Moderate-Heeled Shoes and Knee Joint Torques Relevant to the ...

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Moderate-Heeled Shoes and Knee Joint Torques Relevant to the Development and Progression of Knee Osteoarthritis D. Casey Kerrigan, MD, MS, Jennifer L. Johansson, MS, Mary G. Bryant, MD, Jennifer A. Boxer, BA, Ugo Della Croce, PhD, Patrick O. Riley, PhD ABSTRACT. Kerrigan DC, Johansson JL, Bryant MG, Boxer JA, Della Croce U, Riley PO. Moderate-heeled shoes and knee joint torques relevant to the development and progression of knee osteoarthritis. Arch Phys Med Rehabil 2005; 86:871-5. Objective: To determine if women’s dress shoes with heels of just 1.5in (3.8cm) in height increases knee joint torques, which are thought to be relevant to the development and/or progression of knee osteoarthritis (OA) in both the medial and patellofemoral compartments. Design: Randomized controlled trial. Setting: A 3-dimensional motion analysis gait laboratory. Participants: Twenty-nine healthy young women (age, 26.7⫾5.0y) and 20 healthy elderly adult women (age, 75.3⫾6.5y). Interventions: Not applicable. Main Outcome Measures: Peak external varus knee torque in early and late stance and prolongation of flexor knee torque in early stance. Three-dimensional data on lower-extremity torques and motion were collected during walking while (1) wearing shoes with 1.5-in high heels and (2) wearing control shoes without any additional heel. Data were plotted and qualitatively compared; major peak values and timing were statistically compared between the 2 conditions using paired t tests. Results: Peak knee varus torque during late stance was statistically significantly greater with the heeled shoes than with the controls, with increases of 14% in the young women and 9% in the elderly women. With the heeled shoes, the early stance phase knee flexor torque was significantly prolonged, by 19% in the young women and by 14% in elderly women. Also, the peak flexor torque was 7% higher with the heeled shoe in the elderly women. Conclusions: Even shoes with moderately high heels (1.5in) significantly increase knee torques thought to be relevant in the development and/or progression of knee OA. Women, particularly those who already have knee OA, should be advised against wearing these types of shoes. Key Words: Biomechanics; Gait; Kinetics; Knee; Osteoarthritis; Rehabilitation; Shoes; Women. © 2005 by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

From the Department of Physical Medicine and Rehabilitation, University of Virginia, Charlottesville, VA (Kerrigan, Bryant, Boxer, Della Croce, Riley); Spaulding Rehabilitation Hospital, Boston, MA (Johansson); and Department of Biomedical Sciences, University of Sassari, Sassari, Italy (Della Croce). Supported by the Ellison Foundation and by the Public Health Service (grant no. NIH HD01351). No party having a direct interest in the results of the research supporting this article has or will confer a benefit on the author(s) or on any organization with which the author(s) is/are associated. Reprint requests to D. Casey Kerrigan, MD, MS, Dept of Physical Medicine and Rehabilitation, University of Virginia School of Medicine, 545 Ray C Hunt Dr, Charlottesville, VA 22908, e-mail: [email protected]. 0003-9993/05/8605-9141$30.00/0 doi:10.1016/j.apmr.2004.09.018

