KNEE OSTEOARTHRITIS (OA) is a degenerative joint

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1 503 ORIGINAL ARTICLE Biomechanical and Clinical Outcomes With Shock-Absorbing in Patients With Knee Osteoarthritis: Immediate Effects and Changes After 1 Month of Wear Kevin M. Turpin, MPT, Adrian De Vincenzo, BKin, Amy M. Apps, MPT, Thea Cooney, MPT, Megan D. MacKenzie, MPT, Ryan Chang, PhD, CPed (C), Michael A. Hunt, MPT, PhD ABSTRACT. Turpin KM, De Vincenzo A, Apps AM, Cooney T, MacKenzie MD, Chang R, Hunt MA. Biomechanical and clinical outcomes with shock-absorbing insoles in patients with knee osteoarthritis: immediate effects and changes after 1 month of wear. Arch Phys Med Rehabil 2012; 93: Objectives: To examine the effectiveness of shock-absorbing insoles in the immediate reduction of knee joint load, as well as reductions in knee joint load, pain, and dysfunction after 1 month of wear, in individuals with knee osteoarthritis (OA). Design: Pre-post design with participants exposed to 2 conditions (normal footwear, shock-absorbing insoles) with a 1-month follow-up. Setting: University laboratory for testing and general community for intervention. Participants: Community-dwelling individuals (N 16; 6 men, 10 women) with medial compartment knee OA. Intervention: Participants were provided with sulcus length shock-absorbing insoles to be inserted into their everyday shoes. Main Outcome Measures: Primary outcome measures included the peak, early stance peak, and late stance peak external knee adduction moment (KAM); the KAM impulse (positive area under the KAM curve); and peak tibial vertical acceleration. Secondary outcomes included walking pain, the Western Ontario and McMaster Universities Osteoarthritis Index pain subscale and total score, and a timed stair climb task. Results: There was a significant reduction in the late stance peak KAM with shock-absorbing insoles (P.03) during follow-up compared with the baseline test session. No other immediate or longitudinal significant changes (P.05) in the other KAM parameters or peak tibial acceleration after use of a shock-absorbing insole were observed. However, significant improvements in all measures of pain and function (P.05) were observed. Conclusions: Shock-absorbing insoles produced significant reductions in self-reported knee joint pain and physical dysfunction with 1 month of wear in patients with knee OA despite no consistent changes in knee joint load. Further research using randomized controlled trials, with larger sample sizes and From the Department of Physical Therapy, University of British Columbia, Vancouver (Turpin, De Vincenzo, Apps, Cooney, MacKenzie, Hunt); and Kintec, Surrey (Chang), BC, Canada. Supported in part by a research grant from The Arthritis Society/Arthritis Health Professions Association. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Reprint requests to Michael A. Hunt, MPT, PhD, Assistant Professor, Dept of Physical Therapy, University of British Columbia, Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3, michael.hunt@ubc.ca /12/ $36.00/0 doi: /j.apmr explorations into long-term use of shock-absorbing insoles and their effect on disease progression, is warranted. Key Words: Biomechanics; Gait; Orthoses; Osteoarthritis, knee; Rehabilitation by the American Congress of Rehabilitation Medicine KNEE OSTEOARTHRITIS (OA) is a degenerative joint disease that is characterized by a degradation of articular cartilage and the corresponding subchondral bone. It is a progressive disease that can be very debilitating, with signs and symptoms such as joint pain, stiffness, and localized swelling. Although it can affect any joint, OA occurs most often at the knee and can result in limitations or restrictions in a person s daily activities, especially walking. Affecting almost 1 in 6 people older than 15 years, 1 OA presently has no cure. Increased loading of the medial tibiofemoral compartment during walking has been implicated in the progression of knee OA. 2,3 Higher loads at the knee joint cause an increased rate of breakdown of articular cartilage 4,5 and lead to more severe disease. Because of the difficulty in measuring knee load directly, the external knee adduction moment (KAM) is often used as an indirect measurement of medial tibiofemoral loading. 6,7 In the knee OA population, there is evidence that a higher peak KAM during stance is associated with more severe disease and changes in joint structure. 8,9 Given the clinical and biomechanical relevance of the KAM, it has become an accepted proxy for dynamic loading and has provided important outcome information in studies assessing OA pathogenesis or the effectiveness of treatment. Given the clinical importance of joint load, successful treatment approaches for knee OA should not only address clinically important variables such as pain and function, but provide a means of reducing knee joint load to slow disease progression. Conservative mechanical interventions such as valgus bracing have been found to improve clinical results 10,11 and reduce the KAM, although the effects on structural deterioration have not been assessed. 12,13 However, these can be cumbersome and expensive 14 and may not be appropriate in the long term for those with peripheral vascular disease, those who are morbidly obese, or those prone to skin irritation. 11 Surgical intervention, such as high tibial osteotomy, can provide GRF KAM KL OA WOMAC List of Abbreviations ground reaction force knee adduction moment Kellgren & Lawrence osteoarthritis Western Ontario and McMaster Universities Osteoarthritis Index

