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CLINICAL SCIENCES

Bracing of the Reconstructed and Osteoarthritic Knee during High Dynamic Load Tasks

HART, HARVI F.1,2; CROSSLEY, KAY M.1; COLLINS, NATALIE J.3; ACKLAND, DAVID C.2

Author Information
Medicine & Science in Sports & Exercise: June 2017 - Volume 49 - Issue 6 - p 1086-1096
doi: 10.1249/MSS.0000000000001201
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Abstract

Anterior cruciate ligament (ACL) injury is an important risk factor for the development of posttraumatic knee osteoarthritis (OA), with radiographic knee OA evident in more than 50% of people 10 to 20 yr after ACL injury (29). Unfortunately, ACL reconstruction (ACLR) does not improve prognosis for knee OA in this patient population (38). Knee OA after ACLR is a condition that is faced by increasing numbers of young adults (45) and is associated with significantly worse knee-related symptoms, functional and psychological impairments, and poorer quality of life than those without knee OA after ACLR (19,39).

Lateral knee OA is present in more than 50% of individuals with knee OA after ACLR (1,3,51). Valgus aligned knees are associated with increased risk of lateral compartment cartilage damage and lateral knee OA progression (12), in addition to distinct gait characteristics (17), including greater knee abduction (valgus) angles and moments. Individuals with lateral compartment OA and concomitant patellofemoral joint OA walk with greater knee abduction compared with those with medial compartment OA and patellofemoral joint OA (11). Patellofemoral joint OA is frequently associated with valgus malalignment (6), and it is thought that patellofemoral joint OA may share similar biomechanical features with patellofemoral pain (56). Higher knee abduction is evident in women with patellofemoral pain (31,32,35); therefore, targeting knee abduction angle in lateral tibiofemoral compartment and patellofemoral joint OA could have important implications for symptomatic and structural disease progression.

No scientific evidence supports the efficacy of bracing in individuals after ACLR (55); however, knee bracing is considered an effective conservative treatment to manage knee OA (42). Valgus bracing can reduce frontal plane malalignment (8), external knee adduction moments (8), and medial knee load (40) and improve pain and function (8) in individuals with nontraumatic predominant medial compartment OA. By contrast, varus bracing is designed to provide an external knee varus moment and thus reduce lateral compartment loads. Nontraumatic knee OA research has primarily focused on medial compartment OA, perhaps because of much higher prevalence of medial compartment OA relative to lateral compartment OA. As a result, few studies have explored the effects of varus bracing for lateral compartment OA in nontraumatic population. However, a varus knee brace can mitigate gait characteristics associated with lateral knee OA after ACLR (18) regardless of whether the brace is configured for sagittal or frontal plane support, for example, by reducing the knee abduction angle and increasing the external knee adduction moment during overground gait (18). Because knee abduction angle is associated with lateral compartment knee OA (12), reducing knee malalignment with the brace may have implications for reducing or slowing disease progression.

Although knee bracing has been shown to modulate knee joint function during overground gait, the effects of bracing during higher-demand tasks that generate greater knee joint loads may differ substantially. Posttraumatic knee OA populations frequently comprise younger adults who are active and attempting to return to recreational or sporting activities. High impact or demand tasks such as running, jumping, hopping, and stair ambulation are known to create large ground reaction forces, joint moments, and joint contact loading (36,41,53) and may present a greater risk factor for posttraumatic knee OA after ACLR.

The unloader knee brace can improve knee-related symptoms such as stability, pain, and confidence in people with knee OA after ACLR during walking (20); however, the influence of varus unloader knee bracing during higher-demand physical activities in individuals with lateral knee OA after ACLR is not well understood. The use of a functional knee brace that can reduce excessive knee valgus and joint loading may ultimately be used to mitigate OA progression in ACLR patients. The aim of this study was to evaluate immediate knee biomechanical changes produced by adjusted (sagittal plane support with varus realignment) and unadjusted (sagittal plane support with neutral frontal plane support) varus brace conditions during hopping, stair ascent, and stair descent activities in individuals with lateral knee OA after ACLR that present with valgus malalignment. We hypothesize that a varus unloader brace will reduce the knee valgus angle and external knee joint moment and increase knee stiffness relative to the no brace condition during high dynamic loading tasks. We also hypothesize that this brace effect will be greater in the case of the adjusted brace condition.

