Patellofemoral pain syndrome (PFPS) is one of the most. Joint Stiffness and Pain in Individuals With Patellofemoral Syndrome

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1 Joint Stiffness and Pain in Individuals With Patellofemoral Syndrome Karrie L. Hamstra-Wright, PhD, ATC 1 C. Buz Swanik, PhD, ATC 2 Theresa Y. Ennis, MEd, ATC 3 Kathleen A. Swanik, PhD, ATC 4 Journal of Orthopaedic & Sports Physical Therapy Study Design: Pretest-posttest matched control group design. Objectives: To measure passive knee joint stiffness and pain in participants with and without patellofemoral pain syndrome (PFPS) and to determine the relationship between mechanical knee joint stiffness, self-reported stiffness, and pain. Background: Patients with PFPS complain of knee joint stiffness and pain, but no research has quantified both of these characteristics in this population. Methods and Measures: Twenty-eight individuals (14 with PFPS [mean age ± SD, 25.5 ± 4.8 years] and 14 healthy controls [mean age ± SD, 22.8 ± 5.4 years]) volunteered for this study. Mechanical passive knee joint stiffness was calculated using the damped natural frequency of oscillation of the lower leg while sitting. Mechanical stiffness was compared to self-reports of knee stiffness and pain. All measurements were recorded presitting and after 20 minutes of sitting. Results: Sitting for 20 minutes did not induce significant changes in mechanical knee joint stiffness. However, participants with PFPS reported significantly greater (P.01) knee stiffness after sitting for 20 minutes. A significant correlation (r = 0.70, P.01) was found between self-reported stiffness and pain in participants with PFPS; however, no significant relationship was observed between mechanical and self-reported knee joint stiffness. Conclusions: Despite frequent complaints of joint stiffness, the knees of individuals with PFPS do not appear physiologically stiffer than those of control subjects. Individuals with PFPS perceive increased knee stiffness after sitting, but may misinterpret the sensation of pain as joint stiffness. J Orthop Sports Phys Ther 2005;35: Key Words: anterior knee pain, knee chondromalacia, movie theater sign, patella Patellofemoral pain syndrome (PFPS) is one of the most prevalent knee conditions in adolescents and young adults. 3,26 Individuals with PFPS often complain of knee joint stiffness after prolonged periods in knee flexion ( movie theater sign). 15 Stiffness is the resistance of a body part to changes in shape or position. 19 Mechanical measures of passive knee joint stiffness 1 Postdoctoral Research Fellow, Department of Movement Sciences, University of Illinois at Chicago, Chicago, IL; Doctoral student (at time of study), Department of Kinesiology, Temple University, Philadelphia, PA. 2 Assistant Professor, Department of Health, Nutrition & Exercise Sciences, University of Delaware, Newark, DE. 3 Graduate student (at the time of the study), Department of Kinesiology, Temple University, Philadelphia, PA. 4 Assistant Professor, Undergraduate Athletic Training Director, Department of Kinesiology, Temple University, Philadelphia, PA. Temple University Institutional Review Board approved the protocol for this study. Address correspondence to Karrie L. Hamstra-Wright, Department of Movement Sciences, University of Illinois at Chicago, 901 W. Roosevelt Rd., 331 PEB, MC 194, Chicago, IL khamst1@uic.edu are affected by the joint capsule, muscles, tendons, skin, and ligaments. 14 Although individuals with PFPS often complain of joint stiffness and pain, no research has been conducted quantifying these variables in this population. Previous research indicates a possible relationship between pain and subjective complaints of stiffness. Patients with rheumatoid arthritis reported feelings of joint stiffness, but their elastic (mechanical) stiffness was actually less than that of a disease-free population. 10 A number of explanations have been proposed for this finding, the most common relating to patients misinterpretation of the stiffness symptom. The authors concluded that patients appear to confuse pain and stiffness. 10 It may be that patients with rheumatoid arthritis experience limitations in movement due to pain rather than increased resistance to movement (stiffness). 10 Similar to rheumatoid arthritis, stiffness and pain are common complaints associated with PFPS; but it remains unknown if the knee is physiologically stiffer in patients with PFPS. Assessing stiffness and pain in those with PFPS may facilitate greater understanding of the most effective treatment techniques for this condition. Therefore, the purpose of this study was to measure passive me- Journal of Orthopaedic & Sports Physical Therapy 495

