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Effects of a Knee Varus Brace on Nonoperative Lateral Compartment Osteoarthritis

Fenter, Paula Click PT, DHSc, GCS

JPO Journal of Prosthetics and Orthotics: April 2014 - Volume 26 - Issue 2 - p 113–117
doi: 10.1097/JPO.0000000000000019
Original Research Article
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ABSTRACT The aim of this study was to evaluate the effectiveness of the OAdjuster® (dj Orthopedics, Vista, CA, USA) brace on lateral compartment osteoarthritis (OA). The OAdjuster knee brace will effectively control joint angles in the frontal plane throughout the stance phase of the gait cycle. Two patients with valgus knee deformity diagnosed with lateral compartment OA in the right knee were included in this study. Both patients have been fitted with the OAdjuster knee brace in the treatment of OA. A subjective history was taken of each patient through a personal interview. Objective tests and measures were taken to rule out any other joint pathology. Each patient ambulated with and without the unloading brace and was filmed with two digital cameras. Analysis of joint angles and gait parameters was performed with the Ariel Performance Analysis System® (APAS) (Ariel Dynamics, Inc, San Diego, CA, USA). In case 1, the knee valgus angle at midstance decreased from 4.4° of valgus to 1.7° of valgus with the use of the brace. The hyperextension angle in the sagittal plane also decreased during single-limb stance on the braced limb from 12.1° to a neutral alignment. Other gait parameters in case 1 showed very little change with the use of the OAdjuster brace. Case 2 exhibited a decrease in valgus angle during midstance from 8.4° to 7.0°. The hyperextension angle during single-limb stance also decreased from 11.2° to 4.4°. Gait parameters also showed an improvement in case 2 with the use of the unloading brace. The OAdjuster brace may become a viable option for patients with lateral compartment OA and who are unable to undergo surgical procedures because of other comorbidities. The OAdjuster brace effectively controlled joint angles in the frontal and the sagittal plane throughout the stance phase of the gait cycle.

PAULA CLICK FENTER, PT, DHSc, GCS, is affiliated with the School of Allied Health Professions, Program in Physical Therapy, Louisiana State University Health, Shreveport, Louisiana.

Disclosure: The author declares no conflict of interest.

Correspondence to: Paula Click Fenter, PT, DHSc, GCS, School of Allied Health Professions, Program in Physical Therapy, Louisiana State University Health Shreveport, 1501 Kings Hwy, Shreveport, LA 71103; email: pclick@lsuhsc.edu

Knee osteoarthritis (OA), also known as degenerative joint disease, is the most prevalent form of arthritis that affects the ability to walk.1 The disruption of the articular surfaces causes pain with weightbearing along with stiffness during movement. Excessive repetitive impact force on the knee causes abnormal mechanical forces to act on the articular surfaces with resultant changes. Functional mobility then becomes difficult on a daily basis. The most common location of OA in the weightbearing joints is the knee. It is estimated that 46% of individuals in their lifetime will develop painful OA of the knee,2 causing abnormal gait changes to occur over time. These changes in function and increased aging of the “baby boomers” will subsequently be passed along as increased health care costs.3 It should also be noted that medial compartment OA of the knee is affected nine times more often than the lateral compartment.4

The management of knee OA is multifaceted and must be tailored to the individual patient.5,6 Conservative intervention options commonly use nonsteroidal anti-inflammatory drugs (NSAIDs) or other pharmacological agents for pain and inflammatory control, wedges to shift biomechanical forces, physical therapy to increase the range of motion and strength of the musculature around the joint,5–9 and bracing to shift the load via external support.10 Surgical interventions may involve arthroscopic debridement, osteotomies, or total knee replacement.6 In many instances, individuals may opt for conservative treatment because of the inability to undergo surgical procedures because of comorbidities or medical history.11

Conservative management of unicompartmental knee OA has been studied in the literature to analyze the effectiveness of conservative intervention options.8,10–15 Functional knee braces or offloading braces use the idea of distraction and shifting the forces from an arthritic articular joint that is narrowed to the opposite joint surface with a periarticular brace.16 Unloading in the sagittal plane with bracing has been studied more by authors than that in the frontal plane.8,10–12,14–16 Both Self et al.14 and Pollo et al.13 found that bracing for varus unloading was effective in medial compartment OA; however, few studies address bracing for lateral compartment OA. During gait analysis, forces about the knee in the frontal plane are a major determinant of loads on the articular surfaces of the knee.17–19

