Toe-in and toe-out walking require different lower limb neuromuscular patterns in people with knee osteoarthritis
Introduction
Osteoarthritis (OA) is a chronic disease which can result in substantial disability and pain (Salaffi et al., 2005). The knee is often afflicted by the disease and a variety of risk factors are associated with the development and progression of knee OA. Two important and modifiable risk factors are excessive joint load and neuromuscular dysfunction (Bennell et al., 2011, Miyazaki et al., 2002, Oiestad et al., 2015). Traditional treatment approaches (joint replacement and pharmacology) are not intended to address knee joint load or neuromuscular factors, and are associated with a high risk of side effects. Therefore, an urgent need exists for alternative treatments to manage the disease by addressing these factors. This is becoming more important as recent investigations have shown a rise in symptomatic knee OA, particularly in younger age categories (Deshpande et al., 2016). This will lead to individuals living longer with the disease, thereby increasing strain on the health care system.
Gait modification is a viable conservative strategy, encompassing a variety of alterations to one’s gait (Richards et al., 2017, Simic et al., 2011). The objectives of these gait modifications are to redistribute knee load, primarily via reductions in the external knee adduction moment (KAM), and to improve symptoms such as pain. The KAM is an accepted proxy of knee joint load distribution, and is an outcome measure linked to disease progression (Bennell et al., 2011, Hatfield et al., 2016, Miyazaki et al., 2002).
Toe-in (TI) and toe-out (TO) walking, in particular, have gained attention in recent years due to their potential to improve knee load and symptoms. A single-session study observed that TI and TO walking of varying degrees has the potential to reduce KAM magnitudes in people with knee OA (Simic et al., 2013). Two clinical trials in knee OA populations expanded these findings by reporting reductions in early stance peak KAM of 20% (Shull et al., 2013) and late stance peak KAM of 10.5% (Hunt and Takacs, 2014), and self-reported pain by 29% and 28.4% during TI and TO walking, respectively. These studies highlight the effectiveness of TI and TO walking as a conservative treatment strategy for knee OA; however little is known regarding how altering gait in this manner may affect neuromuscular patterns of the lower extremities or the mechanics of joints other than the knee. Neuromuscular patterns may have both beneficial and detrimental effects on knee joint mechanics; therefore, advancing our current understanding of how TI and TO walking may change these patterns is important prior to clinical implementation.
During natural walking, individuals with knee OA typically exhibit greater muscle activation and co-contraction of the lateral thigh musculature, and greater muscle activation duration of the periarticular knee muscles (Childs et al., 2004, Heiden et al., 2009, Hubley-Kozey et al., 2006, Hubley-Kozey et al., 2009, Lynn and Costigan, 2008). The effect of gait modification on the neuromuscular function of young healthy participants and people with knee OA is less known. Individualized TI and TO walking modification elicited immediate quadriceps and hamstrings co-contraction increases in healthy adults (Uhlrich et al., 2018). In those with knee OA, toe-out walking has been shown to increase lateral hamstrings activation relative to the medial hamstrings, (Lynn and Costigan, 2008). Additionally, a delay in gastrocnemii activation onset, and an increase in quadriceps activation (both duration and magnitude), have been observed during TO walking compared to natural walking (Rutherford et al., 2010). Taken together these findings suggest a possible magnification of the already abnormal neuromuscular characteristics of individuals with knee OA, compared to healthy or asymptomatic individuals, when performing toe-in or toe-out walking.
The present study compared the neuromuscular patterns, specifically: average muscle activity, peak muscle activity and co-contraction indices of the thigh muscles and medial to lateral thigh muscle activation ratio during four commonly researched foot rotation conditions: 10° TI (TI10), 0° (ZR), 10° TO (TO10) and 20° TO (TO20) in people with knee OA. The purpose was to examine the neuromuscular patterns elicited during walking with these foot rotation magnitudes. We hypothesized that TO walking would increase lateral muscle activation and co-contraction while TI walking would increase medial muscle activation and co-contraction.
Section snippets
Participants
Fifteen individuals diagnosed with medial tibiofemoral OA (6 male, 9 female; mean (standard deviation (SD)) age = 67.9 (9.4) years; height = 1.68 (0.11) m; body mass = 75.6 (15.0) kg; n = 7 mild OA; n = 8 moderate OA) were recruited from the community via print media and existing laboratory databases. Individuals participated in a study examining overall lower limb biomechanical changes (kinematics, kinetics and electromyography) during different foot rotation-based gait patterns. Data reported
Results
Foot rotation magnitude differed between all conditions at approximately 10° intervals. Mean (SD) foot rotation angles were −7.7 (8.1), +10.1° (1.7), −0.1° (2.1), −10.4° (1.4), and −20.1° (0.9) for Natural, TI10, ZR, TO10 and TO20 conditions, respectively. A main effect for foot rotation angle was observed (p < 0.001) and pairwise comparisons revealed all conditions were significantly different compared to one another (p < 0.001).
Discussion
This study examined neuromuscular patterns exhibited during TI and TO walking in people with knee OA. We observed an increase in MH and LG average neuromuscular activity and MH peak activity during TI walking compared with TO walking conditions. An increase in medial thigh co-contraction during TI walking was observed, and a decrease in the MG:LG ratio during TI10 compared to ZR. Overall, our findings suggest that TI walking exhibits greater medial co-contraction and generally higher muscle
Conclusion
This study provides the most thorough examination of neuromuscular patterns during viable TI and TO walking in people with knee OA to-date. Neuromuscular activation differences exist between TI and TO, walking which may be important in deciding which strategy to employ in clinical settings. Specifically, TI walking increased medial knee periarticular muscle activity which suggests that individuals who wish to undergo TI gait retraining may benefit from supplemental muscle strengthening,
Conflict of interest statement
The authors have no conflicts of interest to report.
Acknowledgments
JMC was supported by the Canadian Institutes of Health Research (CIHR) Canada Graduate Scholarship, GLH was supported by a Fellowship award from the CIHR, JAG was supported by a Scholar Award from the Michael Smith Foundation for Health Research (MSFHR) and a Clinical Rehabilitation New Investigator Award from the CIHR, and MAH was supported by a New Investigator Award from the CIHR and a Career Clinical Scholar Award from the MSFHR. None of the authors have any conflicts of interest to report.
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