2 chanical knee joint stiffness and pain in subjects with and without PFPS and to determine if a relationship exists between mechanical knee joint stiffness, selfreported stiffness, and pain. It was hypothesized that patients with PFPS would exhibit greater mechanical knee joint stiffness and pain than those without PFPS, and that a positive relationship would exist between mechanical knee joint stiffness, self-reported stiffness, and pain. METHODS Subjects Twenty-eight participants between the ages of 18 and 35 volunteered for this study. Fourteen participants (2 male, 12 female; mean ± SD age, 25.5 ± 4.8 years; mean ± SD body mass, 67.1 ± 28.5 kg) clinically diagnosed with PFPS by an orthopedic physician were matched by gender and age with 14 healthy control participants (2 male, 12 female; mean ± SD age, 22.8 ± 5.4 years; mean ± SD body mass, 63.4 ± 30.2 kg). Temple University Institutional Review Board approved the study, written consent was obtained from the participants, and the rights of the participants were protected. The characteristic history of PFPS used to diagnose the condition included retropatellar pain during physical activities such as climbing, descending stairs, running, or squatting, along with complaints of stiffness after sitting for a long period of time. 15,26 In addition, the participants exhibited at least 2 of the following clinical criteria on assessment: pain upon direct compression of the patella against the femoral condyles with the knee in full extension, tenderness on the posterior surface of the patella with palpation, pain with resisted knee extension, and pain during isometric quadriceps muscle contraction. 5,12,15,26 Participants diagnosed with PFPS had patellofemoral pain for a minimum of 1 year prior to testing. All participants were asked not to take part in physical activity during the 24 hours prior to testing. Participants were excluded from the study if they were asymptomatic during the 4 weeks prior to testing, 22 took nonsteroidal anti-inflammatory drugs the week before testing, or if they had previous knee surgery. Participants were also excluded from the study if they had a history of knee injury other than PFPS within the past year, for which they sought medical attention. Instrumentation The leg was modeled as a single-degree-of-freedom mass spring system with a damping component. 1,11,18,19,24 Lower leg segment anthropometric data were used to obtain lower leg and foot mass and center of mass. 25 With these data, joint stiffness was calculated using the damped frequency of lower leg oscillation of the first 2 oscillatory peaks and the coefficient of damping (Appendix A). 23 Two-dimensional kinematic data (knee flexion and extension angular displacement) were collected at 60 Hz using the PEAK Motus Motion Analysis System (Peak Performance Technologies, Inc, Englewood, CO). Trials were recorded using a video camera positioned at 90 to the plane of movement. Reflective markers were placed on the skin over the lateral malleolus and lateral femoral condyle of the symptomatic leg to aid in digitizing. The participants wore dark-colored, form-fitting shorts on which a third reflective marker was placed over the greater trochanter. Passive knee joint stiffness was calculated using the damped natural frequency of oscillation of the lower leg (Nm rad 1 /kg) while sitting. 19 Myoelectric activity was assessed with the Noraxon Telemyo system (Noraxon USA, Inc, Scottsdale, AZ) to verify quadriceps and hamstring muscle relaxation during testing. The skin over the biceps femoris and vastus medialis muscles was shaved, lightly abraded, and cleaned with a 70% alcohol solution prior to electrode application. Two self-adhesive Ag/AgCl bipolar surface electrodes (Multi Bio Sensors, Inc, El Paso, TX) were placed on each of the muscles to detect myoelectric activity. The electrodes were 10 mm apart and parallel to the fiber orientation of the underlying muscle. 4 The investigator determined electrode placement by palpating the mid length of the muscle during isometric hamstring flexion and quadriceps extension. 