Laxity and flexibility of the ankle following reconstruction with the Chrisman-Snook procedure.

The effect of reconstruction of the anterior talofibular ligament with the Chrisman-Snook procedure on neutral zone laxity (anterior-posterior displacement at low loads) and flexibility (a measure of the nonlinear load-displacement response) of the ankle was investigated in vitro during the anterior drawer test. Neutral zone laxity was defined as the magnitude of anterior-posterior displacement of the ankle joint at +/- 2.5 N of applied load. The flexibility parameter was defined as the slope of a line between the natural logarithm of the anterior load applied to the ankle and the resulting displacement. After reconstruction with the Chrisman-Snook procedure, the values for neutral zone laxity of the ankle were significantly less than normal at 0 degree of plantar flexion, whereas the flexibility values were significantly greater than normal. This study revealed that, after the Chrisman-Snook procedure, values for ankle flexibility are not restored to normal even if those for neutral zone laxity are reduced to less than normal. The findings suggest that this nonanatomical reconstruction procedure does not reproduce normal kinematics of the ankle joint. This may help explain some of the adverse clinical reports associated with the Chrisman-Snook reconstruction procedure.