Aims. While mechanical alignment (MA) is the traditional technique in total knee arthroplasty (TKA), its potential for altering constitutional alignment remains poorly understood. This study aimed to quantify unintentional changes to constitutional coronal alignment and joint line obliquity (JLO) resulting from MA. Methods. A retrospective cohort study was undertaken of 700 primary MA TKAs (643 patients) performed between 2014 and 2017. Lateral distal femoral and medial proximal tibial angles were measured pre- and postoperatively to calculate the arithmetic hip-knee-ankle angle (aHKA), JLO, and Coronal Plane Alignment of the Knee (CPAK) phenotypes. The primary outcome was the magnitude and direction of aHKA, JLO, and CPAK alterations. Results. The mean aHKA and JLO increased by 0.1° (SD 3.4°) and 5.8° (SD 3.5°), respectively, from pre- to postoperatively. The most common phenotypes shifted from 76.3% CPAK Types I, II, or III (apex distal JLO) preoperatively to 85.0% IV, V, or VI (apex horizontal JLO) postoperatively. The proportion of knees with apex proximal JLO increased from 0.7% preoperatively to 11.1% postoperatively. Among all MA TKAs, 60.0% (420 knees) were changed from their constitutional alignments into CPAK Type V, while 40.0% (280 knees) either remained in constitutional Type V (5.0%, 35 knees) or were unintentionally aligned into other CPAK types (35.0%; 245 knees). Conclusion. Fixed MA targets in TKA lead to substantial changes from constitutional alignment, primarily a significant increase in JLO. These findings enhance our understanding of alignment alterations resulting from both unintended changes to knee phenotypes and surgical resection imprecision. Cite this article: Bone Jt Open 2024;5(2):109–116

Objectives. Successful total knee arthroplasty (TKA) is predicated on accurate bony resection, mechanical alignment and component positioning. An active robotic TKA system is designed to achieve reliable and accurate bony resection based upon a preoperatively developed surgical plan. Surgical resections are executed intra-operatively according to this pre-operative plan. The goal of this study was to determine the accuracy of final implant positioning and alignment using this active robotic device, as well as its early clinical outcomes. Materials and Methods. An FDA prospective study under investigational device exemption was conducted from 2017–2018. Pre-operative CT scans were used to create a pre-operative plan using the TSolution One? Surgical System (THINK Surgical, Inc). TKA was performed using a standard approach, with planned and robotically executed femoral and tibial resections. Subjects completed 3-month follow-up with post-operative CT scans. A validated method was used to compare pre- and post-operative CT scans to determine differences between planned and achieved implant position. Femoral and tibial component sizing, and mean differences in implant position and alignment were compared. Short Form 12 Physical (PCS) and Mental Component Summary (MCS) scores as well as Knee Society (Objective and Functional) scores at 12 weeks post-operatively were compared with pre-operative scores. Paired-sample t-tests were used for comparisons. Results. Fifty-five subjects whom underwent active robotic TKA and completed 3-month follow-up and were included for analysis. Proximal-distal, antero-posterior and varus-valgus translations, and flexion-extension, internal-external rotations for the FEMUR were statistically different from plan, but the differences were small (<1.7mm, <0.6 deg- p<0.04 for all) and of no clinical significance. The proximal-distal and flexion-extension rotational alignment were also statistically different for the TIBIA but clinically minimal (<0.7 mm, p<0.005). There was no difference in hip-knee angle between planned and post-operative measurements (0 ± 2 degrees p=0.900). No infections, neurovascular, tendon or ligament injuries or fractures were identified. There were no differences in femoral sizing in any case, and 3 tibial components differed by one size. Furthermore, SF-12 PCS and Knee Society (Objective and Functional) scores all statistically improved from pre-operatively to 12 weeks post-operatively (p<0.001 for all), however SF-12 MCS did not improve at 12-weeks (p=0.600). Conclusion. The findings of this early clinical study suggest minimal deviations in final implant position from the pre-operative plan, with improvements in clinical outcome scores and no complications in early follow-up

Aims

An algorithm to determine the constitutional alignment of the lower limb once arthritic deformity has occurred would be of value when undertaking kinematically aligned total knee arthroplasty (TKA). The purpose of this study was to determine if the arithmetic hip-knee-ankle angle (aHKA) algorithm could estimate the constitutional alignment of the lower limb following development of significant arthritis.

The aim of this study was to compare the maximum laxity conferred by the cruciate-retaining (CR) and posterior-stabilised (PS) Triathlon single-radius total knee arthroplasty (TKA) for anterior drawer, varus–valgus opening and rotation in eight cadaver knees through a defined arc of flexion (0º to 110º). The null hypothesis was that the limits of laxity of CR- and PS-TKAs are not significantly different.

The investigation was undertaken in eight loaded cadaver knees undergoing subjective stress testing using a measurement rig. Firstly the native knee was tested prior to preparation for CR-TKA and subsequently for PS-TKA implantation. Surgical navigation was used to track maximal displacements/rotations at 0º, 30º, 60º, 90º and 110° of flexion. Mixed-effects modelling was used to define the behaviour of the TKAs.

The laxity measured for the CR- and PS-TKAs revealed no statistically significant differences over the studied flexion arc for the two versions of TKA. Compared with the native knee both TKAs exhibited slightly increased anterior drawer and decreased varus-valgus and internal-external roational laxities. We believe further study is required to define the clinical states for which the additional constraint offered by a PS-TKA implant may be beneficial.

Cite this article: Bone Joint J 2015; 97-B:642–8.

Objectives

There remains a lack of data on the reliability of methods to estimate tibial coverage achieved during total knee replacement. In order to address this gap, the intra- and interobserver reliability of a three-dimensional (3D) digital templating method was assessed with one symmetric and one asymmetric prosthesis design.