KNEE OSTEOARTHRITIS, which occurs symptomatically

Transcription

1 ARTICLES Effectiveness of a Lateral-Wedge on Knee Varus Torque in Patients With Knee Osteoarthritis D. Casey Kerrigan, MD, MS, Jennifer L. Lelas, MS, Joyce Goggins, MPH, Greg J. Merriman, MPH, Robert J. Kaplan, MD, David T. Felson, MD, MPH 889 ABSTRACT. Kerrigan DC, Lelas JL, Goggins J, Merriman GJ, Kaplan RJ, Felson DT. Effectiveness of a lateral-wedge insole on knee varus torque in patients with knee osteoarthritis. Arch Phys Med Rehabil 2002;83: Objectives: To test whether a lateral-wedged insole, inclined at 5 or 10, significantly reduces knee varus torque during walking in patients with knee osteoarthritis compared with both using no insole and with wearing nonwedged control insoles of the same material and average thickness. Design: Patients with medial knee osteoarthritis were studied while they walked wearing their comfortable shoes (1) without an insole; (2) with a 5 lateral wedge compared with a nonwedged, mm ( 1 8-in) even-thickness control insole; and (3) with a 10 lateral wedge compared with a nonwedged 6.35-mm ( 1 4-in) even-thickness control insole. Setting: A gait laboratory with 3-dimensional motion analysis and force platform equipment. Participants: Fifteen patients with clinical and radiographic osteoarthritis of the medial compartment of 1 knee. Interventions: Not applicable. Main Outcome Measures: Peak external knee varus torques during the stance period of gait. Data regarding lowerextremity joint torques and motions were collected, and knee joint torques using the different insoles and wedges were compared by analysis of variance. Results: Although responses varied among individuals, as a group, both the 5 and 10 lateral-wedge insoles significantly reduced the knee varus torque during walking compared with walking with no insole and walking with nonwedged mm and 6.35-mm control insoles. Compared with no insole, the 5 wedge reduced the peak knee varus torque values by about 6% and the 10 wedge reduced the peaks by about 8%. Although there were no significant differences in speed of walking between the conditions, the 10 wedge and 6.35-mm control insoles were associated with varying degrees of discomfort. Conclusion: Both wedge insoles are effective in reducing the varus torque during walking beyond what theoretically could be explained by a reduced walking speed or cushioning From the University of Virginia, Department of Physical Medicine and Rehabilitation (Kerrigan); Harvard Medical School, Department of Physical Medicine and Rehabilitation (Kaplan); Spaulding Rehabilitation Hospital Center for Rehabilitation Science (Lelas, Merriman, Kaplan); and Arthritis Center, Boston University School of Medicine (Goggins, Felson), Boston, MA. Accepted in revised form August 30, Supported by the Ellison Foundation and by the US Public Health Service (grant no. NIH AR20613). 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. Reprint requests to D. Casey Kerrigan, MD, MS, University of Virginia School of Medicine, Department of Physical Medicine and Rehabilitation, 545 Ray C. Hunt Dr, Ste 240, PO Box , Charlottesville, VA , dck7b@ virginia.edu /02/ $35.00/0 doi: /apmr effect from the insole. These data imply that wedged insoles are biomechanically effective and should reduce loading of the medial compartment in persons with medial knee osteoarthritis. Although the effect of the 5 wedge was smaller, it may be more comfortable than the 10 wedge to wear inside one s own shoes. Key Words: Biomechanics; Gait; Kinetics; Knee; Rehabilitation; Shoes by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation KNEE OSTEOARTHRITIS, which occurs symptomatically in approximately 6% of adults 30 years of age and older and in 11% of adults 65 years of age and older, accounts for more mobility disability in the elderly than any other disease. 1 Osteoarthritis typically affects joints in a nonuniform manner; of the 3 knee components, the one most frequently affected in knee osteoarthritis is the medial compartment. 2 The predominance of medial compartment osteoarthritis likely results from the high medial compartment forces during weight-bearing activities such as walking, 3,4 which is by far the most common daily activity exerting the greatest repetitive forces through the knee. 3 During walking, the normal forces acting on the leg produce a varus torque (ie, a torque tending to adduct the knee into varus). 