Accuracy and Alignment of Patient-Specific Instrumentation for INBONE II Total Ankle Arthroplasty

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Total ankle arthroplasty (TAA) is a surgical procedure that has been shown to effectively reduce pain and improve mobility in patients with ankle arthritis. Achieving optimal alignment is crucial for implant longevity and patient outcomes. The PROPHECY patient-specific instrumentation (PSI) (Stryker, Mahwah, NJ, USA) has been developed to aid in accurate and efficient implant placement, including the INBONE II implant, which has been shown to offer enhanced stability and alignment correction. This study aimed to determine the accuracy of PSI regarding implant alignment and implant size, and compare outcomes between PSI implantation and the traditional jig method. We hypothesized that compared to the standard jig method (non-PSI group), PSI will improve alignment accuracy, deformity correction, and reduce radiation exposure, tourniquet and operative time. Methods: This retrospective study of 92 patients (46 PSI and 46 non-PSI cases) was performed at a single institution between 2006- 2024 and included patients who had a TAA with INBONE II implants. The PSI group (n=46) was matched with the non-PSI group (n=46) by age (+/- 3 years) and sex. Chart review was performed to collect demographic data including primary surgeon, concomitant procedures, body mass index (BMI), age, tibial and talus implant sizes, total procedure time and total inflated tourniquet time. Intraoperative radiographs were used for fluoroscopy time. Radiographic evaluation using the Picture Archiving and Communication System (PACS, Sectra Inc. Shelton CT) of pre- and post-operative radiographs were analyzed to assess the accuracy of PROPHECY by comparing alignment of the implant in the PSI group to the intended preoperative plan, as well as compare the post operative deviation of the tibiotalar angle (TTA) and talar tilt (TT) in both groups. Results: The PROPHECY PSI demonstrated high accuracy in predicting correct implant size, 68% (n=32) of talus implants and 89% (n=42) of tibial implants. Most changes stemmed from downsizing the talus by one size. The median absolute deviation in the mortise and sagittal planes was less than 2 degrees, indicating accurate surgical alignment with the preoperative plan. 71% of PSI cases were performed by one surgeon, while a different surgeon with extensive experience with the jig, performed 96% of the non-PSI cases. For both groups, median TTA deviation was less than 2 degrees and median post-operative TT was less than or equal to 1 degree. While no difference between groups for fluoroscopic time was found, the PSI group had a longer total inflated tourniquet and procedure time. Conclusion: For INBONE II implantation, PSI achieves similar alignment and implant sizing compared to standard instrumentation. Surgeons reliably and accurately aligned the tibial component per the preoperative plan. This study, the first to compare the two techniques with INBONE II, has strengths of matched pair analysis and validated outcomes. The longer tourniquet and operative time in the PSI group likely reflects the primary surgeon’s initial experience with the guides, while a surgeon experienced with the jig opted for the extramedullary approach. The patient-specific approach may help less experienced surgeons achieve desired alignment with less operative time. Accuracy and Alignment of Patient-Specific Instrumentation in Comparison with Prophecy Predicted Values and Non-PSI Cases using Radiographic and Intra-operative Measurements Fgure 1. A) Accuracy of alignment in INBONE II TAAs performed using PSI cases. In the mortise and sagittal views, mean implant deviation from the anatomic axis was below 2 degrees. B) Comparison of Deviation of TTA from Anatomic Axis, Post-Operative Talar Tilt, Fluoroscopy, Tourniquet and Procedure Time for INBONE IITAA Performed with or without PSI. Post-operative Mortise View TTA was measured using the medial angle created from the anatomic axis with the base of the tibial implant (Mortise View Tibial Base) and with the superior margins of the articular surface of the talar dome (Mortise View Talus Surface). In the sagittal view, post-operatively, the TTA was measured using the anterior angle created from the anatomic axis with the base of the tibial implant. Post-operative TT was calculated using the angle created from the superior margins of the articular surface of the talar dome and the base of the tibial implant.