knee-osteoarthritis-abd-orthotic-biomechanics by Lori@go4-d.com

Clinical Biomechanics 17 (2002) 603–610 www.elsevier.com/locate/clinbiomech

Static and dynamic biomechanics of foot orthoses in people with medial compartment knee osteoarthritis Monica R. Maly a, Elsie G. Culham a

a,*

, Patrick A. Costigan

Faculty of Health Sciences, School of Rehabilitation Therapy, Queen’s University, Kingston, Ont., Canada K7L 3N6 b Department of Physical Health and Education, Queen’s University, Kingston, Ont., Canada K7L 3N6 Received 13 February 2001; accepted 9 July 2002

Abstract Objective. Gait biomechanics (knee adduction moment, center of pressure) and static alignment were investigated to determine the mechanical effect of foot orthoses in people with medial compartment knee osteoarthritis. Design. Repeated measures design in which subjects were exposed to three conditions (normal footwear, heel wedge and orthosis) in random order. Background. The knee adduction moment is an indirect measure of medial compartment loading. It was hypothesized that the use of a 5° valgus wedge and 5° valgus modified orthosis would shift the center of pressure laterally during walking, thereby decreasing the adduction moment arm and the adduction moment. Methods. Peak knee adduction moment and center of pressure excursion were obtained in nine subjects with medial compartment knee OA during level walking using an optoelectric system and force plate. Static radiographs were taken in 12 subjects using precision radiographs. Results. There was no difference between conditions in static alignment, the peak adduction moment or excursion of the center of pressure in the medial-lateral direction. No relationship was found between the adduction moment and center of pressure excursion in the medial-lateral plane. The displacement of the center of pressure in the anterior–posterior direction, measured relative to the laboratory coordinate system, was decreased with the orthosis compared to the control condition (P ¼ 0:036) and this measure was correlated with the adduction moment (r ¼ 0:45, P ¼ 0:019). Conclusions. The proposed mechanism was not supported by the findings. The reduction in the center of pressure excursion in the anterior–posterior direction suggests that foot positioning was altered, possibly to a toe-out position, while subjects wore the orthoses. Based on the current findings, we hypothesize that toe-out positioning may reduce medial joint load. Relevance Knee Osteoarthritis is the most common cause of chronic disability amongst seniors. Developing inexpensive, non-invasive treatment strategies for this large population has potential to impact health care costs, quality of life and clinical outcomes. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Gait; Alignment; Biomechanics; Orthoses; Knee joint; Osteoarthritis

1. Introduction In knee osteoarthritis (OA), a common musculoskeletal disorder associated with aging [1,2], the medial compartment is more commonly aﬀected because it carries higher loads [3,4]. In the healthy knee, between 71% and 91% of total joint load is transmitted through the

Corresponding author. E-mail address: culhame@post.queensu.ca (E.G. Culham).

medial tibiofemoral compartment [5–7] compared to 100% in the OA knee [8,9]. Treatment strategies for the knee OA population aim to minimize the forces on the medial compartment [10,11]. For example, a high tibial osteotomy (HTO) alters static lower extremity alignment thereby decreasing medial compartment loading. As well, conservative treatment strategies, such as knee braces and valgus heel wedges, aﬀect lower limb mechanics and attempt to reduce medial compartment loading. Subjective reports of decreased pain and improved function, particularly during walking, in patients with

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mild to moderate medial compartment knee OA have been observed with the use of a valgus heel wedge [12– 14]. This treatment has reduced the need for pain medication [15], altered lower limb alignment [13] and in a young healthy population it reduced the knee’s adduction moment [16]. While the alteration in limb alignment may alter the knee joint load, the relationship between static alignment and dynamic loading of the medial compartment remains equivocal [17–19]. On the other hand, since direct measurement of medial compartment loading is difficult, the knee adduction moment serves as an indirect measure of the load [6,17,18] such that a change in the adduction moment signifies a change in load distribution across the knee joint. Even considering the effects on alignment and the adduction moment, the above studies did not propose a mechanism for the dynamic effect a valgus heel wedge would have on the mechanics of level walking in the OA knee population. The purpose of this study was to determine the immediate mechanical effect of a 5° valgus heel wedge and a modified orthosis, where the lateral aspect of the rearfoot is raised into a 5° valgus position, on the peak knee adduction moment (PAM) and displacement of center of pressure during level walking in the OA knee population. Specifically, it was hypothesized that valgus heel wedges and modified orthoses would shift the center of pressure laterally on the foot during level walking, reducing the moment arm of the adduction moment in the frontal plane, thereby resulting in a decrease in the knee adduction moment (Fig. 1). Secondly, the effect of

the interventions on static lower limb alignment was investigated.

