Summary

A retrospective cohort study comparing robotic TKA using either a quantified gap balancing technique (MAKO) or a measured resection technique (OMNIbot) which shows that while the two techniques result in different implant positions and rates of recuts, both systems achieve equal sagittal deformity correction with good patient outcomes at short term follow-up.

Abstract

Introduction

Robotically-assisted total knee arthroplasty (TKA) is a surgical delivery tool aimed to improve implant planning and positioning. Multiple proprietary robotic platforms have been developed for TKA, however not all systems provide the same information to the surgeon resulting in different workflow and ability to alter planning and resection in a quantified fashion. Systems such as the Stryker MAKO robotic system provide anticipated gap balancing information which can be used to alter implant position to achieve surgeon desired gaps prior to resection while others such as OMNIbot robotic system do not provide this virtual gap information until after bony cuts have been made. The aim of this study was to examine the effect of these differences in information inputs to the surgeon might have on implant positioning, limb alignment, surgical workflow and patient reported outcomes (PROMS) in patients undergoing primary total knee arthroplasty (TKA) using the same surgeon goals of balance and deformity correction.

Methods

A retrospective cohort study was performed on patients who underwent primary TKA with a restricted kinematic alignment philosophy performed by a single surgeon using either the MAKO or OMNIbot robotic systems. Intra-operative data regarding limb and component alignment and positioning had been collected verified and recorded. Patients were evaluated at 12-month follow-up using Knee Injury & Osteoarthritis Outcome Score (KOOS) and Oxford Knee Score (OKS) and Veterans Rand-12 (VR-12) scores. Continuous parametric data was analysed using unpaired Student’s t tests and Chi Square tests for categorical data with an alpha value set at P>0.05.

Results

207 MAKO TKA and 298 OMNIbot TKAs were included. MAKO TKA patients were slightly younger (67 vs 69, p=0.002) than OMNIbot TKA patients. There were no other demographic or pre-operative alignment differences. Regarding implant positioning, MAKO TKAs had more varus femoral cuts (1.6 vs 2.7 valgus, p<0.001) and tibial cuts (2.4 vs 1.9 varus, p<0.001), were more externally rotated in relation to the posterior condylar axis (2.3 vs 0.1, p<0.001) and had more bone resected compared to OMNIbot TKAs. OMNIbot tibial cuts were more likely to be recut than MAKO tibial cuts (15% vs 2%, p<0.001). There were no differences in femur recut rates, soft tissue releases nor rate of achieving target coronal and sagittal leg alignment between robots. A subgroup analysis of 100 MAKO and 100 OMNIbot propensity matched TKAs with 12-month follow-up showed no significant difference in OKS (42 vs 43, p=0.7) or OKS PASS scores (83% vs 91%, p=0.1). MAKO TKAs reported significantly better symptoms according to their KOOS symptoms score than patients that had OMNIbot TKAs (87 vs 82, p=0.02). There were no other differences in PROMS. There were no revisions in either group.

Conclusion

A gap balanced technique with an image based robotic system (MAKO) results in different implant positioning, bone resection and reduces tibial recuts compared to a measured resection technique with an imageless robotic system (OMNIbot). Both systems achieve equal coronal and sagittal deformity correction (full extension) and good patient outcomes at short term follow-up irrespective of these differences.