Cranio-caudal and medio-lateral navicular translation are representative surrogate measures of foot function in asymptomatic adults during walking

Introduction
The translation of the navicular bone is thought to be a representative surrogate measure to assess foot pronation and hence foot function; however, it is not known how it is related to multi-segment foot kinematics.
Methods
Cranio-caudal (NCC) and medio-lateral (NML) navicular translation and multi-segment foot kinematics from the Oxford Foot Model (OFM) were simultaneously assessed during the stance phase of walking in 20 healthy adults. Relationships to forefoot to hindfoot (FFtoHF), hindfoot to tibia (HFtoTBA) and global hindfoot (HFL) motion were explored by cross-correlations at zero phase shift.
Results
FFtoHF sagittal, transversal and frontal plane angles showed median cross correlations of -0.95, 0.82 and 0.53 with NCC and of 0.78, -0.81 and -0.90 with NML. HFtoTBA transversal and frontal plane angles had correlations of 0.15 and 0.74 with NCC and of -0.38 and -0.83 with NML. The HFL frontal plane angle showed correlations of 0.41 and -0.44 with NCC and NML, respectively.
Discussion
The strongest relationships were found between FFtoHF sagittal plane angles and NCC and between FFtoHF frontal plane angles and NML. However, cranio-caudal and medio-lateral navicular translation seem to be reasonable surrogates for the triplanar motion between the fore- and hindfoot. The medial longitudinal arch dropped and bulged medially, while the forefoot dorsiflexed, abducted and everted with respect to the hindfoot and vice-versa. The lower cross-correlation coefficients between the rear foot parameters and NCC/NML indicated no distinct relationships between rearfoot frontal plane and midfoot kinematics. The validity of rearfoot parameters, like Achilles tendon or Calcaneal angle, to assess midfoot function must be therefore questioned. The study could also not confirm a systematic relationship between midfoot kinematics and the internal/external rotation between the hindfoot and the tibia. The measurement of navicular translation is suggested as an alternative to more complex multi-segment foot models to assess foot function.

引言
舟骨 (navicular bone) 位移被认为是评估足旋前 (foot pronation) 及足部功能的代表性替代指标，但目前尚不明确其与多节段足部运动学 (multi-segment foot kinematics) 之间的关联机制。

研究方法
本研究对20名健康成人行走支撑期 (stance phase) 的头尾向 (cranio-caudal, NCC) 与内外侧向 (medio-lateral, NML) 舟骨位移，以及牛津足部模型 (Oxford Foot Model, OFM) 输出的多节段足部运动学数据进行同步采集与评估。通过零相位移互相关分析，本研究探究了足前后段 (forefoot to hindfoot, FFtoHF)、后足-胫骨 (hindfoot to tibia, HFtoTBA) 及整体后足 (global hindfoot, HFL) 的运动与两类舟骨位移指标的关联。

研究结果
足前后段的矢状面 (sagittal plane)、横断面 (transversal plane) 及冠状面 (frontal plane) 角度与NCC的中位数互相关系数分别为-0.95、0.82与0.53，与NML的中位数互相关系数分别为0.78、-0.81与-0.90。后足-胫骨的横断面与冠状面角度与NCC的互相关系数分别为0.15与0.74，与NML的互相关系数分别为-0.38与-0.83。整体后足冠状面角度与NCC、NML的互相关系数分别为0.41与-0.44。

讨论
本研究发现，足前后段矢状面角度与NCC的关联最强，足前后段冠状面角度与NML的关联亦最为显著。尽管如此，头尾向与内外侧向舟骨位移均可作为足前后段三平面运动的合理替代指标。当足前相对于后足背屈、外展并外翻时，内侧纵弓会出现塌陷并向内侧隆起，反之亦然。后足相关参数与NCC/NML之间的互相关系数较低，提示后足冠状面运动与中足运动学之间无显著关联。因此，以跟腱 (Achilles tendon) 参数或跟骨角度 (Calcaneal angle) 等后足指标评估中足功能的有效性值得商榷。本研究亦未证实中足运动学与后足-胫骨之间的内/外旋转存在系统性关联。综上，舟骨位移测量可作为评估足部功能的替代方案，替代更为复杂的多节段足部模型。