Is TKA Using Patient-specific Instruments Comparable to Conventional TKA? A Randomized Controlled Study of One System

Background Patient-specific CT-based instrumentation may reduce implant malpositioning and improve alignment in TKA. However, it is not known whether this innovation is an advance that benefits patients.

Questions/purposes We evaluated (1) the precision of patient-specific TKA by comparing the incidence of outliers in postoperative alignment between TKAs using patient-specific instruments and TKAs using conventional instruments, and (2) the reliability of patient-specific instruments by intraoperatively investigating whether the surgery could be completed with patient-specific instruments alone.

Methods In this randomized controlled trial, we compared patient-specific TKA instruments from one manufacturer (n = 50) with conventional TKA instruments (n = 50). Postoperative hip-knee-ankle angles, femoral component rotation, and coronal and sagittal alignments of each component were measured. The validity of the patient-specific instrument was examined using cross-checking procedures with conventional instruments during the surgeries. When the procedure could not be completed accurately with patient-specific instruments, the procedure was converted to TKA using conventional instruments, and the frequency of this occurrence was tallied.

Results Outliers in the hip-knee-ankle angle were comparable between groups (12% in the patient-specific instrument group and 10% in the conventional instrument group). Other parameters such as sagittal alignment and femoral component rotation did not differ in terms of outliers. Patient-specific guides were abandoned in eight knees (16%) during the surgery because of malrotation of the femoral components and decreased slope of the tibia.

Conclusions Accuracy was comparable between TKAs done with patient-specific instruments and those done with conventional instruments. However, the patient-specific instrument procedures had to be aborted frequently, incurring expenses that did not benefit patients.

Level of Evidence Level II, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.