Patient-specific instrumentation combined with a new tool for gap balancing is useful in total knee replacement: a 3-year follow-up of a retrospective study

Abstract

Objective: The purpose of this study was to determine whether the gap-balancing technique with patient-specific instrumentation (PSI) and a new balancing device in total knee arthroplasty (TKA) can improve knee function to a greater extent than can the measured resection technique.

Materials and methods: Data from 150 patients who underwent TKA from August 2014 to June 2016 were studied retrospectively. The gap-balancing technique assisted by PSI and the new balancing device was used in 80 patients (82 knees), and the measured resection technique was used in 70 patients (70 knees). The surgical, imaging, and knee function data were compared.

Results: The gap-balancing technique assisted by PSI and the new balancing device was found to be feasible in all operated knees and reliable. In total, 150 patients (152 knees) of ages ranging from 52 to 78 years (mean 67 years) underwent TKA during the study period. The follow-up period ranged from 35 to 52 months (mean 45 months). Only one patient, who was included in the gap-balancing group, underwent a revision surgery at 2 years postoperatively due to infection. There were no differences in the incidence of anterior knee pain between the two groups. The mean flexion angle, KSS scores, and VAS scores did not significantly differ between the measured resection group and gap-balancing group at 12 weeks or 36 weeks postoperatively. The average joint line displacement was 1.3 ± 1.1 mm (range 0-3) proximally in the GB (gap-balancing) group and 1.2 ± 1.4 mm in the MR (measured-resection) group. No outliers >5 mm in either group were recorded. The mean leg axis deviation from the neutral mechanical axis was 1.8°±1.5° varus (range 0°-3°varus) versus the neutral mechanical axis in the GB group and 1.4°±1.2°(range 0°-3°)in the MR group. No outliers with >3° deviation in either group were recorded.

Conclusions: The gap-balancing technique performed with the new balancing device and PSI can yield accurate femoral component alignment as well as outcomes similar to those of measured resection at 3 years. The new balancing device can be taken into consideration by surgeons who prefer performing the gap-balancing technique with PSI.

Keywords: Balancer device; Equipment design; Flexion-extension gap surgical technique; Gap balance; Implantation technique; Ligament balance; Measured resection technique; Total knee arthroplasty.

Fig. 1

The new gap balancing tool (a, b) and CAD drawings (c, d)

Fig. 2

Design of the PSI (a, b). Resection of the proximal tibia assisted by PSI (c); Resection of the distal femur assisted by PSI (d). Comparing the thickness of the bone we cut with preoperative planning (e). Flexion gap balancing procedure assisted by the new balancing device that we designed (f, g)

Fig. 3

The lower extremity long-standing radiograph and positive X-ray with preoperative and postoperative alignment (red line). HKA is defined as the angle between a line from the femoral head center to the tibial spine center and a line from the tibial spine center to the talus joint surface centre (a, b). The method of measuring the change of joint line before and after operation with the insertion point of the adductor femur as the reference point (c, d)