MATERIALS AND METHODS

Study design and participants

A within-subject study design was used to investigate the immediate effects of a varus unloader brace on knee joint function during single-leg hopping and stair climbing in individuals with lateral knee OA after ACLR and valgus malalignment. This investigation is an extension of our previous research evaluating the effects of a varus brace on lower-limb biomechanics during level walking, with the recruitment method and eligibility criteria previously described (18). Volunteers who had undergone a primary ACLR (hamstring tendon or patellar tendon graft) 5 to 20 yr prior were recruited from the community via advertisements and referrals from orthopedic surgeons and health and medical practitioners. Participants were included if they were 16 yr or older at the time of ACLR and had symptomatic (Knee Injury and Osteoarthritis Outcome Score [KOOS] criteria) (9) and radiographic (≥1 grade osteophyte) OA in the lateral tibiofemoral and/or patellofemoral joint compartment (2), graded from semiflexed posterior anterior (PA) weight-bearing short film radiographs, with the feet externally rotated by 10°. Participants were defined as having symptomatic knee OA if the responses to at least half of the items within a subscale were at least one-step down from the best possible response on the KOOS QOL subscale (i.e., indicating no pain/symptoms or best possible function/QOL) and two of the four additional subscales (9). Tibiofemoral and patellofemoral joint disease severity was graded by a trained observer (KMC) (intrarater reliability, kappa = 0.75–0.84) (17). The radiographs in PA views were used to assess static frontal plane knee alignment by a single investigator (HFH) (intraclass correlation coefficient = 0.89), using previously described methods (26). The anatomic axis was first determined by a line from the tibial spine centers to a point 10 cm above the tibial spines, midway between the medial and the lateral femoral surfaces, and a line from the tibial center to a point 10 cm below the tibial spines, midway between the medial and the lateral tibial surfaces. The angle of the femoral and tibial axes intersection was subsequently measured. Angles between 178.5° and 180° defined neutral alignment, angles less than 178.5° defined varus malalignment, and angles greater than 180° defined valgus malalignment (17). Joint alignment measurments determined from short-film radiographs are associated with full-leg radiographs (23). Exclusion criteria for all participants were as follows: (i) previous lower limb arthroplasty; (ii) previous hip or knee fractures; (iii) concomitant pain from the hips, ankles, feet, or lumbar spine; (iv) neurological or medical conditions; (v) contraindications for x-ray, such as pregnancy; (vi) greater osteophyte severity in the medial tibiofemoral joint than lateral tibiofemoral joint; and (vii) an inability to understand written and spoken English. All participants provided written informed consent before data collection. Ethical approval for the study was obtained from the University of Melbourne Human Research Ethics Committee (HREC: 1238328.2).

Human movement experiments

Participants performed hopping, stair ascent, and stair descent tasks under three test conditions: (i) no brace, (ii) unadjusted brace with sagittal plane support and no varus alignment, and (iii) adjusted brace with sagittal plane support and varus realignment. Tests were conducted without the brace initially to ensure there were no carryover effects of the brace on baseline data, whereas the unadjusted and the adjusted brace conditions were subsequently randomized. Participants were fitted with a varus unloader brace (DJO Global, Inc., CA, USA) designed to control joint translations and abnormal sagittal and transverse plane motions associated with ACLR (21), in addition to correcting frontal plane malalignment (12). The brace, an upright structure with a solid base, lateral hinges, and a series of Velcro straps to fit to the participant's knee, was designed to apply an external varus moment to the knee using two settings: an unadjusted brace setting to provide sagittal and transverse plane support with neutral frontal plane support and an adjusted brace setting to provide sagittal and transverse plane rotational support with varus realignment. The brace alignment was adjusted by applying one-and-a-half turns of the three turns available. This adjustment was selected based on patient-reported comfort during walking and represented the largest brace alignment adjustment while ensuring a comfortable pressure distribution across contacting surfaces. All participants received 50% of the maximum adjustment available. The brace was fitted by a trained investigator, and participants were blinded to the applied brace condition.

