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Application of a Lateral Heel Wedge as a Nonsurgical Treatment for Varum Gonarthrosis

J. Robert Giffin
William D. Stanish, MD, FRCS(G), FACS
Scott N. MacKinnon, MSc
Donald A. MacLeod, MSc

ABSTRACT

Although anecdotal evidence supports the application of a lateral heel wedge (LHW) as a nonoperative treatment for varum gonarthrosis, objective evaluation of its mechanism of action is limited. Roentgenograms, ground reaction forces and electromyographical (EMG) profiles were incorporated to study the effect of LHW on the medial osteoarthritic knee of seven males during static and dynamic conditions.

Results indicated both static and dynamic changes associated with the application of a LHW. Roentgenograms indicated a varum to valgum directional change (p<05) in the capito-midcondylar-tibial shaft angle during static standing. There was minimal impact on the mean vertical forces while there were increases in the maximum lateral forces (p<.05) during walking with the LHW treatment. No statistical differences were observed for the EMG profiles between conditions. These results provide some insight into the functional effects of the LHW on the kinetics of the lower leg during static standing and free-speed gait.

Introduction

Varum gonarthrosis, or medial osteoarthritis of the knee, is a common medical problem that produces considerable functional limitations for afflicted patients. Although the etiology of this disease is not well defined, many investigators suggest that factors such as obesity, heavy physical labor, prior knee trauma as well as structural deformity of the lower limb play a significant role in the pathophysiology of osteoarthritis of the knee (1,2). A variety of surgical and nonsurgical treatments for varum gonarthrosis have been described in the literature, including tibial osteotomy (3,4), knee orthoses (5) and heel wedges (6-8). These biomechanical treatments are designed to reduce the compressive forces across the medial aspect of the osteoarthritic joint.

Although realignment by proximal tibial osteotomy generally has been an accepted procedure for varum gonarthrosis (9-14), its usage has been limited by the relative unpredictability of its clinical outcome (9,13,15-17). The rationale for this procedure is based on the assumption that realignment of the varum deformity reduces stresses on the joint's medial compartment (18). However, recent studies have shown that distribution of knee joint loads depends not only on static angular deformity, but also on dynamic variations that occur during gait (13,17,19,20). The variability in clinical results following proximal tibial osteotomy, therefore, may be associated with the dynamic factors associated with gait.

Appropriate clinical selection of patients, in addition to the correction of the varum deformity, does not ensure a successful clinical outcome. Harrington (19) found that patients with deformity of their knees can dynamically alter the transmission of force through their joints. It has been suggested that some patients have compensatory mechanisms (decreased walking speed, toeing out of foot) in their characteristic gait that may reduce their knee-joint load, thereby achieving a better functional result (13,17,19). Some have advocated incorporating either gait training or using an orthosis to improve the clinical result following osteotomy surgery (17). Although surgical treatment for the osteoarthritic knee has produced favorable results, nonoperative treatments remain desirable.

Anecdotal evidence supports the use of a lateral heel wedge (LHW) as a nonsurgical treatment for varum gonarthrosis. Applying LHWs has provided symptomatic relief (6,7), thus extending the time before more aggressive procedures have to be taken. Few reports on a lateral wedge treatment are available (6-8), and little is known about the orthosis' effect on the knee joint, indicating the need for more conclusive investigation.

A static analysis conducted by Yasuda and Sasaki (8) showed that their wedged insole changed the spatial position of the lower limb. The lateral wedge aligned the femur and tibia to a more upright position without any significant change in the femorotibial angle and also shifted the calcaneus in a valgum direction in relation to the tibia. These associated changes in the orientation of the femur, tibia and calcaneus jointly caused the extended mechanical axis of the lower limb (i.e., from the center of the femoral head to the calcaneal point of heelstrike) to attain a more vertical position in space.

Their two-dimensional static analysis of the spatial alterations concluded that the symptomatic relief provided by the lateral heel wedge was related to a reduction of the excessive loading on the medial joint surface and the excessive tensile force of the lateral side. The investigators hypothesized that the changes in the spatial positions of the lower limb were induced by activation of the supportive muscles and change in the trunk's posture.