16 A reference electrode was positioned on the proximal medial tibia. Signals from the electrodes were passed to a battery-operated 8-channel FM transmitter worn by the subject. The signal was amplified (gain 1000) with a differential amplifier (input impedance, 10 M ) and filtered with a single-order Butterworth high-pass filter (10 Hz), a fourth-order Butterworth low-pass filter (500 Hz), and a common-mode rejection ratio of 130 db at direct current (minimum 85 db across entire frequency of 10 to 500 Hz). An antenna receiver (Antennex, Inc, Glendale, IL) with a sixth-order filter (frequency, Hz; gain, 2; total gain, 2000) further amplified the signal. The analog signal was converted to a digital signal by an analog-to-digital converter card (Keithley KPCMCIA 12A1-C; Keithley Instruments, Inc, Cleveland, OH) and was stored in the MyoResearch Software, Version 2.02 (Noraxon USA, Scottsdale, AZ). The raw digital signal was sampled at a rate of 1000 Hz, rectified, and smoothed using a root-mean-square algorithm. Two separate visual analog scales (VASs) were used to measure self-reported complaints of knee stiffness and pain. 9 Patients were asked to draw an x at the point on the 10-cm line that best described their current level of stiffness or pain. One end of the VAS 496 J Orthop Sports Phys Ther Volume 35 Number 8 August 2005

3 indicated no stiffness or pain, while the opposite end signified the worse stiffness or pain ever experienced. 9 Data Collection Journal of Orthopaedic & Sports Physical Therapy Data collection began with each participant reporting their level of perceived stiffness and pain on the 2 separate VASs, while sitting with the knee and hip positioned in 90 of flexion to replicate the position in which persons with PFPS often experience stiffness and pain (Figure 1). 15,26 The tested limb was then completely extended and held at the foot by the examiner (Figure 2). The hip remained flexed at a 90 angle. When the tested limb was completely relaxed (as indicated by lack of EMG activity), the examiner released the foot and allowed the leg to oscillate freely until it came to a stop in a vertical position. 19 Based upon visual inspection, the first 3 acceptable trials (smooth oscillations and insignificant muscle activity) were averaged for statistical analysis (presitting stiffness). EMG was not statistically analyzed, as previous authors have indicated that significant muscle activity would be characterized by undamped lower leg oscillations. 13,18 All accepted trials illustrated damped oscillations. FIGURE 1. Sitting position while watching a movie for 20 minutes. FIGURE 2. Testing position immediately prior to lower leg oscillation. Subsequent to the first measurement of mechanical knee joint stiffness, the participants remained seated in the testing chair (Figure 1), with their knee positioned in 90 of flexion for 20 minutes, while watching a movie. Following the movie, the participants completed the VASs a second time, after which time mechanical knee joint stiffness was measured again (postsitting stiffness). The first 3 postsitting mechanical stiffness trials were averaged for statistical analysis. Data Analysis A pretest-posttest matched control group design was employed. Mechanical stiffness and self-reported stiffness between participants with PFPS and without PFPS were analyzed using 2 separate 2 2 (group by time) mixed-model ANOVAs, with time as the repeated measure. Pearson product moment coefficients of correlation were used to determine the level of association between self-reported and mechanical knee joint stiffness, pain and mechanical knee joint stiffness, and self-reported knee joint stiffness and pain. Significant levels for all statistical analyses were P.05. RESULTS Statistical analysis revealed no significant difference in mechanical stiffness between the 2 groups presitting to postsitting (F 1,26 = 0.11, P =.92) (Figure 3). A significant interaction (P.05) in self-reported stiffness over time was found (Figure 4). Post hoc analysis using paired sample t tests with Bonferroni correction J Orthop Sports Phys Ther Volume 35 Number 8 August

