Comparison of the iAssist Handheld Guidance System to Conventional Instruments for Mechanical Axis Restoration in Total Knee Arthroplasty.

Document Type


Publication Date


Publication Title

The Journal of arthroplasty


computer navigation; handheld navigation; mechanical axis alignment; primary total knee arthroplasty; surgical technique; Adult; Aged; Aged, 80 and over; Arthroplasty, Replacement, Knee/instrumentation; Female; Femur/surgery; Humans; Intraoperative Period Knee Joint/surgery; Male; Middle Aged; Operative Time; Postoperative Period; Prospective Studies; Radiography; Stress, Mechanical; Surgery, Computer-Assisted/instrumentation; Tibia/surgery


BACKGROUND: Recent advances in total knee arthroplasty (TKA) include an intelligent instrument system designed to provide intraoperative guidance to reduce mechanical alignment errors. Internal position-sensing technology is integrated into microelectronic pods that attach to cutting blocks. The purpose of this prospective, randomized study was to determine whether this iAssist system enables the surgeon to make more accurate bone resections and better restore the mechanical axis compared to conventional instruments in TKA.

METHODS: We randomized patients undergoing TKA into 2 groups. Group I (n = 25) underwent TKA assisted by the iAssist guidance system, group II (n = 25) underwent TKA using conventional instruments. Preoperative and postoperative mechanical axes were measured from full-length lower extremity radiographs to evaluate alignment. Additional surgical parameters were also assessed, including tourniquet time and blood loss.

RESULTS: Patient demographics and preoperative mechanical axis alignments were similar between the groups. Postoperatively, 4.0% of patients had greater than 3° of tibial or femoral component mal-alignment in the guidance-assisted cohort, compared with 36.0% in the conventional group (P < .05). Additionally, group I showed significant improvement in variance seen in both the femoral mechanical axis (1.65° ± 0.17° vs 2.23° ± 0.33°, P < .005) and tibial mechanical axis (1.28° ± 0.13° vs 1.71° ± 0.24°, P < .005) compared to group II. There were no significant differences in tourniquet time (P = .86) or blood loss (P = .39) between groups.

CONCLUSION: Use of the iAssist system in TKA results in an improved postoperative mechanical axis and decreased alignment variability compared to conventional instruments, without significantly increasing operative time.

Clinical Institute

Orthopedics & Sports Medicine