5 This varus torque is directly associated with the compressive force across the medial aspect of the knee, which is nearly times the force through the lateral aspect of the knee. 3,4 The fact that this varus torque is believed to be responsible for the progression of knee osteoarthritis is supported by data from both animal and clinical studies. An animal study showed that imposing a varus torque directly induced osteoarthritic changes, 6 whereas clinical surgical data show that a tibial osteotomy to increase lateral loading effectively reduces the knee varus torque as well as both knee pain and disease progression. 7,8 Given the importance of the knee varus torque in the progression of medial compartment knee osteoarthritis, conservative means to reduce this torque constitute a logical rehabilitative approach. Sasaki and Yasuda 9,10 first reported the potential of a laterally wedged insole in treating osteoarthritis of the knee. Although they did not directly measure knee varus torque, they showed that when subjects stood on a board that was angulated 5 laterally, there was a change in the spatial position of the lower limb. From that change, they concluded that loading through the medial knee joint would be reduced. 10 These investigators also reported that patients with medial knee osteoarthritis had less knee pain when using a 5 laterally wedged heel insole combined with a nonsteroidal medication compared with a nonsteroidal medication alone. 9 Although a randomized controlled trial of the effect of a wedge insole has not been done, clinical reports suggest such an insole can reduce pain Wolfe and Brueckman 11 reported that 82% of their patients with medial knee osteoarthritis had at least some lessening of pain with a lateral heel wedge, and Keating et al 13

2 890 LATERAL-WEDGE INSOLE FOR KNEE OSTEOARTHRITIS, Kerrigan reported that 61% of knees with medial osteoarthritis had improved pain scores with a lateral heel wedge. Given that the knee varus torque is present throughout the entire stance period and not just at heel strike and early stance, we believe that to be most effective, a lateral-wedge insole should be laterally wedged throughout the full length of the sole. Recently, Crenshaw et al 14 studied the effect of a 5 laterally wedged, full-length insole on knee varus torque during the stance period of walking in unimpaired subjects. They showed that the insole significantly decreased the varus torque by almost 7%. 14 Although this was the first dynamic biomechanical study of the effect of a lateral-wedge insole, it did not include patients with knee osteoarthritis nor did it attempt to control for the compressive effect of the insole. The effect of a wedge may be different in patients with knee osteoarthritis insofar as the knee biomechanics are somewhat different. For instance, knee varus torque is generally greater in patients with knee osteoarthritis, 15 and there are likely compensatory gait patterns used by patients that can affect the knee varus torque. 16 Also, there may be effects from the cushioning nature of the insole material itself, which might account for changes in both biomechanics and pain symptoms. In patients with clinically and radiographically documented medial knee osteoarthritis, we assessed the effect of both a 5 and a 10 laterally wedged insole. We compared wearing the wedge insole with wearing no insole as well as with nonwedged insoles made of the same material worn by study controls. The insoles had an even thickness of 3.175mm ( 1 8in) (average thickness of a 5 lateral wedge insole) and an even thickness of 6.35mm ( 1 4in) (average thickness of a 10 lateral-wedge insole). METHODS Study subjects were selected from the Boston Osteoarthritis of the Knee Study, a natural history study of knee osteoarthritis. 17,18 To be eligible, subjects were required to have had knee pain on most days of a recent month and have radiographic osteoarthritis in that knee defined as a definite osteophyte. The radiographic disease was characterized on semiflexed posteroanterior (PA), 19 skyline, and lateral weight-bearing views. 