Patellofemoral pain during step descents with and without fatigue-induced hip internal rotation

Hong Kong Physiotherapy Journal (2012) 30, 13e17 Available online at www.sciencedirect.com journal homepage: www.hkpj-online.com RESEARCH REPORT Patellofemoral pain during step descents with and without fatigue-induced hip internal rotation Roy T.H. Cheung, PT, PhD* Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hung Hom, Hong Kong KEYWORDS anterior knee pain; functional activity; isokinetic; kinematics Abstract Weakness of hip external rotator muscles may cause excessive hip internal rotation during functional activity and it is associated with the development of patellofemoral pain (PFP). The aetiology of PFP is multifactorial in nature. Therefore, routine enrolment of patients into a hip-strengthening programme may not be effective and cost-effective. The present study examined the effect of fatigue-induced hip internal rotation during functional activity. Twenty subjects with PFP were asked to descend a step in barefoot before and after an isokinetic exercise protocol to induce muscle fatigue of hip external rotators. The hip motion was captured by eight high-speed cameras and analysed by a three-dimensional motion analysis system. The level of PFP during step descent and their usual PFP level were measured by validated instruments. Patients with PFP presented with more pronounced hip pathomechanics (p < 0.001) and greater level of PFP (p Z 0.001) after muscle fatigue. The pain score after muscle fatigue during step descent better reflects the usual functional disturbance associated with PFP (r s Z 0.655, p Z 0.002). Physical examination with induced muscle fatigue may be helpful in clinical decisions on the management programme for patients with PFP, which are related to altered hip mechanics. Copyright ª 2012, Elsevier. All rights reserved. Introduction Patellofemoral pain (PFP) is a common orthopaedic condition for active adults and it manifests as peri- or retropatellar pain during loaded functional activities such as single leg squatting and step descent [1]. Even though the pain is elicited around the knee, there is a growing * Corresponding author. Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hung Hom, Hong Kong. E-mail address: rsroyth@inet.polyu.edu.hk. scientific support for the relationship between PFP and altered mechanics in the hip joint [2]. A series of clinical research has indicated that patients with PFP present with weaker hip external rotator muscles than their healthy counterparts [3], and weakness of such a muscle group leads to greater hip internal rotation (HIR) during functional activities [1,4,5]. Cadaveric studies also have shown that excessive HIR increases lateral shifting of the patella and patellofemoral joint stress [6,7]. It may explain the major rationale to develop PFP in patients with altered hip kinematics. Therefore, a hip-strengthening programme is clinical usual care for patients with PFP. Although most researchers 1013-7025/$ - see front matter Copyright ª 2012, Elsevier. All rights reserved. doi:10.1016/j.hkpj.2012.01.001

14 R.T.H. Cheung have reported improvements in hip strength and reductions in PFP with hip-strengthening programmes [8e11], most of them have not established the relationship between the change in HIR and PFP level. In a study by Blond and Hansen [12], it was reported that 80% of individuals who had engaged in a hip-strengthening programme continued to have PFP 5 years later. This suggests that routine enrolment in a hip-strengthening programme may not lead to a response in every patient with PFP and be cost-effective. The aetiology of PFP is multifactorial in nature. Therefore, it is necessary to establish a simple clinical test to screen patients with PFP, which is associated with altered mechanics of the hip joint. This group of patients is believed to be indicative for a hip-strengthening programme. It has been shown that fatigue of a specific muscle group is associated with an increased counter movement of its agonist [13]. It is logical to speculate that the amount of HIR during a functional activity can be increased after purposeful procedures to induce muscle fatigue of hip external rotators. Therefore, the present study proposed a method to induce HIR during a functional activity in patients with PFP, and investigated the relationship between the change in HIR and the level of PFP. We hypothesized that patients with PFP related to altered hip kinematics would report a higher level of PFP with induced HIR. We also speculated that the level of PFP during functional activity with induced muscle fatigue may better reflect the overall symptoms of the patients. Methods Participants Twenty male patients with unilateral PFP were recruited in this study. All of them were clinically diagnosed by either a medical practitioner or a physiotherapist. PFP was operationally defined as pain located around or beneath the patella that can be reproduced with retropatellar palpation or patellar compression. To ensure sample homogeneity, a qualified physiotherapist screened all the participants, and those with symptoms attributable to ligament, meniscus, tendon or other soft tissue lesions were excluded. Individuals over the age of 45 years were also ruled out to control for the possible effects of degenerative joint disease [14]. Also, recruitment of single-sex participants could avoid the sexrelated gait pattern variance [15]. The experimental