This within-subject study is an extension of our previous research investigating the effects of a varus unloader brace on lower-limb biomechanics during level walking.13 The recruitment and eligibility criteria have been previously described.13 The primary inclusion criteria were as follows: (i) undergone a primary ACLR (hamstring tendon or patellar tendon graft) five to 20 years ago; (ii) aged ≥16 years at the time of ACLR; and (iii) symptomatic [Knee Injury and Osteoarthritis Outcome Score (KOOS) criteria],17 and radiographic (≥1 grade osteophyte) OA in the lateral TFJ and/or PFJ.18 A trained investigator (KMC) graded TFJ and PFJ disease severity (intra-rater reliability: kappa 0.75–0.84).19 The radiographs in postero-anterior views were used to assess static frontal-plane knee alignment by a trained investigator (intraclass correlation coefficient=0.89), using previously described methods.20 Angles between 178.5° to 180° were defined as neutral alignment, angles <178.5° were defined as varus malalignment, and angles greater than 180° defined valgus malalignment.20 The KOOS consisted of five subscales. A normalized score out of 100 is calculated for each subscale, where 0 represents maximum knee-related symptoms, and 100 represented no knee-related symptoms.21 All participants provided written informed consent prior to data collection. Ethical approval for the study was obtained from The University of Melbourne Human Research Ethics Committee (HREC: 1238328.2).

Muscle electromyographic (EMG) data presented in the current study were acquired during quantitative gait analyses. Retro-reflective markers were attached at specific locations on participant's pelvis (left/right anterior superior iliac spine, sacral, left/right posterior superior iliac spine) and both lower extremities — thigh (left/right proximal and anterior aspect, proximal and lateral aspect, distal and anterior aspect, distal and lateral aspect), knee (left/right medial and lateral femoral epicondyles), leg (left/right proximal and distal ends of tibia and lateral aspect of tibia), and foot (left/right medial and lateral malleolus, proximal and distal aspects of the posterior calcaneum, dorsal surface of the distal forefoot at the midpoint between the second and third metatarsophalangeal joints, lateral midpoint over the dorsal and distal aspect of the cuboid, medial midpoint over the distal and dorsomedial aspect of the navicular — for gait analyses,22 with thigh and calf markers positioned to accommodate the brace.23 EMG data were recorded at 1080Hz using pairs of Ag/AgCl surface electrodes (Motion Laboratory Systems, Baton Rouge, LA, USA) mounted on the skin over the following muscles: gluteus maximus (GMAX), gluteus medius (GMED), vastus medialis (VM) and vastus lateralis (VL), rectus femoris (RF), medial hamstrings (MHAM), lateral hamstrings (LHAM), medial gastrocnemius (MGAS), lateral gastrocnemius (LGAS) and tibialis anterior (TA) via a telemetered EMG system (Noraxon USA Inc., Scottdale, AZ, USA). Recommendations of the SENIAM group (Surface ElectroMyoGraphy for the Non-invasive Assessment of Muscles) were followed for skin preparation and electrode placement locations.24 The skin surface was shaved, lightly abraded, and cleaned with alcohol prior to surface electrodes placement. It was not necessary to change the electrode locations to accommodate the brace.

Participants performed gait trials under three test conditions at a self-selected speed on a 10-meter level walkway. The following conditions were tested: (i) no brace, (ii) unadjusted brace, with sagittal-plane support and no frontal plane realignment, and (iii) adjusted brace, with sagittal-plane support with varus realignment. The unloader brace is designed to control sagittal and transverse plane rotations associated with ACLR, in addition to correcting frontal plane malalignment. The adjusted brace condition was used to assess the effects of adding varus realignment to the sagittal and transverse plane rotational support. Approximately one and half turns of the maximum three turns varus adjustment was provided. The unadjusted brace condition was used to assess the effects of sagittal and transverse plane support, without frontal plane realignment. Participants performed walking trials without the brace first, followed by the two brace conditions applied in a randomized order. Participants were blinded to the differences between the two brace conditions.

Immediately following each test, participants rated their average levels of knee pain on 100mm visual analog scales. A score of 0mm indicated no pain and a score of 100mm indicated maximum pain.

