Is TKA using patient-specific instruments comparable to conventional TKA? A randomized controlled study of one system

Abstract

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.

Fig. 1

A flow diagram of the study is shown, which is based on a Consolidated Standards of Reporting Trials (CONSORT) flow diagram for a randomized controlled study. A subgroup (dropout group) was added during the study.

Fig. 2A–B

(A) The femoral component rotations in the patient-specific instrument group were determined preoperatively based on anatomic landmarks. (B) Intraoperative cross checks on the femoral component rotations were performed using the gap-balancing technique. The gravity traction method was used for gap balancing, which was used in the same manner as that for the conventional instrument group. The rectangular flexion gap was estimated using a custom-made ladder.

Fig. 3

Two pairs of pin holes made by the patient-specific instruments (Signature) and the conventional instruments were compared with a goniometer intraoperatively. If the femoral component rotations suggested by the patient-specific instruments differed by greater than 3° from those suggested by the conventional instruments, the operation was performed with the conventional method thereafter.