2 504 SHOCK-ABSORBING INSOLES AND KNEE OSTEOARTHRITIS, Turpin satisfactory long-term results by redistributing weight-bearing forces and thus reducing pain and improving function 15,16 ; however, it is attended by the risks of invasive procedures. 14,17 One area that has received recent attention in the literature for treatment of knee OA is footwear modification. Variablestiffness shoes with varying material properties made to be stiffer on the lateral side worn for 6 months have been shown to decrease the peak KAM, decrease pain, and improve function in those with knee OA. 18 Lateral-wedged insoles, which unload the medial compartment by shifting the load distribution in the foot and knee laterally, 19 have also been shown to produce reductions in KAM and pain, 20 although predominantly in individuals with less severe stages of OA. Custommade lateral wedge orthoses have been recommended for symptomatic relief 21 but can be costly. 22 Another potential intervention that is inexpensive, has minimal side effects, and has no known contraindications is shockabsorbing insoles. These insoles, typically composed of a gel or similar shock-absorbing material, have previously been used in healthy athletic and military populations to prevent overuse injuries and have been shown to reduce impact forces and loading rates of the lower limb as measured using tibial accelerometry It is proposed that by reducing the rate and magnitude of loading at foot strike during gait, the load transmitted to the knee joint will be reduced. 26 Although shock-absorbing insoles are widely available, are used by many individuals with various pathologies, and have been shown to reduce lower limb loading, no studies have assessed their effectiveness in reducing joint loading and pain in patients with knee OA. Therefore, the purpose of this study was to examine the immediate changes in knee joint loading during walking (measured by KAM and tibial acceleration) after the insertion of shock-absorbing insoles into the shoes of individuals with knee OA. A secondary purpose of this study was to assess changes in joint loading, pain, and physical function after 1 month of shock-absorbing insole wear in patients with knee OA. METHODS Participants Individuals with medial compartment knee OA were recruited from the community via advertisements in local newspapers. Inclusion criteria consisted of radiographic evidence of knee OA (Kellgren & Lawrence [KL] grade 2 or greater) 27 as determined from standing short-film posteroanterior radiographs, and varus malalignment as measured from the shortfilm posteroanterior radiographs and using published regression equations to calculate the mechanical axis of the lower limb. 28 All subjects had knee pain during walking that was greater than 3 out of 10 (based on an 11-point scale; 0, no pain; 10, maximal pain) on most days of the previous month, to allow detection of response to treatment. Exclusion criteria consisted of current or recent (within 1mo) oral corticosteroid use; knee surgery or intra-articular corticosteroid injection within 6 months; any muscular, joint, or neurologic condition affecting lower limb function; ankle/foot pathology or pain that precluded the use of insoles; current use of foot orthoses; predominant use of footwear unable to accommodate an insole; inability to walk without a gait aid; and inflammatory arthritic conditions (such as rheumatoid arthritis or gout). Ethical approval was obtained from the Institutional Clinical Research Ethics Board, and all participants provided written informed consent. Procedures Because of the potential effects associated with unfamiliarity with insoles, there were 2 test sessions. Participants underwent testing on the day that the insoles were dispensed (baseline) and after a 1-month period of acclimatization (follow-up). During both testing sessions, measurements of gait, physical function, and pain were taken. After the baseline session, participants were provided with 2 pairs of shock-absorbing insoles. a The insoles were sulcus length, noncustomized orthoses made of triple-density gel with a heel thickness of 8.35mm and forefoot thickness of 4.31mm. Completion of a daily log by the participant provided information pertaining to insole wear time over the 1-month period. Participants were not discouraged from seeking new treatments for OA, but were requested to record any changes in their clinical management, including medication use, during the 1-month trial, as well as changes in symptoms and any adverse effects from the insoles. Gait Analysis