A new total ankle arthroplasty (TAA) system performed through a lateral approach provides direct visualization of the centre of rotation, allowing for accurate reconstruction of the joint alignment and less bone resection. Radiographic references are needed to describe deformities and plan the surgical procedures. The tibial slope is an important factor when treating malalignment. The aim of this study is to show if there is any difference regarding the post-operative tibial slope (β angle) measurement comparing a fixed-bearing TAA through a lateral approach and a mobile-bearing TAA through an anterior approach.
The study included 217 ankles. Between May 2011 and April 2015, 77 patients underwent a TAA with a mobile-bearing implant through an anterior approach and 45 with a fixed-bearing implant through a lateral approach: in these patients the β angle was measured 2 and 12 months postoperatively. 95 subjects with unilateral post-traumatic ankle arthritis composed the control group: in these patients we measured the anterior distal tibial angle (ADTA) of the controlateral, non arthritic tibiotalar joint.
In the mobile-bearing group, the mean β angle at 2 and 12 months postoperatively was 86.4±3.1 and 86.8±3.1 (p-value=0.12). In the fixed-bearing group, the mean β angle at 2 and 12 months postoperatively was 83.1±5.4 and 83.9±6.5 (p-value=0.26). A statistically significant difference was found between the β angle of the two groups. In the control group the mean ADTA was 84.9±2.5. A non-statistically significant difference was observed only between β angle of the fixed-bearing group and the ADTA of the control group.
Regarding the tibial slope, fixed-bearing TAA through a lateral approach showed a more anatomic placement. In contrast, β angle in mobile-bearing group appeared more reproducible than fixed-bearing group.