• Schotanus Martijn G M MGM http://orcid.org/0000-0002-3975-6337 Department of Orthopedic Surgery and Traumatology Zuyderland Medical Center, Dr H vd Ho, Elke Thijs, B Boonen, B Kerens, B Jong, and Nanne P Kort.
• Department of Orthopedic Surgery and Traumatology Zuyderland Medical Center, Dr H vd Hoffplein 1, 6162 AG, Sittard-Geleen, The Netherlands. martijnschotanus@hotmail.com.
• Knee Surg Sports Traumatol Arthrosc. 2018 Jun 1; 26 (6): 1656-1661.

PurposePatient-specific instruments (PSI) were initially developed for the alignment of both total knee- (TKA) and partial knee arthroplasty (PKA). We hypothesize that CT-based PSI for PKA-to-TKA revision surgery can restore biomechanical limb alignment and prosthetic component positioning in vivo as calculated pre-operatively, resulting in a limited percentages of outliers.MethodsAn imaging analysis was performed using CT-based 3D measurement methods based on a pre- and post-revision CT scan. Imaging data were gathered on 10 patients who were operated for PKA-to-TKA revision with the use of PSI based on CT imaging. The planned femur and tibia component position in vivo were compared with the pre-revision planned component position. Outliers were defined as deviations >3.0° from pre-revision planned position for the individual implant components. Adjustments (e.g. resection level and implant size) during surgery were recorded.ResultsThe HKA axis was restored accurately in all patients with a mean post-operative HKA axis of 178.1° (1.4°). Five femoral (2 varus, 2 internal rotation and 1 extension) and 14 tibial guides (2 varus, 6 anterior slope, 3 internal rotation and 3 external rotation) on a total of 60 outcome measures were identified as outliers. During surgery, an intraoperative tibial resection of 2 mm extra was performed in three patients. In 80 and 70% for, respectively, the femur and tibia, the surgeon-planned size was implanted during surgery. All patient-specific guides fitted well in all patients. No intraoperative or post-operative complications related to surgery were registered.ConclusionsThis study introduced a unique new concept regarding PSI, PKA-to-TKA revision surgery. Based on the results, we were unable to fully confirm our hypothesis. PSI as a "new" tool for PKA-to-TKA revision surgery appears to be an accurate tool for the alignment of the TKA femur component. The tibial guide seems more susceptible to errors, resulting in a substantial percentage of outliers.Level Of EvidenceProspective cohort study, Level II.

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