Quantitative motion analysis was performed at the Human Motion Laboratory, Department of Mechanical Engineering, University of Melbourne, to assess the effects of the brace as described previously (24). To accommodate the brace, lateral and anterior thigh retroreflective markers were attached proximally (above the upper frame of the brace), and anterior tibial markers were attached distally (below the strap). Markers were not repositioned between test conditions. An initial static trial was used to calibrate relevant anatomic landmarks. The hip joint center was defined according to Harrington et al. (15), whereas the orientation of the knee flexion–extension axis was determined using a dynamic optimization approach (47).

Participants performed single-leg hop task on their affected leg with their hands on their hips, starting at a distance 50% of their leg length (greater trochanter to floor in standing) in front of the leading edge of a force plate. Participants were asked to land on the force plate in a controlled, balanced manner, maintaining the one-legged position for a minimum 3 s. Trials were excluded and repeated if (i) the contralateral limb contacted the floor, (ii) an additional secondary hop occurred on landing, (iii) excessive swaying of contralateral limb and trunk occurred (>45° from vertical, determined visually by the tester), (iv) hands were removed from the hips at any time, or (v) the entire foot did not contact the force plate on landing. Participants who were unable to perform the hopping task were instructed to repeat the task from a standing position 40% of their leg length from the force plate. Participants were allowed as many practice trials as necessary until they were comfortable with the hopping protocol. Participants then ascended and descended a custom-built staircase comprising three steps of height 16.5 cm, instrumented with force plates. Trials were performed at a self-selected speed without the use of a gait aid (e.g., handrail and walking stick). Participants were also asked to rate their average levels of pain after each task on 100-mm visual analog scales. A score of 0 mm indicated no pain, whereas a score of 100 mm indicated maximum pain.

During hopping tasks, ground reaction forces were simultaneously recorded using one ground-embedded force plate (AMTI, Watertown, MA). For the stairs tasks, ground reaction forces were simultaneously measured using a ground-embedded force plate and two portable force plates (AMTI) mounted in the staircase. Three-dimensional locations of the retroreflective markers affixed to each participant's trunk, pelvis, and lower extremities were measured using a nine-camera video motion analysis system (Vicon, Oxford Metrics Ltd., Oxford) (16,46). The position and the orientation of the portable force plates were recorded at the beginning of each trial by digitizing the position of their four corners. Video and analog force plate data were sampled at 120 and 1080 Hz, respectively. Motion data and ground reaction force data for ambulation were filtered with a fourth-order, zero-lag Butterworth filter with a cutoff frequency of 6 and 30 Hz, respectively. A pilot study investigating different filtering techniques indicated that filtering of motion and ground reaction forces with a fourth-order, zero-lag Butterworth filter with a cutoff frequency 15 Hz, which has been used during single-leg hop landing tasks (30), provided optimal signal response and capacity to detect peak kinematics and moment data at initial contact during hopping tasks.

Joint kinematics and external joint moments were computed for the stance phase of stair climbing using inverse kinematics and inverse dynamics, respectively (46). The knee joint was assumed to be a three-degree-of-freedom ball and socket joint, representing flexion–extension, varus–valgus, and internal–external rotation movements, with joint translations neglected. Joint kinematics and external joint moments for hopping tasks were reported from initial foot contact to body “stabilization,” defined when the vertical component of the ground reaction force was not larger than 5% of the participant's body weight (54). Sagittal, frontal, and transverse plane knee joint angular impulse and sagittal plane stiffness were also calculated for hopping. Angular impulse was defined by the area under the torque–time curve, and joint stiffness defined by the maximum knee joint moment divided by the overall knee angular excursion, as described previously (27). Data for each participant were averaged over three individual trials and mean data for each participant used in statistical analysis.

Data analysis

Kolmogorov–Smirnov analyses were used to assess data homogeneity and normality. Repeated-measures ANOVA with post hoc evaluations of pairwise comparisons using a least significant difference test adjusted for multiple comparisons were used to evaluate variables of interest. No participant characteristics (age, sex, body mass index, radiographic disease severity, and frontal plane knee alignment) were significantly correlated with the primary outcomes (P > 0.05), and thus these were excluded as covariates from data analyses. A Bonferroni correction was not applied to the data, as this may reduce study power and increase the risk of type II error and loss of statistical information (34). All data were analyzed with the Statistical Package for the Social Sciences (PASW Statistics 21, SPSS Inc., Chicago, IL), with significance set at 0.01.