The few reported studies (6-8) about the use of LHWs in treating varum gonarthrosis have used either a biomechanical static analysis or a clinical efficacy trial. This precipitates the need to examine the effect of a lateral heel wedge on the mechanics of the lower limb during dynamic conditions. Although roentgenograms are presently unobtainable during dynamic conditions, the forces acting on the limb and the electromyographical (EMG) activities of key muscles may be examined in attempts to identify functional changes. Thus several key questions underlying the use of LHWs for treatment of the osteoarthritic knee remain unsolved:

• Can foot orthoses positively affect the mechanics of the foot and knee joints?
• What changes in the EMG profiles result from using the wedge?
• Can the changes induced by the wedge be measured in a clinical setting?

In the present study, roentgenograms, ground reaction forces and EMG profiles were studied in both wedged and nonwedged conditions. The 'study's purpose was to determine the effect of LHW on the medial osteoarthritic knee during both static standing and the support phase of free-speed gait.

Materials and Method

Patient population. Seven males with varum gonarthrosis who were considered candidates for high tibial osteotomy surgery participated as subjects (see Table 1 ). The clinical diagnosis was degenerative osteoarthritis for all seven patients. No patient had any measurable flexion contracture, evidence of knee instability or more than moderately severe gonarthrosis as seen radiographically. The lateral compartment was relatively uninvolved in all patients. Four patients had bilateral disease of the knee, but no patient had hip or ankle impairment. Two knees had a history of trauma, both having had a torn medial meniscus. Three knees previously had undergone arthroscopic surgery (a partial medial meniscectomy in two and debridement in one). In cases of bilateral knee disease, the most symptomatic leg, as determined by the subject, was selected for the study.

Shoes and orthosis fabrication. The material used to construct the removable lateral heel wedges was a firm nickleplast with a density of 54 durometer. The shoes worn by the subjects were leather stiff-soled shoes with a 25 mm (1-inch) heel. All shoes used in this study were checked for lateral posterior wear and were modified when necessary, so that the heel area was "squared away." Valgum or lateral wedging of 12.5 mm (1/2-inch) was fixed to the heel from lateral to medial and 6.25-mm (1/4-inch) wedging was tapered to the lateral aspect of the forefoot.

Static analysis. Standing anteroposterior (AP) and lateral roentgenograms of the subject's lower limb positioned in a QUESTOR Precision Radiograph (QPR) Frames were taken for both the wedged and nonwedged conditions. Segment orientations were calculated following a computer digitization of points on the AP hip, AP knee and lateral knee radiographs. Both angular (see Figure 1 ) and linear variables were calculated for each condition using the QPR software.

Dynamic analysis.
Electromyographical data: Bipolar surface EMG electrodes (Ag/AgCl) were applied to the mid-section of vastus lateralis and vastus medialis of the subject's symptomatic leg. Ground electrodes were placed posteriorly on the bicep femoris and semimembranosus. The thigh then was covered with surgical stocking to secure the EMG electrodes and leads to minimize any movement artifact. Telemetered EMG signals were used in the study rather than hard-wired signals to completely free the subject from restrictive cables that might alter gait. The EMG telemetry units were placed anteriorly over the quadricep muscle with double-sided tape. An elastic wrap was wrapped around the subject's thigh to secure the telemetry units. The telemetered EMG signals were full-wave rectified, linear-enveloped (6hz), digitized and stored on a Compaq computer.

Ground reaction force data: Ground reaction forces in three Cartesian directions were collected via a Kistler Force Platform. A single support phase of the symptomatic leg was selected, digitized' and subsequently stored on a Hewlett Packards computer. Photocells were positioned at the level of the iliac crest of the subject and were used to measure the horizontal velocity of the body as the subject walked across the force platform. The time was recorded for each gait trial.

Data collection: The subject was required to cross the force platform at a constant (free) speed three consecutive times for both the wedged and nonwedged conditions. EMG and ground reaction force profiles were synchronized via a common voltage synchronization. Data trials were discarded if there was evidence of EMG drop off, ambient interference, improper foot contact on the force plate or if the subject failed to achieve a consistent trial-to-trial walking velocity.