Because OA is typically identified as medial or lateral compartmental OA, the study of frontal plane parameters may be the cornerstone of conservative treatment,5 although it is not well documented.10 During gait frontal plane, forces at the knee normally produce a moment at heelstrike that shifts the load to the medial compartment of the knee. More studies of frontal plane unloading have been located that focus on medial compartment unloading.10,12–14,20 Although medial compartment deficits are more common, knee deficits from OA of the lateral knee compartment do need to be understood in answering questions about the parameters of gait and characteristics of joint motion including response to bracing. It is important to know whether braces purported to unload the lateral compartment with correctional forces are actually performing that function. A 2005 Cochrane review assessed orthoses for treating OA of the knee but focused only on medial compartment OA.21

Therefore, the primary objective of this study was to quantify the parameters of gait with and without the use of a knee unloading brace in two individuals with OA of the lateral compartment. Gait parameters of frontal and sagittal plane knee movement were measured during comfortable walking with and without the unloading brace for the lateral knee.22

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MATERIALS AND METHODS

After obtaining institutional review board (IRB) approval, two individuals who had been placed in an unloading brace on the right knee volunteered to participate. Both had lateral unicompartmental OA producing a valgus force on the right knee during gait and had already been placed in an OAdjuster® unloading brace. Each person was interviewed and agreed to walk with and without the use of his/her unloading brace. Tests for ligamentous integrity of the right knee were performed. Gait was assessed by video recording each participant ambulating with and without the unloading brace. Reflective markers were used on specified bony prominences for camera capture. The video assessment used two digital cameras (right and left) from an anterior-lateral approach. The ambulation pathway consisted of a 30-ft flat surface that was well lit and at comfortable room temperature to eliminate as many extrinsic variables as possible. Each individual ambulated three times with and without the unloading brace. The third gait was captured by video for analysis. Strength of the affected hip was assessed using a standard manual muscle test on the right, performing a one-repetition maximum.

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ANALYSIS SYSTEM

The video was analyzed using the Ariel Performance Analysis System® (APAS) (Ariel Dynamics, Inc, San Diego, CA, USA) to determine the effectiveness of the unloading brace. The system processed the information to synchronize, digitize, filter, and transform information to determine joint angles and gait parameters and produce a three-dimensional image. Klein and DeHaven23 tested this system, showing an accuracy of 0.3° or less.

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UNLOADING BRACE

The OAdjuster functional unloading brace is lightweight with a sleek profile that is recommended for use on patients with moderate-to-severe OA.22 It incorporates the four-point dynamic leverage system and a biaxial hinge technology. The four-point leverage system includes an anterior thigh cuff, a posterior calf cuff, a posterior thigh strap, and an anterior tibial strap, as seen in Figure 1. The brace allows for a 10° extension stop in the sagittal plane throughout the range and the ability to set frontal plane motions between 20° varus and 20° valgus.22 Each brace was adjusted to the patient’s tolerance for comfort in correction of the deformity, that is, unloading of the lateral compartment. Application of the brace requires stepping the foot through the opening for the rigid bar to be at the posterior calf, and the anterior bar is placed over the thigh. The brace joints should be aligned along the joint line of the knee. Each strap was pulled firmly to be tight enough to hold the knee without pinching soft tissue. Each strap was tested by the patient by placing the index finger under the strap to ensure that it was not too tight so that circulation was not compromised.

Figure 1

Figure 1

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CASE INFORMATION

Case 1 is a 54-year-old white man who is currently employed and has a diagnosis of OA in the right knee. His chief complaint is pain and crepitus near the lateral joint line, which is worse after being in a stationary position for an extended period either in flexion or extension. Additional complaints consist of pain during any load-bearing activities. Strength of the right hip was assessed as 5 of 5 in hip abduction and extension and 4 of 5 in adduction. He used NSAIDs for inflammation and an OAdjuster unloading brace.