2. Methods 2.1. Research design & study participants The study was a single visit, repeated measures design in which subjects were exposed to three conditions in random order: routine footwear (CON), a 5° valgus heel wedge (WED) and an off-the-shelf orthosis modified such that the rearfoot is maintained in 5° valgus (ORT). Because we wanted to know whether foot orthoses were effective through a mechanical effect rather than a neuromuscular adaptation, the study investigated only the immediate mechanical effect of these interventions. Each time the condition changed, subjects took two practice walks to ensure the orthoses were properly placed. The interventions were applied bilaterally and in cases of bilateral disease, only the most symptomatic limb was tested. The university Research Ethics Board approved the study and subjects provided informed consent. The study population consisted of a convenient sample of 12 community-dwelling adults (nine male) between 46 and 70 years of age (Table 1). Three subjects were awaiting HTO, three were low priority for total knee replacement, and three were attending physiotherapy as the primary management strategy for symptoms related to knee OA. All subjects had medial

Fig. 1. Proposed mechanism of pain relief with use of a valgus heel wedge and modiﬁed orthosis. Use of the heel wedge shifts the center of pressure laterally on the foot. The moment arm of the adduction moment is reduced thereby reducing the adduction moment.

M.R. Maly et al. / Clinical Biomechanics 17 (2002) 603–610 Table 1 Subject characteristics Variable

Mean (standard deviation)

Range

Age (years) Weight (kg) Body mass index (kg/m2 )

60.00 (9.39) 99.17 (15.89) 32.42 (5.03)

46–70 70–120 25–43

WOMAC Aggregate (/96)a Pain (/20)a Stiﬀness (/8)a Function (/68)a

38.25 (14.72) 7.83 (3.46) 3.67 (1.87) 26.75 (10.16)

11–57 2–13 0–5 9–40

WOMAC: Western Ontario McMaster Universities Osteoarthritis Index. a Total possible score on WOMAC.

compartment knee OA confirmed by their physician and by radiographs taken during the study. No subject had corrective surgery for knee OA on the measured limb or had used footwear alterations to manage their knee OA. The Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) was administered to obtain descriptive information on the sample [20]. This is a valid and reliable self-administered questionnaire consisting of 24 questions categorized in subscales of pain, stiffness and physical function [20,21]. The scores indicated mild to moderate levels of pain and function in the study population (Table 1). No subjects had limitation of knee or ankle joint range of motion as measured with a universal goniometer. Subjects were excluded if their radiation dosage would have reached its yearly maximum with participation in the study. This limited the number of women participating due to bone density measurements taken in the previous year. 2.2. Instrumentation Data were collected using the QUESTOR Gait Analysis in Three Dimensions (QGAIT) system, which has previously been validated for dynamic knee assessment (PARTEQ, Kingston, Canada) [22,23]. This system incorporates knee alignment and joint surface geometry data from standardized radiographs to more accurately transform the surface marker location into the subject-specific joint centers. QGAIT includes an Optotrack optoelectric system (Northern Digital, Waterloo, Canada), a force plate (Advanced Mechanical Technology, Massachusettes, USA) and QUESTOR Precision Radiographs (QPRs) (PARTEQ, Kingston, Canada). A total of eight infrared emitting diodes (IREDs) were used. Diodes were placed over six anatomical landmarks (greater trochanter, lateral femoral condyle, fibular head, lateral malleolus; and on the shoe inferior to the lateral malleolus and head of 5th metatarsal). As well, markers were attached to two anteriorly projecting probes attached to the thigh and shank using spray