Statistical analysis: Differences between the wedged and nonwedged conditions were analyzed using a matched paired t-test. Repeated measures analysis of variance (ANO VA) was used to assess the statistical differences between selected parameters of the force platform and EMG data for the wedged and nonwedged conditions.

Results

Results examined across subjects indicated both static and dynamic changes associated with the application of a lateral heel wedge. Three trials, matched for speed (+/-0. 2m/sec), were selected for each subject across conditions. Control within subject speed was necessary to allow for future comparison of EMG and force plate data without further normalization. Maximum, minimum, mean and integral values were analyzed for both the ground reaction force and EMG data; angular and linear parameters were obtained from the QPR data. No statistical difference in any subject's free gait speed was found between trials or conditions (see Table 2 ). In addition, no statistical differences were found in the anterior! posterior ground reaction forces between trials or conditions as would be expected since the methodology controlled for speed.

The mean values for the free speed of the subjects were 1.5 +/- .19 in/sec for the wedged and 1.15+/- .15 in/sec for the nonwedged conditions. Both values were slightly lower than the corresponding values (1.28 +/- .18 m/sec) for healthy, somewhat younger adults reported by Larsson et. al. (21).

Static analysis. Table 3 lists the values obtained for certain angular parameters determined by the QUESTOR Precision Roentgenograms during the bilateral examination of the lower limbs of the subjects for both the wedged and nonwedged conditions. Radiographs indicated a varum to valgum directional change (p< .05) in the capito-mideondylar-tibial shaft angle (CMTS), (p<.05) in the femoral-shaft-tibial shaft angle (FSTS) and (p< .05) in the capito-midcondylar-capito midmalleolar (CMCM). No statistical differences were found in any of the linear parameters determined by the QPR software.

Dynamic Analysis

The force platform data were normalized to the force due to body weight. The EMG profiles of the vastus lateralis and vastus medialis were normalized to the maximum activity of the muscle within each trial. LHW treatment had minimal impact on the mean vertical forces (see Figure 2 ) and increased the maximum lateral (see Figure 3 ) forces (p< .05). No statistical differences were observed for the EMG profiles between conditions.

Discussion

Several studies have found that patients with osteoarthritic changes in their knees walk much more slowly than normal age- and gender-matched controls (22-24). Reports in the literature (22-24) have shown that patients with degenerative joint disease walk with velocities ranging from 55 percent to 65 percent of normal. The present study revealed that the free speed of the subjects in both wedged and nonwedged conditions was about 90 percent of that of healthy, somewhat younger adults. The normal velocity achieved by the subjects in this study may be explained by the relatively young group of subjects, some of whom had early degenerative changes.

The static analysis conducted by Yasuda and Sasaki (8) on the effects of a wedged insole for varum gonarthrosis did not reveal any significant changes in the femorotibial angle with the application of the orthosis. The QPR results in this study indicated a small varum to valgum directional change in the femoral-shaft-tibial shaft angle and the capito-mideondylar-tibial shaft angle although the alignment of the leg remained in a relative varum position. The mechanical axis (CMCM) of the lower limb of the subjects assumed a more upright position during the LHW treatment as previously reported by Yasuda and Sasaki (8).

The magnitude of change induced by the LHW treatment, however, was small in comparison to the static realignment that can be achieved by the high tibial osteotomy surgery. The clinical significance of this static change remains of questionable value as Harrington (19) and others (13,17, 20) have concluded that static analyses are unreliable in accurately determining loading patterns across the knee during dynamic conditions. Although correcting the varum deformity of the knee does not ensure a successful clinical outcome following high tibial osteotomy (9,13,15-17), the static realignment of the lower limb, from varum to valgum, is the underlying rationale for this surgical procedure.

Yasuda and Sasaki (8) suggested the wedged insole serves as a stimulant to patients with osteoarthritic knees because it causes an everted orientation of the foot relative to the floor and, thus, alters normal standing and walking. They hypothesized that the patients adapt by changing the spatial position of their lower limbs through shifts in muscle activity and trunk postures, resulting in a decreased loading of the medial joint surface of their knees. No significant differences in the EMG profiles between the wedged and nonwedged conditions were found for the vastus lateralis and vastus medialis muscles examined in this study. The absence of a LHW effect on the EMG profiles of these muscles surrounding the knee could suggest that the patient compensated by functional changes in the hip adductor musculature; however, these muscles were not monitored during this study. The LHW might influence kinetic profiles rather than muscular function at the knee joint during dynamic activities. Results from this study do not conclusively support using EMG analysis as an adequate clinical tool for assessing LHW function.