Case 2 is a 55-year-old African American woman with a diagnosis of OA of the lateral compartment in the right knee. Her subjective complaints were knee pain during gait activities, swelling during long-term ambulation, and occasional “giving away” of the knee with pivoting activities. Strength was 3 of 5 in right hip abduction, extension, and adduction. Her current treatment is over-the-counter medications, NSAIDs, and ice; exercise; and the recent addition of the OAdjuster unloading brace.

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RESULTS

Each individual had normal passive range of motion of the knee, hip, and ankle joints and no torn ligaments; however, laxity was present in the frontal plane in both valgus and varus directions for both individuals. A comparison of gait parameters for the braced and unbraced condition is noted in Table 1.

Table 1

Table 1

In case 1, change was noted in several gait parameters when walking with and without the brace. During gait with the unloading brace, there was a decrease in the maximum valgus angle at midstance from 4.4° to 1.7° (−2.7°), a decrease of hyperextension in the knee during single-limb stance from 12.1° to 0° (neutral alignment), a decrease in lateral excursion of the center of gravity (COG) by 2.7 cm, and a decrease in braced step length by 2.7 cm with a slight increase in step length of the opposite leg (0.9 cm). Other gait parameters revealed minimal changes (≤0.5°, ≤0.5 cm, ≤0.4 seconds, or no change). This individual subjectively reports that the unloading brace is easy to apply and gives an increased sense of support as well as confidence during gait.

In case 2, changes were found in gait parameters between braced and unbraced conditions. During gait with the unloading brace, there was a decrease in the maximum valgus angle at midstance from 8.4° to 7.0° (−1.4°), a decrease of hyperextension in the knee during single-limb stance from 11.2° to 4.4° (−6.8°), a decrease in lateral excursion of the COG by 4.3 cm, a decrease in base of support (BOS) by 3.6 cm, and an increase in step length of the opposite leg by 7.6 cm and a decrease in braced step by 1.4 cm. Other gait parameters revealed minimal or no change.

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DISCUSSION

The most dramatic finding in these cases is the change in joint angles during single-limb stance in the sagittal plane during bracing. The decrease in hyperextension during single-limb stance is 2° and 7° in case 1 and case 2, respectively. These findings illustrate that the unloading knee brace can assist in bringing sagittal plane angles to a more neutral alignment, moving them toward the direction of normal gait. Abnormal knee hyperextension during stance positions the anatomic knee joint posterior to the knee axis, thus reducing the demand on a weak quadriceps during walking and changing the lower-limb biomechanics.24 This results in decreased shock absorption during the stance phase and interference with forward progression during the swing phase.24 In both cases, knee hyperextension was decreased during the braced condition. By bringing the knee joint to a more normal alignment of the sagittal plane, more efficient use of the quadriceps allows better stability during the stance phase of gait. In both cases, the decrease in the arthritic limb step length agrees with Gaasbeek et al.16 When it is accompanied by a slight increase in opposite step length, it implies that the braced limb is more stable for support and the opposite limb can progress forward more readily. This is congruent with the subjective report of more confidence when using the brace. In case 2, the braced control of knee hyperextension coupled with significant quadriceps weakness provided a dramatic 7.4-cm increase in opposite limb step length. Again, the brace produced an increase in stability and forward progression for the individual, as noted in symmetric step length of both arthritic and unaffected limbs. Draper et al.11 in 2000 noted consistent and immediate improvement in symmetry indices and decreased pain with the medial unloading brace.