HE POSSIBILITY THAT different types of shoe wear T contribute to the development and/or progression of knee osteoarthritis (OA) deserves consideration, because shoe wear is a potentially controllable and easily modifiable factor for this prevalent and disabling disease.1,2 We3 previously found that stiletto high-heeled shoes with heels averaging 2.5in (6.35cm) in height exaggerate knee external varus and flexor torques during walking—torques that are thought to be relevant to the development and/or progression of knee OA. Specifically, we showed an increase in varus torque during walking with highheeled shoes. This increase implies exaggerated compressive forces through the medial aspect of the knee,4-6 the typical tibiofemoral site for knee OA.7 An increased varus torque is likely to be clinically significant, given animal data showing that increasing knee varus torque leads to degenerative changes in the knee’s medial compartment.8 Because repetitive loading is believed to be an important etiologic factor in the development of OA, and walking is by far the most common daily activity causing the greatest force about the knee,6 an increase in varus torque is likely to be important. Similarly, we showed a prolongation of the knee flexor torque in early to midstance, implying increased work of the quadriceps muscles,4,9,10 increased strain through the patella tendon, and increased pressure across the patellofemoral joint.11 During walking, the increased strain that occurs through the patella tendon, with its associated patellofemoral pressures, may be important with respect to the development of degenerative joint changes within the patellofemoral compartment. A study12 comparing women’s wide-based high-heeled shoes with narrow-based high-heeled shoes (each with an average heel height of 2.8in [7.1cm]) found that both types of shoes exaggerated the knee varus torques (by an increase of 26%) and the sagittal torques (by an increase in peak torque of 30%). Having learned that shoes with heels averaging 2.5 to 2.8in in height significantly increase knee joint torques, we hypothesized that even moderately high heels would increase these knee joint torques for the reasons noted previously3,12: that the shoe’s heel so compromises foot and ankle kinetics that biomechanic compensations to maintain stability and forward progression during walking must occur at the knee. Many women, both young and old, continue to wear shoes with moderately high heels that are less than 2in (5.1cm) high, in the belief that these are sensible shoes. In fact, it is typically recommended that shoes with heels less than 2in are safe to wear.13,14 We have observed in our clinical experience that even women who already have knee OA often wear dress shoes with heels (that are typically wide) that are slightly less than 2in high. We hypothesized that dress shoes with heels only 1.5in (3.8cm) high significantly increase the same knee joint torques believed to be relevant to the development and/or progression of knee OA. To test our hypothesis, we used standard 3-dimensional gait analysis techniques, commonly used in gait laboratories, to evaluate joint torques and motion at the knee.12,15-20 Arch Phys Med Rehabil Vol 86, May 2005

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MODERATE-HEELED SHOES AND KNEE JOINT TORQUES, Kerrigan

Fig 1. Custom shoes, size 9, with (A) moderate heel (1.5-in heel height) and (B) no heel (control).

METHODS Healthy, able-bodied young (age, 18 –35y) and elderly (age, ⬎65y) women were studied. We posted fliers to recruit subjects from the general population. Subjects had to be accustomed to walking while wearing shoes with 1.5-in heels and not suffer from musculoskeletal, cardiac, or pulmonary disease. The study protocol was approved by both the institutional review board where the data were collected and by the institutional review board where the data were analyzed. Written informed consent was obtained from each subject. Each subject was asked to walk at her comfortable walking speed across a 10-m gait laboratory walkway under 2 conditions: with 1.5-in– heeled shoes and with control shoes, the order of which was randomized. Both the heeled and control shoes were custom-made by Lerness Shoes.a The heeled shoes (fig 1A) had a consistent 1.5-in heel height across all sizes, and the control shoes (fig 1B) had zero heel height. All shoes had an identical upper and midsole design. Although we previously found no difference in effect of knee torques between wide- and narrow-heeled shoes,12 we decided to use a shoe with a wide heel in this study, because this style is conventionally believed to be especially sensible and is commonly worn by both young adult and elderly women. Subjects were fitted with test shoes by the study staff based on the subject’s self-reported size. The subjects practiced walking with each test shoe to assure adequate fit and comfort and to become accustomed to the shoe. Knee joint torque data in 3 planes (sagittal, coronal, transverse) were collected bilaterally, over 3 trials, for each of the 2 conditions. The procedures are based on standard techniques reported elsewhere.3,12,15,16,19,21,22 We used a 6-camera videobased motion analysis system (Vicon 512 system)b to measure the 3-dimensional position of 15-mm diameter markers, at 120 frames per second. Markers were attached to the following bony landmarks on the pelvis and lower extremities during walking: the bilateral anterior and posterior superior iliac spines, lateral femoral condyles, lateral malleoli, and forefeet. Additional markers attached to lateral wands were placed over the midfemur and midshank. Ground reaction forces were measured synchronously with the motion analysis data using 2 staggered force platformsc imbedded in the walkway. Joint torques in each plane were calculated by a commercially available full-inverse dynamic model.b Accordingly, joint torque calculations were based on 3 things: (1) the mass and inertial characteristics of each lower-extremity segment, (2) the derived linear and angular velocities and accelerations of each lower-extremity segment, and (3) the ground reaction force and joint center position estimates. Joint torques, normalized for body weight and overall barefoot height, were reported in Arch Phys Med Rehabil Vol 86, May 2005