Wang et al. (17) noted the preoperative adduction moment of the knee during gait to be the best predictor of the long-term outcome following high tibial osteotomy surgery. These authors did not find any correlation between the preoperative static measurement of the varum deformity of the knee and the adduction moment as suggested by others (19,20). Wang et al. (17) reported that the patients with the low knee adduction moments had altered their gait to include shorter stride lengths and slower speeds. An important finding from their study was the linear relationship between the inversion moment of the ankle and the adduction moment at the knee. The tendency for the ankle to sustain an inversion or eversion moment is related to the rotational position (toe in or toe out) of the foot during stance phase.

Study results demonstrated positive changes in the support leg kinetics during gait. The LHW condition revealed an increase in the maximum lateral force and a minimal decrease in the mean vertical force between the shoe/ ground interface. This should effectively reduce the tendency for the ankle joint to experience an inversion moment at the ankle during support. In addition, the observed changes in the kinetic profiles may reflect a relative toeing out of the foot from heelstrike to the foot flat position. Further evaluation, incorporating kinematic data, will be required to fully appreciate the mechanistic effect of a LHW on the adduction moments at the knee.

In the study by Keating et al. (6), patients who received relief from wedges felt relief in the first three to seven days. Those patients who received no relief in the first week generally did not receive relief with continued use. The remainder of the patients who showed improvement continued to wear the wedge, and 38 percent of patients reported little or no pain in their knees since using the wedge Three- to five-year follow-up by Seasick and Yasuda (7) concluded only 30 per cent of patients continued to use the wedge for an extended period, and those patients who stopped using the( wedge usually did so in the first year The results of these studies may indicate that subject-specific anthropometries and gait style may make some patients more suitable candidates for LHW treatment. Patients with calcaneal varum may respond more favorably to LHW than patients with calcaneal valgum since their nonsurgical treatment of choice may be the use of a knee orthosis.

Conclusion

These results provide some insight into the functional effects of the LHW on the kinetics of the lower leg during static standing and free-speed gait. The therapeutic alterations in the support leg kinetics induced by the LHW make it a useful treatment modality in the management of varum gonarthrosis. Future considerations for study should incorporate kinematics to determine the effects of a lateral heel wedge on the moments of the knee and examine the relationship of subject-specific anthropometrics on the outcome of gait. Anthropometric parameters, such as mass, adiposity and foot characteristics, should influence lower-limb static and dynamic mechanics.

Since reducing the adduction moment through changes in the placement of the foot during gait appears to be an important mechanism for reducing load at the knee (17), using orthoses as a nonsurgical therapy (singularly or as adjuncts to surgery) can be successful for the treatment of varum gonarthrosis. The question remains: "Does incorporating axial rotation into the standard proximal tibial osteotomy improve the clinical results of this surgical procedure?"

Acknowledgments

Supported by the Summer Student Research Program, 1991, and the Bachelor of Science (Medicine) Program, 1992. Faculty of Medicine. Dalhousie University, Halifax, Nova Scotia.

The authors also thank Freeman Churchill, Orthotics East of Halifax, Nova Scotia, and Dr. Monty MacMillan, Radiology Department, Victoria General Hospital, Halifax, Nova Scotia.

J. ROBERT GRIFFEN is a fourth-year medical student at Dalhousie University in Halifax, Nova Scotia.

WILLIAM D. STANISH, MD, FRCS(C), FACS, is a professor in the division of orthopedic surgery at Dalhousie University.

SCOTT N. MacKINNON, MSc, is a lecturer in the school of recreation, physical and health education at Dalhousie University.

DONALD A. MacLEOD, MSc, is a research associate at the clinical locomotor function laboratory at the Nova Scotia Rehabilitation Center in Halifax.

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