The effect of partial deltoid ligament injuries on the external rotation stability: A cadaveric study

The anterior and posterior part of the deltoid ligament have different functions during ankle flexion motion. Partial ligament injuries have been demonstrated in previous clinical reports. However, the efficacy of external rotation stress test in partial injured cases is unavailable till now.

Thirty-two fresh cadaveric specimens were included and allocated into two destabilization groups. In the first group, the anterior portion of deltoid ligament (DL) and syndesmotic ligament were sequentially severed, while in the second group, the posterior portion of DL and syndesmotic ligament were sequentially severed. Mortise view radiographs were taken after each destabilization stage when the ankles were placed at plantarflexion and dorsiflexion positions and stressed in standard external rotation force. The medial clear space (MCS) and talar tilt (TT) angle were measured and compared among different destabilization stages.

When the ankles were placed at neutral position, the TT significantly increased in all destabilization stages. The MCS significantly increased after the partial deltoid ligament ruptures only with presence of syndesmotic ligament injuries. There was no significant difference of MCS at plantarflexion for all stages of destabilization if the anterior portion of DL is preserved. Similarly, no significant increase of MCS was detected at dorsiflexion if the posterior portion of DL and posterior inferior tibiofibular ligament are intact.

Partial DL rupture causes ankle rotational instability at different ankle joint positions, especially when combined with syndesmotic injuries. The neutral position is recommended for diagnosis of partial DL ruptures under external rotation stress.