A functional unloading brace is designed to reduce the load from the involved arthritic component of the knee in unicompartmental OA through application of an external force in the frontal plane.16 A shift of the distal tibia from knee center alignment limits stability and causes joint and ligamentous laxity and ipsilateral abductor weakness.24 An unloading brace should decrease the excursion of the knee joint from extremes of motion that take place during arthritic conditions in which typical loss of stability and joint erosion allow for extremes of motion. When lateral compartment arthritis causes knee angle changes, unloading should occur particularly during the weightbearing components of gait to unload the lateral compartment and align the tibia. In both of these cases, the angle of knee alignment during midstance is moved toward neutral alignment, thus causing limitation of extremes of motion in midstance. One study13 found a 4° reduction in frontal plane angle with medial OA, but no comparisons were found for lateral OA. In both of these cases, a smaller change was found in alignment; however, according to Krohn25 (2005), valgus malalignment of the knee is associated with increased risk for OA progression in lateral knee OA at 5°. Theoretically, a reduction in valgus angle should assist in decreasing the load to the lateral compartment and thus reduce forces on that part of the joint. Butler et al.26 compared frontal plane mechanics in medial and lateral compartmental OA with controls. He determined that there were greater differences between lateral knee OA and controls than between medial knee OA and control groups in the frontal plane when assessing gait. The changes noted in these case studies seem to support the finding of Pollo et al.13 that bracing does change frontal plane angle. Malalignment has been associated with the progression of radiographic joint space loss and deterioration in function.27 Varus alignment increases the risk for medial OA progression, and valgus alignment increases the risk for lateral OA progression.28 An alignment of more than 5° (in either direction) in both knees at baseline is associated with significantly greater functional deterioration than an alignment of 5° or less in both knees, after adjustment for age, sex, body mass index, and pain.26

In explaining forces, Perry and Burnfield24 found that from initial contact of the foot that occurs along with knee valgus, with subsequent loading to midstance, a force of 50% to 500% of body weight is placed on the joint. This amount of force placed on an arthritic joint could add to the pain during each step of ambulation. An appropriately fitted unloading brace could provide support from knee valgus excursion that may have the potential to decrease pain during gait.

Lateral excursion of the COG is described as the lateral shift over the BOS as someone walks and is associated with stability of the trunk over the limb.24 In both cases, lateral excursion of the COG decreased by 2.7 cm and 4.3 cm. Lateral excursion of the COG is associated with increased energy expenditure,24 often due to weakness, thus contributing to extra compensatory movements of the trunk over the limbs to prevent instability and falls. In both of these individuals, the braced condition produced a decrease in lateral excursion, reducing lateral movement and thereby decreasing the amount of energy expended. Noteworthy is the fact that the individual with quadriceps weakness, case 2, experienced a greater decrease in excursion, which implies more support of the trunk over the limb. In addition, a decrease was found in BOS of case 2 by 3.6 cm. Because a wider BOS is associated with instability, a decrease in that width would imply that the individual experienced greater stability during the braced condition and was able to decrease the BOS during the gait cycle.

When studying frontal plane mechanics, Butler et al.26 found that the knee adduction excursion for lateral OA was not significantly different from controls by 1.8° (p = 0.01). The difference occurring with lateral knee unicompartmental OA coupled with the findings of these two case studies should encourage more detailed assessment between the medial and the lateral compartment OA when using an unloading brace. This is timely and important information to differentiate, because the population of individuals who are at risk for knee OA are baby boomers who want to stay active. Surely, the information gleaned from these two cases cannot be generalized to the population, but it does give measurable, objective information that can direct further investigation and emphasize the differences of lateral compartment OA. It presents the idea that bracing may be a valuable conservative treatment alternative to more aggressive modes of intervention in the treatment.

Many factors should be taken into consideration when prescribing and using knee orthoses. Unloading knee braces purport to control motions to benefit the patient’s gait and functional activities, yet evidence is not always present in the literature to support these claims. Conservative options are less costly than surgery and may be good alternatives for many people; however, evidence for their use should be specific and clear. This study has provided insight into the gait parameters and angular changes that are associated with the use of a functional unloading brace. Few studies have quantified the changes in gait parameters in individuals with and without unloading braces of knee OA. These results offer encouragement to individuals with lateral compartment OA who may be interested in conservative intervention or may not be ideal surgical candidates for knee arthroplasty.

In the future, it would be desirable to have follow-up testing of the individuals for information on continued wear and tolerance as well as effectiveness in controlling both mechanics and function. Another kinematic assessment, functional mobility along with perceptions of usefulness over time, would provide useful information on the long-term use of this type of unloading brace.

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Keywords:

knee orthosis; brace; valgus deformity; osteoarthritis; lateral knee; arthritis

© 2014 by the American Academy of Orthotists and Prosthetists.