18 We additionally required that in a painful knee, subjects have radiographic osteoarthritis of at least grade 3 severity according to the Kellgren and Lawrence scale 20 on the PA semiflexed view, with definite joint space narrowing in the medial compartment but not in the lateral compartment. Patients were excluded if they were currently using a wedge insole or other custom-made orthotics in their shoes on a regular basis; had undergone tibial osteotomy surgery; had significant peripheral or central nervous system disease; had concurrent clinically active arthritis of the hip, ankle, hindfoot or midfoot; or were unable to walk without a cane or walker. Fifteen subjects (8 men, 7 women) with documented osteoarthritis of the medial compartment of the knee were studied. Ten subjects had a grade 3 severity and 5 subjects had a grade 4 severity according to the Kellgren and Lawrence scale. Both the laterally wedged insoles and the nonwedged, eventhickness control insoles were manufactured by NovaCare/ Hanger a and consisted of a rubber-like material called Amerifoam (a 55-durometer density foam). a The wedged insoles were laterally inclined 5 and 10 along the full length of the insole from hindfoot to forefoot. The nonwedged, even-thickness control insoles were each 3.175mm and 6.35mm thick (even thickness medially to laterally as well as from hindfoot to forefoot), each reflecting the average thickness of, respectively, a 5 and a 10 lateral-wedge insole. All of the insoles were trimmed along the perimeter of each subject s feet to fit inside the subject s own comfortable shoes. None required hindfoot to forefoot trimming of the wedge medially or laterally. The protocol to evaluate the biomechanical effect of the wedges was approved by the Spaulding Rehabilitation Hospital and the Boston University School of Medicine institutional review boards, and written informed consent was obtained from each subject. Subjects were asked to first stand and then walk at their comfortable walking speed across a 10-m gait laboratory walkway. They were tested wearing (1) their own comfortable shoes, (2) those same shoes with the nonwedged mm thick control insole on the affected side, (3) the 5 lateral wedge on the affected side, (4) the nonwedged 6.35-mm thick control insole on the affected side, and (5) the 10 lateral wedge on the affected side. The order of testing of each condition was randomized. Full pelvic and lower-extremity 3-dimensional kinematic and kinetic data were collected over 3 walking trials for each condition. The procedures used for this analysis are based on standard techniques described previously A video-based motion analysis system (Vicon 512 System) b was used to measure the 3-dimensional position of retroreflective markers at 120 frames per second. These markers were attached to the skin with adhesive tape over the following bony landmarks on the subjects pelvis and lower extremities: bilateral anterior superior iliac spines, lateral femoral condyles, lateral malleoli, forefeet, and heels. Additional markers were placed over the sacrum and rigidly attached to wands over the midfemur and midshank. Ground reaction forces were measured synchronously with the motion analysis data by using 2 staggered force platforms c imbedded in the walkway. Joint torques in each plane were calculated with a commercialized, full-inverse dynamic model (Vicon Clinical Manager). b Accordingly, joint torque and power calculations were based on the mass and inertial characteristics of each lower-extremity segment, the derived linear and angular velocities and accelerations of each lower-extremity segment, as well as ground reaction force and joint center position stimates. Joint torques were normalized for body weight and height and reported in Newton meters per kilogram meters. Gait velocity and stride length were obtained by using the force platform and kinematic information to define initial foot contact times and distance parameters. Table 1: Temporal Parameters No Walking speed (m/s) Stride length (m) Cadence (strides/s) NOTE. Values are mean SD.

3 LATERAL-WEDGE INSOLE FOR KNEE OSTEOARTHRITIS, Kerrigan 891 Fig 1. Knee varus torque during walking plotted over an averaged gait cycle. Effect of 5 lateral-wedge insole and 10 lateral-wedge insole versus no insole (N 15). Coronal knee joint torque data in 3 planes, averaged for each condition, were plotted over the walking cycle (0% 100% at 2% intervals) and visually inspected. The 2 parameters statistically evaluated were peak knee varus torque in early and late stance, reflecting the compressive force on the medial tibiofemoral aspect of the knee that occurs during walking. 