Abstract
When total ankle arthroplasty (TAA) is performed, although tibial osteotomy is instructed to be perpendicular to long axis of tibia, there is no established index for the talar bone corrective osteotomy. Then, we have been deciding the correction angle at the plan for adjustment of the loading axis through whole lower extremities. We studied 17 TAA cases with rheumatoid arthritis (RA). X-ray picture of hip to calcaneus view (hip joint to tip of the calcaneus) defined to show more approximated loading axis has been referred for the preoperative planning. Furthermore, the data of correction angle has been reflected to pre-designed custom-made surgical guide. If soft tissue balance was not acceptable, malleolar sliding osteotomy was added. The distance between the centre of ankle joint and the axis (preD) was measured (mm) preoperatively, and the distance between the centre of prosthesis and the axis (postD) was measured postoperatively. Next, the tilting angle between tibial and talar components (defined as the index of prosthesis edge loading) were measured with X-rays during standing. Tibio Calcaneal (TC) angle was also measured pre and postoperatively.
TC angle was significantly improved from 8.3±6.0° to 3.5±3.6° postoperatively (P=0.028). PreD was 12.9±9.6mm, and that was significantly improved to 4.8±6.3mm (postD) (P=0.006). Within 17 cases, 8 cases showed 0–1mm of postD, 4 cases showed 1–5mm of postD, remaining 5 cases concomitant subtalar fusion with severe valgus and varus hindfoot deformity showed over 8mm of postD. All of the 12 cases showing within 5mm of postD indicated within 13mm of preD. The tilting angle between components was 0.17±0.37° postoperatively.
Taken together, pre-designed corrective talar osteotomy based on preoperative planning using hip to calcaneus view was useful to adjust the mechanical axis for replaced ankle joint in RA cases. Furthermore, after surgery, the hip to calcaneus view was useful to evaluate post-operative mechanical axis of whole lower extremities.