RESULTS

Nineteen individuals with lateral knee OA (15 [79%] males; age = 37 ± 7 yr, height = 1.72 ± 0.06 m, body mass = 80 ± 10 kg, body mass index = 27 ± 3 kg·m−2) who were 12 ± 4 yr post-ACLR with valgus malalignment (187° ± 3°) participated. Participants had mild to moderate knee-related symptoms (KOOS-pain = 79 ± 15, KOOS-symptoms = 74 ± 13, KOOS-activities of daily living = 88 ± 15, KOOS-sports and recreation = 87 ± 15, and KOOS-quality of life = 58 ± 23). There were no statistically significant differences in pain during hopping (no brace = 14 mm, unadjusted brace = 14 mm, and adjusted brace = 16 mm; P = 0.369) and stairs (no brace = 14 mm, unadjusted brace = 9 mm, and adjusted brace = 12 mm; P = 0.137) between the three test conditions. Compartment-specific radiographic OA grades are presented in Table 1.

TABLE 1
TABLE 1:
Compartment-specific radiographic OA grades based on the Osteoarthritis Research Society International grading criteria.

Hopping

Compared with no brace, the adjusted and the unadjusted brace conditions significantly increased the maximum knee flexion angle (mean difference = 4.7°, 95% confidence interval [CI] = 2.7–6.7, P < 0.001, and mean difference = 5.8°, 95% CI = 2.9–8.7, P = 0.001, respectively) (Fig. 1B) and that occurring at initial ground contact (mean difference = 4.1°, 95% CI = 2.4–5.8, P < 0.001, and mean difference = 3.7°, 95% CI = 1.7–5.7, P = 0.001, respectively) (Table 1). The adjusted brace condition also increased the maximum external knee flexion moment (0.27 N·m·kg−1, 95% CI = 0.13–0.41, P = 0.001) (Fig. 1D). The adjusted brace conditions also significantly increased the maximum knee adduction angle (2.8°, 95% CI = 0.8–5.0, P = 0.010) (Fig. 2B) and knee adduction angle at initial ground contact (2.7°, 95% CI = 0.8–4.7, P = 0.008) (Table 1). The adjusted and the unadjusted brace conditions increased knee flexion angular impulses (0.06 N·m·kg−1, 95% CI = 0.03–0.09, P < 0.001, and 0.09 N·m·kg−1, 95% CI = 0.05–0.13, P < 0.001, respectively). The unadjusted brace condition increased knee adduction angular impulse (0.04 N·m·kg−1, 95% CI = 0.02–0.07, P = 0.001), whereas the adjusted brace increased knee stiffness (6.6 N·m per degree, 95% CI = 3.7–9.6, P < 0.001) compared with the no brace condition. There were no significant differences in kinematics or moments between the adjusted and the unadjusted brace conditions (P > 0.01) (Table 2, Fig. 1).

FIGURE 1
FIGURE 1:
Knee kinematics and external joint moments for no brace, unadjusted, and adjusted brace conditions during hopping. Sagittal plane kinematics (A), frontal plane kinematics (B), transverse plane kinematics (C), sagittal plane moments (D), frontal plane moments (E), and transverse plane moments (F) at time to stabilization (TS) are shown with dashed lines.
FIGURE 2
FIGURE 2:
Knee kinematics and external joint moments during stance for no brace, unadjusted, and adjusted brace conditions during stairs ascent. Sagittal plane kinematics (A), frontal plane kinematics (B), transverse plane kinematics (C), sagittal plane moments (D), frontal plane moments (E), and transverse plane moments (F) at contralateral toe-off (CTO) and contralateral heel strike (CHS) are shown with dashed lines.
TABLE 2
TABLE 2:
Knee kinematics and external joint moments, angular impulses, and knee stiffness data for no brace, unadjusted brace, and adjusted brace conditions during hopping.