newton meters per kilogram meters (Nm/kg-m). Sagittal knee joint angle motion was also studied and was reported in degrees. Knee joint torque and sagittal plane motion data were graphed over the walking cycle (0%–100%). Averaged torque values (in the sagittal, coronal, and transverse planes) and motion values (in the sagittal plane) for each subject for both conditions were obtained from 3 trials (average of both right and left lower extremities, providing an average of 6 values for each condition). We used a Student paired t test for both the young group and the elderly group to compare knee torque and motion values between the 2 conditions. Specifically, in the coronal plane, we examined peak knee varus torques in both early and late stance phases. We also examined prolongation of the sagittal flexor knee torque, calculating the time from initial contact until the sagittal torque became extensor as a percentage of the gait cycle. Although the peak knee varus torques and the timing of the knee flexor torque were our main variables of interest, we also evaluated the peak knee flexor torque during early stance, peak internal rotation torque, and peak knee flexion in stance and in swing. Applying a Bonferroni adjustment for the use of multiple t tests, 3 variables in 2 groups, we defined statistical significance at P less than .008 (.05/6). RESULTS A total of 50 subjects, 30 healthy young women and 20 healthy elderly subjects, were assessed and found eligible for the study. One young subject was excluded from the final analysis because of technical problems with her data set. Further, 1 young and 3 elderly subjects were not included in the analysis of knee flexor torque prolongation. Thus, most of the results reflect the analysis of data from 29 young and 20 elderly subjects, with a subgroup of 28 young and 17 elderly women for the analysis of knee flexor torque prolongation. The young women averaged (mean ⫾ standard deviation [SD]) 26.7⫾5.0 years in age, 1.65⫾0.06m in height, and 58.7⫾8.99kg in body mass. The elderly women averaged 75.3⫾6.5 years in age, 1.60⫾0.07m in height, and 63.4⫾13.3kg in body mass. There was no significant difference in walking speed between the heeled-shoe and control-shoe conditions for either the young women (1.32⫾0.13m/s and 1.32⫾0.12m/s, respectively; P⫽.990) or the elderly adult women (1.25⫾0.15m/s and 1.25⫾0.16m/s, respectively; P⫽.768). The elderly women walked more slowly in both conditions, as would be expected, but the differences were not significant (control shoe, P⫽.069; heeled shoe, P⫽.089). The torque values (mean ⫾ SD) and P values for comparisons between heeled and control shoes, for young adult and elderly women, are listed in table 1. Graphs of the coronal

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MODERATE-HEELED SHOES AND KNEE JOINT TORQUES, Kerrigan Table 1: Knee Torque Parameters Young Women

Elderly Women

Parameters

Heeled Shoes

Control Shoes

P*

Heeled Shoes

Control Shoes

P*

Peak varus torque, early stance (Nm/kg-m) Peak varus torque, late stance (Nm/kg-m) Flexor torque prolongation (% gait cycle) Peak flexor torque, early stance (Nm/kg-m) Peak internal rotation torque (Nm/kg-m)

0.33⫾0.07 0.25⫾0.05 31⫾4.4 0.28⫾0.11 0.11⫾0.02

0.32⫾0.06 0.22⫾0.05 26⫾3.8 0.28⫾0.11 0.11⫾0.02

.021 ⬍.001 ⬍.001 .490 .104

0.33⫾0.07 0.25⫾0.05 33⫾3.3 0.31⫾0.10 0.10⫾0.03

0.31⫾0.07 0.23⫾0.05 29⫾4.4 0.29⫾0.11 0.10⫾0.03

.001 ⬍.001 ⬍.001 .007 .319

NOTE. Values are mean ⫾ SD. *Applying a Bonferroni adjustment for multiple tests; P⬍.008 is significant.

