Revision of partial knee to total knee arthroplasty with use of patient-specific instruments results in acceptable femoral rotation
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Patient-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.
An 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.
The 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.
This 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 evidence
Prospective cohort study, Level II.
KeywordsPatient-specific instruments PSI Revision Partial knee arthroplasty PKA Unicompartmental knee arthroplasty UKA Total knee arthroplasty TKA CT-based Outliers Planning Alignment
The authors would like to thank Mr. K. Chellaoui for his expertise and work on measuring the radiographic alignments with the use of shape-match technology.
MGMS: Designed the study, gathered and analyzed all the data, wrote the initial draft of the manuscript and managed the study; ET: Analyzed the data, wrote and revised the manuscript; BB: Ensured the accuracy of the data, revised the manuscript; BK, BJ: Designed the study, ensured the accuracy of the data and revised the manuscript; NPK: Conceived the study and revised the manuscript.
Compliance with ethical standards
Conflict of interest
One author (NK) is a paid consultant for Zimmer Biomet, Europe. The other authors certify that they have no commercial associations (e.g. consultancies, stock ownership, equity interest and patent/licensing arrangements) that might pose a conflict of interest in connection with the submitted manuscript.
No funding was received for this study.
For this type of study formal consent is not required.
For this type of study informed consent is not required.
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