Stair ascent

There were no statistically significant differences in speed between no brace (0.55 m·s−1), unadjusted (0.56 m·s−1), and adjusted brace conditions (0.57 m·s−1) (P = 0.066). The adjusted and the unadjusted brace conditions significantly increased knee flexion angles at contralateral toe-off (CTO) (2.2°, 95% CI = 1.2–3.3, P < 0.001, and 2.4°, 95% CI = 1.3–3.5, P < 0.001, respectively) and contralateral heel strike (CHS) (6.3°, 95% CI = 3.3–9.2, P < 0.001, and 4.8°, 95% CI = 3.1–6.5, P < 0.001, respectively) compared with the no brace condition (Table 3, Fig. 2A). Both adjusted and unadjusted brace conditions also increased the knee adduction angle at CTO (4.2°, 95% CI = 2.5–5.9, P < 0.001, and 4.0°, 95% CI = 2.2–5.8, P < 0.001, respectively) (Fig. 2B) and reduced knee internal rotation angles at both CTO (−2.8°, 95% CI = −3.6 to −1.9, P < 0.001, and −2.6°, 95% CI = −3.4 to −1.9, P < 0.001, respectively) and CHS (−4.2°, 95% CI = −5.2 to −3.1, P < 0.001, and −3.3°, 95% CI = −4.3 to −2.2, P < 0.001, respectively) (Fig. 2C). The adjusted and the unadjusted brace conditions significantly increased external knee adduction moments at CTO compared with the no brace condition (0.09 N·m·kg−1, 95% CI = 0.04–0.13, P = 0.001, and 0.08 N·m·kg−1, 95% CI = 0.04–0.12, P = 0.001, respectively) (Fig. 2E). The unadjusted brace reduced external rotation (−0.02 N·m·kg−1, 95% CI = −0.34 to −0.01, P = 0.009) moment at CHS compared with the no brace condition (Fig. 2F). There were no significant differences between the adjusted and the unadjusted brace conditions (P > 0.01) (Fig. 2).

TABLE 3
TABLE 3:
Knee kinematics and external joint moments for no brace, unadjusted brace, and adjusted brace conditions during stair ascent and descent.

Stair descent

There were no statistically significant differences in speed between no brace (0.58 m·s−1), unadjusted (0.62 m·s−1), and adjusted brace conditions (0.61 m·s−1) (P = 0.189). Compared with no brace, the adjusted and the unadjusted brace conditions significantly increased knee flexion angles (3.0°, 95% CI = 1.3–4.7, P = 0.002, and 3.0°, 95% CI = 1.4–4.5, P = 0.001, respectively) at CTO (Fig. 3A), and the unadjusted brace condition significantly increased external knee flexion moment (0.12 N·m·kg−1, 95% CI = 0.04–0.21, P = 0.006) (Fig. 3D) at CTO (Table 3). Both adjusted and unadjusted brace conditions significantly increased knee adduction angles at CTO (3.7°, 95% CI = 2.2–5.2, P < 0.001, and 3.4°, 95% CI = 1.9–4.8, P < 0.001, respectively) and CHS (4.6°, 95% CI = 2.6–6.6, P < 0.001, and 4.6°, 95% CI = 2.4–6.8, P = 0.001, respectively) (Fig. 3B) and reduced knee internal rotation angles at CTO (−4.1°, 95% CI = −5.2 to −3.0, P < 0.001, and −3.6°, 95% CI = −4.6 to −2.6, P < 0.001, respectively) and CHS (−2.2°, 95% CI = −3.3 to −1.0, P = 0.001, and −2.4°, 95% CI = −3.2 to −1.6, P = 0.001, respectively) (Fig. 3C). However, there were no differences between the adjusted and the unadjusted brace conditions (P > 0.01) (Fig. 3).

FIGURE 3
FIGURE 3:
Knee kinematics and external joint moments during stance for no brace, unadjusted and adjusted brace conditions during stairs descent. Sagittal plane kinematics (A), frontal plane kinematics (B), transverse plane kinematics (C), sagittal plane moments (D), frontal plane moments (E), and transverse plane moments (F) at contralateral toe-off (CTO) and contralateral heel strike (CHS) are shown with dashed lines.

