Abnormal rate of intraoperative and postoperative implant positioning outliers using "MRI-based patient-specific" compared to "computer assisted" instrumentation in total knee replacement.

purposeThe aim of this study was to analyze first intraoperative alignment and reason to abandon the use of patient-specific instrumentation using intraoperative CAS measurement, secondly assess by postoperative CT analysis if CI, based on preoperative 3D-MRI data, improved postoperative component positioning (including femoral rotation) and lower limb alignment as compared with results obtained with CAS.

methodsIn this randomized controlled trial, 80 consecutive patients scheduled to undergo TKA were enrolled. Eligible knees were randomized to the group of PSI-TKAs (n = 40) or to the group of CAS-TKAs (n = 40). In the CAS group, CAS determined and controlled cutting block positioning in each plane. In the PSI group, CAS allowed to measure adequacy of intraoperative alignment including femoral component rotation. At 3 months after surgery, implants position were measured and analyzed with full-weight bearing plain radiographs and CT scan.

resultsIntraoperatively, there was a significant difference concerning Sagittal Femoral mechanical, Frontal tibial mechanical angle and tibial slope between the two groups (respectively p = 0.01, p = 0.02, p = 0.046). Custom instrumentation was abandoned intraoperatively in seven knees (17.5 %). Abnormal tibial cuts were responsible of the abandon in three out of seven cases, femoral cut in 1/7 and dual abnormalities in 3/7. Postoperatively, tibial slope outliers percentage was higher in the patient specific instrumentation group with six patients (18.18 %) versus one patient (2.5 %) in the CAS group (p = 0.041).

conclusionPatient specific instrumentation was associated with an important number of hazardous cut and a higher rate of outliers in our series and thus should be used with caution as related to. This study is the first to our acknowledgement to compare intra-operative ancillary and implant positioning of PSI-TKA and CAS-TKA. High rate of malposition are sustained by our findings, as such PSI-TKA should be used with caution, by surgeons capable to switch to conventional instrumentation intra-operatively. LEVEL OF EVIDENCE: Randomized control trial, Level I.