procedures were approved by the institutional review board of Hong Kong Polytechnic University and all the participants provided their written informed consent before being tested. The demographic data of participants are presented in Table 1. Kinematics measurement The kinematics of the symptomatic limb was measured by a three-dimensional motion capturing system (Vicon Ò Mx; Oxford Metrics Ltd., Oxford, UK) with eight high-speed cameras. The capturing frequency of the system was 100 Hz. A total of seven reflective markers were placed on the tested limb according to the recommendations of the International Society of Biomechanics [16] (Fig. 1). Estimation of the hip centre of rotation was based on an Table 1 anatomical prediction approach described by Davis et al [17]. The trajectory data were filtered using a fourthorder, zero-lag, low-pass Butterworth filter with a cutoff frequency of 10 Hz. A customized computer program (Matlab; MathWorks, Natick, MA, USA) was used to calculate the maximum amount of HIR, which was defined as the peak internal femoral rotation in relation to the pelvis girdle during the step descent task. Test procedures The participants were asked to descend a step (width: 470 mm; depth: 317.5 mm; height: 175 mm) in barefoot at a self paced speed on three occasions (Fig. 2). The initial and final step placements were standardised according to the recommendation of McIlroy and Maki [18], and this position should have the least effect of forcing the participants into an unnatural upright posture. The joint positions were recorded for 3 seconds as offset while the participant was standing on the step before the test. The participant was then asked to descend the step with the symptomatic leg, followed by the other leg. All of the participants were given practice trials before testing until they reported that they were comfortable with the task. Procedures to induce muscle fatigue of hip external rotators The participants underwent a standardised isokinetic exercise protocol to induce muscle fatigue of hip external rotators after the first set of the step descent task. Baseline peak torque of hip external rotator was quantified by an isokinetic dynamometer (Humac Norm Ò Model 770, Computer Sports Medicine Inc, Stoughton, MA, USA) at a speed of 60 per second in concentric mode. Peak torque was defined as the maximum value recorded over five consecutive repetitions of maximum voluntary contraction [19]. Muscle fatigue of hip external rotators was achieved by continuous repetitions of maximum voluntary contraction at 60 per second until an at least a 50% drop of initial peak torque in three consecutive repetitions [20]. The drop in force production was confirmed by another peak torque assessment. If the drop in force production did not meet the criteria, the fatigue procedure was resumed. Once the target level of muscle fatigue was achieved, participants were immediately requested to perform the step descent task for another three trials. Evaluation of PFP Demographics of the participants Mean Age (y) 30.4 4.8 Height (m) 1.71 0.09 Weight (kg) 66.9 15.6 Patellofemoral pain chronicity (mo) 11.5 9.5 SD Z standard deviation. Each of the participants was asked to report the severity of PFP by two validated instruments. The overall level of PFP SD

15 Figure 1 Reflective markers were located at bilateral anterior superior iliac spines (ASISs), bilateral posterior superior iliac spines (PSISs), greater trochanter, medial and lateral femoral condyles. was assessed by a Chinese version of the Kujala scale [21], which is one of the most widely used instruments to quantify the functional disturbance associated with PFP. The Kujala scale consists of 13 multiple choice questions that measure the level of signs and symptoms, and extent of disturbance of functional activities that are related to PFP. An overall score of 0 (worst) to 100 (normal knee without symptoms and no restriction to daily functions) is indicative of the condition severity corresponding to PFP. In addition, the immediate PFP level was measured by a 10-cm visual analogue scale (VAS) [22] once the participants completed the step descent task. The 10-cm straight line encompasses the end-point descriptors of none (at 0 cm) and unbearable (at 10 cm). The score of each statement was determined by measuring the point along the line where the subject placed their mark. The pre- and post-vas scores were obtained from the average values reported from the three trials before and after muscle fatigue. The VAS score will be standardised to a percentage out of 100 and ranged from 0 (normal knee without symptom during daily activities) to 100 (worst pain imaginable). Figure 2 Step descent with standardised step placement. Statistics The amount of HIR and the VAS score during the step descent were compared between pre- and post-muscle fatigue conditions by paired t tests. Correlations between the change in HIR and VAS scores were evaluated by the Spearman s rank correlation coefficient (r s ). In addition, the correlations between the VAS scores (both pre- and post-fatigue) and Kujala score were examined by the same correlation statistics. A coefficient value of r s >0.75 indicated good to excellent association, whereas a value between 0.25 and 0.75 indicated fair to good association [23]. Statistical package, PASW for Windows, version 18 (SPSS Software, Chicago, IL, USA) was used for statistical analysis. The global a level was set at 0.05.