DISCUSSION

In younger adults with predominant lateral knee OA and valgus malalignment after ACLR, an unloader knee brace produced significant changes in knee kinematics, moments, angular impulses, and stiffness during hopping, as well as alterations in knee kinematics and moments during stair ambulation. Contrary to our hypothesis, decreasing the degree of valgus malalignment using the brace had no substantial effect on knee biomechanics.

Lower peak knee flexion angles and external knee joint moments have been associated with posttraumatic knee OA after ACLR (7,44). In the current study, the unloader knee brace significantly increased knee flexion angles during hopping and stair climbing, which resulted in an increased external knee flexion moment. Knee bracing for medial compartment OA has also been shown to significantly decrease muscle activation and cocontraction levels (vastus lateralis/lateral hamstring and vastus medialis/medial hamstrings) (10). It has been suggested that changes in muscle activation may be produced by mechanical stabilization of the knee with the brace because of a decrease in perceived knee instability resulting in less muscle cocontraction (43). The unloader brace used in the present study may increase perceived knee stability (20), resulting in deeper knee flexion, and an increased external knee flexion moment. Medial and lateral compartment OA has been associated with reduced knee flexion or quadriceps avoidance (50). Reduction in knee flexion may have the potential to reduce the muscle-generated joint contact force, which could potentially reduce pain and discomfort, whereas increased knee flexion may ultimately produce a predominant joint force in the direction normal to joint surface. The increased knee flexion associated with the brace may ultimately reduce the likelihood of quadriceps disuse atrophy in posttraumatic knee OA after ACLR, provided the increase is not excessive (i.e., greater than that of the healthy controls), which may ultimately adversely load the patellofemoral joint (4). Further analysis of muscle EMG data in this population is required to evaluate the influence of bracing on muscle cocontraction and quadriceps muscle activity in light of the observed changes in joint moment and angular excursion.

Increases in the maximum external knee flexion moment and angular impulse during hopping with the adjusted brace were associated with increased knee stiffness, or a greater peak joint moment over a given angular excursion of the knee joint. Higher leg stiffness may be beneficial for regulating power output and reduced metabolic cost of movement (5,25). The coactivation patterns of the antagonist muscles also contribute to joint stiffness and reduced joint laxity (14). The increases in knee stiffness with the brace observed in the current study may result in heightened activation of the quadriceps muscles in response to the deeper knee flexion. This increase in knee stiffness may be beneficial for this relatively active population, as it may provide greater resistance against external perturbations and reduce the risk of reinjury that may occur in a reflexive manner. However, further analysis is required to evaluate the degree of preactivation (just before foot contact), cocontraction, and stretch reflexes in the overall muscle stabilizing effect, in addition to the inherent mechanical stiffness of the brace design.

In a valgus malaligned knee, the ground reaction force may tend to pass more laterally to the knee resulting in increased loading on the lateral knee compartment (52) and an increased risk of cartilage damage, OA onset, and progression (12). The unloader brace significantly decreased knee abduction angles in individuals with lateral knee OA after ACLR and valgus malalignment. Reduction in knee abduction angles with the brace was associated with an increase in the external knee adduction moment and is likely to result in smaller lateral compartment joint loading. Reducing the contact force at the lateral compartment may have important implications for OA progression; however, it is important that the unloader brace does not create an excessively high knee adduction moment (i.e., higher than healthy controls), which may adversely load the medial knee compartment (48). The knee adduction moment that we observed with the unadjusted (mean = 0.26 N·m·kg−1, 95% CI = 0.19–0.34) and adjusted (0.27 N·m·kg−1, 95% CI = 0.20–0.35) brace conditions is well below the peak knee adduction moment reported in healthy adults older than 40 yr during stair climbing (0.78 ± 0.16 N·m·kg−1) (33). Another study reported peak knee adduction moment of 0.32 ± 0.14 N·m·kg−1 in young adults and 0.35 ± 0.16 N·m·kg−1 in older adults (37). In human knees, valgus loading can increase ACL force (28). Because increased knee abduction angles and moments have been shown to be significant predictors of future ACL injury (22), reduction in valgus angles and moments (within the range of healthy knees) with the unloader brace could also have important implications for ACL reinjury.

