Abstract
Purpose: We evaluated the role of the Distal Tibial Line (DTL by Saltzman et al, 2005) in measuring the pre-operative and postoperative position of the talus on ‘lateral’ radiographs following a Total Ankle Replacement (TAR). Currently there is no validated measure of anteroposterior (AP) alignment of a TAR.
Arthritis in the ankle causes considerable malalignment in the anteroposterior plane. The DTL is not affected by the destruction of the tibiotalar joint and is independent of slight variations in the positioning of the foot and radiological magnification.
Method: DTL divides the talus into two sections and the proportionate length of the posterior segment is presented as a ratio. The size of the posterior segment and ratio decreases with anterior subluxation.
Radiographs of 200 cases of TAR were reviewed. The anterior and posterior outlines of the talus could not be seen in all cases (e.g. preoperative talonavicular fusion). As a result 49 cases of inflammatory arthritis (49 of 119) and 6 of osteoarthritis (6 of 81) could not be assessed.
Results: The osteoarthritic ankle (OA) in particular showed a tendency for anterior subluxation. The average ratio in OA cases increased from ‘34.8′ before surgery to ‘40.4’ after surgery, confirming a trend for this subluxation to reduce with a TAR.
There was a lesser tendency for subluxation in the inflammatory group of patients although the body of the talus itself was more deformed. The average preoperative value was ‘36.1’ and the post operative value was ‘38.9’.
Conclusion: We found the Distal Tibial line to be a reproducible parameter for measurement of AP alignment in TAR in the vast majority of OA cases. The change of anteroposterior alignment post surgery appears to be due to the restoration of soft tissue balance.
Correspondence should be addressed to the Honorary Secretary, BOFSS, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
