Tibiotalar motion - Effect of fibular displacement and deltoid ligament transection: In vitro study

The purpose of this study was to quantify tibiotalar translation and rotati on under various stages of fibular displacement and injury to the syndesmot ic and deltoid ligaments. Ten unpaired specimens amputated below the knee w ere studied using an unconstrained testing apparatus. The specimens were mo ved through a dorsi-flexing and plantarflexing are of 55 degrees (20 degree s dorsiflexion and 35 degrees plantarflexion). Dorsiflexion of the intact l ower leg was associated with an average of 4.2 degrees of external talar ro tation, and plantarflexion was associated with an average of 1.4 degrees of internal talar rotation. Fibular osteotomy and displacement of the distal fibular fragment did not change the talar rotation significantly. Additiona l transection of the deltoid ligament, however, decreased external talar ro tation significantly, to 1.4 degrees, and decreased talar internal rotation to 0.6 degrees. Talar shift was not affected in dorsiflexion or plantarfle xion by fibular fracture, displacement of the distal fibular fragment, or t ransection of the deltoid ligament. These data may suggest that in dorsifle xion or plantarflexion, an intact lateral malleolus is not necessary for ph ysiological talar tracking. They further suggest that in a fibular fracture with a significant injury to the deltoid ligament, healing of the ligament at its resting length is crucial to restoring physiological talar rotation .