The ACL resists the combined motions of anterior tibial translation and internal tibial rotation. Abnormal internal–external tibial rotation after ACLR indicates that rotation restraint provided by the graft may not be as effective as the intact ACL. The unloader brace significantly reduced tibial internal rotation angles relative to the no brace condition during high dynamic loading activities. Although speculative, it may be that the brace could augment the function of the ACL by reducing the internal rotation angle and potentially protect the ACL from injury associated with tibial rotation during higher impact dynamic load tasks, including sporting activities.

The changes that we observed in knee kinematics and external joint moments when high dynamic loading tasks were performed with the brace are consistent with those changes observed with the unloader brace during overground walking, including increased knee flexion and adduction angles as well as increased external flexion and adduction moments (17). It was hypothesized that although the unadjusted brace condition with neutral frontal plane adjustment would produce notable changes in knee biomechanics, the changes produced with the adjusted brace condition with varus realignment would be more pronounced. It was anticipated that the high dynamic loading activities used in this study would provide more sensitivity to joint-level biomechanical changes between the two brace conditions compared with those during gait; however, the varus adjustment of the brace does not provide any additional benefit over the use of the brace when unadjusted. This suggests that a smaller or more lightweight brace without varus adjustment, or the use of adhesive taping, may be able to replicate the function of the unloader brace (13). Future studies ought to consider investigating immediate and longer-term effects of lower profile braces or taping on gait characteristics, neuromuscular patterns, and knee-related symptoms in individuals with knee OA after ACLR. Given that the knee brace in the present study has the potential to improve pain, stability, and confidence as well as modulate knee biomechanics, the long-term brace used during activities of daily living as well as high knee-loading sports, including netball and basketball, may be beneficial for this patient population. Knee braces can at times be cumbersome to use and fear of functional hindrance may result in poor patient compliance (49). Therefore, a brace without frontal plane adjustment, or taping in place of bracing, may reduce bulkiness and improve comfort, leading to better adherence. Poor brace compliance has been previously shown in patients with knee OA after 1 month of brace use despite pain relief (49).

There are a number of limitations of this study. First, our findings apply to forward hopping tasks in people with lateral knee OA after ACLR. The controlled landing performed in the laboratory may not represent landings that occurs in sporting activities. Second, the findings reported represent the immediate effects of bracing on knee-joint function. Thus, the technical relevance of these biomechanical changes is unknown until longer-term studies of bracing on lower limb biomechanics have been evaluated. Third, a standard criterion was used to define valgus malalignment in men and women in this study (tibiofemoral angle greater than 180°). Finally, half of the maximum varus adjustment (i.e., 1.5 turns of the maximum 3 turns available) was prescribed with the knee brace. It is unknown whether the maximum adjustment (i.e., 3 turns) is necessary to produce more discernible biomechanical differences between the adjusted and the unadjusted brace conditions; however, our decision to prescribe this adjustment was based on patient-reported comfort and was intended to avoid excessively loading the medial knee compartment.

CONCLUSIONS

A varus unloader brace can modulate knee kinematics and external joint moments during high dynamic loading activities in individuals with predominant lateral knee OA after ACLR and valgus malalignment. Increasing the degree of varus realignment using the brace did not significantly influence knee joint function; therefore, a less-bulky brace without varus realignment may be as effective and could be used with increased user compliance. Longer-term application of knee bracing, particularly during high dynamic loading sporting activities, may have implications for reducing OA progression in these patients.

N. J. C. is supported by a University of Queensland Postdoctoral Fellowship. D. J. O. Global provided braces for the study and funding for the radiographs. H. F. H. was supported by a National Health and Medical Research Council postgraduate scholarship (Australia) (no. 813021) at the time of the study. H. F. H. is supported by a National Health and Medical Research Council project grant (no. GNT1106852). The authors declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

The authors have no conflict of interest to disclose. The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

ANTERIOR CRUCIATE LIGAMENT; OSTEOARTHRITIS; HOPPING; STAIRS; BIOMECHANICS; VARUS BRACE

© 2017 American College of Sports Medicine