(varus) knee torque with heeled and control shoes, averaged over the gait cycle, are illustrated in figure 2A (young women) and figure 2B (elderly women). Similarly, graphs of the sagittal knee (flexor and extensor) torque with heeled and control shoes are illustrated in figure 3A (young women) and 3B (elderly women). The peak knee varus torque in late stance was significantly greater for the heeled shoe compared with the control shoe for both the young and elderly women. The rate of occurrence of increased late stance knee varus torque was quite high, with 24 of 29 young and 16 of 20 elderly subjects. The early stance peak knee varus torque was not significantly higher in either group when the Bonferroni adjustment was applied. Although the increase in early stance varus torque was not significant, 22 young subjects and 16 elderly subjects showed an increase in this peak value. Twenty-six of 29 young

subjects and 19 of 20 elderly subjects showed an increase in either the early stance (not significantly increased) or late stance (significantly increased) peak knee varus torque when wearing heels. In 21 young and 14 elderly subjects, both varus torque peaks increased with heels. In 1 young woman and 3 elderly women, the sagittal knee torque remained flexed with the heeled shoe throughout the entire stance period. These subjects were excluded from the analysis of flexor torque prolongation, because an appropriate value for crossover time could not be assigned. For the remaining subjects, the sagittal knee flexor torque was prolonged with heeled shoes in both the young and elderly women. Among the other variables evaluated there were some incidental findings of interest. The peak sagittal knee flexor torque

Fig 2. Knee varus torque during walking plotted over an averaged gait cycle. Effect of moderate-heeled shoe (solid line) versus control shoe (dotted line) in (A) young women and (B) elderly women.

Fig 3. Knee sagittal torque during walking plotted over an averaged gait cycle. Effect of moderate-heeled shoe (solid line) versus control shoe (dotted line) in (A) young women and (B) elderly women.

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was significantly greater for the heeled shoe than for the control shoe for the elderly women but not for the young. No significant differences existed in peak internal rotation torque in late stance in either group. Knee flexion angle in early stance was greater with the heeled shoe in the elderly women (16°⫾5° vs 14°⫾6°, P⫽.003) but not in the young women (15°⫾4° vs 15°⫾4°, P⫽.758). Peak knee flexion angle in swing was reduced with the heeled shoe in both young women (59°⫾3° vs 63°⫾3°, P⬍.001) and elderly women (57°⫾4° vs 61°⫾4°, P⬍.001). DISCUSSION As hypothesized, the late stance peak varus knee torque increased significantly with moderately high heels of 1.5in in both young adult and elderly women. There was no significant increase in the early stance peak knee varus torque, but an increase occurred in over half the subjects in both groups. The late stance varus torque was increased, with a magnitude of increase compared with the control shoe of 14% in the young women and 9% in the elderly women. Although in prior studies with higher heels (2.5- and 2.8-in height) we found 23% and 26% increases in both early and late stance peak knee varus moments, the increases found here with moderate-heeled shoes are still clinically notable. Often an aim of rehabilitation in patients with medial knee OA is to reduce the knee varus torque, to reduce the medial compartment loading. For instance, a lateral shoe wedge is often prescribed for patients with medial compartment OA and has been reported to help reduce symptoms of knee OA.23,24 We25 showed that a 5° lateral shoe wedge reduces knee varus torque by a significant 5% and 7% in early and late stance, respectively. Crenshaw et al26 similarly found in subjects with no knee OA that a lateral shoe wedge reduces knee varus torque by approximately 7%. This amount of change is of similar magnitude to what we found in this study, albeit in an opposite direction. Also as hypothesized, we found a significant prolongation of the early external knee flexor torque. Although the heeled shoes were associated with prolongation of the knee flexor torque throughout the entire stance period in 1 young woman and 3 elderly women, the characteristic early peak knee flexor torque was prolonged by 19% and 14% in the remaining young and elderly women, respectively. Further, in the elderly women the heeled shoe was associated with a significant 7% increase in peak knee flexor torque. Although the magnitudes are smaller, these findings are similar to those we found previously: with stiletto 2.5-in high-heeled shoes knee flexor torque is prolonged but there is no increase in the peak torque,3 and with the narrow and wide 2.8-in high-heeled shoes peak torque is both prolonged and increased.12 The current study is the first on the effects of shoes on knee biomechanics that has included a group of elderly women with ages similar to those with knee OA. The heeled shoes had essentially the same effect in the elderly women as in the young adult women, with 2 additional effects in the elderly women. One was the increase in peak knee flexor torque, already noted above. The second was an increase in peak knee flexion in stance, which is likely related to the increased knee flexor torque. Although the reason for these age-related differences is not clear, it is clear that overall, the elderly women’s knee biomechanics were affected by the heeled shoes to the same degree as the younger women, if not more so. As was observed with the higher-heeled shoes, we found in this study no changes in internal rotation torque. Also as observed with the higher-heeled shoes, we found here a reduction in peak knee flexion in swing in both the young and elderly women. Because speed can affect the magnitude of both joint Arch Phys Med Rehabil Vol 86, May 2005

