1 Department of Orthopedics and Rehabilitation, University of Iowa, Iowa City, IA, USA.
2 Department of Orthopedics, Chiang Mai University, Chiang Mai, Thailand.
Foot Ankle Int. 2019 Jul;40(7):826-835. doi: 10.1177/1071100719840993. Epub 2019 Apr 25.
External rotation stress (ERS) identifies ankle instability after fibular reduction of rotational ankle injuries. Combined hindfoot and ankle motions and an inconsistent starting position could mask differing degrees of instability resulting from syndesmotic and/or deltoid ligament disruption. The goal of this work was to use full 3D talar kinematics to evaluate the effects of hindfoot orientation and foot starting position during ERS on the ability to detect instability caused by ligament disruptions.
Six cadaveric ankles with metallic fiducial markers were CT scanned in neutral and 3 stress positions: varus hindfoot internal rotation stress (IRS-var), valgus hindfoot ERS (ERS-val), and varus hindfoot ERS (ERS-var). Scans were obtained in stress positions after transecting the deep deltoid ligament (tDDL) and then the syndesmotic ligaments (tDDL+Syn). Talar rotations and translations were computed in the axial, coronal, and sagittal planes in each stress position. Changes in a fixed center of rotation (CoR) relative to the intact sequence were calculated.
Axial plane rotation beginning from IRS-var increased significantly for each level of ligamentous instability ( < .05 for all conditions) (10.9 degrees, intact; 14.1 degrees, tDDL; 22.7 degrees, tDDL+Syn during ERS-val; and 16.4 degrees, intact; 23.1 degrees, tDDL; 29.9 degrees, tDDL+Syn during ERS-var). With ERS-val, the talar CoR moved medially (3.6-5.4 mm) and posteriorly (0.5-5.2 mm); ERS-var moved anterior/laterally or posterior/medially depending on the specific ligamentous instability. With tDDL+Syn the ankle became grossly unstable and there were no clear trends in sagittal/coronal rotation or translation.
An ERS test from internal to external rotation consistently differentiates between normal, tDDL, and tDDL+Syn. Talar CoR moved outside the mortise with ligamentous instability.
Significant residual deep deltoid instability is likely underrecognized with current practice. The most discriminatory test for detecting such instability in our laboratory was an ERS test performed by internally rotating the foot to a hard, bony endpoint, positioning the hindfoot in varus, and then performing the entire external rotation maneuver while maintaining the varus hindfoot position.
在外旋应力（ERS）下，腓骨复位后旋转性踝关节损伤可识别出踝关节不稳定。距下关节和踝关节的联合运动以及起始位置的不一致可能会掩盖因胫腓联合和/或距腓前韧带断裂导致的不同程度的不稳定。本研究的目的是使用全 3D 距骨运动学来评估距下关节方位和足起始位置在 ERS 下对内翻和外翻两种情况下，检测韧带断裂引起的不稳定的能力。
6 具尸体踝关节，带有金属基准标记，在中立位和 3 种应力位下进行 CT 扫描：内旋距下内翻应力（IRS-var）、外旋距下内翻应力（ERS-val）和外旋距下内翻应力（ERS-var）。在切断深层距腓前韧带（tDDL）和胫腓联合韧带（tDDL+Syn）后，在应力位下进行扫描。在每个应力位中，计算轴向、冠状和矢状平面的距骨旋转和平移。相对于完整序列计算固定旋转中心（CoR）的变化。
从 IRS-var 开始的轴向旋转在每个韧带不稳定水平上均显著增加（所有条件均<.05）（完整时为 10.9 度，切断 tDDL 时为 14.1 度，在 ERS-val 时为 22.7 度，在 ERS-var 时为 16.4 度；完整时为 14.1 度，切断 tDDL 时为 16.4 度，在 ERS-val 时为 23.1 度，在 ERS-var 时为 29.9 度）。在 ERS-val 下，距骨 CoR 向内侧（3.6-5.4mm）和向后（0.5-5.2mm）移动；ERS-var 向前/外侧或向后/内侧移动，具体取决于特定的韧带不稳定情况。在 tDDL+Syn 时，踝关节变得明显不稳定，矢状面/冠状面旋转或平移没有明显趋势。
从内旋到外旋的 ERS 测试可始终区分正常、切断 tDDL 和切断 tDDL+Syn。距骨 CoR 在韧带不稳定时移出关节。
目前的实践可能低估了严重的深层距腓前韧带不稳定。在我们的实验室中，检测这种不稳定最具鉴别力的测试是在进行 ERS 测试时，先将足部内旋至一个硬性、骨性终点，将距下关节置于内翻位，然后在保持距下关节内翻位的情况下，完成整个外旋运动。