All participants underwent 3-dimensional gait analysis using 8 high-speed digital cameras b sampling at 120Hz. These were synchronized with 2 force platforms c placed in the center of an 8-m walkway that sampled ground reaction force (GRF) data at 1200Hz. Reflective markers were placed on the participants skin using a 22-marker, modified Helen Hayes marker set, 29 which included lower body placements at the lumbosacral junction and bilaterally on the anterior superior iliac spine, lateral femoral condyle, tibial tubercle, lateral malleolus, heel, and base of the second metatarsal. In addition, extra markers were placed bilaterally over the medial malleolus and medial knee joint line during an initial static standing trial. This trial was collected on the force platform to measure body mass, to calibrate marker orientation, and to determine the positions of joint centers of rotation for the ankle, knee, and hip. These additional markers were removed before gait testing. In addition, a biaxial accelerometer d was affixed to the tibial tuberosity of the study limb (most painful in cases of bilateral signs and symptoms) with medical tape to measure vertical acceleration of the tibia during gait. Participants walked at a self-selected speed in their usual walking shoes under 2 randomly presented conditions: (1) shoes only and (2) insertion of the shock-absorbing insoles into their shoes. A total of 5 walking trials with and without insoles was obtained. All gait data were processed by researchers (K.M.T., A.M.A., T.C., M.D.M.) blinded to test condition and using commercially available software b to calculate the external KAM during gait and custom written software to identify peak tibial acceleration during stance. The primary outcome measures were the maximum peak external KAM (KAM p ), the peak KAM of the first half of stance (KAM 1 ), the peak KAM of the second half of stance (KAM 2 ), the KAM impulse (KA- M imp ; defined as the positive area under the KAM-time graph), and the peak vertical tibial acceleration. Pain and Function Participants completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC; Likert version) 30 to obtain the pain subscale (0 20, with higher scores indicating more pain) and the total WOMAC score (0 96, with higher scores indicating more pain, stiffness, and physical dysfunction). Participants were also asked to rate their average knee pain over the previous week using an 11-point numeric rating scale where 0 indicated no pain and 10, the worst pain ever. Objective physical function was assessed as the time it took to

3 SHOCK-ABSORBING INSOLES AND KNEE OSTEOARTHRITIS, Turpin 505 Table 1: KAM Parameters, Including Overall KAM p, KAM 1, KAM 2, and KAM imp, As Well As Peak Tibial Vertical Acceleration and Self- Selected Walking Velocity Measured Within-Session (n 16) Between-Session (n 14) P Gait Parameters No Difference (95% CI) Follow-up Difference (95% CI) Within-Session Between-Session Interaction KAM p (%BW ht) (.57 to.78) (.38 to 1.66) KAM 1 (%BW ht) (.61 to.51) (.55 to 1.28) KAM 2 (%BW ht) (.59 to 1.00) (.08 to 1.73).72.03*.49 KAM imp (%BW ht s) (.17 to.24) (.11 to.51) Tibial acceleration (g) (.27 to.18) (.20 to.27) Gait velocity (m/s) (.02 to.05) (.09 to.02) NOTE. Values are mean SD, mean (95% CI), or as otherwise indicated. Within-session comparisons are reported between the insoles and no-insoles trials at baseline for all 16 participants, while between-session (baseline vs follow-up) comparisons of the insoles-only trials are reported for the 14 participants who completed the study. Note that data for the baseline and follow-up no-insoles trials were similar and are not reported. Abbreviations: %BW, percent body weight; CI, confidence interval; ht, height; KAM 1, early stance peak KAM; KAM 2, late stance peak KAM; KAM imp, KAM impulse; KAM p, peak KAM. *Values are significant at P.05. ascend 12 stairs. Each subject climbed the stairs twice, both times were recorded, and the faster time was used. Statistical Analysis Statistical analyses were performed with the Statistical Package for the Social Sciences software, e using an level of.05. KAM and tibial acceleration data were evaluated using a 2- factor, repeated-measures analysis of variance to determine the main effect for condition (insoles vs no insoles) and session (baseline vs follow-up) and their interaction effect. Mean differences in the pain and function outcomes between baseline and follow-up were evaluated using paired t tests. RESULTS A total of 16 participants (10 women) with a mean age SD of years, body mass index of kg/m 2, and radiographic lower limb alignment of indicative of varus malalignment were recruited. Ten participants had mild knee OA (KL grade 2), 2 had moderate knee OA (KL grade 3), and 4 had severe knee OA (KL grade 4) in the medial compartment of the tibiofemoral joint. Fourteen participants (88%) returned for follow-up testing, a mean SD of days after the baseline testing. Participants reported a mean SD wear of hours of the shock-absorbing insoles over the course of the intervention. Three participants