Patient Specific Instrumentation With Preexisting Ipsilateral Hardware

Introduction: Total knee arthroplasty (TKA) is an effective operation for the management of osteoarthritis of the knee. Conventional technique utilizing manual instrumentation (MI) allows for reproducible and accurate execution of the procedure. The most common techniques make use of intramedullary femoral guides and either extrameduallary or intrameduallary tibial guides. While these methods can achieve excellent results in the majority of patients, those with ipsilateral hardware, post-traumatic deformity or abnormal anatomy may preclude the accurate use of these techniques. Patient-specific instrumentation (PSI) is an alternative innovation for total knee arthroplasty. Utilizing magnetic resonance imaging (MRI) or computed tomography (CT), custom guide blocks are fabricated based on a patient9s unique anatomy. This allows for the benefits of computer assisted navigation (CAN) but without the increased operative times or the high learning curve associated with it. Furthermore it allows the use of familiar cutting blocks and guides to check the accuracy of the PSI guide blocks. In this study we sought to evaluate the accuracy of PSI techniques in patients with previous ipsilateral hardware, which would make the use of MI technically challenging and possibly subject to inaccuracy. Methods: After reviewing our database of 300 PSI total knee arthroplasty patients, 16 patients were identified (10 male, 6 female) using the Zimmer NexGen Patient Specific Instrumentation System. Fourteen patients included in the study had a preexisting total hip arthroplasty on the ipsilateral side, 1 had a preexisting sliding hip screw, and 1 patient had a preexisting cephalomedullary nail. Postoperative mechanical axis alignment measurements were performed using plain long-standing radiographs. The American Knee Society Score was used to evaluate clinical outcomes postoperatively. Results: Sixteen total knee arthroplasties were performed using PSI, all in the setting of previous ipsilateral hardware placement. The average age at the time of surgery was 72, with patients ranging from 56 to 85 years of age. Eleven of the included knees had a preoperative varus alignment and 5 had valgus alignment. The average value of a deformity identified via the preoperative planning software was 7.85°. The average value of a deformity identified via preoperative radiographs was 10.1°. Average postoperative mechanical axis was 3.1° measured from plain radiographs. Average angle between the femoral mechanical axis and femoral component was 90.0°. The average angle between the tibial mechanical axis and tibial component was 90.6°. The average difference between the femoral mechanical and anatomic axes was 5.9°. The average discrepancy between medial and lateral joint space on an anterior-posterior standing radiograph was 0.4 mm. At an average of 4.5 months follow-up, American Knee Society knee scores show an aggregate average score of 82.94. Conclusion: Patient specific instrumentation is an innovative technology in TKA that replaces the use of intramedullary femoral guides and either extramedullary or intramedullary tibial guides. This study demonstrates that PSI is capable of producing favorable radiographic and clinical outcomes despite preexisting ipsilateral hardware, which may preclude the use of customary manual instrumentation. We believe PSI is an accurate and effective tool for use in patients with preexisting ipsilateral hardware.