perform to their maximum and so would reduce that component of error in the results. This may be because they stand to directly benefit from an accurate assessment.26 Another study design factor that might have influenced the results was the lack of randomization of the test protocol itself, and the inevitable fatigue in the muscles that the protocol will have induced. The encouragement offered in the study might have played a pivotal role in the reproducibility. Subjects’ motivational status, along with physical fatigue, might have varied both intrasession and intersession. Offering everyone the same level of encouragement might have resulted in some strictly adhering to the instructions provided at the start and others less so.27 Furthermore, the testing process took approximately 1 hour per session. Much of the time was engaged in setting up the necessary equipment and not in the subject being actively exercised. Mental fatigue might have further played an interactive role with motivation.26 Additionally, a learning effect might have contributed to mental and physical preparedness (eg, having a snack beforehand or training between sessions) and thus produced torque values differing from those of the previous session. Cheaper and simpler alternatives to isokinetic dynamometry are widely in use. Subjective MMT grading is quick and is commonly used in medical clinics28; however, it is not sensitive enough to detect small improvements.29 The HHD is a more accurate way of manually measuring muscle strength, but it carries the disadvantage of examiner error and cannot be used to acquire isokinetic data. Evidence suggests that the use of HHDs in lower-limb testing is unreliable because of differences in strength between the examiner and patient and of the unexpected movements that may occur.30 This hurdle has been overcome with the introduction of a specially designed HHD anchoring station as described by Nadler et al.28 These portable hip dynamometer anchoring stations have been shown to be reliable28, 31 and provide a cheaper and quicker alternative to the Cybex dynamometer, but at the cost of accuracy. Conclusions Reduction of transverse pelvic rotation had little effect on enhancing repeatability for measuring peak torque during hip adduction and abduction, in health young controls. Furthermore, maximum pelvic rotation angle has a weak correlation with peak torque production. Directions for future work should include further analysis to look at the torque pattern produced throughout the whole ROM as well as isolating both femoral and pelvic rotation. In addition testing in different positions (ie, sitting, lying) with different groups of athletes/subjects and to examine the feasibility of the interventions among diseased patients and the elderly are also further avenues worth exploring. Suppliers References 1. 1Inman VT. Functional aspects of the abductor muscles of the hip. J Bone Joint Surg. 1947;29:607–619. 2. 2Lorentzon R, Wedren H, Pietila T. Incidence, nature, and causes of ice hockey injuries (A three-year prospective study of a Swedish elite ice hockey team). Am J Sports Med. 1988;16:392–396. MEDLINE |
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Biosurgery and Surgical Technology, Division of Surgery, Oncology and Reproductive Medicine, Faculty of Medicine, Charing Cross Hospital, Imperial College London, U.K.  Reprint requests to Alison H. McGregor, PhD, Reader in Biodynamics, Biosurgery and Surgical Technology, Div of Surgery, Oncology, Reproductive Biology and Anaesthetics, Faculty of Medicine, Imperial College London, Charing Cross Hospital, London, W6 8RF, UK
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. PII: S0003-9993(07)00381-4 doi:10.1016/j.apmr.2007.05.017 © 2007 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved. | |
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