reported an adverse effect (foot discomfort) in the first week of insole wear that subsided within 7 days. No participants reported seeking additional treatments during the intervention. Two participants reported a reduction in medication use during the trial, while 1 participant reported an increase in medication use. The only significant reduction in knee joint loading was observed for the KAM 2 (P.03) in the insoles trials when comparing follow-up and baseline test sessions. No other immediate or longitudinal significant changes (P.05) in the other KAM parameters or peak tibial acceleration were observed (table 1), nor were any significant interactions (P.05). Self-selected walking speeds were similar for each participant at baseline and follow-up, with differences in speed ranging from 1.1% to 11.8%. In contrast, use of shock-absorbing insoles for 1 month significantly improved all measures of pain and function (P.05) (table 2). Specifically, average pain during the week before testing significantly improved from a mean SD of out of 10 to out of 10 (P.04). Also, WOMAC pain ( vs ; P.02) and WOMAC total ( vs ; P.04) scores were significantly reduced after 1 month. Finally, the time to ascend 12 stairs significantly improved from to seconds (P.02) at the follow-up testing session. DISCUSSION Findings from the present study suggest that shock-absorbing insoles can produce significant improvements in knee joint pain and physical function after 1 month of wear. However, the role of biomechanics in improvements in clinical measures is unclear based on our data. Although a significant reduction was observed for the late stance KAM peak (KAM 2 ), no significant reductions were found in any other measure of knee joint loading during walking. Given that previous research has demonstrated that knee joint loading is an important determinant predicting knee OA progression, these findings suggest that Table 2: Self-Reported Average Pain Over the Previous Week, WOMAC Pain, WOMAC Total, and Time Required to Ascend 12 Stairs Before () and After 1 Month (Follow-up) of Wear Pain Measures and Function Session Follow-up Mean Difference (95% CI) Average pain (0 10) ( ).04* WOMAC pain (0 20) ( ).02* WOMAC total (0 96) ( ).04* Stair climb (s) ( ).02* NOTE. Values are mean SD, mean (95% CI), or as otherwise indicated. Abbreviations: CI, confidence interval; s, second. *Values are significant at P.05. P

4 506 SHOCK-ABSORBING INSOLES AND KNEE OSTEOARTHRITIS, Turpin shock-absorbing insoles may not have a protective role against disease progression in individuals with knee OA. Before this study, there have been no published clinical trials that have examined the effects of shock-absorbing insoles on biomechanical and clinical outcomes in the knee OA population. However, shock-absorbing insoles have been well studied in healthy athletic populations, as well as in soldiers, with mixed results. O Leary et al 23 demonstrated that shock-absorbing insoles reduce vertical GRF peak impact and loading rate, as well as peak tibial acceleration at initial contact, in recreational runners. In another study, Windle et al 24 inserted 4 commercially available insoles into the boots of soldiers during running and marching and found that all 4 insoles reduced the peak pressures generated during heel strike and forefoot loading compared with the no-insole condition. These previous results led to our hypothesis that shock-absorbing insoles would reduce impact and joint loading in individuals with knee OA. However, our data did not support this hypothesis. Similarly, other authors have found no decreases in vertical force peak or maximum loading rate with the use of shock-absorbing insoles in the healthy running population. 31,32 It has been suggested that runners may alter their kinematics in response to insoles, which would in turn remove any changes in knee loading. Specifically, runners may decrease knee flexion at initial contact, which is known to increase GRFs and resultant tibial acceleration magnitudes. 23 These kinematic adjustments during running may be related to perceived comfort, because comfort is known to be correlated with kinematic and kinetic outcomes during running. 33 Although not reported above, no changes in peak knee flexion were observed during the loading response phase across conditions or testing sessions in the present study. Therefore, any perceived change in comfort did not translate to kinematic alterations during gait. Changes in the KAM can occur because of changes in the magnitude of the GRF, the lever arm distance between the GRF vector and the knee joint center, or both. 34 In theory, shockabsorbing insoles would have little influence on the magnitude of the reaction force that the ground exerts onto the foot during stance compared with other factors such as body mass 35 or walking speed. 