4 (P.01) revealed that participants with PFPS displayed significantly greater self-reported stiffness postsitting versus presitting (t 13 = 5.18, P.01). Additionally, participants with PFPS had significantly greater self-reported stiffness postsitting versus controls (t 13 = 4.56, P.01) (Figure 4). Pearson product moment correlations did not reveal a significant relationship between mechanical and self-reported stiffness in participants with PFPS (r = 0.16, P =.41) or in controls (r = 0.30, P =.13). Mechanical stiffness and pain was also unrelated in participants with PFPS (r = 0.19, P =.32) and in controls (r = 0.03, P =.89). However, a significant positive correlation between self-reported stiffness and pain existed in participants with PFPS (r = 0.70, P.01) that was not evident in those without PFPS (r =.08, P =.69). Self-reported descriptive statistics are found in the Table and the distribution of the self-reported stiffness and pain data in both groups is illustrated in Figure 5. FIGURE 3. Mechanical stiffness values between individuals with patellofemoral pain syndrome (PFPS) and those without PFPS presitting and postsitting (mean and SEM). Statistical analysis (2-way mixed-model ANOVA) indicated no significant interaction, difference between groups, or difference between times (P.05). Report Stiffness Stiffness (Nm rad -1 /kg) Presitting 0.93 Presitting * 4.93 Postsitting FIGURE 4. Self-reported stiffness values between individuals with patellofemoral pain syndrome (PFPS) and those without PFPS presitting and postsitting (mean and SEM). Statistical analysis (2-way mixed-model ANOVA) indicated a significant time-by-group interaction (P.05). *Significantly greater reported stiffness postsitting for those with PFPS compared to controls (P.01). Significantly greater reported stiffness postsitting compared to presitting for those with PFPS (P.01) Postsitting 1.46 PFPS Controls PFPS Controls TABLE. Self-reported knee stiffness and pain in participants with patellofemoral pain syndrome (PFPS) and controls presitting and postsitting. Self-Report Measure/Group and Time Mean ± SEM (cm) Minimum, Maximum (cm) Knee stiffness PFPS presitting 2.68 ± , 6.0 PFPS postsitting 4.93 ± , 8.5 Control presitting 0.93 ± , 5.0 Control postsitting 1.46 ± , 8.0 Knee pain PFPS presitting 1.46 ± , 7.0 PFPS postsitting 3.21 ± , 7.0 Control presitting 0.14 ± , 2.0 Control postsitting 0.32 ± , 3.0 To assess the ability of this study to detect clinically relevant differences, we calculated a post hoc power analysis using a minimum difference of 1.42 Nm rad 1, reflecting related research comparing nonnormalized passive knee joint stiffness measures. 19 Because previous research using similar methodology has not reported significant differences between groups using normalized values, we based our calculations on nonnormalized data. The post hoc power analysis indicated that the current study had adequate statistical power (95%) to detect a minimum difference between groups of at least 1.42 Nm rad 1 (Sample Power, Version 2.0; SPSS Inc, Chicago, IL). Therefore, we concluded that mechanical stiffness between participants with PFPS and those without were not significantly different prior to and after 20 minutes of sitting (average ± SD PFPS presitting, 8.01 ±2.67Nmrad 1 ; average ± SD PFPS postsitting, 8.10 ±2.81Nmrad 1 ; average ± SD control group presitting, 8.02 ± 2.52 Nm rad 1 ; average ± SD control group postsitting, 8.39 ± 2.73 Nm rad 1 ). DISCUSSION Stiffness is a common complaint associated with PFPS. Individuals with this condition often report increased stiffness after prolonged periods of sitting. The results of this investigation indicated that no significant differences exist in mechanical knee joint stiffness between patients with PFPS and matched controls prior to and after 20 minutes of sitting. However, those with PFPS had significantly greater self-reported stiffness symptoms postsitting when compared to controls. Participants with PFPS also reported a significant increase in self-reported stiffness presitting to postsitting. In addition, a significant correlation between self-reported stiffness and pain was found in the PFPS group. These findings suggest that individuals with PFPS possibly misinterpret the sensation of knee pain as joint stiffness. 498 J Orthop Sports Phys Ther Volume 35 Number 8 August 2005

5 FIGURE 5. (A) Scatter plot of self-reported stiffness and pain in those with patellofemoral pain syndrome (PFPS) presitting and postsitting (r = 0.70, P.01). Numbers corresponding to symbols indicate the number of repeated responses for that value. (B) Scatter plot of self-reported stiffness and pain in those without PFPS presitting and postsitting (r = 0.08, P =.69). Numbers corresponding to symbols indicate the number of repeated responses for that value. J Orthop Sports Phys Ther Volume 35 Number 8 August

