Piazza Stephen J, Adamson Robert L, Moran Matthew F, Sanders James O, Sharkey Neil A
The Pennsylvania State University, University Park 16802, USA.
J Bone Joint Surg Am. 2003 May;85(5):858-65. doi: 10.2106/00004623-200305000-00013.
Split transfers of the tibialis anterior and posterior tendons are commonly performed to address hindfoot varus deformities in patients with cerebral palsy, stroke, or brain injury. Poor outcomes from these procedures are often attributed to a failure to tension the transferred tendon properly, but the mechanical effects of this aspect of the procedure have not been quantified, to our knowledge. The purpose of the present study was to use a cadaver model to examine changes in the actions of these muscles that occur when the tensions in the halves of the split tendon are intentionally balanced or unbalanced to varying degrees.
Tendon excursion was measured in seven cadaveric specimens before and after split tendon transfer with experimentally controlled tensions in the halves of the split tendon. The muscle moment arm, a quantitative indicator of the action of a muscle about a joint axis, was calculated as the derivative of tendon excursion with respect to the subtalar joint angle.
The tibialis anterior had an eversion moment arm with the subtalar joint in a neutral position following surgery, but the tibialis posterior had virtually no action in the neutral position. Following the split transfers with ideally balanced tension, subtalar joint rotations of >5 degrees strongly influenced the moment arm of the tibialis posterior (p < 0.0002), indicating that its action depends on the position of the hindfoot. The moment arm of the tibialis anterior, however, was influenced only by rotations of >/=20 degrees (p > 0.1741 for each angle pair comparison of <20 degrees ). Moment arms were generally insensitive to imbalances in tension between the medial and lateral tendon halves; significant differences in the moment arm (p < 0.05), compared with that in the balanced condition, were seen only when one half was slack or nearly so.
These results suggest that it is possible for a split tendon transfer to be successful over a large range of tensionings. Split transfer of the tibialis posterior tendon produced the desired mechanical outcome in that the tibialis posterior had an eversion moment arm when the foot was inverted and an inversion moment arm when the foot was everted. Split transfer of the tibialis anterior to the cuboid, however, produced a muscle that consistently functioned as an everter regardless of the position of the hindfoot.
胫前肌腱和胫后肌腱的分期转移常用于治疗脑瘫、中风或脑损伤患者的后足内翻畸形。这些手术效果不佳通常归因于未能正确张紧转移的肌腱，但据我们所知，该手术这一方面的力学效应尚未得到量化。本研究的目的是使用尸体模型来研究当分期肌腱的两半张力有意平衡或不平衡到不同程度时，这些肌肉的作用会发生哪些变化。
在七具尸体标本上，在分期肌腱转移前后测量肌腱的移动度，实验控制分期肌腱两半的张力。肌肉力臂是肌肉围绕关节轴作用的定量指标，计算为肌腱移动度相对于距下关节角度的导数。
术后，在距下关节处于中立位时，胫前肌有外翻力臂，但胫后肌在中立位几乎没有作用。在张力理想平衡的分期转移后，距下关节旋转>5度强烈影响胫后肌的力臂（p<0.0002），表明其作用取决于后足的位置。然而，胫前肌的力臂仅受>/=20度旋转的影响（对于<20度的每个角度对比较，p>0.1741）。力臂通常对内侧和外侧肌腱半侧之间的张力不平衡不敏感；仅当一半松弛或几乎松弛时，与平衡状态相比，力臂才有显著差异（p<0.05）。
这些结果表明，分期肌腱转移在很大范围的张紧情况下都有可能成功。胫后肌腱的分期转移产生了理想的力学结果，即当足内翻时胫后肌有外翻力臂，当足外翻时胫后肌有内翻力臂。然而，将胫前肌分期转移至骰骨后，产生的肌肉无论后足位置如何都始终发挥外翻肌的作用。