3,4 The averaged temporal parameters and averaged peak knee torques were compared by using a repeated-measures analysis of variance and post hoc t test assessment. Statistical evaluations were performed with the software program Stata 6.0 d with significance defined as P less than.05. In addition, the peak knee torques with and without insoles were reported separately (means and standard deviations [SDs]) for each Kellgren and Lawrence grade (3 and 4) and qualitatively compared. RESULTS The subjects averaged years of age, had an average weight of kg, and an average height of m. All subjects were comfortable wearing the 5 wedged and the nonwedged mm thick insoles; however, nearly every subject reported varying degrees of mild discomfort wearing the 10 wedge and the nonwedged 6.35-mm thick insole, stating that their feet felt somewhat constricted or cramped inside their shoes. The averaged temporal parameters are listed in table 1. Use of wedges or insoles was not associated with changes in walking speed, stride length, or cadence. The general pattern of varus knee torque was similar among all 5 conditions. The varus knee torque curves of the 5 lateral wedge and the 10 lateral wedge versus no insole are shown in figure 1. The averaged peak torque values of each condition, including the nonwedged mm and 6.35-mm thick control insoles, are listed in table 2. The first peak knee varus torque in early stance was significantly less for the 5 lateral wedge insole compared with both no insole (a 5.3% reduction, P.007) and the nonwedged mm thick control insole condition (a 3.8% reduction, P.047). The second peak knee torque in late stance was similarly reduced for the 5 lateral wedge compared with no insole (a 6.5% reduction, P.001) and with the mm thick control (a 4.2% reduction, P.016). The reductions in peak knee varus torque were somewhat larger in magnitude for the 10 lateral wedge compared with both no insole and the 6.45-mm control insole. The first peak knee varus torque for the 10 lateral wedge was reduced by 8.3% compared with no insole (P.001) and by 8.1% compared with the 6.35-mm thick control insole (P.001). The second peak knee varus torque for the 10 lateral wedge was reduced by 8% compared with no insole (P.001) and by 6.9% compared with the 6.35-mm thick control insole (P.001). There were slight differences in peak knee varus torque between using no insole and wearing the mm and 6.35-mm nonwedged, eventhickness control insoles (see table 2); however, none of these differences was statistically significant. Table 3 lists the means and SDs of the peak knee torques for each group of subjects according to Kellgren and Lawrence grade. There was a reduction in each knee torque for each wedge compared either with no insole or with its respective nonwedged control insole for both grades 3 and 4. Also, the knee torques were generally greater for subjects with a Kellgren and Lawrence grade 4 compared with those with a grade 3, but the magnitude of difference with the lateral wedges was similar between the 2 grades. DISCUSSION This study s results support the hypothesis that a lateralwedge insole of either 5 or 10 significantly reduces knee varus torque during walking in patients with knee osteoarthritis, compared with both having no insole and with wearing nonwedged control insoles of the same material and average thickness. Compared with having no insole, the 5 lateralwedge insole was associated with an almost 6% overall reduction in knee varus torque (5.3% reduction in the first knee varus torque, 6.5% reduction in the second knee varus torque). Our significant differences between the lateral wedges and control insoles show that the effect of the wedge is the result of directly altering the knee joint biomechanics rather than being merely the result of insole cushioning. Moreover, the fact that there were no differences in temporal parameters between the conditions supports the conclusion that the reduced measured knee varus torque with the lateral wedge was not merely the result of a slower walking speed or stride length. To our knowledge, no previous study has evaluated the effect on gait of a 10 lateral wedge, either clinically or biomechanically. The discomfort or cramping noted with the 10 wedge (that also occurred with the 6.35-mm control insoles) implies that the discomfort is largely a result of inadequate shoe depth. This discomfort, or feeling of the foot being cramped, was sufficiently mild that it did not affect walking speed or other temporal parameters. Nonetheless, the discomfort is likely to prohibit using such an insole on a regular basis outside the laboratory. A trial combining a 10 wedge with Table 2: Group Peak Knee Varus Torque Values During Walking (N 15) No First peak in early stance Second peak in late stance NOTE: Values are mean SD, measured in N m/kg m.