6 In patients with rheumatoid arthritis, researchers debate the underlying mechanisms contributing to the relationship between mechanical stiffness, selfreported stiffness, and pain. 6,8 One hypothesis is that chronic pain leads to central nervous system plasticity. Chronic pain may elicit joint, ligament, and capsule mechanoreceptor sensitivity alterations at the spinal level, impairing proprioceptive joint responses and ultimately resulting in perceived joint stiffness. 2,6,7 Although a neurophysiological mechanism likely contributes to stiffness and pain, it may simply be that individuals with PFPS have difficulty distinguishing between these 2 symptoms. 10 Similar to those with rheumatoid arthritis, individuals with PFPS may use the term stiffness to generally describe various joint sensations that are unrelated to an increased resistance to motion (mechanical stiffness). 10 Partially due to the ambiguous definition of stiffness, patients with PFPS may report feelings of joint stiffness when it is more likely they are referring to pain. 20 Due to the confusion surrounding these terms and, because of the chronic pain nature of PFPS, clinicians may need to focus on disrupting the pain cycle to relieve stiffness and pain sensations in these patients. Although numerous researchers have used similar methodology to quantify joint stiffness, a limitation of the current study is the sensitivity of the instrumentation to detect angle specific changes in joint stiffness. Also, the number of trials required to obtain 3 acceptable (smooth oscillations and insignificant muscle activity) presitting stiffness trials was not recorded. Trial repetition may have a thixotropic effect, potentially decreasing stiffness. 17 However, presitting trials were only repeated if reflexive EMG activity was observed when the limb was released, as this muscle recruitment would heighten joint stiffness. 21 The current research findings have important implications for clinicians who frequently attempt to relieve complaints of joint stiffness in patients with PFPS. The results of this study suggest that reports of stiffness by persons with PFPS after 20 minutes of immobility, with the knee flexed to 90, appear to be subjective and unrelated to physiological or anatomical impediments to motion. To treat PFPS and alleviate these symptoms, more aggressive pain management may be warranted. This study provides initial insight into the common complaint of stiffness associated with PFPS. Future work investigating the exact etiology of the stiffness sensation may continue to enhance clinical care of this condition. CONCLUSION This study provides quantitative data on knee joint stiffness within the PFPS population. The results indicate that although stiffness after prolonged periods in knee flexion is a common complaint associated with PFPS, no significant changes occur in mechanical stiffness values after sitting for 20 minutes. However, those with PFPS complained of increased stiffness sensations after 20 minutes of sitting and a significant correlation existed between selfreported stiffness and pain in those with PFPS. Individuals with this condition may be misinterpreting the sensation of stiffness. Determining if patients with PFPS are confusing stiffness and pain sensations allows clinicians to select more aggressive, therapeutic pain management strategies for PFPS to maximize the effectiveness of rehabilitation exercises and functional performance. REFERENCES 1. Blackburn JT, Riemann BL, Padua DA, Guskiewicz KM. Sex comparison of extensibility, passive, and active stiffness of the knee flexors. Clin Biomech (Bristol, Avon). 2004;19: Cook AJ, Woolf CJ, Wall PD, McMahon SB. Dynamic receptive field plasticity in rat spinal cord dorsal horn following C-primary afferent input. Nature. 1987;325: Cox JS. Patellofemoral problems in runners. Clin Sports Med. 1985;4: De Luca CJ. The use of surface electromyography in biomechanics. Appl Biomech. 1997;13: Dehaven KE, Dolan WA, Mayer PJ. Chondromalacia patellae in athletes. Clinical presentation and conservative management. Am J Sports Med. 1979;7: Haigh RC, McCabe CS, Halligan PW, Blake DR. Joint stiffness in a phantom limb: evidence of central nervous system involvement in rheumatoid arthritis. Rheumatology (Oxford). 