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adhesive underneath a neoprene and Velcro cuff. Walking trials were sampled at 100 Hz. A manually triggered footswitch coupled with the ground reaction force (GRF) data were used to indicate initial and final contact. QPRs were obtained with the subjects barefoot on a calibrated turntable inside a frame that is fixed relative to the X-ray source. The pelvis was secured and the feet were centered over marks 9 cm apart and aligned such that a transverse line through the femoral condyles was in the coronal plane. While radiographs were taken, subjects were instructed to bear equal weight on the left and right legs. Single limb stance on the affected limb was not used because of pain and difficulty in maintaining the hip in the standardized position. Surface landmarks (to be used for the placement of the active markers in walking trials) were marked with a felt-tipped pen and a lead bead. Anterior–posterior and lateral radiographs in the three conditions were obtained by rotating the turntable 90°. One anterior–posterior hip radiograph was obtained in control condition. Also, anterior–posterior and lateral radiographs of the knee joint were taken in the control condition. Radiographs were then taken of the knee in the coronal and sagittal planes to evaluate alignment with the 5° valgus heel wedge and the 5° modified orthosis. No shoes were worn for the control, wedge or orthosis conditions and the interventions were placed under the feet bilaterally. Hip X-rays were not taken during the wedge or orthosis conditions to limit radiation exposure. 2.3. Dynamic measurements Gait variables included the PAM, displacement of the center of pressure, and GRF. Spatio-temporal and kinematic variables were analyzed to detect possible covariates. The adduction moment waveform was automatically calculated by the QGAIT system. The PAM was chosen and averaged over five trials. The peak GRF were averaged over five trials. Two methods of calculating peak displacement of center of pressure were used to more thoroughly investigate this measurement (Fig. 2). In Method A, calculations were made relative to the x (sagittal) and y (coronal) axes of the laboratory coordinate system. For these measurements, the point of initial contact was taken as zero. From zero, the peak displacement of center of pressure along the x-axis (CoPx ) and y-axis (CoPy ) were determined during stance. Method B involved calculation of peak displacement of center of pressure relative to the foot. The lateral border of the foot was defined by markers on the shoe at the heel and toe-break (base of the 5th metatarsal). The peak displacement of center of pressure parallel to the lateral border of the foot (in the anterior–posterior direction

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Fig. 2. Calculation of displacement of center of pressure. Note that in Method A, calculations are made relative to the laboratory x-axis and the point of initial contact. In Method B, calculations are made relative to the lateral border of the foot. : initial contact; : peak displacement of center of pressure in lateral direction; : peak displacement of center of pressure in anterior–posterior direction; : infrared markers (at heel and toe-break).

(CoPAP )) was calculated, as was the peak displacement of center of pressure perpendicular to the lateral border of the foot (in the mediolateral direction, CoPML ). Because the reference line used in this analysis was the most lateral point on the foot, the smallest distance from the lateral border of the foot was deﬁned as the peak CoPML . The value for CoPML was denoted by a negative sign to indicate its position relative to the lateral border of the foot. 2.4. Static alignment measurements From the radiographs the angle between the femoral and tibial shaft was evaluated in the coronal (varus/ valgus angle) and sagittal (ﬂex/ext angle) planes for all three conditions. Additionally, the hip–knee–ankle (HKA) angle, the angle between a line from the hip to the knee joint centers and a line from the knee to ankle joint centers [4], was measured. The HKA angle represents deviation from a line of load-bearing (line from center of hip to talus) and was determined for each subject in each condition.

data (Kruskal–Wallis test) was performed to determine if the small sample size included skewed the results. 3. Results 3.1. Dynamic measurements No differences were found between conditions in the spatio-temporal variables including gait velocity, cadence and stride length (Table 2). Kinematics of the tibia relative to the femur (peak external and internal rotation) also did not differ between conditions (P ¼ 0:30). No temporal shift in the waveforms of the knee joint kinematics was visually observed between conditions. Kinetic data from nine subjects collected during level walking are presented in Table 3. Gait data from three subjects were lost due to equipment failure. No differences were observed between conditions in PAM, indicating no difference in medial compartment joint loading while subjects wore their routine footwear, the valgus heel wedge and the modified orthosis. No differences in the anterior–posterior (GRFx ), medial-lateral