4 892 LATERAL-WEDGE INSOLE FOR KNEE OSTEOARTHRITIS, Kerrigan Table 3: Kellgren and Lawrence Grades 3 and 4 for Peak Knee Varus Torque Values During Walking No First peak in early stance Grade 3 (n 10) Grade 4 (n 5) Second peak in late stance Grade 3 (n 10) Grade 4 (n 5) NOTE: Values are mean SD, measured in N m/kg m. extra-depth shoes may be worthwhile. Moreover, it is likely, given individual variation among subjects, that each subject will respond best to a lateral wedge of a certain inclination. A case could be made for individually assessing each patient wearing lateral-wedge insoles with various degrees of inclination to find the one that is both comfortable and effective in reducing the knee varus torque. The magnitude of reduction with a 5 lateral wedge (nearly 6%) is remarkably similar to that reported by Crenshaw et al 14 in subjects without osteoarthritis (approximately 7% reduction). The actual magnitudes of torque values for the trials without insoles (.396N m/kg m for the first peak, equivalent to 4% of body weight height) is similar to that reported by others. Schipplein and Andriacchi 4 measured a 4.2% torque value in patients with osteoarthritis, whereas Sharma et al 15 included values (in bar graphs) of between 3% and 5% body weight by height. Similar to Sharma, we observed higher peak torque values for subjects with greater disease severity (a Kellgren and Lawrence grade 4 compared with a grade 3). Meanwhile, the values obtained in subjects without osteoarthritis reported by Crenshaw 14 (.429N m/kg m or.27n m/ kg m, normalizing for height, equivalent to 2.7% body weight height) are somewhat lower than that reported by Kadaba et al 23 (3.3% estimated from graphs), and by Andrews et al 16 (3.5%). The difference in actual magnitude reported by Crenshaw may reflect a difference in the biomechanical model they used to define joint torques. Nonetheless, the relative differences that Crenshaw and we found are of similar magnitude, indicating that a lateral-wedge insole has a similar effect on knee varus torque in people with and without medial knee osteoarthritis. The effect of the wedges seem to be similar whether or not the subject has a Kellgren and Lawrence grade 3 or grade 4 disease severity (table 3). Nonetheless, further studies might be performed to assess statistically the effect of a lateral wedge for larger numbers of patients, grouped according to disease severity. Although previous reports suggest that a lateral-wedge insole can reduce pain in patients with medial knee osteoarthritis, this biomechanical study shows that such a wedge is effective in reducing the knee varus torque. This may be the mechanism by which the wedge reduces pain and, if studies with animals or persons postosteotomy are a guide, it may also reduce the progression of knee osteoarthritis. Reducing both pain and knee varus torque is particularly appealing because treatment modalities that may reduce pain do not necessarily reduce the knee varus torque. 26 For instance, although analgesic medications such as nonsteroidal anti-inflammatory drugs and opiates may be effective in reducing pain, nonsteroidal drugs actually increase the knee varus torque during walking, and this may tend to accelerate the progression of the disease. 26,27 The fact that a lateral wedge may be effective in both reducing pain and knee varus torque is of particular clinical importance because current treatment options for medial knee osteoarthritis are limited. A surgical tibial osteotomy, although often effective in reducing the knee varus torque and knee progression, is rarely performed because it is invasive, is technically demanding, and requires substantial healing time. Knee replacement surgery can offer tremendous relief, but it is generally reserved for people with severe disease who are in a restricted age range. Medial compartment knee osteoarthritis causes a loss of joint space in that compartment leading to knee varus angulation. Because this elevates varus torque, this medial joint space loss potentiates progressive joint space loss and angulation, leading to a vicious cycle. Thus, rehabilitative modalities aimed at interrupting this cycle by reducing the knee varus torque may be the most effective. Encouraging a person to lose weight and prescribing an assistive device such as a cane are among the methods used to reduce the overall force through the leg and knee. Valgus bracing to reduce varus angulation could reduce knee varus torque. Further studies, including randomized controlled trials that study the long-term effect of a lateral-wedge insole, are needed. CONCLUSION Medial compartment knee osteoarthritis causes a loss of joint space in that compartment, elevating the knee varus torque and potentiating progressive joint space loss and angulation, creating a vicious cycle. Thus, rehabilitative modalities aimed at interrupting this cycle by reducing the knee varus torque may be the most effective. In this study, we provide evidence that a simple lateral-wedge insole of either 5 or 10 directly reduces the knee varus torque in patients with medial knee osteoarthritis; this can potentially interrupt this vicious osteoarthritis cycle, slowing the progression of this disease and its associated disability. References 1. Guccione AA, Felson DT, Anderson JJ. Defining arthritis and measuring functional status in elders: methodological issues in the study of disease and physical disability. Am J Public Health 1990;80: Windsor RE, Insall JN. Surgery of the knee. In: Sledge CB, Ruddy S, Harris ED, Kelley WN, editors. Arthritis surgery. 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