2003;42: Harvey AR. Neurophysiology of rheumatic pain. Baillieres Clin Rheumatol. 1987;1: Helliwell PS. Central nervous system involvement in perceived joint stiffness. Rheumatology (Oxford). 2004;43:255; author reply Helliwell PS. Use of an objective measure of articular stiffness to record changes in finger joints after intraarticular injection of corticosteroid. Ann Rheum Dis. 1997;56: Helliwell PS, Howe A, Wright V. Lack of objective evidence of stiffness in rheumatoid arthritis. Ann Rheum Dis. 1988;47: Hunter DG, Spriggs J. Investigation into the relationship between the passive flexibility and active stiffness of the ankle plantar-flexor muscles. Clin Biomech (Bristol, Avon). 2000;15: Insall J, Falvo KA, Wise DW. Chondromalacia Patellae. A prospective study. J Bone Joint Surg Am. 1976;58: Jennings AG, Seedhom BB. The measurement of muscle stiffness in anterior cruciate injuries an experiment revisited. Clin Biomech (Bristol, Avon). 1998;13: Johns RJ, Wright V. Relative importance of various tissues in joint stifness. J Appl Physiol. 1962;17: Kannus P, Niittymaki S. Which factors predict outcome in the nonoperative treatment of patellofemoral pain syndrome? A prospective follow-up study. Med Sci Sports Exerc. 1994;26: J Orthop Sports Phys Ther Volume 35 Number 8 August 2005

7 16. Kram JR, Kasman GS. Introduction to Surface Electromyography. Gaithersburg, MD: Aspen Publishers, Inc; Lakie M, Robson LG. Thixotropic changes in human muscle stiffness and the effects of fatigue. Q J Exp Physiol. 1988;73: McNair PJ, Wood GA, Marshall RN. Stiffness of the hamstring muscles and its relationship to function in anterior cruciate ligament defient individuals. Clin Biomech (Bristol, Avon). 1992;7: Oatis CA. The use of a mechanical model to describe the stiffness and damping characteristics of the knee joint in healthy adults. Phys Ther. 1993;73: Rhind VM, Unsworth A, Haslock I. Assessment of stiffness in rheumatology: the use of rating scales. Br J Rheumatol. 1987;26: Sinkjaer T, Toft E, Andreassen S, Hornemann BC. Muscle stiffness in human ankle dorsiflexors: intrinsic and reflex components. J Neurophysiol. 1988;60: Appendix 22. Stiene HA, Brosky T, Reinking MF, Nyland J, Mason MB. A comparison of closed kinetic chain and isokinetic joint isolation exercise in patients with patellofemoral dysfunction. J Orthop Sports Phys Ther. 1996;24: Thomson WT. Theory of Vibration With Applications. 2nd ed. Englewood Cliffs, NJ: Prentice-Hall; Wilson GJ, Elliott BC, Wood GA. The effect on performance of imposing a delay during a stretch-shorten cycle movement. Med Sci Sports Exerc. 1991;23: Winter DA. Biomechanics and Motor Control of Human Movement. New York, NY: John Wiley & Sons; Witvrouw E, Lysens R, Bellemans J, Cambier D, Vanderstraeten G. Intrinsic risk factors for the development of anterior knee pain in an athletic population. A two-year prospective study. Am J Sports Med. 2000;28: APPENDIX A = ln(x 1 /x 2 ) Where, = logarithmic decrement = the natural logarithm of the ratio of any 2 successive amplitudes x 1 = amplitude of the first peak x 2 = amplitude of the second peak Journal of Orthopaedic & Sports Physical Therapy Stiffness is calculated from knowledge of the damped frequency of oscillation of the first 2 oscillatory peaks and the coefficient of damping: k =4 2 mf d 2 + c 2 /4m Where, k = stiffness (N/m) m = lower leg and foot mass (kg) c = coefficient of damping (Ns/m) f d = damped frequency of oscillation (Hz) = 1/T And, T = time period between the first 2 oscillatory peaks Knowing the lever arm distance between the knee joint and the center of mass of the lower leg and foot allows for transformation of k into angular equivalent units (Nm rad 1 ), followed by normalization to the lower leg and foot segment mass (Nm rad 1 /kg). The amount of damping is obtained from measuring the rate of decay of free oscillations and expressed as: The damping factor ( ) is calculated as: = / (2 ) The relationship between the damped frequency of oscillation (f d ), the time period (T), and frequency of damped oscillation ( d ) is: d =2 f d = 2 /T The undamped circular natural frequency ( n ) and d are related by: n = d / 1 2 The coefficient of damping (c) is calculated utilizing the natural frequency of oscillation ( n ), the damping factor ( ), and the mass (m): c =2m n J Orthop Sports Phys Ther Volume 35 Number 8 August