16 R.T.H. Cheung Results The amount of HIR and VAS scores before and after the muscle fatigue programme and the Kujala scores are shown in Table 2. Participants exhibited a significantly greater amount of HIR (p < 0.001) and more severe PFP (p Z 0.001) after the isokinetic exercise programme. The increase in HIR was significantly associated with the increase in VAS score (r s Z 0.536, p Z 0.015). The Kujala score was moderately correlated with both VAS score before (r s Z 0.534, p Z 0.015) and after (r s Z 0.655, p Z 0.002) muscle fatigue during step descent. Discussion The present study reported an isokinetic exercise programme to induce muscle fatigue of hip external rotators, leading to an increase of HIR during a functional task. Patients reported a greater level of PFP with an increase of HIR, and a change in VAS score was associated with the change in HIR. The association between Kujala scale and VAS score was stronger in the fatigued than pre-fatigue condition. This indicated a better reflection of usual symptoms while the patient was assessed in the state of muscle fatigue. Muscle fatigue can be operationally defined as a reduction of ability to work against resistance. However, a prospective study has suggested that isometric hip muscle strength might not be a predisposing factor for the development of PFP [24]. Muscle strength evaluation by isokinetic measurement is a more functional than isometric muscle test [25]. Therefore, the exercise protocol to induce hip muscle fatigue was designed in an isokinetic manner and this programme was shown to be successful in inducing fatigue of hip external rotators and excessive HIR during a functional activity. Gait assessment is a common outcome to evaluate the effectiveness of the treatment programme [8e11]. Compared with sagittal (e.g., hip flexion/extension) and coronal plane (e.g., hip abduction/adduction) movements, measurement of axial rotation of the hip is always a challenge for both researchers and clinicians [26]. Enlargement of the effect size in an outcome variable is favourable for both researchers and clinicians. To the best of our knowledge, the current research is the first study to examine the changes in PFP level in altered hip mechanics evoked by muscle fatigue. Previous studies have aimed to mitigate PFP by improving hip mechanics using strengthening exercise [11,27]. Based on the same principal, the faulty hip mechanics should able to be enlarged in a controlled and systemic manner. The present study introduced a safe and clinical method for this purpose. This manipulation may be helpful for clinicians to diagnose, monitor rehabilitation progress, and make clinical judgments. A temporary increase in PFP level during the step descent is believed to relate with more lateral shifting of the patella and corresponding joint stress with increased HIR [6,7]. Compared with the VAS score before muscle fatigue during step descent (r s Z 0.534, p Z 0.015), our results found a stronger association between the Kujala score and VAS score after muscle fatigue (r s Z 0.655, p Z 0.002). Kujala score is a very common clinical tool to measure the overall symptoms related to PFP in functional activities, including stair descent [21]. This result indicated that the immediate PFP perception during step descent after induction of increased HIR better reflects the usual functional disturbance associated with PFP. Such a finding could have the clinical implication that assessment of patients with PFP necessitates a more extreme condition such as induced muscle fatigue. False-negative assessment could result if the patients are not evaluated at their limit. One of the major limitations of this study was that the current isokinetic exercise protocol only applied to a functional activity that involved slow movements. Although the malalignment of hip joint may also be a predisposing factor for the development of PFP during running motion [28], the exercise protocol reported in the present study may not be applicable to other forms of activity such as running. In addition, the fact that this study only tested single-sex subjects limits generalisation of the findings. An isokinetic exercise protocol was reported to induce HIR in patients with PFP during step descent. Patients with PFP presented with more pronounced hip pathomechanics and greater PFP after muscle fatigue. The pain score after muscle fatigue during step descent better reflects the usual level of PFP symptoms. Physical examination with induced muscle fatigue may be helpful in clinical decisions on management programmes for patients with PFP, which are related to altered hip mechanics. Acknowledgements The author is indebted to Ms Polly Chung and Mr. Robbie Cheung for their technical assistance. Table 2 Level of patellofemoral pain and hip internal rotation before and after muscle fatigue Pre-fatigue Post-fatigue p Hip internal 8.98 3.14 10.35 3.68 <0.001 rotation (degree) Visual analogue 10.60 5.71 13.05 6.92 0.001 scale score (%) Kujala score (%) 57.11 23.44 N/A N/A Z not applicable. References [1] Bolgla LA, Malone TR, Umberger BR, Uhl TL. Hip strength and hip and knee kinematics during stair descent in females with and without patellofemoral pain syndrome. J Orthop Sports Phys Ther 2008;38:12e8. [2] Powers CM. The influence of abnormal hip mechanics on knee injury: a biomechanical prospective. J Orthop Sports Phys Ther 2010;40:42e51. 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