Characteristics and predictors of muscle strength deficit in mechanical ankle instability

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RESEARCH ARTICLE

Open Access

Characteristics and predictors of muscle strength deficit in mechanical ankle instability Zong-chen Hou1†, Xin Miao1†, Ying-fang Ao1, Yue-lin Hu1, Chen Jiao1, Qin-wei Guo1, Xing Xie1, Feng Zhao1, Yan-bin Pi1, Nan Li2, Zhi-yu Zhang1 and Dong Jiang1*

Abstract Purpose: Muscle strength training is a common strategy for treating chronic ankle instability (CAI), but the effectiveness decreases for mechanical ankle instability (MAI) patients with initial severe ligament injuries. The purpose of this study was to investigate the characteristics and the potential predictors of muscle strength deficit in MAI patients, with a view to proposing a more targeted muscle strength training strategy. Methods: A total of 220 MAI patients with confirmed initial lateral ankle ligament rupture and a postinjury duration of more than 6 months were included. All patients underwent a Biodex isokinetic examination of the ankle joints of both the affected and unaffected sides. Then, the associations between the limb symmetry index (LSI) (mean peak torque of the injury side divided by that of the healthy side) and the patients’ sex, body mass index, postinjury duration, presence of intra-articular osteochondral lesions, presence of osteophytes and ligament injury pattern (i.e., isolated anterior talofibular ligament (ATFL) injury or combined with calcaneofibular ligament injury) were analysed. Results: There was significantly weaker muscle strength on the affected side than on the unaffected side in all directions (p < 0.05). The LSI in plantar flexion was significantly lower than that in dorsiflexion at 60°/s (0.87 vs 0.98, p < 0.001). A lower LSI in eversion was significantly correlated with female sex (0.82 vs 0.94, p = 0.016) and isolated ATFL injury (0.86 vs 0.95, p = 0.012). No other factors were found to be associated with muscle strength deficits. Conclusion: MAI patients showed significant muscle strength deficits on the affected side, especially in plantar flexion. There were greater strength deficits in eversion in females and individuals with an isolated ATFL injury. Thus, a muscle strength training programme for MAI patients was proposed that focused more on plantar flexion training and eversion training for females and those with an isolated ATFL injury. Keywords: Chronic ankle instability, Muscle strength deficit, Sports rehabilitation, Limb symmetry index, Predictors

* Correspondence: [email protected] † Zong-chen Hou and Xin Miao contributed equally to this work. 1 Institute of Sports Medicine, Peking University Third Hospital, Beijing Key Laboratory of Sports Injuries, No.49 North Garden Road, Haidian, Beijing 100191, China Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, pr