VALIDATION OF THE MOBILITY TOTAL ANKLE REPLACEMENT JIG

Aim: To validate the accuracy of the MobilityTotal Ankle Replacement alignment jig. Method: The early radiological alignment outcomes (angles ‘A, B, C’) of 35 Mobility ankle replacements were determined from weight bearing X rays. These radiological outcomes were compared with alignment outcomes for ‘Star’ total ankle replacement, as published by PLR Wood. (Total Ankle Replacement JBJS April 2003 85B, pg 334) Results: Indication: osteoarthritis 25, posttraumatic osteoarthritis 6, rheumatoid arthritis 4. 32/35 Angle A were within the published accepted range (850–950). 23/35 Angle B were within the published accepted range (800–900). 35/35 Angle C were within the published accepted range (200–400) No statistical difference between the distribution of angle A, B and C and the means for A, B and C for the published results. Discussion: Results for angle B are skewed toward the upper limit of the current accepted range (800–900). The author (MSS) attempts to reproduce this, to place the anterior margin of the tibial component on subchondral bone. A lower angle B positions the implant on metaphyseal bone with a risk of subsidence. Comparing Angle B with a modified acceptable range (850–950) 31/35 fell in the new range. Conclusion: Early radiological alignment for Mobility is reproducible and compares favourably with published data.