The retro-reflective marker attached to the heel was labeled and trajectory data were filtered with a low pass, fourth order Butterworth filter (zero lag, 6Hz). Data were exported from Noraxon into a csv file and the EMG data were exported and processed using R statistical software (Version 3.3.2 http://www.R-project.org/). Trials were excluded where EMG data was affected by artifact (visually inspected). After correcting for DC offset, the EMG signal was high-pass filtered (20Hz, 4th order Butterworth) and full-wave rectified. EMG signals were low-pass filtered (50Hz, 4th order Butterworth) for the purpose of onset and offset detection. Criteria for EMG burst onset and offset were established as >15% peak amplitude for ≥10% of the gait cycle and <10% of peak amplitude for ≥10% of the gait cycle, respectively.25 Data collected using a ground-embedded force plate13 were used to establish initial foot contact and foot off, while the traces from the heel trajectory marker were used to establish subsequent foot contact, stance time and stride time. EMG traces were analyzed to establish onset, offset, and duration for each muscle. Muscle co-contraction duration was established by determining onset/offset of antagonistic muscle pairs (e.g. VM and MHAM) and measuring duration of dual activity.26 Mean and peak EMG amplitude activity was also recorded for the burst duration. Each participant's data were averaged over three individual trials for each condition. The investigator analyzing the EMG data was blinded to the test conditions. Variables of interest included onset, offset, duration, average and peak magnitude of GMAX, GMED, VM, VL, RF, MHAM, LHAM, MGAS, LGAS, and TA. Co-contraction indices were calculated for different muscle pairs (i.e., medial and lateral) and groups (i.e., flexors and extensors). The following muscles were evaluated: (i) VM and VL; (ii) MHAM and LHAM; (iii) VM and MHAM; (iv) VL and LHAM; (v) MGAS and LGAS; and (iv) flexors (VM, VL, RF) and extensors (MHAM and LHAM).

Homogeneity and normality were assessed using Kolmogorov–Smirnov analyses. Repeated measures analysis of variance with Least Significant Difference post hoc evaluations were used to assess differences in variables of interest. Greenhouse–Geisser corrections were applied where assumptions of sphericity were not met. All data were analyzed with the Statistical Package for the Social Sciences (SPSS Statistics Version 23, IBM Cooperation. Armonk, NY), with significance set at 0.05.

This study included 19 individuals with predominant lateral knee OA (15 [79%] men; mean±SD age 37±7 years; height 1.72±0.06m; body mass 80±10kg; body mass index 27±3kg/m2; 13 hamstring-tendon graft; six patellar-tendon graft) who were 12±4 years post-ACLR with valgus malalignment (187°±3). 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; KOOS-quality of life, 58±23). Thirteen participants (68.4%) had lateral TFJ OA and PFJ OA, 5 participants (26.3%) had PFJ OA without lateral TFJ OA, and 1 participant (5.3%) had lateral TFJ OA without PFJ OA.

There were no statistically significant differences in knee pain during walking (mean VAS: no brace=3±4mm, adjusted brace=8±13mm, and unadjusted brace=5±10mm; p=0.151). There were significant differences in gait speed between no brace (1.46±0.13m/s), adjusted brace (1.43±0.11m/s), and unadjusted brace conditions (1.46±0.14m/s) (p=0.011). Gait speed was slower with the adjusted brace condition relative to the no brace (mean difference [95% confidence interval], p-value: −0.038 [−0.062, −0.013], 0.005) and the unadjusted brace (−0.028 [−0.050, −0.006], p=0.014) conditions.

There were no statistically significant differences in muscle co-contraction between the no brace, adjusted, and unadjusted brace conditions (Fig. 1). There were also no significant differences in co-contraction of flexor-extensor muscle groups (p=0.160).

Figure 1.

Co-contraction indices for predefined muscle pairs for each brace condition.

(0.12MB).

Relative to the no brace condition, the adjusted (72ms [24, 119], p=0.005) and unadjusted (75ms [24, 126], p=0.007) brace conditions delayed offset time of GMAX (Table 1). The unadjusted brace also significantly increased the duration of GMAX activity compared to no brace (54ms [1, 127], p=0.047); however, differences between no brace and the adjusted brace did not reach statistical significance (p=0.051). Relative to no brace, the adjusted and unadjusted brace conditions resulted in earlier onset of GMED (59ms [21, 97], p=0.004; 43ms [5, 82], p=0.030; respectively). There were no statistically significant differences in GMAX and GMED timing between the two brace conditions. The adjusted brace resulted in delayed offset of LGAS compared to no brace (53ms [28, 78], p<0.001) and the unadjusted brace (39ms [7, 71], p=0.020). There were no other statistically significant differences observed in timing between the three test conditions (Table 1).

Relative to no brace, the adjusted brace reduced average amplitude of GMAX (−4mV [−6, −1], p=0.015) and LGAS (−9mV [−16, −2], p=0.020). There were no other statistically significant differences observed between the three test conditions (Table 1).