SLR - October 2017 - Joshua J. Wilder

Change in Talar Translation in the Coronal Plane After Mobile-Bearing Total Ankle Replacement and Its Association with Lower-Limb and Hindfoot Alignment

Reference: Yi Y, Cho JH, Kim JB, Kim JY, Park SY, Lee WC. Change in Talar Translation in the Coronal Plane after Mobile-Bearing Total Ankle Replacement and Its Association with Lower-Limb and Hindfoot Alignment. The Journal of Bone and Joint Surgery. American Volume.,15 Feb. 2017.

Scientific Literature Review

Reviewed By: Joshua J. Wilder, DPM
Residency Program: The Western Pennsylvania Hospital, Pittsburgh, PA

Podiatric Relevance: A common condition treated by foot and ankle surgeons is that of ankle arthritis, which is more and more frequently treated by total ankle replacements given specific parameters. Proper placement of the total ankle replacement is crucial and has a direct impact on the longevity and effectiveness of the implant. Mobile-bearing total ankle replacements enable motion at the tibial implant-polyethylene insert interface. This motion could lead to coronal translation of the talus relative to the tibia leading to coronal and sagittal translations of the talus relative to the tibia. This may affect radiographic outcomes postoperatively. The authors aimed to assess the translation of the talus before and after mobile-bearing TAR to determine whether translation of the talus after TAR is associated with coronal plane alignment of the lower limb and hindfoot as well as to investigate the complications associated with talar translation.

Methods: This is a retrospective, level IV, cohort study, in which the authors enrolled 153 patients (159 ankles) who underwent a mobile-bearing total ankle replacement between January 2004 and December 2012. The minimum follow-up period was three years. The location of the talus in the coronal plane was quantified with the use of talar center migration (TCM) defined as the distance between the tibial axis and the center of the talus on full-length weightbearing anteroposterior radiographs. Other radiographic parameters in the coronal plane were also measured, evaluated and compared, including the mechanical axis deviation (MAD), lateral distal tibial angle (LDTA), hindfoot alignment angle and hindfoot moment arm using the same radiographic views. These views and measurement were obtained at both preoperative and postoperative intervals, and the relationships between them were investigated. The ankles were divided into three groups using the TCM values at three years postoperatively being medial talar translation group, neutral talar group and lateral talar translation group.

Results:
During the 36-month follow-up period, the postoperative TCM showed a strong relationship with the preoperative TCM in the medial talar translation group and lateral translation group. As expected, varus slope of the tibial plafond was related to medial translation of the talus, and valgus slope was related to lateral translation. The TCM at the three-year follow-up demonstrated a significant positive correlation with radiographic parameters of proximal alignment (MAD and LDTA p < 0.001) and demonstrated a significant negative correlation with hindfoot alignment ( p <0.001). All radiographic parameters showed favorable results. Complications included medial malleolar impingement in five cases (including delayed medial malleolar fracture due to medial impingement in two cases), insert dislocation in one case and edge-loading in two cases; all of the cases with complications demonstrated implant overhang with talar translation.

Conclusions: The authors concluded that talar translation in the coronal plane after mobile-bearing TAR correlates with the preoperative talar translation. The MAD and hindfoot alignment are factors that are strongly associated with talar translation and may be accompanied by various complications as observed on coronal radiography. Therefore, additional realignment procedures for coronal malalignment should be considered to prevent talar translation after mobile-bearing TAR. Overall, this was a good study with some limitations being sample size and intraoperative factors. The most common intraoperative factors experienced were those of the cutting angle of the talar dome, positioning of the talar component relative to the talus and ligamentous balancing.

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