Purpose: The purpose of the study was to evaluate the accuracy of the planning of the patient-specific pin guides in total knee arthroplasty (TKA). This planning was performed primarily by a technician of the company and offered to the surgeon. All parameters of the implantation can either be modified or accepted by the surgeon. The hypothesis was that the plan needs preoperative intervention by the surgeon.
Methods: A prospective study in 50 patients was carried out. All patients received the same posterior-stabilised implant with patient-specific instrumentation. All surgical parameters (coronal, sagittal, rotational alignment, femoral and tibial resection levels and implant sizes) were checked by the orthopaedic surgeon and changed if necessary.
Results: Preoperatively, the femoral size was changed in 8 patients (16 %), the femoral flexion in 23 patients (46 %), the femoral shift in 34 patients (68 %), the tibial size in 24 patients (48 %) and the tibial rotation in all patients. The epicondylar axis was accepted in 47 patients (94 %) in the technician plan. Mean planning time was 8 ± 4 min. Intraoperatively, the femoral anterior-posterior size was in 50 patients (100 %) the same as in the surgeon and in 42 patients (84 %) the same as in the technician plan (p = 0.003). The tibial component implanted was in 42 patients (84 %) the same as in the surgeon and in 19 patients (38 %) the same as in the technician plan (p < 0.0001). A femoral distal recut was necessary in 31 patients (62 %) and a change of the tibial proximal cut in 17 patients (34 %) during surgery. Intraoperatively, no changes of the femoral and tibial alignment, the femoral anterior-posterior size, the femoral flexion, the femoral shift, the femoral and tibial rotation were necessary. Postoperatively, the coronal mechanical overall axis was within ±3° in 47 patients (94 %) with a maximum deviation of 5.6°.
Conclusions: Significant changes of the technician plan were necessary to get an accurate preoperative plan. Intraoperative changes were significant less compared to the surgeon than to the technician plan. No major changes (alignment, femoral anterior-posterior size and rotation) of the surgeon plan were necessary. Surgeons using patient-specific pin guides in TKA may verify the default plan provided by the technician. A blind reply on the technician plan may be not recommended.
Level of evidence: Therapeutic study, Level III.