2.5. Statistical analysis A repeated measures A N O V A was performed with the PAM as the dependent variable and the conditions as the independent variable. A Neuman–Keuls post-hoc test was applied to determine where differences existed between conditions. The same statistical technique was applied to the CoP, GRF and the varus/valgus, flex/ext and HKA angles. Pearson correlation coefficients were calculated to determine the relationship between CoP and PAM. In addition, non-parametric analysis of the

Table 2 Mean spatio-temporal gait variables (standard deviation) Variable

CON

WED

ORT

Gait velocity (m/s)

0.93 (0.16) 45.74 (4.85) 1.21 (0.12)

0.92 (0.16) 44.35 (4.33) 1.24 (0.14)

0.93 (0.16) 45.34 (4.21) 1.23 (0.14)

0.029

0.971

1.368

0.260

0.564

0.571

Cadence (stride/min) Stride length (m)

CON: control condition (normal footwear); WED: 5° valgus or lateral heel wedge; ORT: 5° valgus modiﬁed orthosis.

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Table 3 Mean kinetic gait variables (standard deviation) Variable (peak)

CON

WED

ORT

PAM (N m/kg)

0.48 (0.13)

0.47 (0.11)

0.50 (0.11)

2.658

0.101

Method A CoPx (mm) CoPy (mm)

282.41 (12.95) 13.66 (7.03)

283.11 (10.86) 13.81 (6.40)

275.88 (12.89) 15.68 (7.08)

4.111 0.673

0.036 0.524

Method B CoPAP (mm) CoPML (mm)

102.57 (28.76) )37.16 (8.01)

103.85 (30.66) )36.80 (8.11)

102.00 (20.60) )36.96 (9.85)

0.078 0.039

0.925 0.962

GRFx (N) GRFy (N) GRFz (N)

129.49 (22.17) 54.27 (20.94) 1007.40 (100.29)

126.79 (21.37) 54.00 (17.42) 1008.61 (97.79)

133.24 (26.79) 51.51 (18.28) 1030.78 (111.77)

0.832 0.611 1.801

0.453 0.555 0.197

CON: control condition (normal footwear); WED: 5° valgus or lateral heel wedge; ORT: 5° valgus modified orthosis; PAM: peak knee adduction moment; CoPx : peak displacement of center of pressure along x-axis; CoPy : peak displacement of center of pressure along y-axis; CoPAP : peak displacement of center of pressure parallel to lateral border of foot; CoPML : peak displacement of center of pressure perpendicular to lateral border of foot; GRFx : ground reaction forces in x-axis; GRFy : ground reaction forces in y-axis; GRFz ground reaction forces in z-axis. * Significant difference between CON and ORT at P < 0:05.

(GRFy ) or vertical (GRFz ) ground reaction forces were observed between conditions. Means and standard deviations for peak displacement of center of pressure measurements are given in Table 3. The orthoses did not influence the point on the heel that initially contacted the floor (P ¼ 0:78). Mediallateral displacement of center of pressure (CoPy and CoPML ) did not differ between conditions regardless of the method of measurement (Method A and B). A significant reduction in the peak displacement of center of pressure along the x-axis (CoPx , Method A) was found while subjects wore the 5° valgus modified orthosis compared to control (P ¼ 0:036). When displacement of center of pressure was processed relative to the lateral border of the foot (Method B), there was no difference in the peak displacement of center of pressure in the anterior–posterior (CoPAP ) direction between conditions. Reanalysis using non-parametric statistics for all variables yielded the same results. 3.2. Relationship between kinetic variables Correlations between kinetic gait variables are presented in Table 4. Data from the control, wedge and Table 4 Correlations between kinetic gait variables Variables

r value

R2 value

PAM CoPx PAM CoPy PAM CoPAP PAM CoPML

0.448 )0.181 0.020 0.098

0.21 0.03 0.00 0.01

0.019 0.367 0.921 0.625

PAM: peak knee adduction moment; CoPx : peak displacement of center of pressure along x-axis; CoPy : peak displacement of center of pressure along y-axis; CoPAP : peak displacement of center of pressure parallel to lateral border of foot; CoPML : peak displacement of center of pressure perpendicular to lateral border of foot. * Signiﬁcant correlation at P < 0:075 (corrected P < 0:02).

