BACKGROUND Following an amputation, the human postural control system develops neuromuscular adaptations to regain an effective postural control. We investigated the compensatory mechanisms behind these adaptations and how sensorimotor integration is affected after a lower-limb transfemoral amputation. METHODS Center of pressure (CoP) data of 12 unilateral transfemoral amputees and 12 age-matched able-bodied subjects were recorded during quiet standing with eyes open (EO) and closed (EC). CoP adjustments under each leg were recorded to study their contribution to posture control. The spatial structure of the CoP displacements was characterized by measuring the mean distance, the mean velocity of the CoP adjustments, and the sway area. The Entropic Half-Life (EnHL) quantifies the temporal structure of the CoP adjustments and was used to infer disrupted sensory feedback loops in amputees. We expanded the analysis with measures of weight-bearing imbalance and asymmetry, and with two standardized balance assessments, the Berg Balance Scale (BBS) and Timed Up-and-Go (TUG). RESULTS There was no difference in the EnHL values of amputees and controls when combining the contributions of both limbs (p = 0.754). However, amputees presented significant differences between the EnHL values of the intact and prosthetic limb (p <  0.001). Suppressing vision reduced the EnHL values of the intact (p = 0.001) and both legs (p = 0.028), but not in controls. Vision feedback in amputees also had a significant effect (increase) on the mean CoP distance (p <  0.001), CoP velocity (p <  0.001) and sway area (p = 0.007). Amputees presented an asymmetrical stance. The EnHL values of the intact limb in amputees were positively correlated to the BBS scores (EO: ρ = 0.43, EC: ρ = 0.44) and negatively correlated to the TUG times (EO: ρ = - 0.59, EC: ρ = - 0.69). CONCLUSION These results suggest that besides the asymmetry in load distribution, there exist neuromuscular adaptations after an amputation, possibly related to the loss of sensory feedback and an altered sensorimotor integration. The EnHL values suggest that the somatosensory system predominates in the control of the intact leg. Further, suppressing the visual system caused instability in amputees, but had a minimal impact on the CoP dynamics of controls. These findings points toward the importance of providing somatosensory feedback in lower-limb prosthesis to reestablish a normal postural control. TRIAL REGISTRATION DRKS00015254 , registered on September 20th, 2018.

中文翻译：

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单侧经股截肢后的神经肌肉适应和感觉运动整合。

背景技术截肢后，人类姿势控制系统发展出神经肌肉适应以重新获得有效的姿势控制。我们研究了这些适应背后的代偿机制以及下肢经股截肢后感觉运动整合如何受到影响。方法 记录 12 名单侧股骨截肢者和 12 名年龄匹配的健全受试者在睁眼 (EO) 和闭眼 (EC) 安静站立时的压力中心 (CoP) 数据。记录每条腿下的 CoP 调整，以研究它们对姿势控制的贡献。CoP 位移的空间结构通过测量 CoP 调整的平均距离、平均速度和摇摆面积来表征。熵半衰期 (EnHL) 量化了 CoP 调整的时间结构，并用于推断截肢者的感觉反馈环被破坏。我们通过测量负重不平衡和不对称性以及两种标准化平衡评估（伯格平衡量表 (BBS) 和定时起立行走 (TUG)）来扩展分析。结果 当结合双肢的贡献时，截肢者和对照者的 EnHL 值没有差异 (p = 0.754)。然而，截肢者完整肢体和假肢的 EnHL 值之间存在显着差异 (p < 0.001)。抑制视力会降低完整腿 (p = 0.001) 和双腿 (p = 0.028) 的 EnHL 值，但在对照组中则不然。截肢者的视觉反馈对平均 CoP 距离 (p < 0.001)、CoP 速度 (p < 0.001) 和摇摆面积 (p = 0.007) 也有显着影响（增加）。截肢者呈现出不对称的姿势。截肢者完整肢体的 EnHL 值与 BBS 评分呈正相关（EO：ρ = 0.43，EC：ρ = 0.44），与 TUG 次数呈负相关（EO：ρ = - 0.59，EC：ρ = - 0.69） ）。结论 这些结果表明，除了负荷分布的不对称性之外，截肢后还存在神经肌肉适应，可能与感觉反馈的丧失和感觉运动整合的改变有关。EnHL 值表明体感系统在完整腿部的控制中占主导地位。此外，抑制视觉系统会导致截肢者不稳定，但对控制的 CoP 动态影响很小。这些发现指出了在下肢假肢中提供体感反馈以重建正常姿势控制的重要性。试用注册 DRKS00015254，注册于2018年9月20日。