motion and torques,27 it is important to note that even though subjects chose their own comfortable walking speeds, they tended to walk at similar speeds with the heeled and control shoes. The methods used in this study are considered to be the best, most technologically advanced, noninvasive techniques available to assess biomechanics during walking. Nevertheless, a limitation of our study, and of noninvasive gait analysis in general, is that we must infer rather than measure directly the joint contact forces from the measured net joint torques. Biomechanic modeling has shown that differences in net knee varus torques are the major determinants of differences in medial and lateral compartment contact forces.4 Similarly, the knee extension torque determines patellofemoral contact forces. Thus, it is appropriate that these torques, rather than the net joint forces, become the focus in looking for the cause of medial compartment and patellofemoral joint OA. However, the development of new procedures that directly assess joint forces about the patellofemoral interface and medial compartment of the knee would be useful in at least corroborating the joint torque information obtained using current methods. This study is the first to use a standard shoe for all subjects to wear, rather than relying on the shoes that the subjects normally wore. This approach allowed us to construct and use a control shoe with no heel. (In previous studies, we used barefoot walking as the control.) The advantage of the design in our study was that we could evaluate more purely the effect of the added heel. We28 previously showed that men’s sneakers and dress shoes with an average 0.5-in heel do not, in men, exaggerate knee joint torques compared with walking barefoot. Thus, it is likely that shoes with heels up to 0.5in high do not significantly affect knee joint torques in women; however, it is unknown what effect of heels between 0.5 and 1.5in high may have on knee joint torques. Moreover, it is unclear what type of relation exists between heel height and knee torques at higher heel heights. Future study should include varying heel heights across a wide range using a controlled shoe design. This approach would show whether a relation, linear or otherwise, exists between heel height and knee torques. Such a study would require special fabrication of shoes over a range of heel heights, controlled for design of everything except heel height. This is an expensive and time-consuming endeavor, requiring different lasts to be made for each heel height. Nonetheless, knowing the precise relation between heel height and knee joint torques would allow proper epidemiologic studies to evaluate the effect of heel height on the predisposition for knee OA. Having precise biomechanic data to guide epidemiologic studies is essential, because women tend to wear shoes with varying heel heights that likely have varying effects on knee joint torques. Future epidemiologic studies also must consider the length of time and conditions under which different heel heights are worn. CONCLUSIONS Shoes with heels 1.5in high significantly increase peak external varus knee torque in late stance and prolong knee flexor torque in early to midstance. These are the same knee joint torques believed to be related to the development and/or progression of knee OA. Our findings show that even moderately high-heeled shoes cause alterations in knee joint torques that are similar to those caused by women’s dress shoes with heel heights averaging 2.5 and 2.8in. Women, particularly those who already have knee OA, should be advised against wearing these types of shoes.


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