Fig. 3. Relationship between PAM and the peak displacement of center of pressure in the anterior–posterior direction (CoPx ).

orthosis conditions are included. A significant relationship was found between PAM and CoPx (r ¼ 0:45, R2 ¼ 0:21, P ¼ 0:019, Fig. 3). No correlation was found between PAM and the displacement of center of pressure relative to the force plate in the y direction (Method A). As well, center of pressure displacement relative to the lateral border of the foot (Method B), was not related to PAM in either the anterior–posterior (CoPAP ) or medial-lateral (CoPML ) directions. 3.3. Static alignment Static alignment data for 12 subjects is presented in Table 5. No differences in the varus/valgus, flex/ext or HKA angles were found when subjects stood on the wedge or orthosis compared to the control condition.

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Table 5 Mean static alignment (standard deviation) Variable (peak) Varus/Valgus (°) Flex/Ext (°) HKA angle (°)

CON

WED

ORT

)1.83 (3.71) 5.85 (5.95) )6.67 (4.23)

)1.50 (4.32) 5.83 (7.58) )5.92 (4.85)

)1.33 (3.87) 6.25 (7.64) )6.33 (4.23)

1.085 0.236 0.248

0.355 0.791 0.783

CON: control condition (normal footwear); WED: 5° valgus or lateral heel wedge; ORT: 5° valgus modiﬁed orthosis; varus/valgus: alignment of knee in coronal plane; ﬂex/ext: alignment of knee in sagittal plane; HKA: hip–knee–ankle angle. * Negative values indicate deviation to varus alignment.

4. Discussion It was hypothesized that both a 5° valgus heel wedge and 5° valgus modified orthosis move the center of pressure laterally during walking shortening the adduction moment arm and decreasing the joint moment. Changes in the adduction moment infer changes in the load distribution across the knee joint, which could explain why these shoe inserts reduce pain and increase capacity in OA patients. However, we found no differences in the peak displacement of the center of pressure along the laboratory y-axis (CoPy ––Method A), nor in the peak displacement of center of pressure perpendicular to the lateral border of the foot (CoPML ––Method B). As well, there were no differences in the PAM across the control, wedge and orthosis conditions. Thus, from this study, there is no evidence that these shoe inserts alter medial compartment knee load by shifting the center of pressure thereby reducing the adduction moment. Unlike other studies [13,24,25], there was no evidence that the shoe inserts altered lower limb static alignment. No differences were observed between conditions in the varus/valgus, flex/ext or HKA angles. Yasuda and Sasaki [13] found lower limb alignment differences when subjects stood on a 5° inclined board compared to a flat surface. However, the inclined board used in the Yasuda and Sasaki study affected the entire foot and subjects stood in single limb rather than bilateral stance. Our study wedged only the heel and subjects were in bilateral stance to control hip and pelvis position for radiographs. Giffin et al. [24] reported a reduction in the HKA angle between a control and wedge condition in an OA knee population. In their case, the shoe insert used was applied unilaterally creating a potential leg length discrepancy of 12.5 mm, the reported height of shoe inserts [24]. Differences of greater than 12 mm have been reported to alter lower limb mechanics significantly [26]. The intervention used by Giffin et al. [24] also involved wedging the entire lateral border of the foot rather than just the heel. In the current study the interventions were applied bilaterally with the height changing at the heel only. Toda et al. [25] demonstrated that the use of a lateral wedge and ankle support together altered femoral–tibial and talar tilt angles

