Prospective, Multicentre, Single-arm, Open, Confirmatory Trial to Assess Efficacy and Safety of a Navigation System Providing Personalized Soft Tissue Balance Data in Medially-stabilized Total Knee Arthroplasty
Phase: NA
Conditions: Musculoskeletal Diseases
Sponsor: Medacta International SA

STUDY SYNOPSIS  
Sponsor:  
Medacta International SA 
Strada Regina 
CH 6874 Castel San Pietro 
Switzerland 
 
Study Title: 
Prospective, multicentre, single-arm, open, confirmatory trial to assess efficacy 
and safety of a navigation system providing personalized soft tissue balance data 
in medially-stabilized total knee arthroplasty. 
 
Short Title / 
Study ID: 
Personalized soft tissue balance in TKA. 
Protocol 
Version and 
Date: 
P02.022.02 version 7.0 dated 04 March 2024.   
Trial 
registration: 
The study is registered in a publicly accessible database (ClinicalTrials.gov 
Identifier: NCT04844879) as well as in the Swiss National Clinical Trial Portal 
(SNCTP via BASEC) 
 
Study category 
and rationale: 
Risk category C according to HRA (the investigational device is a medical device 
with no assessment of conformity) 
Phase of 
development: 
Confirmatory phase 
Study design: 
Prospective, multicentre, single-arm, open, confirmatory clinical investigation, 
designed as a non-inferiority trial with respect to a benchmark. 
 
Background 
and Rationale: 
Total knee arthroplasty (TKA) is a well-established procedure that generally results 
in the relief of pain, improved physical function, and a high level of patient 
satisfaction. In order to achieve good clinical outcomes, appropriate soft tissue 
balancing is recognized as an essential procedure, together with accurate 
osteotomy and implantation.  
The NextARTM TKA system developed by Medacta International SA is a surgical 
guidance system which measures intra-operatively the effect of prosthesis 
alignment and positioning on soft tissue balance. Specifically, it provides a visual 
representation of collateral ligament strain throughout the knee flexion range. 
Differently from other surgical guidance systems present on the market, collateral 
ligament strain is measured by detecting bony landmarks of the medial and lateral 
collateral ligaments and not by measuring joint component gaps. However, to date 
it is unknown whether this translates to satisfactory clinical and functional 
outcomes for patients operated with the NextARTM TKA system.   
 
Objective(s): 
Primary objective: 
1. To evaluate the efficacy of the NextARTM TKA system in providing soft 
tissue balance patterns by comparing the patient-reported functional 
outcomes with a benchmark.  
 
Secondary objectives: 
1. To evaluate objective and patient-reported clinical / functional outcomes. 
2. To evaluate radiological outcomes. 
3. To evaluate the viability of the system in the surgical workflow. 
4. To evaluate safety outcomes. 
 

Outcome(s): 
Primary outcome: 
1. Oxford Knee Score (OKS) at 6 months of follow-up.  
 
Secondary outcomes: 
1. OKS, Knee Society Score (KSS), Forgotten Joint Score (FJS) and patient 
satisfaction at 6 months and 12 months of follow-up. 
2. Radiological analysis at 2 and 12 months of follow-up. 
3. All assessments immediately after / during surgery:  
- 
Surgical time (min)  
- 
Necessity of soft tissue release to obtain ligament or patellar balance (Y/N) 
- 
Time to discharge (days) 
4. Device deficiencies and peri- and postoperative adverse events (incl. 
instrument-related issues and delays experienced during surgery) at all 
time points. 
 
Inclusion / 
Exclusion 
criteria: 
Inclusion criteria: 
1. Males and females aged over 18 years at time of surgery. 
2. Patients who are scheduled to receive Medacta GMK® Sphere system for 
primary TKA (class III, CE-marked). 
3. Patients with functional contralateral knee (i.e. without the need to use 
walking aids). 
4. Patients willing and able to provide written informed consent for 
participation. 
5. Patients willing to comply with the pre and post-operative evaluation 
schedule. 
 
Exclusion criteria: 
1. Patients with one or more medical conditions identified as a 
contraindication defined by the labelling on any Medacta implants used in 
this study: 
- Patients presenting with progressive local or systemic infection 
- Muscular loss, neuromuscular disease or vascular deficiency of the 
affected limb, making the operation unjustifiable. 
- Severe instability secondary to advanced destruction of condralar 
structures or loss of integrity of the medial or lateral ligament 
2. Patients whose prospects for a recovery to independent mobility would be 
compromised by known coexistent, medical problems. 
3. Patients affected by concomitant spine, hip, ankle or contralateral knee 
pathologies that can affect walking capacity. 
4. Patients unable to understand and take action. 
5. Patients with known allergy to the materials used. 
6. Patients in which Medacta GMK® Sphere system is used in emergency 
interventions. 
Study Product / 
Intervention:  
NextARTM TKA system 
Control 
Intervention (if 
applicable): 
Not applicable 

Number of 
Participants 
with Rationale: 
A power analysis for a one sample t-test was performed with G-Power 3.1.9.4. 
The benchmark data were gathered from an ongoing ODEP study in which the 
GMK® Sphere is implanted with either standard instrumentation or with patient-
specific instrumentation. In that study, the mean Oxford Knee Score (OKS) at 6 
months was 37 with standard deviation of 9 (n=482).  
Considering that the minimal clinically important difference (MCID) for the Oxford 
Knee Score for TKA has been defined in the literature to be 5 points, we consider 
that a mean OKS of 32 at 6 months obtained with the NextARTM TKA system would 
indicate clinically significant worse functional outcomes.  
The null hypothesis of the study is H0 = 37, and the alternative hypothesis is Ha= 
32. As the test is to show a discrepancy from the null hypothesis and not 
specifically a greater or lesser value, a two-tailed test was chosen. By choosing a 
significance level of 0.05 and power of 0.9, the resulting sample size is n=37, which 
was rounded up to n=40 patients to account for possible dropouts and patients lost 
to follow-up.  
A rejection of the alternative hypothesis (Ha= H0) would indicate that the NextARTM 
TKA system provides comparable functional outcomes than the conventional 
operation. 
 
Study Duration: 
The duration of the project is foreseen for 3.25 years, starting in March 2021 and 
ending in June 2024. The enrolment of patients is foreseen between March 2021 
and June 2023 (27 months). 
 
Investigator(s) 
and centers: 
Prof. Dr. med. Sandro Fucentese 
Uniklinik Balgrist 
Forchstrasse 340 
8008 Zurich (Switzerland) 
sandro.fucentese@balgrist.ch  
+41 76 488 87 45 
PD. Dr. med. Peter Koch 
Kantonsspital Winterthur 
Brauerstrasse 15 
8401 Winterthur (Switzerland) 
peter.koch@ksw.ch  
+41 79 652 23 65 
PD. Dr. med. Peter Koch 
Privatklinik Lindberg  
Schickstrasse 11, 
8400 Winterthur (Switzerland) 
peter.koch@gzw.ch   
+41 52 266 12 12 
PD. Dr. med. Peter Koch 
Privatklinik Belair  
Rietstrasse 30, 
8200 Schaffhausen (Switzerland) 
peter.koch@gzw.ch  
+41 52 266 12 12