Radiographic Outcomes of Preoperative CT Scan–Derived Patient-Specific Total Ankle Arthroplasty

Abstract

Background:

Preoperative computer navigation and patient-specific instrumentation have had promising results in total knee arthroplasty and in a previous cadaveric total ankle arthroplasty (TAA) study. Potential benefits of patient-specific guides include improved implant alignment and decreased surgical time. The purpose of this retrospective case series was to evaluate the accuracy, reproducibility, and limitations of TAA tibia and talar implant placement and radiographic alignment using preoperative computed tomography (CT) scan–derived instrumentation in a clinical setting.

Methods:

Between 2012 and 2014, 42 consecutive TAA cases in 42 patients using preoperative CT scan–derived patient-specific plans and guides (PROPHECY, Wright Medical Technology, Memphis TN) were reviewed from a single center of foot and ankle fellowship–trained orthopaedic surgeons. TAA implants used included 29 intramedullary referencing implants (INBONE II, Wright Medical Technology) and 13 low-profile tibia and talar resurfacing implants (Infinity, Wright Medical Technology). All patients had standardized preoperative CT scans before surgery that were used to create custom surgical plans and 3-dimensional solid cutting guides and models. All patients had a minimum 3-month follow-up with weightbearing postoperative radiographs. Patient demographics were recorded, and coronal and sagittal alignments were compared among weightbearing preoperative radiographs, CT scan–derived surgical plans, and weightbearing postoperative radiographs using a digital picture archiving and communication system.

Results:

Average age for all patients was 63 ± 9 years, with a body mass index of 29.8 ± 5.9. Average total surgical time for all TAAs was 100 ± 11 minutes, with Infinity TAAs taking less time than INBONE II TAAs (92 vs 104 minutes; P < .05). Average preoperative coronal alignment was 1.9 degrees varus ± 6.4 (range, 14 degrees valgus to 10 degrees varus). Postoperative weightbearing alignments for all TAA cases were within ±3° of the predicted coronal and sagittal alignments from the CT scan–derived surgical plans. There were no significant differences in pre- or postoperative weightbearing alignments between INBONE II and Infinity TAA cases. Neutral coronal and sagittal alignments were obtained for all TAA cases regardless of preoperative deformity. Patient-specific surgical plans were accurate to within 1 size for tibia and talar implants used. Surgical plans predicted the actual tibia implant size used in 100% of INBONE II cases and 92% of Infinity cases. Plans were less accurate for talar implants and predicted the actual talar implant size used in 76% of INBONE II cases and 46% of Infinity cases. In all cases of predicted tibia or talar size mismatch, surgical plans predicted 1 implant size larger than actually used.

Conclusions:

Results from this study provide early clinical evidence that preoperative CT scan–derived patient-specific surgical plans and guides can help provide accurate and reproducible TAA radiographic alignments. Talar implant sizing was not as accurate due to individual surgeon preference regarding the extent of gutter debridement. Similar to other modern computer navigation and patient-specific instrumentation systems, final coronal and sagittal alignments were within 3 degrees of the predicted surgical plans, and sizing was accurate within 1 implant size. Future studies are warranted to investigate the clinical and functional implications of patient-specific TAA and the overall cost-effectiveness of this technique.

Level of Evidence:

Level IV, retrospective case series.