in single limb stance suggesting that adaptations to shoe inserts may occur at the ankle rather than the knee. The results demonstrating that the adduction moment is unaffected by altered footwear is contradictory to Crenshaw’s results [16]. While using a 5° valgus heel wedge, Crenshaw [16] demonstrated that both the external varus (adduction) moment and calculated medial compartment loads were reduced. However, Crenshaw investigated heel wedges in a healthy, young population that may have greater adaptability to altered footwear than those with knee OA. Winter [27] has previously demonstrated that older adults have reduced neural plasticity and therefore a reduced ability to adapt to changing circumstances. In addition, studies of conservative and surgical interventions demonstrate the gait kinetics remain unchanged in people with medial compartment knee OA. For example, Prodromos et al. [17] investigated the adduction moment in 21 subjects with OA varus knees before, one year post-HTO and 3.2 years post-HTO. Despite surgical alteration of lower limb alignment, those subjects with a high knee adduction moment pre-operatively (52% of subjects) maintained a high adduction moment post-operatively compared to others studied. Goh et al. [28] found similar results in a study of 21 HTO patients. Thus evidence exists that older adults, even with invasive surgery, do not readily adapt their gait mechanics in response to intervention. Unexpectedly, a significant reduction in CoPx , the peak displacement of center of pressure along the x-axis (Method A), was observed while subjects wore the 5° valgus modified orthoses compared to control. By comparison, the CoPAP , the peak anterior displacement of center of pressure parallel to the foot’s lateral border (Method B), was not different across conditions. This finding may be the result of foot rotation, which would shorten CoPx but would have no effect on CoPAP (see Fig. 2). The magnitude of foot rotation would be small since the CoPy measurement was not significantly affected. External rotation of the foot, a potential mechanism of pain relief, has been reported previously [29,30]. Andriacchi [30] suggested that out-toeing shifts the vector of the ground reaction forces closer to the knee joint center thus reducing the knee adduction

M.R. Maly et al. / Clinical Biomechanics 17 (2002) 603–610

moment. This possible adaptation might require an accommodation period and would be a neuromuscular effect rather than a mechanical effect. The correlation between CoPx and PAM (r ¼ 0:45, P ¼ 0:019), suggesting a relationship between out-toeing and medial compartment joint loading has been reported by others [29,31]. Based on the results of this study and others, we hypothesize that out-toeing may be a mechanism to reduce pain and warrants further study. Since there was a significant reduction in CoPx but no reduction in the knee adduction moment was found in this study, it can also be concluded that despite the relationship between these variables, the orthotic intervention was not sufficient to reduce joint loading. Gait analyses used in this study were based on assumptions that limit the generalizability of the results. It was assumed that hip position was adequately controlled between the control, wedge and orthosis conditions during radiographic analysis for the HKA angle. Regarding the knee models created for each subject, it is assumed that limb segments are rigid without skin motion. Because the study population was predominantly people with mild to moderate medial compartment knee OA, the results can only be generalized to this population. It must also be considered that the majority of subjects were male. Since women have slightly different anthropometrics and etiology of medial compartment OA [32], the results of this study may not reflect the true pattern in women.

5. Conclusions The use of a 5° valgus heel wedge and 5° valgus modified orthosis did not affect the static alignment or knee adduction moment in level walking in a sample of people with mild to moderate medial compartment knee OA. The proposed mechanism that hypothesized a lateral shift in the center of pressure resulted in a reduced adduction moment in this population was not supported. However, the significant reduction in the peak displacement of center of pressure relative to the x-axis of the laboratory suggests out-toeing occurred while subjects wore a modified orthosis. Since this center of pressure variable was correlated with the knee adduction moment, out-toeing may be a mechanism of reducing medial joint loading in people with knee OA and warrants further investigation. The results challenge the theory that reduced pain and improved function in people with medial compartment OA are related to mechanical alterations including static alignment or reduced medial knee joint loading with the use of valgus heel wedges or orthoses. Future work that investigates neuromuscular adaptations to the interventions, such as foot rotation, is warranted.

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Acknowledgements Financial contributions to this study have been provided by the Drummond Foundation and the Natural Sciences and Engineering Research Council of Canada. Superfeetâ donated the orthoses and wedge material used in this study. The authors would like to thank Dr. J. Rudan for assisting in study design and subject recruitment, and the physical therapists at Providence Continuing Care Center at St. Mary’s site for their assistance with subject recruitment.

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