Frontal plane alignment after total knee arthroplasty using patient-specific instruments

Abstract

Purpose Although total knee arthroplasty (TKA) is regularly associated with favorable outcomes, considerable research efforts are still underway to improve its ability to achieve a neutral postoperative mechanical axis. Patientspecific instrumentation (PSI) was introduced with this and other goals in mind. The current retrospective study was designed to determine whether PSI would lead to a hipknee-ankle angle (HKA) within ±3°of the ideal alignment of 180°. Methods A long-leg x-ray of the knee was performed after an average of 3.5 months (SD, three to four months), following 124 TKAs performed by a single surgeon using PSI technology (VISIONAIRE; Smith & Nephew). In addition to HKA, the zone of the mechanical axis (ZMA; zone of the tibial base plate where the mechanical axis of the limb intersects with the tibial base plate) was analysed, with the ideal intersection occurring centrally. Results There were 100 knees (average age, 66.8 years) with follow-up data available. The average HKA changed from 175.5±5.6°preoperatively to 178.5±1.7°postopera-tively. The rate of ±3°and ±5°HKA outliers was 11 % and 3 %, respectively. In terms of ZMA, the mechanical axis passed through the central third of the knee in the majority of cases (93 knees, 93 %). There were no intra-operative complications with the use of PSI.Conclusions The use of PSI technology was able to achieve a neutral mechanical axis on average in patients undergoing TKA. Further follow-up will be needed to ascertain the long-term impact of these findings.

A comparison of conventional and patient-specific instruments in total knee arthroplasty

“…As this is an update of an earlier study [12], in which data from 50 additional patients were available, these results also reconfirm the earlier conclusion that this specific technology is effective in addressing the issue of malalignment. Further follow-up will be needed to ascertain the long-term impact of these findings.…”

“…By using pre-operative MRI data and full-length anterior/posterior radiographs to ascertain the current and planned mechanical axis, engineers are able to produce tibial and femoral resection guides fitted to the patient's specific anatomy. This is the latest study to support the accuracy of this technology [12,18,31]. It also represents an update of an earlier analysis in which results for a smaller cohort (100 knees) operated with this technology were presented without a comparison cohort [12].…”

“…This is the latest study to support the accuracy of this technology [12,18,31]. It also represents an update of an earlier analysis in which results for a smaller cohort (100 knees) operated with this technology were presented without a comparison cohort [12]. With the addition of 50 knees to the PMCB cohort, alignment outcomes continued to be highly positive, and the number of knees ±3°beyond the ideal alignment of 180°actually fell slightly from 11 % to the 9.3 % noted in the current analysis.…”

“…The study is based to our previous clinical results with a single analysis of the clinical outcome of PSI technology [12].…”

Patient-specific computed tomography based instrumentation in total knee arthroplasty: a prospective randomized controlled study

“…2 Determination of the zone of mechanical axis (ZMA), i.e. the zone of the tibial base plate (divided into three equal regions) that intersect with the mechanical axis of the limb [24]; intersection with zones II-V was considered an outlier et al [31], who found no statistically significant differences between MRI-based Signature PSI and traditional instrumentation in terms of obtaining a neutral mechanical axis and individual component alignment in the frontal plane. Nunley et al [8] compared coronal alignment measurements after TKA performed using traditional instrumentation and two different types of custom-made guides: Signature™ MRIbased PSI, and OtisMed™ MRI-based PSI (manufactured to restore kinematic alignment).…”