36 Indeed, this has been demonstrated previously by Nigg et al, 31 where shock-absorbing insoles were shown to have no effect on vertical forces, and previous research has shown no significant correlation between selfselected walking speed and KAM in people with knee OA. 37 In contrast, the acceleration of lower limb segments and the resultant joint force experienced at the joint depends both on the magnitude of the GRF and on the ability of the body to naturally dissipate these forces. 38 The addition of shockabsorbing insoles has been shown to be effective in absorbing these forces as measured using tibial accelerometry, with an anticipated benefit to the knee joint. 25 However, there was no observable significant change in peak tibial acceleration in the present study. These findings may be due to the relatively smaller GRFs that occur during walking compared with running. As a result, the cushioning provided by shock-absorbing insoles may not have been of sufficient magnitude to be detected via indirect measures. The second primary way to affect the load passing through the medial knee joint is to shorten the GRF lever arm, thus redistributing the load. 39 Although other studies have looked at the impact of shock-absorbing insoles on linear measures of force (ie, tibial acceleration and GRFs), none have also examined the possible influence of shock-absorbing insoles on the KAM, which as a joint moment involves both linear force and the magnitude of the lever arm. Previous studies 40,41 involving laterally wedged insoles have reported reductions in the peak KAM, possibly resulting from changes in lower limb alignment 42 or alterations in the position of the center of pressure, although this latter mechanism has been debated. 43 Either of these mechanisms would presumably reduce the GRF magnitude at the knee, thus reducing the peak KAM. Failure to observe a reduction in KAM variables in the present study is likely because the shock-absorbing insoles used were of neutral alignment (ie, no wedging), resulting in no shift of the center of pressure or change in lower limb alignment, and hence no decrease in the length of the lever arm. Despite inconsistent knee joint load findings, significant improvements in pain and function were observed. As previously mentioned, no published studies exist reporting the biomechanical and symptomatic effects of shock-absorbing insoles in the medial knee OA population. However, a number of studies have examined the effects of laterally wedged insoles on clinical symptoms in patients with knee OA. Two nonrandomized and uncontrolled studies 42,44 have found short-term improvements in pain with the use of wedged insoles, while more rigorous randomized and controlled studies have found contrasting results pertaining to pain relief. Indeed, while previous studies have failed to show significant long-term improvements in pain, Pham et al 46 did find a reduction in pain medication intake with the use of wedged insoles, implying a modest and indirect beneficial effect on symptoms. Our findings of improved pain and function after 1 month of shockabsorbing insole wear may be the result of a perceived improvement in comfort after the insertion of the insoles, as has been reported previously. 33 However, the significant reduction of pain seen in our study may reflect an actual treatment effect, a reflection of the natural history of the disease, or simply a placebo effect. Regardless, these findings further highlight the apparent disconnect between subjective measures of pain and function and objective measures of knee joint loading as quantified indirectly using 3-dimensional motion analysis. Study Limitations There are some limitations to this study. The sample size used was 16 individuals, and it is possible that much smaller reductions in joint loading may have gone undetected. However, our a priori sample size calculation indicated that 16 individuals would be sufficient to detect a 5% to 10% reduction in the peak KAM consistent with previous studies of conservative interventions with 80% power. Further, although we did not observe significant reductions in measures of knee joint loading, we were able to detect significant changes in the other outcome measures used in this study. Furthermore, the lack of a control group limits the conclusions that may be drawn regarding the findings from this study. Despite these limitations, this exploratory study is to our knowledge the first to examine the effects of shock-absorbing insoles on improving symptoms experienced by people with knee OA. These preliminary findings provide a rationale for further research using randomized controlled trials with larger sample sizes, and explorations into long-term use of shock-absorbing insoles and their effect on clinical and biomechanical outcomes. CONCLUSIONS Shock-absorbing insoles can significantly improve measures of knee joint pain and physical dysfunction after 1 month of wear in patients with knee OA. Although these results may not have been the result of altered lower limb biomechanics during walking, there is now evidence for the role of shock-absorbing insoles in the clinical self-management of this disease. Indeed, shock-absorbing insoles represent an intervention that is inex-

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